Apparatus and method for testing dynamic extinction ratio

Abstract

The application relates to a device and method for testing dynamic extinction ratio, which obtains the peak power of signal light after frequency shift pulse modulation of a modulation module, obtains the attenuation degree of an adjustable attenuator for power attenuation of the signal light after the frequency shift pulse modulation, and measures the value of the dynamic extinction ratio based on the weakest signal intensity that can be processed by a signal processing module, the attenuation degree of the adjustable attenuator and the peak power, so as to screen out devices with high dynamic extinction ratio in advance, thereby enabling the use of an acousto-optic modulator with high dynamic extinction ratio in a Doppler laser wind measurement radar system, reducing noise interference caused by leakage signals, and being beneficial to the calculation and processing of wind field information by the radar system.

Description

Technical Field

[0001] This application relates to the field of lidar, and in particular to a testing device and method for dynamic extinction ratio. Background Technology

[0002] Coherent Doppler lidar utilizes aerosol backscattering signals and the beat frequency signal of the local oscillator to obtain the Doppler frequency shift of the backscattered signal, thereby acquiring wind speed information. The magnitude of the frequency shift is typically obtained using edge detection, but this method can only determine the absolute value of the shift, not its direction. Therefore, a fixed frequency shift is often added to the measurement optical path to achieve this. Acousto-optic modulators are increasingly widely used due to their small size and ease of installation, and are also key components for achieving fixed frequency shifts in lidar detection systems.

[0003] When performing pulse modulation, the acousto-optic modulator emits pulsed ultrasound towards the acousto-optic crystal. As the ultrasound passes through the crystal, it modulates the optical signal. However, the ultrasound does not completely disappear after passing through the crystal; it is repeatedly refracted and reflected within the device and then passes through the crystal again, generating leakage pulses, which leads to inaccurate detection results. Summary of the Invention

[0004] This application provides a testing apparatus and method for reducing dynamic extinction ratio interference from leakage pulses, in order to solve the above-mentioned technical problems.

[0005] In a first aspect, this application provides a testing device for dynamic extinction ratio, comprising:

[0006] A laser used to output continuous laser light;

[0007] A beam splitter is used to separate the continuous laser output from a laser into signal light and local oscillator light.

[0008] The modulation module is used to receive signal light from the beam splitter and emit a synchronous radio frequency signal, perform frequency shift pulse modulation on the signal light based on the pulse radio frequency signal, and obtain the peak power of the frequency shift pulse modulated signal light.

[0009] An adjustable attenuator is used to receive signal light modulated by a frequency-shifted pulse and attenuate the power of the signal light modulated by the frequency-shifted pulse, while obtaining the attenuation degree of the adjustable attenuator.

[0010] A coupler for coupling the signal light from the adjustable attenuator and the local oscillator light from the beam splitter;

[0011] The signal processing module is used to receive the beam coupled by the coupler, process the beam based on the synchronous radio frequency signal, and obtain the dynamic extinction ratio of the modulation module based on the weakest signal strength that the signal processing module can process, the attenuation degree of the adjustable attenuator, and the peak power.

[0012] In one embodiment, the modulation module includes:

[0013] Arbitrary waveform generator, used to generate pulse radio frequency signals;

[0014] An acousto-optic driver is used to receive pulsed radio frequency signals output by an arbitrary waveform generator and drive an acousto-optic modulator based on the pulsed radio frequency signals.

[0015] An acousto-optic modulator is used to receive signal light from a beam splitter and pulsed radio frequency signals from an acousto-optic driver, and to perform frequency-shift pulse modulation on the signal light based on the pulsed radio frequency signals.

[0016] In one embodiment, the arbitrary waveform generator is further used to generate a synchronous radio frequency signal, and the signal processing module includes:

[0017] A detector is used to receive the coupled light beam from the coupler and convert the coupled light beam into an electrical signal after frequency beat;

[0018] The signal processing system receives the electrical signal output by the detector and the synchronous radio frequency signal emitted by the arbitrary waveform generator. Based on the synchronous radio frequency signal, the system processes the electrical signal output by the detector, transforming the electrical signal from a time-domain signal to a frequency-domain signal, thereby calculating the spectral intensity. Based on the weakest signal intensity that the signal processing module can process, the attenuation degree of the adjustable attenuator, and the peak power, the system obtains the dynamic extinction ratio of the modulation module.

[0019] In one embodiment, the modulation module includes an optical power meter for measuring the average power of the signal light modulated by the frequency-shifted pulse, and obtaining the peak power of the signal light modulated by the frequency-shifted pulse based on the average power.

[0020] Secondly, this application also provides a method for testing dynamic extinction ratio, which uses the testing apparatus as described in any of the first aspects, and the testing method includes:

[0021] The laser is controlled to output continuous laser light, which is then split into local oscillator light and signal light by a beam splitter.

[0022] Obtain the weakest signal strength that the signal processing module can process;

[0023] The control modulation module modulates the signal light using a frequency-shift pulse based on a pulse radio frequency signal to obtain the peak power of the signal light after frequency-shift pulse modulation.

[0024] After being modulated by a frequency-shifting pulse, the signal light is attenuated by an adjustable attenuator. The attenuated signal light is then coupled with the local oscillator light through a coupler and enters the detector for beat frequency. The detector then converts the signal light into an electrical signal.

[0025] The signal processing system receives electrical signals and processes them based on the synchronous radio frequency signal output by the modulation module.

[0026] Adjust the adjustable attenuator to obtain the attenuation degree of the adjustable attenuator;

[0027] The dynamic extinction ratio is obtained based on the weakest signal strength that the signal processing module can handle, the attenuation degree of the adjustable attenuator, and the peak power.

[0028] In one embodiment, the signal processing system receives the electrical signal and processes the electrical signal based on the synchronous radio frequency signal output by the modulation module; adjusting the adjustable attenuator to obtain the attenuation degree of the adjustable attenuator includes:

[0029] The signal processing system receives electrical signals and processes them based on the synchronous radio frequency signal output by the modulation module, transforming the electrical signals from time-domain signals to frequency-domain signals.

[0030] Adjust the adjustable attenuator to obtain the attenuation degree of the adjustable attenuator when the spectrum output by the signal processing system contains only the main pulse signal.

[0031] In one embodiment, the control modulation module performs frequency-shift pulse modulation on the signal light based on the pulsed radio frequency signal, and the peak power of the signal light after frequency-shift pulse modulation includes:

[0032] Control the arbitrary waveform generator to produce pulse radio frequency signals and synchronous radio frequency signals;

[0033] The acousto-optic driver receives the pulse radio frequency signal output by the arbitrary waveform generator;

[0034] The signal light from the beam splitter is modulated by an acousto-optic modulator to obtain the peak power of the signal light after frequency-shift pulse modulation; wherein the acousto-optic modulator modulates the signal light by frequency-shift pulse modulation based on the pulse radio frequency signal.

[0035] In one embodiment, obtaining the weakest signal strength that the signal processing module can process includes:

[0036] The signal light is DC modulated by an acousto-optic modulator to obtain the initial power of the signal light; wherein the acousto-optic driver inputs a DC signal to the acousto-optic modulator;

[0037] The DC-modulated signal light is attenuated by an adjustable attenuator. The attenuated signal light is then coupled with the local oscillator light through a coupler and enters the detector for beat frequency, where it is converted into an electrical signal.

[0038] The signal processing system receives and processes electrical signals, and uses Fourier transform to transform the time-domain signal into a frequency-domain signal;

[0039] Adjust the adjustable attenuator to obtain the initial attenuation of the adjustable attenuator when the leakage pulse of the spectrum output by the signal processing system is completely suppressed;

[0040] The weakest signal strength that the signal processing system can process is obtained based on the initial power of the signal light and the initial attenuation of the adjustable attenuator.

[0041] In one embodiment, the signal light is DC modulated via an acousto-optic modulator to obtain the initial power of the signal light; wherein the acousto-optic driver inputs a DC signal to the acousto-optic modulator including:

[0042] A DC signal is input to the acousto-optic driver by an arbitrary waveform generator, and the acousto-optic driver drives the acousto-optic modulator with DC.

[0043] The signal light is modulated by DC after passing through a DC-driven acousto-optic modulator;

[0044] The initial power of the signal light is obtained by measuring the power of the DC-modulated signal light using an optical power meter.

[0045] In one embodiment, before obtaining the dynamic extinction ratio based on the weakest signal strength that the signal processing module can process, the attenuation degree of the adjustable attenuator, and the peak power, the following steps are included:

[0046] At different time points, the adjustable attenuator is adjusted to obtain the corresponding spectrum of the signal processing system;

[0047] The attenuation of the adjustable attenuator is obtained when the leakage pulse in the spectrum is completely suppressed.

[0048] The aforementioned dynamic extinction ratio testing device and method, by obtaining the peak power of the signal light after frequency-shift pulse modulation by the modulation module, by obtaining the attenuation degree of the adjustable attenuator that attenuates the power of the signal light after frequency-shift pulse modulation, and by measuring the value of the dynamic extinction ratio based on the weakest signal strength that the signal processing module can process, the attenuation degree of the adjustable attenuator, and the peak power, is beneficial for screening devices with high dynamic extinction ratios in advance. This enables the use of acousto-optic modulators with high dynamic extinction ratios in Doppler laser wind radar systems, reducing noise interference caused by leakage signals, and facilitating the calculation and processing of wind field information by the radar system. Attached Figure Description

[0049] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0050] Figure 1 A schematic diagram of the system signal used to generate leakage pulses for the acousto-optic modulator;

[0051] Figure 2 This is a schematic diagram of a test apparatus for dynamic extinction ratio in one embodiment;

[0052] Figure 3 This is a schematic diagram of the testing device for dynamic extinction ratio in yet another embodiment;

[0053] Figure 4 This is a flowchart illustrating a method for testing the dynamic extinction ratio in one embodiment;

[0054] Figure 5 This is a flowchart illustrating the dynamic extinction ratio testing method in yet another embodiment;

[0055] Figure 6 This is a schematic diagram illustrating whether a component of a certain frequency exists at a certain point in time when the weakest signal strength that the signal processing system can process is obtained.

[0056] Figure 7 This is a schematic diagram showing whether a component of a certain frequency exists at a certain point in time. Detailed Implementation

[0057] To facilitate understanding of this application, a more complete description will be provided below with reference to the accompanying drawings. Preferred embodiments of this application are shown in the drawings. However, this application can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a thorough and complete understanding of the disclosure of this application.

[0058] Coherent Doppler lidar utilizes the aerosol backscattering signal and the beat frequency signal of the local oscillator to obtain the Doppler frequency shift of the backscattered signal, thereby acquiring wind speed information. The magnitude of the frequency shift is usually obtained using edge detection, but this method can only determine the absolute value of the frequency shift, not its direction. Therefore, a fixed frequency shift is often added to the measurement optical path to achieve this.

[0059] Acousto-optic modulators are increasingly widely used due to their small size and ease of installation. In the field of lidar wind measurement, acousto-optic modulators are also used as key components for achieving fixed frequency shifting due to these advantages. When the acousto-optic modulator performs pulse modulation, it emits pulsed ultrasound to the acousto-optic crystal; the ultrasound waves modulate the optical signal as they pass through the crystal.

[0060] However, the ultrasonic waves do not completely disappear after passing through the acousto-optic crystal. They are repeatedly refracted and reflected within the device, causing them to re-pass through the acousto-optic crystal and generating leakage pulses, such as... Figure 1 The diagram shown illustrates the system signal when the acousto-optic modulator generates a leakage pulse. (Refer to...) Figure 1The horizontal axis represents time, and the vertical axis represents the amplitude of the detected optical signal. It can be seen that in addition to the required pulse circled by the dashed line 102, multiple pulses were generated at subsequent time points. These are leakage pulses from the acousto-optic modulator. This results in leakage pulse components in the aerosol backscattered light received by the Doppler lidar. After beating with the local oscillator, the leakage pulse and the local oscillator beat frequency portion form a secondary peak in the time domain signal, interfering with the system's calculation of wind speed information. Since it takes time for sound waves to re-cross the acousto-optic crystal after refraction and reflection within the device, the static extinction ratio is not meaningful for medium- to long-range radar. The dynamic extinction ratio reflects the device's operation across the entire time domain and is therefore of great significance for medium- to long-range detection radar.

[0061] In one exemplary embodiment, such as Figure 2 As shown, a dynamic extinction ratio testing device is provided, comprising: a laser 202 for outputting continuous laser light; a beam splitter 204 for splitting the continuous laser light output by the laser into signal light and local oscillator light; a modulation module 206 for receiving signal light from the beam splitter and emitting a synchronous radio frequency signal, performing frequency-shift pulse modulation on the signal light based on the pulse radio frequency signal, and obtaining the peak power of the frequency-shift pulse modulated signal light; an adjustable attenuator 208 for receiving the frequency-shift pulse modulated signal light and attenuating the power of the frequency-shift pulse modulated signal light, and obtaining the attenuation degree of the adjustable attenuator; a coupler 210 for coupling the signal light from the adjustable attenuator and the local oscillator light from the beam splitter; and a signal processing module 212 for receiving the beam coupled by the coupler, processing the beam based on the synchronous radio frequency signal, and obtaining the dynamic extinction ratio of the modulation module based on the weakest signal intensity that the signal processing module can process, the attenuation degree of the adjustable attenuator, and the peak power.

[0062] Specifically, laser 202 emits continuous laser light, which is incident on beam splitter 204 and split into two beams, referred to as signal light and local oscillator light, respectively. The signal light is incident on modulation module 206, which performs frequency-shift pulse modulation on the signal light based on a pulsed radio frequency signal and detects the peak power of the frequency-shifted pulse modulated signal light. The frequency-shifted pulse modulated signal light is then incident on adjustable attenuator 208, which attenuates the signal light to a corresponding attenuation degree. The attenuated signal light is then incident on coupler 210, and the local oscillator light separated by beam splitter 204 is also incident on coupler 210. Coupler 210 couples the local oscillator light and the signal light, and then incident the coupled beam on signal processing module 212. The signal processing module 212 receives the coupled beam from the coupler and processes the coupled beam based on the synchronous radio frequency signal emitted by the modulation module. The dynamic extinction ratio of the modulation module is obtained based on the weakest signal strength that the signal processing module can process, the attenuation degree of the adjustable attenuator, and the peak power.

[0063] The aforementioned dynamic extinction ratio testing device obtains the peak power of the signal light after frequency-shift pulse modulation by the modulation module, the attenuation degree of the adjustable attenuator that attenuates the power of the signal light after frequency-shift pulse modulation, and measures the dynamic extinction ratio based on the weakest signal strength that the signal processing module can process, the attenuation degree of the adjustable attenuator, and the peak power. This is beneficial for screening devices with high dynamic extinction ratios in advance, so that acousto-optic modulators with high dynamic extinction ratios can be used in Doppler laser wind radar systems, reducing noise interference caused by leakage signals, and facilitating the radar system's calculation and processing of wind field information.

[0064] In one exemplary embodiment, such as Figure 3 As shown, Figure 3 This is a schematic diagram of a dynamic extinction ratio testing device in another embodiment of this application, wherein the modulation module 206 includes: an arbitrary waveform generator 2066 for generating pulsed radio frequency signals; an acousto-optic driver 2064 for receiving the pulsed radio frequency signals output by the arbitrary waveform generator and driving the acousto-optic modulator 2062 based on the pulsed radio frequency signals; and an acousto-optic modulator 2062 for receiving signal light from a beam splitter and pulsed radio frequency signals from the acousto-optic driver, and performing frequency-shift pulse modulation on the signal light based on the pulsed radio frequency signals.

[0065] Refer again Figure 3In one exemplary embodiment, the arbitrary waveform generator 2066 is also used to generate a synchronous radio frequency signal. The signal processing module 212 includes: a detector 2122, used to receive the beam coupled by the coupler and convert the coupled beam into an electrical signal after frequency beating; and a signal processing system 2124, which receives the electrical signal output by the detector 2122 and the synchronous radio frequency signal emitted by the arbitrary waveform generator 2066, and processes the electrical signal output by the detector 2122 based on the synchronous radio frequency signal, transforming the electrical signal from a time-domain signal to a frequency-domain signal, thereby calculating the spectral intensity, and obtaining the dynamic extinction ratio of the modulation module based on the weakest signal intensity that the signal processing module can process, the attenuation degree of the adjustable attenuator, and the peak power.

[0066] Additionally, optionally, the modulation module 206 includes an optical power meter for measuring the average power of the signal light modulated by the frequency-shifted pulse, and obtaining the peak power of the signal light modulated by the frequency-shifted pulse based on the average power.

[0067] For example, please refer to Figure 3 , Figure 3 A test apparatus for the dynamic extinction ratio of an acousto-optic modulator is shown in one embodiment of this application. The apparatus includes: a laser 202, a beam splitter 204, an arbitrary waveform generator 2066, an acousto-optic driver 2064, an acousto-optic modulator 2062, an adjustable attenuator 208, a coupler 210, a detector 2122, and a signal processing system 2124.

[0068] The system includes a laser 2022 for outputting continuous laser light; a beam splitter 204 for separating signal light and local oscillator light; an arbitrary waveform generator 2066 for generating adjustable pulsed radio frequency (RF) signals and a synchronization RF signal; an acousto-optic driver 2064 for receiving the pulsed RF signal output by the arbitrary waveform generator 2066; an acousto-optic modulator 2062 for receiving the signal light from the beam splitter 204 and the pulsed RF signal from the acousto-optic driver 2064, and performing frequency-shifting pulse modulation on the signal light; an adjustable attenuator 208 for receiving the modulated signal light and performing power attenuation; a coupler 210 for coupling the signal light from the adjustable attenuator 208 and the local oscillator light from the beam splitter 204; a detector 2122 for receiving the two coupled signals, performing beat frequency analysis, and converting them into electrical signals; and a signal processing system 2124 for receiving the electrical signal output by the detector 2122 and the synchronization RF signal emitted by the arbitrary waveform generator 2066, processing the signals, acquiring data, performing corresponding analysis, and calculating the spectral intensity.

[0069] Specifically, laser 202 emits continuous laser light, which is incident on beam splitter 204 and split into two beams, referred to as signal light and local oscillator light, respectively. The signal light is incident on acousto-optic modulator 2062. Acousto-optic modulator 2062 receives the signal light from the beam splitter and the pulsed radio frequency signal from the acousto-optic driver, and performs frequency-shift pulse modulation on the signal light based on the pulsed radio frequency signal. Arbitrary waveform generator 2066 generates the pulsed radio frequency signal; acousto-optic driver 2064 receives the pulsed radio frequency signal output by the arbitrary waveform generator and drives acousto-optic modulator 2062 based on the pulsed radio frequency signal, so that when receiving the signal light from the beam splitter, acousto-optic modulator 2062 uses the pulsed radio frequency signal from the acousto-optic driver to perform frequency-shift pulse modulation on the signal light, thereby causing the signal light to be frequency-shifted, and at the same time, the signal light is modulated from continuous light to pulsed light. The average power of the frequency-shift pulse modulated signal light is measured using an optical power meter, and the peak power of the frequency-shift pulse modulated signal light is obtained according to formula (1).

[0070] Peak power = Average power / Repetition frequency / Pulse width (1)

[0071] The signal light modulated by the frequency-shifted pulse is incident on the adjustable attenuator 208, which attenuates the signal light to obtain a corresponding attenuation degree. The attenuated signal light is then incident on the coupler 210, and the local oscillator light separated by the beam splitter 204 is also incident on the coupler 210. The coupler 210 couples the local oscillator light and the signal light, and the coupled beam is incident on the detector 2122. The coupled beam can be split into multiple beams, and noise is filtered using a differential method. Optionally, the detector 2122 can be a balanced detector, where the coupled light is split into two beams and incident on the balanced detector for beat frequency conversion and then converted into an electrical signal. The signal processing system 2124 receives the electrical signal output by the detector 2122 and the synchronization radio frequency signal emitted by the arbitrary waveform generator 2066, and processes the electrical signal output by the detector 2122 based on the synchronization radio frequency signal, thereby enabling the signal processing system 2124 to synchronize its processing of the electrical signal with the modulation of the signal light by the electro-optic modulator 2063. Signal processing system 2124 transforms the electrical signal from a time-domain signal to a frequency-domain signal, thereby calculating the spectral intensity. For example, signal processing system 2124 uses Fourier transform to transform the electrical signal from a time-domain signal to a frequency-domain signal. Further, signal processing module 212 obtains the dynamic extinction ratio of the modulation module based on the weakest signal strength that the signal processing module can process, the attenuation degree of the adjustable attenuator, and the peak power.

[0072] In this embodiment, by performing a dynamic extinction ratio test on the acousto-optic modulator, an acousto-optic modulator with a high dynamic extinction ratio can be selected to improve the signal-to-noise ratio of the emitted laser, thereby ensuring the accuracy of the lidar in calculating wind speed information.

[0073] Based on the same inventive concept, embodiments of this application also provide a method for testing dynamic extinction ratio, referring to... Figure 4 , Figure 4 This is a flowchart illustrating a method for testing the dynamic extinction ratio in one embodiment. The method uses the testing apparatus described in any of the foregoing embodiments, and includes:

[0074] Step 402: Control the laser to output continuous laser light, which is then split into local oscillator light and signal light by a beam splitter.

[0075] Step 404: Obtain the weakest signal strength that the signal processing module can process.

[0076] Step 406: The control modulation module performs frequency shift pulse modulation on the signal light based on the pulse radio frequency signal to obtain the peak power of the signal light after frequency shift pulse modulation.

[0077] Step 408: The signal light after frequency shift pulse modulation is attenuated by an adjustable attenuator. The attenuated signal light and the local oscillator light are coupled by a coupler and then enter the detector for beat frequency. The detector then converts the signal light into an electrical signal.

[0078] Step 410: The signal processing system receives the electrical signal and processes it based on the synchronous radio frequency signal output by the modulation module.

[0079] Step 412: Adjust the adjustable attenuator to obtain the attenuation degree of the adjustable attenuator.

[0080] Step 414: The dynamic extinction ratio is obtained based on the weakest signal strength that the signal processing module can process, the attenuation degree of the adjustable attenuator, and the peak power.

[0081] For example, the laser outputs continuous laser light, and the beam splitter splits the continuous laser light into local oscillator light and signal light; the weakest signal intensity that the signal processing system can process is measured and recorded as P0 (dBm); the signal light output by the beam splitter enters the modulation module, and the modulation module controls the signal light to be frequency-shifted pulse modulated based on the pulse radio frequency signal to obtain the peak power of the signal light after frequency-shifted pulse modulation; optionally, the average power of the signal light is measured using an optical power meter, and the peak power is obtained according to formula (1) and recorded as P1 (dBm); the signal light after frequency-shifted pulse modulation is input to the adjustable attenuator for attenuation and then coupled with the local oscillator light split by the beam splitter into the coupler, and then enters the detector for beat frequency, and is converted into an electrical signal output to the signal processing system; the signal processing system receives the output electrical signal and processes the electrical signal based on the synchronous radio frequency signal output by the modulation module. For example, the Fourier transform is used to transform the time domain signal into a frequency domain signal; the adjustable attenuator is adjusted and the spectrum output by the signal processing system is observed until the leakage pulse in the spectrum is completely suppressed, at which point there is exactly only the main pulse signal in the frequency domain. Obtain the attenuation of the adjustable attenuator at this time, denoted as A (dB); based on the weakest signal strength P0 (dBm) that the signal processing module can process, the attenuation of the adjustable attenuator A (dB), and the peak power P1 (dBm), obtain the dynamic extinction ratio DER. For example, the dynamic extinction ratio DER can be obtained by formula (2):

[0082] DER = P1 – A - P0 (2)

[0083] The aforementioned dynamic extinction ratio testing method obtains the peak power of the signal light after frequency-shift pulse modulation by the modulation module, the attenuation degree of the adjustable attenuator that reduces the power of the signal light after frequency-shift pulse modulation, and the dynamic extinction ratio is measured based on the weakest signal strength that the signal processing module can process, the attenuation degree of the adjustable attenuator, and the peak power. This method can determine the dynamic extinction ratio value, which is beneficial for early screening of devices with high dynamic extinction ratios. As a result, acousto-optic modulators with high dynamic extinction ratios can be used in Doppler laser wind radar systems, reducing noise interference caused by leakage signals and facilitating the radar system's calculation and processing of wind field information. Furthermore, the aforementioned dynamic extinction ratio testing method has a simple definition standard, requiring only the determination of the presence or absence of a frequency domain signal without analyzing the intensity of the frequency domain signal.

[0084] In one embodiment, the control modulation module performs frequency-shift pulse modulation on the signal light based on the pulsed radio frequency signal, and the peak power of the signal light after frequency-shift pulse modulation includes:

[0085] The arbitrary waveform generator is controlled to generate pulse radio frequency signals and synchronous radio frequency signals; the acousto-optic driver receives the pulse radio frequency signals output by the arbitrary waveform generator; the signal light from the beam splitter is modulated by the acousto-optic modulator to obtain the peak power of the signal light after frequency shift pulse modulation; wherein the acousto-optic modulator modulates the signal light based on the pulse radio frequency signal.

[0086] In one embodiment, the signal processing system receives an electrical signal and processes the electrical signal based on the synchronous radio frequency signal output by the modulation module; adjusting the adjustable attenuator to obtain the attenuation degree of the adjustable attenuator includes:

[0087] The signal processing system receives electrical signals and processes them based on the synchronous radio frequency signal output by the modulation module, transforming the electrical signals from time-domain signals to frequency-domain signals; it adjusts the adjustable attenuator to obtain the attenuation degree of the adjustable attenuator when the spectrum output by the signal processing system contains only the main pulse signal.

[0088] In one exemplary embodiment, obtaining the weakest signal strength that the signal processing module can process includes:

[0089] The signal light is DC modulated by an acousto-optic modulator to obtain the initial power of the signal light; the acousto-optic driver inputs a DC signal to the acousto-optic modulator; the DC-modulated signal light is attenuated by an adjustable attenuator, and the attenuated signal light is coupled with the local oscillator light through a coupler and enters the detector for beat frequency, and is converted into an electrical signal by the detector; the signal processing system receives and processes the electrical signal, and uses Fourier transform to transform the time domain signal into a frequency domain signal; the adjustable attenuator is adjusted to obtain the initial attenuation degree of the adjustable attenuator when the leakage pulse of the spectrum output by the signal processing system is completely suppressed; the weakest signal strength that the signal processing system can process is obtained based on the initial power of the signal light and the initial attenuation degree of the adjustable attenuator.

[0090] For example, obtaining the weakest signal strength that the signal processing module can process includes the following steps:

[0091] The laser outputs continuous laser light, which is split into local oscillator light and signal light by a beam splitter. The signal light output from the beam splitter enters the acousto-optic modulator, and a DC signal is input to the acousto-optic driver by an arbitrary waveform generator. The modulated signal light is output by the acousto-optic modulator, and the power of the signal light is measured by an optical power meter and recorded as the initial power P2 (dBm).

[0092] The signal light output from the acousto-optic modulator is input to an adjustable attenuator. The attenuated signal light couples with the local oscillator light split by the beam splitter and enters the coupler, where it is evenly split into two beams. These beams then enter the detector for beat frequency analysis and are converted into electrical signals, which are output to the signal processing system. It is understood that the light incident on the detector can be two or more beams, and the intensity of these beams can be evenly distributed or distributed according to a certain ratio before being incident on the detector; the detector can be a balanced detector; however, the embodiments of this application do not limit this.

[0093] The signal processing system processes the output electrical signal and uses Fourier transform to transform the time-domain signal into a frequency-domain signal. The adjustable attenuator is adjusted, and the frequency-domain signal analyzed by the signal processing system is observed until the noise in the frequency domain just reaches the shot noise level. The attenuation degree of the adjustable attenuator is recorded as the initial attenuation degree B (dB). Based on the initial power P2 (dBm) of the signal light and the initial attenuation degree B (dB) of the adjustable attenuator, the weakest signal strength P0 (dBm) that the signal processing system can process is obtained. For example, the weakest signal strength P0 (dBm) can be obtained using formula (3):

[0094] P0 = P2 - B (3)

[0095] In this embodiment, the weakest signal intensity of different signal processing systems is obtained by specific analysis of different signal processing systems, and the dynamic extinction ratio of the system is obtained based on the weakest signal intensity that the specific signal processing system can process, so that the obtained dynamic extinction ratio has higher accuracy; and considering the insufficient sensitivity of the light intensity detector, the time domain signal is converted into a frequency domain signal for detection, thereby improving the detection sensitivity.

[0096] In one embodiment, the signal light is DC modulated by an acousto-optic modulator to obtain the initial power of the signal light; wherein the acousto-optic driver inputs a DC signal to the acousto-optic modulator including:

[0097] A DC signal is input to the acousto-optic driver by an arbitrary waveform generator, and the acousto-optic driver drives the acousto-optic modulator with DC. The signal light is obtained by passing through the DC-driven acousto-optic modulator and then being modulated by DC. The power of the DC-modulated signal light is measured by an optical power meter to obtain the initial power of the signal light.

[0098] In one embodiment, before obtaining the dynamic extinction ratio based on the weakest signal strength that the signal processing module can process, the attenuation degree of the adjustable attenuator, and the peak power, the following steps are included:

[0099] At different time points, the adjustable attenuator is adjusted to obtain the corresponding spectrum of the signal processing system; the attenuation degree of the adjustable attenuator when the leakage pulse in the spectrum is completely suppressed is obtained.

[0100] For example, this embodiment can measure the dynamic extinction ratio at any distance from the door: Refer to Figure 1 , Figure 1 This is a schematic diagram of the system signal when the acousto-optic modulator generates a leakage pulse. The horizontal axis represents the system signal measured at different times after modulation by the acousto-optic modulator to generate the leakage pulse. Therefore, by obtaining the time using formula (4), the system signal values ​​at different distance gates can be obtained:

[0101] Distance (L) = Speed ​​of light × Time (T) (4)

[0102] Read Figure 1 Given the abscissa value T of the time-domain signal, calculate the distance L, adjust the adjustable attenuator, and observe the spectrum output by the signal processing system until the leakage pulse at point T in the spectrum is completely suppressed. Record the attenuation degree of the adjustable attenuator, denoted as B. L (dB).

[0103] For example, the dynamic extinction ratio DER at any distance L L It can be obtained through formula (5), where B L The attenuation of the adjustable attenuator at different distances; P0 (dBm) is the weakest signal strength that the signal processing system can handle; P1 (dBm) is the peak power of the signal light after frequency-shift pulse modulation.

[0104] DER L = P1 - B L - P0 (5)

[0105] In this embodiment, by acquiring system signals at different times, the dynamic extinction ratio at any distance from the gate can be measured.

[0106] In one exemplary embodiment, such as Figure 5 As shown, another embodiment of this application provides a method for testing dynamic extinction ratio, including steps 502 to 518. Wherein:

[0107] Step 502: Control the laser to output continuous laser light, which is then split into local oscillator light and signal light by a beam splitter.

[0108] Step 504: A DC signal is input to the acousto-optic driver by an arbitrary waveform generator, and the acousto-optic driver drives the acousto-optic modulator with DC. The signal light is obtained by passing through the DC-driven acousto-optic modulator and then being modulated by DC. The power of the DC-modulated signal light is measured by an optical power meter to obtain the initial power of the signal light.

[0109] Step 506: The DC-modulated signal light is attenuated by an adjustable attenuator. The attenuated signal light and the local oscillator light are coupled together by a coupler and then enter the detector for beat frequency, and are converted into an electrical signal by the detector.

[0110] Step 508: The signal processing system receives and processes the electrical signal, and uses Fourier transform to transform the time-domain signal into a frequency-domain signal; adjusts the adjustable attenuator to obtain the initial attenuation degree of the adjustable attenuator when the leakage pulse of the spectrum output by the signal processing system is completely suppressed; and obtains the weakest signal strength that the signal processing system can process based on the initial power of the signal light and the initial attenuation degree of the adjustable attenuator.

[0111] Step 510: Control the arbitrary waveform generator to generate a pulse radio frequency signal and a synchronous radio frequency signal; make the acousto-optic driver receive the pulse radio frequency signal output by the arbitrary waveform generator; the signal light from the beam splitter obtains the peak power of the signal light after frequency-shift pulse modulation by the acousto-optic modulator; wherein the acousto-optic modulator performs frequency-shift pulse modulation on the signal light based on the pulse radio frequency signal.

[0112] Step 512: The signal light after frequency shift pulse modulation is attenuated by an adjustable attenuator. The attenuated signal light and the local oscillator light are coupled by a coupler and then enter the detector for beat frequency. The detector then converts the signal light into an electrical signal.

[0113] Step 514: The signal processing system receives the electrical signal and processes it based on the synchronous radio frequency signal output by the modulation module, transforming the electrical signal from a time-domain signal to a frequency-domain signal; the adjustable attenuator is adjusted to obtain the attenuation degree of the adjustable attenuator when the spectrum output by the signal processing system contains only the main pulse signal.

[0114] Step 516: At different time points, adjust the adjustable attenuator and obtain the corresponding spectrum of the signal processing system; obtain the attenuation degree of the adjustable attenuator when the leakage pulse in the spectrum is completely suppressed.

[0115] Step 518: The dynamic extinction ratio is obtained based on the weakest signal strength that the signal processing module can process, the attenuation degree of the adjustable attenuator, and the peak power.

[0116] Specifically, in one embodiment, an 80M acousto-optic modulator is used as the acousto-optic modulator under test, a balanced detector is used as the detector, and a computer is used as the signal processing system.

[0117] The weakest signal strength that the signal processing system can handle is measured as follows: When the measured signal optical power P2 = -50 dBm (0.00001 mW), and the attenuation of the adjustable attenuator B = 60 dB, there is exactly noise in the frequency domain, with no light leakage caused by the photoelectric modulator. For example... Figure 6 As shown, Figure 6This is a schematic diagram illustrating whether a component of a certain frequency exists at a given time point when acquiring the weakest signal strength that the signal processing system can handle. The horizontal axis represents frequency, with units of MHz. Z The vertical axis represents intensity. From Figure 6 As can be seen, there is a slight bulge at 80MHz in the frequency domain, but it is too weak to be detected by the system.

[0118] The weakest signal strength that the signal processing system can process is calculated using formula (3): P0 = P2 - B = -110dBm.

[0119] According to the test method of dynamic extinction ratio of acousto-optic modulator, the average power of the output signal light of 80M acousto-optic modulator is measured with an optical power meter; the peak power is calculated according to peak power = average power / repetition frequency / pulse width, and is recorded as P1 = 5 dBm.

[0120] Adjust the adjustable attenuator until leakage pulses in the spectrum are completely suppressed, such as... Figure 7 As shown, Figure 7 This diagram illustrates whether a component of a certain frequency exists at a specific point in time, where the horizontal axis represents frequency in MHz. Z The vertical axis represents intensity. Record the attenuation of the adjustable attenuator, denoted as A = 71 dB.

[0121] The dynamic extinction ratio DER = P1 – A - P0 = 44dB is calculated using formula (2).

[0122] Using the formula distance = speed of light × time, the dynamic extinction ratios at 500m, 2km, and 8km were measured according to the above procedure, and were found to be 44dB, 49dB, and 56dB, respectively. This means that the 80M acousto-optic modulator has a greater leakage at 500m than at 2km, and a greater leakage at 2km than at 8km.

[0123] In this embodiment, by obtaining the peak power of the signal light after frequency-shift pulse modulation by the modulation module, and by obtaining the attenuation degree of the adjustable attenuator that attenuates the power of the signal light after frequency-shift pulse modulation, and by measuring the dynamic extinction ratio based on the weakest signal strength that the signal processing module can process, the attenuation degree of the adjustable attenuator, and the peak power, the dynamic extinction ratio can be measured. This allows for the early screening of devices with high dynamic extinction ratios, enabling the use of acousto-optic modulators with high dynamic extinction ratios in Doppler laser wind radar systems. This reduces noise interference caused by leakage signals and facilitates the radar system's calculation and processing of wind field information. By acquiring system signals at different times, the dynamic extinction ratio at any distance from the gate can be measured. Through specific analysis of different signal processing systems, the corresponding weakest signal intensity of each system is obtained. Based on the weakest signal intensity that a specific signal processing system can handle, the dynamic extinction ratio of the system is acquired, resulting in higher accuracy. Furthermore, considering the insufficient sensitivity of the light intensity detector, the time-domain signal is converted to a frequency-domain signal for detection, thereby improving detection sensitivity. Moreover, the testing method in this embodiment has a simple definition standard, requiring only the determination of the presence or absence of a frequency-domain signal without analyzing its intensity.

[0124] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0125] The embodiments described above are merely illustrative of several implementation methods of this application, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the patent application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this patent application should be determined by the appended claims.

Claims

1. A device for testing dynamic extinction ratio, characterized in that, include: A laser used to output continuous laser light; A beam splitter is used to separate the continuous laser output from the laser into signal light and local oscillator light; The modulation module is used to receive signal light from the beam splitter and emit a synchronous radio frequency signal, perform frequency shift pulse modulation on the signal light based on the pulse radio frequency signal, and obtain the peak power of the frequency shift pulse modulated signal light. An adjustable attenuator is used to receive signal light modulated by a frequency-shifted pulse and attenuate the power of the signal light modulated by the frequency-shifted pulse, while obtaining the attenuation degree of the adjustable attenuator. A coupler for coupling signal light from the adjustable attenuator and local oscillator light from the beam splitter; The signal processing module is used to receive the beam coupled by the coupler, process the beam based on the synchronous radio frequency signal, and obtain the dynamic extinction ratio of the modulation module based on the weakest signal strength that the signal processing module can process, the attenuation degree of the adjustable attenuator, and the peak power; wherein, the dynamic extinction ratio = peak power - attenuation degree of the adjustable attenuator - weakest signal strength that the signal processing module can process.

2. The testing apparatus according to claim 1, characterized in that, The modulation module includes: Arbitrary waveform generator, used to generate pulse radio frequency signals; An acousto-optic driver is used to receive the pulse radio frequency signal output by the arbitrary waveform generator and drive the acousto-optic modulator based on the pulse radio frequency signal; An acousto-optic modulator is used to receive signal light from a beam splitter and pulsed radio frequency signals from an acousto-optic driver, and to perform frequency-shift pulse modulation on the signal light based on the pulsed radio frequency signals.

3. The testing apparatus according to claim 2, characterized in that, The arbitrary waveform generator is also used to generate a synchronous radio frequency signal, and the signal processing module includes: A detector is used to receive the beam coupled by the coupler and convert the coupled beam into an electrical signal after frequency beating; The signal processing system receives the electrical signal output by the detector and the synchronous radio frequency signal emitted by the arbitrary waveform generator, and processes the electrical signal output by the detector based on the synchronous radio frequency signal, transforming the electrical signal from a time-domain signal to a frequency-domain signal, thereby calculating the spectral intensity, and obtaining the dynamic extinction ratio of the modulation module based on the weakest signal intensity that the signal processing module can process, the attenuation degree of the adjustable attenuator, and the peak power.

4. The testing apparatus according to claim 1, characterized in that, The modulation module includes an optical power meter for measuring the average power of the signal light after frequency-shift pulse modulation, and obtaining the peak power of the signal light after frequency-shift pulse modulation based on the average power.

5. A method for testing dynamic extinction ratio, characterized in that, The method uses the testing apparatus as described in any one of claims 1-4, and the method includes: The laser is controlled to output continuous laser light, which is then split into local oscillator light and signal light by a beam splitter. Obtain the weakest signal strength that the signal processing module can process; The control modulation module performs frequency-shift pulse modulation on the signal light based on the pulse radio frequency signal to obtain the peak power of the signal light after frequency-shift pulse modulation; The signal light modulated by the frequency-shifting pulse is attenuated by an adjustable attenuator to obtain attenuated signal light. The attenuated signal light is coupled with the local oscillator light through a coupler and then enters the detector for beat frequency. The detector then converts the signal light into an electrical signal. The signal processing system receives the electrical signal and processes it based on the synchronous radio frequency signal output by the modulation module; Adjust the adjustable attenuator to obtain the attenuation degree of the adjustable attenuator; The dynamic extinction ratio is obtained based on the weakest signal strength that the signal processing module can process, the attenuation degree of the adjustable attenuator, and the peak power; wherein, the dynamic extinction ratio = peak power - attenuation degree of the adjustable attenuator - weakest signal strength that the signal processing module can process.

6. The test method according to claim 5, characterized in that, The signal processing system receives the electrical signal and processes the electrical signal based on the synchronous radio frequency signal output by the modulation module; Adjusting the adjustable attenuator to obtain its attenuation includes: The signal processing system receives the electrical signal and processes it based on the synchronous radio frequency signal output by the modulation module, transforming the electrical signal from a time-domain signal to a frequency-domain signal. Adjust the adjustable attenuator to obtain the attenuation degree of the adjustable attenuator when the spectrum output by the signal processing system contains only the main pulse signal.

7. The test method according to claim 5, characterized in that, The control modulation module performs frequency-shift pulse modulation on the signal light based on the pulse radio frequency signal, and the peak power of the signal light after frequency-shift pulse modulation includes: Control the arbitrary waveform generator to produce pulse radio frequency signals and synchronous radio frequency signals; The acousto-optic driver receives the pulse radio frequency signal output by the arbitrary waveform generator; The signal light from the beam splitter is modulated by an acousto-optic modulator to obtain the peak power of the signal light after frequency-shift pulse modulation; wherein the acousto-optic modulator modulates the signal light by frequency-shift pulse modulation based on the pulse radio frequency signal.

8. The test method according to claim 5, characterized in that, The weakest signal strength that the signal processing module can process includes: The signal light is DC modulated by an acousto-optic modulator to obtain the initial power of the signal light; wherein the acousto-optic driver inputs a DC signal to the acousto-optic modulator; The DC-modulated signal light is attenuated by an adjustable attenuator. The attenuated signal light is then coupled with the local oscillator light via a coupler and enters the detector for beat frequency, where it is converted into an electrical signal. The signal processing system receives and processes the electrical signal, and uses Fourier transform to transform the time-domain signal into a frequency-domain signal; Adjust the adjustable attenuator to obtain the initial attenuation of the adjustable attenuator when the leakage pulse of the spectrum output by the signal processing system is completely suppressed; The weakest signal strength that the signal processing system can process is obtained based on the initial power of the signal light and the initial attenuation of the adjustable attenuator.

9. The test method according to claim 8, characterized in that, The signal light is DC modulated by an acousto-optic modulator to obtain the initial power of the signal light; The DC signal input from the acousto-optic driver to the acousto-optic modulator includes: A DC signal is input to the acousto-optic driver by an arbitrary waveform generator, and the acousto-optic driver drives the acousto-optic modulator with DC. The signal light is obtained by passing through a DC-driven acousto-optic modulator to obtain DC-modulated signal light; The initial power of the signal light is obtained by measuring the power of the DC-modulated signal light using an optical power meter.

10. The test method according to claim 5 or 7, characterized in that, Before obtaining the dynamic extinction ratio based on the weakest signal strength that the signal processing module can process, the attenuation degree of the adjustable attenuator, and the peak power, the following steps are also included: At different time points, the adjustable attenuator is adjusted to obtain the corresponding spectrum of the signal processing system; The attenuation of the adjustable attenuator is obtained when the leakage pulse in the spectrum is completely suppressed.

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