阅读说明：本技术 确定使用纤芯加扰的多纤芯光纤传输系统中的纤芯相关损耗的方法和设备 (Method and apparatus for determining core-related losses in a multi-core fiber transmission system using core scrambling ) 是由 G·雷卡亚 A·阿布赛义夫 Y·雅欧恩 于 2019-04-10 设计创作，主要内容包括：本发明的各个实施例提供了一种光传输系统(100),其包括：光发射器(11),所述光发射器(11)被配置为在包括多纤芯光纤的光纤传输信道(13)上传输数据,所述数据由光信号承载,所述光信号根据两个或更多个纤芯沿所述多纤芯光纤传播,所述多纤芯光纤与光纤参数和未对准损耗值相关联；至少一个加扰设备(133),其布置在所述光纤传输信道(13)中,以用于根据加扰函数对所述两个或更多个纤芯进行加扰,其中,所述光纤传输信道(13)包括系统配置设备(17),所述系统配置设备(17)被配置为依据所述光纤参数、至少一个未对准损耗值、所述至少一个加扰设备(133)的数量、以及所述加扰函数来确定纤芯相关损耗值。(Various embodiments of the present invention provide an optical transmission system (100) comprising: an optical transmitter (11), the optical transmitter (11) being configured to transmit data over an optical fiber transmission channel (13) comprising a multi-core optical fiber, the data being carried by an optical signal propagating along the multi-core optical fiber according to two or more cores, the multi-core optical fiber being associated with optical fiber parameters and misalignment loss values; at least one scrambling device (133) arranged in the optical fiber transmission channel (13) for scrambling the two or more cores according to a scrambling function, wherein the optical fiber transmission channel (13) comprises a system configuration device (17), the system configuration device (17) being configured to determine a core dependent loss value depending on the optical fiber parameter, at least one misalignment loss value, the number of the at least one scrambling device (133), and the scrambling function.)

1. An optical transmission system (100), comprising: an optical transmitter (11), the optical transmitter (11) being configured to transmit data over an optical fiber transmission channel (13) comprising a multi-core optical fiber, the data being carried by an optical signal propagating along the multi-core optical fiber according to two or more cores, the multi-core optical fiber being associated with optical fiber parameters and misalignment loss values; at least one scrambling device (133) arranged in the optical fiber transmission channel (13) for scrambling the two or more cores according to a scrambling function, wherein the optical fiber transmission channel (13) comprises a system configuration device (17), the system configuration device (17) being configured to determine a core dependent loss value depending on the optical fiber parameter, at least one misalignment loss value, the number of the at least one scrambling device (133), and the scrambling function.

2. The optical transmission system (100) according to claim 1, wherein the fiber parameters comprise a fiber length, a number of cores at least equal to two, crosstalk coefficients, each crosstalk coefficient representing crosstalk between two cores in the multi-core fiber, and coupling coefficients, each coupling coefficient representing coupling between two cores in the multi-core fiber.

3. The optical transmission system (100) of claim 1, wherein the misalignment loss value represents a misalignment of the multi-core optical fiber selected from the group consisting of longitudinal misalignment, lateral misalignment, and angular misalignment.

4. The optical transmission system (100) according to claim 1, wherein the system configuration device (17) is configured to determine a core loss value associated with each core of the multi-core optical fiber in dependence on the optical fiber parameter, the at least one misalignment loss value, the number of the at least one scrambling device (133), and the scrambling function.

5. The optical transmission system (100) according to claim 4, wherein the system configuration device (17) is configured to determine each core loss value as a random variable of a lognormal distribution defined by mean and variance values, the mean and variance values being dependent on the fiber parameter and at least one misalignment loss value.

6. The optical transmission system (100) of claim 5, wherein a mean value of each core loss value associated with each core of the multi-core optical fiber is a product between a first value corresponding to a mean value of a lognormal random variable representing a total misalignment loss associated with the each core and a second value corresponding to a total crosstalk coefficient associated with the each core, the total crosstalk coefficient associated with a given core being determined by a crosstalk coefficient representing crosstalk between the given core and a core of the multi-core optical fiber other than the given core, a variance value of each core loss value associated with each core of the multi-core optical fiber being a multiplication of a square value of the total crosstalk coefficient associated with the each core and a third value corresponding to a variance of the lognormal random variable representing the total misalignment loss associated with the each core And (4) accumulating.

7. The optical transmission system (100) according to claim 1, wherein the system configuration device 17 is further configured to determine a target core dependent loss value and to select at least one of the fiber parameters of the multi-core fiber in dependence on the core dependent loss value with respect to the target core dependent loss value.

8. The optical transmission system (100) according to claim 8, wherein the target performance indicator is selected from the group consisting of a target signal-to-noise ratio and a target bit or symbol error rate.

9. The optical transmission system (100) according to claim 1, wherein the optical transmission system (100) comprises a scrambling configuration device (16) configured to determine a scrambling function according to a deterministic scrambling criterion.

10. The optical transmission system (100) according to claim 9, wherein the deterministic scrambling criterion depends on one or more of core parameters associated with the cores of the multi-core fiber, the core parameters associated with each core of the multi-core fiber being selected from the group consisting of a core type and a core loss value.

11. The optical transmission system (100) according to claim 10, wherein the scrambling configuration device (16) is configured to order the two or more cores of the multi-core optical fiber according to a given order of core loss values associated with the two or more cores, the deterministic scrambling criterion depending on the order of the core loss values associated with the two or more cores.

12. The optical transmission system (100) according to claim 9, wherein the multicore optical fiber is a heterogeneous multicore optical fiber, the scrambling configuration device (16) being configured to determine the deterministic scrambling criterion depending on the core type associated with the two or more cores, the scrambling function according to the deterministic scrambling criterion corresponding to a pairwise permutation of the two or more cores depending on a permutation of at least a first core and a second core, the first core and the second core being associated with different core types.

13. The optical transmission system (100) according to claim 10, wherein the multicore optical fiber is a heterogeneous multicore optical fiber, the scrambling configuration device (16) being configured to determine the deterministic scrambling criterion as a function of the core type and the core loss value associated with the two or more cores, the scrambling function according to the deterministic scrambling criterion corresponding to a pairwise permutation of the two or more cores according to a permutation of at least a first core and a second core, the first core and the second core being associated with a different core type and a different core loss value.

14. A method for determining core dependent loss values for a fiber optic communication system (100), in which fiber optic communication system (100) data is transmitted on a fiber transmission channel (13) comprising a multi-core fiber, the data being carried by an optical signal propagating along the multi-core fiber according to two or more cores, the multi-core fiber being associated with a fiber parameter and a misalignment loss value, the method comprising scrambling the two or more cores according to a scrambling function, wherein the method comprises: determining a core dependent loss value as a function of the fiber parameter, at least one misalignment loss value, and the scrambling function.

Technical Field

The present invention relates generally to optical communications, and more particularly to an apparatus and method for core dependent loss determination in multi-core optical fibers implementing core scrambling.

Background

Over the past few decades, optical fiber has been widely used in optical transmission systems for transferring data (e.g., voice, multimedia, video) over distances of less than a meter to thousands of kilometers.

Optical fibers are optical waveguides that guide electromagnetic waves in the optical spectrum. The optical fiber includes a transparent core surrounded by a transparent cladding material having a relatively low refractive index. After a series of internal reflections, the light propagates in the optical fiber. Compared to wired or wireless based communication systems, light carries data and allows long distance transmission with higher bandwidth.

As internet traffic increases, the amount of data traffic in optical communication networks grows exponentially. The transmission capability and coverage (reach) of an optical communication system using a single mode optical fiber are improved due to practical use of Wavelength Division Multiplexing (WDM), coherent detection and Polarization Division Multiplexing (PDM), and advanced signal processing.

However, the WDM-PDM system using the conventional single mode optical fiber, which has a small core radius in which a wave propagates along a single propagation mode, almost reaches the nonlinear capacity limit of an optical transmission system and cannot meet the exponential increase in the demand for a higher network bandwidth.

Space Division Multiplexing (SDM) implemented using multimode fiber (MMF) or multi-core fiber (MCF) is expected to overcome the capacity limitations of current optical transmission systems. Space division multiplexing utilizes space in an optical fiber as the last degree of freedom available to increase capacity over optical fiber transmission. Space is used as a multiplexing dimension for creating multiple independent spatial channels over which independent data streams can be multiplexed and carried in the same fiber. Using SDM, the capacity can be multiplied by the number of independent spatial channels, thereby increasing the coverage and transmission capacity of the fiber transmission link.

Multimode optical fibers allow light to propagate according to different spatial propagation modes. The core of a multimode optical fiber is enlarged to allow propagation of more than one spatial mode. The number of reflections that occur as light passes through the core increases, establishing the ability to propagate more data in a given time slot.

Multimode fibers can provide higher transmission rates than single mode fibers. However, multimode fibers can suffer from several impairments, mainly due to imperfections in optical components (e.g., fibers, amplifiers, spatial multiplexers), cross-talk effects between spatial modes, and non-unity cross-talk effects known as Mode Dependent Loss (MDL).

Multi-core fibers incorporate multiple identical or different cores, each of which is single or multimode, in a single fiber. Multi-core fibers can be classified into uncoupled MCFs and coupled MCFs.

In an uncoupled MCF, each core must be properly positioned so that inter-core crosstalk remains small enough for long-haul applications to detect the signal from each core individually (i.e., no multi-input multi-output equalization is required at the receiver). Several types of uncoupled multi-core fibers have been designed based on different core arrangements. These designs include "homogeneous MCFs" and "homogeneous MCFs with trench assist" in which multiple equivalent cores are incorporated, while "heterogeneous MCFs" incorporate several types of multiple cores.

In a coupled MCF, several cores are placed such that they are strongly and/or weakly coupled to each other. Coupled MCFs that support a single spatial mode and multiple spatial modes may be used in high power fiber laser applications.

Multi-core optical fibers suffer from several impairments due to misalignment losses and crosstalk effects. Crosstalk and misalignment losses cause Core Dependent Losses (CDL). CDL is a damaging effect similar to MDL affecting multimode fibers.

Misalignment losses increase due to imperfections in the fiber at the splice and at the connector portion. There are three types of misalignment loss, including longitudinal displacement loss, lateral displacement loss, and angular displacement loss.

The crosstalk effect is the generation of crosstalk between adjacent cores due to the presence of multiple cores in one cladding. Crosstalk increases with decreasing inter-core distance and represents a major limitation on capacity in terms of optical signal quality and the number of cores integrated within a multi-core optical fiber. Furthermore, the low crosstalk effect leads to a reduced decoding complexity at the optical receiver, since no multiple-input multiple-output equalization is required for small crosstalk values.

To reduce crosstalk effects, optical solutions may be applied during the manufacturing process of the optical fiber.

The first method consists in increasing the inter-core distance. This approach can reduce the effects of crosstalk, but due to the cladding diameter it limits the number of cores inside the fiber and therefore reduces core density and capacity.

The second approach is based on trench assist using trench-assisted homogeneous multi-core fibers. The trench assists in reducing the coupling coefficient by surrounding each core with a low index trench layer. The crosstalk in trench-assisted fiber designs is dependent on the inter-core distance and is lower than the inter-core crosstalk in fibers without trench assistance.

A third solution uses a heterogeneous MCF, where an intrinsic refractive index profile is introduced between adjacent cores, thereby reducing cross-talk effects.

Furthermore, random core scrambling techniques have recently been proposed to mitigate CDL and enhance system performance in heterogeneous trench-assisted MCFs, a.aboroseif, g.r.ben-Othman and Y in "Asia Communications and Photonics Conference, OSA Technical Digest, 2017.Core Mode Scramblers for ML-detection based Multi-Core Fibers Transmission (Core Mode scrambler in ML detection based Multi-Core fiber Transmission) in (1). It is proved that the randomCore scrambling may achieve better performance in terms of error probability. However, random scrambling requires the installation of a large number of random scramblers, which introduces additional implementation complexity and cost on the transmission system.

Although existing solutions can reduce crosstalk in multi-core optical fibers, they do not enable estimation of core-related losses and prediction of the performance behavior of the optical transmission system, which depends on the values of the core-related losses. Therefore, there is a need to develop channel modeling and calculation techniques that are capable of determining the core-dependent loss value for a given configuration of a multi-core fiber-based optical transmission system in which core scrambling is used.

Disclosure of Invention

To address these and other problems, an optical transmission system is provided that includes an optical transmitter configured to transmit data over an optical fiber transmission channel made of a multi-core optical fiber. An optical signal carrying data propagates along a multi-core optical fiber according to two or more cores. The multi-core fiber is associated with a fiber parameter and a misalignment loss value. At least one scrambling device is arranged in the optical fiber transmission channel for scrambling the two or more cores according to a scrambling function. The optical fiber transmission channel includes a system configuration device configured to determine a core dependent loss value as a function of a fiber parameter, a misalignment loss, at least one scrambling device, and a scrambling function.

In some embodiments, the fiber parameters include a fiber length, a number of cores equal to at least two, crosstalk coefficients, each crosstalk coefficient representing crosstalk between two cores in the multi-core fiber, and coupling coefficients, each coupling coefficient representing coupling between two cores in the multi-core fiber.

In some embodiments, the misalignment loss value represents a misalignment of the multi-core optical fiber selected in the group consisting of longitudinal misalignment, lateral misalignment, and angular misalignment.

In some embodiments, the system configuration device may be configured to determine a core loss value associated with each core of the multi-core optical fiber as a function of the fiber parameter, the misalignment loss value, the at least one scrambling device, and the scrambling function.

According to some embodiments, the system configuration device may be configured to determine each core loss value as a random variable of a lognormal distribution defined by mean and variance values that are dependent on the fiber parameters and the misalignment loss values.

According to some embodiments, the mean value of each core loss value associated with each core of the multi-core optical fiber is a product between a first value corresponding to a mean value of a lognormal random variable representing a total misalignment loss associated with said each core and a second value corresponding to a total crosstalk coefficient associated with said each core, the total crosstalk coefficient associated with a given core being determined by a crosstalk coefficient representing crosstalk between said given core and a core of the multi-core optical fiber different from said given core. The variance value for each core loss value associated with each core of a multi-core optical fiber is a product of a squared value of a total crosstalk coefficient associated with said each core and a third value corresponding to a variance of a lognormal random variable representing a total misalignment loss associated with said each core.

According to some embodiments, the system configuration device may be further configured to determine a target core dependent loss value and to select at least one of the fiber parameters of the multi-core fiber in dependence on the core dependent loss value in relation to the target core dependent loss value.

According to some embodiments, the target performance metric may be selected in a group comprising a target signal-to-noise ratio and a target bit or symbol error rate.

In some embodiments, the optical transmission system may include a scrambling configuration device configured to determine a scrambling function according to a deterministic scrambling criterion.

According to some embodiments, the deterministic scrambling criteria may be dependent on one or more of core parameters associated with the cores of the multi-core fiber, the core parameters associated with each core of the multi-core fiber being selected from the group consisting of a core type and a core loss value.

According to some embodiments, the scrambling configuration device may be configured to order the two or more cores of the multi-core optical fiber according to a given order of core loss values associated with the two or more cores, the deterministic scrambling criterion depending on the order of the core loss values associated with the two or more cores.

In some embodiments, in which the multi-core fiber is a heterogeneous multi-core fiber, the scrambling configuration device may be configured to determine a deterministic scrambling criterion as a function of core types associated with the two or more cores, the scrambling function according to the deterministic scrambling criterion corresponding to a pairwise permutation of the two or more cores as a function of a permutation of at least a first core and a second core, the first core and the second core being associated with different core types.

In some embodiments, in which the multi-core fiber is a heterogeneous multi-core fiber, the scrambling configuration device may be configured to determine a deterministic scrambling criterion as a function of core types and core loss values associated with the two or more cores, the scrambling function according to the deterministic scrambling criterion corresponding to a pairwise permutation of the two or more cores according to a permutation of at least a first core and a second core, the first core and the second core being associated with different core types and different core loss values.

A method for determining a core dependent loss value for a fiber optic communication system in which data is transmitted over a fiber transmission channel formed of a multi-core fiber is also provided. An optical signal carrying data propagates along a multi-core optical fiber according to two or more cores. The multi-core fiber is associated with a fiber parameter and a misalignment loss value. The method includes scrambling two or more cores according to a scrambling function, and determining core dependent loss values as a function of fiber parameters, misalignment loss values, and the scrambling function.

Advantageously, the core dependent loss value calculation apparatus and method according to various embodiments are able to estimate and predict the performance behavior of a multi-core optical fiber transmission channel by evaluating the core dependent loss for a given optical fiber transmission channel configuration (including a given number of fiber spans and fiber misalignment values), a given fiber parameter, a given number of core scrambler/scrambling devices, and a given core scrambling technique (random or deterministic, same or different).

Advantageously, optical channel modeling techniques according to various embodiments of the present invention provide efficient tools for designing and manufacturing multi-core fiber optic transmission systems with reduced core-related loss effects and a reduced number of scrambling devices (e.g., optical multiplexers) for core scrambling.

Other advantages of the invention will become apparent to those skilled in the art upon review of the drawings and detailed description.

Drawings

The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate various embodiments of the invention.

Fig. 1 shows a schematic diagram of an exemplary application of the present invention in an optical communication system.

FIG. 2 illustrates a cross-sectional view of an exemplary multi-core optical fiber;

FIG. 3 depicts a cross-sectional view of a multi-core fiber having a 12-core homogeneous multi-core fiber including twelve cores arranged in a ring about the fiber axis and a 19-core homogeneous fiber including nineteen cores including one central core arranged in a two-dimensional grid, according to some embodiments;

FIG. 4 depicts a cross-sectional view of a multi-core optical fiber according to some embodiments, wherein the multi-core optical fiber is a 12-core homogeneous trench-assisted multi-core optical fiber;

FIG. 5 illustrates a cross-sectional view of a multi-core optical fiber according to some embodiments, wherein the multi-core optical fiber is a 12-core heterogeneous multi-core optical fiber including twelve cores arranged in a ring around the fiber axis;

FIG. 6 illustrates a cross-sectional view of a multi-core optical fiber having a 7-core hetero-fiber including seven cores and a 19-core hetero-fiber including three groups of cores, the cores in each different group being of a different type, according to some embodiments;

FIG. 7 illustrates a cross-sectional view of a multi-core fiber having a 12-core heterogeneous trench assisted multi-core fiber and a 7-core heterogeneous trench assisted multi-core fiber, the 12-core heterogeneous trench assisted multi-core fiber including twelve cores arranged in a ring around a fiber axis, according to some embodiments;

FIG. 8 is a block diagram illustrating the structure of a light emitter according to some embodiments of the invention;

FIG. 9 is a block diagram illustrating the structure of an optical receiver according to some embodiments of the invention;

FIG. 10 is a flow diagram illustrating a method for determining core dependent loss values in a multi-core fiber transmission system using core scrambling, single polarization, single wavelength, single carrier uncoded modulation without application of time-space coding, according to some embodiments of the invention;

FIG. 11 illustrates a cross-sectional view of a multi-core fiber in accordance with some embodiments, in which snail scrambling techniques are considered;

FIG. 12 illustrates a cross-sectional view of a multi-core optical fiber in accordance with some embodiments, in which a rotational scrambling technique is considered, an

FIG. 13 illustrates a cross-sectional view of a multi-core optical fiber in accordance with some embodiments, wherein a serpentine scrambling technique is contemplated.

Detailed Description

Embodiments of the present invention provide apparatus and methods for channel modeling of a multi-core fiber transmission system and estimating core dependent losses for a given configuration and a given core scrambling of the multi-core fiber transmission system, the determination of the core dependent losses enabling an advantageously efficient design of a multi-core fiber transmission system with a reduced impact of core dependent losses and a reduced number of core scrambling devices.

Apparatus and methods according to various embodiments of the present invention may be implemented in fiber optic transmission systems for a variety of applications. Exemplary applications include, but are not limited to, fiber optic communications, aerospace and avionics, data storage, automotive industry, imaging, transportation, sensing, and photonics.

Exemplary communication applications include desktop computers, terminals, and nationwide networks. Optical fibers may be used to transport light, and thus information/data, over short distances (less than one meter) or long distances (e.g., up to hundreds or thousands of kilometers in communications via metropolitan, wide area, transoceanic links). Such applications may relate to the delivery of voice (e.g., telephony), data (e.g., data provision to homes and offices, known as fiber to the home), images or video (e.g., the delivery of internet traffic), or connections to networks (e.g., connections to switches or routers and data center connections in high-speed local area networks).

In exemplary embodiments of the invention in the field of the aerospace industry, optical fiber-based products may be used for military and/or commercial applications. Fiber optic technology and products are designed in such applications to meet stringent testing and certification requirements in demanding environments and conditions.

In exemplary embodiments of the present invention in data storage applications, an optical fiber may be used in a data storage device as a link between multiple devices in a network and/or as part of a storage system. Fiber optic connections provide very high bandwidth even over extended distances.

In another exemplary application of the invention to the automotive industry, fiber optic technology may be used, for example, in lighting/lighting, communication and sensing of safety and control devices and systems.

In yet another exemplary application of the present invention to imaging applications (e.g., telemedicine), the light transmission characteristics of the optical fibers may be used to transmit an image of a target or object region to an image viewing end for analysis and/or interpretation.

The invention can also be used in transportation systems where intelligent highways with intelligent traffic lights, automatic toll booths and variable message signs can use fiber optic based telemetry systems.

The invention may further be used in sensing applications where fiber optic sensors may be used to sense quantities such as temperature, displacement, vibration, pressure, acceleration, rotation, and concentration of chemical substances. Exemplary applications of fiber optic sensors include sensing in high voltage and high power machinery or microwaves, distributed temperature and strain measurements in buildings for remote monitoring (e.g., monitoring wings of aircraft, wind turbines, bridges, pipelines), downhole sensing in oil exploration applications, and the like

In another application of the invention to photonics, optical fibers may be used to connect components in fiber optic equipment, such as interferometers and fiber lasers. In such applications, the optical fiber plays a similar role as the electrical wire in the electronic device.

For purposes of illustration only, the following description of certain embodiments will be made with reference to communication applications. However, the skilled person will readily appreciate that various embodiments of the invention may be applied to other types of systems for different applications.

Fig. 1 shows an exemplary embodiment of the present invention in an optical transmission system 100 (also referred to as "optical communication system") based on optical fiber transmission. The optical transmission system 100 comprises at least one optical transmitter device 11 (hereinafter referred to as "optical transmitter") 11 configured to encode an input data sequence into an optical signal and to optically transmit the optical signal to at least one optical receiver device 15 (hereinafter referred to as "optical receiver") via an optical fiber transmission channel 13 (hereinafter referred to as "optical fiber link"), said optical fiber transmission channel 13 being configured to transmit light over a distance.

The optical communication system 100 may include a computer and/or software to control the operability of the system.

The fiber transmission channel 13 comprises a multi-core fiber comprising a concatenation of a plurality of fiber segments 131 (also referred to as "fiber spans" or "fiber slices"). The optical fiber segments 131 may be aligned or misaligned.

A multi-core optical fiber is a cylindrical nonlinear waveguide composed of two or more cores, a cladding surrounding the two or more cores, and a coating. Each core has a refractive index. The optical signals transmitted by the optical transmitter 11 are multiplexed and guided in each core of the multi-core optical fiber by total internal reflection due to the difference between the refractive index of the core and the refractive index of the cladding.

In some embodiments in which the multi-core fiber is an uncoupled fiber, each core of the multi-core fiber may act as a separate waveguide, such that the optical signals may be considered to propagate independently through the cores.

In some embodiments where the multi-core fiber is a coupled fiber, some coupling between the cores may exist if the distance between the two cores is too small for optical signals propagating along the different cores to overlap.

Optical fibers can be made of glass (e.g., silica, quartz glass, fluoride glass), which is typically used for long distance transmission. For short distance transmission, the optical fiber may be a plastic optical fiber.

Multi-core optical fibers can be characterized by geometric and optical parameters. The geometric parameters may include the cladding diameter, the core-to-core distance, and the core-to-outer cladding distance. The optical parameters may include wavelength, crosstalk coefficient representing crosstalk between different cores of the multi-core optical fiber, and refractive index difference between each core and the cladding.

In some embodiments, the fiber optic communication system 100 may operate in a wavelength region corresponding to a region selected from the group consisting of:

-a wavelength window in the range of 800-900nm suitable for short-range transmission;

a wavelength window of about 1.3 μm, for example for long distance transmission;

a wavelength window of about 1.5 μm, which is used more since the loss of silica fiber is lowest in this wavelength region.

FIG. 2 depicts a cross-section of a six-core fiber, D_cladRepresents the diameter of the cladding, d_c-cSpecifies the inter-core distance, and d_c-CladRepresenting the core-outer cladding distance.

In some embodiments, the cores in a multi-core fiber may be arranged in a ring around the fiber axis, for example on the edges of a hexagon. In other embodiments, the cores may be arranged on some two-dimensional grid.

In an embodiment, the multi-core optical fiber may be a homogeneous multi-core optical fiber including two or more cores of the same type.

Fig. 3 depicts two cross-sections of two exemplary homogeneous multi-core fibers, a first 12-core fiber comprising 12 cores of the same type arranged on a ring around the fiber axis, and a second 19-core fiber comprising 18 cores arranged on the edges of a hexagon and one central core.

In an embodiment, the multi-core fiber may be a homogeneous trench-assisted multi-core fiber, each core surrounded by a low index trench layer.

FIG. 4 shows a cross-section of an exemplary trench-assisted homogeneous multi-core fiber including 12 cores of the same type.

In another embodiment, the multi-core fiber may be a heterogeneous multi-core fiber including a plurality of cores, of which at least two cores are of different types.

Fig. 5 shows a cross-section of an exemplary heterogeneous multi-core fiber comprising 12 cores, of which 12 cores the cores numbered 2i +1 (where i is 0, …,5) are identical, the cores numbered 2i +2 (where i is 0, …,5) are identical, and the core type of the core numbered 2i +1 is different from the core type of the core numbered 2i +2 for i 0, …, 5. Each core in the heterogeneous multi-core optical fiber has two adjacent cores, and the core type of each core is different from that of the adjacent core.

Fig. 6 shows two cross-sections of two exemplary 7-core fibers and 19-core hetero-fibers. The 7-core fiber includes six cores numbered 1-6 and a center core numbered 7 on the edge of the hexagon. The 7-core fiber contains three different core types, the core type of the central core being different from the core type of the cores on the edges of the hexagon, and the core type of each core arranged on the edges of the hexagon being different from the core type of its neighboring core. The 19-core fiber includes three different core types, a central core having a core type different from the type of core on the edges of the hexagon.

In an embodiment, the multi-core fiber may be a trench-assisted heterogeneous multi-core fiber.

FIG. 7 depicts two cross-sections of two exemplary 12-core and 7-core trench-assisted heterogeneous multi-core fibers.

In some embodiments, each core of a multi-core optical fiber may be single mode including one spatial propagation mode.

In some embodiments, the multi-core optical fiber may include at least one multimode core including two or more spatial propagation modes.

The optical fiber transmission channel 13 may further include one or more amplifiers 132 inserted into the optical fiber for re-amplifying the optical power and compensating for fiber attenuation without regenerating the optical signal, so that sufficient signal power can be maintained over long distances where periodic amplification of the optical signal is required.

An amplifier 132 may be interposed between each pair of fiber slices 131. In particular, an amplifier 132 inserted at the end of the optical fiber transmission channel performs signal amplification prior to signal detection at the receiver 15.

Each amplifier 132 may be configured to simultaneously amplify optical signals corresponding to multiple cores in a multi-core optical fiber.

In some embodiments, the amplifier 132 may comprise a copy of a single fiber amplifier.

In other embodiments, the amplifier 132 may be an optical multi-fiber core amplifier. Exemplary optical amplifiers include multiple-core erbium-doped fiber amplifiers (EDFAs), such as core-pumped, multiple-core EDFAs and cladding-pumped EDFA amplifiers. Core pumped and cladding pumped amplifiers may use single or multiple pump diodes. In particular, the pump diodes of each core may be used in EDFA amplifiers.

In some embodiments, optical signal amplification may be performed in a distributed manner using nonlinear simulated raman scattering effects. In such embodiments, the optical fiber serves as both a transmission link and an amplification medium.

In other embodiments, signal amplification may be achieved by using regularly arranged optical amplifiers in common with the simulated raman scattering effect.

In other embodiments, signal amplification may be performed in the electrical domain by optical/electrical conversion (not shown in fig. 1). In such an embodiment, the fiber transmission channel 13 may comprise, at each amplification stage:

-a photodiode for converting the optical signal back to the electrical domain;

-an electrical amplifier for amplifying the converted electrical signal; and

-a laser diode for generating an optical signal corresponding to the amplified electrical signal.

According to some embodiments (not shown in fig. 1), the optical transmission channel 13 may further comprise one or more of:

a dispersion compensator for counteracting the effects of dispersion, e.g. configured to cancel or compensate for dispersion before the optical signal is detected at the receiver 15;

optical switches and multiplexers implemented in wavelength division multiplexing systems, such as optical add-drop multiplexers;

-one or more devices for regenerating optical signals, such as electronic and optical regenerators.

In some embodiments, where optical devices are used to perform core scrambling in the optical domain, an optical multiplexer may be used as the core scrambler.

Fig. 8 illustrates components of a light emitter 11 according to some embodiments. The optical transmitter 11 may be configured to convert the input data sequence into an optical signal to be transmitted over the optical transmission channel 13. Thus, the light emitter 11 may comprise:

a forward error correction code (FEC) encoder 81 (also referred to as "error correction code encoder 81") configured to encode an input data sequence of length k (i.e. comprising k symbols) into an encoded sequence of codeword vectors of length n > k by applying at least one forward error correction code (FEC) (also referred to as "error correction code");

an interleaver 83 configured to mix the coded sequences to add a protection layer to the coded symbols before being modulated to prevent burst errors;

a modulator 85 configured to modulate the data by applying a modulation scheme to the dataThe interleaved code sequence (or, in embodiments where transmitter 11 does not include an interleaver, the codeword vector) to determine a modulation symbol vector s_cA set of modulation symbols in the form of (1). Different modulation schemes may be implemented, e.g. with 2^q2 of a symbol or state^q-QAM or 2^q-PSK. Modulation vector s_cMay be a complex-valued vector comprising k complex-valued symbols s having q bits per symbol₁,s₂,…,s_к. When using a device such as 2^qModulation format of QAM, 2^qEach symbol or state representing an integer fieldA subset of (a). The corresponding constellation diagram is composed of 2 representing different states or symbols^qAnd (4) dot composition. In addition, in the case of square modulation, the real and imaginary parts of the information symbols belong to the same finite alphabet a [ - (q-1), (q-1)]；

A space-time encoder 87 configured to determine a codeword matrix carrying data symbols to be transmitted over the optical transport channel 13 during a Time Transmission Interval (TTI) by applying a space-time code. The time-space encoder 25 may be configured to modulate Q modulation symbols s₁,s₂,…,s_QEach received sequence (or block) of (a) is transformed into a size of N_tX T. The codeword matrix comprises an arrangement at N_tComplex values in rows and T columns, where N_tRepresents the number of propagating cores used to propagate the optical signal, and T represents the time length of the time-space code and corresponds to the number of time channel usages. Thus, each value of the codeword matrix corresponds to a time of use and a propagating core for signal propagation. The time-space encoder 87 may generate a codeword matrix using linear time-space block coding (STBC). The code rate of this code is equal to the usage per channelA complex symbol, where, in this case,. kappa is the vector s constituting dimension k_c＝[s₁,s₂,…,s_к]^tHas already been preparedThe number of complex valued symbols is encoded. When using a full-rate code, the space-time encoder 87 is for k ═ N_tT complex-valued symbols are encoded. An example of STBC is perfect code. Perfect code passing over the number of complex information symbolsThe encoding is performed to provide the full encoding rate and to satisfy the non-vanishing determinant property.

In some embodiments, the space-time encoder 87 may use a spatial multiplexing scheme known as the V-BLAST scheme by multiplexing received complex-valued information symbols on different propagation cores, without performing encoding in the time dimension.

According to some embodiments, the input data sequence may be a binary sequence comprising k bits. In such embodiments, the FEC encoder 81 may be configured to encode the input binary sequence into a binary codeword vector comprising n bits by applying at least one binary FEC code.

In other embodiments, the input data sequence may include symbols that take on values in a galois field gf (q), where q >2 represents the order of the galois field. In such embodiments, the FEC encoder 22 may be configured to encode the input data sequence into a codeword vector comprising n symbols, each symbol comprised in the codeword vector taking the value in the galois field gf (q). The encoding process in this case may be performed using a non-binary FEC code constructed over gf (q), where q > 2.

By performing the encoding operation, the FEC encoder 81 adds redundant bits (typically redundant symbols) to the input binary sequence so that the receiver can detect and/or correct common transmission errors. The use of FEC codes provides additional protection and resistance to transmission errors and allows for significant performance improvements over uncoded transmissions (i.e., transmissions of modulated data without FEC coding).

Additional improvements and reduction of error probability can be achieved by concatenation of two or more FEC codes. The concatenation of codes may follow a serial, parallel or multi-layer architecture. FEC encoder 81 may accordingly be configured to implement two or more FEC codes.

The optical transmitter 11 may further comprise a plurality of multicarrier modulators 88 configured to generate multicarrier symbols by implementing multicarrier modulation techniques within each optical carrier involving a number of orthogonal subcarriers. In addition, multi-carrier modulation may be implemented to provide better resistance to inter-symbol interference due to fiber dispersion and cross-talk between individual cores in a multi-core fiber. Exemplary multi-carrier modulation formats include Orthogonal Frequency Division Multiplexing (OFDM) and filter bank multi-carrier (FBMC).

The frequency domain signal delivered by the multicarrier modulator 88 may then be processed by a digital optical front end 89, which digital optical front end 89 is configured to convert the received frequency domain signal to the optical domain. Digital optical front end 88 may perform the conversion using a plurality of lasers of a given wavelength and a plurality of optical modulators (not shown in fig. 8) associated with the polarization states used and the spatial propagation modes in the core of the multi-core fiber. The lasers may be configured to generate laser beams of the same or different wavelengths using Wavelength Division Multiplexing (WDM) techniques. Different laser beams can then be modulated with different outputs of the OFDM symbols (or different values of the codeword matrix in embodiments using single carrier modulation) by means of the optical modulator and polarized according to different polarization states of the optical fiber. Exemplary modulators include mach-zehnder modulators. Phase and/or amplitude modulation may be used. In addition, the modulation schemes used by the various optical modulators for modulating different optical signals may be similar or different.

The number of optical modulators and lasers depends on the number of polarization states used, the number of propagation modes used in each core of the multi-core fiber, and the number of cores in the fiber.

Digital optical front-end 88 may further include a FAN-IN device (not shown IN fig. 8) configured to inject the generated optical signal into each core of the multi-core optical fiber to propagate according to the available propagation modes IN each core. Optical connectors may be used to connect the output of the FAN-IN device to the input of the multi-fiber optical transmission channel 13.

An optical signal generated according to any of the preceding embodiments may propagate along the optical fibre until reaching the other end of the optical transmission channel 13, where it is processed by the optical receiver 15.

Fig. 9 is a block diagram of an optical receiver 15 according to some embodiments. The optical receiver 15 is configured to receive the optical signal transmitted by the optical transmitter 11 through the transmission channel 13 and to generate an estimate of the original input data sequence. Accordingly, the optical receiver 15 may include:

an optical digital front end 91 configured to detect the optical signal using, for example, one or more photodiodes and convert it into a digital signal. The optical digital front end 91 may include a FAN-OUT device (not shown in fig. 9);

a plurality of multicarrier demodulators 92 configured to remove the cyclic prefix and generate a set of decision variables to be fed to a space-time decoder 93;

a space-time decoder 93 configured to generate an estimate of the modulated data sequence from the set of decision variables by applying a space-time decoding algorithm;

a demodulator 94 configured to generate a binary sequence by performing demodulation on the modulated data sequence estimated by the space-time decoder 93;

a deinterleaver 95 configured to rearrange the order of the bits (typically symbols) in the binary sequence delivered by the demodulator 94 to restore the original order of the bits; and

an FEC decoder 96 (also referred to as "error correction code decoder 96") configured to convey an estimate of the input data sequence processed by the optical transmitter device 11 by applying a soft-decision or hard-decision FEC decoder to the reordered binary sequence conveyed by the de-interleaver 95. An exemplary soft-decision FEC decoder includes a viterbi algorithm.

The time-space decoder 93 may implement a time-space decoding algorithm selected from the group consisting of a maximum likelihood decoder, a zero-forcing decision feedback equalizer, and a minimum mean square error decoder.

Exemplary maximum likelihood decoders include sphere decoders, Schnorr-Euchner decoders, stack decoders, sphere-boundary-stack decoders.

In embodiments using single carrier modulation, the multiple multi-carrier modulators 92 may be replaced by a single modulator. Similarly, the multi-carrier demodulator 92 may be replaced by a single demodulator.

In some embodiments where FEC encoder 81 implements a concatenation of two or more forward error correction codes, FEC decoder 96 may implement a corresponding structure. For example, in an embodiment based on a serial concatenation of an inner code and an outer code, FEC decoder 96 may include an inner code decoder, a deinterleaver, and an outer code decoder (not shown in fig. 9). In embodiments involving two codes in a parallel architecture, FEC decoder 96 may include a demultiplexer, a deinterleaver, and a joint decoder (not shown in fig. 9).

For purposes of illustration only, certain embodiments of the present invention will be described below with reference to an optical communication system 100 that uses a single polarization, a single wavelength, single carrier modulation, a single error correction code without space-time encoding, and a single mode multi-fiber core fiber. However, those skilled in the art will readily appreciate that various embodiments of the present invention may also be applied in multi-core optical fibers in combination with polarization multiplexing using two polarizations, and/or in combination with wavelength multiplexing using multiple wavelengths, and/or in combination with mode multiplexing using a multi-mode fiber core, and/or in combination with multi-carrier modulation formats, and/or in combination with space-time coding.

To facilitate an understanding of some embodiments of the invention, some symbols and/or definitions are used below:

l represents the total length of the multicore optical fiber in the optical fiber transmission channel 13;

k represents the number of fiber segments (also called "fiber slices" or "fiber spans") connected in series in the multi-core fiber;

-d represents the correlation length;

-R_brepresents the radius of curvature;

-N_c≧ 2 denotes the total number of cores in the multi-core fiber, the cores being numbered (i.e., the number of cores is one)Each core is connected with 1 and N_cAssociated with a core number that varies) to assign the core as core-N, where N assumes 1 and N_cA value in between;

-R_nrepresents the radius of the core n;

core-N per core (where N is 1, …, N)_c) And is formed by { T_n；λ_n,pDenotes the core parameter, where T is_nDenotes the core type of core-n, and λ_n,pRepresenting the core loss value and the result of core scrambling associated with core-n;

-XT_n,mrefers to the crosstalk coefficient (also referred to as "inter-core crosstalk coefficient") that quantifies the crosstalk between core-n and core-m (also referred to as "inter-core crosstalk"), where n ≠ m;

-k_n,mrefers to a coupling coefficient (also referred to as "inter-core coupling") that quantifies the coupling between core-n and core-m (also referred to as "inter-core coupling"), where n ≠ m;

-Δβ_nmrepresents the propagation constant difference between core-n and core-m, where n ≠ m;

-pi represents the scrambling function used for core scrambling and passes through N_c×N_cThe permutation matrix is represented in a matrix form;

various embodiments of the present invention provide efficient channel modeling and calculation equipment for determining the core-related loss of a given optical fiber transmission channel 13 in an optical transmission system 100. The optical fiber transmission channel 13 is made of a multi-core optical fiber that is associated with a predefined fiber configuration and fiber parameters, misalignment loss values. At least one scrambling device 133 is arranged in the optical transmission channel 13 for scrambling two or more cores of the multi-core optical fiber according to a scrambling function pi. The channel modeling and CDL determination techniques according to the present invention may be advantageously used during design or manufacture of an optical fiber to select a multi-core optical fiber and/or to determine the number of fiber spans/slices and/or to determine the configuration of transmission parameters, such as modulation scheme, error correction coding scheme, space-time coding scheme, and the number and/or type of scrambling devices 133.

In some embodiments, the optical transmission system 100 comprises a system configuration device 17, the system configuration device 17 being configured to determine a core dependent loss value from a predefined fiber configuration, at least one misalignment loss value, at least one scrambling device 133 (type (i.e. random or deterministic) of the at least one scrambling device 133 and number of the at least one scrambling device 133) and a scrambling function pi in dependence on fiber parameters.

In embodiments in which two or more scrambling devices 133 are disposed in the fiber transmission channel 13, the two or more scrambling devices 133 may be the same (i.e., implementing the same scrambling function) or different (i.e., implementing different scrambling functions).

According to some embodiments, the fiber parameters include a fiber length L, a number of cores N at least equal to two_cGreater than or equal to 2 and crosstalk coefficient XT_n,m(where N, m. epsilon. {1, …, N)_c}) and a coupling coefficient k_n,m(where N, m. epsilon. {1, …, N)_c}), each crosstalk coefficient XT_n,mRepresents the crosstalk between core-n and core-m in a multicore optical fibre, where n ≠ m, each coupling coefficient k_n,mRepresents the coupling between core-n and core-m in a multicore fiber, where n ≠ m.

The fiber parameters may further include a bend radius, a number of fiber slices K, a cladding diameter, a radius of each core of the multi-core fiber, and a type T of each core-n of the multi-core fiber_n(for N-1, …, N_c)。

IN some embodiments, misalignment losses may arise due to imperfections IN the optical fibers and connectors at the fiber spans (e.g., connectors between the FAN-IN/FAN-OUT devices and the input/output ends of the fiber transmission channels). The misalignment may comprise a misalignment selected from the group consisting of longitudinal misalignment, lateral misalignment, and angular misalignment.

According to some embodiments, the misalignment loss may be modeled as a random gaussian variable. More specifically, the misalignment loss associated with core-n can be modeled as a random gaussian variable with zero mean and standard deviation, the standard deviation being expressed by σ according to the following equation_(x,y),nRepresents:

in equation (1), r_dIndicating the lateral displacement of the multi-core fiber in the "x" and "y" directions.

In embodiments where the optical fiber transmission channel 13 experiences inter-core crosstalk effects and misalignment effects, the optical transmission channel 13 may be represented by an optical multiple-input multiple-output (MIMO) system, which is described by the following relationship:

Y＝H.X+N (2)

in equation (2):

-X represents a length N_cComprising N transmitted over the optical transmission channel 13_cSymbols such that the nth symbol is transmitted on core-N, where N is 1, …, N_c；

Y is the length N_cA complex-valued vector representing the signal received at the optical receiver 15;

h is the size N_c x N_cRepresents the optical channel matrix and represents, in addition to the misalignment losses, the attenuation and losses experienced by the cores during propagation of optical signals on different cores in the multi-core optical fiber, an

-N is a length N_cA real-valued vector representing the optical channel noise.

According to some embodiments, the optical channel noise may be zero mean and variance N₀White gaussian noise.

In some embodiments, the scrambling function pi may be represented in matrix form by a permutation matrix denoted by P, the entries of which are given by:

a multi-core fiber consists of a series of K fiber spans/slices. Accordingly, the optical transmission channel 13 may comprise a channel according to K_scrPresented scrambling period periodicityAt least one scrambling device 133 arranged in the optical transmission channel 13, i.e. if k is a multiple of the scrambling period, the scrambling device 133 may be arranged in the kth fiber slice.

In such an embodiment, each fiber span is equivalent to a crosstalk channel matrix, a misalignment channel matrix, and a permutation matrix P^(k)P, the permutation matrix is N representing the scrambling function pi applied by the kth scrambling device 133 in the kth fiber span_c×N_cThe matrix, k, is a multiple of the crypto period.

Thus, the optical MIMO system of equation (2) can be equivalently expressed according to the following equation:

in equation (4):

-L represents a normalization factor for compensating for fiber link losses;

-H_XT,kspecifying a crosstalk channel matrix associated with a kth optical fiber span, an

-M_kA misaligned channel matrix associated with the kth fiber span is specified.

The crosstalk effect between the fiber cores can be changed from H_XTCross-talk channel matrix representation of the representation, H_XTExpressed according to the following equation:

in equation (5), the diagonal term of the crosstalk channel matrix is represented by XT_n＝1-∑_n≠mXT_n,mIt is given. Crosstalk represents the exchange energy between the cores and can be estimated based on coupled power theory known to those skilled in the art.

According to some embodiments in which the multi-core fiber is homogeneous, crosstalk coefficients XT that quantify crosstalk between each core-n and core-m_n,mExpressed according to the following equation, where n ≠ m:

in equation (6), Λ represents the core-to-core distance, and β²Representing the propagation constant.

According to some embodiments where the multi-core fibers are heterogeneous, crosstalk coefficients XT that quantify crosstalk between each core-n and core-m_n,mExpressed according to the following equation, where n ≠ m:

according to some embodiments, the system configuration device 17 may be configured to determine the core loss value λ associated with each core-n in dependence on the fiber parameters, the at least one misalignment loss value, the at least one scrambling device 133 (i.e., of a random or deterministic type and the number of the at least one scrambling device 133), and the scrambling function π_n,pWhere N is 1, …, N_c。

According to some embodiments, the system configuration device 17 may be configured to determine the core loss value λ associated with each core-n by applying a singular value decomposition to the channel matrix H_n,pWhere N is 1, …, N_cWhere H represents the optical fiber transmission channel 13 and the channel matrix is based on the permutation matrix P. In particular, the system configuration device 17 may first be configured to perform a QR decomposition of the optical channel matrix according to the following equation:

H＝QR (8)

in equation (6), Q is N_c×N_cOrthogonal matrix, and R is N_c×N_cAnd (4) an upper triangular matrix. The values of the diagonal terms of the upper triangular matrix R are given by the following equation:

in equation (9), α_i,pRepresenting the total misalignment loss associated with core-i of the coreAnd is a permutation matrix P^(k)And XT, and_i＝1-∑_i≠mXT_i,ma total crosstalk coefficient is specified which quantifies the total crosstalk associated with the core-i at the end of the optical transmission channel 13, the total crosstalk coefficient associated with the core-i being dependent on the crosstalk coefficient which quantifies the crosstalk between said core-i and the remaining cores in the multi-core optical fiber.

Using QR decomposition of the optical channel matrix, the singular value decomposition of the optical channel matrix can be represented according to the following equation:

H＝U.∑.V (10)

in equation (10), the matrix Σ is N given by the following equation_c×N_cDiagonal matrix:

by using fiber decomposition into fiber spans, the misalignment loss factor α_i,pCan be given by:

in equation (12), c represents a constant multiplier factor,and(for i ═ 1, …, N_c) Representing a chi-square distributed random variable with one degree of freedom, the mean being equal to (σ)_(x,y),i)²And variance is equal to 2(σ)_(x,y),i)⁴。

Core type T for a given multi-core fiber_nAnd using series connection of K slices in a multi-core optical fibre, variable Z_i,pCan be expressed according to the following equation:

in equation (13):

-T represents the total number of different types of cores associated with the cores of the multi-core optical fiber,

-K_j(for j ═ 1, …, T) specifies the number of cores of the jth core type, among the total number of different types of cores associated with the cores of the multi-core fiber, and

-X_j(for j ═ 1, …, T) normal distribution variables are specified, the mean of whichSum varianceAre expressed according to the following equations, respectively:

considering the embodiment in which the number of fiber spans K is high, the inventors have shown that each variable Z_i,pCan be modeled as having a mean valueSum varianceIs normally distributed. Therefore, the total loss factor α_i,pCan be modeled by lognormal random variables, the mean of whichSum variance valueAre given by the following equations, respectively:

from the derivation of the singular value decomposition of the optical channel matrix, the optical MIMO system of equation (10) can be represented according to the following equation:

according to equation (18), the system configuration device 17 may be configured to determine a core-N (for N ═ 1, …, N) with each core_c) Associated core loss value λ_n,pAnd applying the result of the scrambling function pi such that the core loss value lambda is_n,pIs to have a mean valueSum varianceThe mean and variance of the loss values of each core in terms of relating to the total crosstalk coefficient XT associated with said each core_nAccording to the total loss factor alpha_i,pThe mean and variance of the lognormal distribution and the scrambling function pi. More specifically, each core loss value λ associated with each core-n of the multi-core optical fiber_n,pMean value ofIs the product between a first value and a second value, the first valueCorresponding to the representative and core coRe-n associated lognormal random variable alpha of total misalignment loss_nMean value of (2), second value XT_nCorresponding to the total crosstalk coefficient associated with the core-n of the core. Each core loss value λ associated with each core-n of the multi-core optical fiber_n,pVariance value ofIs the total crosstalk coefficient XT associated with the core-n of the core_nSquare value ofA product with a third value corresponding to a lognormal random variable α representing a total misalignment loss associated with the core-n of the core_nVariance of (2)

In some embodiments where the multi-core optical fiber is heterogeneous, the system configuration device 17 may be configured to be controlled by the CDL_heterThe core-related loss value represented is determined by_max,pA first core loss value represented by_min,pA ratio between second core loss values of the representation, the first value being given by a highest one of the core loss values associated with each core of the multi-core optical fiber, the second value being given by a lowest one of the core loss values associated with each core of the multi-core optical fiber. Core dependent loss CDL_heterCan be expressed on a logarithmic scale according to the following equation:

given a determined core loss value λ associated with each core of a multi-core optical fiber_n,pThe system configuration device 17 may be configured to configure the system according to the user's profile μ_CDLMean and variance of the representation σ 2_CDLThe Gaussian distribution of (A) determines the core-related loss value on a logarithmic scale from mu_CDLMean and variance of the representation σ 2_CDLAre respectively given by:

in equations (20) and (21), imax and imin represent the first core loss value λ, respectively_max,pAnd a second core loss value λ_min,pThe associated core-imax and core-imin index.

According to other embodiments in which the multi-core fiber is homogeneous, the system configuration device 17 may be configured to perform the pairing of CDLs based on setting the confidence interval instead of using the theoretical estimate given by equation (15)_homAn estimate of the core dependent loss value is shown. In fact, the core loss value λ of the homogeneous multi-core fiber_n,pHaving the same lognormal distribution with mean valuesSum varianceWherein alpha is_n,totalRepresenting the total misalignment loss at the end of the optical fibre link, which is of mean valueSum varianceLognormal distribution, mean ofSum varianceAre given according to the following equations, respectively:

in equations (18) and (19), Z is a variable having a normal distribution with a mean value μ_Z＝-2Kb(σ_(x,y))²Sum variance

The confidence interval consists of a series of values that can serve as a good estimate of the random parameter. The desired/target confidence level is predefined. The most common confidence levels are 68%, 90%, 95% and 99%. The critical value γ of the confidence interval C of the gaussian distribution can be obtained using the inverse of the cumulative distribution function Φ according to the following equation:

in equation (20), θ is equal to

For a homogeneous multi-core fiber, the core-related loss value may be determined as the ratio between the upper and lower limits of the confidence interval of the lognormal distribution corresponding to a predefined confidence level. The system configuration device 17 may be configured to determine in a first step the upper and lower limits of the gaussian distribution Z. In a second step, the system configuration device 17 may be configured to convert the determined upper and lower limits by using an exponential function.

In some embodiments with a confidence level set to 90%, the inventors determined that I is separately defined by_max,pAnd I_min,pUpper and lower limits of confidence interval expressed:

accordingly, the core-related loss value in the logarithmic domain is determined as:

in some embodiments, the system configuration device 17 may be configured to determine the CDL by which to determine_targetA target core dependent loss value is represented and at least one fiber parameter of the multi-core fiber is selected in dependence on the core dependent loss value relative to the target core dependent loss value.

In some embodiments, the system configuration device 17 may be further configured to determine a target core correlation loss value, CDL, as a function of the specified one or more target performance indicators_target. The target performance indicator may be selected in a group comprising a target signal-to-noise ratio and a target bit/symbol error rate.

According to some embodiments, the system configuration device 17 is configured to select one or more of the error correction code, the modulation scheme and the time-space code implemented at the transmitter device 11 in dependence on the core dependent loss value with respect to a target core dependent loss value.

According to some embodiments, the system configuration device 17 is configured to select one or more of the space-time decoding algorithm and the error correction code decoding algorithm implemented at the optical receiver 15 in dependence on the core correlation loss value with respect to the target core correlation loss value.

In some embodiments, the system configuration device 17 is configured to determine the core-related loss values offline (e.g., using simulations) during the design phase of the optical transmission channel 13, thereby enabling tailoring the fiber parameters and design of the optical transmission channel 13 to the system/application/transmission requirements and target specifications.

In other embodiments, the system configuration device 17 is configured to determine the core dependent loss value in response to a core dependent loss calculation request, e.g. after design of the optical transmission channel 13, for adaptively adjusting the optical fiber parameters and/or the configuration of the optical transmitter 11 (e.g. adaptive selection of the modulation scheme and/or the error correction code and/or the space-time code) and/or the configuration of the optical receiver 13 (e.g. adaptive selection of the space-time decoding algorithm and/or the error correction code decoder) according to one or more target performance indicators.

According to some embodiments, the scrambling function pi is a random function according to which the first core-n is randomly displaced from the second core-m, the second core being randomly selected among the cores of the multicore fiber, where n ≠ m. In such an embodiment, the entries of the permutation matrix P representing the scrambling function pi are randomly selected, for example using a random number generator.

In other embodiments, a scrambling configuration device 16 is included that is configured to determine the scrambling function according to a deterministic scrambling criterion.

In some embodiments, the deterministic scrambling criteria depend on one or more of core parameters associated with the cores of the multi-core fiber, the core parameters associated with each core of the multi-core fiber being selected from the group consisting of core type and core loss value.

For purposes of illustration, the following description will refer to a multi-core optical fiber in which each core-n includes a core type T_nAnd a core loss value lambda corresponding to the scrambling function pi_n,pOf a set of core parameters T_n；λ_n,pAre associated.

According to some embodiments, core scrambling may be performed in dependence on core loss values to average the losses experienced by different cores, advantageously enabling a reduction of core dependent loss values.

In such embodiments, scrambling configuration device 16 may be configured to align two of the multi-core fibers according to a given sequence (increasing or decreasing) of core loss values associated with the two or more coresThe one or more cores are ordered. For adopting in 1 to N_cI of a value in between can beThe cores core-i are ordered in the indicated numbering list accordingly, so that the numbering list is in accordance with the given order in which the cores are orderedEach core in_iAnd greater or less than and core_i+1,pAssociated core loss value λ_i+1,pCore loss value λ of_i,pAnd (4) associating.

For example, for an increasing order of core loss values, N for i-1, …_c-1, core to core in list_iOrdering to be core with core_iAssociated core loss value λ_i,pLess than or equal to core of fiber_i+1Associated core loss value λ_i+1,pI.e. λ_i,p≤λ_i+1,p。

In embodiments using a decreasing order of core loss values, N for i-1, …_c-1, core to core in list_iOrdering to be core with core_iAssociated core loss value λ_i,pHigher than or equal to core of core_i+1Associated core loss value λ_i+1,pI.e. λ_i,p≥λ_i+1,p。

For N-1, …, N_cThe deterministic scrambling criterion may accordingly be dependent on a core loss value λ associated with the core-n_n,pThe order of (a).

Using the notation of the numbering list, the scrambling configuration device 16 may be configured to determine a deterministic scrambling criterion and a corresponding scrambling function π to core the cores in the numbering list_iCore with core_jSubstitution wherein i takes 1 and N_cAnd j ═ N_c-i + 1. Thus, the scrambling function π can implement a core₁Core with core_NcReplacement, core₂And a fiber coreAnd so on, such that the core associated with the first lowest core loss value is replaced with the core associated with the first highest core loss value, the core associated with the second lowest core loss value is replaced with the core associated with the second highest core loss value, and so on.

Number of cores N in a multi-core fiber_cIn some embodiments where ≧ 2 is an even number, the scrambling configuration device 16 may be configured to determine a deterministic scrambling criterion and a corresponding scrambling function π, to determine the core associated with the ith highest core loss value_iAnd the core associated with the ith lowest core loss valueBy replacing two or more cores, where i is comprised between 1 and half the number of cores in a multi-core fiber, i.e. by replacing two

Number of cores N in a multi-core fiber_cIn other embodiments where ≧ 2 is odd, the scrambling configuration device 16 may be configured to determine a deterministic scrambling criterion and a corresponding scrambling function π, to determine the core associated with the ith highest core loss value_iAnd the core associated with the ith lowest core loss valueThe replacement is carried out pairwise for two or more cores, where i is comprised between 1 and a lower limit value (floor part) of half the number of cores in said multicore fiber, i.e. twoOperatorExpression solutionAnd (5) performing lower limit operation. Thus, the coreMay not be permuted.

In particular, in some embodiments in which the cores are arranged in the fiber according to a 2D grid, the coresMay correspond to the central core.

The deterministic scrambling criteria and the determination of the corresponding scrambling function pi in terms of the core loss value may be performed for optical transmission systems using homogeneous or heterogeneous multi-core fibers.

According to some embodiments in which the multi-core fibers are heterogeneous, the scrambling configuration device 16 may be configured to be dependent on the core type T associated with the two or more cores_n(for N-1, …, N_c) To determine a deterministic scrambling criterion and a corresponding scrambling function pi, the scrambling function pi according to said deterministic scrambling criterion corresponding to the scrambling function pi according to at least a first core_nAnd the second core_mA replacement by two of said two or more cores, where n ≠ m, the first core_nAnd a second core_mWith different core types T_n≠T_mAnd (4) associating.

In some embodiments in which the multi-core fiber is a heterogeneous multi-core fiber, scrambling configuration device 16 may be configured to operate in accordance with N_cCore associated core type T_n(for N-1, …, N_c) And core loss value λ_n,p(for N-1, …, N_c) To determine a deterministic scrambling criterion and a corresponding scrambling function pi, the scrambling function pi according to said deterministic scrambling criterion corresponding to the scrambling function pi according to at least a first core_nAnd the second core_mA replacement by two of said two or more cores, where n ≠ m, the first core_nAnd a second core_mWith different core types T_n≠T_mAssociated with different core loss values.

The scrambling configuration device 16 may be configured to transmit the determined scrambling function pi to at least one scrambling device 133 arranged in the optical transmission channel 13 for scrambling the cores in the multi-core optical fiber by applying the scrambling function pi.

In some embodiments where the optical fiber is a concatenation of K fiber slices, the optical transmission channel 13 may include a fiber according to K_scrThe represented scrambling periods are periodically arranged at least one scrambling device 133 in the optical transmission channel 13. Thus, if k is a multiple of the crypto period, then the scrambling device 133 may be disposed in the kth fiber slice.

Can be based onRepresenting the scrambling function pi in two dimensions, with core_iCore with different type of core_j＝π(core_i) And (4) replacement.

The scrambling function pi can be represented in matrix form by a permutation matrix denoted by P, the entries of which are given by:

according to some embodiments in which the multi-core fiber is heterogeneous, the scrambling configuration device 17 may be configured to determine the core type T associated with the core in the multi-core fiber by applying a scrambling technique selected from the group consisting of, for example and without limitation, a snail scrambling technique, a spin scrambling technique, and a serpentine scrambling technique_n(for N-1, …, N_c) To determine the scrambling function pi.

To apply one of snail, spin and snake scrambling techniques, the scrambling configuration device 17 may first be configured to operate as a scrambling deviceFor core-i (for taking 1 and N) in the indicated set of numbers_cI) of values in between, such that N is 1, … for i_cList of numbersEach core in_iAssociated with different core types.

Use groupAnd according to any of the snail, spin or serpentine scrambling techniques, the scrambling configuration device 17 may determine the scrambling function pi such that for a groupEach core in_i(where i is 1, …, N)_c-1) core_iAnd core pi (core)_i)＝core_i+1Replacement and coreAnd a fiber coreAnd (4) replacement. Thus, the scrambling function π is represented in two dimensions asPermuting symbols propagating through different cores based on the scrambling function such that core passes through the cores_iThe i-th symbol of propagation passes through the core pi (core) after applying the scrambling function_i) And (5) spreading.

In a first example, in a heterogeneous multi-core fiber comprising an odd number of cores, the snail scrambling technique corresponds to applying a scrambling rule of pi (core)_i)＝core_i+1(for i ═ 1, …, N_c-1) andof the odd number of cores, one core is a central core and the remaining cores are arranged at the edges of a hexagon. In particular, according to groupsOf a core of₁May correspond to the central core.

FIG. 11 is a cross-sectional view of a 7-core heterogeneous multi-core fiber in which seven cores are scrambled according to a clockwise direction using a snail scrambling technique such that the central core is displaced from its adjacent core on the right hand side and each of the remaining cores is displaced from its different type of adjacent core on the left hand side, the core on the left hand side of the central core being displaced from the central core. In this example, the scrambling function may be written in two dimensions asSo that core is enabled₁Corresponding to the central core and in a matrix representation according to the following equation:

correspondingly, for the symbol s₁,s₂,…,s₇Permutation is performed such that the symbol s is after application of the scrambling function₁Core through core₂Propagation of each symbol s_i(…,6 for i ═ 2) through the core_i+1Spread and symbol s₇Propagating through the central core.

FIG. 12 shows a cross-sectional view of a 12-core heterogeneous multi-core fiber in which twelve cores are displaced in a clockwise direction using a rotational scrambling technique. The cores are arranged in a ring. By using a rotational scrambling technique, each core is displaced from its right-hand neighboring core of a different type, such that pi (core)_i)＝core_i+1(…,11 for i ═ 1), and core₁₂Core with core₁And (4) replacement.

FIG. 13 shows a cross-sectional view of a 32-core heterogeneous multi-core fiber in which the cores are displaced in a clockwise direction using a serpentine scrambling technique. The cores are arranged in a two-dimensional grid comprising six layers. The first upper layer comprises four fiber cores which are numbered as core₁、core₂、core₃、core₄. The second layer, which is located below the first layer, includes six cores, numbered core₅-core₁₀. The third layer, located below the second layer, comprises six cores, numbered core₁₁-core₁₆. The fourth layer, which is located below the third layer, includes six cores, numbered core₁₇-core₂₂. The fifth layer, which is located below the fourth layer, includes six cores, numbered core₂₃-core₂₈. And finally, the next layer includes four cores, numbered core₂₉-core₃₂. According to the serpentine scrambling technique, each core in each layer is replaced with its right-hand adjacent core of a different type, the last core of each layer is replaced with the first core of the layer below said each layer, and the core₃₂(i.e., the last core of the lower layer) and core₁(i.e., the first core of the upper layer).

Fig. 11, 12 and 13 illustrate examples of applying snail, spin and serpentine scrambling techniques according to displacement of the core in a clockwise direction. It should be noted, however, that the snail, spin, and serpentine scrambling techniques may also be applied based on the displacement of the core in the counterclockwise direction.

Using the matrix symbols of the scrambling function, the optical fiber transmission channel including the scrambling device 133 can be represented according to the following equation:

in equation (29), the matrix P^(k)Is N_c×N_cA matrix representing the scrambling function pi applied by the kth scrambling device in the kth span of optical fiber, k being a multiple of the scrambling period.

According to some embodiments, the at least one scrambling device 133 may be configured to apply a scrambling function pi in an electric field.

In other embodiments, the at least one scrambling device 133 may be an optical device configured to apply a scrambling function pi in the optical field. Exemplary optical scrambling devices include converters, optical multiplexers, optical multiplexing devices, and photonic lanterns.

According to some embodiments, scrambling configuration device 16 may be configured to determine the scrambling function during the design phase of the optical fiber transmission channel prior to installing scrambling device(s) 133.

In other embodiments, the scrambling configuration device 16 may be configured to determine a scrambling function of the configuration of the one or more scrambling devices 133 in the operating optical transmission channel 13. In such embodiments, the scrambling configuration device 15 may be configured to transmit the determined scrambling function to the system configuration device 17.

Also provided is a method for determining a core-related loss value of an optical fiber communication system 100, in which optical fiber communication system 100 data is transmitted on an optical fiber transmission channel 13 made of a multi-core optical fiber, an optical signal carrying said data being dependent on N_c≧ 2 (two or more) cores propagate along a multi-core fiber, the multi-core fiber being associated with a fiber parameter and a misalignment loss value, the method including scrambling the two or more cores according to a scrambling function π. The method includes determining a core dependent loss value as a function of a fiber parameter, a misalignment loss value, and a scrambling function pi.

Fig. 10 is a flow chart depicting a method for determining core-related loss values in a multi-core optical fiber transmission system 100 in which single polarization, single wavelength, single carrier uncoded modulation without application of time-space coding is used, and each core of the multi-core optical fiber is a single mode core, according to some embodiments of the invention.

In step 1001, fiber parameters and misalignment loss values for a multi-core fiber may be received.

In some embodiments, the fiber parameters include the number of cores N_cNot less than 2, length L of optical fiber, crosstalk coefficient XT_n,m(where N, m. epsilon. {1, …, N)_c}) and a coupling coefficient k_n,m(where N, m. epsilon. {1, …, N)_c}) of each crosstalk coefficient XT_n,mRepresenting the crosstalk between core-n and core-m (where n ≠ m) in a multicore fiber, each coupling coefficient k_n,mRepresenting the coupling between core-n and core-m (where n ≠ m) in a multi-core fiber.

In some embodiments, the fiber parameters may further include a bend radius R_bA cladding diameter, a number K of fiber slices, a radius of each core of the multi-core fiber, and a type T of each core-n of the multi-core fiber_nWhere N is 1, …, N_c。

In some embodiments, the misalignment may be selected from the group consisting of longitudinal misalignment, lateral misalignment, and angular misalignment.

In some embodiments, the misalignment loss value may be previously determined according to equation (1).

In step 1003, a scrambling function π represented by permutation matrix P may be received.

In some embodiments, the scrambling function π is a random function according to which a first core-n is randomly displaced from a second core-m, the second core being randomly selected among the cores of the multi-core fiber, where n ≠ m. In such an embodiment, the entries of the permutation matrix P representing the scrambling function pi are randomly selected, for example using a random number generator.

In other embodiments, the scrambling function pi is a deterministic function that is predetermined according to a deterministic scrambling criterion.

In some embodiments, the deterministic scrambling criteria depend on one or more of core parameters associated with the cores of the multi-core fiber, the core parameters associated with each core of the multi-core fiber being selected from the group consisting of core type T_nAnd core loss value λ_n,p(for N-1, …, N_c) Selected from the group of (1).

According to an embodiment, the deterministic scrambling criterion depends on core loss values associated with two or more cores of the multi-core fiber.

In some embodiments, the list of numbers may be in the list of numbersIn which the cores are ordered so that the list is numbered according to a given order considered for ordering the coresEach core in_iAnd greater or less than and core_i+1Associated core loss value λ_i+1,pCore loss value λ of_i,pAnd (4) associating. Given the order of core loss values, the deterministic scrambling criteria and corresponding scrambling function π may be in accordance with the order of core loss values associated with two or more cores.

In embodiments that consider a numbered list of ordered cores, the deterministic scrambling criteria may correspond to the core associated with the ith highest core loss value_iAnd the core associated with the ith lowest core loss valueFor an even number of cores N_c，And for an odd number of cores N_c，

The determination of the scrambling criteria and the corresponding scrambling function pi in dependence on the determination of the core loss value associated with the core of the multi-core fiber may be performed in embodiments that consider homogeneous or heterogeneous multi-core fibers.

In some embodiments in which the multi-core fiber is heterogeneous, the core type T associated with the cores in the multi-core fiber may be dependent upon_n(for N-1, …, N_c) To determine a deterministic scrambling criterion and a corresponding scrambling function pi. In such an embodiment, the deterministic scrambling criterion corresponds to a code according to at least a first core_nAnd the second core_m(where n ≠ m) two-by-two replacement of the replaced cores, the first core_nAnd a second core_mWith different core types T_n≠T_mAnd (4) associating.

In some embodiments, the scrambling function may be determined in terms of core type using one of snail, spin, or serpentine scrambling techniques.

In other embodiments where the multi-core fiber is heterogeneous, the method may be based on N_cCore type T associated with each core_n(for N-1, …, N_c) And core loss value λ_n,p(for N-1, …, N_c) To determine a deterministic scrambling criterion and a corresponding scrambling function pi, in such an embodiment the deterministic scrambling criterion corresponds to a scrambling function according to at least a first core_nAnd the second core_m(where N ≠ m) of permuted N_cPairwise displacement of individual cores, first core_nAnd a second core_mWith different core types T_n≠T_mAssociated with different core loss values.

At step 1005, a core loss value λ associated with each core-n may be determined_n,p(for N-1, …, N_c). In particular, according to equation (18), a core loss value associated with the core of the multi-core optical fiber may be determined as a function of the crosstalk coefficient and the at least one misalignment loss value for a given scrambling function π.

According to some embodiments in which the multi-core fiber is heterogeneous, the core dependent loss value, CDL, may be determined at step 1005_heterIs determined by_max,pA first core loss value represented by_min,pA ratio between second core loss values of the representation, the first value being given by the highest of the core loss values associated with each core of the multi-core optical fiber and the second value being given by the smallest of the core loss values associated with each core of the multi-core optical fiber. Core associated loss value CDL_heterCan be expressed on a logarithmic scale according to equation (19).

According to some embodiments in which the multi-core fiber is homogeneous, the core dependent loss value CDL may be determined in step 1005 according to equation (27)_homA ratio between an upper and a lower limit of a confidence interval of the lognormal distribution is determined as corresponding to the predefined confidence level.

According to some embodiments, the determined core dependent loss value may be taken into account for selecting and/or adapting at least one of the fiber parameters and/or the scrambling function pi and/or the number of scrambling devices used to perform core scrambling in dependence of the core dependent loss value with respect to a target core dependent loss value.

In some embodiments, the target core-related loss may be predetermined in accordance with one or more target performance indicators, e.g., selected from the group consisting of a target signal-to-noise ratio and a target bit/symbol error rate.

In some embodiments, the method of determining the core dependent loss value for a given configuration of the fiber transmission channel 13 (i.e. a given fiber parameter, the number of scrambling devices 133) is performed offline before designing the fiber transmission channel 13, thereby adapting the fiber parameters and the design of the optical transmission channel 13 to the system/application/transmission requirements and target specifications.

In other embodiments, the method of determining a core-related loss value for a given configuration of the optical fiber transmission channel 13 is performed after designing the optical fiber transmission channel 14 for performing an adaptive selection of one or more optical fiber parameters and/or an adaptive manufacturing of a multi-core optical fiber and/or an adaptive selection of one or more transmission configuration parameters, the transmission configuration parameters comprising:

error correction codes for encoding data transmitted on the optical transmission channel 13;

-a modulation scheme for modulating the encoded data into a set of modulation symbols;

-a space-time code for determining a space-time codeword from the modulation symbols;

-a space-time decoding algorithm for determining an estimate of said space-time codeword, and

an error correction code decoder for determining an estimate of the data transmitted on the optical transmission channel 13.

Although various embodiments have been described in detail in the context of a single core multimode optical fiber using single polarization, single wavelength and single carrier modulation, it should be noted that the invention may also be applied to a multi-fiber core multimode optical fiber in combination with polarization multiplexing using two polarizations and/or in combination with wavelength multiplexing using several wavelengths and/or using a multi-carrier modulation format.

Furthermore, the invention is not limited to communication applications and may be integrated in other applications, such as data storage and medical imaging. The invention can be used in several optical transmission systems, such as automotive industry applications, oil or gas markets, aerospace and avionics fields, sensing applications, etc.

While embodiments of the invention have been illustrated by a description of various examples and while these embodiments have been described in considerable detail, it is not the intention of the applicants to restrict or in any way limit the scope of the appended claims to such detail. Additional advantages and modifications will readily appear to those skilled in the art. The invention in its broader aspects is therefore not limited to the specific details, representative method, and illustrative examples shown and described.