Multimode optical fiber transmission system based on high-speed single-mode optical module
阅读说明：本技术 一种基于高速单模光模块的多模光纤传输系统 (Multimode optical fiber transmission system based on high-speed single-mode optical module ) 是由 胡贵军 冯泽亮 于 2021-09-10 设计创作，主要内容包括：本发明公开了一种基于高速单模光模块的多模光纤传输系统,属于光纤通信技术领域。该系统由信号发生模块、模式激发模块、信号传输模块、信号接收模块及信号分析模块构成,利用高速单模光模块在多模光纤中传输,实现了高速短距离通信,相较其他高速短距离通信系统,降低了通信的成本,且可实现大规模的覆盖。同时,对系统中的偏芯距设计提出一种方法,通过设计合理的偏芯距,得到了保证系统传输性能的最大偏芯距,使系统误码率低于2×10～(-4),为系统的实际搭建提供了基础,实现了系统的有效传输。(The invention discloses a multimode optical fiber transmission system based on a high-speed single-mode optical module, and belongs to the technical field of optical fiber communication. The system is composed of a signal generating module, a mode exciting module, a signal transmission module, a signal receiving module and a signal analyzing module, high-speed single-mode optical modules are used for transmitting in multimode optical fibers, high-speed short-distance communication is achieved, compared with other high-speed short-distance communication systems, communication cost is reduced, and large-scale coverage can be achieved. Meanwhile, a method is provided for designing the eccentric distance in the system, the maximum eccentric distance for ensuring the transmission performance of the system is obtained by designing the reasonable eccentric distance, and the error rate of the system is lower than 2 multiplied by 10 ‑4 The method provides a foundation for the actual construction of the system and realizes the effective transmission of the system.)
1. A multimode optical fiber transmission system based on a high-speed single-mode optical module is characterized by comprising a signal generation module (1), a mode excitation module (2), a signal transmission module (3), a signal receiving module (4) and a signal analysis module (5); the output port of the signal generation module (1) is connected with the input port of the mode excitation module (2), the output port of the mode excitation module (2) is connected with the input port of the signal transmission module (3), the output port of the signal transmission module (3) is connected with the input port of the signal receiving module (4), and the output port of the signal receiving module (4) is connected with the input port of the signal analysis module (5).
2. The multimode optical fiber transmission system based on the high-speed single-mode optical module according to claim 1, wherein the signal generating module (1) is composed of a signal generator (11), a laser (12) and an optoelectronic modulator (13); the mode excitation module (2) consists of a first single-mode fiber (21) and a first core-shifting mode excitation module (22); the signal transmission module (3) consists of a first multimode optical fiber (31), a second core-shifting mode excitation module (32) and a second multimode optical fiber (33); the signal receiving module (4) consists of an eccentric mode coupling (41) and a second single-mode optical fiber (42); the output port of the signal generator (11) is connected with the first input port (131) of the photoelectric modulator (13), and the output port of the laser (12) is connected with the second input port (132) of the photoelectric modulator (13); an output port of the photoelectric modulator (13) is connected with an input port of a first single-mode fiber (21), and an output port of the first single-mode fiber (21) is connected with an input port of a first core-shifting mode excitation module (22); the output port of the first core-shifting mode excitation module (22) is connected with the input port of a first multimode fiber (31), the output port of the first multimode fiber (31) is connected with the input port of a second core-shifting mode excitation module (32), and the output port of the second core-shifting mode excitation module (32) is connected with the input port of a second multimode fiber (33); the output port of the second multimode fiber (33) is connected with the input port of the core-offset mode coupling (41), and the output port of the core-offset mode coupling (41) is connected with the input port of the second single-mode fiber (42); the output port of the second single-mode optical fiber (42) is connected with the input port of the signal analysis module (5).
3. The multimode optical fiber transmission system based on the high-speed single-mode optical module according to claim 1, wherein the first single-mode optical fiber (21) is connected with the first multimode optical fiber (31) by shifting the fiber core by a first offset distance, the first multimode optical fiber (31) is connected with the second multimode optical fiber (32) by shifting the fiber core by a second offset distance, and the second multimode optical fiber (32) is connected with the second single-mode optical fiber (42) by shifting the fiber core by a third offset distance.
4. The high speed single mode optical module based multimode fiber transmission system of claim 1 wherein the first, second and third sections have an eccentricity of no more than 10 um.
5. The multimode fiber transmission system based on the high-speed single-mode optical module according to claim 3, wherein the method for designing the eccentric distance comprises the following steps:
simulating the mode excitation condition of light entering a first multimode fiber from a first single-mode fiber under different eccentric distances by utilizing Rsoft software to obtain the mode types, the number and the power ratio of LP01 excited in the first multimode fiber under different eccentric distances;
secondly, modifying the number of attenuators, attenuation coefficients, the number of time delayers and time delay values in a first core-offset mode excitation module in the system according to the mode excitation condition of the first single-mode fiber entering the first multimode fiber under different core-offset distances, and obtaining system error rates under different mode couplings and different differential mode group time delay interferences by inputting the mode excitation conditions under different core-offset distances;
thirdly, simulating the mode excitation condition when light subjected to mode coupling under different eccentric distances is transmitted into the second multimode fiber from the first multimode fiber by utilizing Rsoft software to obtain the type, the quantity and the power ratio of the modes excited in the second multimode fiber by different modes in the first multimode fiber under different eccentric distances;
fourthly, modifying the first core-shifting mode excitation module and the second core-shifting mode excitation module in the system according to the simulation result, wherein the modification of the first core-shifting mode excitation module is consistent with the modification of the second step, then modifying the number and attenuation coefficient of the attenuators and the number and delay value of the time delay devices in the second core-shifting mode excitation module in the system according to the mode excitation condition that the first multimode optical fiber enters the second multimode optical fiber under different core-shifting distances, and obtaining the system error rate under different mode couplings and different differential mode group delay interferences under different core-shifting distances by inputting the mode excitation conditions under different core-shifting distances;
fifthly, simulating the coupling condition of the light subjected to mode coupling at different eccentric distances to LP01 when the light enters the second single-mode fiber from the second multimode fiber to obtain the power ratio of different modes in the second multimode fiber to the LP01 mode coupling at different eccentric distances by utilizing Rsoft software;
sixthly, modifying the first eccentric mode excitation module, the second eccentric mode excitation module and the eccentric mode coupling module in the system according to the simulation result, wherein the modification of the first eccentric mode excitation module and the modification of the second eccentric mode excitation module are consistent with the modification in the fourth step; then, modifying the number and attenuation coefficient of attenuators, the number and coupling ratio of couplers and the number and delay value of time delayers in an offset core mode coupling module in the system according to the coupling condition of different modes to LP01 when the second multimode fiber enters the second single mode fiber under different offset core distances, and obtaining the system error rate under different offset core distances by inputting the mode excitation and mode coupling conditions under different offset core distances;
seventhly, firstly, according to the error rate condition of a system when the first single-mode fiber enters the first multimode fiber under different core offset distances, obtaining the maximum core-offset range between the first single-mode fiber and the first multimode fiber under the limit FEC; then, according to system error rate conditions of the joint of the first single-mode fiber and the first multimode fiber and the joint of the first multimode fiber and the second multimode fiber under different core offset distances, obtaining the maximum core offset distance range between the first multimode fiber and the second multimode fiber under the limit FEC when the core offset distance between the first single-mode fiber and the first multimode fiber is determined; finally, according to the system error rate conditions of the first single-mode fiber and the first multimode fiber at the joint, the first multimode fiber and the second multimode fiber at the joint and the second multimode fiber and the second single-mode fiber at different core offset distances, the maximum range of core offset between the second multimode fiber and the first single-mode fiber under the limit FEC is obtained when the core offset distance between the first single-mode fiber and the first multimode fiber and the core offset distance between the first multimode fiber and the second multimode fiber are determined; the maximum range of three-section eccentric distance which can be effectively transmitted by the system can be obtained.
6. The multimode fiber transmission system based on the high-speed single-mode optical module according to claim 6, wherein the number of the attenuators in the second step is the number of the excited modes when the first single-mode fiber enters the first multimode fiber, the attenuation coefficients of the different attenuators are the power ratios of the different modes excited when the first single-mode fiber enters the first multimode fiber, the number of the retarders is the number of the modes excited when the first single-mode fiber enters the first multimode fiber, the number of the retarders is reduced by one, and the delay value is the delay difference between the different modes and LP 01.
7. The multimode fiber transmission system based on the high-speed single-mode optical module according to claim 6, wherein the number of the attenuators in the second step is the number of the excited modes when the first single-mode fiber enters the first multimode fiber, the attenuation coefficients of the different attenuators are the power ratios of the different modes excited when the first single-mode fiber enters the first multimode fiber, the number of the retarders is the number of the modes excited when the first single-mode fiber enters the first multimode fiber, the number of the retarders is reduced by one, and the delay value is the delay difference between the different modes and LP 01.
8. The multimode fiber transmission system according to claim 6, wherein the number of attenuators in the second eccentric mode excitation module in the fourth step is the number of excitation modes when the first multimode fiber enters the second multimode fiber, the attenuation coefficients of different attenuators are power ratios of different modes excited when the first multimode fiber enters the second multimode fiber, the number of retarders is the number of modes when the first multimode fiber enters the second multimode fiber minus one, and the delay value is a delay difference between the different modes and the fundamental mode LP 01.
9. The multimode fiber transmission system based on the high-speed single-mode optical module according to claim 6, wherein the number of the attenuators in the sixth step is the number of transmission modes in the second multimode fiber, the attenuation coefficients of the different attenuators are power ratios of the transmission modes in the second multimode fiber, the number of the couplers is the number of transmission modes in the second multimode fiber minus one, and the coupling ratio of the different couplers is a coupling ratio of the different modes to the LP01 mode when the second multimode fiber enters the second single-mode fiber.
Technical Field
The invention belongs to the technical field of optical fiber communication, and particularly relates to a multimode optical fiber transmission system based on a high-speed single-mode optical module.
Background
The development and application of new generation information technologies such as 5G technology, cloud computing, big data and the like push the data flow to be developed in a centralized way. As a functional device for interconnecting internal and external devices of a data center, an optical module has been rapidly developed with the increase in the scale of the data center. Due to the explosive requirements of data traffic and cloud services, the data center needs to be migrated to a higher transmission rate, and the development of the optical module in a high-rate direction is promoted.
The transmission based on the multimode fiber is an important means for optical interconnection in the data center, and the data center has a requirement on high speed, so that high-speed multimode fiber communication becomes a research hotspot of optical communication. In addition, the traditional data center still uses multimode optical fiber for optical interconnection, and how to realize high-speed transmission by using the laid multimode optical fiber is a significant work. The high-speed multimode optical module is needed to be used for realizing high-speed information transmission by utilizing multimode optical fibers, the high-speed multimode optical module is not mature at present, the rate of the mature high-speed multimode optical module which is put into commercial use at present is 25Gbit/s at most, and multiplexing is needed to realize higher rate, so that the cost is increased, and the communication cost is increased for the multimode networking architecture multimode optical module equipment; on the other hand, the technology of the high-speed single-mode optical module tends to be mature, the highest speed at the present stage can reach 400Gbit/s, and the single-mode optical module can carry out short-distance transmission in a multimode optical fiber.
In practical application, an output pigtail of the single-mode optical module is a single mode, and when the single-mode optical module is connected with a multimode optical fiber, the center alignment of the single-mode optical fiber and the multimode optical fiber cannot be strictly ensured, and a certain core deviation may exist. When the single-mode optical fiber is used for receiving, a certain core deviation is also inevitable between the multimode optical fiber and the single-mode optical fiber. In addition, due to the complexity of the practical application scenario, a plurality of connection points inevitably exist in the multimode optical fiber transmission link, and a certain eccentric distance also exists between the multimode optical fibers. The existence of these core-offset distances can cause different mode excitations and mode couplings at the fiber connection, thereby affecting the inter-mode coupling and mode group delay conditions during the transmission process. The mode coupling can cause energy exchange among multiple paths of signals in the transmission process, so that channel interference is generated; due to the existence of the differential mode group delay, the coupling between two paths of signals is not the coupling between corresponding code elements at the same time, but the code element at a certain time of one path of signals is superposed with the code elements corresponding to other times of the other path of signals, so that intersymbol interference is generated. It can be seen that different modes coupling and differential mode group delay caused by different core offsets have different effects on the signal.
Disclosure of Invention
The invention provides a multimode optical fiber signal transmission system based on a high-speed single-mode optical module, aiming at the immature technology of the high-speed multimode optical module and the requirement of short-distance high-speed communication. The invention realizes short-distance high-speed communication by utilizing the existing large-scale high-speed single-mode optical module to transmit in the multimode optical fiber, and can effectively reduce the communication cost.
In order to achieve the purpose, the invention adopts the following technical scheme:
a multimode optical fiber transmission system based on a high-speed single-mode optical module is disclosed, and a system framework of the multimode optical fiber transmission system is shown in figure 1 and comprises a signal generation module 1, a mode excitation module 2, a signal transmission module 3, a signal receiving module 4 and a signal analysis module 5; the output port of the signal generation module 1 is connected with the input port of the mode excitation module 2, the output port of the mode excitation module 2 is connected with the input port of the signal transmission module 3, the output port of the signal transmission module 3 is connected with the input port of the signal receiving module 4, and the output port of the signal receiving module 4 is connected with the input port of the signal analysis module 5.
Furthermore, the signal generating module 1 is composed of a signal generator 11, a laser 12 and a photoelectric modulator 13; the mode excitation module 2 consists of a first single-mode fiber 21 and a first core-shifting mode excitation module 22; the signal transmission module 3 consists of a first multimode fiber 31, a second eccentric mode excitation module 32 and a second multimode fiber 33; the signal receiving module 4 consists of an eccentric mode coupling 41 and a second single mode fiber 42; the output port of the signal generator 11 is connected to the first input port 131 of the electro-optical modulator 13, and the output port of the laser 12 is connected to the second input port 132 of the electro-optical modulator 13; an output port of the photoelectric modulator 13 is connected with an input port of the first single-mode fiber 21, and an output port of the first single-mode fiber 21 is connected with an input port of the first eccentric mode excitation module 22; an output port of the first core-shifting mode excitation module 22 is connected with an input port of a first multimode fiber 31, an output port of the first multimode fiber 31 is connected with an input port of a second core-shifting mode excitation module 32, and an output port of the second core-shifting mode excitation module 32 is connected with an input port of a second multimode fiber 33; the output port of the second multimode fiber 33 is connected with the input port of the core-shifted mode coupling 41, and the output port of the core-shifted mode coupling 41 is connected with the input port of the second single-mode fiber 42; the output port of the second single mode fibre 42 is connected to the input port of the signal analysis module 5.
Further, when the first single mode fiber 21 is connected to the first multimode fiber 31, the fiber core is shifted by a first offset distance, when the first multimode fiber 31 is connected to the second multimode fiber 32, the fiber core is shifted by a second offset distance, and when the second multimode fiber 32 is connected to the second single mode fiber 42, the fiber core is shifted by a third offset distance.
Further, the first section of eccentricity, the second section of eccentricity and the third section of eccentricity are not more than 10 um.
Further, the method for designing the eccentric distance comprises the following specific steps:
simulating the mode excitation condition of light entering a first multimode fiber from a first single-mode fiber under different eccentric distances by utilizing Rsoft software to obtain the mode types, the number and the power ratio of LP01 excited in the first multimode fiber under different eccentric distances;
secondly, modifying the number of attenuators, attenuation coefficients, the number of time delayers and time delay values in a first core-offset mode excitation module in the system according to the mode excitation condition of the first single-mode fiber entering the first multimode fiber under different core-offset distances, and obtaining system error rates under different mode couplings and different differential mode group time delay interferences by inputting the mode excitation conditions under different core-offset distances;
thirdly, simulating the mode excitation condition when light subjected to mode coupling under different eccentric distances is transmitted into the second multimode fiber from the first multimode fiber by utilizing Rsoft software to obtain the type, the quantity and the power ratio of the modes excited in the second multimode fiber by different modes in the first multimode fiber under different eccentric distances;
fourthly, modifying the first core-shifting mode excitation module and the second core-shifting mode excitation module in the system according to the simulation result, wherein the modification of the first core-shifting mode excitation module is consistent with the modification of the second step, then modifying the number and attenuation coefficient of the attenuators and the number and delay value of the time delay devices in the second core-shifting mode excitation module in the system according to the mode excitation condition that the first multimode optical fiber enters the second multimode optical fiber under different core-shifting distances, and obtaining the system error rate under different mode couplings and different differential mode group delay interferences under different core-shifting distances by inputting the mode excitation conditions under different core-shifting distances;
fifthly, simulating the coupling condition of the light subjected to mode coupling at different eccentric distances to LP01 when the light enters the second single-mode fiber from the second multimode fiber to obtain the power ratio of different modes in the second multimode fiber to the LP01 mode coupling at different eccentric distances by utilizing Rsoft software;
sixthly, modifying the first eccentric mode excitation module, the second eccentric mode excitation module and the eccentric mode coupling module in the system according to the simulation result, wherein the modification of the first eccentric mode excitation module and the modification of the second eccentric mode excitation module are consistent with the modification in the fourth step; then, modifying the number and attenuation coefficient of attenuators, the number and coupling ratio of couplers and the number and delay value of time delayers in an offset core mode coupling module in the system according to the coupling condition of different modes to LP01 when the second multimode fiber enters the second single mode fiber under different offset core distances, and obtaining the system error rate under different offset core distances by inputting the mode excitation and mode coupling conditions under different offset core distances;
seventhly, obtaining a limit FEC (the error rate is less than 2 multiplied by 10) according to the error rate of the system when the first single-mode fiber enters the first multimode fiber under different eccentric distances-4) (Limited FEC is the maximum bit error rate of the system that can be corrected by FEC techniques, below which the system bit error rate can be effectively transmitted. ) The maximum range of the core-bias between the lower first single-mode fiber and the first multimode fiber; then, according to the system error rate conditions of the joint of the first single-mode fiber and the first multimode fiber and the joint of the first multimode fiber and the second multimode fiber under different core offset distances, the first single-mode fiber and the first multimode fiber are obtainedWhen the core offset distance between the optical fibers is determined, the maximum range of core offset between the first multimode optical fiber and the second multimode optical fiber under the limit FEC; finally, according to the system error rate conditions of the first single-mode fiber and the first multimode fiber at the joint, the first multimode fiber and the second multimode fiber at the joint and the second multimode fiber and the second single-mode fiber at different core offset distances, the maximum range of core offset between the second multimode fiber and the first single-mode fiber under the limit FEC is obtained when the core offset distance between the first single-mode fiber and the first multimode fiber and the core offset distance between the first multimode fiber and the second multimode fiber are determined; the maximum range of three-section eccentric distance which can be effectively transmitted by the system can be obtained.
Further, the number of the attenuators in the second step is the number of the excitation modes when the first single-mode fiber enters the first multimode fiber, the attenuation coefficients of the different attenuators are power ratios of different modes excited when the first single-mode fiber enters the first multimode fiber, the number of the time delayers is the number of the modes excited when the first single-mode fiber enters the first multimode fiber minus one, and the time delay value is the time delay difference between the different modes and the LP 01.
Further, the number of attenuators in the second core-shifting mode excitation module in the fourth step is the number of excitation modes when the first multimode fiber enters the second multimode fiber, the attenuation coefficients of different attenuators are power ratios of different modes excited when the first multimode fiber enters the second multimode fiber, the number of time delays is the number of modes when the first multimode fiber enters the second multimode fiber minus one, and the time delay value is the time delay difference between the different modes and the fundamental mode LP 01.
Further, the number of the attenuators in the sixth step is the number of the transmission modes in the second multimode optical fiber, the attenuation coefficients of the different attenuators are the power ratio of the transmission modes in the second multimode optical fiber, the number of the couplers is the number of the transmission modes in the second multimode optical fiber minus one, and the coupling ratio of the different couplers is the coupling ratio of the different modes to the LP01 mode when the second multimode optical fiber enters the second single mode optical fiber.
Compared with the prior art, the invention has the following advantages:
the invention firstly realizes high speedThe single-mode optical module is applied to multimode optical fiber transmission, high-speed short-distance transmission is achieved, compared with other high-speed short-distance communication systems, communication cost is reduced, and large-scale coverage can be achieved. Moreover, a core offset distance design method is provided, and the error rate of the system is lower than 2 multiplied by 10 by designing reasonable core offset distance-4And effective transmission of the system is realized.
Drawings
FIG. 1: the invention discloses a structural schematic diagram of a multimode optical fiber transmission system based on a high-speed single-mode optical module;
FIG. 2: the invention discloses a structural schematic diagram of a multimode optical fiber transmission system based on a high-speed single-mode optical module;
FIG. 3: the invention relates to a flow diagram of a core offset distance design method;
FIG. 4: delay of each mode;
FIG. 5: mode excitation conditions under different core offset distances between the first single-mode fiber and the first multimode fiber;
FIG. 6: the system error rates of the first single-mode fiber and the first multimode fiber under different core offset distances;
FIG. 7: mode excitation of different modes in the second section of multimode fiber;
wherein, (a) LP01, (b) LP11, (c) LP02, (d) LP12, (e) LP21
FIG. 8: the system error rates of the first multimode fiber and the second multimode fiber under different core offset distances;
FIG. 9: the high-order mode is coupled to the LP01 mode under different core offset distances between the second multimode fiber and the second single-mode fiber;
FIG. 10: error rate when the core offset between the second multimode fiber and the second single mode fiber is (a)2um, (b)4um, (c)6um, (d)8um, (e)10 um;
FIG. 11: system error rate lower than 2 x 10-4The maximum eccentricity of the core at each position;
in the figure: the optical fiber core-shifting device comprises a signal generating module 1, a mode exciting module 2, a signal transmission module 3, a signal receiving module 4, a signal analyzing module 5, a signal generator 11, a laser 12, an electro-optical modulator 13, a first single-mode fiber 21, a first core-shifting mode exciting module 22, a second multimode fiber 31, a second core-shifting mode exciting module 32, a second multimode fiber 33, a core-shifting mode coupling 41, a second single-mode fiber 42, an electro-optical modulator input port 131 and an electro-optical modulator input port 132.
Detailed Description
The invention is described in detail below with reference to the drawings and specific example embodiments
Example 1
The invention establishes a multimode optical fiber signal transmission system based on a high-speed single-mode optical module, and the implementation framework is shown in fig. 2. The system block diagram is shown in fig. 1, and the system block diagram is composed of a signal generating module 1, a mode exciting module 2, a signal transmission module 3, a signal receiving module 4 and a signal analyzing module 5, wherein an output port of the signal generating module 1 is connected with an input port of the mode exciting module 2, an output port of the mode exciting module 2 is connected with an input port of the signal transmission module 3, an output port of the signal transmission module 3 is connected with an input port of the signal receiving module 4, and an output port of the signal receiving module 4 is connected with an input port of the signal analyzing module 5.
Further, the signal generating module 1 is composed of a signal generator 11, a laser 12 and a photoelectric modulator 13; the mode excitation module 2 consists of a first single-mode fiber 21 and a first core-shifting mode excitation module 22; the signal transmission module 3 consists of a first multimode fiber 31, a second eccentric mode excitation module 32 and a second multimode fiber 33; the signal receiving module 4 consists of an eccentric mode coupling 41 and a second single mode fiber 42; the output port of the signal generator 11 is connected to the first input port 131 of the electro-optical modulator 13, and the output port of the laser 12 is connected to the second input port 132 of the electro-optical modulator 13; an output port of the photoelectric modulator 13 is connected with an input port of the first single-mode fiber 21, and an output port of the first single-mode fiber 21 is connected with an input port of the first eccentric mode excitation module 22; an output port of the first core-shifting mode excitation module 22 is connected with an input port of a first multimode fiber 31, an output port of the first multimode fiber 31 is connected with an input port of a second core-shifting mode excitation module 32, and an output port of the second core-shifting mode excitation module 32 is connected with an input port of a second multimode fiber 33; the output port of the second multimode fiber 33 is connected with the input port of the core-shifted mode coupling 41, and the output port of the core-shifted mode coupling 41 is connected with the input port of the second single-mode fiber 42; the output port of the second single mode fibre 42 is connected to the input port of the signal analysis module 5.
The fiber core offset distance when the first single mode fiber 21 is connected with the first multimode fiber 31 is a first segment core offset distance, the fiber core offset distance when the first multimode fiber 31 is connected with the second multimode fiber 32 is a second segment core offset distance, and the fiber core offset distance when the second multimode fiber 32 is connected with the second single mode fiber 42 is a third segment core offset distance.
The first section of eccentricity, the second section of eccentricity and the third section of eccentricity are not more than 10 um.
In this example, the output power of the laser in the signal generation module is 10mw, and the signal rate is 25 Gbit/s; the multimode optical fiber parameters in the signal transmission module are all set as OM3 optical fiber parameters, wherein the diameter of a fiber core/cladding is 50/125um, the central wavelength is 1310nm, the central refractive index is 1.477, the numerical aperture is 0.2 +/-0.015, the length of the optical fiber is 150m, the loss is less than or equal to 0.6dB/Km, and the dispersion is less than or equal to 0.101ps/nm x Km. The time delay of the modes transmitted in the multimode fiber is different, the parameters of the multimode fiber are obtained by simulating the multimode fiber through VPI, and the time delay of main modes LP01, LP02, LP03, LP04, LP11, LP12, LP13, LP14, LP21, LP22, LP31 and LP41 in the multimode fiber is shown in FIG. 4. The number of the modes excited by the mode excitation module is represented by adding couplers at the optical fiber connection position, the power occupation ratio of the modes is represented by adding attenuators, the mode types are represented by adding different time delays, the added time delays are the time delay difference between a high-order mode and a basic mode, the number of the couplers of an initial system is set, the number of the attenuators is 1, and the number of the time delays is 0; the mode coupling coefficient of the mode coupling module is self-carried by a multimode fiber model in VPI, the mode coupling coefficient of the corresponding fiber can be obtained by setting other parameters of the fiber, a section of multimode fiber is added behind each core-offset excitation module to simulate the mode-to-mode coupling, the differential mode group delay and the transmission loss in the transmission process, and the multimode fiber parameters are consistent with the OM3 light parameters.
Example 2
The embodiment provides a method for designing eccentric distance, which comprises the following specific steps:
simulating the mode excitation condition of light incident into the first multimode fiber from the first single-mode fiber by utilizing Rsoft, setting the fiber core/diameter of the first single-mode fiber to be 9/125m, the central refractive index to be 1.469, the fiber core/cladding diameter of the first multimode fiber to be 50/125um, the central refractive index to be 1.477, the incident mode to be LP01, the incident light power to be 1, and the core offset distance to be 0-10um in sequence; at this time, mode excitation at different eccentricity is obtained as shown in fig. 5. It can be seen from fig. 5 that when the first single mode fiber is eccentrically incident to the first multimode fiber, a plurality of modes are excited, and the number of excited modes increases with the increase of the eccentric distance, wherein the modes mainly excited are LP01, LP11, LP12, LP02 and LP 21. The number of the excitation modes and the power ratio of the modes under different eccentric distances are different, which causes different coupling conditions between the modes and different mode group delay conditions in the multimode fiber under different eccentric distances, and further causes different degrees of inter-channel interference and inter-code interference, thereby causing different influences on system performance. From fig. 5, it can be seen that when LP01 is launched into a multimode fiber from a single mode fiber, the type, number and power ratio of the modes excited at different core-offset distances provide parameters for the construction of the first core-offset mode excitation module 22 in the link.
And secondly, constructing the link shown in the figure 2 by using VPI software. The off-center mode excitation 22 is modified according to the mode excitation conditions under different off-center distances shown in FIG. 5, since the main excitation modes mainly comprise LP01, LP11, LP12, LP02 and LP21, the number of attenuators is set to 5, the number of time delays is set to 4, the attenuation coefficient of each attenuator is modified according to the excitation power ratio of each mode under different off-center distances obtained in FIG. 5, and the time delays are sequentially set to 2.5028 × 10-14s/m、5.8144×10-14s/m、8.98×10-14s/m、5.3348×10-14s/m. The system error rates under different core offset distances are obtained as shown in fig. 6. As can be seen from FIG. 6, as the eccentricity of the eccentric center increasesLarge, the error rate of the system also gradually increases. The error rate lower than 2 x 10 can be obtained from fig. 6-4The maximum eccentric distance of the first section is 6 um.
And thirdly, analyzing the excitation conditions of the modes LP01, LP11, LP02, LP12 and LP21 in the second section of multimode fiber respectively by using Rsoft. Setting the diameter of a fiber core/cladding of the second multimode fiber to 50/125um, the central refractive index to 1.477, the incident mode to LP01, the incident light power to 1, and the eccentric distance to 0-10um, where the mode excitation situation under different eccentric distances is as shown in fig. 7 a; setting the incident mode as LP11, the incident light power as 1, and the eccentric distance as 0-10um, where the mode excitation situation under different eccentric distances is as shown in FIG. 7 b; setting the incident mode as LP02, the incident power as 1, and the eccentric distance as 0-10um, where the mode excitation situation under different eccentric distances is as shown in FIG. 7 c; setting the incident mode as LP12, the incident power as 1, and the eccentric distance as 0-10um, where the mode excitation situation under different eccentric distances is as shown in FIG. 7 d; setting the incident mode to LP21, the incident power to be 1, and the eccentricity to be 0-10um, the mode excitation situation at different eccentricity is shown in FIG. 7 e. As can be seen from fig. 7a-e, as a new segment of the eccentricity is added, there are more modes of transmission in the system; the number of the excitation modes is gradually increased along with the increase of the eccentric distance between the multimode optical fiber and the multimode optical fiber; when the core deviation is maximum, the main modes transmitted in the second multimode optical fiber are LP01, LP02, LP03, LP04, LP11, LP12, LP13, LP21 and LP 22; the number of the excitation modes and the power ratio of the modes under different eccentric distances are different, which causes different coupling conditions between the modes and different mode group delay conditions in the multimode fiber under different eccentric distances, and further causes different degrees of inter-channel interference and inter-code interference, thereby causing different influences on system performance. From fig. 7a-e, it can be obtained that the number of excited modes, the type of the excited modes and the power ratio of each mode at the incidence of LP01, LP11, LP02, LP12 and LP21 under different eccentricity offsets provide parameters for the construction of the second eccentricity excitation module 32.
And fourthly, constructing a link shown in the figure 2 by utilizing VPI software, and modifying the first core-shifting mode excitation module 22 and the second core-shifting mode excitation module 32 according to the mode excitation condition. Wherein the pairThe first eccentric mode excitation module 22 is modified as in the second step. Then, the core-offset mode excitation module 32 is modified according to the mode excitation conditions of the different modes at different core-offset distances shown in fig. 7, the number of attenuators is set according to the number of excitation modes shown in the figure, the attenuation coefficient is set according to the power ratio of each excitation mode shown in the figure, the number of retarders is set according to the type of the excitation mode shown in the figure, the delay difference between each excitation mode and LP01 is obtained according to the delay of each mode shown in fig. 4, and the parameters of the retarders are set. The system error rates under different core offset distances when the core offset distances of the first two sections exist are obtained by modifying the link under the core offset distance as shown in fig. 8. It can be seen from fig. 8 that when the core offset distance between the first single-mode fiber and the first multimode fiber is fixed, the system error rate increases with the increase of the core offset distance between the first multimode fiber and the second multimode fiber; ensure the system error rate to be lower than 2 x 10-4The core offset distance between the first multimode optical fiber and the second multimode optical fiber increases with the increase of the core offset distance between the first single mode optical fiber and the first multimode optical fiber. From FIG. 8, it can be obtained that the system error rate is expected to be lower than 2 × 10-4And when the core offset distance between the first single mode fiber and the first multimode fiber is 3um, 4um, 5um and 6um in sequence, the core offset distance between the first multimode fiber and the second multimode fiber is 7um, 3um, 1um and 0um in sequence to the maximum.
And fifthly, analyzing the coupling condition of main modes LP01, LP02, LP03, LP04, LP11, LP12, LP13, LP21 and LP22 in the previous section of multimode fiber to LP01 by using Rsoft. The core/diameter of the second single mode fiber is 9/125m, the center refractive index is 1.469, the core/cladding diameter of the multimode fiber is 50/125um, the center refractive index is 1.477, the incident light power is 1, the eccentric distance is 0-10um, and the incident modes are sequentially set to LP01, LP02, LP03, LP04, LP11, LP12, LP13, LP21 and LP22, and at this time, the coupling of each mode to LP01 is obtained as shown in fig. 9. It can be seen from fig. 9 that different modes couple different powers to LP01, and different powers couple to LP01 in the same mode at different eccentricity, which causes different interference of the different modes to the LP01 mode channel at different eccentricity, and thus different effects on the performance of the system. From fig. 9, the coupling ratios of modes LP01, LP02, LP03, LP04, LP11, LP12, LP13, LP21, and LP22 to LP01 at different eccentricity can be obtained, providing parameters for the construction of the eccentric mode coupling module 41.
And sixthly, constructing the link shown in the figure 2 by using VPI software. The off-center mode excitation module 22 is modified according to the mode excitation at different off-center distances shown in fig. 5, and the modification method is the same as the second step. The off-center mode excitation 32 is modified according to the mode excitation conditions of different modes at different off-center distances shown in fig. 7, and the modification method is consistent with the fourth step. The core-offset mode coupling 41 is modified according to fig. 7 and 9, the number of attenuators and the number of couplers are set according to the number of transmission modes in the second multimode optical fiber shown in fig. 7, the attenuation coefficient of the attenuators is the power ratio of the modes transmitted in the second multimode optical fiber, and the coupling ratio of each coupler is set according to the ratio of coupling of each mode to LP01 at different core-offset distances shown in fig. 9. The system bit error rate when three sections of eccentric distances exist is obtained by modifying the link under different eccentric distances, and is shown in figure 10. As can be seen from fig. 10, with the addition of the eccentric distance in the third section, the error rate of the system becomes large; when the core offset distance between the first single-mode fiber and the first multimode fiber and the core offset distance between the first multimode fiber and the second multimode fiber are fixed, the system error rate is increased along with the increase of the core offset distance between the second multimode fiber and the first single-mode fiber; ensure the system error rate to be lower than 2 x 10-4The eccentricity of the third segment is also reduced along with the increase of the eccentricity of the first two segments. According to FIG. 10, it can be obtained that the system error rate is guaranteed to be lower than 2 × 10-4The maximum range of the eccentricity of three segments of (a) is shown in fig. 11.
Seventh, comparing fig. 6, fig. 8 and fig. 10, it can be seen that when only the first off-center distance exists, the system error rate is guaranteed to be lower than 2 × 10-4The core offset distance must be less than 6 um; when the two current eccentric distances exist, the system error rate is ensured to be lower than 2 multiplied by 10-4When the core offset distance between the first single mode fiber and the first multimode fiber is 3um, 4um, 5um and 6um in sequence, the core offset distance between the first multimode fiber and the second multimode fiber is 3um, 4um, 5um and 6umThe core offset distances are 7um, 3um, 1um and 0um in sequence at the maximum; when three eccentric distances exist, the system error rate is ensured to be lower than 2 multiplied by 10-4When the core offset distances of the three sections are in the range shown in fig. 11, when the core offset distance of the first section is 0um and the core offset distances of the third section are 4um, 6um, 8um and 10um in sequence, the core offset distance of the second section cannot exceed 10um, 7um, 6um and 5um in sequence to the maximum extent; when the eccentric distance of the first section is 1um, and the eccentric distances of the third section are 4um, 6um, 8um and 10um in sequence, the eccentric distance of the second section cannot exceed 8um, 5um, 4um and 3um in sequence to the maximum extent; when the eccentric distance of the first section is 2um, and the eccentric distances of the third section are sequentially 2um, 4um, 6um, 8um and 10um, the eccentric distances of the second section sequentially cannot exceed 7um, 4um, 2um, 1um and 1um to the maximum extent; when the eccentric distance of the first section is 3um, and the eccentric distances of the third section are 0um, 2um and 4um in sequence, the eccentric distances of the second section cannot exceed 7um, 4um and 1um in sequence to the maximum extent; when the eccentric distance of the first section is 4um, and the eccentric distances of the third section are 0um and 2um in sequence, the eccentric distances of the second section cannot exceed 3um and 1um in sequence to the maximum extent; when the eccentric distance of the first section is 5um and the eccentric distances of the third section are 0um in sequence, the eccentric distances of the second section cannot exceed 1um at most in sequence.
The above contents describe the multimode optical fiber transmission system based on the high-speed single-mode optical module and the core offset design method in detail, and the above description is mainly used for further understanding the method and the core concept of the method of the present invention; while the invention has been described with reference to specific embodiments and applications, it will be apparent to those skilled in the art that various changes in form and detail may be made therein without departing from the spirit and scope of the invention.