A device and method for evaluating the response stability of photodiodes based on fiber optic interferometer structure

Abstract

This invention discloses a photodiode response stability evaluation device and method based on a fiber optic interferometer structure, comprising a tunable laser source module, an unbalanced Michelson fiber optic interferometer module, and a data acquisition and processing module. The tunable laser source module provides an adjustable light source. The unbalanced Michelson fiber optic interferometer module enables passive external modulation of the optical signal. The interference optical signals of the reference photodiode and the photodiode under test are detected by a dual-channel transimpedance amplifier and converted into interference voltage signals. The data acquisition and processing module analyzes and demodulates the fluctuation of the phase difference between the two detection signals from the reference photodiode and the photodiode under test, converting the light intensity error caused by the response stability of the photodiode under test into a phase error, obtaining the standard deviation of the phase difference of the dual-channel interference voltage signals, and comparing it with a preset phase detection accuracy to evaluate whether the response stability of the photodiode under test meets the system requirements.

Description

Technical Field

[0001] This invention belongs to the field of photoelectric detection, and specifically relates to a photodiode response stability evaluation device and method based on a fiber optic interferometer structure. Background Technology

[0002] Michelson fiber optic interferometers and Mach-Zehnder interferometers have very important and wide applications. Laser interferometry uses light wavelength as the unit of measurement and has extremely high phase detection sensitivity. It can convert the tiny phase changes caused by the measured physical quantity into light intensity changes that the photodetector can respond to. By detecting the light intensity changes and performing phase demodulation, high-precision measurement of the measured physical quantity can be achieved. As one of the commonly used photodetectors, the stability of the response of the photodiode under time-varying light intensity directly affects the accuracy of photodetection and the accuracy of the demodulation results of the measured physical quantity.

[0003] However, most manufacturers only provide typical responsivity values ​​and two related static test curves in their photodiode datasheets: one for responsivity variation at different light wavelengths and the other for responsivity variation at different light powers. These data are insufficient to demonstrate the response stability of the photodiode. Summary of the Invention

[0004] To meet the high stability requirements of photoelectric detection in interferometric measurement systems, this invention proposes a dynamic evaluation device and method for the response stability of photodiodes based on a fiber optic interferometer structure. This method differs from traditional static measurement methods for photodiodes and requires no additional optical modulation devices or signal generators. It achieves passive external modulation of optical signals using only an unbalanced Michelson fiber optic interferometer structure.

[0005] A photodiode response stability evaluation device based on a fiber optic interferometer structure includes a tunable laser source module, an unbalanced Michelson fiber optic interferometer module, and a data acquisition and processing module. The tunable laser source module includes a light source and an optical attenuator connected in sequence. The unbalanced Michelson fiber optic interferometer module includes an optical isolator, a 3×3 fiber coupler, a fiber optic jumper, a Faraday rotator, a reference photodiode, a photodiode under test, and a dual-channel transgroup amplifier. The data acquisition and processing module includes a connected data acquisition card and a processor.

[0006] The tunable laser source module is used to output continuous light with adjustable wavelength and intensity to the unbalanced Michelson fiber interferometer module; the unbalanced Michelson fiber interferometer module causes the light reflected by the Faraday rotator to interfere within a 3×3 fiber coupler, and transmits the interference light to the reference photodiode and the photodiode under test respectively. The reference photodiode and the photodiode under test convert the interference light signal into an interference current signal; and the interference electrical signal is detected by the dual-channel transimpedance amplifier and converted into an interference voltage signal.

[0007] The data acquisition card is used to acquire the dual-channel interference voltage signal output by the dual-channel transimpedance amplifier. The processor is used to analyze and demodulate the fluctuation of the phase difference between the two detection signals from the reference photodiode and the photodiode under test, convert the light intensity error caused by the response stability of the photodiode under test into a phase error, obtain the standard deviation of the phase difference of the dual-channel interference voltage signal, and compare it with the preset phase detection accuracy to evaluate whether the response stability of the photodiode under test meets the system requirements.

[0008] The 3×3 fiber optic coupler includes a first port, a second port, a third port, a fourth port, a fifth port, and a sixth port.

[0009] The first port is connected to the optical isolator;

[0010] The second and third ports are connected to the reference photodiode and the photodiode under test, respectively.

[0011] The fourth port is connected to the first Faraday rotator via an optical fiber patch cord;

[0012] The fifth port is unused; it should be connected to an optical power meter when in use.

[0013] The sixth port connects to the second Faraday rotator.

[0014] The light reflected by the first and second Faraday rotators interferes within the 3×3 fiber coupler. One beam of interference light is output from the second port to the reference photodiode, and the other beam of interference light is output from the third port to the photodiode under test.

[0015] Furthermore, the light source is a tunable continuous laser used to generate continuous light with a wavelength adjustable within a certain range; the optical attenuator is an adjustable optical attenuator used to adjust the attenuation of the continuous light.

[0016] Furthermore, the dual-channel transimpedance amplifier is connected to the photodiode leads via a fully gold-plated circular pin.

[0017] Furthermore, the optical path difference generated by the fiber optic patch cord cannot exceed the coherence length of the light source.

[0018] The response stability evaluation method for a photodiode response stability evaluation device based on a fiber optic interferometer structure includes:

[0019] Pre-debugging phase: Input a continuous optical signal, connect the fifth port of the 3×3 fiber coupler to the optical power meter, adjust the optical attenuator so that the optical power value measured by the optical power meter does not exceed 70% of the maximum input optical power of the reference photodiode and the photodiode under test, and the maximum value of the dual-channel interference voltage level does not exceed 80% of the power supply voltage of the dual-channel transimpedance amplifier and the maximum output voltage of the data acquisition card;

[0020] Sample data acquisition stage: After the optical power is adjusted, the dual-channel interference voltage data of the dual-channel transimpedance amplifier is continuously acquired for a predetermined time as sample data;

[0021] Data processing stage: The processor generates a sliding window to process the sample data. With the data of the reference photodiode as the horizontal axis and the data of the photodiode under test as the vertical axis, the dual-channel sample data are sequentially subjected to least-squares elliptic fitting in a sliding window manner, and the phase difference of the dual-channel signals is calculated. The fluctuation of the phase difference between the two detection signals from the reference photodiode and the photodiode under test is obtained;

[0022] Calculate the phase difference of the dual-channel signal Standard deviation σ θ The standard deviation σ θ To compare the required phase detection accuracy of the interferometric measurement system, the standard deviation σ of the dual-channel signal of the photodiode under test is used. θ If the phase detection accuracy is less than or equal to the preset value, the stability of the current photodiode under test is considered to meet the system requirements; otherwise, it does not meet the system requirements.

[0023] Furthermore, in the sliding window processing, the window width should be set so that the data captured by each sliding window can form a closed Lissajous figure. The size of the sample data should not be less than 5 times the window width. Otherwise, it is necessary to return to the sample data acquisition stage to increase the acquisition time. The sliding step size should be set so that it can be divided by the window width and does not exceed half of the window width. At the same time, the number of sliding windows should not be less than 30.

[0024] Compared with the prior art, the beneficial effects of the technical solution of the present invention are:

[0025] 1) It provides a dynamic measurement method, unlike traditional static measurement methods;

[0026] 2) No additional optical modulation devices or signal generators are required. Passive external modulation of optical signals can be achieved using only the unbalanced Michelson fiber interferometer structure. The system is simple, easy to build, and highly feasible.

[0027] 3) By fitting a series of Lissajous figures formed by the output signals of the reference photodiode and the photodiode under test, the fluctuation of the phase difference between the two detection signals is obtained. In fact, the light intensity error caused by the response stability of the photodiode under test is transformed into a phase error, which is the most sensitive part of interferometric measurement. Therefore, the present invention uses the standard deviation of the phase difference as a parameter to evaluate the response stability of the photodiode, which is reliable and has certain reference value for the selection and development of photodetectors. Attached Figure Description

[0028] Figure 1 This invention presents a schematic diagram of a photodiode response stability evaluation device based on a fiber optic interferometer structure.

[0029] Figure 2 This is a flowchart of the evaluation method for the photodiode response stability evaluation device based on the fiber optic interferometer structure;

[0030] Figure 3 This is a schematic diagram of the sliding window in step four of the embodiment;

[0031] Figure 4 Elliptic fitting test diagram for three non-homogeneous photodiodes;

[0032] Figure 5 The response stability test curves are for three non-homogeneous photodiodes.

[0033] In the picture:

[0034] 1: Tunable continuous laser; 2: Tunable optical attenuator; 3: Optical isolator

[0035] 4: 3×3 fiber optic coupler; 5: fiber optic patch cord; 6A: First Faraday rotator.

[0036] 6B: Second Faraday rotator; 7: Reference photodiode; 8: Photodiode under test.

[0037] 9: Dual-channel transimpedance amplifier; 10: Data acquisition card; 11: Processor Detailed Implementation

[0038] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. The specific embodiments described are only for explanation and illustration of the present invention and are not intended to limit the present invention.

[0039] like Figure 1As shown, a photodiode response stability evaluation device based on a fiber optic interferometer structure includes a tunable continuous laser 1, a tunable optical attenuator 2, an optical isolator 3, a 3×3 fiber optic coupler 4, a fiber optic patch cord 5, a first Faraday rotator 6A, a second Faraday rotator 6B, a reference photodiode 7, a photodiode under test 8, a dual-channel transgroup amplifier 9, a data acquisition card 10, and a processor 11.

[0040] The output of the tunable continuous laser 1 is connected to the input of the tunable optical attenuator 2, the output of the tunable optical attenuator 2 is connected to the input of the optical isolator 3, and the output of the optical isolator 3 is connected to the first port of a 3×3 fiber coupler 4. The 3×3 fiber coupler 4 has six ports: the first port, the second port, the third port, the fourth port, the fifth port, and the sixth port. The fourth port of the 3×3 fiber coupler 4 is first connected to a fiber optic jumper 5 of a certain length and then connected to the first Faraday rotator 6A. The fifth port is left unused, and the sixth port is directly connected to the second Faraday rotator 6B. The second and third ports are respectively connected to the reference photodiode 7 and the photodiode under test 8, thus forming an unbalanced Michelson fiber interferometer. The dual-channel transimpedance amplifier 9 is connected to the leads of the reference photodiode 7 and the photodiode under test 8 through a fully gold-plated circular pin. The output of the dual-channel transimpedance amplifier 9 is connected to the data acquisition card 10 to realize the conversion of analog signals to digital signals. The data acquisition card 10 is electrically connected to the processor 11 and transmits the obtained digital signals to the processor 11.

[0041] In use, the continuous light generated by the tunable continuous laser 1 passes through the tunable optical attenuator 2 and the optical isolator 3 in sequence, and is then transmitted to the first port of the 3×3 fiber coupler 4, where it is split into three paths. The first path of light passes through the fourth port of the 3×3 fiber coupler 4 and the fiber jumper 5 in sequence, and is then reflected by the first Faraday rotator 6A. The second path of light exits from the fifth port of the 3×3 fiber coupler 4 without any processing. The third path of light exits directly from the sixth port of the 3×3 fiber coupler 4 and is reflected by the second Faraday rotator 6B.

[0042] Two beams of light reflected by the first Faraday rotator 6A and the second Faraday rotator 6B maintain almost the same polarization state in the 3×3 fiber coupler 4. After interference, they are output from the first port, the second port, and the third port, respectively. The optical isolator 3 connected to the first port blocks the interference light output from the first port to prevent it from affecting the stability of the tunable continuous laser 1. The reference photodiode 7 receives the interference light output from the second port, and the photodiode under test 8 receives the interference light output from the third port.

[0043] The reference photodiode 7 and the photodiode under test 8 convert the interference light signal into an interference current signal, which is then converted into interference voltage signals U1(t) and U2(t) by the dual-channel transimpedance amplifier 9. These signals are then output sequentially to the data acquisition card 10 and the processor 11 for subsequent evaluation and processing.

[0044] like Figure 2 As shown, the evaluation method for the photodiode response stability evaluation device based on the fiber optic interferometer structure includes the following steps:

[0045] Step 1: Adjust the knob of the adjustable optical attenuator 2 to the maximum attenuation position, connect all components of the evaluation device and power it on; the center wavelength of the tunable continuous laser 1 used for testing is 1550.12nm, the linewidth is 3kHz, the length of the fiber optic patch cord 5 used is 10m, and the sampling rate is set to 1kHz; the data acquisition card 10 acquires the electrical signal from the dual-channel transimpedance amplifier 9 and acquires the dual-channel interference voltage level;

[0046] Step 2: Connect the fifth port of the 3×3 fiber optic coupler to the optical power meter. While observing the optical power value and the dual-channel acquisition level, gradually reduce the attenuation of the adjustable optical attenuator 2 until the optical power value does not exceed 70% of the maximum input optical power of the reference photodiode 7 and the photodiode under test 8, and the maximum value of the dual-channel interference voltage level does not exceed 80% of the power supply voltage of the dual-channel transimpedance amplifier 9 and the maximum output voltage of the data acquisition card 10. Then proceed to the next step.

[0047] Step 3: After the optical power is adjusted, continuously collect dual-channel data for 600 seconds as sample data;

[0048] Step 4: As Figure 3 As shown, the processor generates a sliding window with a window width of 120s and a sliding step size of 10s, and performs segmented fitting on the dual-channel sample data obtained in step 3 in the manner of sliding window.

[0049] The reference photodiode 7 and the photodiode under test 8 convert the interference light signal into an interference current signal, which is then converted into interference voltage signals U1(t) and U2(t) by the dual-channel transimpedance amplifier 9. These signals are then output sequentially to the data acquisition card 10 and the processor 11. The expressions for the interference voltage signals U1(t) and U2(t) can be written as follows:

[0050]

[0051]

[0052] Where A1 and A2 represent the DC components of the interference signal, and B1 and B2 represent the AC coefficients of the interference signal. This indicates a large low-frequency phase shift caused by inherent laser frequency noise, fiber thermal noise, and environmental noise. The phase difference of the output light from an ideal 3×3 fiber coupler. This represents the phase deviation of the output light from the actual 3×3 fiber coupler. The terms represent the phase difference of the output light from the actual 3×3 fiber coupler, the DC components A1 and A2 of the interference signal, the AC coefficients B1 and B2 of the interference signal, and the phase difference. The laser intensity, laser polarization degree, the properties of the 3×3 fiber coupler itself, the external environment, the response of the photodiode and circuit parameters will cause certain fluctuations.

[0053] Using the interference voltage signal U1(t) of the reference photodiode 7 as the horizontal axis and the interference voltage signal U2(t) of the photodiode 8 under test as the vertical axis, the scatter plot formed by the two signals approximates an ellipse. The window width should be set so that the data captured by each sliding window can form a closed Lissajous figure, and the size of the sample data should not be less than 5 times the window width. Otherwise, it is necessary to return to step 3 to increase the acquisition time of dual-channel data. The sliding step size should be set so that it is divisible by the window width and does not exceed half of the window width, and the number of sliding windows should not be less than 30.

[0054] Step 5: By fitting the above scattered points using a least-squares-based ellipse fitting algorithm, a smooth elliptic curve can be obtained, and the DC components A1 and A2 of the interference signal, the AC coefficients B1 and B2 of the interference signal, and the phase difference of the two-channel signal can be calculated.

[0055] Step 6: Because A1, A2, B1, and B2 are greatly affected by the individual parameters of the photodiode and its amplification circuit, and the phase difference of the dual-channel signals... Since the phase difference between the two channels is relatively constant, this invention only considers the phase difference between the two channels. Standard deviation σ θ This parameter is used to evaluate the response stability of the photodiode 8 under test.

[0056] After sliding window fitting, multiple phase difference data are obtained. The standard deviation σ of the phase difference is calculated according to the following formula. θ :

[0057]

[0058] Where: n represents the number of window slides. This represents the phase difference obtained from the i-th sliding window fitting. This represents the mean of n phase differences.

[0059] Standard deviation σ θTo compare the required phase detection accuracy of the interferometric measurement system, the standard deviation σ of the dual-channel signal of the photodiode 8 under test is used. θ If the phase detection accuracy is less than or equal to the preset value, the stability of the current photodiode 8 under test is considered to meet the system requirements; otherwise, it does not meet the system requirements.

[0060] This implementation provides an example evaluation of three InGaAs PIN photodiodes (photodiode I, photodiode II, and photodiode III) from different manufacturers. Figure 4 The image shows an elliptic fitting test pattern of three photodiodes over 600 seconds. Figure 4 The measured scatter plots of the gray areas of photodiodes II and III in (b) and (c) are relatively... Figure 4 In (a), photodiode I is closer to the black elliptical fitting curve.

[0061] Figure 5 The phase difference fluctuation curves of the three photodiodes were calculated using 49 sliding window operations over 600 seconds. It is evident that photodiode III exhibits the best response stability, followed by photodiode II, while photodiode I shows the worst. If the required phase detection accuracy of the interferometric measurement system is 5 mrad, then this implementation is based on σ... θ The response stability of photodiodes II and III meets the system requirements, while the response stability of photodiode I does not.

[0062] Although preferred embodiments of the present invention have been described above in conjunction with the accompanying drawings, the present invention is not limited to the specific embodiments described above. The specific embodiments described above are merely illustrative and not restrictive. Those skilled in the art can make many other forms under the guidance of the present invention without departing from the spirit and scope of the claims, and all of these are within the scope of protection of the present invention.

Claims

1. A photodiode response stability evaluation device based on a fiber optic interferometer structure, characterized in that, The system includes a tunable laser source module, an unbalanced Michelson fiber interferometer module, and a data acquisition and processing module. The tunable laser source module includes a light source (1) and an optical attenuator (2) connected in sequence. The unbalanced Michelson fiber interferometer module includes an optical isolator (3), a 3×3 fiber coupler (4), a fiber jumper (5), a Faraday rotator, a reference photodiode (7), a photodiode under test (8), and a dual-channel transgroup amplifier (9). The data acquisition and processing module includes a connected data acquisition card (10) and a processor (11). The tunable laser source module is used to output continuous light with adjustable wavelength and intensity to the unbalanced Michelson fiber interferometer module; the unbalanced Michelson fiber interferometer module causes the light reflected by the Faraday rotator to interfere in the 3×3 fiber coupler (4), and transmits the interference light to the reference photodiode (7) and the photodiode under test (8) respectively. The reference photodiode (7) and the photodiode under test (8) convert the interference light signal into an interference current signal; and the interference electrical signal is detected and converted into an interference voltage signal by the dual-channel transimpedance amplifier (9); The data acquisition card (10) is used to acquire the dual-channel interference voltage signal output by the dual-channel transimpedance amplifier (9). The processor (11) is used to analyze and demodulate the fluctuation of the phase difference between the two detection signals from the reference photodiode (7) and the photodiode under test (8), and to convert the light intensity error caused by the response stability of the photodiode under test (8) into a phase error, obtain the standard deviation of the phase difference of the dual-channel interference voltage signal, and compare it with the preset phase detection accuracy to evaluate whether the response stability of the photodiode under test meets the system requirements. The 3×3 fiber optic coupler (4) includes a first port, a second port, a third port, a fourth port, a fifth port, and a sixth port. The first port is connected to the optical isolator (3); The second and third ports are respectively connected to the reference photodiode (7) and the photodiode under test (8); The fourth port is connected to the first Faraday rotator (6A) via an optical fiber patch cord (5); The fifth port is unused; it should be connected to an optical power meter when in use. The sixth port is connected to the second Faraday rotator (6B); The light reflected by the first Faraday rotator (6A) and the second Faraday rotator (6B) interferes within the 3×3 fiber coupler (4). One beam of interference light is output from the second port to the reference photodiode (7), and the other beam of interference light is output from the third port to the photodiode under test (8).

2. The photodiode response stability evaluation device based on fiber optic interferometer structure according to claim 1, characterized in that, The light source (1) is a tunable continuous laser used to generate continuous light with a wavelength adjustable within a certain range; the optical attenuator (2) is an adjustable optical attenuator used to adjust the attenuation of the continuous light.

3. The photodiode response stability evaluation device based on fiber optic interferometer structure according to claim 1, characterized in that, The dual-channel transimpedance amplifier (9) is connected to the leads of the reference photodiode (7) and the photodiode under test (8) through a fully gold-plated round hole pin.

4. The photodiode response stability evaluation device based on fiber optic interferometer structure according to claim 1, characterized in that, The optical path difference generated by the fiber optic patch cord (5) cannot exceed the coherence length of the light source.

5. The response stability evaluation method of the photodiode response stability evaluation device based on the fiber optic interferometer structure according to any one of claims 1-4, comprising: Pre-debugging stage: Input a continuous optical signal, connect the fifth port of the 3×3 fiber coupler (4) to the optical power meter, adjust the optical attenuator (2) so that the optical power value measured by the optical power meter does not exceed 70% of the maximum input optical power of the reference photodiode (7) and the photodiode under test (8), and the maximum value of the dual-channel interference voltage level does not exceed 80% of the power supply voltage of the dual-channel transimpedance amplifier (9) and the maximum output voltage of the data acquisition card (10); Sample data acquisition stage: After the optical power is adjusted, the dual-channel interference voltage data of the dual-channel transimpedance amplifier (9) is continuously acquired for a predetermined time as sample data; Data processing stage: The processor generates a sliding window to process the sample data. With the data of the reference photodiode as the horizontal axis and the data of the photodiode under test as the vertical axis, the dual-channel sample data are sequentially subjected to least-squares elliptic fitting in a sliding window manner, and the phase difference of the dual-channel signals is calculated. The fluctuation of the phase difference between the two detection signals from the reference photodiode (7) and the photodiode under test (8) is obtained; Calculate the phase difference of the dual-channel signal Standard deviation σ θ The standard deviation σ θ To compare the required phase detection accuracy of the interferometric measurement system, the standard deviation σ of the dual-channel signal of the photodiode (8) under test is used. θ If the phase detection accuracy is less than or equal to the preset value, the stability of the current photodiode (8) under test is considered to meet the system requirements; otherwise, it does not meet the system requirements.

6. The response stability evaluation method according to claim 5, characterized in that, In the sliding window processing, the window width should be set so that the data captured by each sliding window can form a closed Lissajous figure. The size of the sample data should not be less than 5 times the window width. Otherwise, it is necessary to return to the sample data acquisition stage and increase the acquisition time. The sliding step size should be set so that it can be divided by the window width and does not exceed half of the window width. At the same time, the number of sliding windows should not be less than 30.

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