Method for evaluating frequency response characteristic of linear optical module

Abstract

The invention relates to the technical field of optical module performance testing, and discloses a method for evaluating frequency response characteristics of a linear optical module, which comprises the following steps that: a code pattern generator sends a signal to a plug-in module, an electric oscilloscope captures an electric signal waveform output by the plug-in module, converts the electric signal waveform into a frequency domain, and sends the frequency response characteristics to the plug-in module; obtaining a frequency response characteristic of a driving chip from the code pattern generator to the linear optical module; the code pattern generator sends a signal to the linear optical module, and the optical oscilloscope captures an optical signal waveform output by the linear optical module and converts the optical signal waveform into a frequency domain to obtain frequency response characteristics from the code pattern generator to a transmitting end of the linear optical module; and performing matrix point division on the frequency response characteristic from the code pattern generator to the driving chip of the linear optical module and the frequency response characteristic from the code pattern generator to the transmitting end of the linear optical module to obtain the frequency response characteristic of the transmitting end of the linear optical module. According to the invention, the frequency response characteristic of the transmitting end of the linear optical module can be effectively evaluated, the cost can be saved, the efficiency is improved, and the producibility is realized.

Description

Technical Field

[0001] The present invention relates to the technical field of optical module performance testing, and particularly relates to a method for evaluating the frequency response characteristics of a linear optical module. Background Art

[0002] With the explosion of digital communication and AI technologies, the demand for optical modules has increased sharply. Among them, linear optical modules are very popular due to their characteristics such as low power consumption and low latency. When manufacturers mass-produce linear optical modules, it is very important to evaluate the performance of linear optical modules on the production line to ensure product quality. For linear optical modules, it is particularly important to evaluate the frequency response characteristics of their transmitting ends.

[0003] In the prior art, it is a common method to evaluate the frequency response characteristics of the transmitting end of a linear optical module (such as a linear drive pluggable optical module LPO, a co-packaged optics CPO, etc.) based on a Vector Network Analyzer (VNA) and a Lightwave Component Analyzers (LCA). As Figure 1 shown, after the VNA transmits sine wave signals of different frequencies to the Module Compliance Board (MCB, a kind of test fixture) at the transmitting end and then gives them to the electrical receiving end of the linear optical module (i.e., the Device Under Test, DUT), the sine wave signals are output to the LCA after passing through the MCB and the linear optical module. After the LCA performs optoelectronic conversion, finally the sine wave signals are returned to the VNA. The VNA compares the differences between the transmitted and received sine wave signals, and after removing the influence of the MCB, the frequency response characteristics of the transmitting end of the linear optical module can be obtained. Evaluating the frequency response characteristics of the transmitting end of a linear optical module based on the VNA and the LCA has extremely high equipment costs, and after each evaluation of a channel in the linear optical module, the test fixture connection needs to be changed to perform the test on the next channel of the linear optical module. The test time for a linear optical module is very long and the efficiency is extremely low. Therefore, a method for evaluating the performance of optical modules suitable for large-scale mass production is needed, especially a method for evaluating the frequency response characteristics of the transmitting end of linear optical modules. Summary of the Invention

[0004] The purpose of the present invention is to propose a method for evaluating the frequency response characteristics of the transmitting end suitable for the production of linear optical modules, which can effectively evaluate the frequency response characteristics of the transmitting end of linear optical modules, save costs, improve efficiency, and have producibility.

[0005] To achieve the above-mentioned invention purpose, the embodiments of the present invention provide the following technical solutions:

[0006] A method for evaluating the frequency response characteristics of a linear optical module, comprising the following steps:

[0007] Step 1, connect the plug-in module to the pattern generator, connect the output end of the plug-in module to the electrical oscilloscope, the pattern generator sends a signal to the plug-in module, the electrical oscilloscope captures the waveform of the electrical signal output by the plug-in module, and after converting it to the frequency domain, the frequency response characteristic from the pattern generator to the driver chip of the linear optical module is obtained;

[0008] Step 2, connect the linear optical module to the pattern generator, connect the transmitting end of the linear optical module to the optical oscilloscope, the pattern generator sends a signal to the linear optical module, the optical oscilloscope captures the waveform of the optical signal output by the linear optical module, and after converting it to the frequency domain, the frequency response characteristic from the pattern generator to the transmitting end of the linear optical module is obtained;

[0009] Step 3, perform matrix point division on the frequency response characteristic from the pattern generator to the driver chip of the linear optical module and the frequency response characteristic from the pattern generator to the transmitting end of the linear optical module to obtain the frequency response characteristic of the transmitting end of the linear optical module.

[0010] Compared with the prior art, the beneficial effects of the present invention are:

[0011] (1) The present invention is very suitable for large-scale production requirements. The electrical oscilloscope is only used to evaluate the test equipment of BERT or BERT+MCB. After the evaluation, the linear optical module can be taken for production use without a large number of electrical oscilloscopes; while the optical oscilloscope is a common device in optical module manufacturers and there are many of them. Therefore, the test equipment required by the present invention can fully realize the test and evaluation of a large number of linear optical modules.

[0012] (2) The present invention has high test efficiency and can quickly perform the frequency response characteristics of the linear optical module. After the evaluation by the electrical oscilloscope, it can be taken to the production line for batch testing of the module. Moreover, for the optical port test of different channels, optical switches can be used for switching tests without adjusting the test fixture, and the test speed is extremely fast. Taking an 8-channel linear optical module as an example, the frequency response time of 8 channels is about 32s, while the fixture adjustment and test time of the traditional VNA+LCA test method are longer. The same test takes about 240s, and the costs of VNA and LCA are very high. Description of the Drawings

[0013] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following will briefly introduce the drawings required for the embodiments. It should be understood that the following drawings only show some embodiments of the present invention, so they should not be regarded as limiting the scope. For those of ordinary skill in the art, other related drawings can also be obtained based on these drawings without creative efforts.

[0014] Figure 1 Schematic diagram of the test equipment for the frequency response characteristics of the transmitting end of a linear optical module in the background technology;

[0015] Figure 2 Schematic diagram of the test equipment for the frequency response characteristics of the transmitting end of a linear optical module in the first implementable manner of Embodiment 1 of the present invention;

[0016] Figure 3(a) is a schematic diagram of the internal structure wiring and equivalent of the linear optical module in the embodiment of the present invention;

[0017] Figure 3(b) is a schematic diagram of the path equivalent in the embodiment of the present invention;

[0018] Figure 4 Schematic diagram of the test equipment for the frequency response characteristics of the transmitting end of a linear optical module in the second implementable manner of Embodiment 1 of the present invention;

[0019] Figure 5 Comparison diagram of the frequency response characteristics of the transmitting end of the linear optical module of the present solution (dashed line) and the background technology solution (solid line) when the Gain of the linear optical module in Embodiment 1 of the present invention is 21 dB and peaking is 0 dB;

[0020] Figure 6 Comparison diagram of the frequency response characteristics of the transmitting end of the linear optical module of the present solution (dashed line) and the background technology solution (solid line) when the Gain of the linear optical module in Embodiment 1 of the present invention is 21 dB and peaking is 3 dB;

[0021] Figure 7 Comparison diagram of the frequency response characteristics of the transmitting end of the linear optical module of the present solution (dashed line) and the background technology solution (solid line) when the Gain of the linear optical module in Embodiment 5 of the present invention is 21 dB and peaking is 0 dB;

[0022] Figure 8 Comparison diagram of the frequency response characteristics of the transmitting end of the linear optical module of the present solution (dashed line) and the background technology solution (solid line) when the Gain of the linear optical module in Embodiment 5 of the present invention is 21 dB and peaking is 3 dB;

[0023] Figure 9 Frequency response characteristic diagram from the bit error rate tester to the starting point of the drive chip of the linear optical module in the first implementable solution of Embodiment 1 of the present invention;

[0024] Figure 10 Frequency response characteristic diagram from the bit error rate tester to the transmitting end of the linear optical module in the first implementable manner of Embodiment 1 of the present invention;

[0025] Figure 11Frequency response characteristic diagram of the transmitting end of the linear optical module in the first implementable manner of Embodiment 1 of the present invention;

[0026] Figure 12 Frequency response characteristic diagram from the bit error rate tester to the starting point of the drive chip of the linear optical module in Embodiment 3 of the present invention;

[0027] Figure 13 Frequency response characteristic diagram from the bit error rate tester to the transmitting end of the linear optical module in Embodiment 3 of the present invention;

[0028] Figure 14 Frequency response characteristic diagram of the transmitting end of the linear optical module in Embodiment 3 of the present invention;

[0029] Figure 15 Frequency response characteristic diagram from the bit error rate tester to the starting point of the drive chip of the linear optical module in Embodiment 4 of the present invention;

[0030] Figure 16 Frequency response characteristic diagram from the bit error rate tester to the transmitting end of the linear optical module in Embodiment 4 of the present invention;

[0031] Figure 17 Frequency response characteristic diagram of the transmitting end of the linear optical module in Embodiment 4 of the present invention;

[0032] Figure 18 Frequency response characteristic diagram from the bit error rate tester to the starting point of the drive chip of the linear optical module in Embodiment 5 of the present invention;

[0033] Figure 19 Frequency response characteristic diagram from the bit error rate tester to the transmitting end of the linear optical module in Embodiment 5 of the present invention;

[0034] Figure 20 Frequency response characteristic diagram of the transmitting end of the linear optical module in Embodiment 5 of the present invention. Specific implementation manners

[0035] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Usually, the components of the embodiments of the present invention described and shown in the accompanying drawings here can be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the present invention to be protected, but only represents the selected embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative efforts belong to the scope of protection of the present invention.

[0036] It should be noted that similar reference numerals and letters denote similar items in the following figures. Therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures. At the same time, in the description of the present invention, terms such as "first" and "second" are only used for distinguishing descriptions, and cannot be understood as indicating or implying relative importance, or implying any such actual relationship or order between these entities or operations. In addition, terms such as "connected" and "coupled" can be directly connected between components or devices, can also be indirectly connected via other components or devices, or can be plugged between components or devices.

[0037] Embodiment 1:

[0038] The present invention is implemented through the following technical solutions. A method for evaluating the frequency response characteristics of a linear optical module is proposed, which is used to evaluate the frequency response characteristics of the transmitting end of the linear optical module. As Figure 2 shown, this method is implemented based on a set of test equipment. The test equipment includes: a pattern generator, a plug-in module, an electrical oscilloscope, and an optical oscilloscope. The pattern generator is used to send signals to the plug-in module and the linear optical module to be evaluated. The plug-in module is connected to the electrical oscilloscope, and the electrical oscilloscope can capture the electrical signal waveform output by the plug-in module; the linear optical module is connected to the optical oscilloscope, and the optical oscilloscope can capture the optical signal waveform output by the linear optical module.

[0039] Specifically, the signal output by the pattern generator is a digital signal. Therefore, in this solution, the pattern generator is preferably a bit error ratio tester (BERT). The signal pattern sent by the bit error ratio tester to the plug-in module or the linear optical module is PRBSQ (Pseudo-Random Bit Sequence for Pulse Amplitude Modulation 4, 4th-order pulse amplitude modulation pseudo-random bit sequence), such as PRBS13Q (Pseudo-Random Bit Sequence 13 for Pulse Amplitude Modulation 4, 4th-order pulse amplitude modulation pseudo-random bit sequence 13), or PRBS15Q (Pseudo-Random Bit Sequence 15 for Pulse Amplitude Modulation 4, 4th-order pulse amplitude modulation pseudo-random bit sequence 15), etc. The signal pattern sent by it is not limited in this embodiment and is only for example.

[0040] As the first implementable manner of this embodiment, the plug-in module is a Host Compliance Board (HCB); the Host Compliance Board is plugged into the bit error rate tester, and the output end of the Host Compliance Board is connected to an electrical oscilloscope; the linear optical module is plugged into the bit error rate tester, and the output end of the linear optical module is connected to an optical oscilloscope, and the linear optical module and the Host Compliance Board are not plugged into the bit error rate tester at the same time.

[0041] Based on this test device, the present invention proposes a method for evaluating the frequency response characteristics of a linear optical module, including the following steps:

[0042] Step 1, connect the plug-in module to the pattern generator, connect the output end of the plug-in module to the electrical oscilloscope, the pattern generator sends a signal to the plug-in module, the electrical oscilloscope captures the waveform of the electrical signal output by the plug-in module, and after converting it to the frequency domain, the frequency response characteristics from the pattern generator to the driver chip of the linear optical module are obtained.

[0043] Specifically, in this embodiment, the bit error rate tester (BERT) has a module insertion port, so the plug-in module can use the Host Compliance Board (HCB) to be directly inserted into the bit error rate tester. The Host Compliance Board and the electrical oscilloscope are connected by a radio frequency cable, and the electrical oscilloscope is a sampling oscilloscope or a real-time oscilloscope.

[0044] After completing the connection of the test device, the bit error rate tester outputs a signal to the Host Compliance Board. The pattern of this signal is PRBS, preferably PRBS13Q, that is, a pseudo-random sequence. The PRBS signal has rich frequency components and is easier to achieve frequency sweeping compared to the single-frequency sine wave of the VNA. In this embodiment, the frequency signal output by the bit error rate tester can also be a signal of other patterns as long as it can be captured by the electrical oscilloscope. When the electrical oscilloscope captures the waveform of the electrical signal, it is necessary to capture at least one complete PRBS pattern output by the bit error rate tester to avoid frequency truncation.

[0045] The host compliance board complies with TP1a (Test Point_1a) defined by the IEEE (Institute of Electrical and Electronics Engineers) protocol. The oscilloscope captures the electrical signal output by the host compliance board and displays the waveform of the electrical signal. The bandwidth of the oscilloscope needs to be greater than the Nyquist frequency of the signal being tested (the purpose is to avoid filtering out the fundamental frequency signal). In this embodiment, the bandwidth of the oscilloscope is set to 39.8 GHz, and the filter of the oscilloscope uses a fourth-order Bessel filter. After the oscilloscope captures the electrical signal output by the host compliance board, the function of the forward feedback equalizer (FFE) of the oscilloscope is used to optimize the electrical signal. Specifically, the forward feedback equalizer optimizes the electrical signal through the minimum mean squared error (MMSE) algorithm to obtain the FFE coefficients. Then, the optimized FFE coefficients are subjected to a fast Fourier transform (FFT) to convert the electrical signal from the time domain to the frequency domain, and then the logarithm is taken after dividing 1 by the frequency domain amplitude, so as to obtain the frequency response characteristic from the bit error rate tester to the driver chip of the linear optical module.

[0046] The electrical signal captured by the oscilloscope is equivalent to the signal given by the bit error rate tester to the driver chip of the linear optical module. Therefore, the frequency response characteristic from the bit error rate tester to the driver chip of the linear optical module can be obtained through the electrical signal output by the host compliance board captured by the oscilloscope.

[0047] Specifically, as shown in Figure 3(a), the structure of the linear optical module from input to output includes in sequence: a gold finger (i.e., the slot of the electrical receiving end of the linear optical module, equivalent to the electrical receiving end), a section of PCB line, a driver chip (i.e., Driver), a modulator, and a transmitting end (the end point of the modulator is the transmitting end of the linear optical module). After inserting the host compliance board into the bit error rate tester, the host compliance board is equivalent to the gold finger plus a section of PCB line in the linear optical module, as shown in Figure 3(a). Therefore, the electrical signal captured by the oscilloscope is equivalent to the signal given by the bit error rate tester to the driver chip of the linear optical module. In other words, it is the signal from the bit error rate tester to the gold finger and the signal from the gold finger through a section of PCB line to the starting point of the driver chip. Therefore, the frequency response characteristic from the bit error rate tester to the driver chip of the linear optical module (or the frequency response characteristic from the bit error rate tester to the starting point of the driver chip of the linear optical module) can be obtained through the electrical signal captured by the oscilloscope, which is equivalent to the frequency response characteristic of path 1 in Figure 3(b). As Figure 9The figure shows the frequency response characteristic diagram from the bit error rate tester to the starting point of the driver chip of the linear optical module.

[0048] It should be noted that after the electrical oscilloscope captures the electrical signal output by the host compliance board, the RF cable between the host compliance board and the electrical oscilloscope needs to be removed through the Remove S2P function of the electrical oscilloscope to eliminate the influence of the RF cable on the frequency response characteristics.

[0049] Step 2: Connect the linear optical module to the pattern generator, connect the transmitting end of the linear optical module to the optical oscilloscope. The pattern generator sends signals to the linear optical module, and the optical oscilloscope captures the optical signal waveform output by the linear optical module. After converting it to the frequency domain, the frequency response characteristic from the pattern generator to the transmitting end of the linear optical module is obtained.

[0050] Since the bit error rate tester has a module insertion port, after obtaining the frequency response characteristic from the bit error rate tester to the driver chip of the linear optical module, unplug the host compliance board from the bit error rate tester, and then insert the linear optical module (i.e., the device under test DUT) into the bit error rate tester in the same way as the host compliance board. Or, insert the linear optical module into another identical bit error rate tester in the same way as the host compliance board, which can realize step 2 and step 1 being carried out simultaneously or without a sequence to improve the test efficiency. The linear optical module and the optical oscilloscope are connected by an optical fiber. The optical oscilloscope is a sampling oscilloscope or a real-time oscilloscope, but it should be the same as the selection of the electrical oscilloscope. In this embodiment, both the electrical oscilloscope and the optical oscilloscope use sampling oscilloscopes; or, both the electrical oscilloscope and the optical oscilloscope use real-time oscilloscopes.

[0051] After completing the connection of the test equipment, the bit error rate tester outputs a signal to the linear optical module. The type of this signal should be the same as the signal output by the bit error rate tester to the host compliance board. In this embodiment, the PRBS code pattern is used, preferably PRBS13Q. The optical signal output by the transmitting end of the linear optical module is captured by the optical oscilloscope. When the optical oscilloscope captures the optical signal, it needs to capture at least one complete PRBS code pattern output by the bit error rate tester to avoid frequency truncation. The bandwidth of the optical oscilloscope needs to be greater than the Nyquist frequency of the signal under test. In this embodiment, the bandwidth of the optical oscilloscope is set to 39.8 GHz, and the filter of the optical oscilloscope uses a fourth-order Bessel filter. It should be noted that the bandwidth of the optical oscilloscope should be the same as the bandwidth of the electrical oscilloscope to avoid test errors caused by inconsistent bandwidths.

[0052] After the optical oscilloscope captures the optical signal waveform emitted by the linear optical module, the function of the forward feedback equalizer (FFE) of the optical oscilloscope is used to optimize the optical signal. Specifically, the forward feedback equalizer optimizes the optical signal through the minimum mean squared error (MMSE) algorithm to obtain the FFE coefficients. Then, the obtained FFE coefficients are subjected to a fast Fourier transform (FFT) to transform the optical signal from the time domain to the frequency domain, and then the logarithm is taken after dividing 1 by the frequency domain amplitude, so as to obtain the frequency response characteristic from the bit error rate tester to the transmitting end of the linear optical module.

[0053] Specifically, as shown in Fig. 3(a), the structure of the linear optical module from input to output includes, in sequence: a gold finger, a section of PCB circuit, a driver chip, a modulator, and a transmitting end. The optical signal captured by the optical oscilloscope is the signal from the bit error rate tester to the transmitting end of the linear optical module, as can be seen in Fig. 3(b). Therefore, the frequency response characteristic from the bit error rate tester to the transmitting end of the linear optical module can be obtained through the optical signal captured by the optical oscilloscope, that is, the frequency response characteristic of path 2 in Fig. 3(b). As Figure 10 shown is the frequency response characteristic diagram from the bit error rate tester to the transmitting end of the linear optical module.

[0054] Step 3: Perform matrix point division on the frequency response characteristic from the pattern generator to the driver chip of the linear optical module and the frequency response characteristic from the pattern generator to the transmitting end of the linear optical module to obtain the frequency response characteristic of the transmitting end of the linear optical module.

[0055] Based on the principle of matrix point division in the frequency domain, which is the inverse application of the time-domain convolution theorem, perform matrix point division on the frequency response characteristic from the bit error rate tester to the driver chip of the linear optical module and the frequency response characteristic from the bit error rate tester to the transmitting end of the linear optical module. As shown in Fig. 3(b), that is, remove the frequency response characteristic from the bit error rate tester to the starting point of the driver chip of the linear optical module (path 1) in the frequency response characteristic from the bit error rate tester to the transmitting end of the linear optical module (path 2), so as to obtain the frequency response characteristic from the starting point of the driver chip of the linear optical module to the transmitting end (path 3), which is also the frequency response characteristic of the transmitting end of the linear optical module. As Figure 11 shown is the frequency response characteristic diagram of the transmitting end of the linear optical module.

[0056] As the second implementable manner of this embodiment, as Figure 4As shown in the figure, the plug-in module includes a Module Compliance Board (MCB) and a Host Compliance Board (HCB); the Module Compliance Board is connected to the bit error rate tester through a radio frequency cable, the Host Compliance Board is plugged onto the Module Compliance Board, and the output end of the Host Compliance Board is connected to an electrical oscilloscope; the linear optical module is plugged onto the Module Compliance Board, the output end of the linear optical module is connected to an optical oscilloscope, and the linear optical module and the Host Compliance Board are not plugged onto the bit error rate tester simultaneously.

[0057] Based on this test equipment, the present invention proposes a method for evaluating the frequency response characteristics of a linear optical module, including the following steps:

[0058] Step 1, connect the plug-in module to the pattern generator, connect the output end of the plug-in module to the electrical oscilloscope, the pattern generator sends a signal to the plug-in module, the electrical oscilloscope captures the waveform of the electrical signal output by the plug-in module, and after converting it to the frequency domain, the frequency response characteristics from the pattern generator to the driver chip of the linear optical module are obtained.

[0059] Specifically, the Bit Error Ratio Tester (BERT) does not have a module insertion port, so a Module Compliance Board (MCB) is used to achieve the indirect connection between the bit error rate tester and the Host Compliance Board. The bit error rate tester is connected to the Module Compliance Board through a radio frequency cable, the Host Compliance Board is plugged onto the Module Compliance Board, and the output end of the Host Compliance Board is connected to the electrical oscilloscope through a radio frequency cable.

[0060] The electrical oscilloscope captures the electrical signal output by the Host Compliance Board and displays the waveform of the electrical signal. After the electrical oscilloscope captures the electrical signal output by the Host Compliance Board, the function of the Forward Feedback Equalizer (FFE) of the electrical oscilloscope is used to optimize the electrical signal. Specifically, the Forward Feedback Equalizer optimizes the electrical signal through the Minimum Mean Squared Error (MMSE) algorithm to obtain the FFE coefficient. Then, the optimized FFE coefficient is subjected to a Fast Fourier Transform (FFT) to convert the electrical signal from the time domain to the frequency domain, and then the logarithm is taken after dividing 1 by the frequency domain amplitude, so as to obtain the frequency response characteristics from the bit error rate tester to the driver chip of the linear optical module.

[0061] Step 2: Connect the linear optical module to the pattern generator. Connect the transmitting end of the linear optical module to the optical oscilloscope. The pattern generator sends signals to the linear optical module, and the optical oscilloscope captures the waveform of the optical signal output by the linear optical module. After converting it to the frequency domain, the frequency response characteristic from the pattern generator to the transmitting end of the linear optical module is obtained.

[0062] Since the bit error rate tester does not have a module insertion port, after connecting it to the bit error rate tester through a radio frequency cable with the help of a module compliance board, pull out the host compliance board inserted into the module compliance board in Step 1, and insert the linear optical module (i.e., the device under test DUT) into the module compliance board in the same way as the host compliance board. Alternatively, connect another identical module compliance board to another identical bit error rate tester through a radio frequency cable, and insert the linear optical module into this module compliance board in the same way as the host compliance board, so that Step 1 and Step 2 can be carried out simultaneously or without a sequence to improve the test efficiency. The linear optical module is connected to the optical oscilloscope through an optical fiber.

[0063] After the optical oscilloscope captures the optical signal emitted by the linear optical module, use the function of the forward feedback equalizer (FFE) of the optical oscilloscope to optimize the optical signal. Specifically, the forward feedback equalizer optimizes the optical signal through the minimum mean squared error (MMSE) algorithm to obtain the FFE coefficients. Then, perform a fast Fourier transform (FFT) on the optimized FFE coefficients to convert the optical signal from the time domain to the frequency domain, and then take the logarithm after dividing 1 by the frequency domain amplitude, so as to obtain the frequency response characteristic from the bit error rate tester to the transmitting end of the linear optical module.

[0064] Step 3: Perform a matrix point division on the frequency response characteristic from the pattern generator to the driver chip of the linear optical module and the frequency response characteristic from the pattern generator to the transmitting end of the linear optical module to obtain the frequency response characteristic of the transmitting end of the linear optical module.

[0065] In this embodiment, the difference between the second implementation and the first implementation lies in whether the bit error rate tester has a module insertion port. If the bit error rate tester has a module insertion port, directly insert the host compliance board into the bit error rate tester through the first implementation. Similarly, the linear optical module can also be directly inserted into the bit error rate tester. If the bit error rate tester does not have a module insertion port, after connecting it to the bit error rate tester with the help of a module compliance board through the second implementation, then insert the host compliance board or the linear optical module into the module compliance board.

[0066] This solution can accurately evaluate the frequency response characteristic of the transmitting end of the linear optical module. Figure 5Frequency response characteristic diagram of the transmitting end of a linear optical module for the present solution (dashed line) and the prior art VAN+LCA solution (solid line) when Gain = 21 dB and peaking = 0 dB. The abscissa is frequency, and the ordinate is signal amplitude. Figure 6 Frequency response characteristic diagram of the transmitting end of a linear optical module for the present solution (dashed line) and the prior art solution (solid line) when Gain = 21 dB and peaking = 3 dB. It can be seen that the frequency response difference between the present solution and the prior art solution is small, but the present solution saves costs and improves efficiency compared with the prior art, and has producibility. It should be noted that the frequency response characteristic comparison diagrams for the two implementation methods in Embodiment 1 are both Figure 5 and Figure 6 . Among them, Gain represents gain, peaking represents peak compensation, and dB represents decibel.

[0067] It should also be noted that there is no strict sequence between Step 1 and Step 2 in the present solution. Step 1 can be executed first and then Step 2, or Step 2 can be executed first and then Step 1, or Step 1 and Step 2 can be executed simultaneously. Even if several linear optical modules need to be evaluated in the present solution, Step S1 only needs to be executed once to obtain the frequency response characteristic from the pattern generator to the driver chip of the linear optical module. For example, if the frequency response characteristics of the transmitting ends of 100 linear optical modules need to be evaluated in this batch, and each linear optical module has 8 optical channels, the following at least 3 methods can be used to achieve this:

[0068] 1. Execute Step S1 once to obtain the frequency response characteristic from the pattern generator to the driver chip of the linear optical module; pull out the host compliance board on the pattern generator used in Step S1, and insert the first linear optical module into the pattern generator in the same way. The testing of all channels of this linear optical module can be completed in about 32 s; then directly replace the first linear optical module with the second linear optical module and insert it into the pattern generator in the same way until all 100 linear optical modules are tested.

[0069] 2. Execute Step S1 once to obtain the frequency response characteristic from the pattern generator to the driver chip of the linear optical module; insert the linear optical module into another pattern generator with the same structure in Step S2, and the patterns sent by the two pattern generators are exactly the same. The testing of all channels of this linear optical module can be completed in about 32 s, and Step S2 can be carried out simultaneously with Step S1 because two pattern generators with the same structure are used respectively; then pull out the first linear optical module, and directly replace it with the second linear optical module and insert it into the pattern generator in the same way until all 100 linear optical modules are tested.

[0070] 3. Execute step S1 once to obtain the frequency response characteristic from the pattern generator to the driver chip of the linear optical module; in step S2, insert 100 linear optical modules into another 100 pattern generators with the same structure respectively, and the patterns sent by these 100 pattern generators are exactly the same. All channels of the 100 linear optical modules can be tested in about 32 s, and step S2 can be carried out simultaneously with step S1 because 100 pattern generators with the same structure are used respectively.

[0071] It can be seen that compared with the VNA+LCA solution in the background art, since the costs of the VNA and LCA are very high, the proposed solution can not only greatly reduce the cost, but also significantly reduce the evaluation time and improve the efficiency because manufacturers of linear optical modules all have a large number of pattern generators and optical oscilloscopes.

[0072] Embodiment 2:

[0073] Based on the test equipment with two feasible implementation schemes in Embodiment 1, as Figure 2 shown, the present invention provides a method for evaluating the frequency response characteristic of a linear optical module, including the following steps:

[0074] Step 1: Connect the plug-in module to the pattern generator, connect the output end of the plug-in module to the electrical oscilloscope. The pattern generator sends a signal to the plug-in module, and the electrical oscilloscope captures the waveform of the electrical signal output by the plug-in module. After converting it to the frequency domain, the frequency response characteristic from the pattern generator to the receiving end of the linear optical module is obtained.

[0075] The difference between this embodiment and Embodiment 1 is that after the electrical oscilloscope captures the electrical signal output by the host compliance board, the RF cable between the host compliance board and the electrical oscilloscope needs to be removed through the Remove S2P function of the electrical oscilloscope. Then the host compliance board is equivalent to a section of PCB line between the gold finger and the starting point of the driver chip in the linear optical module. If the accurate S-parameter model of the host compliance board is further known (the S-parameter model refers to the S-parameter file that can reflect the frequency response characteristic, and this S-parameter file usually contains the amplitude and phase corresponding to different frequencies), the S-parameter model can be removed through the RemoveS2P function of the electrical oscilloscope. Please refer to Fig. 3(a). The electrical signal obtained after removal is equivalent to the signal given by the bit error rate tester to the gold finger, that is, the signal given by the bit error rate tester to the receiving end of the linear optical module, so as to obtain the frequency response characteristic from the bit error rate tester to the receiving end of the linear optical module.

[0076] Step 2: Connect the linear optical module to the pattern generator. Connect the transmitting end of the linear optical module to the optical oscilloscope. The pattern generator sends a signal to the linear optical module, and the optical oscilloscope captures the optical signal waveform output by the linear optical module. After converting it to the frequency domain, the frequency response characteristic from the pattern generator to the transmitting end of the linear optical module is obtained.

[0077] Step 3: Perform matrix point division on the frequency response characteristic from the pattern generator to the receiving end of the linear optical module and the frequency response characteristic from the pattern generator to the transmitting end of the linear optical module to obtain the frequency response characteristic of the linear optical module.

[0078] Based on the principle of matrix point division in the frequency domain for the inverse application of the time-domain convolution theorem, perform matrix point division on the frequency response characteristic from the bit error rate tester to the receiving end of the linear optical module and the frequency response characteristic from the bit error rate tester to the transmitting end of the linear optical module. In other words, remove the frequency response characteristic from the bit error rate tester to the receiving end of the linear optical module in the frequency response characteristic from the bit error rate tester to the transmitting end of the linear optical module, so as to obtain the frequency response characteristic from the receiving end to the transmitting end of the linear optical module, that is, the frequency response characteristic of the entire linear optical module.

[0079] Other parts of this embodiment are the same as those of Embodiment 1, so they will not be elaborated here.

[0080] Embodiment 3:

[0081] The difference between this embodiment and Embodiment 1 or Embodiment 2 is that the electrical oscilloscope and the optical oscilloscope do not have the function of a Forward Feedback Equalizer (FFE), so it is necessary to save and export the electrical signal waveform and the optical signal waveform.

[0082] After exporting the electrical signal waveform or the optical signal waveform, first perform channel estimation based on the Least Squares (LS) method to obtain the channel matrix H, the signal power , the noise power , and the specific steps are as follows:

[0083] Send a known PRBS signal at the transmitting end of the channel, and use an electrical oscilloscope / optical oscilloscope to capture the channel output waveform at the receiving end of the channel. According to the least squares solution, there is:

[0084] where H1 is the channel impulse response matrix, with a dimension of N1×1, and N1 is the pulse length of the channel estimation; X is the PRBS signal matrix input to the channel, with a dimension of N2×N1 and is a circulant matrix, and N2 is the length of the PRBS signal; X H is the Hermitian matrix of X; Y is the channel output signal matrix captured by the optical oscilloscope / electrical oscilloscope, with a dimension of N2×1.

[0085] The convolution matrix of the channel impulse response matrix H1 is the channel matrix , channel matrix The dimension is (N1+N-1)×N, where N is the length of the FFE coefficient.

[0086] Based on the channel matrix , the FFE coefficient is calculated according to the Minimum Mean Squared Error (MMSE) algorithm:

[0087] Among them, G is the FFE coefficient, and the dimension is N×(N1+N-1); for The Hermitian matrix of the channel impulse response matrix H1 is the square of the maximum value of the signal power. ; The variance of H1X-Y is the noise power ; I is the unit matrix with dimension (N1+N-1)×(N1+N-1).

[0088] Based on the first implementation method in Example 1, after the electrical signal and the optical signal are derived, the FFE coefficient obtained by external algorithm optimization is subjected to Fast Fourier Transform (FFT) to convert from the time domain to the frequency domain, and then the frequency domain amplitude is divided by 1 to obtain the logarithm, thereby obtaining the frequency response characteristics from the bit error rate tester to the starting point of the driver chip of the linear optical module, such as Figure 12 As shown; the frequency response characteristics of the bit error rate tester to the transmitting end of the linear optical module can also be obtained, such as Figure 13 As shown; the frequency response characteristics from the bit error rate tester to the starting point of the driver chip of the linear optical module and the frequency response characteristics from the bit error rate tester to the transmitting end of the linear optical module are matrix-divided to obtain the frequency response characteristics of the transmitting end of the linear optical module, as shown in Figure 14 shown.

[0089] The other parts of this embodiment are the same as those of the other embodiments described above, and thus will not be described in detail.

[0090] Embodiment 4:

[0091] In one solution, based on the test equipment proposed in Example 1, this embodiment proposes a method for evaluating the frequency response characteristics of a linear optical module, including the following steps:

[0092] Step 1: Connect the plug-in module to the pattern generator. Connect the output end of the plug-in module to the oscilloscope. The pattern generator sends signals to the plug-in module, and the oscilloscope captures the electrical signal waveform output by the plug-in module. After converting it to the frequency domain, the frequency response characteristic from the pattern generator to the driver chip of the linear optical module is obtained.

[0093] After the oscilloscope captures the electrical signal output by the host compliance board, the oscilloscope converts the electrical signal from the time domain to the frequency domain through the Fast Fourier Transform (FFT), so as to obtain the frequency response characteristic from the bit error rate tester to the starting point of the driver chip of the linear optical module, as Figure 15 shown.

[0094] Step 2: Connect the linear optical module to the pattern generator. Connect the transmitting end of the linear optical module to the optical oscilloscope. The pattern generator sends signals to the linear optical module, and the optical oscilloscope captures the optical signal waveform output by the linear optical module. After converting it to the frequency domain, the frequency response characteristic from the pattern generator to the transmitting end of the linear optical module is obtained.

[0095] After the optical oscilloscope captures the optical signal emitted by the linear optical module, the optical oscilloscope converts the optical signal from the time domain to the frequency domain through the Fast Fourier Transform (FFT), so as to obtain the frequency response characteristic from the bit error rate tester to the transmitting end of the linear optical module, as Figure 16 shown.

[0096] Step 3: Perform matrix point division on the frequency response characteristic from the pattern generator to the driver chip of the linear optical module and the frequency response characteristic from the pattern generator to the transmitting end of the linear optical module to obtain the frequency response characteristic of the transmitting end of the linear optical module.

[0097] Based on the principle of matrix point division in the frequency domain for the inverse application of the time-domain convolution theorem, perform matrix point division on the frequency response characteristic from the bit error rate tester to the starting point of the driver chip of the linear optical module and the frequency response characteristic from the bit error rate tester to the transmitting end of the linear optical module, and then use piecewise fourth-order polynomial fitting to reduce the influence of spectral noise, so as to obtain the frequency response characteristic of the transmitting end of the linear optical module, as Figure 17 shown.

[0098] The difference between this embodiment and Embodiment 1 is that in Steps 1 and 2, no FFE optimization is performed on the captured electrical and optical signals, and the Fast Fourier Transform (FFT) is directly performed, and no operation of dividing 1 by the frequency domain amplitude and then taking the logarithm is performed on the Fast Fourier Transform result. However, after performing matrix point division in Step 3, it is necessary to use piecewise fourth-order polynomial fitting to reduce the influence of spectral noise, so as to obtain the frequency response characteristic of the transmitting end of the linear optical module.

[0099] This embodiment can accurately evaluate the frequency response characteristics of the transmitting end of a linear optical module. In the scheme where the electrical oscilloscope and the optical oscilloscope perform FFT transformation directly without optimizing the electrical signal and the optical signal with FFE, Figure 7 When the Gain of the linear optical module is 21 dB and the peaking is 0 dB, the figure shows the frequency response characteristics of the transmitting end of the linear optical module of this embodiment (dashed line) and the prior art scheme (solid line). The abscissa is the frequency, and the ordinate is the signal amplitude. Figure 8 When the Gain of the linear optical module is 21 dB and the peaking is 3 dB, the figure shows the frequency response characteristics of the transmitting end of the linear optical module of this embodiment (dashed line) and the prior art scheme (solid line). It can be seen that the frequency response difference between this scheme and the prior art scheme is small, but this scheme saves costs and improves efficiency compared with the prior art, and has producibility. It should be noted that the comparison diagrams of the frequency response characteristics of the two schemes in Embodiment 1 are all Figure 7 and Figure 8 . Among them, Gain represents gain, peaking represents peak compensation, and dB represents decibel.

[0100] Other parts of this embodiment are the same as those of Embodiment 1, so they will not be described in detail.

[0101] In another scheme, this embodiment can also be implemented on the basis of Embodiment 2.

[0102] Embodiment 5:

[0103] On the basis of Embodiment 1, this embodiment saves the electrical signal waveform captured by the electrical oscilloscope and the optical signal waveform captured by the optical oscilloscope and then exports them. Using an external Fast Fourier Transform (FFT) algorithm, the electrical signal and the optical signal are converted from the time domain to the frequency domain, and the frequency response characteristics from the error rate tester to the starting point of the drive chip of the linear optical module as shown in Figure 18 can be obtained, and the frequency response characteristics from the error rate tester to the transmitting end of the linear optical module as shown in Figure 19 can be obtained. Finally, after performing matrix point division and then using piecewise fourth-order polynomial fitting to reduce the influence of spectral noise, the frequency response characteristics of the transmitting end of the linear optical module as shown in Figure 20 can be obtained.

[0104] In this embodiment, the captured electrical and optical signals are saved and exported in Steps 1 and 2, without FFE optimization, and directly subjected to external Fast Fourier Transform (FFT). Moreover, the operation of dividing 1 by the frequency-domain amplitude and then taking the logarithm of the Fast Fourier Transform result is not performed. However, after matrix point division in Step 3, it is necessary to use external piecewise fourth-order polynomial fitting to reduce the influence of spectral noise, so as to obtain the frequency response characteristics of the transmitting end of the linear optical module.

[0105] The above are only specific embodiments of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art within the technical scope disclosed by the present invention can easily think of changes or substitutions, which should all be covered within the protection scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the protection scope of the claims.

Claims

1. A method for evaluating the frequency response characteristics of a linear optical module, characterized in that: The following steps are involved: Step 1, connect the plug-in module to the pattern generator, connect the output end of the plug-in module to the electrical oscilloscope, the pattern generator sends a signal to the plug-in module, the electrical oscilloscope captures the electrical signal waveform output by the plug-in module, converts it to the frequency domain, and obtains the frequency response characteristics of the driving chip from the pattern generator to the linear optical module; Step 2, connecting the linear optical module to the pattern generator, connecting the transmitting end of the linear optical module to the optical oscilloscope, the pattern generator sends a signal to the linear optical module, the optical oscilloscope captures the optical signal waveform output by the linear optical module, converts it to the frequency domain, and obtains the frequency response characteristics from the pattern generator to the transmitting end of the linear optical module; Step 3: Perform matrix dot division on the frequency response characteristic from the pattern generator to the driver chip of the linear optical module and the frequency response characteristic from the pattern generator to the transmitting end of the linear optical module to obtain the frequency response characteristic of the transmitting end of the linear optical module.

2. The method for evaluating the frequency response characteristics of a linear optical module according to claim 1, wherein: The code generator is a bit error rate tester.

3. The method for evaluating the frequency response characteristics of a linear optical module according to claim 2, characterized in that: The signal code type sent by the bit error rate tester to the plug-in module and the linear optical module is PRBS.

4. The method for evaluating the frequency response characteristics of a linear optical module according to claim 3, characterized in that: When the electrical oscilloscope captures the electrical signal waveform and the optical oscilloscope captures the optical signal waveform, it is necessary to capture at least one complete PRBS pattern output by the bit error rate tester.

5. The method for evaluating the frequency response characteristics of a linear optical module according to claim 1, characterized in that: The plug-in module is a host compliance board; In the step 1, the host compliance board is plugged into the pattern generator, and the output end of the host compliance board is connected to the electrical oscilloscope via a radio frequency cable; In the step 2, the host compliance board is unplugged from the code generator, the linear optical module is plugged into the code generator, and the transmitting end of the linear optical module is connected to the optical oscilloscope via optical fiber; or, in the step 2, the linear optical module is plugged into another identical code generator, and the transmitting end of the linear optical module is connected to the optical oscilloscope via optical fiber.

6. The method for evaluating the frequency response characteristics of a linear optical module according to claim 1, characterized in that: The plug-in module includes a module compliance board and a host compliance board; In the step 1, the module compliance board is connected to the code generator through a radio frequency cable, the host compliance board is plugged into the module compliance board, and the output end of the host compliance board is connected to the electrical oscilloscope through a radio frequency cable; In the step 2, the host compliance board is unplugged from the module compliance board, the linear optical module is plugged into the module compliance board, and the transmitting end of the linear optical module is connected to the optical oscilloscope through the optical fiber; or, in the step 2, other identical module compliance boards are connected to another identical code generator through a radio frequency cable, the linear optical module is plugged into the module compliance board, and the transmitting end of the linear optical module is connected to the optical oscilloscope through the optical fiber.

7. A method for evaluating the frequency response characteristics of a linear optical module according to claim 1, 5 or 6, characterized in that: In step 1, the electrical oscilloscope captures the electrical signal waveform output by the plug-in module, converts it into the frequency domain, and obtains the frequency response characteristics of the driving chip from the code generator to the linear optical module, which specifically includes: After the electrical oscilloscope captures the electrical signal waveform output by the host compliance board, the electrical signal is optimized using the forward feedback equalizer function of the electrical oscilloscope. The forward feedback equalizer optimizes the electrical signal through the minimum mean square error algorithm to obtain the FFE coefficient. The optimized FFE coefficient is then subjected to a fast Fourier transform to convert the electrical signal from the time domain to the frequency domain, and then the logarithm is calculated by dividing 1 by the frequency domain amplitude, thereby obtaining the frequency response characteristics of the driver chip from the pattern generator to the linear optical module. In step 2, the optical oscilloscope captures the optical signal waveform output by the linear optical module, converts it into the frequency domain, and obtains the frequency response characteristics of the code generator to the transmitting end of the linear optical module, which specifically includes: After the optical oscilloscope captures the optical signal waveform transmitted by the linear optical module, the optical signal is optimized by using the forward feedback equalizer function of the optical oscilloscope. The forward feedback equalizer optimizes the optical signal through the minimum mean square error algorithm to obtain the FFE coefficient. The optimized FFE coefficient is then subjected to a fast Fourier transform to convert the optical signal from the time domain to the frequency domain. The logarithm is then calculated by dividing 1 by the frequency domain amplitude to obtain the frequency response characteristics from the pattern generator to the transmitting end of the linear optical module.

8. The method for evaluating the frequency response characteristics of a linear optical module according to claim 1, 5 or 6, characterized in that: In step 1 and step 2, after the electrical oscilloscope captures the electrical signal waveform output by the plug-in module and the optical oscilloscope captures the optical signal waveform output by the linear optical module, the electrical signal waveform and the optical signal waveform are saved and exported, and the FEE coefficient is calculated using an external algorithm. First, channel estimation is performed based on the least squares solution to obtain the channel matrix , signal power , Noise Power , the specific steps are as follows: A known PRBS signal is sent at the transmitting end of the channel, and an electrical oscilloscope / optical oscilloscope is used at the receiving end of the channel to capture the channel output waveform. According to the least squares solution, we have: Among them, H1 is the channel impulse response matrix, with a dimension of N1×1, N1 is the pulse length of the channel estimation; X is the PRBS signal matrix of the channel input, with a dimension of N2×N1, and is a circulant matrix, N2 is the PRBS signal length; X H is the Hermitian matrix of X; Y is the channel output signal matrix captured by the optical oscilloscope / electrical oscilloscope, with a dimension of N2×1; The convolution matrix of the channel impulse response matrix H1 is the channel matrix , channel matrix The dimension is (N1+N-1)×N, where N is the length of the FFE coefficient; Based on the channel matrix , calculate the FFE coefficient according to the minimum mean square error algorithm: Among them, G is the FFE coefficient, and the dimension is N×(N1+N-1); for The Hermitian matrix of the channel impulse response matrix H1 is the square of the maximum value of the signal power. ; The variance of H1X-Y is the noise power ; I is the unit matrix with dimension (N1+N-1)×(N1+N-1).

9. A method for evaluating the frequency response characteristics of a linear optical module according to claim 1, 5 or 6, characterized in that: In step 1, the electrical oscilloscope captures the electrical signal waveform output by the plug-in module, converts it into the frequency domain, and obtains the frequency response characteristics of the driving chip from the code generator to the linear optical module, which specifically includes: The electrical oscilloscope captures the electrical signal waveform output by the host compliance board, performs fast Fourier transform to convert the electrical signal from the time domain to the frequency domain, and obtains the frequency response characteristics of the driver chip from the code generator to the linear optical module; In step 2, the optical oscilloscope captures the optical signal waveform output by the linear optical module, converts it into the frequency domain, and obtains the frequency response characteristics of the code generator to the transmitting end of the linear optical module, which specifically includes: The optical oscilloscope captures the optical signal waveform emitted by the linear optical module, performs fast Fourier transform to convert the optical signal from the time domain to the frequency domain, and obtains the frequency response characteristics from the code generator to the transmitting end of the linear optical module; In step 3, after the step of performing matrix dot division on the frequency response characteristic from the pattern generator to the driving chip of the linear optical module and the frequency response characteristic from the pattern generator to the transmitting end of the linear optical module, the method further includes: The frequency response characteristics of the transmitting end of the linear optical module are obtained by using piecewise fourth-order polynomial fitting to reduce the influence of spectrum noise.

10. A method for evaluating frequency response characteristics of a linear optical module according to claim 5 or 6, characterized in that: In step 1, after the electrical oscilloscope captures the electrical signal output by the host compliance board, the S parameter model is removed by using the Remove S2P function of the electrical oscilloscope according to the known S parameter model of the host compliance board, thereby obtaining the frequency response characteristics from the pattern generator to the receiving end of the linear optical module; Then in step 3, the frequency response characteristic from the pattern generator to the receiving end of the linear optical module is matrix-divided with the frequency response characteristic from the pattern generator to the transmitting end of the linear optical module to obtain the frequency response characteristic of the linear optical module.

11. The method for evaluating the frequency response characteristics of a linear optical module according to claim 1, characterized in that: In step 1, after the electrical oscilloscope captures the electrical signal waveform output by the plug-in module, the RF cable between the host compliance board and the electrical oscilloscope is removed through the Remove S2P function of the electrical oscilloscope.

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