Apparatus and method for estimating polarization skew

Abstract

To provide an estimation device and a method of polarization skew.SOLUTION: The method includes the steps of: acquiring multiple coefficients of an adaptive equalizer of the reception end; the coefficient of the adaptive equalizer including at least the following component; i.e., a polarization skew sum of the polarization skew at the receiving end of the sending end, and calculating the polarization skew at the transmission end and the polarization skew at the reception end based on the multiple coefficients of the adaptive equalizer.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present invention relates to communication technology, and more particularly to an apparatus and method for estimating polarization skew. [Background technology]

[0002] In a coherent optical communication system based on dual polarization modulation, the transmitting end and the receiving end each have four channels, which correspond to the in-phase and quadrature paths of the two polarization states of the transmitting end and the receiving end. Due to differences in the performance of components in each channel, each channel will produce different skews for the signal, which may result in skews between the in-phase and quadrature paths in the polarization states (hereinafter referred to as in-phase quadrature skew, represented by IQ skew) and skews between the polarization states (hereinafter referred to as polarization skew, represented by polarization skew).

[0003] Generally speaking, the existence of polarization skew can affect system performance. For example, in a system that employs polarization interleave coding, the polarization skew of the transmitter and receiver can affect the signal performance after de-interleaving at the receiving end.

[0004] For adaptive equalizers of signals with high baud rates and high-order modulation formats, the coefficients of the constant modulus algorithm (CMA) are usually updated by interpolating the Quadrature Phase Shift Keying (QPSK) pilot (QPSK-pilot) signal, and the polarization skew in the transmitter may cause misalignment of the QPSK-pilot symbols in the two polarization states, which may affect the calculation of the equalizer coefficients. The polarization skew can be compensated by a digital signal processing (DSP) algorithm, but the compensation of a relatively large polarization skew may increase the complexity of the DSP implementation.

[0005] Non-patent literature [1]: M. Paskov et al., “Blind Equalization of Receiver In-Phase / Quadrature Skew…”, Photon. Technol. Lett., Vol. 25, no. 24, p. 2446 (2013) [2] RR Muller et al., “Blind Receiver Skew Compensation and Estimation…”, J. Lightwave Technol., Vol. 33, no. 7, p. 1315 (2015) Non-patent document [3]: S Savory, “Digital filters for coherent optical receivers”, Optics Express, Vol. 16, No. 2, pp 804 (2008) Summary of the Invention [Problem to be solved by the invention]

[0006] In view of the above technical problems, an object of the present invention is to provide an apparatus and method for estimating polarization skew that can estimate polarization skew accurately and effectively at a relatively low cost. [Means for solving the problem]

[0007] According to a first aspect of an embodiment of the present invention, there is provided an apparatus for estimating a polarization skew, the apparatus comprising: A coefficient acquisition unit for acquiring a plurality of coefficients of an adaptive equalizer at a receiving end, in which the coefficients of the adaptive equalizer include at least the following components: a polarization skew at a transmitting end and a polarization skew at a receiving end; and A skew calculation unit is included for calculating a polarization skew of the transmitting end and a polarization skew of the receiving end based on a plurality of coefficients of the adaptive equalizer.

[0008] According to a second aspect of an embodiment of the present invention, there is provided a method for estimating polarization skew, the method comprising: Obtain a plurality of coefficients of an adaptive equalizer at a receiving end, in which the coefficients of the adaptive equalizer include at least the following components: a polarization skew at a transmitting end and a polarization skew at a receiving end; and The method further includes calculating a polarization skew at the transmitting end and a polarization skew at the receiving end based on a plurality of coefficients of the adaptive equalizer.

[0009] The beneficial effects of the embodiment of the present invention are as follows: the sum of the polarization skew at the transmitting end and the polarization skew at the receiving end are estimated by the coefficients of the adaptive equalizer, and the polarization skew can be accurately and effectively estimated without using expensive measuring equipment. In addition, the cost is relatively low, and the present invention can be applied to calibration in the production stage and real-time monitoring of the transmitter and receiver in an actual optical transmission system. [Brief description of the drawings]

[0010] [Figure 1] FIG. 1 illustrates a dual-polarized optical transmitter according to an embodiment of the present invention. [Diagram 2] FIG. 1 is a diagram showing a dual-polarized optical coherent receiver according to an embodiment of the present invention. [Diagram 3] FIG. 4 is a diagram illustrating a method for estimating a polarization skew in the first embodiment of the present invention. [Figure 4] FIG. 2 is a diagram showing an adaptive equalizer with a 4×4 structure in the first embodiment of the present invention. [Diagram 5] FIG. 2 is a diagram showing an adaptive equalizer with a 4×2 structure in the first embodiment of the present invention. [Figure 6] FIG. 2 is a diagram showing an adaptive equalizer with a 2×2 structure in the first embodiment of the present invention. [Figure 7] FIG. 11 is a diagram illustrating a polarization skew estimation device according to a second embodiment of the present invention. [Figure 8] FIG. 11 is a diagram illustrating a receiver according to a third embodiment of the present invention. [Figure 9] FIG. 11 is a diagram illustrating a polarization skew estimation device according to a third embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

[0012] Fig. 1 is a diagram showing a dual-polarized optical transmitter in an embodiment of the present invention, and as shown in Fig. 1, the transmitting end has four channels, which respectively correspond to in-phase (I) and quadrature (Q) paths of two polarization states HV, and are represented as HI, HQ, VI and VQ. As shown in Fig. 1, the transmitting end further includes a digital-to-analog converter (DAC), a driver, a laser diode (LD), a Mach-Zehnder modulator (MZM), a phase modulator (PM), etc.

[0013] 2 is a diagram showing a dual-polarized optical coherent receiver in an embodiment of the present invention, and as shown in FIG. 2, the receiving end also has four channels, which correspond to the in-phase (i) and quadrature (q) paths of two polarization states xy, respectively, and are represented as xi, xq, yi, and yq. As shown in FIG. 2, the receiving end further includes an analog-to-digital converter (ADC), a frequency mixer (Hybrid), a local oscillator (LO), a phase demodulator (PD), etc.

[0014] As shown in Fig. 1 and Fig. 2, the skew in the in-phase and quadrature paths in the H polarization state at the transmitting end is τ hi and τ hq and the skew in the in-phase and quadrature paths for the V polarization state is τ vi and τ vq Similarly, the skew of the four channels in the x and y polarization states at the receiving end is τ xi , τ xq , τ yi and τ yq In this case, the polarization skew τ xy,T and the polarization skew τ at the receiving end xy,R may be defined as follows:

number

[0015] The optical transmitter and receiver shown in Figures 1 and 2 constitute a back-to-back system, such as a multiple-input-multiple output (MIMO) system including four input paths and four output paths, whose losses can be compensated for by an adaptive equalizer at the receiving end, such as a 4x4 structure.

[0016] The inventor has found that the coefficients of the adaptive equalizer at the receiving end include at least the following components, namely, the polarization skew at the transmitting end and the polarization skew at the receiving end, and thus the polarization skew at the transmitting end τ xy,T and the polarization skew τ at the receiving end xy,R Hereinafter, an embodiment of the present invention will be described in detail. EXAMPLES

[0017] An embodiment of the present invention provides a method for estimating polarization skew. Figure 3 is a diagram showing the method for estimating polarization skew in an embodiment of the present invention. As shown in Figure 3, the method includes the following steps:

[0018] Step 301: obtain a plurality of coefficients of an adaptive equalizer at a receiving end, in which the coefficients of the adaptive equalizer include at least the following components: a polarization skew of a transmitting end plus a polarization skew of a receiving end; and Step 302: Calculate the polarization skew of the transmitting end and the polarization skew of the receiving end according to a plurality of coefficients of the adaptive equalizer.

[0019] In this embodiment, an adaptive equalizer may be configured in the DSP of the receiving end. For example, the adaptive equalizer for polarization skew compensation in the embodiment of the present invention may be located before the frequency offset compensator and the phase noise compensator, and the coefficient of the adaptive equalizer may be calculated by using a constant modulus algorithm (CMA), a least mean square (LMS) algorithm based on decision feedback, etc. After the adaptive equalizer converges, the coefficient can be used to estimate the polarization skew. For the specific content of the DSP and the adaptive equalizer of the receiving end, reference may be made to the prior art.

[0020] In this embodiment, the structure of the adaptive equalizer can be determined according to a plurality of coefficients of the adaptive equalizer, for example, the adaptive equalizer can be a 4×4 structure, a 4×2 structure, or a 2×2 structure. For example, if the number of coefficients obtained after the adaptive equalizer converges is 16, the adaptive equalizer can be determined to be a 4×4 structure, and if the number of coefficients obtained after the adaptive equalizer converges is 8, the adaptive equalizer can be determined to be a 4×2 structure. However, the present invention is not limited thereto, and the structure of the adaptive equalizer can be determined in other ways.

[0021] In one embodiment, the coefficients of the adaptive equalizer may further include the following components: in-phase quadrature skew in the x polarization state of the receiving end, and / or in-phase quadrature skew in the y polarization state of the receiving end. Also, by calculating multiple coefficients of the adaptive equalizer, the components of the in-phase quadrature skew in the x polarization state of the receiving end and the in-phase quadrature skew in the y polarization state of the receiving end can be removed, and the components of the polarization skew of the transmitting end and the polarization skew of the receiving end can be left.

[0022] In one embodiment, the diagonal element parameters φ are calculated by calculating some of the coefficients of the adaptive equalizer. + (f) is obtained, and other coefficients of the adaptive equalizer are calculated to obtain the subdiagonal element parameters φ - (f) is obtained, and the diagonal element parameters φ + (f) and the subdiagonal element parameters φ - (f) based on the polarization skew τ xy,T and the polarization skew τ of the receiving end xy,R Calculate the sum and difference of and τ xy,T and τ xy,R Based on the sum and difference of τ xy,T and τ xy,R It is possible to calculate

[0023] For example, τ xy,T and τ xy,R The sum and difference can be calculated by the following formula:

[0024] If the two polarization states output by the adaptive equalizer are not swapped,

number

[0025] If the two polarization states output by the adaptive equalizer are swapped,

number

[0026] where, slope(·) is a function for calculating the slope, f0>0, and f=n / N*fs, where N is a positive integer indicating the number of taps of the adaptive equalizer, and n is an integer greater than or equal to -N+ceil(N / 2) and less than or equal to ceil(N / 2)-1, where ceil(·) is a round-up function, and fs is the sampling rate of the input signal of the adaptive equalizer.

[0027] As a result, the polarization skew τ at the transmitting end is calculated by the coefficient of the adaptive equalizer. xy,T and the polarization skew τ at the receiving end xy,R Estimate τ xy,T and τ xy,R The signal at the transmitting end and / or the receiving end can be calibrated based on the above. Compared with the conventional compensation by DSP, the embodiment of the present invention not only does not require expensive measuring equipment and has a relatively low cost, but also can be applied to calibration at the production stage and real-time monitoring of the transceiver in the actual optical transmission system.

[0028] Hereinafter, an embodiment of the present invention will be described using a 4×4 structure as an example.

[0029] 4 is a diagram showing an adaptive equalizer with a 4×4 structure in an embodiment of the present invention. As shown in FIG. 4, in the time domain, the coefficients of each sub-filter are all real numbers, and in the frequency domain, the frequency response of each sub-filter contains information about the skew of the transmitter and receiver.

[0030] For example, in a back-to-back coherent optical communication system, there is usually a frequency offset between the local oscillator laser and the transmitting end laser. Then, the H xi-xi for, (outside 1) TIFF0007622931000004.tif12127 components, namely, the polarization skew of the transmitter and receiver and the in-phase and quadrature skew of the polarization state of the receiver x, respectively, τ xy,T , τ xy,R and τ R,x Among them, τ R,x =(τ xq -τ xi ) / 2, and similarly, τ R,y =(τ yq -τ yi ) / 2.

[0031] For example, by calculating some of the coefficients of the adaptive equalizer (as shown by 401 in FIG. 4), the diagonal element parameters φ + (f) and calculate the other part of the coefficients of the adaptive equalizer (as shown by 402 in FIG. 4) to obtain the subdiagonal element parameters φ - (f) can be obtained. In such a case, the diagonal element parameters and the sub-diagonal element parameters can be expressed as follows:

number

[0032] Among them, arg(·) indicates the operation to obtain the argument of a point, and unwrap(·) indicates the operation to calibrate the radian phase angle. For example, when the hop of the adjacent phase angle is π or more, the current phase angle is calibrated after adding an integer multiple of ±2π, and (·) * denotes the conjugate operation and H is the frequency response of the adaptive equalizer, i.e. the Fourier transform of the coefficients of the adaptive equalizer.

[0033] Then, use the following formula to calculate τ xy,T and τ xy,R The sum and difference can be calculated.

[0034] If the two polarization states output by the adaptive equalizer are not swapped,

number

[0035] If the two polarization states output by the adaptive equalizer are swapped,

number

[0036] Among them, the slope(·) function is used to calculate the slope, where the frequency range for calculating the slope is [-f0,f0] (f0>0). In order to estimate the polarization skew accurately, an appropriate f0 may be selected, for example, f0=fs / 4, where fs is the sampling rate of the input signal of the equalizer.

[0037] Hereinafter, an embodiment of the present invention will be described using a 4×2 structure as an example.

[0038] 5 is a diagram illustrating an adaptive equalizer with a 4×2 structure in an embodiment of the present invention. As shown in FIG. 5, in the time domain, the coefficients of each sub-filter are all real numbers, and in the frequency domain, the frequency response of each sub-filter contains information about the skew of the transmitter and receiver.

[0039] Similar to the 4×4 structure, when the adaptive equalizer has a 4×2 structure, for example, the diagonal element parameters φ are calculated by calculating some of the coefficients of the adaptive equalizer (as shown in 501 in FIG. 5 ). + (f) and calculate the other part of the coefficients of the adaptive equalizer (as shown in 502 in FIG. 5 ) to obtain the subdiagonal element parameters φ - (f) can be obtained. In such a case, the diagonal element parameters and the sub-diagonal element parameters can be expressed as follows:

[0040]

number

[0041] Among them, arg(·) indicates the operation to calculate the argument of a point, and (·) * denotes the conjugate operation and H is the frequency response of the adaptive equalizer, i.e. the Fourier transform of the coefficients of the adaptive equalizer.

[0042] Then, we use the following formula to calculate τ xy,T and τ xy,R The sum and difference can be calculated.

[0043] If the two polarization states output by the adaptive equalizer are not swapped,

number

[0044] If the two polarization states output by the adaptive equalizer are swapped,

number

[0045] Among them, the slope(·) function is used to calculate the slope, where the frequency range for calculating the slope is [-f0,f0] (f0>0). In order to estimate the polarization skew accurately, an appropriate f0 may be selected, for example, f0=fs / 4, where fs is the sampling rate of the input signal of the equalizer.

[0046] An embodiment of the present invention will be described below using a 2×2 structure as an example.

[0047] 6 is a diagram illustrating an adaptive equalizer with a 2×2 structure in an embodiment of the present invention. As shown in FIG. 6, in the time domain, the coefficients of each sub-filter are all real numbers, and in the frequency domain, the frequency response of each sub-filter contains information about the skew of the transmitter and receiver.

[0048] When the adaptive equalizer has a 2×2 structure, similarly to the 4×4 structure, the diagonal element parameters φ are calculated by, for example, calculating some of the coefficients of the adaptive equalizer (as shown by 601 in FIG. 6 ). + (f) and calculate the other part of the coefficients of the adaptive equalizer (as shown by 602 in FIG. 6 ) to obtain the subdiagonal element parameters φ - (f) can be obtained. In such a case, the diagonal element parameters and the sub-diagonal element parameters can be expressed as follows:

number

[0049] Among them, arg(·) represents the operation to find the argument of a point, and (·) * denotes the conjugate operation and H is the frequency response of the adaptive equalizer, i.e. the Fourier transform of the coefficients of the adaptive equalizer.

[0050] Then, use the following formula to calculate τ xy,T and τ xy,R The sum and difference can be calculated.

[0051] If the two polarization states output by the adaptive equalizer are not swapped,

number

[0052] If the two polarization states output by the adaptive equalizer are swapped,

number

[0053] Among them, the slope(·) function is used to calculate the slope, where the frequency range for calculating the slope is [-f0,f0] (f0>0). In order to estimate the polarization skew accurately, an appropriate f0 may be selected, for example, f0=fs / 4, where fs is the sampling rate of the input signal of the equalizer.

[0054] Although the above description has been given using the 4×4, 4×2, and 2×2 structures of the adaptive equalizer as examples, the present invention is not limited to these and can be extended to other structures, for example. xy,T and τ xy,R Calculate the sum and difference of τ xy,T and τ xy,R However, the present invention is not limited to this, and the coefficients of the adaptive equalizer may be appropriately modified, and the embodiment of the present invention is not limited to a specific calculation method.

[0055] In one embodiment, after changing the polarization state of the received signal, multiple coefficients of an adaptive equalizer at the receiving end may be obtained multiple times; and processing (e.g., filtering, averaging, etc.) may be performed on the multiple coefficients of the adaptive equalizer.

[0056] For example, during the monitoring process, the polarization states of the transmitter and receiver may be aligned or rotated with a difference of 90 degrees. In these two cases, the sub-diagonal elements (e.g., as shown by 402 in FIG. 4) or the sub-diagonal elements (e.g., as shown by 401 in FIG. 4) of the above equalizers have zero sub-filters, and therefore cannot provide sufficient monitoring information.

[0057] Therefore, in order to improve the accuracy of the monitoring result, the polarization state of the received signal can be changed multiple times (or the monitoring can be performed again after the polarization state of the received signal is changed) to perform monitoring in different polarization states. Then, after removing possible mutation monitoring values ​​from the monitoring values ​​(which may encounter the above two types of unsupported polarization states), the average monitoring value can be taken as the polarization skew of the transmitter and receiver.

[0058] It should be noted that the above drawings are merely illustrative of the embodiments of the present invention, and the present invention is not limited thereto. For example, the order of steps may be adjusted, or some steps may be added or removed. In addition, those skilled in the art may make appropriate modifications based on the above contents, and the present invention is not limited to the description of the above drawings.

[0059] In addition, although only each step or process related to the present invention has been described above, the present invention is not limited thereto. The polarization skew estimation method may include other steps or processes, and the specific contents of such steps or processes can be referred to the prior art. In addition, although the above formulas have been used as examples to exemplify how to perform calculations in the embodiments of the present invention, the present invention is not limited to these formulas, and these formulas may be appropriately modified, and all such modified implementation methods fall within the scope of the embodiments of the present invention.

[0060] As can be seen from the above embodiments, the polarization skew at the transmitting end and the polarization skew at the receiving end can be estimated by the coefficients of the adaptive equalizer, and the polarization skew can be accurately and effectively estimated without using expensive measuring equipment. In addition, the cost is relatively low, and the present invention can be applied to calibration in the production stage and real-time monitoring of transmitters and receivers in actual optical transmission systems. EXAMPLES

[0061] An embodiment of the present invention provides a polarization skew estimation device, which may be disposed in a receiver or may be disposed separately from the receiver. The embodiment of the present invention corresponds to the estimation method in the first embodiment, and the description of the same content will be omitted.

[0062] 7 is a diagram illustrating a polarization skew estimating apparatus according to an embodiment of the present invention. As shown in FIG 7, the polarization skew estimating apparatus 700 includes:

[0063] A coefficient acquisition unit 701: acquires a plurality of coefficients of an adaptive equalizer at a receiving end, in which the coefficients of the adaptive equalizer include at least the following components: a polarization skew sum of a transmission end and a polarization skew of a receiving end; and A skew calculation unit 702: calculates the polarization skew of the transmitting end and the polarization skew of the receiving end according to multiple coefficients of the adaptive equalizer.

[0064] As shown in FIG. 7, the apparatus 700 may further include:

[0065] A structure determining unit 703: determining a structure of the adaptive equalizer based on a plurality of coefficients of the adaptive equalizer.

[0066] In one embodiment, the coefficients of the adaptive equalizer may further include the following components: in-phase quadrature skew of the x polarization state at the receiving end, and / or in-phase quadrature skew of the y polarization state at the receiving end.

[0067] The skew calculation unit 702 can further calculate multiple coefficients of the adaptive equalizer to remove the in-phase quadrature skew components of the x polarization state of the receiving end and the in-phase quadrature skew components of the y polarization state of the receiving end, leaving the polarization skew components of the transmitting end and the polarization skew components of the receiving end.

[0068] In one embodiment, the skew calculation unit 702 calculates some of the coefficients of the adaptive equalizer to obtain a diagonal element parameter φ + (f) is obtained, and other coefficients of the adaptive equalizer are calculated to obtain the subdiagonal element parameters φ - (f) is obtained, and the diagonal element parameters φ + (f) and the subdiagonal element parameters φ - (f) based on the polarization skew τ xy,T and the polarization skew τ of the receiving end xy,R Calculate the sum and difference of τ xy,T and τ xy,R Based on the sum and difference of xy,T and τ xy,R may be configured to calculate

[0069] In one embodiment, τ xy,T and τ xy,R The following formulas may be used to calculate the sum and difference:

[0070] If the two polarization states output by the adaptive equalizer are not swapped,

number

[0071] If the two polarization states output by the adaptive equalizer are swapped,

number

[0072] where, slope(·) is a function for calculating the slope, f0>0, and f=n / N*fs, where N is a positive integer indicating the number of taps of the adaptive equalizer, and n is an integer greater than or equal to -N+ceil(N / 2) and less than or equal to ceil(N / 2)-1, where ceil(·) is a round-up function, and fs is the sampling rate of the input signal of the adaptive equalizer.

[0073] For example, when the adaptive equalizer has a 4×4 structure, the diagonal element parameters and the sub-diagonal element parameters can be expressed as follows:

number

[0074] Among them, arg(·) is the operation to find the argument of a point, unwrap(·) is the operation to correct the radian phase angle, and (·) * denotes the conjugate operation and H is the frequency response of the adaptive equalizer, i.e. the Fourier transform of the coefficients of the adaptive equalizer.

[0075] For example, when the adaptive equalizer has a 4×2 structure, the diagonal element parameters and the sub-diagonal element parameters can be expressed as follows:

number

[0076] Among them, arg(·) represents the operation to calculate the argument of a point, and (·) * denotes the conjugate operation and H is the frequency response of the adaptive equalizer, i.e. the Fourier transform of the coefficients of the adaptive equalizer.

[0077] Furthermore, for example, when the adaptive equalizer has a 2×2 structure, the diagonal element parameters and the sub-diagonal element parameters can be expressed as follows:

number

[0078] Among them, arg(·) indicates the operation to find the argument of a point, and (·) * denotes the conjugate operation and H is the frequency response of the adaptive equalizer, i.e. the Fourier transform of the coefficients of the adaptive equalizer.

[0079] In one embodiment, the coefficient acquisition unit 701 may be further configured to acquire multiple coefficients of an adaptive equalizer at the receiving end multiple times after the polarization state of the received signal is changed; and perform processing on the multiple coefficients of the adaptive equalizer.

[0080] Although only the components related to the present invention have been described above, the present invention is not limited thereto. The polarization skew estimation device 700 may further include other components or modules, and the specific contents of these components or modules can be found in the prior art.

[0081] As can be seen from the above embodiments, the sum of the polarization skew at the transmitting end and the polarization skew at the receiving end can be estimated by the coefficients of the adaptive equalizer, and the polarization skew can be accurately and effectively estimated without using expensive measuring equipment. In addition, the cost is relatively low, and the method can be applied to calibration in the production stage and real-time monitoring of transmitters and receivers in actual optical transmission systems. EXAMPLES

[0082] An embodiment of the present invention provides a receiver, and the receiver may include the polarization skew estimation device 700 described in the second embodiment. In the embodiment of the present invention, the same contents as those in the first and second embodiments are omitted. In the following description, an optical receiver in an optical communication system is taken as an example, but the present invention is not limited thereto.

[0083] 8 is a diagram showing a receiver in an embodiment of the present invention, and the receiver will be further described by taking dual polarization states as an example. As shown in FIG. 8, the receiver 800 includes a local oscillator laser 810, an optical frequency mixer 801, photoelectric detectors (O / E) 802, 804, 806, 808, analog-to-digital converters (ADC) 803, 805, 807, 809, and a digital signal processor 811.

[0084] A local oscillator laser 810 provides a local light source, and an optical signal is converted into a baseband signal of one polarization state through an optical frequency mixer 801, photoelectric detectors (O / E) 802, 804, and analog-to-digital converters (ADC) 803, 805, and the optical signal is converted into a baseband signal of another polarization state through an optical frequency mixer 801, photoelectric detectors (O / E) 806, 808, and analog-to-digital converters (ADC) 807, 809. Note that the specific process is similar to that of the conventional technology, and therefore a detailed description thereof will be omitted here.

[0085] The digital signal processor 811 may include an adaptive equalizer (not shown in FIG. 8). As shown in FIG. 8, the receiver 800 may further include the polarization skew estimation device 700 according to the embodiment of the present invention. This allows the embodiment of the present invention to be applied to real-time monitoring of a receiver in an actual optical transmission system.

[0086] Moreover, the receiver 800 may further include a dispersion compensator, etc. (not shown in FIG. 8). When the frequency difference and phase noise affect the estimation of the linear crosstalk, the receiver 800 may further include a frequency difference compensator and a phase noise compensator (not shown in FIG. 8). That is, the receiver 800 may further include each component such as a dispersion compensator, a frequency difference compensator, a phase noise compensator, etc., but the present invention is not limited thereto.

[0087] It should be noted that Fig. 8 is for illustrative purposes only and the present invention is not limited thereto. Receiver 800 does not need to include all of the components shown in Fig. 8. Receiver 800 may further include components not shown in Fig. 8, but reference can be made to the prior art for such components.

[0088] In one embodiment, the polarization skew estimator 700 of the embodiment of the present invention may be located independently of the receiver 800. The polarization skew estimator may also adopt the architecture of a general-purpose computer, so that the embodiment of the present invention may be applied to production-stage calibration.

[0089] 9 is a block diagram of a polarization skew estimation device according to an embodiment of the present invention. As shown in FIG. 9, the polarization skew estimation device 900 may include a processor 910 (e.g., a central processing unit CPU) and a memory 920, which is connected to the processor 910. The memory 920 can store various data, and can further store a program 921 for information processing, and can execute the program 921 under the control of the processor 910.

[0090] For example, the processor 910 may be configured to execute a program to realize the polarization skew estimation method described in the first embodiment. For example, the processor 910 may be configured to perform the following control: obtain a plurality of coefficients of an adaptive equalizer at a receiving end, in which the coefficients of the adaptive equalizer include at least the following components: a sum of the polarization skew at a transmitting end and the polarization skew at a receiving end; and calculate the polarization skew at the transmitting end and the polarization skew at the receiving end based on the plurality of coefficients of the adaptive equalizer.

[0091] As shown in Fig. 9, the polarization skew estimation device 900 may further include an input / output (I / O) device 930, a display 940, etc., among which the functions of these components are similar to those of the conventional technology, and therefore detailed description thereof will be omitted here. Note that the polarization skew estimation device 900 does not need to include all the components shown in Fig. 9. Furthermore, the polarization skew estimation device 900 may further include components not shown in Fig. 9, and in this regard, reference can be made to the conventional technology.

[0092] In addition, the apparatus, method, etc. according to the embodiments of the present invention may be realized by software, hardware, or a combination of hardware and software. The present invention also relates to such a computer readable program, i.e., the program, when executed by a logic component, can cause the logic component to realize the above-mentioned apparatus or component, or cause the logic component to realize the above-mentioned method or steps thereof. Furthermore, the present invention also relates to a storage medium, such as a hard disk, a magnetic disk, an optical disk, a DVD, a flash memory, etc., storing the above-mentioned program.

[0093] Although the preferred embodiment of the present invention has been described above, the present invention is not limited to this embodiment, and any modification to the present invention falls within the technical scope of the present invention as long as it does not depart from the spirit of the present invention.

Claims

1. An apparatus for estimating polarization skew, comprising: A coefficient acquisition unit for acquiring a plurality of coefficients of an adaptive equalizer at a receiving end, the coefficients of the adaptive equalizer including at least a component of polarization skew at a transmitting end and a component of polarization skew at a receiving end; and A skew calculation unit is provided for calculating a polarization skew at the transmitting end and a polarization skew at the receiving end according to a plurality of coefficients of the adaptive equalizer; The skew calculation unit includes: Obtaining diagonal element parameters φ + (f) by calculating a part of coefficients of the adaptive equalizer, and obtaining subdiagonal element parameters φ − (f) by calculating another part of coefficients of the adaptive equalizer; Calculate the sum and difference of the polarization skew τ xy,T at the transmitting end and the polarization skew τ xy,R at the receiving end based on the diagonal element parameters φ + (f) and the sub-diagonal element parameters φ − (f); and The apparatus is configured to calculate τ xy,T and τ xy,R based on the sum and difference of τ xy,T and τ xy,R .

2. 2. The apparatus of claim 1, The apparatus further includes a structure determination unit for determining a structure of the adaptive equalizer based on a plurality of coefficients of the adaptive equalizer.

3. 2. The apparatus of claim 1, The coefficient obtaining unit further comprises: Obtaining a plurality of coefficients of the adaptive equalizer at the receiving end a plurality of times after changing the polarization state of the received signal; and An apparatus configured to perform operations on a plurality of coefficients of the adaptive equalizer.

4. 1. A method for estimating polarization skew, comprising: Obtaining a plurality of coefficients of an adaptive equalizer at a receiving end, the coefficients of the adaptive equalizer including at least a component of a polarization skew at a transmitting end and a component of a polarization skew at a receiving end; and Calculating a polarization skew at the transmitting end and a polarization skew at the receiving end based on a plurality of coefficients of the adaptive equalizer; Calculating a polarization skew at the transmitting end and a polarization skew at the receiving end based on a plurality of coefficients of the adaptive equalizer includes: Obtaining diagonal element parameters φ + (f) by calculating a part of coefficients of the adaptive equalizer, and obtaining subdiagonal element parameters φ − (f) by calculating another part of coefficients of the adaptive equalizer; Calculate the sum and difference of the polarization skew τ xy,T at the transmitting end and the polarization skew τ xy,R at the receiving end based on the diagonal element parameters φ + (f) and the sub-diagonal element parameters φ − (f); and A method for calculating τ xy,T and τ xy,R based on the sum and difference of τ xy,T and τ xy,R .

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