阅读说明：本技术 一种可重构纤芯模式选择系统和方法 (Reconfigurable fiber core mode selection system and method ) 是由 刘博� 忻向军 任建新 毛雅亚 沈佳佳 吴泳锋 孙婷婷 赵立龙 于 2021-08-23 设计创作，主要内容包括：本发明公开了一种可重构纤芯模式选择系统和方法,模分复用信号通过EDFA放大后通过少模多芯光纤传输进入光子灯笼进行解复用,解复用后的模式输入SLM调制每个模式光信号的光强,均衡EDFA放大后的光功率差异,然后通过全反射镜将均衡后的模式反射到光子灯笼指定的模式位置,即交换模式之间所加载的信号,最后利用光子灯笼复用到少模光纤输出,完成模式的调度与均衡。可解决少模多芯传输系统的资源调度。(The invention discloses a reconfigurable fiber core mode selection system and a method, wherein a mode division multiplexing signal is amplified by an EDFA and then transmitted into a photon lantern through a few-mode multi-core fiber for demultiplexing, the demultiplexed mode is input into an SLM for modulating the light intensity of each mode optical signal, the optical power difference amplified by the EDFA is equalized, then the equalized mode is reflected to the mode position appointed by the photon lantern through a holophote, namely, signals loaded between the modes are exchanged, and finally the photon lantern is multiplexed to the few-mode fiber for output, so that the scheduling and equalization of the modes are completed. The resource scheduling of the few-mode multi-core transmission system can be solved.)

1. A reconfigurable fiber core mode selection system is characterized by comprising an EDFA, a first few-mode multi-core fiber, a first photon lantern, an SLM, a holophote, a second photon lantern and a second few-mode multi-core fiber;

the EDFA amplifies the mode division multiplexing signals;

the first few-mode multi-core optical fiber transmits the amplified signal to a first photon lantern;

the first photon lantern demultiplexes an input signal;

the SLM modulates the light intensity of each mode optical signal for the demultiplexing mode, and balances the optical power difference after EDFA amplification;

the holophote reflects the equalized mode to a mode position appointed by the second photon lantern;

and the second photon lantern multiplexes the modes in different directions to the second few-mode optical fiber for output.

2. A reconfigurable core mode selection system according to claim 1, wherein the first few-mode multicore fiber and the second few-mode multicore fiber comprise seven cores in a regular hexagonal distribution with equal spacing between adjacent cores;

each core comprises 6 different modes;

a circle of air holes are formed outside each fiber core, so that crosstalk among the fiber cores can be effectively reduced, and signals transmitted in the fiber cores are bound in the fiber cores;

the fiber core spacing of the first few-mode multi-core fiber and the second few-mode multi-core fiber is in a micron order.

3. The reconfigurable core mode selection system of claim 1, wherein the first and second photonic lanterns are multiplexed photonic lanterns with one multimode fiber at one end and a plurality of single mode fiber clusters at the other end, and a tapered transition region in the middle.

4. A reconfigurable core mode selection system according to claim 1, wherein the SLM is a twisted nematic SLM.

5. The reconfigurable core mode selection system according to claim 1, wherein a rotatable base is mounted under the holophote, the rotation angle is controlled by a central control circuit, the light waves emitted from the SLM are reflected and coupled into the next photonic lantern, and the mode control is completed.

6. The reconfigurable core mode selection method of a reconfigurable core mode selection system according to any of claims 1-5, comprising:

step 1, a mode division multiplexing signal is amplified by an EDFA, transmitted through a first few-mode multi-core fiber and enters a first photon lantern;

step 2, the first photon lantern demultiplexes the multiplexed mode into an independent mode and outputs the independent mode;

step 3, the output independent mode enters an SLM to control the light intensity of the optical signal, the light intensity is balanced, and the transmission direction of the signal is changed by independently controlling the rotation angle of the total reflection mirror;

and 4, enabling the modes in different directions to enter a second photon lantern, and multiplexing the modes to a second few-mode optical fiber output through the second photon lantern to finish the scheduling and balancing of the modes.

Technical Field

The invention belongs to the technical field of communication, and particularly relates to a reconfigurable fiber core mode selection system and method.

Background

In recent years, with the rapid increase of communication traffic of backbone networks, the capacity of transmission systems based on single-mode optical fibers approaches the shannon limit, and it is difficult to continue increasing. Therefore, a space division multiplexing technology capable of increasing the system capacity by times has been developed, and a mode division multiplexing technology based on few-mode optical fibers has been intensively studied and developed as the most important branch of the space division multiplexing technology. Multiplexing techniques that create multiple independent spatial modes in a single fiber to transmit parallel data are known as Space Division Multiplexing (SDM) techniques. The SDM technique can be divided into a core division multiplexing technique and a mode division multiplexing technique, and in addition, a plurality of few-mode fiber cores can be multiplexed in the optical fiber to perform few-mode and multi-core multiplexing. Taking a 7-core 6-mode optical fiber as an example, one 7-core 6-mode optical fiber includes 7 few-mode cores, and 6 modes can be transmitted in parallel in each few-mode core, so that compared with a single-core single-mode optical fiber, the transmission capacity can be improved by 42 times by 7 × 6. Optical transmission systems based on few-mode multi-cores have attracted considerable attention and research interest. However, inevitably, the loss of the high-order mode in the few-mode multi-core fiber is larger than that of the fundamental mode, and the mode coupling strength is also higher, so that the quality of the optical signal transmitted based on the fundamental mode is better, and the quality of the optical signal transmitted based on the high-order mode is poorer.

In a conventional communication system, information transmitted in each mode cannot be changed at will, and a receiving end can only receive all the modes at the same time and separate the required modes from the modes, which has a certain influence on the demodulation quality and transmission efficiency of signals. Therefore, the invention designs a mode selection method of a reconfigurable fiber core, which can randomly select and change signals transmitted by a basic mode and each high-order mode according to requirements, thereby increasing the flexibility of system transmission and realizing mode selection scheduling optimization.

Since the technology of preparing optical fiber has been improved since high-roll invention optical fiber communication, it is now possible to reduce the optical fiber transmission loss to below 0.2dB/km, however, the optical signal will be attenuated when propagating through the optical fiber, especially in long-distance large-capacity transmission systems, the attenuation of the optical signal will become more serious, and thus the repeater amplifier is an important component in long-distance large-capacity transmission systems. Optical regenerators were used to gain the amplification of optical signals before the advent of pure optical amplifiers, however the signal bit rate and signal format of the regenerators have limited their development. The optical amplifier is a great progress in optical fiber communication instead of the regenerator, and an erbium-doped fiber amplifier (EDFA) is the most widely used relay optical amplifier with its excellent performance. The EDFA has the advantages of small noise, large amplification bandwidth, good gain curve, high pumping efficiency, stable working performance, mature technology, low price and the like.

With the development of space division multiplexing technology, the EDFA of single-mode fiber cannot meet the requirements of a transmission system, however, few-mode EDFAs developed in recent years and suitable for a mode division multiplexing system have different gains for different modes, the optical power amplification of each channel is unbalanced after long-distance transmission, so that the optical power difference between the channels is too large, some signals are submerged at a receiving end, and some signal powers are too large, so that a receiver is overloaded, and the transmission system cannot work normally, and meanwhile, the design method for few-mode EDFA equalization is complex. Therefore, a simpler method is needed to perform optical power equalization after signal amplification, so as to avoid serious nonlinear effect.

Disclosure of Invention

The invention aims to solve the technical problems in the prior art, and provides a reconfigurable fiber core mode selection system and a reconfigurable fiber core mode selection method, which are used for carrying out independent light intensity modulation on each mode by utilizing the electro-optic characteristic of a Spatial Light Modulator (SLM), can effectively balance the amplified light power, can solve the resource scheduling problem of a few-mode multi-core transmission system, simultaneously solve the problem of uneven amplification of an EDFA, balance the power of different modes in a channel, and improve the transmission efficiency and quality of the few-mode multi-core transmission system.

In order to achieve the technical purpose, the technical scheme adopted by the invention is as follows:

a reconfigurable fiber core mode selection system comprises an EDFA, a first few-mode multi-core fiber, a first photon lantern, an SLM, a holophote, a second photon lantern and a second few-mode multi-core fiber;

the EDFA amplifies the mode division multiplexing signals;

the first few-mode multi-core optical fiber transmits the amplified signal to a first photon lantern;

the first photon lantern demultiplexes an input signal;

the SLM modulates the light intensity of each mode optical signal for the demultiplexing mode, and balances the optical power difference after EDFA amplification;

the holophote reflects the equalized mode to a mode position appointed by the second photon lantern;

and the second photon lantern multiplexes the modes in different directions to the second few-mode optical fiber for output.

In order to optimize the technical scheme, the specific measures adopted further comprise:

the first few-mode multi-core fiber and the second few-mode multi-core fiber comprise seven fiber cores which are distributed in a regular hexagon shape, and the distances between the adjacent fiber cores are equal;

each core comprises 6 different modes;

a circle of air holes are formed outside each fiber core, so that crosstalk among the fiber cores can be effectively reduced, and signals transmitted in the fiber cores are bound in the fiber cores;

the fiber core spacing of the first few-mode multi-core fiber and the second few-mode multi-core fiber is in a micron order.

The first photon lantern and the second photon lantern are multiplex photon lanterns, one end of each photon lantern is a multimode optical fiber, the other end of each photon lantern is a plurality of single-mode optical fiber clusters, and the middle portion of each photon lantern is a conical transition area.

The above described SLM uses a twisted nematic SLM.

A rotatable base is arranged below the total reflector, the rotation angle is controlled through a central control circuit, light waves emitted from the SLM are reflected and coupled into the next photon lantern, and the mode regulation and control are completed.

A method of reconfigurable core mode selection, comprising:

step 1, a mode division multiplexing signal is amplified by an EDFA, transmitted through a first few-mode multi-core fiber and enters a first photon lantern;

step 2, the first photon lantern demultiplexes the multiplexed mode into an independent mode and outputs the independent mode;

step 3, the output independent mode enters an SLM to control the light intensity of the optical signal, the light intensity is balanced, and the transmission direction of the signal is changed by independently controlling the rotation angle of the total reflection mirror;

and 4, enabling the modes in different directions to enter a second photon lantern, and multiplexing the modes to a second few-mode optical fiber output through the second photon lantern to finish the scheduling and balancing of the modes.

The invention has the following beneficial effects:

the method comprises the steps of solving resource scheduling of a few-mode multi-core transmission system, enabling mode division multiplexing signals to enter a photon lantern for demultiplexing after being amplified through an EDFA, inputting a mode after demultiplexing into an SLM (selective laser modulator) to modulate light intensity of optical signals of each mode, balancing optical power difference after the EDFA is amplified, reflecting the balanced mode to a mode position appointed by the photon lantern through a holophote, namely exchanging signals loaded between the modes, and finally multiplexing to the few-mode optical fiber output through the photon lantern to finish scheduling and balancing of the modes.

The invention reconstructs the structure of the fiber core on the basis of a few-mode multi-core optical fiber transmission system, can randomly select and change signals transmitted by a base mode and each high-order mode according to requirements, increases the flexibility of system transmission and realizes the selection, scheduling and optimization of the modes; the SLM is used for modulating the light power of each mode, the light power amplified by the EDFA is balanced through a simple method, the transmission quality is improved, and the mode error rate is reduced.

Drawings

FIG. 1 is a block diagram of a reconfigurable core mode selection system of the present invention;

FIG. 2 is a cross-sectional view of a 7-core 6-mode optical fiber;

FIG. 3 is a schematic diagram of a multiplexed photonic lantern;

FIG. 4 is a schematic diagram of the basic structure of a twisted nematic SLM;

FIG. 5 is a schematic diagram of polarization modulation;

fig. 6 is a schematic diagram of the SLM changing the transmission direction of the optical signal.

Detailed Description

Embodiments of the present invention are described in further detail below with reference to the accompanying drawings.

Referring to fig. 1, a reconfigurable fiber core mode selection system includes an EDFA, a first few-mode multicore fiber, a first photon lantern, an SLM, a holophote, a second photon lantern, and a second few-mode multicore fiber;

the EDFA amplifies the mode division multiplexing signals;

the first few-mode multi-core optical fiber transmits the amplified signal to a first photon lantern;

the first photon lantern demultiplexes an input signal;

the SLM modulates the light intensity of each mode optical signal for the demultiplexing mode, and balances the optical power difference after EDFA amplification;

the holophote reflects the equalized mode to a mode position appointed by the second photon lantern;

the second photon lantern multiplexes the modes in different directions to the second few-mode optical fiber for output, so that the mode scheduling is realized, namely, signals borne by different modes in the original photon lantern are exchanged, and meanwhile, the balance of the optical power is realized.

In an embodiment, a cross-sectional view of the first few-mode multicore fiber and the second few-mode multicore fiber is shown in fig. 2, seven cores in a cladding in the drawing are distributed in a regular hexagon, and the intervals between adjacent cores are equal;

six different color triangles in each fiber core represent six different modes;

a circle of air holes are formed outside each fiber core, so that crosstalk among the fiber cores can be effectively reduced, and signals transmitted in the fiber cores are bound in the fiber cores;

meanwhile, the fiber core space between the first few-mode multi-core fiber and the second few-mode multi-core fiber is very small and is only in a micron level, and the fiber core space has the characteristics of low nonlinearity, low modal dispersion and the like, and is favorable for building a stable and compact fiber transmission system. In the few-mode multi-core fiber, a small number of low-order modes can be transmitted, so that the regulation and control of the transmission mode can be easily realized.

In an embodiment, the first and second photon lanterns are multiplexing photon lanterns, as shown in fig. 3, one end is a multimode fiber, the other end is a plurality of single mode fiber clusters, and the middle part is a tapered transition region;

the basic structure of the multiplexing photon lantern is that a single-mode optical fiber is placed in a manufactured low-refractive-index thin pipeline, then a single-mode optical fiber bundle is subjected to hot tapering, the cladding of the single-mode optical fiber in a tapered transition region is gradually fused with the cladding of other single-mode optical fibers, the cladding is continuously shrunk until a multimode optical fiber core is formed, and finally the manufactured thin pipeline becomes the cladding of a new multimode optical fiber.

The light signal is incident from the single-mode fiber and is output from the few-mode fiber, and in the process, the photon lantern completes mode conversion from a basic mode to a high-order mode. Conversely, one few-mode fiber is separated into a plurality of single-mode fibers in an adiabatic tapering manner, a high-order mode in the few-mode fiber can enter a fundamental mode in the single-mode fiber formed after tapering in a lossless manner, and in the process, the photon lantern completes mode conversion from the high-order mode to the fundamental mode. The main function of the photon lantern module is to multiplex/demultiplex the mode of mode division multiplexing.

In an embodiment, the SLM uses a twisted nematic SLM, and its basic structure is shown in fig. 4, the SLM can regulate and control the amplitude parameter of the optical wave in real time, and its amplitude modulation characteristic mainly uses the optical rotation effect of the liquid crystal.

As shown in fig. 5, the polarization directions of the polarizer and the analyzer of the liquid crystal cell are perpendicular to each other, when no voltage is applied to the two ends of the liquid crystal cell, the optical signal with the same polarization state as the polarizer can enter the liquid crystal cell, after entering the liquid crystal cell, the polarization state of the optical signal continuously changes along with the twist direction of the liquid crystal molecules, and the optical signal is consistent with the polarization direction of the analyzer when being output from the liquid crystal cell, and can be completely emitted through the analyzer, so that the transmittance of the SLM is maximized, and the emission light intensity is strongest. When voltage is applied to two ends of the liquid crystal box, the twist direction of the liquid crystal changes along with the direction of an applied electric field, the polarization direction of light waves entering the liquid crystal box through the polarizer also changes along with the twist direction of the liquid crystal in the liquid crystal box, the polarization direction of the light waves exiting the liquid crystal box is not parallel to the analyzer, and the light intensity emitted from the analyzer is attenuated. When the voltage applied to the liquid crystal cell is large enough, the liquid crystal molecules twist by 90 degrees, so that the polarization direction of the light wave emitted from the liquid crystal cell is vertical to the analyzer, and the light cannot pass through the analyzer, and the emergent light intensity is the weakest. The polarization state of the light beam is changed by changing the voltage applied on the liquid crystal, namely the light wave is attenuated, and the attenuation of the light wave is realized.

In an embodiment, as shown in fig. 6, a rotatable base is installed below the total reflection mirror, the rotation angle is controlled by a central control circuit, the light wave emitted from the SLM is reflected, and the light wave is coupled into the next photon lantern, so that the mode regulation and control are completed.

A method of reconfigurable core mode selection, comprising:

step 1, a mode division multiplexing signal is amplified by an EDFA, transmitted through a first few-mode multi-core fiber and enters a first photon lantern;

step 2, the first photon lantern demultiplexes the multiplexed mode into an independent mode and outputs the independent mode;

step 3, the output independent mode enters an SLM to control the light intensity of the optical signal, the light intensity is balanced, the transmission direction of the signal is changed by independently controlling the rotation angle of a total reflection mirror, namely, the balanced mode is reflected to the mode position appointed by the photon lantern through the total reflection mirror, and the loaded signal between the modes is exchanged;

and 4, enabling the modes in different directions to enter a second photon lantern, and multiplexing the modes to a second few-mode optical fiber output through the second photon lantern to finish the scheduling and balancing of the modes.

The above is only a preferred embodiment of the present invention, and the protection scope of the present invention is not limited to the above-mentioned embodiments, and all technical solutions belonging to the idea of the present invention belong to the protection scope of the present invention. It should be noted that modifications and embellishments within the scope of the invention may be made by those skilled in the art without departing from the principle of the invention.