A system and method of self-coherent transmission

Abstract

The application provides a self-coherent transmission system and method, which comprises a main laser for generating an optical signal to be transmitted; a first coupler for dividing the optical signal to be transmitted into a first energy optical signal and a second energy optical signal according to a first preset energy ratio; a dual-biased signal modulator for performing dual-biased modulation on the first energy optical signal to generate a third energy optical signal; a polarization rotation module for performing polarization rotation on the second energy optical signal to obtain a downlink local oscillator light; an optical injection locking module for performing injection locking processing on the downlink local oscillator light to generate a fourth energy optical signal; and an integrated coherent receiver for performing coherent demodulation on the third energy optical signal and the fourth energy optical signal to recover the optical signal to be transmitted. According to the system provided by the application, controllable amplification of the local oscillator light power can be ensured, carrier polarization fading can be avoided, and transmission performance can be improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of optical transmission, and more particularly, to a system and method for self-homodyne transmission BACKGROUND

[0002] In self-homodyne coherent (SHC) transmission, the optical signal to be transmitted is split into two paths, one path of light is used for signal modulation, and the other path of light is transmitted to the receiving end through the fiber link as the local oscillator (LO) light for coherent detection, and is received together at the receiving end, and then coherent demodulation is performed. Compared with the current standard coherent transmission, because the same laser source is used, there is no frequency difference between the signal light and the local oscillator light LO after transmission, so it is not necessary to set a high-performance laser at the receiving end, instead a non-cooled distributed feedback laser (DFB) with a larger linewidth can be used, thereby greatly reducing the cost. And the self-homodyne coherent transmission has small phase noise, which can simplify the carrier phase recovery (CPR) algorithm, so it has become a research hotspot in the industry.

[0003] However, in the current self-homodyne coherent transmission, the local oscillator light LO also needs to pass through the link, which may cause random rotation of the polarization state of the local oscillator light LO and power drop. The random rotation of the polarization state may cause carrier polarization fading phenomenon, and the power drop may cause insufficient power budget of the link.

[0004] Therefore, there is an urgent need for a self-homodyne coherent transmission method that can ensure stable amplification of the power of the local oscillator light LO, while avoiding the occurrence of carrier polarization fading phenomenon and improving transmission performance. SUMMARY

[0005] The present application provides a system and method for self-homodyne transmission, which can ensure controllable amplification of the power of the local oscillator light, while helping to avoid carrier polarization fading and improve transmission performance.

[0006] In a first aspect, a self-coherent transmission system is provided, comprising: a master laser for generating an optical signal to be transmitted; a first coupler for splitting the optical signal to be transmitted into a first energy optical signal and a second energy optical signal according to a first preset energy ratio; a dual-biased signal modulator for performing dual-biased modulation on the first energy optical signal to generate a third energy optical signal; a polarization rotation module for performing polarization rotation on the second energy optical signal to obtain a downstream local oscillator (LO); an optical injection locking (OIL) module for performing injection locking processing on the downstream LO to generate a fourth energy optical signal, the frequency of the fourth energy optical signal being the same as that of the downstream LO, and the power of the fourth energy optical signal being greater than that of the downstream LO; and an integrated coherent receiver (ICR) for performing coherent demodulation on the third energy optical signal and the fourth energy optical signal to recover the optical signal to be transmitted.

[0007] According to the system provided in the present application, the polarization rotation module performs polarization rotation processing on the optical signal to be transmitted, and the optical injection locking module performs injection locking processing, so as to ensure controllable amplification of the LO power, avoid carrier polarization fading, and improve transmission performance.

[0008] In combination with the first aspect, in some implementations of the first aspect, the polarization rotation module comprises: a first polarization beam splitter (PBS) for processing the second energy optical signal according to a second preset energy ratio to generate a fifth energy optical signal and a sixth energy optical signal, the fifth energy optical signal and the sixth energy optical signal being orthogonal to each other; a first phase modulator (PM) for performing phase modulation on the sixth energy optical signal according to a first random phase and a first modulation period to generate a seventh energy optical signal; and a first polarization combiner (PBC) for combining the fifth energy optical signal and the seventh energy optical signal to generate the downstream LO.

[0009] According to the polarization rotation module provided in the present application, the polarization rotation module performs polarization rotation processing on the optical signal to be transmitted, so as to improve the problem of random rotation of the polarization state of the downstream LO at the receiving end, avoid carrier polarization fading, and improve transmission performance.

[0010] In combination with the first aspect, in some implementations of the first aspect, the first random phase is in a range of 0 to 2π.

[0011] In combination with the first aspect, in some implementations of the first aspect, the first random phase adopts a uniform distribution sequence, a Gaussian distribution sequence, or other random distribution manners.

[0012] In combination with the first aspect, in some implementations of the first aspect, the first modulation period is in a first threshold range, and the first threshold is greater than or equal to 1 kHz and less than or equal to 1000 kHz.

[0013] With reference to the first aspect, in some implementations of the first aspect, the optical injection locking OIL module includes: a second polarization beam splitter PBS configured to polarize the downstream local oscillator light LO to generate an eighth energy optical signal; a slave laser configured to injection-lock the eighth energy optical signal to generate a fourth energy optical signal; and a circulator configured to input the eighth energy optical signal to the slave laser and input the fourth energy optical signal to the integrated coherent receiver ICR.

[0014] According to the optical injection locking OIL module provided in the present application, the downstream local oscillator light LO is injection-locked, which can ensure controllable amplification of the local oscillator light power and help solve the problem of insufficient downstream local oscillator light LO power in a self-coherent transmission system.

[0015] With reference to the first aspect, in some implementations of the first aspect, the system further includes: a multi-core optical fiber including a first core and a second core, the first core being configured to transmit the third energy optical signal, and the second core being configured to transmit the downstream local oscillator light LO, the first core being different from the second core.

[0016] The second aspect provides a self-coherent transmission method, including: dividing a to-be-transmitted optical signal into a first energy optical signal and a second energy optical signal according to a first preset energy ratio; performing double polarization modulation on the first energy optical signal to generate a third energy optical signal; performing polarization rotation on the second energy optical signal to generate a downstream local oscillator light LO; performing injection locking on the downstream local oscillator light LO to generate a fourth energy optical signal, the frequency of the fourth energy optical signal being the same as that of the downstream local oscillator light LO, and the power of the fourth energy optical signal being greater than that of the downstream local oscillator light LO; and performing coherent demodulation on the third energy optical signal and the fourth energy optical signal to recover the to-be-transmitted optical signal.

[0017] According to the technical solution provided in the present application, the to-be-transmitted optical signal is subjected to polarization rotation and injection locking, which can ensure controllable amplification of the local oscillator light power and help avoid carrier polarization fading and improve transmission performance.

[0018] With reference to the second aspect, in some implementations of the second aspect, the polarization rotation on the second energy optical signal to obtain the downstream local oscillator light LO includes: processing the second energy optical signal according to a second preset energy ratio to generate a fifth energy optical signal and a sixth energy optical signal, the fifth energy optical signal and the sixth energy optical signal being orthogonal to each other; performing phase modulation on the sixth energy optical signal according to a first random phase and a first modulation period to generate a seventh energy optical signal; and combining the fifth energy optical signal and the seventh energy optical signal to generate the downstream local oscillator light LO.

[0019] According to the technical solution provided in the application, the polarization rotation processing is performed on the to-be-sent optical signal, which helps to improve the problem of random rotation of the polarization state of the downlink local oscillator (LO) at the receiving end, thereby helping to avoid carrier polarization fading and improving transmission performance.

[0020] With reference to the second aspect, in some implementations of the second aspect, the first random phase is in a range of 0 to 2π.

[0021] With reference to the second aspect, in some implementations of the second aspect, the first random phase is in a uniform distribution sequence, a Gaussian distribution sequence, or other random distribution manners.

[0022] With reference to the second aspect, in some implementations of the second aspect, the first modulation period is in a first threshold range, and the first threshold is greater than or equal to 1 kHz and less than or equal to 1000 kHz.

[0023] With reference to the second aspect, in some implementations of the second aspect, the injection locking processing on the downlink local oscillator (LO) to generate the fourth energy optical signal includes: performing a polarization processing on the downlink local oscillator (LO) to generate an eighth energy optical signal; and performing an injection locking processing on the eighth energy optical signal to generate the fourth energy optical signal.

[0024] According to the technical solution provided in the application, the injection locking processing is performed on the downlink local oscillator (LO), which can ensure controllable amplification of the local oscillator (LO) power and help to solve the problem of insufficient downlink local oscillator (LO) power in a self-coherent transmission system.

[0025] With reference to the second aspect, in some implementations of the second aspect, the method further includes: transmitting the third energy optical signal in a first core of a multi-core optical fiber and transmitting the downlink local oscillator (LO) in a second core of the multi-core optical fiber, the first core being different from the second core. BRIEF DESCRIPTION OF DRAWINGS

[0026] Figure 1 FIG. 1 is a schematic diagram of a self-coherent transmission system 100.

[0027] Figure 2 FIG. 2 is a schematic diagram of an existing self-coherent transmission system 200.

[0028] Figure 3 FIG. 3 is a schematic diagram of a self-coherent transmission system 300 provided in the application.

[0029] Figure 4 FIG. 4 is a schematic diagram of a polarization rotation module provided in the application.

[0030] Figure 5 FIG. 5 is a schematic diagram of an optical injection locking module provided in the application.

[0031] Figure 6This application presents an example of an output diagram of a laser and an example of a constellation diagram recovered from an integrated coherent receiver.

[0032] Figure 7 This is an example of a schematic flowchart of the self-coherent transmission method provided in this application.

[0033] Figure 8 This is a schematic structural diagram of an example of the control device provided in this application. Detailed Implementation

[0034] The technical solutions in this application will now be described with reference to the accompanying drawings.

[0035] Figure 1 A schematic diagram of a self-coherent transmission system 100 is shown. For example... Figure 1 As shown, the self-coherent transmission system 100 includes: a laser 110, a coupler 120, a dual-polarization modulator 130, a link 140, a link 150, and an integrated coherent receiver (ICR) 160. The laser 110 generates the optical signal to be transmitted. The coupler 120 splits the optical signal into two paths: one path is input to the dual-polarization modulator 130, where it undergoes dual-polarization modulation to obtain a modulated signal, which is then input to the integrated coherent receiver 160 via the link 140; the other path is transmitted to the integrated coherent receiver 160 via the link 150. The integrated coherent receiver 160 coherently demodulates the dual-polarization signal and the downlink local oscillator (LO) to recover the optical signal to be transmitted.

[0036] Self-coherent transmission is short for self-zero difference coherent transmission. In this application, for the sake of convenience, self-zero difference coherent transmission is referred to as self-coherent transmission.

[0037] In the aforementioned self-coherent transmission system 100, since the modulation signal and the local oscillator (LO) utilize the same laser 110, the frequency difference between the modulation signal and the LO after transmission is minimal. Therefore, compared to current standard coherent transmission, the self-coherent transmission system 100 does not require a high-performance laser at the receiver; instead, a larger-linewidth uncooled distributed feedback laser (DFB) can be used, significantly reducing costs. Furthermore, the self-coherent transmission system 100 has low phase noise, simplifying the carrier phase recovery (CPR) algorithm, thus becoming a hot research topic in the industry.

[0038] However, in the self-coherent transmission system 100, the local oscillator (LO) also passes through the link (e.g., link 150), which may cause random rotation of the polarization state of the local oscillator (LO) and power reduction. Random rotation of the polarization state will lead to carrier polarization fading, and power reduction will lead to insufficient link power budget.

[0039] In the face of the above problems, the prior art generally uses the following processing methods:

[0040] (1) Set a slave laser at the receiving end, and use a slow phase-locked loop to realize optical injection locking (OIL) of the slave laser. In actual systems, the frequencies of the transmitting laser and the local oscillator LO will drift due to the drift of their driving electronics (e.g., temperature and current controllers). After processing by the slow phase-locked loop, the optical signal (or carrier) within the injection locking range will be attached with a phase, which depends on the position of the optical signal (or carrier) within the locking range. Therefore, the frequency difference between the optical signal (or carrier) and the slave laser can be calculated by measuring the phase difference between them. For example, a carrier pilot is inserted into the guard band of the carrier of a modulated orthogonal frequency division multiplexing (OFDM) signal. Since the pilot, carrier and OFDM signal are all generated together in the digital domain, just before the digital-to-analog converter, no additional components are needed, and the OIL locking range is set to be narrower than the frequency of the pilot, so that the pilot sideband is outside the locking range, and thus they will not experience a phase shift. Therefore, this phase difference information can be extracted by measuring the phase of the beat signal between the injection-locked carrier and the pilot sideband, and all this information can be conveniently obtained at the output end of the slave laser. Further, the phase shift information can be used as a phase-locked loop error signal to achieve negative feedback regulation, thereby achieving stable OIL.

[0041] Therefore, this technology can use the injection locking principle to amplify the carrier recovery in the self-coherent transmission scheme after filtering out the carrier at the receiving end using a filter. However, this technology cannot solve the carrier polarization fading phenomenon caused by the random change of the polarization state in the optical fiber link.

[0042] (2) Use an adaptive polarization controller (APC) to complete bidirectional locking of the polarization state, thereby realizing bidirectional self-coherent detection independent of the link. For example, Figure 2As shown, a simplified self-coherent transceiver structure without multi-input multi-output (MIMO) is used at both ends of the link. For each transceiver, the signal carrying information and a copy of the continuous wave carrier from the same laser are transmitted through a pair of full duplex fibers. For example, laser 1 is split into two branches by polarization maintaining coupler 1. One branch is modulated with the signal and transmitted in fiber 2 (double solid line), while the other branch is transmitted in fiber 1 (double dashed line) as the remote local oscillator light LO. Since the local oscillator light LO has the same center wavelength and reference phase as the transmitted signal, there is no need for DSP to compensate for frequency offset and carrier phase noise in short haul transmission, which relaxes the requirement for laser wavelength stability and allows the use of large linewidth lasers without cooling devices. Optical circulators C1 (C3) and C4 (C2) direct the modulated signal from transceiver 1 (transceiver 2) and the LO from transceiver 2 (transceiver 1) to be transmitted in the double solid line (double dashed line) fiber, respectively. In order to achieve self-homodyne coherent reception, optical circulators C4 (C2) and C3 (C1) are used to extract the modulated signal from transceiver 1 (transceiver 2) and the remote LO into the ICR of transceiver 2 (transceiver 1).

[0043] Wherein, the APC used is realized by an integrated optical Soleil-Babinet compensator in a lithium niobate waveguide and driven using a specific polarization tracking circuit (or algorithm). It should be noted that the SOP of the local oscillator light LO emitted from the transceiver is X linear SOP. APC1 (APC2) can track the SOP of LO2 (LO1) propagating in fiber 2 (fiber 1) and lock it in the X polarization state, which means that the Jones matrix product of APC1 (APC2) and fiber 2 (fiber 1) is a unit matrix. That is, APC1 (APC2) pre-compensates the effect of fiber 2 (fiber 1) on the signal SOP.

[0044] However, in this technology, the APC will bring a large insertion loss, which will cause the attenuation of the local oscillator light LO to be aggravated, and this technology also cannot solve the carrier polarization fading phenomenon caused by the random change of the polarization state in the fiber link.

[0045] Based on the above reasons, the present application provides a self-coherent transmission system and method, which can ensure controllable amplification of the local oscillator light power, while helping to avoid carrier polarization fading and improve transmission performance.

[0046] Figure 3 A schematic diagram of an example of a self-coherent transmission system 300 provided by the present application is shown. As shown in FIG. 1, the system 300 includes a transmitter 310 and a receiver 320. The transmitter 310 includes a laser 311, a polarization maintaining coupler 312, a modulator 313, a polarization controller 314, a first fiber 315, a second fiber 316, a first optical circulator 317, a second optical circulator 318, and an APC 319. The receiver 320 includes a third fiber 321, a fourth fiber 322, a third optical circulator 323, a fourth optical circulator 324, a polarization controller 325, a demodulator 326, and an ICR 327. Figure 3As shown, the self-coherent transmission system 300 includes a main laser 310, a first coupler 320, a dual-biased signal modulator 330, a polarization rotation module 340, an optical injection locking OIL module 350, an integrated coherent receiver 360, and a multi-core fiber 370. Among them, the laser 310, the first coupler 320, the dual-biased signal modulator 330, and the integrated coherent receiver 360 are respectively connected to the polarization rotation module 340 and the optical injection locking OIL module 350 through the first coupler 320. Figure 1 The structures of the laser 110, the coupler 120, the dual-biased signal modulator 130, and the integrated coherent receiver 160 shown are basically the same, and will not be described here.

[0047] Among them, the main laser 310, the first coupler 320, the dual-biased signal modulator 330, and the polarization rotation module 340 can also be referred to as a sending end (transmitter), and the optical injection locking OIL module 350 and the integrated coherent receiver 360 can also be referred to as a receiving end (receiver).

[0048] In the embodiment of the present application, the main laser 310 is configured to generate a to-be-sent optical signal; the first coupler 320 is configured to divide the to-be-sent optical signal into a first energy optical signal and a second energy optical signal according to a first preset energy ratio; the dual-biased signal modulator 330 is configured to perform dual-biased modulation on the first energy optical signal to generate a third energy optical signal; the polarization rotation module 340 is configured to perform polarization rotation on the second energy optical signal to obtain a downstream local oscillator light LO; the optical injection locking OIL module 350 is configured to perform injection locking processing on the downstream local oscillator light LO to generate a fourth energy optical signal, the frequency of the fourth energy optical signal being the same as the frequency of the downstream local oscillator light LO, and the power of the fourth energy optical signal being greater than the power of the downstream local oscillator light LO; and the integrated coherent receiver ICR 360 is configured to perform coherent demodulation on the third energy optical signal and the fourth energy optical signal to recover the to-be-sent optical signal.

[0049] By way of example, and without limitation, the first preset energy ratio can be 19:1.

[0050] Optionally, the self-coherent transmission system 300 can further include a multi-core fiber 370, the multi-core fiber 370 including a first core and a second core, the first core being configured to transmit the third energy optical signal, and the second core being configured to transmit the downstream local oscillator light LO, the first core being different from the second core. Among them, the structure, material, etc. of the first core and the second core are the same, and the first core being different from the second core means that the first core and the second core belong to two cores under the same multi-core fiber 370, that is, the third energy optical signal and the local oscillator light LO are transmitted through different links.

[0051] Optionally, the self-coherent transmission system 300 can further include a control module 380, which can be configured to drive the devices of the self-coherent transmission system 300, or to perform the functions of the devices of the self-coherent transmission system 300.

[0052] Optionally, although not shown in the figure, the self-coherent transmission system 300 also includes other elements necessary for implementing self-coherent transmission, such as an adjustable attenuator.

[0053] According to the system provided in the present application, the polarization rotation module is used to perform polarization rotation processing on the to-be-sent light signal, and the optical injection locking module is used to perform injection locking processing, so as to ensure controllable amplification of the local oscillator light power, and to help avoid carrier polarization fading and improve transmission performance.

[0054] The embodiment will be described in detail below in combination with Figure 4 , Figure 5 and Figure 6 .

[0055] Figure 4 An example structure of the polarization rotation module provided in the present application is shown. As shown in Figure 4 , the polarization rotation module 340 includes a first polarization beam splitter 341, a first phase modulator 342, and a first polarization combiner 343. The first polarization beam splitter 341 is used to process the second energy light signal according to a second preset energy ratio to generate a fifth energy light signal and a sixth energy light signal, the fifth energy light signal and the sixth energy light signal are orthogonal to each other, and the fifth energy light signal and the sixth energy light signal have similar frequencies. The first phase modulator 342 is used to perform phase modulation on the sixth energy light signal according to a first random phase and a first modulation period to generate a seventh energy light signal. The first polarization combiner 343 is used to combine the fifth energy light signal and the seventh energy light signal to generate a downlink local oscillator light LO.

[0056] The polarization rotation module 340 uses a launch scrambling technique to process the to-be-sent signal light, that is, a partial depolarizer based on random phase modulation at the launch end can solve the problem of carrier polarization fading without changing the integrated coherent receiver.

[0057] Specifically, for a short-distance standard single-mode fiber channel, the polarization mode dispersion effect can usually be ignored, and the Jones transformation matrix of the Cayley-Klein form of the polarization state (SOP) rotation can be expressed as:

[0058]

[0059] where δ and β represent the phase delay, and θ represents the rotation angle. A typical polarization state is linear polarization, and when the SOP is located on the equator of the Poincaré sphere, serious carrier polarization fading phenomenon will occur. Therefore, for simplicity, we set δ and β to 0, and then the SOP Jones vector at the receiving end can be expressed as:

[0060]

[0061] where r Tx represents the Jones vector of the SOP at the transmitting end, and the angle a is defined as tan a = E X / E y , E X and E y represent the light field amplitudes of X and Y polarization states respectively. θ = 2πft, f represents the rotation speed, and t represents time. It can be seen from the formula that if the condition is met:

[0062]

[0063] The most serious carrier polarization fading phenomenon will occur, that is, all the power is transferred to one polarization state. However, if a first random phase (ψ) is intentionally introduced between the two orthogonal SOPs of the Jones vector of the transmitter, in this case r Rx will become:

[0064]

[0065] It should be noted that in general, the polarization state of the laser in the transmitting end is controlled to be π / 4, so that the most serious carrier polarization fading phenomenon can be avoided by setting ψ to be not 0. However, the above formula (4) only involves a special case. In fact, due to the influence of time-varying birefringence in the optical fiber, the angle θ of the RSOP is a function of time t. In addition, as long as θ + a is approximately equal to nπ / 2, the carrier polarization fading phenomenon will also be caused. Therefore, it is recommended to use a random phase modulation signal about ψ in general cases. This step of operation is also called partial depolarization. In an actual self-coherent transmission system, by changing the distribution of the random phase, the best configuration for effectively avoiding carrier polarization fading can be found.

[0066] In the embodiments of the present application, the first random phase ψ has a value range of 0 to 2π, and the first random phase ψ adopts a uniform distribution sequence, a Gaussian distribution sequence or other random distribution manners, which are not limited in the present application.

[0067] In the above phase modulation of the sixth signal by using the first random phase ψ, a first modulation period is adopted, the first modulation period belongs to a first threshold range, and the first threshold is greater than or equal to 1 kHz and less than or equal to 1000 kHz.

[0068] According to the polarization rotation module provided in the present application, the polarization rotation processing is performed on the to-be-sent optical signal, which is helpful to improve the problem of random rotation of the polarization state of the downlink optical LO at the receiving end, thereby helping to avoid carrier polarization fading and improving the transmission performance.

[0069] Figure 5 An example structure of the optical injection locking module provided by the present application is shown. As shown, the optical injection locking module 350 includes a second polarization beam splitter 351, a circulator 352 and a slave laser 353. Among them, the second polarization beam splitter 351 is used to polarize the downlink local light LO to generate an eighth energy optical signal; the slave laser 353 is used to injection lock the eighth energy optical signal to generate a fourth energy optical signal; and the circulator 352 is used to input the eighth energy optical signal to the slave laser and input the fourth energy optical signal to the integrated coherent receiver ICR. Figure 5

[0070] Among them, the optical injection locking module 350 uses the OIL technology to process the downlink local light LO, that is, based on the interaction between photons when external light irradiates into the laser resonant cavity, so as to realize the stable amplification of the downlink local light LO.

[0071] Specifically, when the carrier frequency of the master laser 110 is close enough to the carrier frequency of the slave laser 353 running freely, the slave laser 353 will be forced to synchronize (that is, the same) with the master laser 110, that is, to emit laser at a fixed phase offset and the same frequency, and the slave laser 353 will also follow the slow frequency drift of the master laser 110 at a constant output power. The stable OIL frequency range that can be obtained is called the locking range, which can be represented by the following expression:

[0072] Δω LR = Δω max - Δω min (5)

[0073]

[0074] Among them, Po and Pinj represent the output power of the slave laser and the power of the injection signal, respectively. κ is the coupling coefficient, and α is the line width enhancement factor. Since the OIL has a locking range, the OIL can perform stable frequency selective amplification.

[0075] It should be understood that in the embodiments of the present application, the circulator 352 and the master laser 110 and the slave laser 353 constitute a reflective link, so as to avoid the light injection from the master laser 110 into the slave laser 353 and then reflected back to the master laser 110, but those skilled in the art can know that not only the circulator 353 can achieve the above-mentioned effect, other elements that can achieve the above-mentioned function constitute a module or system with the above-mentioned function, which should not be beyond the protection scope of the present application. For example, an optical isolator and the master laser 110 and the slave laser 353 can also be used to constitute a transmissive link, which can also achieve the above-mentioned effect.

[0076] ​According to the optical injection locking OIL module provided in the application, the downlink local light LO is subjected to injection locking processing, so that the controllable amplification of the local light power can be ensured, and the problem of insufficient downlink local light LO power in the self-coherent transmission system can be solved.

[0077] In the embodiment of the application, the polarization rotation module 340 is also used at the sending end to avoid the loss of lock of the receiving end from the laser 353, so that the problem of polarization fading can be better solved.

[0078] Specifically, in the short-distance transmission system, the polarization coherent dispersion can be ignored, so that the Jones matrix of the received downlink LO can be represented as:

[0079]

[0080] After the polarization processing, the downlink local light LO can be represented as:

[0081]

[0082] That is, the downlink local light LO is in the form of amplitude fluctuation with the link polarization rotation angle, and in the extreme case, the link polarization rotation angle can make the output light amplitude be 0 and remain in this state for a long time, which can cause the optical injection locking module 350 to lose lock. In the application, after the polarization rotation module 340 is added, the downlink local light LO becomes the eighth energy optical signal after the second polarization beam splitter 351, and the amplitude is the result of the joint action of the link polarization rotation (random change) and the polarization rotation module (artificial) polarization rotation processing.

[0083] In the embodiment of the application, at the receiving end, the third energy optical signal is output from the corresponding core of the multi-core optical fiber 370, and after the power of the control signal is adjusted by the attenuator, it is input into the signal input port of the integrated coherent receiver 360. The downlink local light LO is subjected to polarization processing by the second polarization beam splitter 351 to generate the eighth energy optical signal, the eighth energy optical signal is injected into the injection locking from the laser 353 through the circulator 352 to generate the fourth energy optical signal, and the fourth energy optical signal is input into the local light LO input port of the integrated coherent receiver 360.

[0084] Figure 6 (a) shows an example of output from the laser, and it can be seen that the fourth energy optical signal output from the laser has high power and a wide fluctuation range, which does not affect the signal reception of the integrated coherent receiver 360. Figure 6 (b) shows an example of recovery of the integrated coherent receiver, and it can be seen that the constellation diagram of the to-be-sent optical signal recovered by the integrated coherent receiver 360 is clear and complete.

[0085] Figure 7 An example of the self-coherent transmission method provided in the application is shown in the schematic flowchart.

[0086] S710, divide the to-be-sent optical signal into a first energy optical signal and a second energy optical signal according to a first preset energy ratio.

[0087] As an example but not limitation, the first preset energy ratio can be 19:1.

[0088] S720, perform double-sideband modulation on the first energy optical signal to generate a third energy optical signal.

[0089] S730, process the second energy optical signal according to a second preset energy ratio to generate a fifth energy optical signal and a sixth energy optical signal.

[0090] The fifth energy optical signal and the sixth energy optical signal have similar frequencies and are orthogonal to each other.

[0091] As an example but not limitation, the second preset energy ratio can be 5:5.

[0092] It should be understood that the present application does not limit the relationship between the first preset energy ratio and the second preset energy ratio, which can be the same or different.

[0093] S740, perform phase modulation on the sixth energy optical signal according to a first random phase and a first modulation period to generate a seventh energy optical signal.

[0094] Optionally, the first random phase has a value range of 0 to 2π, and the first random phase adopts a uniform distribution sequence, a Gaussian distribution sequence or other random distribution manners.

[0095] Optionally, the first modulation period belongs to a first threshold range, and the first threshold is greater than or equal to 1 kHz and less than or equal to 1000 kHz.

[0096] S750, combine the fifth energy optical signal and the seventh energy optical signal to generate a downlink local oscillator (LO).

[0097] According to the technical scheme provided in the present application, the to-be-sent optical signal is processed by polarization rotation, which helps to improve the problem of random rotation of the polarization state of the downlink local oscillator (LO) at the receiving end, thereby helping to avoid carrier polarization fading and improving transmission performance.

[0098] S760, perform polarization processing on the downlink local oscillator (LO) to generate an eighth energy optical signal.

[0099] S770, perform injection locking processing on the eighth energy optical signal to generate a fourth energy optical signal.

[0100] According to the technical solution provided in the application, the downlink local light LO is subjected to injection locking processing, so that controllable amplification of the local light power can be ensured, and the problem of insufficient downlink local light LO power in a self-coherent transmission system can be solved.

[0101] S780, the third energy light signal and the fourth energy light signal are subjected to coherent demodulation, and the to-be-sent light signal is recovered.

[0102] According to the technical solution provided in the application, the to-be-sent light signal is subjected to polarization rotation processing and injection locking processing, so that controllable amplification of the local light power can be ensured, and polarization fading of a carrier can be avoided, and transmission performance can be improved.

[0103] Figure 8 An example of a schematic structure of a control module provided in the application is shown. The control module 380 can include a processor 381, a communication interface 382. Optionally, the control device can further include a memory 383. Optionally, the memory 383 can be included in the processor 381. The processor 381, the communication interface 382 and the memory 383 communicate with each other through an internal connection path, the memory 383 is used for storing instructions, and the processor 381 is used for executing the instructions stored in the memory 383 to implement the control method provided in the embodiments of the application.

[0104] Optionally, the control device can be used to execute the functions of the devices of the self-coherent transmission system 300, including the functions of the polarization rotation module 340 and the optical injection locking module 350, wherein the polarization rotation module 340 includes the first polarization beam splitter 341, the first phase modulator 342 and the first polarization combiner 343, and the optical injection locking module 350 includes the second polarization beam splitter 351, the circulator 352 and the slave laser 353.

[0105] Optionally, the control device can be used to execute Figure 7 the control method shown in the above method 700 or the actions performed by the controller in the above self-coherent transmission system 300. The steps performed by the controller or the processor in the above method 700 or the actions performed by the controller in the above self-coherent transmission system 300 can be automatically executed by the controller, that is, the controller can read the software program in the storage unit, interpret and execute the instructions of the software program, process the data of the software program, and then control the devices of the self-coherent transmission system 300 to execute their respective functions, so as to execute the above method 700.

[0106] For example, the controller can be implemented by a processor, and the processor can include a central processor mainly used for controlling the entire terminal device, executing the software program and processing the data of the software program.

[0107] It should be appreciated that, in the embodiments of the present application, the processor can be a central processing unit (CPU), other general-purpose processors, a digital signal processor (DSP), an application specific integrated circuit (ASIC), a field programmable gate array (FPGA) or other programmable logic devices, discrete gates or transistor logic components, discrete hardware components, etc. The general-purpose processor can be a microprocessor or the processor can also be any conventional processor.

[0108] The terms "component," "module," "system" and the like as used herein are intended to refer to a computer-related entity, either hardware, firmware, a combination of hardware and software, software, or software in execution. For example, a component can be, but is not limited to being, a process running on a processor, a processor, an object, an executable, a thread of execution, a program, and / or a computer. By way of illustration, both an application running on a computing device and the computing device can be a component. One or more components can reside within a process and / or thread of execution and a component can be localized, partially localized, and / or distributed across two or more computers. Also, these components can execute from various computer readable media having various data structures stored thereon. The components can communicate via local and / or remote processes such as in accordance with a signal having one or more data packets (e.g., data from one component interacting with another component in a local system, distributed system, and / or across a network such as the Internet with other systems via the signal).

[0109] Those skilled in the art can clearly understand that the units and algorithm steps of the examples described in combination with the embodiments disclosed herein can be realized by electronic hardware or a combination of computer software and electronic hardware. Whether the functions are realized in hardware or software depends on the specific application and design constraints of the technical solution. A person skilled in the art can use different methods to realize the described functions for each specific application, but such implementation should not be considered beyond the scope of the present application.

[0110] Those skilled in the art can clearly understand that, for the convenience and brevity of the description, the specific working processes of the system, device and unit described above can refer to the corresponding processes in the foregoing method embodiments, which will not be described here.

[0111] In several embodiments provided in the present application, it should be understood that the disclosed system, device and method can be implemented in other manners. For example, the described device embodiments are merely schematic. For example, the division of the units is only a logical function division. There can be another division manner for the actual implementation, for example, multiple units or components can be combined or integrated into another system, or some features can be ignored or not executed. In addition, the displayed or discussed mutual couplings or direct couplings or communication connections between different units, can be indirect couplings or communication connections through some interfaces, devices or units, and can be in electrical, mechanical or other forms.

[0112] The units described as separate components can or can not be physically separate, and the components shown as units can or can not be physical units, i.e., can be located in one place, or can be distributed on multiple network units. Some or all of the units can be selected according to actual needs to achieve the purpose of the embodiment.

[0113] In addition, each functional unit in the various embodiments of the present application can be integrated in one processing unit, or each unit can be physically present separately, or two or more units can be integrated in one unit.

[0114] If the functions are realized in the form of software function units and sold or used as independent products, they can be stored in a computer readable storage medium. Based on this understanding, the technical solutions of the present application essentially or the part of the prior art that contributes to the technical solutions or part of the technical solutions can be embodied in the form of a software product. The computer software product is stored in a storage medium, and includes several instructions for causing a computer device (which can be a personal computer, a server, or a network device, etc.) to execute all or part of the steps of the methods described in the various embodiments of the present application. The aforementioned storage medium includes: a U disk, a mobile hard disk, a read-only memory (ROM), a random access memory (RAM), a magnetic disk or an optical disk, and various media that can store program codes.

[0115] It should be understood that in various embodiments of the present application, the size of the sequence number of each process does not mean the order of execution, and the execution order of each process should be determined by its function and inherent logic, and should not constitute any limitation on the implementation process of the embodiments of the present application.

[0116] The above merely provides the specific implementation of the present application, but the protection scope of the present application is not limited to this. Any person skilled in the art can easily think of the changes or replacements within the technical range disclosed by the present application, which should be covered in the protection scope of the present application. Therefore, the protection scope of the present application should be subject to the protection scope of the claims.

Claims

1. A system for self-coherent transmission, characterized by The application relates to a method for transmitting an optical signal. The application comprises: a main laser for generating an optical signal to be transmitted; a first coupler for dividing the optical signal to be transmitted into a first energy optical signal and a second energy optical signal according to a first preset energy ratio; a dual-biased signal modulator for dual-biased modulation of the first energy optical signal to generate a third energy optical signal; a polarization rotation module for performing polarization rotation on the second energy optical signal to obtain downlink local oscillator light; a multicore optical fiber comprising a first core and a second core, the first core being used for transmitting the third energy optical signal, and the second core being used for transmitting the downlink local oscillator light, the first core being different from the second core; an optical injection locking module for injection locking processing of the downlink local oscillator light to generate a fourth energy optical signal, the frequency of the fourth energy optical signal being the same as that of the downlink local oscillator light, and the power of the fourth energy optical signal being greater than that of the downlink local oscillator light; 2. The system of claim 1, wherein, an integrated coherent receiver for coherent demodulation of the third energy optical signal and the fourth energy optical signal to recover the optical signal to be transmitted. The polarization rotation module comprises: a first polarization beam splitter for processing the second energy optical signal according to a second preset energy ratio to generate a fifth energy optical signal and a sixth energy optical signal, the fifth energy optical signal and the sixth energy optical signal being orthogonal to each other; a first phase modulator for phase modulation of the sixth energy optical signal according to a first random phase and a first modulation period to generate a seventh energy optical signal; 3. The system of claim 2, wherein, a first polarization combiner for combining the fifth energy optical signal and the seventh energy optical signal to generate the downlink local oscillator light.

4. The system of claim 2 or 3, wherein, The first random phase ranges from 0 to 2pi.

5. The system of claim 2, wherein, The first random phase adopts a uniform distribution sequence, a Gaussian distribution sequence or other random distribution modes.

6. The system of any one of claims 1 to 3, wherein, The first modulation period belongs to a first threshold range. The optical injection locking module comprises: a second polarization beam splitter for polarization processing of the downlink local oscillator light to generate an eighth energy optical signal; a slave laser for injection locking processing of the eighth energy optical signal to generate the fourth energy optical signal; 7. A method of self-coherent transmission, c h a r a c t e r i s e d by a circulator for inputting the eighth energy optical signal into the slave laser and inputting the fourth energy optical signal into the integrated coherent receiver. The application relates to a method for transmitting an optical signal. The application comprises: dividing an optical signal to be transmitted into a first energy optical signal and a second energy optical signal according to a first preset energy ratio; dual-biased modulation of the first energy optical signal to generate a third energy optical signal; polarization rotation of the second energy optical signal to generate downlink local oscillator light; transmission of the third energy optical signal in a first core of a multicore optical fiber and transmission of the downlink local oscillator light in a second core of the multicore optical fiber, the first core being different from the second core; injection locking processing of the downlink local oscillator light to generate a fourth energy optical signal, the frequency of the fourth energy optical signal being the same as that of the downlink local oscillator light, and the power of the fourth energy optical signal being greater than that of the downlink local oscillator light; coherent demodulation of the third energy optical signal and the fourth energy optical signal to recover the optical signal to be transmitted.

8. The method of claim 7, wherein, The polarization rotation on the second energy optical signal obtains a downlink local light, and the polarization rotation comprises: The second energy optical signal is processed according to a second preset energy ratio to generate a fifth energy optical signal and a sixth energy optical signal, and the fifth energy optical signal and the sixth energy optical signal are orthogonal to each other; The sixth energy optical signal is phase modulated according to a first random phase and a first modulation period to generate a seventh energy optical signal; The fifth energy optical signal and the seventh energy optical signal are combined to generate the downlink local light.

9. The method of claim 8, wherein, The first random phase is in a range of 0 to 2π.

10. The method according to claim 8 or 9, characterized in that, The first random phase adopts a uniform distribution sequence, a Gaussian distribution sequence or other random distribution manners.

11. The method of claim 8, wherein, The first modulation period belongs to a first threshold range.

12. The method according to any one of claims 7 to 9, characterized in that, The downlink local light is injection-locked to generate a fourth energy optical signal, and the injection-locking comprises: The downlink local light is polarized to generate an eighth energy optical signal; The eighth energy optical signal is injection-locked to generate the fourth energy optical signal.

Images