Calculating device and calibrating device for imbalance of optical coherent receiver, and optical communication system

Abstract

The embodiment of the invention provides a calculation device and a calibration device for imbalance of an optical coherent receiver, and an optical communication system. The calculating device comprises a phase shifter which is arranged on a local oscillation circuit or a signal circuit of an input optical coherent receiver to be detected, the phase shifter carries out at least one phase change of 0-2pi within a preset duration, and the local oscillation circuit and the signal circuit share a laser as a light source; the first calculation unit is used for calculating the average power of the I-path signal, the average power of the Q-path signal and the correlation quantity of the I-path signal and the Q-path signal within the preset duration according to the I-path signal and the Q-path signal output by the optical coherent receiver to be detected; and the second calculation unit is used for calculating the amplitude imbalance and the phase imbalance of the optical coherent receiver to be detected according to the average power of the I-path signal, the average power of the Q-path signal and the correlation quantity of the I-path signal and the Q-path signal in the preset duration.

Description

Technical Field

[0001] This application relates to the field of optical communication. Background Art

[0002] In the field of optical communication, optical coherent transceivers play an increasingly important role in achieving greater communication capacity. An optical coherent receiver may include devices such as a 90-degree mixer and a pair of balanced detectors. In actual use, these devices may all have non-ideal situations. For example, the 90-degree mixer has a phase deviation, and the balanced detector has a responsivity deviation (usually described by the common mode rejection ratio CMRR), etc. On the other hand, these non-ideals also change with the change of the environment (such as temperature, humidity). The non-ideals of these devices will all lead to a decline in system performance or affect the monitoring accuracy. Therefore, a simple and feasible solution is needed to monitor and calibrate the imbalance of the optical coherent receiver.

[0003] When different lasers are used for the transmitter and the local oscillator of the receiver, the traditional calibration of the optical coherent receiver imbalance can adopt the GSOP (Gram-Schmidt Orthogonalization Procedure) algorithm. This method utilizes the orthogonal characteristics of the coherent receiver to estimate the phase and amplitude imbalances.

[0004] It should be noted that the above introduction to the technical background is only for the convenience of clearly and completely explaining the technical solution of this application and facilitating the understanding of those skilled in the art. It cannot be considered that the above technical solutions are well-known to those skilled in the art just because these solutions are described in the background art section. Summary of the Invention

[0005] The inventors found that in some cases, the calibration using the GSOP method may fail. For example, for some low-cost optical coherent receivers, such as those in which the optical coherent transmitter and the optical coherent receiver are integrated on the same chip and share a laser, and the self-coherent demodulation scheme, the local oscillators of the optical coherent transmitter and the optical coherent receiver use the same-source lasers. In this case, the traditional GSOP method cannot distinguish the non-ideals of the optical coherent transmitter from those of the optical coherent receiver, resulting in the failure of calibrating the imbalance of the optical coherent receiver.

[0006] To solve at least one of the above problems, an embodiment of this application provides a calculation device, a calibration device for the imbalance of an optical coherent receiver, and an optical communication system.

[0007] According to the first aspect of the embodiments of the present application, there is provided a calculation device for optical coherent receiver imbalance. The device includes: a phase shifter, which is arranged in the local oscillator path or the signal path of the input optical coherent receiver to be measured. The phase shifter performs at least one phase change from 0 to 2π within a preset time period. The local oscillator path and the signal path share a laser as a light source; a first calculation unit, which calculates the average power of the I-channel signal, the average power of the Q-channel signal, and the correlation quantity between the I-channel signal and the Q-channel signal within the preset time period according to the I-channel signal and the Q-channel signal output by the optical coherent receiver to be measured; and a second calculation unit, which calculates the amplitude imbalance and phase imbalance of the optical coherent receiver to be measured according to the average power of the I-channel signal, the average power of the Q-channel signal, and the correlation quantity between the I-channel signal and the Q-channel signal within the preset time period.

[0008] According to the second aspect of the embodiments of the present application, there is provided a calibration device for optical coherent receiver imbalance. The device includes: a phase shifter, which is arranged in the local oscillator path or the signal path of the input optical coherent receiver to be measured. The phase shifter performs at least one phase change from 0 to 2π within a preset time period. The local oscillator path and the signal path share a laser as a light source; a first calculation unit, which calculates the average power of the I-channel signal, the average power of the Q-channel signal, and the correlation quantity between the I-channel signal and the Q-channel signal within the preset time period according to the I-channel signal and the Q-channel signal output by the optical coherent receiver to be measured; a second calculation unit, which calculates the amplitude imbalance and phase imbalance of the optical coherent receiver to be measured according to the average power of the I-channel signal, the average power of the Q-channel signal, and the correlation quantity between the I-channel signal and the Q-channel signal within the preset time period; and a calibration unit, which calibrates the imbalance of the optical coherent receiver according to the calculated amplitude imbalance and phase imbalance of the optical coherent receiver to be measured.

[0009] According to the third aspect of the embodiments of the present application, there is provided an optical communication system, characterized in that the system includes an optical coherent transmitter, an optical coherent receiver, and the calculation device for optical coherent receiver imbalance according to the first aspect of the embodiments of the present application.

[0010] One of the beneficial effects of the embodiments of the present application lies in that: by setting a phase shifter, the signal undergoes a phase change from 0 to 2π before entering the optical coherent receiver to be measured, and during the phase change from 0 to 2π, the amplitude imbalance and phase imbalance of the optical coherent receiver to be measured are calculated according to the average power of the I-channel signal, the average power of the Q-channel signal, and the correlation between the I-channel signal and the Q-channel signal. Thus, the interaction between the non-idealities of the optical coherent transmitter and the non-idealities of the coherent receiver can be avoided, the amplitude imbalance and phase imbalance of the optical coherent receiver can be accurately calculated and calibrated, and it is not affected by the modulation format of the optical coherent transmitter signal and the non-ideal factors of the optical coherent transmitter.

[0011] Referring to the following description and drawings, specific embodiments of the present application are disclosed in detail, indicating the ways in which the principles of the present application can be adopted. It should be understood that the embodiments of the present application are not limited in scope thereby. Within the spirit and terms of the appended claims, the embodiments of the present application include many changes, modifications, and equivalents.

[0012] Features described and / or illustrated for one embodiment can be used in the same or similar way in one or more other embodiments, combined with the features in other embodiments, or substitute for the features in other embodiments.

[0013] It should be emphasized that the term "comprising / including" when used herein refers to the presence of features, whole things, steps, or components, but does not exclude the presence or addition of one or more other features, whole things, steps, or components. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] The accompanying drawings included are used to provide a further understanding of the embodiments of the present application, which form a part of the specification, illustrate the embodiments of the present application, and together with the written description explain the principles of the present application. Obviously, the drawings in the following description are only some embodiments of the present application, and those of ordinary skill in the art can obtain other drawings based on these drawings without creative efforts. In the drawings:

[0015] Figure 1 is a schematic diagram of a calculation device for optical coherent receiver imbalance according to an embodiment of the present application;

[0016] Figure 2 is a schematic diagram of an embodiment of an optical communication system according to an embodiment of the present application;

[0017] Figure 3 is a schematic diagram of another embodiment of an optical communication system according to an embodiment of the present application;

[0018] Figure 4 is a schematic diagram of various forms of an optical modulator according to an embodiment of the present application;

[0019] Figure 5 It is a schematic diagram of the composition of the optical coherent receiver according to an embodiment of the present application;

[0020] Figure 6 It is a schematic of the composition of the polarization multiplexing optical coherent receiver according to an embodiment of the present application;

[0021] Figure 7 It is a schematic diagram of the composition of the modulation unit according to an embodiment of the present application;

[0022] Figure 8 It is a schematic diagram of a calibration device for the imbalance of the optical coherent receiver according to an embodiment of the present application;

[0023] Figure 9 It is a structural diagram of an example of an optical communication system according to an embodiment of the present application;

[0024] Figure 10 is Figure 9 A schematic diagram of the comparison result between the theoretical values and the monitored values of the phase imbalance and amplitude imbalance of the optical coherent receiver of the optical communication system shown;

[0025] Figure 11 It is a schematic diagram of a calculation method for the imbalance of the optical coherent receiver according to an embodiment of the present application;

[0026] Figure 12 It is a schematic diagram of a calibration method for the imbalance of the optical coherent receiver according to an embodiment of the present application. Detailed implementation manners

[0027] Referring to the accompanying drawings and through the following description, the foregoing and other features of the present application will become apparent. In the description and drawings, specific embodiments of the present application are disclosed, which show some embodiments in which the principles of the present application can be adopted. It should be understood that the present application is not limited to the described embodiments. On the contrary, the present application includes all modifications, variations, and equivalents falling within the scope of the appended claims.

[0028] An embodiment of the present application provides a calculation device, a calibration device, and an optical communication system for the imbalance of an optical coherent receiver.

[0029] Figure 1 It is a schematic diagram of a calculation device for the imbalance of the optical coherent receiver according to an embodiment of the present application.

[0030] As Figure 1 shown, the calculation device 100 for the imbalance of the optical coherent receiver includes:

[0031] A phase shifter 101 is disposed in the local oscillator path or the signal path of the input optical coherent receiver to be measured. The phase shifter performs at least one phase change from 0 to 2π within a preset time period. The local oscillator path and the signal path share a laser as a light source.

[0032] A first calculation unit 102 calculates the average power of the I-channel signal, the average power of the Q-channel signal, and the correlation quantity between the I-channel signal and the Q-channel signal within the preset time period according to the I-channel signal and the Q-channel signal output by the optical coherent receiver to be measured; and

[0033] A second calculation unit 103 calculates the amplitude imbalance and phase imbalance of the optical coherent receiver to be measured according to the average power of the I-channel signal, the average power of the Q-channel signal, and the correlation quantity between the I-channel signal and the Q-channel signal within the preset time period.

[0034] In this way, by setting the phase shifter, the signal undergoes a phase change from 0 to 2π before entering the optical coherent receiver to be measured. And within the period of the phase change from 0 to 2π, the amplitude imbalance and phase imbalance of the optical coherent receiver to be measured are calculated according to the average power of the I-channel signal, the average power of the Q-channel signal, and the correlation quantity between the I-channel signal and the Q-channel signal. Thus, the interaction between the non-idealities of the optical coherent transmitter and the non-idealities of the coherent receiver can be avoided, the amplitude imbalance and phase imbalance of the optical coherent receiver can be accurately calculated and calibrated, and it is not affected by the modulation format of the optical coherent transmitter signal and the non-ideal factors of the optical coherent transmitter.

[0035] In some embodiments, the input signal of the signal path is a non-all-zero signal. For example, the signal input to the optical coherent receiver to be measured in the signal path is: the output signal of the optical coherent transmitter, or the split monitoring signal of the output signal of the optical coherent transmitter, or the output signal of the I-jQ port of the optical coherent transmitter coupler, or the output signal or split monitoring signal of the polarization multiplexed optical transmitter.

[0036] In some embodiments, the signal input to the local oscillator path of the optical coherent receiver to be measured is: a direct current optical signal split from the laser or an optical signal modulated from the direct current optical signal.

[0037] In some embodiments, a modulation unit can be set to output a non-all-zero signal or an all-zero signal.

[0038] As Figure 1 shown, for example, the calculation device 100 further includes:

[0039] A modulation unit 104 is disposed in the local oscillator path and is used to output a non-all-zero signal or an all-zero signal.

[0040] The adjustment unit 104 is an optional unit.

[0041] Figure 2 It is a schematic diagram of an implementation manner of the optical communication system according to an embodiment of the present application;

[0042] As Figure 2 shown, the optical communication system 10 includes a laser 200, an optical coherent transmitter 300, an optical coherent receiver 400 to be measured, and Figure 1 each unit of the calculation device 100 for calculating the imbalance of the optical coherent receiver in

[0043] Figure 3 It is a schematic diagram of another implementation manner of the optical communication system according to an embodiment of the present application. Different from Figure 2 that, in the optical communication system 10', the phase shifter 101 is arranged on the signal path, and within a preset time period, the phase shifter 101 causes the signal on the signal path to undergo at least one phase change from 0 to 2π.

[0044] In some embodiments, the preset time is the time required for the signal on the local oscillator path or the signal path to undergo at least one phase change from 0 to 2π.

[0045] In some embodiments, the phase change from 0 to 2π can be performed once or multiple times, and can be set according to actual needs.

[0046] In some embodiments, the phase change from 0 to 2π can be a uniform change or a non-uniform change.

[0047] In some embodiments, the optical modulator 301 in the optical coherent transmitter 300 can be various forms of optical modulators. For example, the optical modulator 301 can be a quadrature modulator (IQ modulator), an amplitude modulator, a phase modulator, or a polarization division multiplexing modulator.

[0048] Figure 4 It is a schematic diagram of various forms of the optical modulator according to an embodiment of the present application. As Figure 4 shown in (a) of Figure 4 the optical modulator is a quadrature modulator, that is, an IQ modulator; as Figure 4 shown in (b) of Figure 4 the optical modulator is an amplitude modulator, such as an MZM modulator; as

[0049] In some embodiments, the optical coherent receiver 400 to be measured can be a receiver in an actual communication system or a receiver for monitoring. For example, Figure 2 and Figure 3 as shown, the optical coherent transmitter 300 and the optical coherent receiver 400 to be measured share a laser, that is, the local oscillator paths of the optical coherent transmitter 300 and the optical coherent receiver 400 use the same laser.

[0050] In addition, in some embodiments, the optical coherent receiver 400 to be measured and the optical coherent transmitter 300 are integrated on a chip.

[0051] In some embodiments, the optical coherent receiver 400 to be measured includes at least one 90-degree mixer and a pair of balanced photodetectors (BPDs).

[0052] Figure 5 is a schematic diagram of the composition of the optical coherent receiver according to an embodiment of the present application. For example, Figure 5 as shown, the optical coherent receiver to be measured includes a 90-degree mixer (90° Hybrid) and a pair of balanced photodetectors (BPDs). The signals S1(t) and S2(t) output by the pair of BPDs represent the I-channel signal and the Q-channel signal respectively, and t is the time coefficient.

[0053] The embodiments of the present application are also applicable to dual-polarization systems. Figure 6 is a schematic diagram of the composition of the polarization multiplexing optical coherent receiver according to an embodiment of the present application. For example, Figure 6 as shown, the polarization multiplexing optical coherent receiver to be measured includes two polarization beam splitters (PBSs), two 90-degree mixers (90° Hybrid) and two pairs of balanced photodetectors (BPDs). The signals S1(t), S2(t), S3(t) and S4(t) output by the two pairs of BPDs represent the I-channel signal and the Q-channel signal of the first polarization state (X polarization state), and the I-channel signal and the Q-channel signal of the second polarization state (Y polarization state) respectively.

[0054] In some embodiments, the modulation unit 104 includes an optical modulator or an optical switch. Figure 7 is a schematic diagram of the composition of the modulation unit according to an embodiment of the present application. As shown in (a) of Figure 7 , the modulation unit can be composed of an MZM modulator; or, as shown in (b) of Figure 7 , the modulation unit can be composed of an optical switch.

[0055] Next, the processing process of the calculation device for the imbalance of the optical coherent receiver according to the embodiment of the present application will be specifically described.

[0056] For example, Figure 2 or Figure 3As shown, the light emitted by the laser 200 is divided into two paths. One path of light is a direct current optical signal, and after being modulated by the modulation unit 104 (when the modulation unit 104 is provided), it is input into the optical coherent receiver 400 to be measured as the signal of the local oscillator path; the other path of light is input into the optical modulator 301 of the optical coherent transmitter 300, and the output signal of the optical modulator 301, or the split beam monitoring signal, or the output signal of the I - jQ port is input into the optical coherent receiver 400 to be measured as the signal of the signal path.

[0057] Within a preset time duration, the phase shifter 101 is used to change the phase of the signal on the local oscillator path or the signal path from 0 to 2π. During this time duration, the I - path signal and the Q - path signal output by the optical coherent receiver 400 to be measured are acquired, and the first calculation unit 102 calculates the average power of the I - path signal, the average power of the Q - path signal, and the correlation quantity between the I - path signal and the Q - path signal during this time duration; the second calculation unit 103 calculates the amplitude imbalance and phase imbalance of the optical coherent receiver 400 to be measured according to the average power of the I - path signal, the average power of the Q - path signal, and the correlation quantity between the I - path signal and the Q - path signal during this time duration.

[0058] In some embodiments, the modulation unit 104 may not be provided. In this case, the signal of the local oscillator path is the optical signal output by the laser 200, which is a non - all - zero signal with a constant amplitude.

[0059] For example, when the signal input into the optical coherent receiver 400 to be measured on the local oscillator path is a non - all - zero signal, the output signals of the optical coherent receiver 400 to be measured are the I - path signal S1(t) and the Q - path signal S2(t), and the average power P1 of the I - path signal calculated by the first calculation unit 102 within a certain time duration is The average power P2 of the Q - path signal is The correlation quantity between the I - path signal and the Q - path signal is <S1(t)S2(t)>.

[0060] In some embodiments, when the modulation unit 104 is provided, the local oscillator path outputs a non - all - zero signal or an all - zero signal through the modulation unit 104. The non - all - zero signal requires that the signal sequence is not all zero, and for example, it can be a random signal, a periodic signal, or a signal with a constant amplitude, etc.

[0061] The first calculation unit 102 calculates the average power of the I - path signal, the average power of the Q - path signal, and the correlation quantity between the I - path signal and the Q - path signal within a preset time duration according to the first I - path signal and the first Q - path signal output by the optical coherent receiver to be measured when the modulation unit 104 outputs a non - all - zero signal, and the second I - path signal and the second Q - path signal output by the optical coherent receiver to be measured when the modulation unit outputs an all - zero signal.

[0062] When a non - all - zero signal is output after modulation by the modulation unit 104, similar to the above situation, the output signals of the optical coherent receiver 400 to be measured are the first I - channel signal S1(t) and the first Q - channel signal S2(t). The average power of the first I - channel signal within a certain duration calculated by the first calculation unit 102 is The average power of the first Q - channel signal is The correlation quantity of the first I - channel signal and the first Q - channel signal within a certain duration is <S1(t)S2(t)>.

[0063] When an all - zero signal is output after modulation by the modulation unit 104, the output signals of the optical coherent receiver 400 to be measured are the second I - channel signal S 01 (t) and the second Q - channel signal and S 02 (t). The average power of the second I - channel signal within a certain duration calculated by the first calculation unit 102 is The average power of the second Q - channel signal is The correlation quantity of the second I - channel signal and the second Q - channel signal within a certain duration is <S 01 (t)S 02 (t)>.

[0064] In the embodiments of the present application, for example, the average power of the I - channel signal, the average power of the Q - channel signal, and the correlation quantity of the I - channel signal and the Q - channel signal within a preset duration are calculated according to the following formula (1):

[0065]

[0066]

[0067] Corr=<S1(t)S2(t)>-k<S 01 (t)S 02 (t)>

[0068] k∈{0,1} (1)

[0069] Wherein, P1 represents the average power of the I - channel signal within a preset duration, P2 represents the average power of the Q - channel signal within a preset duration, Corr represents the correlation quantity of the I - channel signal and the Q - channel signal within a preset duration, S1(t) represents the I - channel signal output by the optical coherent receiver to be measured when the local oscillator path is a non - all - zero signal, S2(t) represents the Q - channel signal output by the optical coherent receiver to be measured when the local oscillator path is a non - all - zero signal, S 01 (t) represents the I - channel signal output by the optical coherent receiver to be measured when the local oscillator path is an all - zero signal, S 02(t) represents the Q-channel signal output by the optical coherent receiver under test when the local oscillator path is a all-zero signal. The value of k depends on whether the modulation unit is set and whether the modulation unit outputs a zero signal. Among them, k = 0 means that the local oscillator path only outputs a non-all-zero signal, and there may or may not be a modulation unit; k = 1 means that the modulation unit is set, and the local oscillator path outputs both all-zero signals and non-all-zero signals.

[0070] The second calculation unit 103 calculates the amplitude imbalance and phase imbalance of the optical coherent receiver under test according to the average power of the I-channel signal, the average power of the Q-channel signal, and the correlation quantity between the I-channel signal and the Q-channel signal within the preset duration. The specific calculation method can refer to the related technology.

[0071] For example, the amplitude imbalance and phase imbalance of the optical coherent receiver under test are calculated according to the following formulas (2) and (3):

[0072]

[0073]

[0074] Among them, a represents the amplitude imbalance of the optical coherent receiver under test, θ represents the phase imbalance of the optical coherent receiver under test, P1 represents the average power of the I-channel signal within the preset duration, P2 represents the average power of the Q-channel signal within the preset duration, and Corr represents the correlation quantity between the I-channel signal and the Q-channel signal within the preset duration.

[0075] The embodiments of the present application are also applicable to a dual-polarization system. For example, the optical coherent receiver under test 400 is a polarization-division multiplexing optical coherent receiver. In this case,

[0076] The first calculation unit 101 calculates the average power of the I-channel signal, the average power of the Q-channel signal, and the correlation quantity between the I-channel signal and the Q-channel signal within the preset duration in the first polarization direction according to the I-channel signal and the Q-channel signal in the first polarization direction output by the optical coherent receiver under test 400, and calculates the average power of the I-channel signal, the average power of the Q-channel signal, and the correlation quantity between the I-channel signal and the Q-channel signal within the preset duration in the second polarization direction according to the I-channel signal and the Q-channel signal in the second polarization direction output by the optical coherent receiver under test.

[0077] The second calculation unit 102 calculates the amplitude imbalance and phase imbalance in the first polarization direction according to the average power of the I-channel signal, the average power of the Q-channel signal, and the correlation quantity between the I-channel signal and the Q-channel signal within the preset duration in the first polarization direction, and calculates the amplitude imbalance and phase imbalance in the second polarization direction according to the average power of the I-channel signal, the average power of the Q-channel signal, and the correlation quantity between the I-channel signal and the Q-channel signal within the preset duration in the second polarization direction.

[0078] The specific calculation method can refer to the calculation process in the aforementioned single-polarization system, and will not be repeated here.

[0079] After calculating the amplitude imbalance and phase imbalance of the optical coherent receiver to be measured, one of the I-channel signal and Q-channel signal output by the optical coherent receiver to be measured can be calibrated using the amplitude imbalance and phase imbalance, or the amplitude imbalance and phase imbalance can be used for other applications, such as evaluating system performance, etc.

[0080] Figure 8 is a schematic diagram of a calibration device for the imbalance of the optical coherent receiver according to an embodiment of the present application. As Figure 8 shown, the calibration device 800 for the imbalance of the optical coherent receiver includes:

[0081] A phase shifter 801, which is arranged in the local oscillator path or the signal path of the optical coherent receiver to be measured. The phase shifter performs at least one phase change from 0 to 2π within a preset time period. The local oscillator path and the signal path share a laser as a light source;

[0082] A first calculation unit 802, which calculates the average power of the I-channel signal, the average power of the Q-channel signal, and the correlation quantity between the I-channel signal and the Q-channel signal within the preset time period according to the I-channel signal and the Q-channel signal output by the optical coherent receiver to be measured;

[0083] A second calculation unit 803, which calculates the amplitude imbalance and phase imbalance of the optical coherent receiver to be measured according to the average power of the I-channel signal, the average power of the Q-channel signal, and the correlation quantity between the I-channel signal and the Q-channel signal within the preset time period; and

[0084] A calibration unit 804, which calibrates the imbalance of the optical coherent receiver according to the calculated amplitude imbalance and phase imbalance of the optical coherent receiver to be measured.

[0085] The phase shifter 801, the first calculation unit 802, and the second calculation unit 803 are the same as the phase shifter 101, the first calculation unit 102, and the second calculation unit 103 in Figure 1 and will not be repeated here.

[0086] In some embodiments, the calibration unit 804 determines the calibrated I-channel signal or Q-channel signal according to the calculated amplitude imbalance and phase imbalance of the optical coherent receiver to be measured and the I-channel signal and the Q-channel signal output by the optical coherent receiver to be measured. The specific calibration method can refer to the related art.

[0087] For example, the calibration unit 804 calibrates the Q-channel signal according to the following formula (4):

[0088]

[0089] Among them, S′2(t) represents the calibrated Q-channel signal, S2(t) represents the Q-channel signal before calibration, S1(t) represents the I-channel signal before calibration, a represents the amplitude imbalance of the optical coherent receiver to be measured, and θ represents the phase imbalance of the optical coherent receiver to be measured.

[0090] In some embodiments, the calculation device 100 for optical coherent receiver imbalance or the calibration device 800 for optical coherent receiver imbalance can be an independent device or integrated in the optical coherent receiver.

[0091] In some embodiments, other data processing can also be performed within the calculation device 100 for optical coherent receiver imbalance or the calibration device 800 for optical coherent receiver imbalance, such as low-pass filtering, removing direct current (such as the mean value), square-wave multiplication frequency shift, etc. The implementation of these processes can be in the analog domain or the digital domain.

[0092] Next, the specific principles and application examples of the embodiments of the present application will be specifically described. Among them, taking the optical coherent receiver as Figure 6 the structure shown as an example for description.

[0093] Considering the possible non-ideal factors of the optical coherent receiver. If the optical signals of the signal path and the local oscillator path are respectively written as E Sig (t) and E LO (t), then the four outputs of the 90-degree mixer are respectively:

[0094]

[0095] Among them, is the optical phase difference between the local oscillator path and the signal path, and are the optical phase errors of the mixer.

[0096] The errors of the balanced detector BPD are divided into two parts, namely the imbalance of the total responses of the two balanced detectors and the imbalance of the positive and negative PD responses of the two balanced detectors (such as CMRR), which can be expressed by the formula as:

[0097]

[0098]

[0099]

[0100] Among them, CMRR1 and CMRR2 represent the response imbalances of the two balanced detectors, r 11Indicates the response of the positive PD on the I path, r 12 Indicates the response of the negative PD on the I path, r1 represents the average response of the BPD on the I path, r 21 Indicates the response of the positive PD on the Q path, r 22 Indicates the response of the negative PD on the Q path, r2 represents the average response of the BPD on the Q path.

[0101] Assume that the optical transmitter is a coherent transmitter, and its output optical signal is the signal at the other output port of the IQ combined 2×2 coupler, written as E Sig (t) = E I (t) - jE Q (t), then the two outputs S1(t) and S2(t) of the optical coherent receiver can be expressed as:

[0102]

[0103]

[0104] Let

[0105]

[0106]

[0107] Then

[0108]

[0109]

[0110] In some embodiments, consider the following two cases, i.e., CMRR can be ignored or CMRR cannot be ignored.

[0111] For the first case, i.e., the case where CMRR can be ignored, that is, CMRR1≈0, CMRR2≈0.

[0112] In the case where CMRR can be ignored, there is no need to set the modulation unit, or set the modulation unit, but the modulation unit outputs a non-all-zero signal. The output signal of the optical receiver is simplified to:

[0113]

[0114]

[0115] That is to say, the non-ideal factors of the considered device only result in amplitude imbalance, and the theoretical expression of the amplitude imbalance is According to the output signal of the optical coherent receiver, the amplitude imbalance a can also be calculated by formula 12 (k = 0):

[0116]

[0117] Equation (12) assumes that <E I (t)E Q (t)> ≥ 0. When there is an imbalance in the optical coherent transmitter, such as then the estimated values a of the amplitude imbalance and the phase of the optical coherent receiver are related to the imbalance of the optical coherent transmitter. At this time, the phase needs to take different values within a preset time duration to average out the influence of the optical coherent transmitter imbalance, so as to separate the imbalance coefficients of the optical coherent receiver and the optical coherent transmitter. At this time, the estimated value a of the amplitude imbalance of the optical coherent receiver is expressed as:

[0118]

[0119] It can be seen that the imbalance coefficient of the optical coherent receiver output by the second calculation unit 103 is consistent with the theoretical value.

[0120] For the second case, that is, the case where CMRR cannot be ignored.

[0121] It can be seen from Equation (10) that when CMRR cannot be ignored, CMRR will not only affect the phase imbalance of the optical coherent receiver, but also introduce a noise term. This noise term cannot be averaged by the rotation of the phase and a modulation unit needs to be used to remove the noise term.

[0122] When there is a modulation unit in the local oscillator path and the output of the modulation unit is zero, that is, E LO (t) = E1(t) = E2(t) = 0. At this time, the output signal of the optical coherent receiver can be expressed as:

[0123]

[0124]

[0125] Since the imbalance of the optical coherent receiver to be tested is the part related to the signals E1(t) and E2(t), the expression of the imbalance coefficient can be obtained from Equation (10):

[0126]

[0127]

[0128]

[0129] Among them, r1ρ1 represents the amplitude change of the I path, r2ρ2 represents the amplitude change of the Q path, ψ1 represents the phase change of the I path, and ψ2 represents the phase change of the Q path.

[0130] Therefore, the theoretical amplitude imbalance and phase imbalance can be expressed as:

[0131]

[0132] Phase imbalance=ψ2 - ψ1 (16)

[0134] Among them, Amplitude imbalance represents the theoretical amplitude imbalance, Phase imbalance represents the theoretical phase imbalance, r1ρ1 represents the amplitude change of the I channel, r2ρ2 represents the amplitude change of the Q channel, ψ1 represents the phase change of the I channel, and ψ2 represents the phase change of the Q channel.

[0135] Therefore, in actual estimation, it is necessary to use the power and correlation of S 01 (t), S 02 (t) to correct the deviation introduced by CMRR, which is expressed by the following formula (17):

[0136]

[0137]

[0138]

[0139] The above formula (17) assumes that compared with is a small quantity, or the DC component removed by the DC module (DC block). Its amplitude and phase imbalance can be calculated according to the corrected power and correlation values and the following formulas (18) and (19):

[0140]

[0141]

[0142] According to the calculated amplitude and phase imbalance, the quadrature component of the optical coherent receiver can be calibrated according to the direction of the in-phase component:

[0143]

[0144] Among them, a represents the amplitude imbalance, θ represents the phase imbalance, and S′2(t) represents the calibrated quadrature component of the optical coherent receiver.

[0145] As can be seen from the above principle, by using the computing device of the embodiments of the present application, the interaction between the imperfections of the optical coherent transmitter and the imperfections of the coherent receiver can be avoided, the amplitude imbalance and phase imbalance of the optical coherent receiver can be accurately calculated and calibrated, and it is not affected by the modulation format of the optical coherent transmitter signal and the imperfections of the optical coherent transmitter.

[0146] Figure 9 is a structural diagram of an example of the optical communication system of the embodiments of the present application. As Figure 9 shown, 95% of the light emitted by the laser is input into the optical modulator of the optical transmitter, and one output I-jQ of the IQ beam combining 2*2 coupler MMI of the optical modulator is used as the signal input of the signal path into the optical coherent receiver; 5% of the other light emitted by the laser is input into the optical phase shifter, and the optical signal output by the optical phase shifter is used as the signal of the local oscillator path into the optical coherent receiver after passing through the modulation unit; the signals output by the two BPDs of the optical coherent receiver are input into the calculation unit (including the first calculation unit and the second calculation unit) for calculation to obtain the amplitude imbalance and phase imbalance of the optical coherent receiver. The specific calculation process can refer to the previous records and will not be repeated here.

[0147] Among them, the optical transmitter is a single polarization state orthogonal transmitter, and its coupler output port I-jQ is used as the signal path input of the coherent optical receiver; a part of the light is split from the carrier laser port of the optical transmitter, passed through the optical phase shifter, and used as the carrier laser of the modulation unit; the modulation unit is a Mach-Zehnder (MZ) type modulator, which can output a non-all-zero constant amplitude signal with B[n]=1 and a all-zero signal with B[n]=0; the output of the modulation unit is used as the local oscillator path input of the optical coherent receiver; the optical coherent receiver to be measured includes a 90-degree mixer and a balanced detector; there is a DC removal device on the output side of the balanced detector; the two output signals of the coherent receiver are used as the input of the calculation unit.

[0148] After the modulation unit sends the signals of B[n]=1 and B[n]=0 respectively, the output signals of the optical coherent receiver with non-all-zero local oscillator path and the output signals of the optical coherent receiver with all-zero local oscillator path are obtained respectively, and then the power and related quantities are calculated to estimate the amplitude imbalance and phase imbalance. Calculate the imbalance coefficient of the optical coherent receiver according to formula (18) and formula (19), and compare it with the theoretical value in formula (16). For example, set a group of non-ideal parameters, such as the non-ideality of the response between the two BPDs is 10%, CMRR1 = 20%, CMRR2 = -20%. At the same time, there are also amplitude and phase non-idealities between the in-phase component and the quadrature component of the optical coherent transmitter.

[0149] Figure 10 is Figure 9Schematic diagram of the comparison results between the theoretical values and the monitored values of the phase imbalance and amplitude imbalance of the optical coherent receiver of the optical communication system shown. In the case where there are various device imperfections in both the optical coherent transmitter and the optical coherent receiver, the phase change of 0 to 2π of the phase shifter within a preset time period successfully separates the imbalances of the optical coherent transmitter and the optical coherent receiver. Using the computing device of the embodiment of the present application, the amplitude and phase imbalance parameters of the optical coherent receiver are accurately calculated, and the difference between the monitored value and the theoretical value is very small. If the phase of the phase shifter does not change within the preset time period, since the optical coherent receiver and the optical coherent transmitter use the same carrier laser, the imperfections of the optical coherent transmitter will be confused with the imbalance coefficient of the optical coherent receiver, resulting in the failure of estimating the amplitude and phase imbalances of the optical coherent receiver.

[0150] As can be seen from the above embodiments, by setting a phase shifter to cause the signal to undergo a phase change of 0 to 2π before entering the optical coherent receiver to be measured, and within the period of the phase change of 0 to 2π, the amplitude imbalance and phase imbalance of the optical coherent receiver to be measured are calculated according to the average power of the I-channel signal, the average power of the Q-channel signal, and the correlation quantity between the I-channel signal and the Q-channel signal. Thus, it is possible to avoid the interaction between the imperfections of the optical coherent transmitter and the imperfections of the coherent receiver, accurately calculate and calibrate the amplitude imbalance and phase imbalance of the optical coherent receiver, and be unaffected by the modulation format of the optical coherent transmitter signal and the imperfect factors of the optical coherent transmitter.

[0151] Embodiment 2

[0152] The embodiment of the present application also provides a calculation method and a calibration method for the imbalance of an optical coherent receiver, and this method corresponds to the calculation device and calibration device for the imbalance of the optical coherent receiver in Embodiment 1.

[0153] Figure 11 It is a schematic diagram of the calculation method for the imbalance of the optical coherent receiver in the embodiment of the present application. As Figure 11 shown, this method includes:

[0154] Step 1101: The phase shifter provided in the local oscillator path or the signal path of the optical coherent receiver to be measured performs at least one phase change of 0 to 2π within a preset time period, and the local oscillator path and the signal path share a laser as a light source;

[0155] Step 1102: According to the I-channel signal and the Q-channel signal output by the optical coherent receiver to be measured, calculate the average power of the I-channel signal, the average power of the Q-channel signal, and the correlation quantity between the I-channel signal and the Q-channel signal within the preset time period; and

[0156] Step 1103: Calculate the amplitude imbalance and phase imbalance of the optical coherent receiver under test according to the average power of the I-channel signal, the average power of the Q-channel signal, and the correlation quantity between the I-channel signal and the Q-channel signal within the preset duration.

[0157] Figure 12 is a schematic diagram of a method for calibrating the imbalance of an optical coherent receiver according to an embodiment of the present application. As Figure 12 shown, the method includes:

[0158] Step 1201: The phase shifter provided in the local oscillator path or the signal path of the input optical coherent receiver under test performs at least one phase change from 0 to 2π within the preset duration, and the local oscillator path and the signal path share a laser as a light source;

[0159] Step 1202: According to the I-channel signal and Q-channel signal output by the optical coherent receiver under test, calculate the average power of the I-channel signal, the average power of the Q-channel signal, and the correlation quantity between the I-channel signal and the Q-channel signal within the preset duration; and

[0160] Step 1203: Calculate the amplitude imbalance and phase imbalance of the optical coherent receiver under test according to the average power of the I-channel signal, the average power of the Q-channel signal, and the correlation quantity between the I-channel signal and the Q-channel signal within the preset duration; and

[0161] Step 1204: Calibrate the imbalance of the optical coherent receiver under test according to the calculated amplitude imbalance and phase imbalance of the optical coherent receiver under test.

[0162] Figure 11 and Figure 12 The specific implementation methods of each step in can refer to the relevant records in Embodiment 1, and will not be repeated here.

[0163] As can be seen from the above embodiments, by setting a phase shifter to make the signal undergo a phase change from 0 to 2π before entering the optical coherent receiver under test, and then within the period of the phase change from 0 to 2π, calculate the amplitude imbalance and phase imbalance of the optical coherent receiver under test according to the average power of the I-channel signal, the average power of the Q-channel signal, and the correlation quantity between the I-channel signal and the Q-channel signal. Thus, it is possible to avoid the interaction between the non-ideality of the optical coherent transmitter and the non-ideality of the coherent receiver, accurately calculate and calibrate the amplitude imbalance and phase imbalance of the optical coherent receiver, and is not affected by the modulation format of the optical coherent transmitter signal and the non-ideality factors of the optical coherent transmitter.

[0164] An embodiment of the present application also provides a computer-readable program, which, when executed in a computing device or a calibration device for optical coherent receiver imbalance, causes the computer to execute the optical coherent receiver imbalance calculation method or calibration method described in Embodiment 2 in the computing device or calibration device for optical coherent receiver imbalance.

[0165] An embodiment of the present application also provides a storage medium storing a computer-readable program, wherein the computer-readable program causes the computer to execute the optical coherent receiver imbalance calculation method or calibration method described in Embodiment 2 in a computing device or a calibration device for optical coherent receiver imbalance.

[0166] The calculation device for optical coherent receiver imbalance or the calculation method for optical coherent receiver imbalance executed in an optical receiver described in combination with the embodiments of the present application can be directly embodied as hardware, a software module executed by a processor, or a combination of both. For example, Figure 1 one or more of the functional block diagrams shown in and / or one or more combinations of the functional block diagrams can correspond to each software module of the computer program flow, and can also correspond to each hardware module. These software modules can respectively correspond to Figure 11 each of the steps shown. These hardware modules can be implemented by solidifying these software modules using a field-programmable gate array (FPGA).

[0167] The software module can be located in a RAM memory, a flash memory, a ROM memory, an EPROM memory, an EEPROM memory, a register, a hard disk, a removable disk, a CD-ROM, or any other form of storage medium known in the art. A storage medium can be coupled to the processor so that the processor can read information from the storage medium and write information to the storage medium; or the storage medium can be a component of the processor. The processor and the storage medium can be located in an ASIC. The software module can be stored in the memory of a mobile terminal or in a memory card insertable into the mobile terminal. For example, if the optical transmitter uses a larger-capacity MEGA-SIM card or a large-capacity flash memory device, the software module can be stored in the MEGA-SIM card or the large-capacity flash memory device.

[0168] Regarding Figure 1 one or more of the functional block diagrams described and / or one or more combinations of the functional block diagrams can be implemented as a general-purpose processor, a digital signal processor (DSP), an application-specific integrated circuit (ASIC), a field-programmable gate array (FPGA), or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, or any suitable combination thereof for performing the functions described in the present application. Regarding Figure 1One or more of the described functional block diagrams and / or one or more combinations of functional block diagrams can also be implemented as a combination of computing devices, e.g., a combination of a DSP and a microprocessor, multiple microprocessors, one or more microprocessors in communication combination with a DSP, or any other such configuration.

[0169] The present application has been described in conjunction with specific embodiments, but those skilled in the art should understand that these descriptions are exemplary and not limitations on the protection scope of the present application. Those skilled in the art can make various variations and modifications to the present application according to the spirit and principle of the present application, and these variations and modifications are also within the scope of the present application.

[0170] The embodiments of the present application also disclose the following appendices:

[0171] 1. A method for calculating the imbalance of an optical coherent receiver, the method comprising:

[0172] A phase shifter disposed in the local oscillator path or the signal path of the input optical coherent receiver to be measured performs at least one phase change from 0 to 2π within a preset time period, and the local oscillator path and the signal path share a laser as a light source;

[0173] According to the I-channel signal and the Q-channel signal output by the optical coherent receiver to be measured, calculate the average power of the I-channel signal, the average power of the Q-channel signal, and the correlation quantity between the I-channel signal and the Q-channel signal within the preset time period; and

[0174] According to the average power of the I-channel signal, the average power of the Q-channel signal, and the correlation quantity between the I-channel signal and the Q-channel signal within the preset time period, calculate the amplitude imbalance and the phase imbalance of the optical coherent receiver to be measured.

[0175] 2. The method according to appendix 1, wherein calculating the average power of the I-channel signal, the average power of the Q-channel signal, and the correlation quantity between the I-channel signal and the Q-channel signal within the preset time period according to the I-channel signal and the Q-channel signal output by the optical coherent receiver to be measured includes:

[0176] According to the first I-channel signal and the first Q-channel signal output by the optical coherent receiver to be measured when the modulation unit disposed in the local oscillator path outputs a non-all-zero signal, and the second I-channel signal and the second Q-channel signal output by the optical coherent receiver to be measured when the modulation unit outputs an all-zero signal, calculate the average power of the I-channel signal, the average power of the Q-channel signal, and the correlation quantity between the I-channel signal and the Q-channel signal within the preset time period.

[0177] 3. The method according to appendix 2, wherein

[0178] The modulation unit includes an optical modulator or an optical switch.

[0179] 4. The method according to Note 1, wherein

[0180] The optical coherent receiver to be measured is a polarization multiplexed optical coherent receiver, wherein

[0181] Calculating the average power of the I-channel signal, the average power of the Q-channel signal, and the correlation quantity between the I-channel signal and the Q-channel signal within the preset time period in the first polarization direction according to the I-channel signal and the Q-channel signal in the first polarization direction output by the optical coherent receiver to be measured, and calculating the average power of the I-channel signal, the average power of the Q-channel signal, and the correlation quantity between the I-channel signal and the Q-channel signal within the preset time period in the second polarization direction according to the I-channel signal and the Q-channel signal in the second polarization direction output by the optical coherent receiver to be measured;

[0182] Calculating the amplitude imbalance and phase imbalance in the first polarization direction according to the average power of the I-channel signal, the average power of the Q-channel signal, and the correlation quantity between the I-channel signal and the Q-channel signal within the preset time period in the first polarization direction, and calculating the amplitude imbalance and phase imbalance in the second polarization direction according to the average power of the I-channel signal, the average power of the Q-channel signal, and the correlation quantity between the I-channel signal and the Q-channel signal within the preset time period in the second polarization direction.

[0183] 5. The method according to Note 1, wherein

[0184] The signal input to the optical coherent receiver to be measured on the signal path is:

[0185] The output signal of the optical coherent transmitter, or

[0186] The split monitoring signal of the output signal of the optical coherent transmitter, or

[0187] The output signal of the I-jQ port of the optical coherent transmitter coupler, or

[0188] The output signal or the split monitoring signal of the output signal of the polarization multiplexed optical transmitter.

[0189] 6. The method according to Note 1, wherein

[0190] The signal input to the optical coherent receiver to be measured on the local oscillator path is:

[0191] The DC optical signal split from the laser or the optical signal after modulating the DC optical signal.

[0192] 7. A calibration method for the imbalance of an optical coherent receiver, the method comprising:

[0193] A phase shifter disposed in the local oscillator path or the signal path of the optical coherent receiver to be measured performs at least one phase change from 0 to 2π within a preset time period, and the local oscillator path and the signal path share a laser as a light source;

[0194] According to the I-channel signal and the Q-channel signal output by the optical coherent receiver to be measured, calculate the average power of the I-channel signal, the average power of the Q-channel signal, and the correlation quantity between the I-channel signal and the Q-channel signal within the preset time period; and

[0195] According to the average power of the I-channel signal, the average power of the Q-channel signal, and the correlation quantity between the I-channel signal and the Q-channel signal within the preset time period, calculate the amplitude imbalance and phase imbalance of the optical coherent receiver to be measured; and

[0196] According to the calculated amplitude imbalance and phase imbalance of the optical coherent receiver to be measured, calibrate the imbalance of the optical coherent receiver to be measured.

[0197] 8. The method according to appendix 7, wherein calibrating the imbalance of the optical coherent receiver to be measured according to the calculated amplitude imbalance and phase imbalance of the optical coherent receiver to be measured includes:

[0198] According to the calculated amplitude imbalance and phase imbalance of the optical coherent receiver to be measured and the I-channel signal and the Q-channel signal output by the optical coherent receiver to be measured, determine the calibrated I-channel signal or Q-channel signal.

Claims

1. A calculation device for optical coherent receiver imbalance, characterized in that The device includes: a phase shifter, which is arranged in the local oscillator path or the signal path of the optical coherent receiver to be measured. The phase shifter performs at least one phase change from 0 to 2π within a preset time period, and the local oscillator path and the signal path share a laser as the light source; a first calculation unit, which calculates the average power of the I-channel signal, the average power of the Q-channel signal, and the correlation quantity between the I-channel signal and the Q-channel signal within the preset time period according to the I-channel signal and the Q-channel signal output by the optical coherent receiver to be measured; and a second calculation unit, which calculates the amplitude imbalance and phase imbalance of the optical coherent receiver to be measured according to the average power of the I-channel signal, the average power of the Q-channel signal, and the correlation quantity between the I-channel signal and the Q-channel signal within the preset time period.

2. The device according to claim 1, characterized in that, The device further includes: a modulation unit, which is arranged in the local oscillator path and is used to output a non-all-zero signal or an all-zero signal.

3. The device according to claim 2, wherein the first calculation unit calculates the average power of the I-channel signal, the average power of the Q-channel signal, and the correlation quantity between the I-channel signal and the Q-channel signal within the preset time period according to the first I-channel signal and the first Q-channel signal output by the optical coherent receiver to be measured when the modulation unit outputs a non-all-zero signal, and the second I-channel signal and the second Q-channel signal output by the optical coherent receiver to be measured when the modulation unit outputs an all-zero signal.

4. The device according to claim 2, wherein the modulation unit includes an optical modulator or an optical switch.

5. The device according to claim 1, wherein the optical coherent receiver to be measured is a polarization multiplexing optical coherent receiver, the first calculation unit calculates the average power of the I-channel signal, the average power of the Q-channel signal, and the correlation quantity between the I-channel signal and the Q-channel signal within the preset time period in the first polarization direction according to the I-channel signal and the Q-channel signal in the first polarization direction output by the optical coherent receiver to be measured, and calculates the average power of the I-channel signal, the average power of the Q-channel signal, and the correlation quantity between the I-channel signal and the Q-channel signal within the preset time period in the second polarization direction according to the I-channel signal and the Q-channel signal in the second polarization direction output by the optical coherent receiver to be measured, the second calculation unit calculates the amplitude imbalance and phase imbalance in the first polarization direction according to the average power of the I-channel signal, the average power of the Q-channel signal, and the correlation quantity between the I-channel signal and the Q-channel signal within the preset time period in the first polarization direction, and calculates the amplitude imbalance and phase imbalance in the second polarization direction according to the average power of the I-channel signal, the average power of the Q-channel signal, and the correlation quantity between the I-channel signal and the Q-channel signal within the preset time period in the second polarization direction.

6. The device according to claim 1, wherein the signal input to the optical coherent receiver to be measured in the signal path is: the output signal of an optical coherent transmitter, or a split monitoring signal of the output signal of an optical coherent transmitter, or The output signal of the I - jQ port of the optical coherent transmitter coupler, or The output signal of the polarization multiplexed optical transmitter or the split monitoring signal of the output signal.

7. The device according to claim 1, wherein The signal input from the local oscillator path to the optical coherent receiver to be measured is: The DC optical signal split from the laser or the optical signal modulated from the DC optical signal.

8. An optical coherent receiver imbalance calibration device, characterized in that The device includes: A phase shifter, which is arranged in the local oscillator path or the signal path input to the optical coherent receiver to be measured. The phase shifter performs at least one phase change from 0 to 2π within a preset time period. The local oscillator path and the signal path share a laser as the light source; A first calculation unit, which calculates the average power of the I - path signal, the average power of the Q - path signal, and the correlation quantity between the I - path signal and the Q - path signal within the preset time period according to the I - path signal and the Q - path signal output by the optical coherent receiver to be measured; A second calculation unit, which calculates the amplitude imbalance and phase imbalance of the optical coherent receiver to be measured according to the average power of the I - path signal, the average power of the Q - path signal, and the correlation quantity between the I - path signal and the Q - path signal within the preset time period; and A calibration unit, which calibrates the imbalance of the optical coherent receiver according to the calculated amplitude imbalance and phase imbalance of the optical coherent receiver to be measured.

9. The device according to claim 8, wherein The calibration unit determines the calibrated I - path signal or Q - path signal according to the calculated amplitude imbalance and phase imbalance of the optical coherent receiver to be measured and the I - path signal and the Q - path signal output by the optical coherent receiver to be measured.

10. An optical communication system, characterized in that, The system includes an optical coherent transmitter, an optical coherent receiver, and a calculation device for the imbalance of the optical coherent receiver according to claim 1.

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