A method for evaluating the frequency response characteristics of linear optical modules

Abstract

The present invention relates to the technical field of optical module performance testing and discloses a method for evaluating the frequency response characteristics of a linear optical module. The method comprises the following steps: a pattern generator sends a signal to a plug-in module, an electrical oscilloscope captures the waveform of the electrical signal output by the plug-in module, converts the waveform to the frequency domain, and obtains the frequency response characteristics from the pattern generator to the driver chip of the linear optical module; a pattern generator sends a signal to the linear optical module, an optical oscilloscope captures the waveform of the optical signal output by the linear optical module, converts the waveform to the frequency domain, and obtains the frequency response characteristics from the pattern generator to the transmitter of the linear optical module; and a matrix dot division is performed between the frequency response characteristics from the pattern generator to the driver chip of the linear optical module and the frequency response characteristics from the pattern generator to the transmitter of the linear optical module to obtain the frequency response characteristics of the transmitter of the linear optical module. The present invention can effectively evaluate the frequency response characteristics of the transmitter of the linear optical module, while also saving costs, improving efficiency, and ensuring manufacturability.

Description

Technical Field

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

[0002] With the rapid development of digital communications and AI technologies, the demand for optical modules has increased dramatically. Linear optical modules are particularly popular due to their low power consumption and low latency. To ensure product quality, manufacturers must evaluate the performance of linear optical modules on the production line. For linear optical modules, evaluating the frequency response characteristics of the transmitter is particularly important.

[0003] In the existing technology, it is a common method to evaluate the frequency response characteristics of the transmitter of linear optical modules (such as linear drive pluggable optical modules LPO, optoelectronic co-package CPO, etc.) based on vector network analyzers (VNA) and lightwave component analyzers (LCA). Figure 1 As shown, the VNA transmitter outputs sinusoidal signals of different frequencies to the Module Compliance Board (MCB), a test fixture. The signals are then fed to the electrical receiver of the linear optical module (DUT). The sinusoidal signals pass through the MCB and the linear optical module before being output to the LCA. The LCA performs optoelectronic conversion and returns the sinusoidal signals to the VNA. The VNA compares the difference between the transmitted and received sinusoidal signals and, after removing the influence of the MCB, determines the frequency response characteristics of the linear optical module's transmitter. Evaluating the frequency response characteristics of the linear optical module's transmitter using a VNA and LCA is extremely costly. Furthermore, after evaluating each channel within a linear optical module, the test fixture must be replaced before testing the next channel. This results in lengthy testing and is extremely inefficient. Therefore, a method for evaluating optical module performance suitable for large-scale mass production is needed, particularly for evaluating the frequency response characteristics of the linear optical module's transmitter. Summary of the Invention

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

[0005] In order to achieve the above-mentioned object of the invention, the embodiment of the present invention provides the following technical solutions:

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

[0007] Step 1: Connect the plug-in module to the pattern generator, and 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 electrical signal waveform output by the plug-in module. After converting it to the frequency domain, the frequency response characteristics of the driver chip from the pattern generator to the linear optical module are obtained.

[0008] Step 2: Connect the linear optical module to the pattern generator. Connect the transmitter 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 and converts it to the frequency domain to obtain the frequency response characteristics from the pattern generator to the transmitter of the linear optical module.

[0009] 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 transmitter of the linear optical module to obtain the frequency response characteristic of the transmitter of the linear optical module.

[0010] Compared with the prior art, the present invention has the following beneficial effects:

[0011] (1) The present invention is very suitable for large-scale production needs. The electrical oscilloscope is only used to evaluate the test equipment of BERT or BERT+MCB. The linear optical module after evaluation can be used in production without the need for a large number of electrical oscilloscopes. Optical oscilloscopes are commonly used equipment by optical module manufacturers and are available in large quantities. Therefore, the test equipment required by the present invention can fully realize the test and evaluation of large quantities of linear optical modules.

[0012] (2) The present invention has high testing efficiency and can quickly measure the frequency response characteristics of linear optical modules. After evaluation on an oscilloscope, the modules can be tested in batches on the production line. In addition, optical switches can be used for switching tests of different channels at the optical port without adjusting the test fixture. The test speed is extremely fast. Taking an 8-channel linear optical module as an example, it takes about 32 seconds to complete the frequency response of 8 channels. The fixture adjustment and test time of the traditional VNA+LCA test method is longer, and the same test takes about 240 seconds. In addition, the cost of VNA and LCA is very high. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for use in the embodiments. It should be understood that the following drawings only illustrate certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other relevant drawings can be obtained based on these drawings without paying any creative work.

[0014] Figure 1 Schematic diagram of a device for testing the frequency response characteristics of a linear optical module transmitter in the background technology;

[0015] Figure 2 Schematic diagram of a test device for frequency response characteristics of a linear optical module transmitter in a first possible implementation manner of Example 1 of the present invention;

[0016] FIG3( a ) is a schematic diagram showing the internal structure and wiring of a linear optical module according to an embodiment of the present invention;

[0017] FIG3( b ) is a schematic diagram of path equivalence according to an embodiment of the present invention;

[0018] Figure 4 Schematic diagram of a device for testing the frequency response characteristics of a linear optical module transmitter in a second possible implementation manner of Example 1 of the present invention;

[0019] Figure 5 This is a comparison chart of the frequency response characteristics of the transmitting end of the linear optical module of this solution (dashed line) and the background art solution (solid line) when the gain of the linear optical module in Example 1 of the present invention is 21 dB and the peaking is 0 dB;

[0020] Figure 6 This is a comparison chart of the frequency response characteristics of the transmitting end of the linear optical module of this solution (dashed line) and the background art solution (solid line) when the gain of the linear optical module in Example 1 of the present invention is 21 dB and the peaking is 3 dB;

[0021] Figure 7 This is a comparison chart of the frequency response characteristics of the transmitting end of the linear optical module of this solution (dashed line) and the background art solution (solid line) when the gain of the linear optical module in Example 5 of the present invention is 21 dB and the peaking is 0 dB;

[0022] Figure 8 This is a comparison chart of the frequency response characteristics of the transmitting end of the linear optical module of this solution (dashed line) and the background art solution (solid line) when the gain of the linear optical module in Example 5 of the present invention is 21 dB and the peaking is 3 dB;

[0023] Figure 9 This is a frequency response characteristic diagram from the bit error rate tester to the starting point of the driver chip of the linear optical module in the first possible implementation scheme of Example 1 of the present invention;

[0024] Figure 10 This is a frequency response characteristic diagram of the transmission end of the bit error rate tester to the linear optical module in the first possible implementation mode of Example 1 of the present invention;

[0025] Figure 11This is a frequency response characteristic diagram of the transmitting end of the linear optical module in the first possible implementation mode of Example 1 of the present invention;

[0026] Figure 12 This is a frequency response characteristic diagram from the bit error rate tester to the starting point of the driver chip of the linear optical module in Example 3 of the present invention;

[0027] Figure 13 This is a frequency response characteristic diagram of the transmission end of the bit error rate tester to the linear optical module in Example 3 of the present invention;

[0028] Figure 14 This is a frequency response characteristic diagram of the transmitting end of the linear optical module in Example 3 of the present invention;

[0029] Figure 15 This is a frequency response characteristic diagram from the bit error rate tester to the starting point of the driver chip of the linear optical module in Example 4 of the present invention;

[0030] Figure 16 This is a frequency response characteristic diagram of the transmission end of the bit error rate tester to the linear optical module in Example 4 of the present invention;

[0031] Figure 17 This is a frequency response characteristic diagram of the transmitting end of the linear optical module in Example 4 of the present invention;

[0032] Figure 18 This is a frequency response characteristic diagram from the bit error rate tester to the starting point of the driver chip of the linear optical module in Example 5 of the present invention;

[0033] Figure 19 This is a frequency response characteristic diagram of the transmission end of the bit error rate tester to the linear optical module in Example 5 of the present invention;

[0034] Figure 20 This is a frequency response characteristic diagram of the transmitting end of the linear optical module in Example 5 of the present invention. DETAILED DESCRIPTION

[0035] The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, not all of the embodiments. The components of the embodiments of the present invention generally described and shown in the drawings herein can be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the present invention provided in the drawings is not intended to limit the scope of the claimed invention, but merely represents 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 making creative work are within the scope of protection of the present invention.

[0036] It should be noted that similar numbers and letters represent similar items in the following figures. Therefore, once an item is defined in one figure, it does not need to be further defined or explained in subsequent figures. At the same time, in the description of the present invention, the terms "first", "second", etc. are only used to distinguish the description and are not to be understood as indicating or implying relative importance, or implying any such actual relationship or order between these entities or operations. In addition, the terms "connected" and "connected" can refer to direct connection between elements or devices, indirect connection via other elements or devices, or plug-in connection between elements or devices.

[0037] Example 1:

[0038] The present invention is implemented through the following technical solutions, and proposes a method for evaluating the frequency response characteristics of a linear optical module, which is used to evaluate the frequency response characteristics of the transmitting end of the linear optical module, such as Figure 2 As shown, this method is implemented using 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, which can capture the waveform of the electrical signal output by the plug-in module; the linear optical module is connected to the optical oscilloscope, which can capture the waveform of the optical signal 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 rate tester (BERT). The signal pattern sent by the BERT to the plug-in module or linear optical module is a PRBSQ (Pseudo-Random Bit Sequence for Pulse Amplitude Modulation 4) pattern, such as PRBS13Q (Pseudo-Random Bit Sequence 13 for Pulse Amplitude Modulation 4) or PRBS15Q (Pseudo-Random Bit Sequence 15 for Pulse Amplitude Modulation 4). This embodiment does not limit the signal pattern sent and is provided for example only.

[0040] As a first feasible implementation method 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 the 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 the 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 the test equipment, the present invention proposes a method for evaluating the frequency response characteristics of a linear optical module, comprising 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, and the electrical oscilloscope captures the electrical signal waveform output by the plug-in module. After converting it to the frequency domain, the frequency response characteristics of the driver chip from the pattern generator to the linear optical module are obtained.

[0043] Specifically, the bit error ratio tester (BERT) described in this embodiment has a module insertion port, so the plug-in module can be directly inserted into the BERT using a host compliance board (HCB). The HCB is connected to an oscilloscope via a radio frequency cable. The oscilloscope can be a sampling oscilloscope or a real-time oscilloscope.

[0044] After the test equipment is connected, the bit error rate tester outputs a signal to the host compliance board. The signal pattern is PRBS, preferably PRBS13Q, which is a pseudo-random sequence. PRBS signals have rich frequency components and are easier to sweep than 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 that can be captured by the oscilloscope. When capturing the electrical signal waveform, the oscilloscope needs to capture at least one complete PRBS pattern output by the bit error rate tester to avoid frequency truncation.

[0045] The host compliance board uses TP1a (Test Point_1a) as defined by the IEEE (Institute of Electrical and Electronics Engineers) protocol. An oscilloscope captures the electrical signal output by the host compliance board and displays its waveform. The oscilloscope's bandwidth must be greater than the Nyquist frequency (Nyquist frequency) of the signal being tested to prevent fundamental signals from being filtered out. In this embodiment, the oscilloscope's bandwidth is set to 39.8 GHz, and a fourth-order Bessel filter is used. After capturing the electrical signal output by the host compliance board, the oscilloscope uses its forward feedback equalizer (FFE) to optimize the signal. Specifically, the FFE optimizes the signal using the minimum mean squared error (MMSE) algorithm to obtain the FFE coefficients. The optimized FFE coefficients are then subjected to a Fast Fourier Transform (FFT) to convert the electrical signal from the time domain to the frequency domain. The frequency domain amplitude is then divided by 1 and the logarithm is calculated to obtain the frequency response characteristics of the driver chip from the bit error rate tester to the linear optical module.

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

[0047] Specifically, as shown in Figure 3(a), the structure of the linear optical module includes, from input to output, the following: a gold finger (i.e., the slot at the electrical receiving end of the linear optical module, equivalent to the electrical receiving end), a section of PCB circuit, a driver chip (i.e., Driver), a modulator, and a transmitter (the end point of the modulator is the transmitter of the linear optical module). After the host compliance board is inserted into the bit error rate tester, the host compliance board is equivalent to the gold finger in the linear optical module plus a section of PCB circuit, as shown in Figure 3(a). Therefore, the electrical signal captured by the electrical 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 to the starting point of the driver chip through a section of PCB circuit. Therefore, the frequency response characteristics of the bit error rate tester to the driver chip of the linear optical module (or the frequency response characteristics of 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 electrical oscilloscope, which is equivalent to the frequency response characteristics of path 1 in Figure 3(b). As shown in Figure 9The figure shows the frequency response characteristics 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 oscilloscope captures the electrical signal output by the host compliance board, the RF cable between the host compliance board and the oscilloscope needs to be removed through the oscilloscope's Remove S2P function to eliminate the impact of the RF cable on the frequency response characteristics.

[0049] In step 2, the linear optical module is connected to the pattern generator. The transmitter of the linear optical module is connected 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 and converts it to the frequency domain to obtain the frequency response characteristics from the pattern generator to the transmitter of the linear optical module.

[0050] Because the bit error rate tester has a module insertion port, after obtaining the frequency response characteristics of the driver chip connecting the bit error rate tester to the linear optical module, the host compliance board is removed from the bit error rate tester, and the linear optical module (i.e., the device under test (DUT)) is then inserted into the bit error rate tester in the same manner as the host compliance board. Alternatively, the linear optical module can be inserted into another identical bit error rate tester in the same manner as the host compliance board. This allows steps 2 and 1 to be performed simultaneously, or in any order, to improve testing efficiency. The linear optical module is connected to an optical oscilloscope via optical fiber. The optical oscilloscope can be a sampling oscilloscope or a real-time oscilloscope, but the choice should be the same as for the electrical oscilloscope. In this embodiment, both the electrical and optical oscilloscopes are sampling oscilloscopes; alternatively, both the electrical and optical oscilloscopes are real-time oscilloscopes.

[0051] After the test equipment is connected, the bit error rate tester outputs a signal to the linear optical module. The signal should be consistent with the signal output by the bit error rate tester to the host compliance board. In this embodiment, a PRBS code pattern is used, preferably PRBS13Q. The optical signal output by the transmitter of the linear optical module is captured by an optical oscilloscope. When capturing the optical signal, the optical oscilloscope 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 tested signal. 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 consistent with the bandwidth of the electrical oscilloscope to avoid test errors caused by inconsistent bandwidth.

[0052] After an optical oscilloscope captures the optical signal waveform transmitted by a linear optical module, the optical signal is optimized using the oscilloscope's forward feedback equalizer (FFE). Specifically, the FFE optimizes the optical signal using the minimum mean squared error (MMSE) algorithm to obtain FFE coefficients. The optimized FFE coefficients are then subjected to a fast Fourier transform (FFT) to convert the optical signal from the time domain to the frequency domain. The logarithm of the frequency domain amplitude is then divided by 1 to obtain the frequency response characteristics from the BERT to the transmitter of the linear optical module.

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

[0054] 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 transmitter of the linear optical module to obtain the frequency response characteristic of the transmitter of the linear optical module.

[0055] Based on the reaction of the time domain convolution theorem and the matrix dot division principle in the frequency domain, the frequency response characteristics of the bit error rate tester to the driver chip of the linear optical module and the frequency response characteristics of the bit error rate tester to the transmitter of the linear optical module are matrix dot divided, as shown in Figure 3(b). That is, the frequency response characteristics of the bit error rate tester to the transmitter of the linear optical module (path 2) are removed from the frequency response characteristics of the bit error rate tester to the starting point of the driver chip of the linear optical module (path 1), thereby obtaining the frequency response characteristics of the starting point of the driver chip of the linear optical module to the transmitter (path 3), that is, the frequency response characteristics of the transmitter of the linear optical module. Figure 11 The figure shows the frequency response characteristics of the transmitting end of the linear optical module.

[0056] As a second possible implementation method of this embodiment, Figure 4As shown, 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 via 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 an electrical oscilloscope; the linear optical module is plugged into the module compliance board, 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.

[0057] Based on the test equipment, the present invention proposes a method for evaluating the frequency response characteristics of a linear optical module, comprising 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, and the electrical oscilloscope captures the electrical signal waveform output by the plug-in module. After converting it to the frequency domain, the frequency response characteristics of the driver chip from the pattern generator to the linear optical module are obtained.

[0059] Specifically, the bit error rate tester (BERT) does not have a module insertion port, so a module compliance board (MCB) is used to achieve an 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, and the host compliance board is plugged into the module compliance board. 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 its waveform. After capturing the signal, the oscilloscope uses the forward feedback equalizer (FFE) to optimize the signal. Specifically, the FFE optimizes the signal using the minimum mean squared error (MMSE) algorithm to obtain FFE coefficients. The optimized FFE coefficients are then subjected to a fast Fourier transform (FFT) to convert the signal from the time domain to the frequency domain. The logarithm of the frequency domain amplitude is then divided by 1 to obtain the frequency response characteristics of the driver chip from the bit error rate tester to the linear optical module.

[0061] In step 2, the linear optical module is connected to the pattern generator. The transmitter of the linear optical module is connected 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 and converts it to the frequency domain to obtain the frequency response characteristics from the pattern generator to the transmitter of the linear optical module.

[0062] Because the BERT lacks a module insertion port, a module compliance board is connected to the BERT via an RF cable. Then, remove the host compliance board plugged 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, following the same insertion method as the host compliance board. Alternatively, connect another identical module compliance board to another identical BERT via an RF cable and insert the linear optical module into that module compliance board, following the same insertion method as the host compliance board. This allows steps 1 and 2 to be performed simultaneously, or in any order, to improve testing efficiency. The linear optical module is connected to an optical oscilloscope via optical fiber.

[0063] After an optical oscilloscope captures the optical signal transmitted by the linear optical module, it uses the oscilloscope's forward feedback equalizer (FFE) to optimize the optical signal. Specifically, the FFE optimizes the optical signal using the minimum mean squared error (MMSE) algorithm to obtain FFE coefficients. The optimized FFE coefficients are then subjected to a fast Fourier transform (FFT) to convert the optical signal from the time domain to the frequency domain. The logarithm of the frequency domain amplitude is then divided by 1 to obtain the frequency response characteristics from the BERT to the transmitter of the linear optical module.

[0064] 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 transmitter of the linear optical module to obtain the frequency response characteristic of the transmitter of the linear optical module.

[0065] In this embodiment, the second implementation differs from the first implementation in whether the bit error rate tester has a module insertion port. If the bit error rate tester has a module insertion port, the host compliance board can be directly inserted into the bit error rate tester using 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, the second implementation uses the module compliance board to connect to the bit error rate tester, and then insert the host compliance board or linear optical module into the module compliance board.

[0066] This solution can accurately evaluate the frequency response characteristics of the transmitter of the linear optical module. Figure 5The frequency response characteristics of the linear optical module transmitter for this solution (dashed line) and the VAN+LCA solution (solid line) in the background technology are shown when the linear optical module has a gain of 21 dB and a peaking of 0 dB. The horizontal axis represents frequency, and the vertical axis represents signal amplitude. Figure 6 When the Gain of the linear optical module is 21dB and the peaking is 3dB, the frequency response characteristic diagram of the linear optical module transmitter of this solution (dashed line) and the background technology solution (solid line) is shown. It can be seen that the frequency response difference between this solution and the background technology solution is small, but this solution saves costs, improves efficiency, and has manufacturability compared to the background technology. It should be noted that the frequency response characteristic comparison diagrams under the two implementation methods of Example 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 order between steps 1 and 2 in this solution. Step 1 can be performed first and then step 2, or step 2 can be performed first and then step 1, or both can be performed simultaneously. Even if this solution is evaluating multiple linear optical modules, step S1 only needs to be performed once to obtain the frequency response characteristics of the driver chip from the pattern generator to the linear optical module. For example, if the frequency response characteristics of the transmitter end of 100 linear optical modules are to be evaluated in this batch, and each linear optical module has 8 optical channels, this can be achieved through at least three of the following methods:

[0068] 1. Perform step S1 once to obtain the frequency response characteristics of the driver chip from the pattern generator to the linear optical module. Remove the host compliance board from the pattern generator used in step S1 and insert the first linear optical module into the pattern generator in the same manner. This will complete the test of all channels of the linear optical module in approximately 32 seconds. Then, directly replace the second linear optical module and insert it into the pattern generator in the same manner until all 100 linear optical modules are tested.

[0069] 2. Perform step S1 once to obtain the frequency response characteristics of the driver chip from the pattern generator to the linear optical module. In step S2, insert the linear optical module into another pattern generator with the same structure. The two pattern generators send exactly the same pattern. This allows the test of all channels of the linear optical module to be completed in approximately 32 seconds. Step S2 can be performed simultaneously with step S1 because two identical pattern generators are used. Then, remove the first linear optical module and directly replace it with the second linear optical module, inserting it into the pattern generator in the same manner. This continues until all 100 linear optical modules have been tested.

[0070] 3. Perform step S1 once to obtain the frequency response characteristics of the code generator to the driver chip of the linear optical module. In step S2, insert the 100 linear optical modules into another 100 code generators with the same structure. The code patterns sent by these 100 code generators are exactly the same. The test of all channels of 100 linear optical modules can be completed in approximately 32 seconds. Step S2 can be performed simultaneously with step S1 because 100 code generators with the same structure are used.

[0071] It can be seen that compared with the background technology using VNA+LCA solution, this solution can significantly reduce costs due to the very high costs of VNA and LCA. Manufacturers of linear optical modules have a large number of pattern generators and optical oscilloscopes, which can also significantly reduce evaluation time and improve efficiency.

[0072] Example 2:

[0073] Based on the test equipment of the two possible implementation schemes in Example 1, Figure 2 As shown, the present invention proposes a method for evaluating the frequency response characteristics of a linear optical module, comprising 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 electrical signal waveform output by the plug-in module. After converting it to the frequency domain, the frequency response characteristics of the code generator to the receiving end of the linear optical module are obtained.

[0075] This embodiment differs from Embodiment 1 in that, after the oscilloscope captures the electrical signal output by the host compliance board, it is necessary to remove the RF cable between the host compliance board and the oscilloscope using the oscilloscope's Remove S2P function. Therefore, the host compliance board is equivalent to a PCB circuit 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 an S-parameter file that can reflect the frequency response characteristics, and the S-parameter file generally contains the amplitude and phase corresponding to different frequencies), the S-parameter model can be removed using the oscilloscope's RemoveS2P function. See Figure 3(a). The electrical signal obtained after removal is equivalent to the signal provided by the bit error rate tester to the gold finger, i.e., the signal provided by the bit error rate tester to the receiving end of the linear optical module, thereby obtaining the frequency response characteristics from the bit error rate tester to the receiving end of the linear optical module.

[0076] In step 2, the linear optical module is connected to the pattern generator. The transmitter of the linear optical module is connected 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 and converts it to the frequency domain to obtain the frequency response characteristics from the pattern generator to the transmitter of the linear optical module.

[0077] Step 3: Perform matrix dot 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 time-domain convolution theorem and the frequency-domain matrix dot division principle, the frequency response characteristics from the bit error rate tester to the linear optical module's receiver and the frequency response characteristics from the bit error rate tester to the linear optical module's transmitter are matrix-divided. In other words, the frequency response characteristics from the bit error rate tester to the linear optical module's transmitter are removed from the frequency response characteristics from the bit error rate tester to the linear optical module's receiver. This yields the frequency response characteristics from the linear optical module's receiver to the transmitter, i.e., the frequency response characteristics of the entire linear optical module.

[0079] The rest of this embodiment is the same as that of embodiment 1, so it will not be described again.

[0080] Example 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 a forward feedback equalizer (FFE) function, so the electrical signal waveform and the optical signal waveform need to be saved and then exported.

[0082] After the electrical signal waveform or optical signal waveform is derived, the channel is estimated based on the least squares solution (LS) to obtain the channel matrix H and signal power , noise power , the specific steps are as follows:

[0083] 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 to capture the channel output waveform. According to the least squares solution, we have:

[0084]

[0085] Among them, H1 is the channel impulse response matrix with dimension N1×1, N1 is the pulse length of the channel estimation; X is the PRBS signal matrix of the channel input with dimension N2×N1 and is a circulant matrix, N2 is the PRBS signal length; X His 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.

[0086] 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.

[0087] Based on the channel matrix , calculate the FFE coefficient according to the Minimum Mean Squared Error (MMSE) algorithm:

[0088]

[0089] Where G is the FFE coefficient and its 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 identity matrix with dimension (N1+N-1)×(N1+N-1).

[0090] 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. The frequency domain amplitude is then divided by 1 and the logarithm is calculated to obtain the frequency response characteristics from the bit error rate tester to the starting point of the driver chip of the linear optical module, as shown in FIG. Figure 12 As shown; the frequency response characteristics of the bit error rate tester to the transmitter of the linear optical module can also be obtained, as shown 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.

[0091] The rest of this embodiment is the same as the other embodiments above, so they will not be described in detail.

[0092] Example 4:

[0093] 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:

[0094] 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 electrical signal waveform output by the plug-in module. After converting it to the frequency domain, the frequency response characteristics of the driver chip from the pattern generator to the linear optical module are obtained.

[0095] After the electrical oscilloscope captures the electrical signal output by the host compliance board, it converts the electrical signal from the time domain to the frequency domain through Fast Fourier Transform (FFT), thereby obtaining the frequency response characteristics of the starting point of the driver chip from the bit error rate tester to the linear optical module, such as Figure 15 shown.

[0096] In step 2, the linear optical module is connected to the pattern generator. The transmitter of the linear optical module is connected 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 and converts it to the frequency domain to obtain the frequency response characteristics from the pattern generator to the transmitter of the linear optical module.

[0097] After the optical oscilloscope captures the optical signal transmitted by the linear optical module, it converts the optical signal from the time domain to the frequency domain through Fast Fourier Transform (FFT), thereby obtaining the frequency response characteristics of the transmission end from the bit error rate tester to the linear optical module, such as Figure 16 shown.

[0098] 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 transmitter of the linear optical module to obtain the frequency response characteristic of the transmitter of the linear optical module.

[0099] Based on the reaction of the time domain convolution theorem, the matrix dot division principle of the frequency domain is used to perform matrix dot division on 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 transmitter of the linear optical module. Then, a piecewise fourth-order polynomial fitting is used to reduce the influence of spectrum noise, thereby obtaining the frequency response characteristics of the transmitter of the linear optical module, such as Figure 17 shown.

[0100] This embodiment differs from Embodiment 1 in that, in steps 1 and 2, the captured electrical and optical signals undergo direct Fast Fourier Transform (FFT) optimization, without dividing the FFE by the frequency domain amplitude and then calculating the logarithm of the FFT result. However, after performing the matrix dot division in step 3, a piecewise fourth-order polynomial fit is used to reduce the influence of spectral noise and thereby obtain the frequency response characteristics of the linear optical module's transmitter.

[0101] This embodiment can accurately evaluate the frequency response characteristics of the transmitter end of the linear optical module. In the case where the electrical oscilloscope or optical oscilloscope does not perform FFE optimization on the electrical signal or optical signal but directly performs FFT transformation, Figure 7 The frequency response characteristics of the linear optical module transmitter of this embodiment (dashed line) and the background art solution (solid line) are shown in the figure when the linear optical module has a gain of 21 dB and a peaking of 0 dB. The horizontal axis represents frequency and the vertical axis represents signal amplitude. Figure 8 When the Gain of the linear optical module is 21dB and the peaking is 3dB, the frequency response characteristic diagram of the linear optical module transmitter of this embodiment (dashed line) and the background technology solution (solid line) is shown. It can be seen that the frequency response difference between this solution and the background technology solution is small, but this solution saves costs, improves efficiency, and has manufacturability compared to the background technology. It should be noted that the frequency response characteristic comparison diagrams of the two solutions in Example 1 are both Figure 7 and Figure 8 Among them, Gain represents gain, peaking represents peak compensation, and dB represents decibel.

[0102] The rest of this embodiment is the same as that of embodiment 1, so it will not be described again.

[0103] In another solution, this embodiment can also be implemented based on embodiment 2.

[0104] Example 5:

[0105] Based on Example 1, this embodiment saves and exports the electrical signal waveform captured by the electrical oscilloscope and the optical signal waveform captured by the optical oscilloscope, and uses an external Fast Fourier Transform (FFT) algorithm to convert the electrical signal and the optical signal from the time domain to the frequency domain, and can obtain the following: Figure 18 The frequency response characteristics of the bit error rate tester to the starting point of the driver chip of the linear optical module are shown, and the Figure 19 The frequency response characteristics of the bit error rate tester to the transmitter of the linear optical module are shown. Finally, after matrix dot division, a piecewise fourth-order polynomial fitting is used to reduce the influence of spectrum noise, thus obtaining the following Figure 20 The frequency response characteristics of the transmitting end of the linear optical module are shown.

[0106] In this embodiment, the captured electrical and optical signals are saved and exported in steps 1 and 2 without FFE optimization. Instead, an external Fast Fourier Transform (FFT) is performed directly. The FFT result is not divided by 1 and then the logarithm is taken. However, after the matrix dot division in step 3, an external piecewise fourth-order polynomial fit is used to reduce the influence of spectral noise and thus obtain the frequency response characteristics of the linear optical module's transmitter.

[0107] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any modifications or substitutions that can be easily conceived by a person skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be based on the scope of protection of the claims.

Claims

1. A method for evaluating the frequency response characteristics of a linear optical module, characterized by: The following steps are involved: Step 1: Connect the plug-in module to the pattern generator, and 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 electrical signal waveform output by the plug-in module. After converting it to the frequency domain, the frequency response characteristics of the driver chip from the pattern generator to the linear optical module are obtained. Step 2: Connect the linear optical module to the pattern generator. Connect the transmitter 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 and converts it to the frequency domain to obtain the frequency response characteristics from the pattern generator to the transmitter 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 transmitter of the linear optical module to obtain the frequency response characteristic of the transmitter 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, wherein: The signal pattern 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, wherein: 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, wherein: The plug-in module is a host compliance board; In 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 oscilloscope via a radio frequency cable; In step 2, the host compliance board is unplugged from the code generator, and 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 an optical fiber; alternatively, in 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 an optical fiber.

6. The method for evaluating the frequency response characteristics of a linear optical module according to claim 1, wherein: The plug-in module includes a module compliance board and a host compliance board; In 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 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 via optical fiber; alternatively, in step 2, another identical module compliance board is connected to another identical pattern generator via an RF 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 via optical fiber.

7. The method for evaluating the frequency response characteristics of a linear optical module according to claim 1, 5, or 6, wherein: 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 driver chip from the pattern 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 oscilloscope's forward feedback equalizer function. The forward feedback equalizer optimizes the electrical signal using 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. The logarithm is then calculated by dividing 1 by the frequency domain amplitude to obtain 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 an optical oscilloscope captures the optical signal waveform transmitted by the linear optical module, the optical signal is optimized using the optical oscilloscope's forward feedback equalizer (FFE) function. The FFE optimizes the optical signal using a minimum mean square error (MMSE) algorithm to obtain the FFE coefficient. The optimized FFE coefficient is then subjected to a fast Fourier transform (FFT) to convert the optical signal from the time domain to the frequency domain. The logarithm of the frequency domain amplitude is then divided by 1 to obtain the frequency response characteristics from the pattern generator to the transmitter 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, wherein: 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 to capture the channel output waveform. According to the least squares solution, we have: Among them, H1 is the channel impulse response matrix with dimension N1×1, N1 is the pulse length of the channel estimation; X is the PRBS signal matrix of the channel input with dimension 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: Where G is the FFE coefficient and its 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 identity matrix with dimension (N1+N-1)×(N1+N-1).

9. The method for evaluating the frequency response characteristics of a linear optical module according to claim 1, 5, or 6, wherein: 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 driver chip from the pattern 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 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: An optical oscilloscope captures the optical signal waveform transmitted by the linear optical module. After performing a fast Fourier transform (FFT) to convert the optical signal from the time domain to the frequency domain, the frequency response characteristics of the transmission end from the pattern generator to the linear optical module are obtained. In step 3, after performing matrix dot division on the frequency response characteristics of the pattern generator to the driver chip of the linear optical module and the frequency response characteristics of the pattern generator to the transmitting end of the linear optical module, the method further includes: A piecewise fourth-order polynomial fitting is used to reduce the influence of spectral noise, thereby obtaining the frequency response characteristics of the transmitting end of the linear optical module.

10. The method for evaluating the frequency response characteristics of a linear optical module according to claim 5 or 6, wherein: In step 1, after the electrical oscilloscope captures the electrical signal output by the host compliance board, the S-parameter model of the host compliance board is removed using the Remove S2P function of the electrical oscilloscope, 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, wherein: 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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