CN113188584B - Method for measuring frequency response parameters of photoelectric detector - Google Patents
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Abstract
The invention discloses a method for measuring frequency response parameters of a photoelectric detector, which comprises the following steps: (1) Isolating and attenuating the light output by the laser source, and then irradiating the photoelectric detector to be detected; (2) The electric signal which is converted and output by the optical signal received by the detection photoelectric detector is connected to the frequency spectrograph; and (3) carrying out calculation analysis on the data obtained by the measurement of the spectrometer. The invention utilizes the spectral response characteristic of the self shot noise of the laser with broadband uniform noise spectral density, can be used as an optical radiation source required by the measurement of a photoelectric detector, can be used as an ideal broadband high-speed signal source, does not need an additional optical modulator, a broadband signal generator, a vector network analyzer and other instruments and equipment, and can realize the measurement of the frequency response characteristic parameters of any photoelectric detector in principle.
Description
Technical Field
The invention relates to the technical field of photoelectric measurement, in particular to a method for measuring frequency response parameters of a photoelectric detector.
Background
The photoelectric detector is used as the most basic photosensitive sensor in the photoelectric measurement technical field, and has the functions of converting various optical radiation signals to be measured into electric signals, and further collecting, processing and analyzing the electric signals, thus being the signal front end in the application fields of various photoelectric sensing and optical communication. The photodetector requires accurate measurement of the frequency response characteristics of the calibrated photodetector to accommodate requirements of various applications.
In the prior art, photoelectric instruments such as a sweep frequency laser source, a light modulator, a vector network analyzer and the like are required to be used, and the connection control and debugging processes are complex, so that the requirements of rapid, simple and accurate measurement are not met. The sweep frequency laser source and the optical modulator have certain modulation frequency bandwidth limitation, are only suitable for measurement within a certain frequency response bandwidth range, and need to adjust instrument selection according to specific specifications of the actual photoelectric detector to be measured, so that universality of a measurement method is further limited.
Disclosure of Invention
The invention aims to solve the technical problem of providing a method for measuring the frequency response parameters of a photoelectric detector, which utilizes the spectral response characteristics of broadband uniform noise spectral density of self shot noise of laser, can be used as an optical radiation source required by the measurement of the photoelectric detector, can be used as an ideal broadband high-speed signal source, and can realize the measurement of the frequency response characteristic parameters of any photoelectric detector.
In order to solve the above technical problems, the present invention provides a measurement device for a frequency response parameter of a photodetector, including: a laser source 1, an optical isolator 2, an optical attenuator 3, an optical coupler 4, a photodetector 5, a spectrometer 6 and an optical power meter 7; the laser source 1 provides the light radiation required by the irradiation of the photoelectric detector 5, the optical isolator 2 isolates the feedback of the reverse stray light in the light path of the laser source 1, so that the light source output is transmitted unidirectionally, the optical attenuator 3 adjusts the light power level input into the photoelectric detector 5 to be measured, the optical coupler 4 and the light power meter 7 split beams and measure and calibrate the light power level input into the photoelectric detector 5 to be measured in real time, the frequency spectrograph 6 performs frequency spectrum analysis on the output signal of the photoelectric detector 5 to be measured, and the output data is collected for analysis and processing to obtain a measurement result.
Preferably, the laser source 1 emits laser light with a determined central wavelength, which is within the spectral response range of the photodetector to be measured. For example, in the application scenes such as optical fiber or space laser communication, optical fiber sensing, laser ranging and the like, a photoelectric detector based on InGaAs semiconductor material is commonly used, the spectral response wavelength of the photoelectric detector is generally 850-1650nm, the laser center wavelength of the photoelectric detector is generally 1.5um C wave band (1535-1565 nm), and the conventional communication single-frequency semiconductor laser can meet the test requirement.
Preferably, the optical isolator 2 is composed of a polarizer, a Faraday gyromagnetic body and an analyzer sequentially, and the analyzer and the polarizer form a 45-degree polarization direction; the forward transmission light signal becomes linear polarized light after passing through the polarizer, and the linear polarized light is rotated 45 degrees by the polarization direction of the Faraday gyromagnetic body and just parallel to the polarization direction of the analyzer, so that the linear polarized light can pass through the analyzer without damage; in contrast, when the linearly polarized light passing through the analyzer passes through the Faraday gyromagnetic body, the deflection direction is perpendicular to the direction of the polarizer, and the light cannot pass through the polarizer, so that any light signal in the system and in the direction opposite to the transmission direction is blocked.
Preferably, the optical attenuator 3 shields the cross-sectional area of the light beam passing through the device by a precise adjusting mechanism in the device, so as to achieve the effect of attenuating the power of the transmitted optical signal, and the optical attenuator is controlled by an electric control automatic adjusting mode or a manual adjusting mode according to an adjusting mode.
Preferably, the optocoupler 4 adopts a one-way input coupler and a two-way output coupler, and the optical power distribution proportion follows that the optical signal power of the irradiation to the to-be-detected photoelectric detector 5 does not exceed the nominal saturation value. For example, an optical signal distributing 99% of the power enters the optical power meter, and the remaining 1% of the power optical signal is used to illuminate the photodetector 5 to be measured for measurement.
Correspondingly, the method for measuring the frequency response parameter of the photoelectric detector comprises the following steps:
(1) The light output by the laser source 1 is isolated and attenuated and then irradiates the photoelectric detector 5 to be detected;
(2) The electric signal which is converted and output by the optical signal received by the detection photoelectric detector 5 is connected to the frequency spectrograph 6;
(3) The data obtained by measuring the spectrometer 6 is calculated and analyzed.
Preferably, in step (1), the optical radiation illuminating the photodetector 5 has the same power spectral density within the detection band.
Preferably, in the step (3), the calculation and analysis of the data obtained by the spectrometer 6 are specifically: in the range of the continuous saturated optical power threshold value input by the photoelectric detector 5, the output differential noise voltage power spectral density and the input optical power at different determined frequencies are in linear change, so that the frequency response characteristic of the photoelectric detector is truly and accurately reflected by the output noise voltage power spectral density along with the frequency change curve, and the output noise voltage power spectral density is expressed as formula (1):
where f is the Fourier frequency, v 0 (f)、v n (f) The background dark current (i.e. no input) and the output noise voltage when the incident light power is, respectively, the basic charge constant e=1.6x10 -19 Coulomb, P opt For the light power of the illuminating photodetector, the detection sensitivity S (λ) is the corresponding photoelectric conversion coefficient at the light wavelength λ, unit: amperes/watt, G (f) is the photoelectric conversion gain at the corresponding fourier frequency f, rewritten as equation (2):
wherein R is L =50 ohm as the matching impedance value, P 0@1Hz (f)、P n@1Hz (f) The detection sensitivity S (lambda) of the photoelectric detector can be determined by consulting the spectral response curve of the photosensitive material of the corresponding detector when the background dark current (namely no light input) and the power spectral density (normalized to 1Hz bandwidth) of the output noise voltage when the incident light power are respectively equal to each other opt Collecting and recording by an optical power meter, and recording and outputting noise voltage power spectral density P by a spectrometer 0@1Hz (f)、P n@1Hz (f) Therefore, the gain G (f) of the photoelectric detector at a certain frequency f is determined, and the frequency response characteristic parameter information such as the frequency response bandwidth, the gain flatness, the average gain and the like of the photoelectric detector can be obtained by scanning a gain curve obtained by covering the whole detection bandwidth by the frequency f.
The beneficial effects of the invention are as follows: the invention utilizes the spectral response characteristic of the self shot noise of the laser with broadband uniform noise spectral density, can be used as an optical radiation source required by the measurement of a photoelectric detector, can be used as an ideal broadband high-speed signal source, does not need an additional optical modulator, a broadband signal generator, a vector network analyzer and other instruments and equipment, and can realize the measurement of the frequency response characteristic parameters of any photoelectric detector in principle.
Drawings
Fig. 1 is a schematic view of the structure of the device of the present invention.
FIG. 2 is a graph showing the power spectrum density of the output noise voltage of the photodetector under the irradiation of different light powers.
FIG. 3 is a schematic diagram of the power spectral density region of the differential noise voltage output by the photodetector at different Fourier frequencies under different light power illumination of the present invention.
FIG. 4 is a schematic diagram of the frequency response of the photodetector of the present invention.
Detailed Description
As shown in fig. 1, a measurement device for a frequency response parameter of a photodetector includes: a laser source 1, an optical isolator 2, an optical attenuator 3, an optical coupler 4, a photodetector 5, a spectrometer 6 and an optical power meter 7; the laser source 1 provides the light radiation required by the irradiation of the photoelectric detector 5, the optical isolator 2 isolates the feedback of the reverse stray light in the light path of the laser source 1, so that the light source output is transmitted unidirectionally, the optical attenuator 3 adjusts the light power level input into the photoelectric detector 5 to be measured, the optical coupler 4 and the light power meter 7 split beams and measure and calibrate the light power level input into the photoelectric detector 5 to be measured in real time, the frequency spectrograph 6 performs frequency spectrum analysis on the output signal of the photoelectric detector 5 to be measured, and the output data is collected for analysis and processing to obtain a measurement result.
Correspondingly, the method for measuring the frequency response parameter of the photoelectric detector comprises the following steps:
(1) The light output by the laser source 1 is isolated and attenuated and then irradiates the photoelectric detector 5 to be detected;
(2) The electric signal which is converted and output by the optical signal received by the detection photoelectric detector 5 is connected to the frequency spectrograph 6;
(3) The data obtained by measuring the spectrometer 6 is calculated and analyzed.
The basic principle of the measurement method is described as follows: in order to accurately measure the frequency response characteristic parameters of the photodetector, it is necessary that the optical radiation illuminating the photodetector has the same power spectral density (white noise) within the detection bandwidth, while the shot noise intrinsic properties of the laser meet this requirement. As long as the photodetector output meets the shot noise limit, namely: and outputting differential noise voltage power spectral density at different determined frequencies within the range of the continuous saturated optical power threshold of the photoelectric detector, wherein the input optical power is in linear change, so that the frequency response characteristic of the photoelectric detector can be truly and accurately reflected by the output noise voltage power spectral density along with the frequency change curve. The output noise voltage power spectral density is expressed as formula (1):
where f is the Fourier frequency, v 0 (f)、v n (f) Respectively, background dark current (i.e. no input), input when the incident light power isNoise voltage is generated, and basic charge constant e=1.6x10 -19 Coulomb, P opt For the light power of the illumination photodetector, the detection sensitivity S (λ) is the corresponding photoelectric conversion coefficient (unit: ampere/watt) at the light wavelength λ, and G (f) is the photoelectric conversion gain at the corresponding fourier frequency f. The above formula can be rewritten as formula (2):
wherein R is L =50Ω is the matching impedance value, P 0@1Hz (f)、P n@1Hz (f) The background dark current (i.e. no input), the output noise voltage power spectral density at the incident optical power (normalized to the 1Hz bandwidth), respectively. The detection sensitivity S (lambda) of the photoelectric detector can be determined by referring to the spectral response curve of the photosensitive material of the corresponding detector, and the value P of the incident light power opt Collecting and recording by an optical power meter, and recording and outputting noise voltage power spectral density P by a spectrometer 0@1Hz (f)、P n@1Hz (f) Therefore, the gain G (f) of the photoelectric detector at a certain frequency f is determined, and the frequency response characteristic parameter information such as the frequency response bandwidth, the gain flatness, the average gain and the like of the photoelectric detector can be obtained by scanning a gain curve obtained by covering the whole detection bandwidth by the frequency f.
Some commercial photodetector test examples are described below, with a nominal frequency response bandwidth of 200MHz and a gain of about 41.8 dB. The measurement data is obtained as follows: according to the above connection method, after the laser source 1 is powered on, stable power optical radiation is output, after the output passes through the optical isolator 2, the optical attenuator 3 is adjusted, so that the optical power of the light irradiated into the to-be-detected photoelectric detector 5 is a plurality of determined values (in the test example, the value range is 0-1 milliwatt, the value interval is 200 microwatts, 0 microwatts corresponds to no optical radiation input, the measurement result is the background noise of the photoelectric detector 5), the spectrometer 6 collects data, as shown in fig. 2, the response spectrum is output by the photoelectric detector under the irradiation of different optical powers, the horizontal axis is fourier frequency, and the vertical axis is the power spectrum density of the output noise voltage.
And then selecting the different optical power curves, recording the power spectrum density values of the output differential noise voltage at the same Fourier frequency (the power spectrum density values are 10/60/120/160/200 MHz) and connecting the power spectrum density values into a curve, as shown in figure 3. It can be seen that the output differential noise voltage power spectral density at different determined frequencies and the input optical power vary linearly over the range of the photodetector 5 input continuous saturated optical power threshold. I.e. the optical radiation required to illuminate the photodetector to satisfy the principles of the present invention has broadband uniform spectrum shot noise characteristics.
And then according to the formula (2), a curve of gain with Fourier frequency under different optical powers, namely a frequency response characteristic curve of the photodetector 5 is drawn, as shown in fig. 4. The frequency response characteristic of the photodetector is independent of the irradiation light power, and is unique. The gain of the photodetector 5 was measured to be about 42-43dB, and the 3dB bandwidth was about 200MHz, substantially in line with the nominal 41.8dB in the specifications of the product.
Claims (2)
1. A method for measuring a frequency response parameter of a photodetector, comprising the steps of:
(1) The light output by the laser source (1) is isolated and attenuated and then irradiates the photoelectric detector (5) to be detected;
(2) The electric signal which is converted and output by the optical signal received by the photoelectric detector (5) to be detected is connected into the frequency spectrograph (6);
(3) Calculating and analyzing the data obtained by measuring the spectrometer (6); in the range of the continuous saturated light power threshold value input by the photoelectric detector (5), the power spectrum density of the output differential noise voltage and the input light power at different determined frequencies are in linear change, so that the frequency response characteristic of the photoelectric detector is truly and accurately reflected by the power spectrum density of the output noise voltage along with the change curve of the frequency, and the power spectrum density of the output noise voltage is expressed as formula (1):
where f is the Fourier frequency, v 0 (f)、v n (f) The output noise voltage when the background dark current and the incident light power are zero, the basic charge constant e=1.6x10 -19 Coulomb, P opt For the light power of the illuminating photodetector, the detection sensitivity S (λ) is the corresponding photoelectric conversion coefficient at the light wavelength λ, unit: amperes/watt, G (f) is the photoelectric conversion gain at the corresponding fourier frequency f, rewritten as equation (2):
wherein R is L =50Ω is the matching impedance value, P 0@1Hz (f)、P n@1Hz (f) The power spectral densities of the output noise voltage when the background dark current and the incident light power are zero respectively, the detection sensitivity S (lambda) of the photoelectric detector can be determined by consulting the spectral response curve of the photosensitive material of the corresponding detector, and the incident light power value P opt Collecting and recording by an optical power meter, and recording and outputting noise voltage power spectral density P by a spectrometer 0@1Hz (f)、P n@1Hz (f) Thus, the gain G (f) of the photoelectric detector at a certain frequency f is determined, and the frequency response bandwidth, the gain flatness and/or the average gain of the photoelectric detector can be obtained by scanning a gain curve obtained by the frequency f covering the whole detection bandwidth.
2. A method of measuring a photodetector frequency response parameter as claimed in claim 1, characterized in that in step (1) the optical radiation illuminating the photodetector (5) has the same power spectral density in the detection band.
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