CN112702119B - Differential mode group delay compensation method and system based on photoelectric fusion - Google Patents

Differential mode group delay compensation method and system based on photoelectric fusion Download PDF

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CN112702119B
CN112702119B CN202110317191.4A CN202110317191A CN112702119B CN 112702119 B CN112702119 B CN 112702119B CN 202110317191 A CN202110317191 A CN 202110317191A CN 112702119 B CN112702119 B CN 112702119B
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CN112702119A (en
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毛雅亚
刘博�
忻向军
任建新
刘轩领
王瑞春
沈磊
吴泳锋
孙婷婷
赵立龙
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Nanjing University of Information Science and Technology
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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B10/00—Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
    • H04B10/07—Arrangements for monitoring or testing transmission systems; Arrangements for fault measurement of transmission systems
    • H04B10/075—Arrangements for monitoring or testing transmission systems; Arrangements for fault measurement of transmission systems using an in-service signal
    • H04B10/079—Arrangements for monitoring or testing transmission systems; Arrangements for fault measurement of transmission systems using an in-service signal using measurements of the data signal
    • H04B10/0795—Performance monitoring; Measurement of transmission parameters
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04J—MULTIPLEX COMMUNICATION
    • H04J3/00—Time-division multiplex systems
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Abstract

The invention discloses a differential mode group delay compensation method based on photoelectric fusion, which comprises the following steps: calculating time delay differences between different modes and a basic mode in the few-mode optical fiber, adding redundant data with different data volumes to original data to be transmitted corresponding to the different modes at a transmitting end, and compensating differential mode group time delay of the few-mode optical fiber for the first time to enable optical signals corresponding to each mode to theoretically reach an optical fiber terminal at the same time; and leading the basic mode signals corresponding to different modes into different micro-ring resonators in a one-to-one correspondence manner, controlling the light speed again by changing the radius of the micro-ring resonators, and performing secondary compensation on the differential mode group delay of the few-mode optical fiber to enable the optical signals output by all the micro-ring resonators to simultaneously reach the photoelectric detector. The invention can reduce the influence of the differential mode group delay on the few-mode optical fiber system and improve the transmission capability of the few-mode optical fiber communication system.

Description

Differential mode group delay compensation method and system based on photoelectric fusion
Technical Field
The invention relates to the technical field of optical transmission, in particular to a differential mode group delay compensation method and system based on photoelectric fusion.
Background
In the past half century or more, the degree of informatization of the society has been gradually improved, and the demand of people for information has rapidly increased. With the explosive development of network data services such as the internet, big data, cloud service, internet of things and the like, and the 5G technology gradually falls to the ground and is put into commercial use, the artificial intelligence technology is emerging, the bandwidth demand in the modern society for optical network transmission is increasing day by day, and great pressure is brought to the current optical network. To address the situation where such single mode fiber transmission systems are unable to meet the increasing network capacity demands, space is considered the last dimension that can be used to increase the capacity of fiber transmission systems. Space division multiplexing technology based on multi-core or few-mode optical fiber space degree of freedom is receiving wide attention from related researchers as an effective solution for breaking through single-mode optical fiber channel capacity.
The few-mode fiber can support a plurality of mutually independent modes in the same fiber core, and each mode is transmitted as an independent channel. Few-mode fibers support a greater number of modes than single-mode fibers, which provides more channels for the system, multiplying channel capacity. And the preparation of the few-mode fiber is simpler compared with a multi-core fiber, and the nonlinearity tolerance of the few-mode fiber is better compared with a single-mode fiber due to the increase of the radius of the fiber core. However, the practical implementation of the mode division multiplexing based on few-mode optical fiber still faces many challenges. The small-mode optical fiber has differential mode group delay, that is, intermodal dispersion, because different modes have different transmission group speeds in the same small-mode optical fiber, different delays exist among the different modes, and finally, received signal pulses are widened, and too long transmission distance causes different arrival times of the different modes at a receiving end, thereby causing error codes. Currently, there are several methods to reduce the impact of differential mode group delay on the receiving end. The first is to compensate by an algorithm, for example a frequency domain equalization algorithm. However, the complexity of the frequency domain equalization algorithm increases logarithmically with the increase of the delay of the differential mode group, and the complexity of the receiving end is very high due to the adoption of the method. Yet another solution is to design and manufacture low differential mode group delay fibers, which are difficult to implement to support more modes, although fibers that support six LP mode transmissions have been implemented. How to reduce the delay of the differential mode group at the minimum cost without increasing the complexity of a system receiving end becomes a new research topic.
Disclosure of Invention
Aiming at the defects in the prior art, the invention provides a differential mode group delay compensation method and a differential mode group delay compensation system based on photoelectric fusion.
In order to achieve the purpose, the invention adopts the following technical scheme:
in a first aspect, an embodiment of the present invention provides a differential mode group delay compensation method based on photoelectric fusion, where the compensation method includes:
calculating time delay differences between different modes and a basic mode in the few-mode optical fiber, adding redundant data with different data volumes to original data to be transmitted corresponding to the different modes at a transmitting end, and compensating differential mode group time delay of the few-mode optical fiber for the first time to enable optical signals corresponding to each mode to theoretically reach an optical fiber terminal at the same time;
the method comprises the steps that after demultiplexing and mode conversion are sequentially carried out on received optical signals at a receiving end, a plurality of basic mode signals are recovered, and the basic mode signals correspond to transmission modes one to one;
and leading the basic mode signals corresponding to different modes into different micro-ring resonators in a one-to-one correspondence manner, controlling the light speed again by changing the radius of the micro-ring resonators, and performing secondary compensation on the differential mode group delay of the few-mode optical fiber to enable the optical signals output by all the micro-ring resonators to simultaneously reach the photoelectric detector.
In order to optimize the technical scheme, the specific measures adopted further comprise:
further, the compensation method further comprises:
and receiving the optical signals output by all the micro-ring resonators by using the photoelectric detector, converting the optical signals into electric signals, and removing redundant data added in the electric signals.
Further, the calculating to obtain the delay difference between different modes in the few-mode fiber and the fundamental mode includes:
measuring and calculating the effective refractive index of each mode under different wavelengths for optical fibers with different refractive index profile structures;
calculating to obtain the mode group delay of the optical fiber
Figure 100002_DEST_PATH_IMAGE001
：
Figure 100002_DEST_PATH_IMAGE003
Wherein
Figure 536923DEST_PATH_IMAGE004
Is a function of the wavelength of the light,
Figure 100002_DEST_PATH_IMAGE005
to be the group velocity, the velocity of the beam,
Figure 985222DEST_PATH_IMAGE006
is the speed of light in vacuum, propagation constant
Figure 100002_DEST_PATH_IMAGE007
，
Figure 703908DEST_PATH_IMAGE008
Is the effective index of refraction of the mode,
Figure 100002_DEST_PATH_IMAGE009
is the wave number of free space;
calculating to obtain the differential mode group delay between the high-order mode and the fundamental mode of the optical fiber
Figure 364697DEST_PATH_IMAGE010
：
Figure 320014DEST_PATH_IMAGE012
In the formula (I), the compound is shown in the specification,
Figure 100002_DEST_PATH_IMAGE013
in order to achieve a high-order mode delay,
Figure 673635DEST_PATH_IMAGE014
is the fundamental mode delay.
Further, the adding of redundant data of different data amounts at the sending end for original data to be transmitted corresponding to different modes includes:
calculating the data transmission time difference between different modes in the transmission process;
and adding redundant data with different data volumes aiming at the original data to be transmitted corresponding to different modes by combining the theoretical transmission time of the single data in different modes, so that the theoretical transmission time of the processed data in each mode is the theoretical transmission time
Figure 100002_DEST_PATH_IMAGE015
：
Figure 100002_DEST_PATH_IMAGE017
In the formula (I), the compound is shown in the specification,
Figure 862040DEST_PATH_IMAGE018
the theoretical transmission time length of the original data of the ith mode;
Figure 100002_DEST_PATH_IMAGE019
the added redundant data bit number of the ith mode;
Figure 733044DEST_PATH_IMAGE020
the theoretical transmission duration of the unit data of the ith mode.
Further, the compensation method further comprises:
and carrying out MIMO signal processing on the electric signal without the redundant data, eliminating signal damage in the transmission process and recovering the original signal.
In a second aspect, an embodiment of the present invention provides a differential mode group delay compensation system based on photoelectric fusion, where the compensation system includes:
the system comprises at least one redundant adding module, a transmission end and a transmission end, wherein the redundant adding module is used for calculating the time delay difference between different modes and a basic mode in the few-mode optical fiber, adding redundant data with different data volumes aiming at original data to be transmitted corresponding to the different modes at the transmission end, and performing first compensation on the differential mode group time delay of the few-mode optical fiber so that optical signals corresponding to each mode after processing theoretically reach an optical fiber terminal at the same time; the number of the redundancy adding modules corresponds to the number of original data to be transmitted;
the optical modulation module is correspondingly connected with the redundancy adding module and is used for modulating each path of electric signal output by the redundancy adding module and loading the electric signal into an optical wave to obtain a corresponding basic mode signal;
the first mode converter is correspondingly connected with the optical modulation module and is used for converting a basic mode signal transmitted in the single-mode optical fiber into other high-order mode signals to carry different information;
the input end of the mode division multiplexer is connected with the first mode converter, the output end of the mode division multiplexer is connected with the transmitting end of the few-mode optical fiber, and the mode division multiplexer is used for coupling each path of mode signals output by the mode converter into a few-mode optical fiber link for transmission;
a few-mode optical fiber;
the input end of the mode decomposition multiplexer is connected with the output end of the few-mode optical fiber, the output end of the mode decomposition multiplexer is connected with the second mode converter, the mode decomposition multiplexer is used for demultiplexing the optical signals transmitted by the few-mode optical fiber, and the optical signals transmitted by the few-mode optical fiber are decomposed into multi-channel parallel signals through the demultiplexing process and are respectively coupled to different single-mode optical fibers;
at least one second mode converter for restoring the optical signals of the plurality of different modes decomposed by the mode decomposition multiplexer into a fundamental mode signal;
the micro-ring resonator is correspondingly connected with the second mode converter and used for controlling the propagation speed of the basic mode signal output by the mode converter again by changing the radius of the micro-ring resonator so as to carry out secondary compensation on the differential mode group delay of the few-mode optical fiber and enable the optical signals output by all the micro-ring resonators to reach the photoelectric detector at the same time;
at least one photoelectric detector which is correspondingly connected with the micro-ring resonators and is used for receiving optical signals output by all the micro-ring resonators and converting the optical signals into electric signals;
the redundancy removing module is correspondingly connected with the photoelectric detector and used for removing redundant data added later in the electric signal;
and the signal processing module is used for carrying out MIMO signal processing on the electric signal without the redundant data, eliminating signal damage in the transmission process and recovering the original signal.
Further, the calculating, by the redundancy addition module, a delay difference between different modes in the few-mode fiber and the fundamental mode includes:
measuring and calculating the effective refractive index of each mode under different wavelengths for optical fibers with different refractive index profile structures;
calculating to obtain the mode group delay of the optical fiber
Figure 401923DEST_PATH_IMAGE001
：
Figure 660866DEST_PATH_IMAGE003
Wherein
Figure 680775DEST_PATH_IMAGE004
Is a function of the wavelength of the light,
Figure 683366DEST_PATH_IMAGE005
to be the group velocity, the velocity of the beam,
Figure 596964DEST_PATH_IMAGE006
for speed of light in vacuum, propagationConstant number
Figure 292387DEST_PATH_IMAGE007
，
Figure 799592DEST_PATH_IMAGE008
Is the effective index of refraction of the mode,
Figure 340295DEST_PATH_IMAGE009
is the wave number of free space;
calculating to obtain the differential mode group delay between the high-order mode and the fundamental mode of the optical fiber
Figure 124711DEST_PATH_IMAGE010
：
Figure 991036DEST_PATH_IMAGE012
In the formula (I), the compound is shown in the specification,
Figure 985537DEST_PATH_IMAGE013
in order to achieve a high-order mode delay,
Figure 454564DEST_PATH_IMAGE014
is the fundamental mode delay.
Further, the redundancy adding module adds redundancy data of different data amounts at a sending end according to original data to be transmitted corresponding to different modes, including:
calculating the data transmission time difference between different modes in the transmission process;
and adding redundant data with different data volumes aiming at the original data to be transmitted corresponding to different modes by combining the theoretical transmission time of the single data in different modes, so that the theoretical transmission time of the processed data in each mode is the theoretical transmission time
Figure 218121DEST_PATH_IMAGE015
：
Figure 255347DEST_PATH_IMAGE017
In the formula (I), the compound is shown in the specification,
Figure 471565DEST_PATH_IMAGE018
the theoretical transmission time length of the original data of the ith mode;
Figure 495016DEST_PATH_IMAGE019
the added redundant data bit number of the ith mode;
Figure 113079DEST_PATH_IMAGE020
the theoretical transmission duration of the unit data of the ith mode.
The invention has the beneficial effects that:
the invention innovatively provides a differential mode group delay compensation method based on photoelectric fusion. At a transmitting end, redundancy addition on an electrical domain is carried out on original data, redundancy addition with different lengths is carried out on data transmitted on different modes, and first compensation on differential mode group delay in a few-mode optical fiber is achieved. And at the receiving end, the light speed is compensated again through the control effect of the micro-ring resonator on the light speed. By means of double compensation of dispersion among the modes, differential time delay among the modes can be effectively reduced, differential mode group time delay in the optical fiber communication system is effectively compensated, complexity of a receiver is reduced, transmission capacity of the system is improved, and high-speed, high-capacity and low-cost transmission of the optical fiber communication system is achieved.
Drawings
Fig. 1 is a flowchart of a differential mode group delay compensation method based on photoelectric fusion according to an embodiment of the present invention.
Fig. 2 is a schematic structural diagram of a differential mode group delay compensation system based on photoelectric fusion according to a second embodiment of the present invention.
Fig. 3 is a schematic diagram of transmission of different modes in a few-mode fiber.
Fig. 4 is a schematic diagram of a manner of adding redundant data.
Fig. 5 is a schematic diagram of the mode conversion principle.
Fig. 6 is a schematic diagram illustrating the principle of controlling the speed of light by the micro-ring resonator.
Fig. 7 is a schematic diagram of a plurality of micro-ring resonators controlling the speed of light.
Detailed Description
The present invention will now be described in further detail with reference to the accompanying drawings.
It should be noted that the terms "upper", "lower", "left", "right", "front", "back", etc. used in the present invention are for clarity of description only, and are not intended to limit the scope of the present invention, and the relative relationship between the terms and the terms is not limited by the technical contents of the essential changes.
Example one
Fig. 1 is a flowchart of a differential mode group delay compensation method based on optoelectronic fusion according to an embodiment, which provides dual compensation for differential mode group delay based on redundancy addition in an electrical domain and a control effect of a micro-ring resonator on an optical speed for solving a problem of differential mode group delay between different modes in a few-mode optical fiber, and reduces an influence of the differential mode group delay on a few-mode optical fiber system by using the compensation method of optoelectronic fusion, thereby improving transmission capability of the few-mode optical fiber communication system. The method can be applied to the few-mode optical fiber communication systems under different scenes, and particularly can realize the second compensation processing of the light speed by configuring a redundancy adding module for performing the first compensation processing on the original data at the foremost end of the few-mode optical fiber communication system and configuring a micro-ring resonator at the tail end of the optical signal transmission of the few-mode optical fiber communication system, so that the technical problem of differential mode group delay of the few-mode optical fiber can be solved.
For convenience of description, the embodiment of the present invention is described by taking an example that 3 different modes can be transmitted in a few-mode fiber as an example. It should be understood that, in practical applications, the compensation method and the compensation system provided by the present invention can arbitrarily select the number of transmission modes according to actual use requirements.
As shown in fig. 1, the compensation method specifically includes:
and S1, calculating the time delay difference between different modes and the basic mode in the few-mode optical fiber, adding redundant data with different data volumes to original data to be transmitted corresponding to different modes at a transmitting end, and performing first compensation on the differential mode group time delay of the few-mode optical fiber to enable optical signals corresponding to each processed mode to theoretically and simultaneously reach an optical fiber terminal.
At a sending end, original data firstly passes through a redundancy adding module, redundancy codes with different lengths are added in front of data transmitted in different modes, and differential mode group delay is compensated for the first time on an electrical domain. Specifically, for optical fibers with different refractive index profile structures, the effective refractive index of each mode under different wavelengths is measured and calculated. Because the propagation speeds of the guided modes supporting transmission in the few-mode optical fiber are different in the optical fiber, the optical signal between the mode channels will have a time delay after propagating for a certain distance, that is, a mode group time delay is generated, which can be expressed as:
Figure 321206DEST_PATH_IMAGE003
wherein
Figure 100002_DEST_PATH_IMAGE021
Is a function of the wavelength of the light,
Figure 414933DEST_PATH_IMAGE022
to be the group velocity, the velocity of the beam,
Figure DEST_PATH_IMAGE023
is the speed of light in vacuum, propagation constant
Figure 366709DEST_PATH_IMAGE024
，
Figure DEST_PATH_IMAGE025
Is the effective index of refraction of the mode,
Figure 245803DEST_PATH_IMAGE026
is the wavenumber of the light wave in free space. Different modes passing through a fixed length of optical fibreThe required time is different, so the differential mode group delay (MDGD) expression between the high-order mode and the fundamental mode is:
Figure 624832DEST_PATH_IMAGE028
in the formula (I), the compound is shown in the specification,
Figure 815641DEST_PATH_IMAGE013
in order to achieve a high-order mode delay,
Figure 305529DEST_PATH_IMAGE014
is the fundamental mode delay.
Through the two formulas, the time delay difference between different modes and the basic mode in the few-mode optical fiber can be calculated, then redundant data with different data volumes are added to different modules through the encoder of the redundant module at the transmitting end, and the differential mode group time delay of the few-mode optical fiber in the system is compensated before the electric signal is subjected to electro-optical conversion.
In few-mode optical fibers, inter-mode dispersion means that light rays of each mode are transmitted to a terminal through different paths, and due to different optical path lengths of each light ray, the time for each mode to reach the optical fiber terminal is different. As shown in FIG. 3, LP01The optical path of the fundamental mode is shortest; LP11For the high order mode, the optical path increases; LP21The highest order mode, the longest optical path. So LP01、LP11、LP21Three modes are transmitted in few-mode optical fiber for time t1、t2、t3The magnitude relation of (1) is t1<t2<t3. If a proper amount of redundant data is added before passing through a mode with short time of the optical fiber, the data needing to be transmitted can simultaneously reach the optical fiber terminal. Here we assume that
Figure DEST_PATH_IMAGE029
2-bit data pass LP01The time for the mode to propagate in the few-mode fiber is
Figure 22818DEST_PATH_IMAGE030
1 bit data is passed through LP11The time for the mode to propagate in the few-mode fiber is
Figure 572748DEST_PATH_IMAGE030
. Then we only need to add the module at redundancy at the original data 1 (at LP)01Transmission in mode) is added with 4 bits of redundant data, at the original data 2 (at LP)11Transmission in mode) before adding 1-bit redundant data, the original data 1, 2 and 3 can arrive at the optical fiber terminal at the same time, namely
Figure DEST_PATH_IMAGE031
As shown in fig. 4.
And S2, processing the electric signal added with the redundant data to convert the electric signal into an optical signal, and transmitting the optical signal to a receiving end through the few-mode optical fiber.
Specifically, electro-optical modulation is carried out on each path of electric signal added with redundant data, and the electric signal is loaded into an optical wave to obtain a corresponding basic mode signal; then converting the fundamental mode signal transmitted in the single mode optical fiber into other high-order mode signals to carry different information; the mutually orthogonal high-order modes are used as independent channels to carry information, and then all the high-order modes carrying the information are coupled into the same few-mode optical fiber to carry out long-distance transmission.
S3, the receiving end sequentially performs demultiplexing and mode conversion on the received optical signals, and then restores the optical signals to a plurality of fundamental mode signals, where the fundamental mode signals correspond to the transmission modes one to one.
And S4, introducing the basic mode signals corresponding to different modes into different micro-ring resonators in a one-to-one correspondence manner, controlling the light speed again by changing the radius of the micro-ring resonators, and performing secondary compensation on the differential mode group delay of the few-mode optical fiber to enable the optical signals output by all the micro-ring resonators to simultaneously reach the photoelectric detector.
The micro-ring resonator is used for realizing the speed control of light, does not need harsh physical conditions, and has the advantages of simple structure, convenience in manufacturing, high integration level and the like. The essence of the light speed control is to realize the effects of fast light and slow light, and even make the light spread at a negative light speed.
When optical signals with different frequencies are input into the micro-ring resonator, the optical signals meeting the resonance condition can be resonantly enhanced in the micro-ring resonator and transmitted for a plurality of turns, and a time delay phenomenon occurs, as shown in fig. 6, when the optical signals lambda1Is the resonance wavelength of the resonator, so that a delay occurs. The microring resonator structure and waveguide materials can be varied to achieve the desired delay characteristics.
After passing through the mode demultiplexer and the mode converter, light transmitted in different modes enters different microring resonators, the light speed is controlled again, and dispersion is compensated. Taking the three modes of few-mode fiber as an example, since the redundancy addition is based on theoretical calculation, although the delay difference can be compensated, there may still be an error. Assuming that the delay difference is compensated for but still exists after the redundancy addition, LP01、LP11、LP21The light of the three modes respectively reaches the micro-ring resonators in sequence, and the resonance wavelength of the resonators is set to be the central wavelength of the light wave, so that the light speed can be controlled by changing the radius of the micro-ring resonators.
As shown in fig. 7, radius R of the microring resonator1>R2>R3So that the path S of the light in the microring resonator1>S2>S3So that the time T of the micro-ring resonator is passed1>T2>T3Here T2-T1、T3-T1Is through LP11Mold, LP21Mode propagation to the microring resonator and through the LP01The difference in time for the mode propagation to reach the microring resonator. Thus, after passing through the microring resonator, the data-carrying light can simultaneously reach the photodetector.
S5, the added redundant data is removed, and crosstalk cancellation processing is performed on the recovered electrical signal. In a mode division multiplexing transmission system, certain inter-mode crosstalk can be brought to signals in a few-mode optical fiber transmission process and a mode division multiplexing/demultiplexing process. Therefore, the digital signal processing module is finally required to perform digital signal processing on the received signal. And eliminating degradation factors such as intermodal crosstalk and the like by using a corresponding demultiplexing algorithm so as to recover the original signal.
Example two
Fig. 2 is a schematic structural diagram of a differential mode group delay compensation system based on photoelectric fusion according to a second embodiment of the present invention. The second embodiment of the present invention can be applied to a few-mode fiber communication system in different scenarios, and specifically, a redundancy addition module for performing a first compensation process on original data can be configured at the frontmost end of the few-mode fiber communication system, and a micro-ring resonator is configured at the end of optical signal transmission of the few-mode fiber communication system to implement a second compensation process on the optical speed, so that the technical problem of group delay in a differential mode of a few-mode fiber can be solved.
As shown in fig. 2, a second embodiment of the present invention provides a differential mode group delay compensation system based on photoelectric fusion, where the compensation system includes a redundancy adding module, an optical modulation module, a first mode converter, a mode division multiplexer, a few-mode optical fiber, a mode division multiplexer, a second mode converter, a micro-ring resonator, a photodetector, a redundancy removing module, and a signal processing module.
(1) At least one redundancy addition module
The number of the redundant adding modules corresponds to the number of original data to be transmitted, the redundant adding modules are used for calculating time delay differences between different modes and a basic mode in the few-mode optical fiber, redundant data adding with different data volumes is carried out on the original data to be transmitted corresponding to the different modes at a transmitting end, first compensation is carried out on differential mode group time delay of the few-mode optical fiber, and optical signals corresponding to each processed mode theoretically reach an optical fiber terminal at the same time.
At a sending end, original data firstly passes through a redundancy adding module, redundancy codes with different lengths are added in front of data transmitted in different modes, and differential mode group delay is compensated for the first time on an electrical domain. Specifically, for optical fibers with different refractive index profile structures, the effective refractive index of each mode under different wavelengths is measured and calculated. Because the propagation speeds of the guided modes supporting transmission in the few-mode optical fiber are different in the optical fiber, the optical signal between the mode channels will have a time delay after propagating for a certain distance, that is, a mode group time delay is generated, which can be expressed as:
Figure 391799DEST_PATH_IMAGE032
wherein
Figure 685377DEST_PATH_IMAGE004
Is a function of the wavelength of the light,
Figure 132539DEST_PATH_IMAGE005
to be the group velocity, the velocity of the beam,
Figure 587791DEST_PATH_IMAGE006
is the speed of light in vacuum, propagation constant
Figure 877827DEST_PATH_IMAGE007
，
Figure 709517DEST_PATH_IMAGE008
Is the effective index of refraction of the mode,
Figure 276765DEST_PATH_IMAGE009
is the wavenumber of the light wave in free space. The different modes require different times to pass through a fixed length of fiber, so the differential mode group delay (MDGD) expression between the higher order mode and the fundamental mode is:
Figure DEST_PATH_IMAGE033
in the formula (I), the compound is shown in the specification,
Figure 43863DEST_PATH_IMAGE013
in order to achieve a high-order mode delay,
Figure 696562DEST_PATH_IMAGE014
is the fundamental mode delay.
Through the two formulas, the time delay difference between different modes and the basic mode in the few-mode optical fiber can be calculated, then redundant data with different data volumes are added to different modules through the encoder of the redundant module at the transmitting end, and the differential mode group time delay of the few-mode optical fiber in the system is compensated before the electric signal is subjected to electro-optical conversion.
In few-mode optical fibers, inter-mode dispersion means that light rays of each mode are transmitted to a terminal through different paths, and due to different optical path lengths of each light ray, the time for each mode to reach the optical fiber terminal is different. As shown in FIG. 3, LP01The optical path of the fundamental mode is shortest; LP11For the high order mode, the optical path increases; LP21The highest order mode, the longest optical path. So LP01、LP11、LP21Three modes are transmitted in few-mode optical fiber for time t1、t2、t3The magnitude relation of (1) is t1<t2<t3. If a proper amount of redundant data is added before passing through a mode with short time of the optical fiber, the data needing to be transmitted can simultaneously reach the optical fiber terminal. Here we assume that
Figure 331942DEST_PATH_IMAGE029
2-bit data pass LP01The time for the mode to propagate in the few-mode fiber is
Figure 488117DEST_PATH_IMAGE030
1 bit data is passed through LP11The time for the mode to propagate in the few-mode fiber is
Figure 675385DEST_PATH_IMAGE030
. Then we only need to add the module at redundancy at the original data 1 (at LP)01Transmission in mode) is added with 4 bits of redundant data, at the original data 2 (at LP)11Transmission in mode) before adding 1-bit redundant data, the original data 1, 2 and 3 can arrive at the optical fiber terminal at the same time, namely
Figure 549800DEST_PATH_IMAGE031
As shown in fig. 4.
(2) Light modulation module
The optical modulation module is used for modulating and loading each path of electric signals into light waves through an electro-optical modulator and transmitting the light waves in optical fibers, and the existing electro-optical modulation mainly comprises intensity modulation, IQ modulation and other modes.
(3) First mode converter
The first mode converter converts the fundamental mode transmitted in the single mode fiber into other higher-order modes to carry different information, as shown in fig. 5, and the first mode converter converts the fundamental mode LP01Conversion to higher order LP11、LP21Two modes.
(4) Mode division multiplexer
After mode conversion by the mode converter, each path of mode signal is coupled into a few-mode optical fiber link through the mode multiplexer for transmission. The optical signals of different modes are independent channels due to the orthogonality of the modes, so that long-distance transmission can be carried out in the same few-mode optical fiber.
(5) Few-mode optical fiber
Few-mode optical fibers are used for long-distance transmission of optical signals.
(6) Mould decomposition multiplexer
After the optical signal is transmitted through the few-mode optical fiber, the optical signal is demultiplexed through the mode demultiplexer at a receiving end, and the optical signal transmitted in the few-mode optical fiber is decomposed into multiple paths of parallel signals through the demultiplexing process and is respectively coupled to different single-mode optical fibers.
(7) Second mode converter
After the different modes are decomposed by the mode demultiplexer, the mode converter at the receiving end restores the optical signals of the plurality of different modes into a base mode signal.
(8) Micro-ring resonator
In this patent, after passing through a mode demultiplexer and a mode converter, light transmitted in different modes enters different microring resonators, and the light velocity is controlled again by changing the radius of the microring resonators to compensate for dispersion. After passing through the microring resonator, the data-carrying light can simultaneously reach the photodetector.
The micro-ring resonator is used for realizing the speed control of light, does not need harsh physical conditions, and has the advantages of simple structure, convenience in manufacturing, high integration level and the like. The essence of the light speed control is to realize the effects of fast light and slow light, and even make the light spread at a negative light speed.
When optical signals with different frequencies are input into the micro-ring resonator, the optical signals meeting the resonance condition can be resonantly enhanced in the micro-ring resonator and transmitted for a plurality of turns, and a time delay phenomenon occurs, as shown in fig. 6, when the optical signals lambda1Is the resonance wavelength of the resonator, so that a delay occurs. The microring resonator structure and waveguide materials can be varied to achieve the desired delay characteristics.
After passing through the mode demultiplexer and the mode converter, light transmitted in different modes enters different microring resonators, the light speed is controlled again, and dispersion is compensated. Taking the three modes of few-mode fiber as an example, since the redundancy addition is based on theoretical calculation, although the delay difference can be compensated, there may still be an error. Assuming that the delay difference is compensated for but still exists after the redundancy addition, LP01、LP11、LP21The light of the three modes respectively reaches the micro-ring resonators in sequence, and the resonance wavelength of the resonators is set to be the central wavelength of the light wave, so that the light speed can be controlled by changing the radius of the micro-ring resonators.
As shown in fig. 7, radius R of the microring resonator1>R2>R3So that the path S of the light in the microring resonator1>S2>S3So that the time T of the micro-ring resonator is passed1>T2>T3Here T2-T1、T3-T1Is through LP11Mold, LP21Mode propagation to the microring resonator and through the LP01The difference in time for the mode propagation to reach the microring resonator. Thus, after passing through the microring resonator, the data-carrying light can simultaneously reach the photodetector.
(9) Photoelectric detector
The photoelectric detector receives the optical signals output by all the micro-ring resonators and converts the optical signals into electric signals.
(10) Redundancy elimination module
After passing through the micro-ring resonator, each path of optical information transmitted in parallel is detected and received by the photoelectric detector, the optical signal is converted into an electric signal, and then the electric signal reaches the redundancy removing module to be subjected to redundancy removal. In the three-mode fiber example above, we only need to remove the redundancy-added module from the original data 1 (at LP)01Transmitted in mode) added 4-bit redundancy data and in original data 2 (at LP)11Transmitted in mode) previously added 1-bit redundancy data.
(11) Signal processing module
The electrical signal after the optical-electrical conversion is sent to a digital signal processing module for MIMO signal processing in the electrical domain, so that signal damage in the transmission process is eliminated and the original signal is recovered.
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.

Claims (7)

1. A differential mode group delay compensation method based on photoelectric fusion is characterized by comprising the following steps:
calculating time delay differences between different modes and a basic mode in the few-mode optical fiber, adding redundant data with different data volumes to original data to be transmitted corresponding to the different modes at a transmitting end, and compensating differential mode group time delay of the few-mode optical fiber for the first time to enable optical signals corresponding to each mode to theoretically reach an optical fiber terminal at the same time;
the method comprises the steps that after demultiplexing and mode conversion are sequentially carried out on received optical signals at a receiving end, a plurality of basic mode signals are recovered, and the basic mode signals correspond to transmission modes one to one;
leading the basic mode signals corresponding to different modes into different micro-ring resonators in a one-to-one correspondence manner, controlling the light speed again by changing the radius of the micro-ring resonators, and performing secondary compensation on the differential mode group delay of the few-mode optical fiber to enable the light signals output by all the micro-ring resonators to simultaneously reach the photoelectric detector;
the compensation method further comprises the following steps:
and receiving the optical signals output by all the micro-ring resonators by using the photoelectric detector, converting the optical signals into electric signals, and removing redundant data added in the electric signals.
2. The differential mode group delay compensation method based on photoelectric fusion of claim 1, wherein the calculating a delay difference between different modes in the few-mode fiber and a fundamental mode comprises:
measuring and calculating the effective refractive index of each mode under different wavelengths for optical fibers with different refractive index profile structures;
calculating to obtain the mode group delay of the optical fiber
Figure DEST_PATH_IMAGE001
：
Figure DEST_PATH_IMAGE003
Wherein
Figure 169099DEST_PATH_IMAGE004
Is a function of the wavelength of the light,
Figure DEST_PATH_IMAGE005
to be the group velocity, the velocity of the beam,
Figure 647485DEST_PATH_IMAGE006
is the speed of light in vacuum, propagation constant
Figure DEST_PATH_IMAGE007
，
Figure 179704DEST_PATH_IMAGE008
Is the effective index of refraction of the mode,
Figure DEST_PATH_IMAGE009
is the wave number of free space;
calculating to obtain the differential mode group delay between the high-order mode and the fundamental mode of the optical fiber
Figure 718133DEST_PATH_IMAGE010
：
Figure 181475DEST_PATH_IMAGE012
In the formula (I), the compound is shown in the specification,
Figure DEST_PATH_IMAGE013
in order to achieve a high-order mode delay,
Figure 712819DEST_PATH_IMAGE014
is the fundamental mode delay.
3. The differential mode group delay compensation method based on photoelectric fusion of claim 1, wherein the adding of redundant data of different data amounts at a transmitting end for original data to be transmitted corresponding to different modes comprises:
calculating the data transmission time difference between different modes in the transmission process;
and adding redundant data with different data volumes aiming at the original data to be transmitted corresponding to different modes by combining the theoretical transmission time of the single data in different modes, so that the theoretical transmission time of the processed data in each mode is the theoretical transmission time
Figure DEST_PATH_IMAGE015
：
Figure DEST_PATH_IMAGE017
In the formula (I), the compound is shown in the specification,
Figure 882901DEST_PATH_IMAGE018
the theoretical transmission time length of the original data of the ith mode;
Figure DEST_PATH_IMAGE019
the added redundant data bit number of the ith mode;
Figure 185706DEST_PATH_IMAGE020
the theoretical transmission duration of the unit data of the ith mode.
4. The differential mode group delay compensation method based on photoelectric fusion according to claim 1, wherein the compensation method further comprises:
and carrying out MIMO signal processing on the electric signal without the redundant data, eliminating signal damage in the transmission process and recovering the original signal.
5. A differential mode group delay compensation system based on photoelectric fusion, the compensation system comprising:
the system comprises at least one redundant adding module, a transmission end and a transmission end, wherein the redundant adding module is used for calculating the time delay difference between different modes and a basic mode in the few-mode optical fiber, adding redundant data with different data volumes aiming at original data to be transmitted corresponding to the different modes at the transmission end, and performing first compensation on the differential mode group time delay of the few-mode optical fiber so that optical signals corresponding to each mode after processing theoretically reach an optical fiber terminal at the same time; the number of the redundancy adding modules corresponds to the number of original data to be transmitted;
the optical modulation module is correspondingly connected with the redundancy adding module and is used for modulating each path of electric signal output by the redundancy adding module and loading the electric signal into an optical wave to obtain a corresponding basic mode signal;
the first mode converter is correspondingly connected with the optical modulation module and is used for converting a basic mode signal transmitted in the single-mode optical fiber into other high-order mode signals to carry different information;
the input end of the mode division multiplexer is connected with the first mode converter, the output end of the mode division multiplexer is connected with the transmitting end of the few-mode optical fiber, and the mode division multiplexer is used for coupling each path of mode signals output by the mode converter into a few-mode optical fiber link for transmission;
a few-mode optical fiber;
the input end of the mode decomposition multiplexer is connected with the output end of the few-mode optical fiber, the output end of the mode decomposition multiplexer is connected with the second mode converter, the mode decomposition multiplexer is used for demultiplexing the optical signals transmitted by the few-mode optical fiber, and the optical signals transmitted by the few-mode optical fiber are decomposed into multi-channel parallel signals through the demultiplexing process and are respectively coupled to different single-mode optical fibers;
at least one second mode converter for restoring the optical signals of the plurality of different modes decomposed by the mode decomposition multiplexer into a fundamental mode signal;
the micro-ring resonator is correspondingly connected with the second mode converter and used for controlling the propagation speed of the basic mode signal output by the mode converter again by changing the radius of the micro-ring resonator so as to carry out secondary compensation on the differential mode group delay of the few-mode optical fiber and enable the optical signals output by all the micro-ring resonators to reach the photoelectric detector at the same time;
at least one photoelectric detector which is correspondingly connected with the micro-ring resonators and is used for receiving optical signals output by all the micro-ring resonators and converting the optical signals into electric signals;
the redundancy removing module is correspondingly connected with the photoelectric detector and used for removing redundant data added later in the electric signal;
and the signal processing module is used for carrying out MIMO signal processing on the electric signal without the redundant data, eliminating signal damage in the transmission process and recovering the original signal.
6. The differential mode group delay compensation system based on photoelectric fusion of claim 5, wherein the redundancy adding module calculates the delay difference between different modes in the few-mode fiber and the fundamental mode, and comprises:
measuring and calculating the effective refractive index of each mode under different wavelengths for optical fibers with different refractive index profile structures;
calculating to obtain the mode group delay of the optical fiber
Figure 293602DEST_PATH_IMAGE001
：
Figure DEST_PATH_IMAGE021
Wherein
Figure 379369DEST_PATH_IMAGE004
Is a function of the wavelength of the light,
Figure 263012DEST_PATH_IMAGE005
to be the group velocity, the velocity of the beam,
Figure 861352DEST_PATH_IMAGE006
is the speed of light in vacuum, propagation constant
Figure 33707DEST_PATH_IMAGE007
，
Figure 985483DEST_PATH_IMAGE008
Is the effective index of refraction of the mode,
Figure 130156DEST_PATH_IMAGE009
is the wave number of free space;
calculating to obtain the differential mode group delay between the high-order mode and the fundamental mode of the optical fiber
Figure 978027DEST_PATH_IMAGE010
：
Figure 877760DEST_PATH_IMAGE012
In the formula (I), the compound is shown in the specification,
Figure 633226DEST_PATH_IMAGE013
in order to achieve a high-order mode delay,
Figure 429144DEST_PATH_IMAGE014
is the fundamental mode delay.
7. The differential mode group delay compensation system based on photoelectric fusion of claim 5, wherein the redundancy adding module adds redundancy data of different data amounts at a transmitting end aiming at original data to be transmitted corresponding to different modes, and the redundancy adding module comprises:
calculating the data transmission time difference between different modes in the transmission process;
and adding redundant data with different data volumes aiming at the original data to be transmitted corresponding to different modes by combining the theoretical transmission time of the single data in different modes, so that the theoretical transmission time of the processed data in each mode is the theoretical transmission time
Figure 385599DEST_PATH_IMAGE015
：
Figure 329284DEST_PATH_IMAGE017
In the formula (I), the compound is shown in the specification,
Figure 91704DEST_PATH_IMAGE018
the theoretical transmission time length of the original data of the ith mode;
Figure 929079DEST_PATH_IMAGE019
the added redundant data bit number of the ith mode;
Figure 649910DEST_PATH_IMAGE020
the theoretical transmission duration of the unit data of the ith mode.
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