Optical module, method and system for calculating pre-distortion filter coefficients

Abstract

The optical module, pre-distortion filter coefficient calculation method and system, and circuit board provided by the present application; an optical transmission component, electrically connected to the circuit board and used for transmitting an optical signal; wherein, a DSP chip is arranged on the circuit board, and a filter is included in the DSP chip, and the filter is electrically connected to the optical transmission component and used for pre-distorting the electrical signal for driving the optical transmission component to emit an optical signal and then transmitting the pre-distorted electrical signal to the optical transmission component to compensate for the damage generated when the optical transmission component modulates to generate an optical signal. The optical module, pre-distortion filter coefficient calculation method and system provided by the present application pre-distort the electrical signal for driving the optical transmission component to emit an optical signal through a filter, and perform electrical signal compensation in advance to compensate for the damage generated when modulating the signal caused by improving the power and rate of the electrical signal.

Description

Technical Field

[0001] This application relates to the field of optical communication technologies, and in particular, to an optical module, a method and a system for calculating pre-distortion filter coefficients. Background Art

[0002] With the development of new services and application models such as cloud computing, mobile Internet, and video, the development and progress of optical communication technologies have become increasingly important. In optical communication technologies, an optical module is a tool for realizing the mutual conversion of optical and electrical signals, and is one of the key components in optical communication devices. Moreover, with the development requirements of optical communication technologies, the transmission rate of optical modules has been continuously increasing.

[0003] As is well known, as the transmission distance increases, the intensity of optical signals will gradually attenuate. Therefore, to ensure the signal transmission quality, it is necessary to control the transmission distance. For example, for the O-band optical signals widely used in optical communication, which have large losses during transmission, to meet the requirements of their transmission distance, the power of the electrical signal is usually increased to enhance the power of the modulated optical signal. However, when the power of the electrical signal is enhanced, it will cause complex electrical signal nonlinear damage brought by the modulator, resulting in an increase in bit errors. Although nonlinear compensation can be performed on the received data at the receiving end, it will increase the signal processing time and transmission delay. In addition, due to the introduction of transmission channel noise, the compensation effect is not ideal.

[0004] Generally, to reduce the bit error rate caused by nonlinear damage, nonlinear pre-distortion can be performed, that is, an inverse transformation is performed based on an empirical function of nonlinear response for nonlinear pre-distortion. However, currently, the inverse transformation based on the empirical function of nonlinear response for nonlinear pre-distortion is mainly for specific nonlinear damage. However, when the transmission rate of the electrical signal is higher than the channel bandwidth, causing inter-symbol interference, enhancing the power of the electrical signal will cause complex electrical signal nonlinear damage brought by the modulator, and this electrical signal nonlinear damage is uncertain nonlinear damage. Therefore, how to perform pre-distortion for uncertain or non-required-to-determine nonlinear damage is a technical problem that needs to be urgently solved by those skilled in the art. Summary of the Invention

[0005] This application provides an optical module, a method and a system for calculating pre-distortion filter coefficients, which are used to alleviate signal damage caused by increasing signal power and rate.

[0006] In a first aspect, a method for calculating pre-distortion filter coefficients provided by this application includes:

[0007] For calculating pre-distortion coefficients for a filter, where the filter is used in an optical module, the method includes:

[0008] Performing pre-distortion processing on original data based on a first filter configured as the current pre-distortion filter coefficient to obtain pre-distortion processed data;

[0009] Generate an optical signal according to the pre-distortion processed data modulation and output the optical signal to an optical signal receiving end, where the optical signal receiving end receives the optical signal and obtains received data through conversion;

[0010] Filter the received data through a second filter to obtain filtered data;

[0011] Compare the pre-distortion processed data with the filtered data;

[0012] If the difference between the pre-distortion processed data and the filtered data is greater than a preset value, train and update the pre-distortion filter coefficient of the first filter to make the difference between the pre-distortion processed data and the filtered data less than or equal to the preset value;

[0013] If the difference between the pre-distortion processed data and the filtered data is less than or equal to the preset value, obtain the corresponding current pre-distortion filter coefficient.

[0014] In a second aspect, a pre-distortion filter coefficient calculation system provided by the present application is used to implement the calculation of the pre-distortion filter coefficient in the first aspect. The system includes:

[0015] A first filter, the input end of which is used to input original data and is used to perform pre-distortion processing on the original data to obtain pre-distortion processed data;

[0016] A digital-to-analog converter, connected to the output end of the first filter, converts the pre-distortion processed data obtained through the first filter from a discrete signal into an analog signal;

[0017] An electrical amplifier, connected to the output end of the digital-to-analog converter, is used to amplify the analog signal;

[0018] A modulator, the input end of which is connected to the output end of the amplifier, generates an optical signal based on the analog signal;

[0019] An optical signal receiving end, the input end of which is connected to the output end of the modulator through an optical fiber, receives the optical signal and converts it into an electrical signal to obtain received data;

[0020] A second filter, used to filter the received data to obtain filtered data;

[0021] A pre-distortion filter coefficient training module, the first input end of which is connected to the output end of the first filter, and the second input end of which is connected to the output end of the second filter, trains and updates the pre-distortion filter coefficient of the filter based on the pre-distortion processed data and the filtered data.

[0022] In a third aspect, an optical module provided by the present application includes:

[0023] Circuit board;

[0024] An optical emission component, electrically connected to the circuit board, for emitting an optical signal;

[0025] Wherein, a DSP chip is arranged on the circuit board, a filter is included in the DSP chip, the filter is electrically connected to the optical emission component, and the predistortion coefficient of the filter is obtained by calculating through the predistortion filter coefficient calculation method described in the first aspect or obtained by calculating through the predistortion filter coefficient calculation system described in the second aspect;

[0026] Based on the predistortion coefficient, the filter predistortion processing is used to drive the electrical signal for the optical emission component to emit an optical signal, so as to compensate for the damage generated when the optical emission component modulates to generate an optical signal.

[0027] For the optical module, predistortion filter coefficient calculation method and system provided in this application, in order to reduce the bit error rate caused by non - linear damage generated when modulating to generate an optical signal due to increasing the electrical signal power, a filter is arranged in the digital signal processing chip. The electrical signal for driving the optical emission component to emit an optical signal is first subjected to predistortion processing by the filter, that is, electrical signal compensation is performed in advance to compensate for the damage generated when modulating the signal caused by increasing the electrical signal power and rate. Therefore, for the optical module provided in this application, the electrical signal for driving the optical emission component to emit an optical signal is subjected to filter predistortion processing, which can pre - compensate for the damage generated when the optical emission component modulates to generate an optical signal, and thus can alleviate the signal damage caused by increasing the signal power and rate. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] In order to more clearly illustrate the technical solutions of the embodiments of this application, the following will briefly introduce the drawings required for use in the embodiments or the description of the prior art. Obviously, the following drawings are only some embodiments of this application. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0029] Figure 1 It is a connection relationship diagram of an optical communication system according to some embodiments;

[0030] Figure 2 It is a structural diagram of an optical network terminal according to some embodiments;

[0031] Figure 3 It is a structural diagram of an optical module according to some embodiments;

[0032] Figure 4 It is an exploded view of an optical module according to some embodiments;

[0033] Figure 5Schematic diagram of the internal structure of an optical module provided according to some embodiments;

[0034] Figure 6 Schematic diagram of the basic structure of a predistortion filter coefficient calculation system according to some embodiments;

[0035] Figure 7 Flowchart of a predistortion filter coefficient calculation method provided according to some embodiments;

[0036] Figure 8 Schematic diagram of the basic structure of another predistortion filter coefficient calculation system provided according to some embodiments;

[0037] Figure 9 Original data constellation diagram provided according to some embodiments;

[0038] Figure 10 Data constellation diagram received at the receiving end provided according to some embodiments;

[0039] Figure 11 Data constellation diagram after equalization processing provided according to some embodiments;

[0040] Figure 12 Data constellation diagram after being processed by a second filter provided according to some embodiments;

[0041] Figure 13 Data constellation diagram after pre-distortion processing at the transmitting end provided according to some embodiments;

[0042] Figure 14 Data constellation diagram after equalization processing at the receiving end provided according to some embodiments;

[0043] Figure 15 Data constellation diagram after pre-distortion processing at the transmitting end for long-distance transmission provided according to some embodiments;

[0044] Figure 16 Data constellation diagram received at the receiving end provided according to some embodiments;

[0045] Figure 17 For Figure 16 Data constellation diagram after equalization processing;

[0046] Figure 18 Data constellation diagram after equalization processing (left figure) and data constellation diagram after non-linear compensation (right figure) without non-linear predistortion;

[0047] Figure 19The data constellation diagrams after equalization (left figure) and after non - linear compensation (right figure) when there is no non - linear pre - distortion and the output power is reduced;

[0048] Figure 20 The data constellation diagram after non - linear pre - distortion at the transmitting end (updating the pre - distortion filter coefficients) and equalization processing at the receiving end when reducing the signal output power;

[0049] Figure 21 The data constellation diagram after non - linear pre - distortion at the transmitting end and equalization processing at the receiving end when reducing the signal output power;

[0050] Figure 22 The data constellation diagrams after equalization processing and non - linear compensation (left figure) when there is no non - linear pre - distortion and after equalization processing when there is non - linear pre - distortion (right figure) when the attenuation coefficient of the channel power is 0.6; Specific implementation manners

[0051] Next, the technical solutions in the embodiments of the present application will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present application.

[0052] Unless otherwise required by the context, throughout the specification and claims, the term "comprise" and its other forms such as the third - person singular form "comprises" and the present participle form "comprising" are interpreted as open and inclusive, that is, "including, but not limited to". In the description of the specification, the terms "one embodiment", "some embodiments", "exemplary embodiments", "example", "specific example" or "some examples", etc. are intended to indicate that the specific features, structures, materials or characteristics related to the embodiment or example are included in at least one embodiment or example of the present disclosure. The schematic representations of the above terms are not necessarily referring to the same embodiment or example. In addition, the described specific features, structures, materials or characteristics can be included in any one or more embodiments or examples in any appropriate manner.

[0053] In the field of optical fiber communication technology, the signals transmitted by information transmission devices such as optical fibers or optical waveguides are optical signals, while the signals that information processing devices such as computers can recognize and process are electrical signals. Therefore, optical modules are needed to achieve the mutual conversion of the above-mentioned optical signals and electrical signals.

[0054] Figure 1 It is a connection diagram of an optical communication system according to some embodiments. As Figure 1 shown, a bidirectional optical communication system is established between the remote server 1000 and the local information processing device 2000 through the optical fiber 101, the optical module 200, the optical network terminal 100, and the network cable 103.

[0055] One end of the optical fiber 101 is connected to the remote server 1000, and the other end is connected to the optical network terminal 100 through the optical module 200. One end of the network cable 103 is connected to the local information processing device 2000, and the other end is connected to the optical network terminal 100.

[0056] The connection between the local information processing device 2000 and the remote server 1000 is completed by the optical fiber 101 and the network cable 103; while the connection between the optical fiber 101 and the network cable 103 is completed by the optical module 200 and the optical network terminal 100.

[0057] In the optical module 200, the optical port is configured to be connected to the optical fiber 101, so that a two-way optical signal connection is established between the optical module 200 and the optical fiber 101; the electrical port is configured to be connected to the optical network terminal 100, so that a two-way electrical signal connection is established between the optical module 200 and the optical network terminal 100. The optical module 200 realizes the mutual conversion of optical signals and electrical signals, so that a connection is established between the optical fiber 101 and the optical network terminal 100.

[0058] The optical network terminal 100 is provided with an optical module interface 102 and a network cable interface 104. The optical module interface 102 is configured to be connected to the optical module 200, so that a two-way electrical signal connection is established between the optical network terminal 100 and the optical module 200; the network cable interface 104 is configured to be connected to the network cable 103, so that a two-way electrical signal connection is established between the optical network terminal 100 and the network cable 103. A connection is established between the optical module 200 and the network cable 103 through the optical network terminal 100. The upper computer of the optical module 200 may further include an Optical Line Terminal (OLT) etc. in addition to the optical network terminal 100.

[0059] Figure 2 It is a structural diagram of an optical network terminal according to some embodiments. As Figure 2As shown, the optical network terminal 100 further includes a PCB circuit board 105 disposed within the housing, a cage 106 disposed on the surface of the PCB circuit board 105, and an electrical connector disposed within the cage 106. The electrical connector is configured to access the electrical port of the optical module 200; the heat sink 107 has raised portions such as fins for increasing the heat dissipation area.

[0060] The optical module 200 is inserted into the cage 106 of the optical network terminal 100, and the optical module 200 is fixed by the cage 106. The heat generated by the optical module 200 is conducted to the cage 106 and then diffused through the heat sink 107. After the optical module 200 is inserted into the cage 106, the electrical port of the optical module 200 is connected to the electrical connector inside the cage 106, thereby establishing a two-way electrical signal connection between the optical module 200 and the optical network terminal 100.

[0061] Figure 3 FIG. is a structural diagram of an optical module provided according to some embodiments. Figure 4 FIG. is an exploded view of an optical module provided according to some embodiments. As Figure 3 and Figure 4 shown, the optical module 200 includes a housing and a circuit board 300 disposed within the housing.

[0062] The housing includes an upper housing 201 and a lower housing 202. The upper housing 201 covers the lower housing 202 to form the above-mentioned housing having two openings 204 and 205; the outer contour of the housing generally presents a rectangular body.

[0063] The direction of the line connecting the two openings 204 and 205 may be consistent with the length direction of the optical module 200 or may not be consistent with the length direction of the optical module 200. Among them, the opening 204 is an electrical port, and the gold fingers of the circuit board 300 extend out from the electrical port 204 and are inserted into the host computer; the opening 205 is an optical port configured to access an external optical fiber 101 so that the optical fiber 101 is connected to the inside of the optical module 200.

[0064] Adopting the assembly method of combining the upper housing 201 and the lower housing 202 facilitates the installation of devices such as the circuit board 300 into the housing, and the upper housing 201 and the lower housing 202 can form a package protection for these devices. In some embodiments, the upper housing 201 and the lower housing 202 are generally made of a metal material, which is conducive to achieving electromagnetic shielding and heat dissipation.

[0065] In some embodiments, the optical module 200 further includes an unlocking member 203 located on the outer wall of its housing. When the optical module 200 is inserted into the cage of the host computer, the engaging member of the unlocking member 203 engages the optical module 200 in the cage of the host computer; when the unlocking member 203 is pulled, the engaging member of the unlocking member 203 moves accordingly, thereby changing the connection relationship between the engaging member and the host computer to release the engagement between the optical module 200 and the host computer.

[0066] The circuit board 300 includes circuit traces, electronic components, and chips, and the electronic components and chips are connected together according to the circuit design through the circuit traces.

[0067] The circuit board 300 is generally a rigid circuit board. Due to its relatively hard material, the rigid circuit board can also achieve a bearing function. For example, the rigid circuit board can stably carry chips; the rigid circuit board can also be inserted into the electrical connector in the host cage.

[0068] The circuit board 300 further includes a gold finger formed on its end surface, and the gold finger is composed of a plurality of independent pins. The circuit board 300 is inserted into the cage 106, and is conductively connected to the electrical connector in the cage 106 by the gold finger. The gold finger is configured to establish an electrical connection with the host computer to achieve power supply, grounding, I2C signal transmission, data signal transmission, etc. Of course, in some optical modules, a flexible circuit board is also used in cooperation with the circuit board 300.

[0069] In the embodiment of the present application, the optical module 200 further includes an optical fiber connector 400, and the optical fiber connector 400 is disposed at the optical port 205. The optical fiber connector 400 is used to realize the optical connection between the external optical fiber and the optical port. Furthermore, the optical signal generated by the optical transceiver component is transmitted to the external optical fiber through the optical fiber connector 400, and the optical signal output by the external optical fiber is transmitted to the optical transceiver component through the optical fiber connector 400.

[0070] In the embodiment of the present application, an optical transceiver component 500 is further disposed on the circuit board 300. The optical transceiver component 500 is electrically connected to the circuit board 300 and is used to generate an optical signal and receive the optical signal output by the external optical fiber. In the embodiment of the present application, the optical transceiver component 500 is connected to the optical fiber connector 400 through an optical fiber ribbon. The optical signal generated by the optical transceiver component 500 is transmitted to the optical fiber connector 400 through the optical fiber ribbon, and the optical signal output by the external optical fiber is transmitted to the optical fiber ribbon through the optical fiber connector 400 and then transmitted to the optical transceiver component 500 through the optical fiber ribbon. In some embodiments of the present application, one optical transceiver component or two optical transceiver components 500 are disposed on the circuit board 300. Of course, in the embodiment of the present application, it is not limited to one or two optical transceiver components 500, and more than two optical transceiver components 500 can be disposed under the condition that space permits.

[0071] Figure 5 It is a schematic diagram of the internal structure of an optical module provided according to some embodiments. Figure 5 It shows the assembly relationship between an optical transceiver component provided in the embodiment of the present application and the circuit board 300. As Figure 5As shown, the optical transceiver module 500 provided in the embodiment of the present application is disposed at a position near the middle of the circuit board 300. Of course, in the embodiment of the present application, the assembly position of the optical transceiver module 500 is not limited thereto and can also be adjusted as needed.

[0072] As Figure 5 shown, the optical transceiver module 500 provided in some embodiments of the present application includes a base 510, a light source 520, a silicon photonics chip 530, and a secondary circuit board 540; the base 510 is disposed on the circuit board 300, and the top of the base 510 is used to carry the light source 520 and the silicon photonics chip 530; the light source 520 is disposed on one side of the silicon photonics chip 530, and a slot is provided at the end of the secondary circuit board 540, and the secondary circuit board 540 is disposed on the other side of the silicon photonics chip 530 through the slot; the secondary circuit board 540 is located above the circuit board 300, the bottom of the secondary circuit board 540 is in electrical contact with the circuit board 300, and the top is used to carry devices such as a digital signal processing chip 550 and is wire-bonded to the silicon photonics chip 530, etc. In this embodiment, the light source 520 is disposed on the side of the silicon photonics chip 530 away from the gold finger on the circuit board 300, that is, the side of the silicon photonics chip 530 close to the optical port. The light source 520 is used to generate light without carrying signals and transmit it to the silicon photonics chip 530. The digital signal processing chip 550 inputs a high-frequency electrical signal to the silicon photonics chip 530. The silicon photonics chip 530 receives the light without carrying signals and modulates it according to the high-frequency electrical signal to output light carrying signals. The light carrying signals are transmitted to the fiber optic connector 400 through the fiber optic ribbon; the optical signal transmitted by the external optical fiber is transmitted to the fiber optic ribbon inside the optical module through the fiber optic connector 400, and is transmitted to the silicon photonics chip 530 through the fiber optic ribbon. The silicon photonics chip 530 receives the optical signal and converts it into an electrical signal. In some embodiments of the present application, the silicon photonics chip 530 includes a Mach-Zehnder Modulator (MZM) for implementing modulation of the silicon photonics chip 530 to generate an optical signal; the optical signals output and received by the silicon photonics chip 530 include but are not limited to O-band optical signals. Of course, the form of the optical transceiver module 500 in the embodiment of the present application is not limited to Figure 5 the structure shown.

[0073] In some embodiments of the present application, the power of the electrical signal is increased to enhance the power of the optical signal generated by modulation of the silicon photonics chip 530, so as to achieve the purpose of increasing the transmission distance of the optical signal generated by the optical module. Further, in order to reduce the bit error rate caused by non-linear damage generated when the silicon photonics chip 530 modulates and generates an optical signal due to the increase in the power of the electrical signal, a filter is included in the digital signal processing chip 550. The high-frequency electrical signal to be transmitted to the silicon photonics chip 530 is pre-distorted by the filter, such as non-linear pre-distortion. The high-frequency electrical signal after pre-distortion by the filter is then transmitted to the silicon photonics chip 530 to generate an optical signal through modulation by the silicon photonics chip 530. Exemplarily, the filter may adopt a Volterra filter.

[0074] Further, to ensure the pre-distortion effect of the filter, an embodiment of the present application also provides a method for calculating pre-distortion filter coefficients, so as to ensure that the filter can perform pre-distortion processing before electrical signal modulation processing based on more appropriate filter coefficients. To implement the calculation of the filter coefficients by the method for calculating pre-distortion filter coefficients, an embodiment of the present application also provides a system for calculating pre-distortion filter coefficients.

[0075] Figure 6 FIG. is a schematic diagram of the basic structure of a system for calculating pre-distortion filter coefficients provided according to some embodiments. As Figure 6 shown in the system for calculating pre-distortion filter coefficients, it includes a first filter, a modulator, an optical signal receiving end, a second filter, and a pre-distortion filter coefficient training module. The output end of the first filter is connected to the electrical signal input end of the modulator, and the output end of the first filter is also connected to the first input end of the pre-distortion filter coefficient training module. The optical signal output end of the modulator is connected to the optical signal input end of the optical signal receiving end through an optical fiber, and the electrical signal output end of the optical signal receiving end is connected to the second input end of the pre-distortion filter coefficient training module. Figure 7 FIG. is a schematic diagram of the flow of a method for calculating pre-distortion filter coefficients provided according to some embodiments.

[0076] Combined with Figure 6 shown in the system for calculating pre-distortion filter coefficients, a method for calculating pre-distortion filter coefficients provided by an embodiment of the present application will be described in detail. As Figure 7 shown, the method for calculating pre-distortion filter coefficients provided by an embodiment of the present application includes:

[0077] S100: Perform pre-distortion processing on the original data based on the first filter configured with the current pre-distortion filter coefficients to obtain pre-distortion processed data.

[0078] The first filter receives the input original data and performs pre-distortion processing on the original data based on the configured current pre-distortion filter coefficients to obtain pre-distorted processed data. The original data can be discrete data, such as discrete digital signal data, etc.; when the original data is discrete digital signal data, digital-to-analog conversion is required before transmitting the pre-distorted processed data to the modulator, that is, converting the digital signal into an analog signal, and finally sending the pre-distorted processed data converted into an analog signal to the modulator, so that the modulator can generate an optical signal according to the pre-distorted processed data. In some embodiments, the original data can be generated by a waveform generator; the pre-distortion processing is non-linear pre-distortion. Generally, to ensure the efficiency and effectiveness of training and updating the pre-distortion filter coefficients, the data length of the original data is greater than or equal to 1000.

[0079] In some embodiments of the present application, the first filter can be a Volterra filter based on the Volterra series. When performing pre-distortion processing on the original data to obtain pre-distorted processed data, the in-phase component I and the quadrature component Q of the original data are respectively pre-processed by the Volterra filter.

[0080] S200: Modulate an optical signal according to the pre-distorted processed data and output the optical signal to an optical signal receiving end, and the optical signal receiving end receives the optical signal and obtains received data through conversion.

[0081] The modulator modulates and generates an optical signal according to the received pre-distorted processed data and outputs the generated optical signal. The output optical signal is transmitted to the optical signal receiving end through an optical fiber. The optical signal receiving end receives the optical signal and converts the optical signal into an electrical signal to obtain received data. In some embodiments, the optical signal receiving end includes an optical receiver, and the optical receiver and the modulator can refer to components such as silicon photonic chips in the optical module provided in the embodiments of the present application for realizing devices for transmitting and receiving optical signals.

[0082] In some embodiments of the present application, the optical receiver receives the optical signal and converts the optical signal into an electrical signal in the form of an analog signal. Therefore, it is usually necessary to convert the analog signal into a digital signal at the optical signal receiving end to obtain received data.

[0083] S300: Filter the received data through a second filter to obtain filtered processed data.

[0084] The received data obtained by receiving and converting through the optical receiver is further filtered through the second filter, so that the obtained received data can undergo the same or similar processing process as the original data, thereby ensuring the effectiveness of training the pre-distortion filter coefficients. In some embodiments, the filter coefficients of the second filter are the same as the current pre-distortion filter coefficients of the first filter.

[0085] S400: Compare the predistortion processed data with the filtered processed data.

[0086] The predistortion filter coefficient training module receives the predistortion processed data obtained after filter predistortion processing and the filtered processed data obtained by receiving and converting through the optical signal receiving end, compares the predistortion processed data and the filtered processed data, and determines the corresponding filter predistortion coefficient when the predistortion processed data and the filtered processed data are close by comparing the predistortion processed data and the filtered processed data, that is, updates the predistortion filter coefficient of the first filter by comparing the predistortion processed data and the filtered processed data to determine the predistortion filter coefficient that makes the filtered processed data approximate the predistortion processed data. Exemplarily, comparing the predistortion processed data and the filtered processed data is usually calculating the difference between the predistortion processed data and the filtered processed data; if the difference between the predistortion processed data and the filtered processed data is greater than a preset value, step S500 is executed; if the difference between the predistortion processed data and the received data is less than or equal to the preset value, step S600 is executed, and the proximity degree between the received data and the predistortion processed data is controlled by the preset value. In some embodiments of the present application, the preset value can be selected according to the requirements of the filter predistortion compensation accuracy.

[0087] S500: If the difference between the predistortion processed data and the filtered processed data is greater than the preset value, train and update the predistortion filter coefficient of the first filter to make the difference between the predistortion processed data and the filtered processed data less than or equal to the preset value.

[0088] S600: If the difference between the predistortion processed data and the filtered processed data is less than or equal to the preset value, obtain the corresponding current predistortion filter coefficient.

[0089] By executing step S500 or step S600, determine the corresponding predistortion filter coefficient when the received data and the predistortion processed data meet the pre - proximity degree, and update the predistortion filter coefficient of the filter in the optical module according to the determined predistortion filter coefficient. Therefore, the predistortion filter coefficient calculation system and the predistortion filter coefficient calculation method provided by the embodiments of the present application can facilitate the determination of the predistortion filter coefficient with better predistortion effect of the filter, so that when the transmission distance and the transmission data volume of the optical signal are increased by increasing the electrical signal power and rate, the nonlinear damage generated by the modulator can be pre - compensated.

[0090] In some embodiments of the present application, the optical signal receiving end receives an optical signal and obtains received data through conversion. Specifically, the optical signal receiving end converts the received electrical signal into a first electrical signal, and first performs analog-to-digital conversion on the first electrical signal and then performs channel equalization processing to obtain the received data. Channel equalization processing facilitates compensating for the impairments generated during the transmission process of electrical signal - optical signal - electrical signal between various devices and device interfaces, so as to reduce the impact of the impairments generated during the transmission process on calculating the pre-distortion filter coefficients. Channel equalization processing can adopt existing processing methods such as the Recursive Least Square (RLS) algorithm.

[0091] In some embodiments of the present application, the optical signal receiving end receives an optical signal and obtains received data through conversion. Specifically, the optical signal receiving end converts the received electrical signal into a first electrical signal, and after performing analog-to-digital conversion on the first electrical signal, it sequentially performs frequency offset compensation, channel equalization, and phase offset compensation processing, and finally obtains the received data. Frequency offset compensation is used to compensate for the frequency offset of the signal, and phase offset compensation is used to compensate for the phase offset of the signal. Usually, there is also a laser in the optical signal receiving end to generate light for coherent demodulation of the received optical signal, but the frequency and phase of the optical signal generated in the optical signal receiving end are not exactly the same as those of the optical signal generated by the transmitting end, that is, there are deviations; when there are deviations, it will cause impairments to the received signal and increase the bit error rate of the received signal. Thus, in this embodiment, through the corresponding frequency offset compensation and phase offset compensation, it is more convenient to compensate for the impairments generated during the transmission process of electrical signal - optical signal - electrical signal between various devices and device interfaces, so as to reduce the impact of the impairments generated during the transmission process on calculating the pre-distortion filter coefficients.

[0092] To ensure the effect of channel equalization processing, the channel equalization processing model can be pre-trained and updated. When pre-training and updating the channel equalization processing model, the data length is greater than 1000. Usually, the data used for pre-training and updating the channel equalization processing model is not used for training and updating the pre-distortion filter coefficients of the filter.

[0093] In some embodiments of the present application, an optical signal is modulated and generated according to the pre-distortion processing data. Specifically, the pre-distortion processed discrete data is first converted from digital to analog to obtain a pre-distortion electrical signal, then the pre-distortion electrical signal is amplified through an amplifier, and then the modulator modulates and generates and outputs an optical signal based on the amplified pre-distortion electrical signal.

[0094] In some embodiments of the present application, the first filter and the second filter adopt Volterra filters. Then, when training and updating the coefficients of the predistortion filter, Volterra filtering processing is respectively performed on the in-phase component and the quadrature component of the predistortion processed data and the filtered processed data, and the Volterra filters of the in-phase component and the quadrature component are respectively updated. And the order p and the memory length m of the Volterra filter are controlled, where 1 ≤ p ≤ 5 and 1 ≤ m ≤ 10. When increasing the power of the output signal, the generated nonlinear distortion will be stronger, and then the order of Volterra will be increased to compensate for the corresponding stronger nonlinear distortion. Thus, in the embodiments of the present application, by controlling the order p and the memory length m of the Volterra filter, it is convenient to realize the effectiveness of training and updating the coefficients of the predistortion filter at different output powers of the electrical signal. Exemplarily, the coefficients or kernel functions of the first filter are the filter coefficients in the RLS algorithm. The values of the m consecutive symbols filtered by the second filter at different orders from 1 to p and the cross products between the m symbols at different orders from 1 to p are the inputs of the filter in the RLS algorithm. The predistortion discrete data at the transmitting end is used as the target output of the filter in the RLS algorithm. The RLS algorithm is applied to update the coefficients of the first filter and the second filter. In the first update process, the initial value of the coefficients of the first filter is 0. In the subsequent update processes, the initial value of the coefficients of the first filter is the result of the previous update.

[0095] The specific mathematical model of the Volterra filter adopted in the embodiments of the present application is as follows:

[0096]

[0097] Where p represents the order of the filter, m represents the memory length of the filter, j represents the imaginary part of the complex number. n represents the nth symbol. I(n) and Q(n) respectively represent the in-phase component I and the quadrature Q component of the nth symbol. h Ip and h Qp respectively represent the kernel functions of the filters corresponding to the I and Q components at the order p. In the embodiments of the present application, Volterra nonlinear processing is respectively performed on the in-phase component I and the quadrature component Q, and the coefficients of the corresponding nonlinear filters are respectively calculated, rather than jointly writing the in-phase component I and the quadrature component Q of the discrete signal as a complex number and then performing the calculation.

[0098] Further, in the embodiments of the present application, the number of stages p and the memory length m in the Volterra filter can also be adjusted at different signal powers and rates to train and update the pre-distortion filter coefficients of the filter, so as to find the balance point of the optimal signal power, rate and received signal quality. Furthermore, when the optical module is specifically used, more appropriate pre-distortion filter coefficients can be selected in combination with specific transmission distance requirements, signal power and rate conditions.

[0099] In some embodiments of the present application, to control the computational amount of training and updating the pre-distortion filter coefficients, when training and updating the pre-distortion filter coefficients, the number of times of training and updating the pre-distortion filter coefficients is not greater than 5, and the difference between the pre-distortion processing data and the filtering processing data corresponding to the training and updating of the distortion filter coefficients is recorded; if the difference between the pre-distortion processing data and the filtering processing data cannot be made less than or equal to the preset value, the pre-distortion filter coefficient corresponding to the minimum absolute value of the difference between the pre-distortion processing data and the filtering processing data is selected.

[0100] Based on the pre-distortion filter coefficient calculation method provided in the above embodiments, the present application also provides another pre-distortion filter coefficient calculation system. Figure 8 The following is a schematic diagram of the basic structure of another pre-distortion filter coefficient calculation system provided according to some embodiments. As Figure 8 shown, the pre-distortion filter coefficient calculation system provided in this embodiment further includes a digital-to-analog converter, an electrical amplifier, an analog-to-digital converter, a frequency offset compensator, a channel equalizer and a phase offset compensator.

[0101] The output end of the first filter is connected to the input end of the digital-to-analog converter, the output end of the digital-to-analog converter is connected to the input end of the electrical amplifier, and the output end of the electrical amplifier is connected to the electrical signal input end of the modulator; the electrical signal output end of the optical receiver is connected to the input end of the analog-to-digital converter, the output end of the analog-to-digital converter is connected to the input end of the frequency offset compensator, the output end of the frequency offset compensator is connected to the input end of the channel equalizer, the output end of the channel equalizer is connected to the input end of the phase offset compensation, the output end of the phase offset compensation is connected to the input end of the second filter, and the output end of the second filter is connected to the second input end of the pre-distortion filter coefficient training module. Before the distortion processing data is transmitted to the modulator, the pre-distortion processing data is first transmitted to the digital-to-analog converter, and the discrete pre-distortion processing data is converted into an analog pre-distortion electrical signal by the digital-to-analog converter, and then the pre-distortion electrical signal is amplified by the electrical amplifier. The first electrical signal converted and output by the optical receiver is first transmitted to the analog-to-digital converter, and after being converted by the analog-to-digital converter, it undergoes frequency offset compensation, channel equalization and phase offset compensation to obtain received data and is transmitted to the second filter, and after being filtered by the second filter, it is transmitted to the pre-distortion filter coefficient training module.

[0102] The following introduces the training update of Volterra filter coefficients and the pre-distortion applied to data in combination with specific examples. A set of 10,000 64QAM data vectors are generated at the transmitting end, and the 64QAM data constellation diagram is shown as Figure 9 . Usually, when the data transmission rate is greater than the bandwidth of the transmission channel, inter-symbol interference of data will be caused; then the data passes through a modulator to generate non-linear impairments; and then after passing through a section of optical fiber to reach the optical signal receiving end, phase noise and channel noise will also be introduced. Here, it is assumed that the channel signal-to-noise ratio (SNR) is 35 dB, and the data received by the optical receiver will be as Figure 10 . The data constellation diagram of the data received by the optical receiver after RLS channel equalization processing is as Figure 11 , and its bit error ratio (BER) is 4.5e-3. Select a part of the data to train and update the filter coefficients of the filter, and apply the trained Volterra filter to the remaining data, and the obtained data constellation diagram is as Figure 12 , where the BER is 0. The coefficients of the trained filter are used in the first filter at the transmitting end for data pre-distortion processing, and its constellation diagram is as shown in 13. The constellation diagram obtained after RLS channel equalization processing at the receiving end is as Figure 14 , and it can be seen that there is an obvious improvement compared with Figure 11 , and the BER is 0.

[0103] Train and update the pre-distortion filter coefficients of the Volterra filter again. At this time, the target output is the pre-distorted data at the transmitting end (see Figure 13 ), and the Volterra filter at this time is used at the transmitting end for pre-distortion again. After this process is carried out multiple times, it is found that the Volterra filter obtained for the first time has the best effect when used for non-linear pre-distortion, and this Volterra filter is used for non-linear pre-distortion processing at the transmitting end during long-distance transmission.

[0104] Considering the scenario of long-distance transmission simulation, the constellation diagram of the data with non-linear pre-distortion at the transmitting end is as Figure 15 . Assuming that the power of the channel noise is 0.1, and since the signal power attenuation coefficient is 0.8 during long-distance transmission, the SNR at this time is 25 dB, and the constellation diagram of the data obtained at the receiving end is as Figure 16 shown. The constellation diagram of the data after RLS channel equalization processing is shown as Figure 17 , and the BER is 6e-3. When no non-linear pre-distortion is carried out, the constellation diagrams of the received data after equalization processing and Volterra non-linear compensation are shown as Figure 18, with BER values of 2e-2 and 1e-2 respectively, and the transmission effect is significantly worse than that with nonlinear pre-distortion ( Figure 17 ). To reduce the nonlinear impairment, the output power of the data at the transmitter is reduced by 0.6. The constellation diagrams of the received data after RLS channel equalization processing and Volterra nonlinear compensation are shown as Figure 19 , with BER values of 1.4e-2 and 9.6e-3 respectively. Although the effect is better than that without reducing the output power at the transmitter end ( Figure 18 ), due to the reduction of the output power, the SNR of the signal is also reduced to 24 dB, and its effect is still worse than that with nonlinear pre-distortion ( Figure 17 ). Now, after reducing the output power of the transmitter data by 0.6, the pre-distortion filter coefficients of the Volterra filter are retrained and updated for use in the pre-distortion of the transmitter data. The constellation diagram of the data of the received signal after RLS channel equalization in back-to-back transmission is shown as Figure 20 , with a BER of 0, and the effect is better than that without reducing the output power of the transmitter data ( Figure 14 ).

[0105] Now, this updated Volterra filter is used for the pre-distortion processing of the transmitter data, and the output power of the signal is reduced to 60% of the previous value. After the signal is transmitted through the channel under the same conditions and the received data is equalized by RLS channel at the receiver, the constellation diagram is shown as Figure 21 , with a BER of 5e-3, and the effect is slightly better than that without reducing the output power of the transmitter ( Figure 17 ), although the SNR is reduced to 24 dB at this time.

[0106] Now, assume that the power of the channel noise is still 0.1, but due to the signal power attenuation coefficient being reduced to 0.6 during longer-distance transmission. Additionally, the transmitter data power is still reduced by 0.6 (which is the optimal value after comparison), and the current SNR is 23 dB. The constellation diagram of the data without nonlinear pre-distortion after RLS equalization and Volterra nonlinear compensation at the receiver is shown as the left figure of Figure 22 , with a BER of 1.5e-2. The constellation diagram of the data after RLS equalization under the condition of nonlinear pre-distortion is shown as the right figure of Figure 22 , with a BER of 9e-3. Combining the above figures, it is obvious that the effect of nonlinear pre-distortion in improving data quality is significant. Additionally, it is found that when the channel attenuation is relatively large, such as when the channel attenuation coefficient is 0.5, when using nonlinear pre-distortion, the signal output power can be not reduced, thereby maintaining a higher SNR and reducing the BER of the recovered data.

[0107] Therefore, the pre-distortion filter coefficient calculation system and method provided by the embodiments of the present application enable relatively accurate filter coefficients to be obtained for use in an optical module, so that the optical module can perform pre-distortion processing on the electrical signal before modulation to compensate for signal damage during the modulation process.

[0108] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them; although the present application has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements on some of the technical features; and these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present application.

Claims

1. A method for calculating pre-distortion filter coefficients, characterized in that, For pre-distortion coefficient calculation of a filter, where the filter is used in an optical module, the method includes: Performing pre-distortion processing on original data based on a first filter configured as a current pre-distortion filter coefficient to obtain pre-distortion processed data, where the first filter is a Volterra filter; Modulating an optical signal according to the pre-distortion processed data and outputting the optical signal to an optical signal receiving end, where the optical signal receiving end converts the received optical signal into a first electrical signal, and the first electrical signal is subjected to analog-to-digital conversion and sequentially passes through frequency offset compensation, channel equalization, and phase offset compensation processing to obtain received data; Filtering the received data through a second filter to obtain filtered processed data; Comparing the pre-distortion processed data with the filtered processed data; If the difference between the pre-distortion processed data and the filtered processed data is greater than a preset value, training and updating the pre-distortion filter coefficient of the first filter to make the difference between the pre-distortion processed data and the filtered processed data less than or equal to the preset value; where, when training and updating the pre-distortion filter coefficient, performing Volterra filtering processing on the in-phase component and the quadrature component of the pre-distortion processed data and the filtered processed data respectively, and updating the Volterra filters of the in-phase component and the quadrature component respectively, and controlling the order p and the memory length m of the Volterra filter, where 1≤p≤5, 1≤m≤10; If the difference between the pre-distortion processed data and the filtered processed data is less than or equal to the preset value, obtaining the corresponding current pre-distortion filter coefficient.

2. The calculation method according to claim 1, characterized in that, Modulating and outputting an optical signal according to the pre-distortion processed data, including: Performing digital-to-analog conversion on the pre-distortion processed data to obtain a pre-distortion electrical signal and performing amplification processing through an electrical amplifier, and modulating an optical signal based on the amplified pre-distortion electrical signal.

3. The calculation method according to claim 1, characterized in that, When training and updating the pre-distortion filter coefficient, including: the number of times of training and updating the pre-distortion filter coefficient is not greater than 5, and recording the difference between the pre-distortion processed data and the filtered processed data corresponding to the training and updating of the distortion filter coefficient; If it is impossible to make the difference between the pre-distortion processed data and the filtered processed data less than or equal to the preset value, selecting the pre-distortion filter coefficient corresponding to the minimum absolute value of the difference between the pre-distortion processed data and the filtered processed data.

4. The calculation method according to claim 1, characterized in that, The method further includes: pre-training and updating a channel equalization processing model; The filter coefficient of the second filter is the same as the current pre-distortion filter coefficient of the first filter.

5. The calculation method according to claim 1, characterized in that, The data length of the original data is greater than or equal to 1000.

6. A pre-distortion filter coefficient calculation system, characterized in that, For implementing the calculation of the pre-distortion filter coefficient in claim 1, the system includes: A first filter, the input end of which is used to input original data, and is used to obtain pre-distortion processed data by pre-distorting the original data; A digital-to-analog converter, connected to the output end of the first filter, and converting the pre-distortion processed data obtained through the first filter from a discrete signal into an analog signal; An electrical amplifier, connected to the output end of the digital-to-analog converter, and used to amplify the analog signal; A modulator, with its input end connected to the output end of the amplifier, generates an optical signal based on the analog signal; An optical signal receiving end, with its input end connected to the output end of the modulator through an optical fiber, receives the optical signal and converts it into an electrical signal to obtain received data; A second filter, which is used to filter the received data to obtain filtered data; A predistortion filter coefficient training module, with its first input end connected to the output end of the first filter and its second input end connected to the output end of the second filter, trains and updates the predistortion filter coefficient of the filter based on the predistortion processed data and the filtered data.

7. The calculation system according to claim 6, characterized in that, The optical signal receiving end includes an optical receiver, an analog-to-digital converter, a frequency offset compensator, a channel equalizer, and a phase offset compensator; the optical signal input end of the optical receiver is connected to the optical output end of the modulator through an optical fiber, the electrical signal output end of the optical receiver is connected to the input end of the analog-to-digital converter, the output end of the analog-to-digital converter is connected to the input end of the frequency offset compensator, the output end of the frequency offset compensator is connected to the input end of the channel equalizer, the output end of the channel equalizer is connected to the input end of the phase offset compensation, and the output end of the phase offset compensation is connected to the input end of the second filter; The optical receiver is used to convert the received optical signal into a first electrical signal; The analog-to-digital converter is used to perform analog-to-digital conversion on the first electrical signal to obtain a digital signal; the frequency offset compensator performs frequency offset compensation processing on the digital signal, the channel equalizer performs signal equalization processing on the digital signal, and the phase offset compensator performs phase offset compensation processing on the digital signal.

8. An optical module, characterized in that, Comprising: A circuit board; An optical transmission component, electrically connected to the circuit board, which is used to transmit an optical signal; Wherein, a DSP chip is arranged on the circuit board, the DSP chip includes a filter, the filter is electrically connected to the optical transmission component, and the predistortion coefficient of the filter is obtained by calculating through the predistortion filter coefficient calculation method according to any one of claims 1-6 or is obtained by calculating through the predistortion filter coefficient calculation system according to claim 7; Based on the predistortion coefficient, the filter performs predistortion processing on the electrical signal used to drive the optical transmission component to transmit an optical signal, so as to compensate for the damage generated when the optical transmission component modulates and generates an optical signal.

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