Free-space optical multi-dimensional multiplexing and multi-dimensional diversity communication system

Abstract

The application provides a free space optical multi-dimensional multiplexing and multi-dimensional diversity communication system, which comprises a modulation module for generating and outputting a plurality of modulated optical signals; and an optical phased array array on chip for regulating phases of the plurality of modulated optical signals to control beam characteristics of the plurality of optical signals emitted to the free space. The free space optical multi-dimensional multiplexing and multi-dimensional diversity communication system based on the optical phased array chip can significantly reduce the system volume, improve flexibility and precision, and realize efficient signal multiplexing, signal diversity and dynamic adjustment in multiple dimensions, thereby greatly improving communication rate, quality and system adaptability.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of optical communication, and particularly relates to a free space optical multi-dimensional multiplexing and multi-dimensional diversity communication system. BACKGROUND

[0002] Traditional wireless communication relies on electromagnetic waves propagating in air, and is limited by the limited bandwidth of radio spectrum resources, resulting in a low data rate. In addition, the terrain, weather and electromagnetic interference in complex environments further affect the communication quality. In contrast, free space optical communication (FSO) utilizes laser propagation in free space, has the advantages of higher frequency, larger bandwidth and anti-electromagnetic interference, and thus can provide higher data transmission rate, and is suitable for high-speed and high-capacity data transmission. Due to its low delay, high bandwidth, license-free spectrum and anti-interference characteristics, FSO technology has shown broad application prospects in satellite communication, ground communication, data center interconnection, military communication and emergency communication fields.

[0003] However, the traditional FSO system usually relies on large optical components, precision lenses and servo motors to realize the shaping and directional transmission of the light beam, which makes the system bulky, complex, expensive and requires strict maintenance. At the same time, in order to achieve higher transmission rate and more stable transmission quality, multi-dimensional multiplexing systems (phase multiplexing, amplitude multiplexing, code division multiplexing, time division multiplexing, wavelength division multiplexing, space division multiplexing, polarization multiplexing and mode division multiplexing systems) and multi-dimensional diversity systems (phase diversity, amplitude diversity, code division diversity, time diversity, frequency diversity, spatial diversity, polarization diversity and mode diversity) are widely used, which require multiple FSO systems to simultaneously transmit multiple wavelength, multiple polarization and multiple mode laser signals in multiple directions and multiple angles at the same transmitting site, which will further increase the volume, cost and complexity of the system.

[0004] Therefore, in scenarios such as satellite communication and unmanned aerial vehicle communication that have strict requirements on space, power consumption and integration, the traditional FSO system is often difficult to implement or has limited performance. With the development of miniaturization and integration technology, on-chip integration technology provides new possibilities for future miniaturized and integrated multi-dimensional multiplexing and multi-dimensional diversity FSO systems. However, integrating large optical components and servo motors in traditional FSO onto a chip faces many technical challenges. For example, the miniaturized integration of optical elements (such as lenses, mirrors and fiber couplers) has high precision requirements, and it is difficult to maintain good optical performance in a small size; and precision driving systems such as servo motors are difficult to integrate in chip-level integration. SUMMARY

[0005] In order to solve the above technical problems existing in the prior art, the application provides a free space optical multi-dimensional multiplexing and multi-dimensional diversity communication system based on an optical phased array (OPA) chip.

[0006] According to an aspect of the application, a free space optical multi-dimensional multiplexing and multi-dimensional diversity communication system is provided, comprising: a modulation module configured to generate and output n modulated optical signals; and an on-chip optical phased array array configured to receive the n modulated optical signals and adjust the phase of each modulated optical signal so that the beam characteristics of each modulated optical signal are changed.

[0007] In one example of the free space optical multi-dimensional multiplexing and multi-dimensional diversity communication system provided in the above aspect, the on-chip optical phased array array is further configured to adjust the initial phase of each modulated optical signal to achieve beam shaping, directional transmission, high-order mode generation and multiplexing of each modulated optical signal.

[0008] In one example of the free space optical multi-dimensional multiplexing and multi-dimensional diversity communication system provided in the above aspect, the on-chip optical phased array array comprises a first optical coupler, n on-chip thermal phase shifters, and a grating array; the first optical coupler is configured to receive the n modulated optical signals and transmit each modulated optical signal to a corresponding on-chip thermal phase shifter; the i-th on-chip thermal phase shifter is configured to receive the i-th modulated optical signal and change the phase of the i-th modulated optical signal so that the beam characteristics of the i-th modulated optical signal are changed, where 1≤i≤n; and the grating array is configured to emit each modulated optical signal with changed beam characteristics into free space.

[0009] In one example of the free space optical multi-dimensional multiplexing and multi-dimensional diversity communication system provided in the above aspect, the n on-chip thermal phase shifters are further configured to change the direction angle of each modulated optical signal in the horizontal direction when a voltage is applied thereto.

[0010] In one example of the free space optical multi-dimensional multiplexing and multi-dimensional diversity communication system provided in the above aspect, the modulation module comprises n lasers, n Mach-Zehnder modulators, and an optical coupler; the i-th Mach-Zehnder modulator is connected to the corresponding i-th laser, where 1≤i≤n; and the n Mach-Zehnder modulators are all connected to the optical coupler; the n lasers are configured to generate n optical carriers with different wavelengths; and the i-th Mach-Zehnder modulator is configured to receive a communication data signal and the i-th optical carrier, and modulate the received communication data signal onto the i-th optical carrier to form the i-th modulated optical signal.

[0011] In an example of the free-space optical multi-dimensional multiplexing and multi-dimensional diversity communication system provided in the above aspect, the modulation module further comprises n first optical amplifiers, and an i-th first optical amplifier is connected between a corresponding i-th laser and an i-th Mach-Zehnder modulator.

[0012] In an example of the free-space optical multi-dimensional multiplexing and multi-dimensional diversity communication system provided in the above aspect, the direction angle of each modulated optical signal in the vertical direction is changed by changing the frequency of each optical carrier.

[0013] In an example of the free-space optical multi-dimensional multiplexing and multi-dimensional diversity communication system provided in the above aspect, the free-space optical multi-dimensional multiplexing and multi-dimensional diversity communication system further comprises a receiving module configured to receive the modulated optical signals with the changed beam characteristics.

[0014] In an example of the free-space optical multi-dimensional multiplexing and multi-dimensional diversity communication system provided in the above aspect, the receiving module comprises n optical antennas, n demultiplexers, n receivers, and n oscilloscopes, an i-th optical antenna is configured to receive the modulated optical signals with the changed beam characteristics, an i-th demultiplexer is configured to convert the high-order mode modulated optical signals received by the i-th optical antenna into low-order mode modulated optical signals, an i-th receiver is configured to demodulate the i-th modulated optical signals, and an i-th oscilloscope is configured to sample the demodulated i-th modulated optical signals.

[0015] In an example of the free-space optical multi-dimensional multiplexing and multi-dimensional diversity communication system provided in the above aspect, the receiving module further comprises n second optical amplifiers, and an i-th second optical amplifier is arranged between an i-th demultiplexer and an i-th receiver.

[0016] Beneficial effects: The application provides a free-space optical multi-dimensional multiplexing and multi-dimensional diversity communication system based on an optical phased array (OPA) chip. Unlike the traditional mechanical scanning method, the optical phased array chip does not require any moving parts. The OPA chip is only composed of an on-chip optical phase shifter array and a grating array. By adjusting the on-chip optical phase shifter array, the phase distribution of the multi-wavelength light beams at the grating array can be quickly and accurately adjusted, and then the direction, wavefront and propagation characteristics of these light beams can be controlled, finally the laser signal beam shaping, emission and transmission in multiple directions, multiple angles, multiple wavelengths, multiple polarizations and multiple modes are realized. The beam forming and wavefront compensation capabilities of the OPA chip also improve the adaptability of the system to atmospheric disturbances and the signal transmission quality.

[0017] In addition, by combining the optical phased array with the free-space optical multi-dimensional multiplexing technology, the system can simultaneously emit multi-wavelength, multi-polarization and multi-mode light beams in multiple directions and angles by using the precise control of the light beam capability of the optical phased array chip and the high transmission capacity capability of the multi-dimensional multiplexing technology, and the transmission capacity of the system is significantly improved through the multiplexing technology; by combining the optical phased array with the free-space optical multi-dimensional diversity technology, the system can simultaneously emit multi-wavelength, multi-polarization and multi-mode light beams in multiple directions and angles by using the precise control of the light beam capability of the optical phased array chip and the redundancy of the diversity technology, and the reliability of the communication system is significantly improved through the redundancy of the signal.

[0018] Further, the proposed system not only meets the requirements of satellite communication, unmanned aerial vehicle communication and other scenarios with high requirements for space and power consumption, but also effectively deals with channel fading and dynamic environmental interference, and enhances the transmission rate, robustness and anti-interference ability of the system in multi-path and multi-wavelength signal transmission.

[0019] Therefore, the free-space optical multi-dimensional multiplexing and multi-dimensional diversity communication system based on the optical phased array chip significantly reduces the system volume, improves flexibility and precision, and realizes efficient signal multiplexing, signal diversity and dynamic adjustment in multiple dimensions, greatly improving the communication rate, quality and system adaptability. BRIEF DESCRIPTION OF DRAWINGS

[0020] The above and other aspects, features and advantages of embodiments of the present application will become more apparent from the following description taken in conjunction with the accompanying drawings, in which:

[0021] Figure 1 is a schematic structural diagram of a free-space optical multi-dimensional multiplexing and multi-dimensional diversity communication system according to an embodiment of the present application;

[0022] Figure 2 is a test result diagram of an optical signal with a specified optical mode, emission angle, polarization state, wavelength, baud rate and phase amplitude multiplexing modulation format by a free-space optical multi-dimensional multiplexing and multi-dimensional diversity communication system according to an embodiment of the present application. DETAILED DESCRIPTION

[0023] Hereinafter, specific embodiments of the present application will be described in detail with reference to the accompanying drawings. However, the present application can be implemented in many different forms, and should not be construed as being limited to the specific embodiments set forth herein. Rather, these embodiments are provided so that the principles of the present application can be understood and various modifications for a specific intended application can be derived from other skilled persons in the art by the principles of the present application.

[0024] As used herein, the terms "includes," "including," "has," "having," "contains," "containing," "comprises," "comprising," "may" and "including," are open-ended terms that are intended to mean "including but not limited to." The terms "based on" and "according to" are intended to mean "based, at least in part, on" or "according, at least in part, to." The terms "one embodiment" and "an embodiment" are intended to mean "at least one embodiment." The term "another embodiment" is intended to mean "at least one other embodiment." The terms "first," "second," "third," etc. are intended to mean different or similar objects. Other definitions can be included in the following description, either explicitly or implicitly. Unless the context clearly indicates otherwise, the definition of a term is consistent throughout the description.

[0025] Figure 1 is a schematic diagram of a principle structure of a free space optical multi-dimensional multiplexing and multi-dimensional diversity communication system according to an embodiment of the present application.

[0026] Referring to Figure 1 The free space optical multi-dimensional multiplexing and multi-dimensional diversity communication system according to an embodiment of the present application comprises: a modulation module 5 for generating and outputting n modulated optical signals; and an on-chip optical phased array 9 for receiving the n modulated optical signals and adjusting phases of the n modulated optical signals so that beam characteristics of the n modulated optical signals are changed.

[0027] In another embodiment, the free space optical multi-dimensional multiplexing and multi-dimensional diversity communication system according to an embodiment of the present application further comprises: a receiving module RM for receiving the n modulated optical signals whose beam characteristics are changed.

[0028] In particular, the modulation module 5 comprises: lasers 11... 1n, Mach-Zehnder modulators 21... 2n, optical amplifiers 31... 3n, and an optical coupler 4.

[0029] The lasers 11... 1n respectively generate and output n optical carriers with different wavelengths.

[0030] The i-th Mach-Zehnder modulator 2i is configured to receive a communication data signal (which is externally provided, e.g., a microwave signal) and the i-th optical carrier output by the i-th laser 1i, and modulate the received communication data signal onto the i-th optical carrier to form an i-th modulated optical signal, where 1≤i≤n. Each Mach-Zehnder modulator operates at a minimum bias point (i.e., a null point).

[0031] The i-th optical amplifier 3i is configured to receive the i-th modulated optical signal and amplify the i-th modulated optical signal. Of course, if the signal strength of the i-th modulated optical signal is strong enough, in another embodiment, the optical amplifiers can be absent.

[0032] The optical coupler 4 is used to couple the modulated light signals amplified by the optical amplifier 31... optical amplifier 3n to an optical waveguide (for example, another optical coupler).

[0033] In addition, the on-chip optical phased array array 9 includes the optical coupler 6, the on-chip thermal phase shifter 71... on-chip thermal phase shifter 7n, and the grating array 8.

[0034] The optical coupler 6 is used to evenly send the energy of the modulated light signal from the modulation module 5 to each on-chip thermal phase shifter, and all frequencies of the modulated light signal will reach each on-chip thermal phase shifter.

[0035] The i-th on-chip thermal phase shifter 7i is used to receive the i-th modulated light signal and change the phase of the i-th modulated light signal so that the beam characteristics of the i-th modulated light signal are changed. Here, the on-chip thermal phase shifter 71... on-chip thermal phase shifter 7n constitute an on-chip optical phase shifter array, which is used to realize the phase compensation and flexible adjustment of the initial phase of the modulated light signal when it is emitted at the grating array 8. In specific embodiments, the on-chip thermal phase shifter is implemented by using a silicon waveguide and a heating sheet, but the present application is not limited thereto.

[0036] The grating array 8 is used to emit the modulated light signals with changed beam characteristics into free space. In specific embodiments, a grating array with a grating spacing of 2um is used.

[0037] That is, in the on-chip optical phased array array 9, by regulating the on-chip optical phase shifter array, the phase distribution of the multi-wavelength modulated light signal at the grating array 8 can be quickly and accurately adjusted, and the direction, wavefront and propagation characteristics of the modulated light signal can be regulated, realizing the beam shaping, emission and transmission of multi-direction, multi-angle, multi-wavelength, multi-polarization and multi-mode laser modulated light signal. The on-chip optical phased array array 9 has the ability of beam shaping and wavefront compensation, thereby improving the adaptability of the system to atmospheric disturbance and the quality of signal transmission.

[0038] Continuing to refer to Figure 1 , the emitted beams at the grating array 8 (i.e., the modulated light signals with changed beam characteristics) 101... 10n. Due to the interference behavior of the wavefront, these beams have some characteristics, for example, by changing the voltage on the on-chip thermal phase shifter, the beam phase distribution when emitted can be changed, further realizing beam shaping, high-order mode light generation and direction angle adjustment in the horizontal direction of the beam; by changing the frequency of the optical carrier, the direction angle in the vertical direction of the beam can be quickly changed, thereby realizing rapid turning in the vertical direction, etc.

[0039] In some examples, the initial phase of each modulated light signal at the grating array 8 is adjusted by the on-chip optical phase shifter array to be The wavefront interference and focusing shaping of the light beam are realized. By changing the voltage applied to the on-chip light phase shifter array, the direction angle of the light beam after focusing shaping can be quickly changed in the horizontal direction to realize the quick turning in the horizontal direction. By changing the frequency of the light carrier through the modulation module 5 (for example, a laser), the direction angle of the light beam in the vertical direction is quickly changed to realize the quick turning in the vertical direction. The multi-direction, multi-angle and multi-wavelength quick response functions provide technical support for wavelength division multiplexing and space division multiplexing.

[0040] Further, by polarization multiplexing, the transmission capacity can be further doubled. By loading specific phase distribution through the on-chip light phase shifter array, high-order mode light beams can be generated, such as first-order or higher-order modes of Laguerre Gaussian beams in orbital angular momentum light beams. The multiplexing of these high-order mode light beams can further improve the transmission capacity. The multi-polarization and multi-mode light beam quick response functions provide technical support for polarization multiplexing and mode division multiplexing.

[0041] Further, when the modulation module 5 modulates the light signal, time division multiplexing is realized by flexibly allocating transmission time periods occupied by different communication data. At the same time, different coherent modulation modes can be selected, such as 16QAM, 64QAM, 256QAM, 1024QAM, etc., to realize phase and amplitude multiplexing of the light signal (if the phase and amplitude multiplexing technology is selectively allocated, code division multiplexing can also be realized).

[0042] At the same time, if the signals modulated in the multiple multiplexing channels are the same copy signal, a free space optical multi-dimensional diversity system can also be realized. By using the redundancy of diversity technology, the reliability of the communication system can be significantly improved.

[0043] In summary, the free space optical multi-dimensional multiplexing and multi-dimensional diversity communication system based on the optical phased array chip is described, which realizes phase multiplexing, amplitude multiplexing, code division multiplexing, time division multiplexing, wavelength division multiplexing, space division multiplexing, polarization multiplexing and mode division multiplexing, as well as the corresponding diversity technology.

[0044] Continuing to refer to Figure 1 , the receiving module RM includes optical antennas 111…11n, demultiplexers 121…12n, optical amplifiers 131…13n, receivers 141…14n, and oscilloscopes 151…15n.

[0045] The i-th optical antenna 11i is used to receive the i-th light beam characteristic changed modulated light signal. In one example, the optical antenna can be composed of an aspherical optical lens, which can effectively receive the light signal.

[0046] The i-th demultiplexer 12i is configured to convert the i-th modulated light signal of high order mode received by the i-th optical antenna into the i-th modulated light signal of low order mode. In one example, the demultiplexer is composed of a spatial light modulator or other similar functional devices, which can convert the high order mode light signal into the low order mode light signal.

[0047] The i-th optical amplifier 13i is configured to receive the i-th modulated light signal and amplify the i-th modulated light signal. Of course, if the signal intensity of the i-th modulated light signal is strong enough, in another embodiment, the optical amplifier does not exist.

[0048] The i-th receiver 14i is configured to demodulate the i-th modulated light signal.

[0049] The i-th oscilloscope 15i is configured to sample the demodulated i-th modulated light signal for subsequent digital signal processing.

[0050] In a specific embodiment, 8-wavelength light signals are obtained by coherent modulation, and the light signals realize the wavefront shaping, high-order mode beam generation and emission of the light signals on the optical phased array chip. Meanwhile, by changing the configuration voltage of the optical phased array chip, the fast steering scanning of the light signals in the horizontal direction can be realized, by changing the frequency values of the 8 wavelengths, the fast steering scanning of the light signals in the vertical direction can be realized, and the wavelength division multiplexing, mode division multiplexing and space division multiplexing are realized; by using different modulation modes, such as multi-order phase modulation (8-PSK, etc.), multi-order amplitude modulation (8-ASK, etc.), coherent modulation (16QAM, etc.), the phase multiplexing, amplitude multiplexing and code division multiplexing of the light signals are realized; by modulating different signals in different time periods, the time division multiplexing of the light signals is realized; by configuring multiple polarization state light signals in the optical phased array chip, the polarization multiplexing of the light signals is realized; by loading the same copy information in each multiplexing technology, the same multi-dimensional diversity technology can be realized.

[0051] In the experiment, the above-mentioned optical signal transmission is transmitted through a 20m free space link, and is received by the optical antenna and received at the receiver without error demodulation. The experimental test results of the optical signal with the specified optical mode, emission angle, polarization state, wavelength (1550nm), baud rate (20Gbaud) and phase amplitude multiplexing modulation format (coherent modulation format: 16QAM) are shown in Figure 2 Referring to Figure 2 , the measured EVM is 10.5%, and the error-free communication result verifies the effectiveness of the proposed system.

[0052] In summary, the potential and ability of the system in phase multiplexing, amplitude multiplexing, code division multiplexing, time division multiplexing, wavelength division multiplexing, spatial division multiplexing, polarization multiplexing and mode division multiplexing, and the corresponding diversity are illustrated and verified. Further, the basic principles and architecture of the free-space optical multi-dimensional multiplexing and multi-dimensional diversity communication system based on the optical phased array chip are fully illustrated and verified. By combining the optical phased array with the free-space optical multi-dimensional multiplexing technology, the system can simultaneously emit multi-wavelength, multi-polarization and multi-mode light beams in multiple directions and angles by using the precise control of the light beam capability of the optical phased array chip and the high transmission capacity capability of the multi-dimensional multiplexing technology, and the transmission capacity of the system is significantly improved through the multiplexing technology. By combining the optical phased array with the free-space optical multi-dimensional diversity technology, the system can simultaneously emit multi-wavelength, multi-polarization and multi-mode light beams in multiple directions and angles by using the precise control of the light beam capability of the optical phased array chip and the redundancy of the diversity technology, and the reliability of the communication system is significantly improved through the redundancy of the signal.

[0053] In addition, the proposed system not only meets the requirements of satellite communication, unmanned aerial vehicle communication and other scenarios with high requirements for space and power consumption, but also effectively deals with channel fading and dynamic environmental interference, enhances the transmission rate, robustness and anti-interference ability of the system in multi-path and multi-wavelength signal transmission. Further, the free-space optical multi-dimensional multiplexing and multi-dimensional diversity communication system based on the optical phased array chip significantly reduces the system volume, improves flexibility and precision, and realizes efficient signal multiplexing, signal diversity and dynamic adjustment in multiple dimensions (the eight dimensions proposed in the architecture are only examples), greatly improving the communication rate, quality and system adaptability. Further, the system is expected to play an important role in future high-bandwidth, low-latency communication applications, such as satellite communication, unmanned aerial vehicle communication and 5G and 6G networks.

[0054] The above describes the optional implementation of the embodiments of the present application in detail in combination with the drawings, but the embodiments of the present application are not limited to the specific details in the above implementation, and various simple modifications can be made to the technical solutions of the embodiments of the present application within the technical concept range of the embodiments of the present application, which all belong to the protection scope of the embodiments of the present application.

Claims

1. A free-space optical multi-dimensional multiplexing and multi-dimensional diversity communication system, characterized by, The free-space optical multi-dimensional multiplexing and multi-dimensional diversity communication system comprises: a modulation module configured to generate and output n modulated optical signals; an on-chip optical phased array configured to receive the n modulated optical signals and adjust phases of the n modulated optical signals so that beam characteristics of the n modulated optical signals transmitted to the free space are changed; the on-chip optical phased array comprises a first optical coupler, n on-chip thermal phase shifters, and a grating array; the first optical coupler is configured to receive the n modulated optical signals and transmit the n modulated optical signals to the n on-chip thermal phase shifters respectively; the i-th on-chip thermal phase shifter is configured to receive the i-th modulated optical signal and change a phase of the i-th modulated optical signal so that a beam characteristic of the i-th modulated optical signal is changed, 1≤i≤n; the grating array is configured to transmit the n modulated optical signals with changed beam characteristics to the free space; the modulation module comprises n lasers, n Mach-Zehnder modulators, and an optical coupler, the i-th Mach-Zehnder modulator is connected to the corresponding i-th laser, 1≤i≤n, and the n Mach-Zehnder modulators are connected to the optical coupler; the n lasers are configured to generate n optical carriers with different wavelengths; the i-th Mach-Zehnder modulator is configured to receive a communication data signal and the i-th optical carrier and modulate the received communication data signal onto the i-th optical carrier to form the i-th modulated optical signal; by changing frequencies of the n optical carriers, the n modulated optical signals change direction angles in a vertical direction; the free-space optical multi-dimensional multiplexing and multi-dimensional diversity communication system further comprises a receiving module configured to receive the n modulated optical signals with changed beam characteristics; the receiving module comprises n optical antennas, n demultiplexers, n receivers, and n oscilloscopes; the i-th optical antenna is configured to receive the i-th modulated optical signal with a changed beam characteristic, the i-th demultiplexer is configured to convert the i-th modulated optical signal with a high-order mode received by the i-th optical antenna into the i-th modulated optical signal with a low-order mode, the i-th receiver is configured to demodulate the i-th modulated optical signal, and the i-th oscilloscope is configured to sample the demodulated i-th modulated optical signal for subsequent digital signal processing.

2. The free-space optical multi-dimensional multiplexing and multi-dimensional diversity communication system of claim 1, wherein, the on-chip optical phased array is further configured to adjust initial phases of the n modulated optical signals to realize beam shaping, directional transmission, high-order mode generation, and multiplexing of the n modulated optical signals.

3. The free-space optical multi-dimensional multiplexing and multi-dimensional diversity communication system according to claim 1 or 2, characterized by the n on-chip thermal phase shifters are further configured to change direction angles of the n modulated optical signals in a horizontal direction when voltages are applied thereto.

4. The free-space optical multi-dimensional multiplexing and multi-dimensional diversity communication system according to claim 1 or 2, wherein, the modulation module further comprises n first optical amplifiers, and the i-th first optical amplifier is connected between the corresponding i-th laser and the i-th Mach-Zehnder modulator.

5. The free-space optical multi-dimensional multiplexing and multi-dimensional diversity communication system according to claim 1 or 2, wherein, the receiving module further comprises n second optical amplifiers, and the i-th second optical amplifier is arranged between the i-th demultiplexer and the i-th receiver.

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