A mode adding and dropping channel device based on Bragg grating

Abstract

The present invention discloses a mode up / down channel device based on Bragg grating, which belongs to the field of communication technology and is composed of an optical signal generating module, a mode division multiplexing module, a mode up / down channel module, a mode demultiplexing module and an optical signal processing module; wherein the output port of the optical signal generating module is connected to the input port of the mode division multiplexing module, the mode division multiplexing module is connected to the mode up / down channel module, a specific down channel mode signal is connected to the optical signal processing module, a normal transmission signal is connected to the input port of the mode demultiplexing module, and is connected to the input port of the optical signal processing module after mode demultiplexing. The present invention is based on the self-coupling reflection characteristics of the Bragg grating and utilizes the unidirectional conduction characteristics of the circulator to realize the reflection, downloading and uploading of a specific transmission mode signal. Since the Bragg grating is simple to prepare, the cost is low, and the access to the mode division multiplexing system is relatively simple, the present invention has the advantages of low cost, easy implementation, and excellent performance.

Description

Technical Field

[0001] The invention belongs to the technical field of communication, and in particular relates to a Bragg grating-based mode up / down channel device. Background Art

[0002] With the rapid development of the Internet industry, the information demand of all walks of life has exploded, and the increase in data volume has put forward higher requirements on the transmission capacity of optical fiber communication networks. However, the transmission capacity of existing single-mode optical fibers is limited by the Shannon limit, and bandwidth exhaustion will soon occur. Few-mode optical fibers have multiple orthogonal modes, and each mode can be used as an independent channel for information transmission. The rapid development of mode division multiplexing technology in recent years can double the information transmission capacity.

[0003] The mode division multiplexing system transmits multiple modes in few-mode optical fibers. During the transmission process of long-distance transmission systems, it is usually necessary to download the information carried by a mode from the trunk line at a specific node. Similarly, information also needs to be uploaded to the trunk line for transmission at a specific node, that is, to implement the up and down paths of a specific mode at the node. The existing up and down path technologies of mode division multiplexing systems can be roughly divided into spatial optical path type and on-chip waveguide type. The spatial optical path type is simple to implement, but the structure is complex and the insertion loss is large. The on-chip waveguide has good controllability and high integration, but it is difficult to implement. Therefore, the development of up and down path technology is of great significance. Summary of the invention

[0004] In view of the problems of complex structure and great difficulty in implementation in the existing mode division multiplexing system up and down channel technology, the present invention proposes a Bragg grating-based mode up and down channel device, which has the advantages of simple structure, small size, low cost and low implementation difficulty.

[0005] To achieve the above object, the present invention adopts the following technical solutions:

[0006] A Bragg grating-based mode add / drop voice channel device, comprising an optical signal generating module, a mode division multiplexing module, a mode add / drop voice channel module 3, a mode division multiplexing module 4 and an optical signal processing module, wherein the optical signal generating module comprises a first optical signal generating module 1 and a second optical signal generating module 6, the mode division multiplexing module comprises a first mode division multiplexing module 2 and a second mode division multiplexing module 7, and the optical signal processing module comprises a first optical signal processing module 5 and a second optical signal processing module 8; wherein the output port of the first optical signal generating module 1 is connected to the input port of the first mode division multiplexing module 2 The output port of the first mode division multiplexing module 2 is connected to an input port of the up / down voice channel module 3, an output port of the up / down voice channel module 3 is connected to the input port of the mode demultiplexing module 4, and the output port of the mode demultiplexing module 4 is connected to the input port of the first optical signal processing module 5; the output port of the second optical signal generating module 6 is connected to the input port of the second mode division multiplexing module 7, the output port of the second mode division multiplexing module 7 is connected to another input port of the up / down voice channel module 3, and the other output port of the mode up / down voice channel module 3 is connected to the input port of the second optical signal processing module 8.

[0007] Furthermore, the optical signal generating module is composed of a tunable laser 11, an electro-optical modulator 12 and a DAC 13; the output port of the tunable laser 11 is connected to the first input port 121 of the electro-optical modulator 12; the output port of the DAC 13 is connected to the second input port 122 of the electro-optical modulator 12; finally, the modulated signal is output from the output port 123 of the electro-optical modulator 12, wherein the output laser wavelength can be selected as 1550.52nm.

[0008] Furthermore, the mode division multiplexing module is composed of a beam splitter 21 and a mode converter 22; wherein, the output port 21 of the beam splitter is connected to the input port of the mode converter 22, and mode multiplexing is realized through the mode converter, wherein the multiplexed modes include modes transmitted in few-mode optical fibers such as LP01, LP11, and LP21.

[0009] Furthermore, the mode up / down channel module 3 is composed of a switch 31, a circulator 32, a Bragg grating 33 and a coupler 34, and is used to realize the up / down channel function in the mode division multiplexing system; when the input signal is connected to the input port of the switch 31, when the selected mode is the down channel, the switch 31 is connected to the first output port 311, which is connected to the first port 321 of the circulator 32, and the selected mode signal is incident to the input port 331 of the Bragg grating 33 of the selected mode through the second port 322 of the circulator, and is self-coupled and reflected by the Bragg grating, and the selected mode signal is self-coupled and reflected back to the second port 322 of the circulator and emitted through the third port 323 of the circulator 32, so as to realize the down channel of the signal; at the same time, other mode signals are normally emitted from the output port 332 of the Bragg grating 33 without interference and are transmitted normally;

[0010] When the selected mode is the uplink, it is connected to the input port 342 of the coupler 34, and other mode signals that are normally transmitted are connected to the first input port 341 of the coupler. After coupling by the coupler, the signal is output from the output port 343 of the coupler, thereby realizing the uplink of the selected mode signal.

[0011] If no specific mode of up / down talk is required, the switch is connected to the second output port 312, the signal is transmitted normally, and no up / down talk is performed in the selected mode.

[0012] Furthermore, the mode demultiplexing module 4 adopts a mode converter 41; wherein the transmitted mode multiplexing signal is incident through the input port of the mode converter 41, mode demultiplexing is completed in the mode converter, and each mode is output respectively through the output port of the mode converter to realize mode demultiplexing.

[0013] Furthermore, the optical signal processing module is composed of a photodetector 51, an oscilloscope 52, a DSP53 and a tunable laser 54; wherein, the optical signal with mode information is input through the first input port 511 of the photodetector 51, and at the same time, due to the use of coherent detection, the tunable laser 54 outputs a beam of local oscillation light for signal reception, and the output light is input at the second input port 512 of the photodetector 51, and the signal mixing and coherent reception are completed in the photodetector, and converted into an electrical signal, which is output from the output port 513 of the photodetector and input from the input port of the oscilloscope 52, and the stored information is input to the input port of the DSP53 to realize offline processing of the signal.

[0014] Furthermore, the DSP processing module 53 includes orthogonalization 531, clock recovery 532, resampling 533, channel equalization 534, frequency offset compensation 535 and phase offset compensation 536; it is used to improve signal quality and compensate for noise and interference. Finally, after DSP processing, signal reception is completed.

[0015] Compared with the prior art, the advantages of the present invention are as follows:

[0016] The present invention proposes a mode add / drop circuit device based on few-mode fiber Bragg gratings, which adopts fiber Bragg gratings and is reasonably designed according to actual needs. It reflects the selected mode signal by relying on its self-coupling reflection characteristics, and can meet the mode add / drop circuit function required by the mode division multiplexing system. It has the advantages of small size, low cost, high performance and system stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following is a brief introduction to the drawings required for the specific embodiments or the description of the prior art. In all the drawings, similar elements or parts are generally identified by similar reference numerals. In the drawings, the elements or parts are not necessarily drawn according to the actual scale.

[0018] Figure 1 It is a structural schematic diagram of a mode add / drop channel device based on few-mode fiber Bragg grating of the present invention;

[0019] Figure 2 It is a structural schematic diagram of the optical signal generating module of the present invention;

[0020] Figure 3 It is a schematic diagram of the structure of the mode division multiplexing module of the present invention;

[0021] Figure 4 This is a schematic diagram of the structure of the up / down voice channel module of the present invention;

[0022] Figure 5 This is a schematic diagram of the structure of the mode demultiplexing module of the present invention;

[0023] Figure 6 It is a schematic diagram of the structure of the optical signal processing module of the present invention;

[0024] Figure 7 It is a schematic diagram of the DSP module structure of the present invention;

[0025] Figure 8 The schematic diagram of the structure of the mode adding and dropping channel device system based on few-mode fiber Bragg grating described in the example;

[0026] Fig. 9 When the signal rate is 8 Gbit / s QPSK signal, the constellation diagrams of LP01 (a), LP11 (b), and LP21 (c) modes before CMA algorithm compensation;

[0027] Fig.10When the signal rate is 8 Gbit / s QPSK signal, the constellation diagrams of LP01 (a), LP11 (b), and LP21 (c) modes after CMA algorithm compensation;

[0028] In the figure: optical signal generating module 1, mode division multiplexing module 2, mode adding and dropping channel module 3, mode division multiplexing module 4, optical signal processing module 5, tunable laser 11, electro-optic modulator 12, DAC 13, electro-optic modulator input port 121, electro-optic modulator input port 122, electro-optic modulator output port 123, beam splitter 21, mode converter 22, switch 31, circulator 32, Bragg grating 33, coupler 34, first output port 311 of switch, second output port 312 of switch, first port 321 of circulator, The second port 322 of the circulator, the third port 323 of the circulator, the first input port 341 of the coupler, the second input port 342 of the coupler, the output port 343 of the coupler, the photodetector 51, the oscilloscope 52, the DSP 53, the first input port 511 of the photodetector, the second input port 512 of the photodetector, the output port 513 of the photodetector, the orthogonalization module 531, the clock recovery module 532, the resampling module 533, the channel equalization module 534, the frequency deviation compensation module 535, and the phase deviation compensation module 536. DETAILED DESCRIPTION

[0029] The embodiments of the technical solution of the present invention will be described in detail below in conjunction with the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solution of the present invention and are therefore only used as examples and cannot be used to limit the protection scope of the present invention.

[0030] It should be noted that, unless otherwise specified, the technical terms or scientific terms used in this application should have the common meanings understood by those skilled in the art to which the present invention belongs.

[0031] Example 1

[0032] The present invention realizes a technology for realizing mode up / down communication based on few-mode fiber Bragg grating, and its system block diagram is as follows: Figure 1As shown, it consists of a first optical signal generating module 1, a second optical signal generating module 6, a first mode division multiplexing module 2, a second mode division multiplexing module 7, an up / down voice channel module 3, an mode demultiplexing module 4, a first optical signal processing module 5, and a second optical signal processing module 8; wherein, the output port of the first optical signal generating module 1 is connected to the input port of the first mode division multiplexing module 2, the output port of the first mode division multiplexing module 2 is connected to an input port of the up / down voice channel module 3, an output port of the up / down voice channel module 3 is connected to the input port of the mode demultiplexing module 4, and the output port of the mode demultiplexing module 4 is connected to the input port of the first optical signal processing module 5; the output port of the second optical signal generating module 6 is connected to the input port of the second mode division multiplexing module 7, the output port of the second mode division multiplexing module 7 is connected to another input port of the mode up / down voice channel module 3, and another output port of the up / down voice channel module 3 is connected to the input port of the second optical signal processing module 8. In this example, the laser module selects a tunable laser to provide the optical carrier required by the system, the modulator module selects an IQ modulator to realize the conversion of electrical signals to optical signals, the mode converter selects a photon lantern, the few-mode fiber selects 8km four-mode few-mode fiber as the basis of the system, and the photodetector module selects a coherent receiver to realize the conversion of optical signals to electrical signals.

[0033] In this embodiment, the first optical signal generating module 1 and the second optical signal generating module 6 are schematically shown in FIG. Figure 2 As shown, it includes a tunable laser 11, an electro-optical modulator 12 and a DAC 13; the output port of the tunable laser 11 is connected to the input port 121 of the electro-optical modulator 12; the output port of the DAC 13 is connected to the input port (122) of the electro-optical modulator 12; finally, the modulated signal is output from the output port 123 of the electro-optical modulator 12. In this example, the output laser wavelength can be selected as 1550.52nm, and the DAC is used to synthesize two 4Gbit / s pseudo-random signals into one 8Gbit / sQPSK signal, and the DAC transmission signal is loaded onto the light through the IQ modulator.

[0034] In this embodiment, the first mode division multiplexing module 2 and the second mode division multiplexing module 7 are schematically shown in FIG. Figure 3 As shown, it includes a beam splitter 21 and a mode converter 22; wherein, the beam splitter output port 21 is connected to the mode converter input port, and mode multiplexing is achieved through the mode converter. In this example, the multiplexed modes include modes transmitted in few-mode optical fibers such as LP01, LP11, and LP21. The multiplexing method uses a photon lantern to multiplex the few-mode optical fiber transmission modes into one few-mode optical fiber for transmission.

[0035] In this embodiment, the mode adding and dropping voice channel module 3 is as shown in the schematic diagram. Figure 4As shown, it includes a switch 31, a circulator 32, a Bragg grating 33 and a coupler 34; wherein, it includes:

[0036] When the input signal is connected to the input port of the switch 31 and the selected mode is the downlink, the switch 31 is connected to the first output port 311, which is connected to the first port 321 of the circulator 32. The selected mode signal is incident to the input port 331 of the Bragg grating 33 of the selected mode through the second port 322 of the circulator, and is self-coupled and reflected by the Bragg grating, and the selected mode signal is self-coupled and reflected back to the second port 322 of the circulator and emitted through the third port 323 of the circulator 32, thereby realizing the downlink of the signal. At the same time, other mode signals are normally emitted from the output port 332 of the Bragg grating 33 without interference and are transmitted normally.

[0037] When the selected mode is the uplink, it is connected to the input port 342 of the coupler 34, and other mode signals that are normally transmitted are connected to the first input port 341 of the coupler. After coupling by the coupler, the signal is output from the output port 343 of the coupler, thereby realizing the uplink of the selected mode signal.

[0038] If no specific mode of up / down talk is required, the switch is connected to the second output port 312, the signal is transmitted normally, and no up / down talk is performed in the selected mode.

[0039] In this embodiment, the mode demultiplexing module 4 has a schematic diagram as shown in FIG. Figure 5 As shown, it includes a mode converter 41; wherein the transmitted mode multiplexing signal is incident through the input port of the photon lantern 41, the mode demultiplexing is completed in the photon lantern, and each mode is output respectively through the output port of the photon lantern to realize the mode demultiplexing.

[0040] In this embodiment, the first optical signal processing module 5 and the second optical signal processing module 8 are schematically shown in FIG. Figure 6 As shown, it includes a photodetector 51, an oscilloscope 52, a DSP 53 and a tunable laser 54; wherein, the optical signal with mode information is input through the first input port 511 of the photodetector 51, and at the same time, due to the use of coherent detection, the tunable laser 54 outputs a beam of local oscillation light for signal reception, and the output light is input at the second input port 512 of the photodetector, and the signal is mixed and coherently received in the photodetector, and converted into an electrical signal, which is output from the output port 513 of the photodetector, input from the input port of the oscilloscope 52, and the stored information is input to the input port of the DSP 53, so as to realize the offline processing of the signal. In this example, the photodetector is selected as a coherent receiver, and a tunable laser is used to output a local oscillation light for coherent demodulation of the signal.

[0041] In this embodiment, the DSP processing module 53, its schematic diagram is as follows Figure 7As shown, it includes orthogonalization 531, clock recovery 532, resampling 533, channel equalization 534, frequency offset compensation 535 and phase offset compensation 536; in order to improve signal quality and compensate for noise and interference, the algorithm can use the Gram-Schmidt algorithm to compensate and orthogonalize IQ imbalance, the Gardner algorithm to perform clock recovery, the CMA algorithm to perform channel equalization and compensation, and the Viterbi-Viterbi algorithm to compensate for frequency offset and phase noise. Finally, after DSP processing, the signal reception is completed.

[0042] The detailed system block diagram of this example is as follows Figure 8 As shown, the workflow is as follows:

[0043] First, set the DAC13 output rate to F (0-64G) two-way pseudo-random sequence RF signal, and then set the output power A (10-40mw) of the laser 11 to output the optical signal. The RF signal and the optical signal are input to the IQ modulator 12 to modulate the electrical signal onto the optical carrier. The modulated optical signal enters the photon lantern 22 through the beam splitter 21 for spatial mode conversion and is transmitted for a distance in the few-mode optical fiber. At the node, the Bragg grating 33 and the circulator 32 are used to realize the downlink of a specific mode, and the coupler 34 is used to realize the uplink of a specific mode. After completing the uplink and downlink functions of the mode, the photon lantern 41 is used to separate the different modes, and the separated optical signal enters the photodetector 51 for photoelectric conversion. Finally, the converted electrical signal is input to the DSP53, and the signal is demodulated after compensation.

[0044] This example uses DAC, laser, and IQ modulator to obtain the output of the modulated signal. The implementation method is as follows: DAC generates the pseudo-random signal required by the system, which is input to the input port 122 of the IQ modulator. By changing the setting of the initial parameters, RF signals of different rates can be obtained; the laser provides the optical carrier of the signal, which is input to the input port 121 of the IQ modulator; the electro-optical conversion unit of the modulator completes the conversion from electricity to light, and the output port 123 outputs the modulated optical signal.

[0045] The mode multiplexing module of this example adopts the method of first photon lantern + few-mode fiber + second photon lantern, in which the first photon lantern is a mode converter and the second photon lantern is a mode demultiplexer. The basic working process is as follows: the modulated signal output by the IQ modulator passes through the beam splitter and enters the three single-mode ports of the first photon lantern respectively. Spatial mode conversion occurs inside the first photon lantern. After the three modes are excited, they are transmitted through 8km few-mode fiber and enter the second photon lantern for mode separation.

[0046] The mode up / down circuit module of this example adopts a self-made few-mode fiber Bragg grating, a switch, a circulator and a coupler to realize the up / down circuit function in the mode division multiplexing system. The implementation method is as follows: when the signal is transmitted to the switch 31, if a specific mode up / down circuit is required, the switch is connected to the first output port 311, and the unidirectional conduction characteristic of the circulator 32 is used to input from the first port 321 of the circulator and output from the second port 322. The self-coupling reflection characteristic of the Bragg grating 33 is used to reflect the specific mode signal back, and the signal is input from the second port 322 of the circulator and output from the third port 323, so as to realize the down circuit of the specific mode signal without affecting the normal transmission of other modes; in the up circuit part, the coupler 34 is used to input the specific mode signal into the port 342 of the coupler 34, and the coupling of each signal is realized in the coupler 34 and then the signal is output from the coupler output port 343, so as to realize the up circuit of the specific mode signal; if the up / down circuit of the specific mode is not required, the switch 31 is connected to the second output port 312, and each mode signal is transmitted normally.

[0047] This example uses coherent detection to receive signals. The three output signals (LP01 mode, LP11 mode, and LP21 mode) of the second photon lantern are connected to the input ports of the coherent receiver 51 at the output port and connected to the local oscillator light.

[0048] The data processing part of this example adopts offline processing. The data processing adopts the Gram-Schmidt algorithm to compensate and orthogonalize IQ imbalance, the Gardner algorithm to recover the clock, the CMA algorithm to equalize and compensate the channel, and the Viterbi-Viterbi algorithm to compensate for the frequency offset and phase noise. Finally, after DSP data processing, the signal demodulation and reception are completed.

[0049] Fig. 9 , Fig.10 The constellation diagrams of the signals after adding and dropping the channels before channel compensation and the constellation diagrams of the signals after adding and dropping the channels after adding the CMA algorithm for compensation are respectively given when the transmission signal is a QPSK signal of 8Gbit / s. Among them, the step size of the CMA algorithm is 1 when the LP01 mode is compensated, the step size of the CMA algorithm is 0.5 when the LP11 mode is compensated, and the step size of the CMA algorithm is 0.1 when the LP21 mode is compensated. It can be seen from the figure that when channel compensation is not performed, due to the influence of the residual signal reflected by the Bragg grating, the constellation diagram will have some divergence. After channel compensation, the influence is eliminated and the signal quality is improved, indicating that the device can be well applied to the mode division multiplexing system.

[0050] The embodiments of the present invention are described in detail above in conjunction with the accompanying drawings; however, the present invention is not limited to the specific details in the above embodiments; within the technical concept of the present invention, a variety of simple modifications can be made to the technical solution of the present invention, and these simple modifications all fall within the protection scope of the present invention.

[0051] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any suitable manner without contradiction. In order to avoid unnecessary repetition, the present invention will not further describe various possible combinations.

[0052] In addition, various embodiments of the present invention may be arbitrarily combined, and as long as they do not violate the concept of the present invention, they should also be regarded as the contents disclosed by the present invention.

Claims

1. A Bragg grating-based mode add / drop voice channel device, It is characterized in that The optical signal generating module comprises an optical signal generating module, an analog division multiplexing module, a mode adding / dropping channel module (3), an analog division multiplexing module (4) and an optical signal processing module, wherein the optical signal generating module comprises a first optical signal generating module (1) and a second optical signal generating module (6), the analog division multiplexing module comprises a first analog division multiplexing module (2) and a second analog division multiplexing module (7), and the optical signal processing module comprises a first optical signal processing module (5) and a second optical signal processing module (8); wherein the output port of the first optical signal generating module (1) is connected to the input port of the first analog division multiplexing module (2), and the first analog division multiplexing module (2) is connected to the input port of the first analog division multiplexing module (2). The output port of the first optical signal generating module (6) is connected to an input port of the up / down speech path module (3), an output port of the up / down speech path module (3) is connected to an input port of the mode demultiplexing module (4), and the output port of the mode demultiplexing module (4) is connected to an input port of the first optical signal processing module (5); the output port of the second optical signal generating module (6) is connected to an input port of the second mode division multiplexing module (7), the output port of the second mode division multiplexing module (7) is connected to another input port of the up / down speech path module (3), and another output port of the mode up / down speech path module (3) is connected to an input port of the second optical signal processing module (8); The mode up / down channel module (3) is composed of a switch (31), a circulator (32), a Bragg grating (33) and a coupler (34), and is used to realize the up / down channel function in the mode division multiplexing system; when the input signal is connected to the input port of the switch (31), and the selected mode is the down channel, the switch (31) is connected to the first output port (311), connected to the first port (321) of the circulator (32), and the selected mode signal is incident on the input port (331) of the Bragg grating (33) of the selected mode through the second port (322) of the circulator, and the selected mode signal is self-coupled and reflected back to the second port (322) of the circulator through the self-coupling reflection of the Bragg grating, and is emitted through the third port (323) of the circulator (32), thereby realizing the down channel of the signal; at the same time, other mode signals are normally emitted from the output port (332) of the Bragg grating (33) without interference, and are normally transmitted; When the selected mode is the uplink, it is connected to the input port (342) of the coupler (34), and other mode signals that are normally transmitted are connected to the first input port (341) of the coupler. After coupling by the coupler, the signal is output from the output port (343) of the coupler, thereby realizing the uplink of the selected mode signal; If no specific mode of up / down talk is required, the switch is connected to the second output port (312), the signal is transmitted normally, and no selected mode of up / down talk is performed.

2. A Bragg grating-based mode add / drop voice channel device as claimed in claim 1, It is characterized in that The optical signal generating module is composed of a tunable laser (11), an electro-optic modulator (12) and a DAC (13); the output port of the tunable laser (11) is connected to a first input port (121) of the electro-optic modulator (12); the output port of the DAC (13) is connected to a second input port (122) of the electro-optic modulator (12); and finally, the modulated signal is output from an output port (123) of the electro-optic modulator (12), wherein the output laser wavelength is 1550.52 nm.

3. A Bragg grating-based mode add / drop voice channel device as claimed in claim 1, It is characterized in that The mode division multiplexing module is composed of a beam splitter (21) and a mode converter (22); wherein the output port (21) of the beam splitter is connected to the input port of the mode converter (22), and mode multiplexing is achieved through the mode converter, wherein the multiplexed modes include modes transmitted in LP01, LP11, and LP21 few-mode optical fibers.

4. A Bragg grating-based mode add / drop voice channel device as claimed in claim 1, It is characterized in that The mode demultiplexing module (4) adopts a mode converter (41); wherein the transmitted mode multiplexing signal is incident through the input port of the mode converter (41), mode demultiplexing is completed in the mode converter, and each mode is output respectively through the output port of the mode converter, thereby realizing mode demultiplexing.

5. A Bragg grating-based mode add / drop voice channel device as claimed in claim 1, It is characterized in that The optical signal processing module is composed of a photodetector (51), an oscilloscope (52), a DSP (53) and a tunable laser (54); wherein an optical signal with mode information is input through a first input port (511) of the photodetector (51); at the same time, due to the use of coherent detection, the tunable laser (54) outputs a beam of local oscillation light for signal reception, and the output light is input through a second input port (512) of the photodetector (51); signal mixing and coherent reception are completed in the photodetector, and the signal is converted into an electrical signal, which is output from an output port (513) of the photodetector and input from an input port of the oscilloscope (52); and the stored information is input into an input port of the DSP (53), thereby realizing off-line processing of the signal.

6. A Bragg grating-based mode add / drop voice channel device as claimed in claim 5, It is characterized in that The DSP processing module (53) includes orthogonalization (531), clock recovery (532), resampling (533), channel equalization (534), frequency offset compensation (535) and phase offset compensation (536); It is used to improve signal quality and compensate for noise and interference. Finally, after DSP processing, signal reception is completed.

Images