CN115792861A - Device and method for realizing coherent accumulation of pulse laser Doppler radar signals - Google Patents
Device and method for realizing coherent accumulation of pulse laser Doppler radar signals Download PDFInfo
- Publication number
- CN115792861A CN115792861A CN202211410990.7A CN202211410990A CN115792861A CN 115792861 A CN115792861 A CN 115792861A CN 202211410990 A CN202211410990 A CN 202211410990A CN 115792861 A CN115792861 A CN 115792861A
- Authority
- CN
- China
- Prior art keywords
- module
- modulator
- phase
- signal
- optical
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Pending
Links
Images
Classifications
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02A—TECHNOLOGIES FOR ADAPTATION TO CLIMATE CHANGE
- Y02A90/00—Technologies having an indirect contribution to adaptation to climate change
- Y02A90/10—Information and communication technologies [ICT] supporting adaptation to climate change, e.g. for weather forecasting or climate simulation
Abstract
The invention belongs to the technical field of laser Doppler radars, and particularly relates to a device and a method for realizing coherent accumulation of pulse laser Doppler radar signals. The invention realizes the adjustment of the amplitude of the end face reflection intermediate frequency signal by controlling the size of the local oscillator optical power, so that the amplitude is in the range of AD quantization measurement range, thereby acquiring and quantizing the end face reflection intermediate frequency signal, and analyzing and extracting the initial phase of the end face reflection intermediate frequency signal by a Fast Fourier Transform (FFT) method. According to the extracted initial phase of the end surface reflection intermediate frequency signal, the initial phase is fed back to the phase modulator through real-time voltage to generate a certain phase shift, and the initial phase of the end surface reflection intermediate frequency signal is adjusted to be a reference phase value, so that the phase alignment of the atmospheric echo pulse intermediate frequency signal is realized, and the coherent accumulation of pulses is realized. In addition, the frequency of the end face reflection intermediate frequency signal obtained through analysis can be used for resolving the Doppler frequency shift, and the speed measurement error caused by resolving the Doppler frequency shift by adopting the fixed frequency shift under the condition that the frequency shift generated by the modulator in the variable temperature environment is changed is reduced.
Description
Technical Field
The invention belongs to the technical field of laser Doppler radars, and particularly relates to a device and a method for realizing coherent accumulation of pulse laser Doppler radar signals.
Background
The echo signal of the laser Doppler wind finding radar is an atmospheric aerosol particle scattering signal, and the backscattering coefficient is usually 10 －6 ～10 －10 And as echo signals are very weak, the signal frequency is usually solved by adopting a Fast Fourier Transform (FFT) and incoherent spectrum accumulation method, and when the signals are very weak, the method is difficult to accurately process the signals, so that many performances of the laser radar are affected, such as the farthest distance or height, the detection precision, the data update rate and the like. If coherent accumulation of pulse signals can be realized before Fast Fourier Transform (FFT) processing, similar to a coherent radar of a radio wave band, the detection signal-to-noise ratio can be improved substantially theoretically, and higher system performance is realized.
Coherent/non-coherent accumulation is a common signal processing method, and because a signal has time correlation and noise generally does not have time correlation, the signal is random white noise, and the signal-to-noise ratio of a system can be improved through accumulation. Theoretically, the incoherent accumulation signal-to-noise ratio can be improved
The coherent accumulation signal-to-noise ratio can be increased by M times, M is the number of pulses used for accumulation, and the increase range of the coherent accumulation signal-to-noise ratio is far higher than that of the incoherent accumulation. However, the coherent accumulation is difficult to realize, and each pulse is required to have the same initial phase. For a radio radar, a transmitting signal, a local oscillation signal and a coherent detection signal are generated and amplified by the same high-purity signal source, frequency multiplication is carried out, and the signal source is derived from the high-purity signal source and the same reference signal during frequency mixing, so that the phase and the waveform of an echo signal are consistent, and a coherent accumulation condition is met. For lidar, due to pulse modulationSignals and frequency shift signals such as an acousto-optic modulator are usually different in source, and an optical path (especially an optical fiber optical path) is easily affected by temperature, vibration and the like, so that the optical paths of signal light and local oscillator light are changed, a heterodyne intermediate frequency pulse signal generates random phase change, and coherent accumulation cannot be directly performed.
Many attempts have been made to coherently accumulate laser pulses. The army team of Harbin industry university (thesis topic: experimental research on method for improving signal-to-noise ratio of laser wind-measuring radar), and the Lixiafeng team of electronics science and technology university (thesis topic: research on Doppler frequency shift estimation technology of coherent laser wind-measuring radar) all try to adopt a quadrature frequency mixing phase discrimination method, digitally discriminate laser radar signals, extract the phase of pulse signals, align the phase of laser echo signals according to the obtained phase value, and finally perform time domain accumulation on the echo signals to realize the coherent accumulation of the laser radar signals. Certain effect is obtained in the test. However, this method requires two additional orthogonal signals, and introduces multiple devices on the optical path, which makes the system complex.
In addition, the traditional laser doppler velocity measurement radar data solution is to perform spectrum analysis on echo signals to obtain peak frequency, and then subtract a fixed frequency shift amount generated by a modulator, however, the frequency shift amount of the acousto-optic modulator is determined by the frequency of radio frequency signals generated by a circuit loaded on the acousto-optic modulator, characteristics of an acousto-optic crystal and a transducer, the frequency shift amount of the electro-optic modulator is determined by the frequency of the saw-tooth wave loaded on the electro-optic crystal, characteristics of the electro-optic crystal and the like, and the frequency shift amount changes slightly with temperature change, so that the solution errors of doppler frequency shift and speed are brought.
Disclosure of Invention
The purpose of the invention is as follows: a device and a method for realizing coherent accumulation of pulse laser Doppler radar signals are provided. Because the initial phase of the end surface reflection intermediate frequency signal and the initial phase of the atmosphere echo pulse intermediate frequency signal have a fixed value, the phase alignment of the atmosphere echo signal can be realized by utilizing the initial phase of the end surface reflection signal. However, the initial phase of the end face reflected intermediate frequency signal is unstable due to temperature, vibration, stress variation and the like; in addition, the end face reflection intermediate frequency signal exceeds the AD quantization voltage range, and it is difficult to extract the initial phase thereof.
The invention realizes the adjustment of the amplitude of the end face reflection intermediate frequency signal by controlling the size of the local oscillator optical power, so that the amplitude is in the range of AD quantization measurement range, thereby acquiring and quantizing the end face reflection intermediate frequency signal, and analyzing and extracting the initial phase of the end face reflection intermediate frequency signal by a Fast Fourier Transform (FFT) method. According to the initial phase of the extracted end face reflection intermediate frequency signal, the initial phase is fed back to the phase modulator through real-time voltage to generate a certain phase shift, and the initial phase of the end face reflection intermediate frequency signal is adjusted to be a reference phase value, so that the phase alignment of the atmospheric echo pulse intermediate frequency signal is realized, and the coherent accumulation of the pulse is realized. In addition, the frequency of the end face reflection intermediate frequency signal obtained through analysis can be used for resolving the Doppler frequency shift, and the speed measurement error caused by resolving the Doppler frequency shift by adopting the fixed frequency shift under the condition of frequency shift change of the modulator in the variable temperature environment is reduced.
The technical scheme of the invention is as follows:
according to a first aspect of the present invention, there is provided an apparatus for implementing coherent accumulation of pulsed laser doppler radar signals, comprising: the device comprises a seed laser 1, a first beam splitter 2, a modulator module 3, an optical fiber amplifier module 4, a circulator module 5 and an optical antenna module 6 which are sequentially connected through optical fibers; the first beam splitter 2 is further connected with a light intensity modulator 7, a phase modulator module 8, a coupler module 9 and a balanced photoelectric detector module 10 in turn through optical fibers; the circulator module 5 is also in optical fiber connection with a coupler module 9;
the signal processing module 11 is electrically connected with the modulator module 3, the light intensity modulator 7, the phase modulator module 8 and the balance detector module 10;
the modulation signal generated by the signal processing module 11 and the clock signal of the AD are both obtained by the same crystal oscillator through a frequency divider; the sum of the pulse width of the modulation signal corresponding to the modulator module 3 and the pulse width of the modulation signal corresponding to the optical intensity modulator 7 is a pulse modulation period.
In one possible embodiment, the modulation signals loaded on the modulator module 3 and the optical intensity modulator 7 have a relative delay in the circuit output.
In one possible embodiment, the optical intensity modulator 7 is an electrically controlled optical power attenuator.
In one possible embodiment, the modulator module 3 comprises at least one modulator; the modulator is an acousto-optic modulator or an electro-optic modulator; the electro-optical modulator is a phase modulator or an intensity modulator; the intensity modulator adopts a Mach-Zehnder type or a cascade, parallel, orthogonal or other deformation structure based on the Mach-Zehnder type.
In a possible embodiment, the phase modulator module 8 comprises at least one modulator, an electro-optical modulator, optionally constituted by an electro-optical crystal, or a modulator capable of generating phase or optical path variations.
In a possible embodiment, the circulator module 5 comprises a circulator; the optical antenna module 6 comprises an optical antenna; the coupler module 9 comprises a coupler; the balanced photodetector module 10 includes a balanced photodetector.
In one possible embodiment, the phase modulator module 8 is connected between the first beam splitter 2 and the optical intensity modulator 7, or between any two adjacent modules on the optical path formed by the first beam splitter 2 to the circulator module 5 to the coupler module 9.
In a possible embodiment, the device further comprises a second beam splitter 12 and a third beam splitter 13; the second beam splitter 12 is arranged between the first beam splitter 2 and the modulator module 3; the third beam splitter 13 is arranged between the light intensity modulator 7 and the phase modulator module 8;
the circulator module 5 comprises a plurality of circulators, the optical antenna module 6 comprises a plurality of optical antennas, the coupler module 9 comprises a plurality of couplers, and the balanced photodetector module 10 comprises a plurality of balanced photodetectors; the modulator module 3 comprises a plurality of modulators; the optical fiber amplifier module 4 comprises a plurality of optical fiber amplifiers;
the second beam splitter 12 is connected between the first beam splitter 2 and each modulator; the plurality of modulators are correspondingly connected with the plurality of optical fiber amplifiers 4; the plurality of optical fiber amplifiers 4, the plurality of circulators and the plurality of optical antennas are connected in sequence in a one-to-one correspondence manner;
the circulators are connected with the couplers and the balance photodetectors in sequence in a one-to-one correspondence manner.
When the third beam splitter 13 is connected between the optical intensity modulator 7 and the phase modulator module 8, the apparatus comprises a plurality of phase modulators 8; the plurality of phase modulators 8 are connected to the plurality of couplers 9 in a one-to-one correspondence.
According to a second aspect of the present invention, a method for implementing coherent accumulation of pulsed laser doppler radar signals is provided, where the apparatus for implementing coherent accumulation of pulsed laser doppler radar signals is adopted, and the method is characterized by including the following steps:
laser emitted by the seed laser 1 passes through the first beam splitter 2 to generate local oscillation light and signal light; the local oscillation light sequentially enters a light intensity modulator 7, a phase modulator module 8 and a coupler module 9; the signal light sequentially enters a modulator module 3, an optical fiber amplifier module 4 and a circulator module 5 and is emitted to the air through an optical antenna module 6; the optical antenna module 6 receives echo signal light scattered back by atmospheric aerosol particles at the same time, the echo signal light enters the coupler module 9 through the circulator module 5, heterodyne interference is carried out on the echo signal light and local oscillation light, and a heterodyne interference signal is detected by the balance detector module 10 to generate an intermediate frequency electric signal;
the signal processing module 11 collects the detected intermediate frequency electric signals, and digital intermediate frequency signals are obtained after AD quantization;
before the signal light is emitted into the air, a reflected signal with an amplitude much larger than that of the atmospheric scattering echo signal is generated on the fiber end face and the lens end face of the second port of the circulator module 5, and the signal light is called an end face reflected signal;
the initial phase of the end face reflection intermediate frequency signal is a fixed value, and the initial phase of the echo intermediate frequency signal is also a fixed value.
According to the end face reflection intermediate frequency signals, the signal processing module 11 calculates phase adjustment quantity to change the phase shift of the phase modulator module 8 in real time, and adjusts the initial phases of different echo intermediate frequency signals to fixed values to meet pulse coherence accumulation conditions.
The invention has the advantages that: the invention provides a device and a method for realizing coherent accumulation of pulse laser Doppler radar signals. The amplitude of the end face reflection intermediate frequency signal is adjusted by controlling the size of the local oscillator optical power to be within the AD quantization range, so that the end face reflection intermediate frequency signal is collected and quantized, and the initial phase of the end face reflection intermediate frequency signal is analyzed and extracted by a Fast Fourier Transform (FFT) method. Because the initial phase of the end surface reflection intermediate frequency signal and the initial phase of the atmospheric echo intermediate frequency signal have a fixed value difference, the initial phase of the end surface reflection intermediate frequency signal can be adjusted to be a reference phase value through real-time feedback, so that the phase alignment of the echo pulse intermediate frequency signal is realized, and the coherent accumulation of pulses is realized. The method can greatly improve the detection sensitivity and the signal-to-noise ratio of the laser Doppler radar system, and is beneficial to high-precision and high-reliability calculation of radar signals. In addition, the frequency value of the end face reflection intermediate frequency signal with the smaller amplitude is estimated through a frequency spectrum, and the frequency value can be used as a monitoring signal of the frequency shift quantity of the modulator for resolving the Doppler frequency shift, so that the measurement error caused by resolving by adopting the fixed frequency shift quantity under the condition of reducing the frequency shift quantity change in the variable temperature environment is reduced.
Description of the drawings:
FIG. 1 is a structural diagram of a device for realizing coherent accumulation of pulsed laser Doppler radar signals according to a preferred embodiment of the present invention
FIG. 2 is a schematic diagram of a signal processing module according to a preferred embodiment of the present invention
FIG. 3 is a schematic diagram of the generation and control of IF signal according to the preferred embodiment of the present invention
FIG. 4 is a flowchart of an algorithm for implementing coherent accumulation of pulses according to a preferred embodiment of the present invention
FIG. 5 is a frequency-amplitude spectrum and a frequency-phase spectrum of a signal according to a preferred embodiment of the present invention
FIG. 6 is a schematic diagram of a coherent accumulation scheme for multiple pulsed lidar signals according to a preferred embodiment of the present invention
FIG. 7 is a schematic diagram of a phase-locked loop module according to a preferred embodiment of the present invention
Description of reference numerals: 1-seed laser, 2-first beam splitter, 3-modulator module, 4-optical fiber amplifier module, 5-circulator module, 6-optical antenna module, 7-optical intensity modulator, 8-phase modulator module, 9-coupler module, 10-balanced photoelectric detector module, 11-signal processing module, 12-second beam splitter, 13-third beam splitter, 21-radio frequency signal loaded to modulator module, 22-end face reflection intermediate frequency signal detected by balanced detector module, 23-phase-locked loop module, 24-phase-locked loop module output signal;
the specific implementation mode is as follows:
the present invention is described in further detail below with reference to the attached drawing figures.
As shown in fig. 1, a laser doppler velocity measuring device includes: the device comprises a seed laser 1, a first beam splitter 2, a modulator module 3, an optical fiber amplifier module 4, a circulator module 5 and an optical antenna module 6 which are sequentially connected through optical fibers;
the first beam splitter 2 is sequentially connected with a light intensity modulator 7, a phase modulator module 8, a coupler module 9 and a balanced photoelectric detector module 10 through optical fibers; the circulator module 5 is in optical fiber connection with the coupler module 9;
the signal processing module 11 is electrically connected with the modulator module 3, the light intensity modulator 7, the phase modulator module 8 and the balance detector module 10;
the signal processing module 11 is configured to digitally collect the heterodyne intermediate frequency signal sent by the balanced photodetector module 9, perform segmentation processing on the obtained digital intermediate frequency signal, determine an initial phase of the echo pulse intermediate frequency signal according to the end-face reflected intermediate frequency signal, calculate a phase change amount according to the obtained initial phase value, adjust a voltage value of the phase modulator module 8 in real time, generate a certain phase value to compensate the change amount of the initial phase, and complete phase alignment and coherent accumulation of the echo pulse digital intermediate frequency signal.
As shown in fig. 2, the signal processing module 11 includes a crystal oscillator, a clock management unit, an AD/a converter, a coherent accumulation module, a frequency estimation module, a phase discrimination module, a phase locking module, a phase signal generator, and a modulation signal/frequency shift signal generator; the generated modulation signal, the frequency shift signal and the AD clock signal are all obtained by the same crystal oscillator through a clock management unit.
All modulation signals, AD acquisition clocks and the like generated by the signal processing module 11 are obtained by frequency division of the same crystal oscillator so as to ensure homology. The pulse modulation signals loaded on the modulator module 3 and the optical intensity modulator 7 have the same repetition frequency and complementary pulse shapes, that is, the sum of the pulse width of the modulation signal corresponding to the modulator module 3 and the pulse width of the modulation signal corresponding to the optical intensity modulator 7 is the pulse modulation period.
The modulation signal pulse width refers to the pulse level duration within a single pulse period.
The modulation signals loaded on the modulator module 3 and the optical intensity modulator 7 have relative time delay at the circuit output.
Optionally, the modulation signal loaded on the modulator module 3 has a repetition frequency and a pulse width of 1KHz to 200KHz and 100ns to 1 μ s, respectively, and the modulation signal loaded on the light intensity modulator 7 has a repetition frequency and a pulse width of 1KHz to 200KHz and 4 μ s to 999.9 μ s, respectively.
The light intensity modulator 7 may be an electrically controlled optical power attenuator based on any principle, such as an electrically controlled mems optical attenuator, an electro-optical intensity modulator, a magneto-optical intensity modulator, an acousto-optical modulator, etc. The purpose is to adjust the magnitude of the local oscillator optical signal power.
Optionally, the modulator module 3 comprises at least one modulator; the modulator is an acousto-optic modulator or an electro-optic modulator.
When the modulator is an electro-optical modulator, the modulator can be a phase modulator or an intensity modulator, the intensity modulator can be of a Mach-Zehnder type or a cascade, parallel, orthogonal or other deformation structure based on the Mach-Zehnder type, and the purpose of the phase or intensity modulator is to enable the frequency of the seed laser to generate a certain variation.
Alternatively, the phase modulator module 8 includes at least one modulator, which may be an electro-optical modulator formed by an electro-optical crystal, or a modulator capable of generating phase or optical path changes, such as an electrically controlled optical delay line.
Optionally, the circulator module 5 comprises a circulator, the optical antenna module 6 comprises an optical antenna, the coupler module 9 comprises a coupler, and the balanced photodetector module 10 comprises a balanced photodetector.
Alternatively, the phase modulator module 8 may be connected between the first beam splitter 2 and the optical intensity modulator 7, or between any two adjacent modules on the optical path formed by the first beam splitter 2 to the circulator module 5 to the coupler module 9.
Optionally, the apparatus further comprises a second beam splitter 12 and a third beam splitter 13; the second beam splitter 12 is arranged between the first beam splitter 2 and the modulator module 3; the third beam splitter 13 is arranged between the light intensity modulator 7 and the phase modulator module 8.
The circulator module 5 comprises a plurality of circulators, the optical antenna module 6 comprises a plurality of optical antennas, the coupler module 9 comprises a plurality of couplers, and the balanced photodetector module 10 comprises a plurality of balanced photodetectors; the modulator block 3 comprises a plurality of modulators; the fiber amplifier module 4 includes a plurality of fiber amplifiers;
a second beam splitter is connected between the first beam splitter 2 and each modulator; the plurality of modulators are correspondingly connected with the plurality of optical fiber amplifiers 4; the plurality of optical fiber amplifiers 4, the plurality of circulators and the plurality of optical antennas are connected in sequence in a one-to-one correspondence manner;
the circulators are connected with the couplers and the balance photodetectors in sequence in a one-to-one correspondence manner.
Optionally, when a third beam splitter is connected between the optical intensity modulator 7 and the phase modulator module 8, the apparatus comprises a plurality of phase modulators 8; the plurality of phase modulators 8 are connected to the plurality of couplers 9 in a one-to-one correspondence.
In another aspect, a method for coherent accumulation of pulsed laser doppler radar signals is provided, the method comprising:
the laser emitted by the seed laser passes through the first beam splitter 2 to generate local oscillation light and signal light; the local oscillation light sequentially enters a light intensity modulator 7, a phase modulator module 8 and a coupler module 9; the signal light sequentially enters a modulator module 3, an optical fiber amplifier module 4 and a circulator module 5 and is emitted to the air through an optical antenna module 6; the optical antenna module 6 receives echo signal light scattered back by atmospheric aerosol particles at the same time, the echo signal light enters the coupler module 9 through the circulator module 5, heterodyne interference is carried out on the echo signal light and local oscillation light, and a heterodyne interference signal is detected by the balance detector module 10 to generate an intermediate frequency electric signal;
the signal processing module 11 collects the detected intermediate frequency electrical signals, obtains digital intermediate frequency signals after AD quantization, analyzes and processes the digital intermediate frequency signals to obtain the speed of the laser sight direction, and measures the speeds of a plurality of laser sight directions to calculate the three-axis speed and the speed direction.
Before the signal light is emitted into the air, a reflection signal (referred to as an end reflection signal) with a much larger amplitude than the atmospheric scattering echo signal is generated at the end face of the optical fiber of the second port of the circulator module 5 and the end face of the lens, and the end reflection signal reaching the coupler module 9 can be represented as an end reflection signal
u eb (t)＝A 1 ·cos[2π(v 0 +v M )t+φ s +Δφ s ]
Wherein v is 0 Is the frequency of light wave, v M For shifting the frequency, phi, of the modulator s The phase, delta phi, generated for transmission of end-face reflected signal light in the optical path of the fiber s The phase change is caused by the optical path change of the optical transmission of the end face reflection signal due to temperature, vibration, stress change and the like.
The signal light emitted into the air reacts with the atmospheric particles to generate Doppler frequency shift, and the atmospheric echo light signal reaching the coupler module 9 can be represented as an atmospheric echo light signal
u bk (t)＝A 3 ·cos[2π(v 0 +v M +f d )t+φ s +Δφ s +φ bk ]
Wherein phi bk Phase generated for transmission of signal light in the atmosphere, f d For the amount of Doppler frequency shift to be generated, it is assumed here that the end surface reflects the signal lightThe time difference between the arrival time of the signal light and the arrival time of the atmospheric echo signal light at the coupler module 9 is very short, and the phase change delta phi of the optical path caused by temperature, vibration, stress change and the like can be considered s And is not changed.
The optical signal of the local oscillator light mixed with the end face reflected signal light reaching the coupler module 9 may be represented as
u LO1 (t)＝A 2 ·cos[2πv 0 t+φ l1 +Δφ l ]
Wherein phi is l1 Phase, Δ φ, of local oscillator optical transmission for mixing with end-face reflected signal light l The phase change is caused by the change of the optical transmission optical path of the local oscillator due to the temperature, vibration, stress change and the like.
It is also considered that the phase change Δ φ generated in the local oscillation optical path due to temperature, vibration, stress variation, etc l If not, the optical signal of the local oscillator light mixed with the atmospheric echo signal light and arriving at the coupler module 9 can be represented as
u LO2 (t)＝A 2 ·cos[2πv 0 t+φ l2 +Δφ l ]
Wherein phi l2 The phase of the local oscillator optical transmission that is mixed with the atmospheric echo signal light.
The end face reflected intermediate frequency signal received by the balanced detector after the signal light and the local oscillator light are heterodyne mixed may be represented as
u r (t)＝B 1 ·cos[2πv M t+φ r +Δφ r ]
Wherein phi r ＝φ s -φ l1 For reflecting the initial phase, delta phi, of the intermediate-frequency signal at the end face r ＝Δφ s -Δφ l The phase of the optical path is changed due to temperature, vibration, stress change and the like.
The atmosphere echo intermediate frequency signal can be expressed as
u eco (t)＝B 2 ·cos[2π(v M +f d )t+φ e +Δφ r +φ bk ]
Wherein phi e ＝φ s -φ l2 Contrast end faceThe phase difference delta phi between the reflected intermediate frequency signal and the atmosphere echo intermediate frequency signal is a fixed value:
Δφ＝φ e -φ r +φ bk ＝φ l1 -φ l2 +φ bk
therefore, if the initial phase of the end face reflection intermediate frequency signal is a fixed value, the initial phase of the echo intermediate frequency signal is also a fixed value, and the pulse coherence accumulation condition is met. Due to the existence of the end face reflection intermediate frequency signal delta phi r The phase modulator generates a certain phase shift in real time to compensate the variable quantity delta phi in the initial phase of the end face reflection intermediate frequency signal r And the phase of the intermediate frequency pulse signal is zero, so that the phase fixation of the intermediate frequency pulse signal of the echo is realized, the coherent accumulation condition is met, and the coherent accumulation of different intermediate frequency pulse signals of the echo can be realized.
Referring to fig. 3, in general, the local oscillation optical path of the laser doppler wind radar does not include the light intensity modulator 7 and the phase modulator module 8, and the local oscillation light is continuous light with fixed and unchanged power; the amplitude of the end face reflection part of the digital intermediate frequency signal (intermediate frequency signal 1) acquired by the signal processing module exceeds the AD quantization range, and accurate frequency and initial phase information cannot be extracted from the end face reflection intermediate frequency signal;
the pulse level of the light intensity modulator 7 is adjusted (the amplitude of the low level is adjusted by the acousto-optic modulator, the amplitude of the high level is adjusted by the electro-optic modulator and the like), the local oscillator light is modulated into pulse light (a local oscillator light signal 2), and meanwhile, the relative delay delta tau between the pulse signal of the light intensity modulator 7 and the pulse modulation signal loaded on the modulator module 3 is adjusted, so that the rising edge of the end surface reflection echo signal is aligned with the falling edge of the local oscillator light pulse, and the end surface reflection intermediate frequency signal (the intermediate frequency signal 2) with the amplitude within the quantization voltage range of AD is obtained. Meanwhile, in order not to reduce the amplitude of the intermediate frequency signal of the echo, the level of the optical intensity modulator 7 should be adjusted to maximize the peak power of the local oscillation optical signal 2.
The phase alignment method can be expressed as follows: referring to fig. 4, the ad collects and quantizes the pulse intermediate frequency signal, extracts the end face reflection intermediate frequency digital signal, and performs Fast Fourier Transform (FFT) operation on the partial digital signal to find the partDividing the frequency-amplitude spectrum and the frequency-phase spectrum of the digital signal, see FIG. 5, to find the frequency f corresponding to the maximum value of the amplitude spectrum 0 The frequency f 0 Corresponding to the phase phi in the phase spectrum 0 Namely the initial phase of the extracted end face reflection intermediate frequency signal. The initial phase can be corrected according to a discrete spectrum correction method, and the initial phase extraction precision is improved. The phase locking module gives an initial phase reference value, and calculates an initial phase adjustment quantity by adopting methods such as proportional-integral (PI) control and the like, wherein the adjustment quantity is used as a feedback quantity to act on the phase signal generator and is used for generating a voltage value for adjusting the phase modulator module 8 in real time, so that the phase modulator module 8 generates a certain phase shift, and phase change of end surface reflection intermediate frequency signals caused by temperature, vibration, stress change and the like is compensated in real time, the initial phase is stabilized near the reference value, phase alignment of echo pulse intermediate frequency signals is realized, coherent accumulation conditions are met, and coherent accumulation of a plurality of different atmospheric echo pulse intermediate frequency signals in the same measurement area can be realized.
AD acquires and quantizes the atmospheric echo intermediate frequency signals corresponding to different pulses to respectively obtain time sequences corresponding to the different pulses, N time sequences are accumulated according to corresponding sequence numbers, and a time sequence D after coherent accumulation A Expressed as:
For time sequence D after coherent accumulation A Fast Fourier Transform (FFT) operation is carried out to obtain a frequency spectrum, peak frequency estimation is carried out to obtain a frequency f corresponding to a frequency spectrum peak, and a frequency shift v of a modulator module is subtracted M The Doppler frequency shift f-v can be obtained M So as to calculate the speed of the laser sight line direction
λ is the laser wavelength.
The working modes of the phase-locking module and the phase signal generator can also be expressed as follows: referring to fig. 7, the radio frequency signal 21 loaded to the modulator module and the intermediate frequency signal 22 detected by the balanced detector module are loaded to the phase-locked loop module 23, the output signal 24 of the phase-locked loop module is loaded to the phase modulator module 8, the phase value of the phase modulator module is changed, and the phase synchronization between the end surface reflected intermediate frequency signal and the radio frequency signal loaded to the modulator module is realized in real time, so that the phase of the end surface reflected intermediate frequency signal is a fixed value, and therefore, the phase of the echo intermediate frequency pulse signal is fixed, and the coherent accumulation condition is met, and the coherent accumulation of different echo pulse intermediate frequency signals can be realized.
The frequency corresponding to the maximum value of the frequency spectrum which can be estimated by the result of coherent accumulation through frequency spectrum analysis is subtracted by the frequency shift quantity generated by the modulator module 3 to obtain the Doppler frequency shift quantity, so that the speed of the laser sight line direction can be calculated. However, the stability of the frequency shift amount of the emitted laser is determined by various factors, for example, the frequency shift amount of the acousto-optic modulator is determined by the frequency of the radio-frequency signal loaded on the acousto-optic modulator, the characteristics of the acousto-optic crystal and the transducer, the frequency shift amount of the electro-optic modulator is determined by the frequency of the radio-frequency signal loaded on the acousto-optic modulator, and the frequency shift amount of the electro-optic modulator is determined by the slope of the sawtooth wave loaded on the electro-optic crystal, the characteristics of the electro-optic crystal and the like. Therefore, the frequency shift amount generated after modulation by the modulator module slightly changes along with the temperature change, and if the fixed frequency shift amount is still subtracted in the temperature changing process, a certain resolving error is generated. The detected frequency of the end face reflection intermediate frequency signal with the smaller amplitude can represent the frequency shift amount generated by the modulator in real time, and the frequency f corresponding to the maximum value of the amplitude spectrum is obtained by analyzing the frequency spectrum-amplitude spectrum of the end face reflection intermediate frequency signal with the smaller amplitude 0 Instead of a fixed amount v of frequency shift M The method is used for resolving the Doppler frequency shift, and the measurement error caused by resolving the fixed frequency shift is still adopted under the condition of reducing the frequency shift change in the variable temperature environment.
Claims (9)
1. An apparatus for implementing coherent accumulation of pulsed laser doppler radar signals, comprising: the seed laser (1), the first beam splitter (2), the modulator module (3), the optical fiber amplifier module (4), the circulator module (5) and the optical antenna module (6) are sequentially connected through optical fibers; the first beam splitter (2) is also sequentially connected with a light intensity modulator (7), a phase modulator module (8), a coupler module (9) and a balanced photoelectric detector module (10) through optical fibers; the circulator module (5) is also connected with a coupler module (9) through an optical fiber;
the signal processing module (11) is electrically connected with the modulator module (3), the light intensity modulator (7), the phase modulator module (8) and the balance detector module (10);
the modulation signal generated by the signal processing module (11) and the AD clock signal are obtained by the same crystal oscillator through a frequency divider; the sum of the pulse width of the modulation signal corresponding to the modulator module (3) and the pulse width of the modulation signal corresponding to the light intensity modulator (7) is a pulse modulation period.
2. The apparatus according to claim 1, wherein the modulator module (3) and the light intensity modulator (7) are loaded with modulation signals having a relative delay at the output of the circuit.
3. The device for realizing coherent accumulation of pulsed laser doppler radar signals according to claim 1, wherein the optical intensity modulator (7) is an electrically controlled optical power attenuator.
4. An apparatus for performing coherent accumulation of pulsed laser doppler radar signals according to claim 1, characterized in that the modulator module (3) comprises at least one modulator; the modulator is an acousto-optic modulator or an electro-optic modulator; the electro-optical modulator is a phase modulator or an intensity modulator; the intensity modulator adopts a Mach-Zehnder type or a cascade, parallel, orthogonal or other deformation structure based on the Mach-Zehnder type.
5. The device for realizing coherent accumulation of pulsed laser doppler radar signals according to claim 1, wherein the phase modulator module (8) comprises at least one modulator, an electro-optical modulator formed by an electro-optical crystal, or a modulator capable of generating phase or optical path change.
6. An apparatus for performing coherent accumulation of pulsed laser doppler radar signals according to claim 1, characterized in that the circulator module (5) comprises a circulator; the optical antenna module (6) comprises an optical antenna; the coupler module (9) comprises a coupler; the balanced photodetector module (10) includes a balanced photodetector.
7. An apparatus for performing coherent accumulation of pulsed laser doppler radar signals according to claim 1, characterized in that the phase modulator module (8) is connected between the first beam splitter (2) and the optical intensity modulator (7), or between any two adjacent modules on the optical path formed by the first beam splitter (2) to the circulator module (5) to the coupler module (9).
8. An apparatus for coherent summation of pulsed laser doppler radar signals according to claim 1, further comprising a second beam splitter (12) and a third beam splitter (13); the second beam splitter (12) is arranged between the first beam splitter (2) and the modulator module (3); the third beam splitter (13) is arranged between the light intensity modulator (7) and the phase modulator module (8);
the circulator module (5) comprises a plurality of circulators, the optical antenna module (6) comprises a plurality of optical antennas, the coupler module (9) comprises a plurality of couplers, and the balanced photodetector module (10) comprises a plurality of balanced photodetectors; the modulator module (3) comprises a plurality of modulators; the fiber amplifier module (4) comprises a plurality of fiber amplifiers;
the second beam splitter (12) is connected between the first beam splitter (2) and each modulator; the modulators are correspondingly connected with the optical fiber amplifiers (4); the optical fiber amplifiers (4), the circulators and the optical antennas are sequentially connected in a one-to-one correspondence manner;
the circulators are connected with the couplers and the balance photodetectors in sequence in a one-to-one correspondence manner.
When the third beam splitter (13) is connected between the optical intensity modulator (7) and the phase modulator module (8), the apparatus comprises a plurality of phase modulators (8); the phase modulators (8) are connected to the couplers (9) in a one-to-one correspondence.
9. A method for realizing coherent accumulation of pulsed laser doppler radar signals, which adopts the apparatus for realizing coherent accumulation of pulsed laser doppler radar signals of any one of claims 1 to 8, characterized by comprising the following steps:
laser emitted by the seed laser (1) passes through the first beam splitter (2) to generate local oscillation light and signal light; local oscillation light sequentially enters a light intensity modulator (7), a phase modulator module (8) and a coupler module (9); the signal light sequentially enters a modulator module (3), an optical fiber amplifier module (4) and a circulator module (5) and is emitted to the air through an optical antenna module (6); the optical antenna module (6) receives echo signal light scattered back by atmospheric aerosol particles at the same time, the echo signal light enters the coupler module (9) through the circulator module (5) and is subjected to heterodyne interference with local oscillation light, and a heterodyne interference signal is detected by the balance detector module (10) to generate a medium-frequency electric signal;
the signal processing module (11) collects the detected intermediate frequency electric signals, and digital intermediate frequency signals are obtained after AD quantization;
before the signal light is emitted into the air, a reflected signal with the amplitude far larger than that of an atmospheric scattering echo signal is generated on the end face of the optical fiber of the second port of the circulator module (5) and the end face of the lens, and the reflected signal is called an end face reflected signal;
according to the end face reflection intermediate frequency signals, the signal processing module (11) calculates phase adjustment quantity to change the phase shift of the phase modulator module (8) in real time, and adjusts the initial phases of different echo intermediate frequency signals to fixed values to meet pulse coherence accumulation conditions.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN202211410990.7A CN115792861A (en) | 2022-11-11 | 2022-11-11 | Device and method for realizing coherent accumulation of pulse laser Doppler radar signals |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN202211410990.7A CN115792861A (en) | 2022-11-11 | 2022-11-11 | Device and method for realizing coherent accumulation of pulse laser Doppler radar signals |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CN115792861A true CN115792861A (en) | 2023-03-14 |
Family
ID=85436871
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CN202211410990.7A Pending CN115792861A (en) | 2022-11-11 | 2022-11-11 | Device and method for realizing coherent accumulation of pulse laser Doppler radar signals |
Country Status (1)
| Country | Link |
|---|---|
| CN (1) | CN115792861A (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN117074719A (en) * | 2023-05-17 | 2023-11-17 | 山东省科学院海洋仪器仪表研究所 | Photon counting coherent ocean flow field velocity measurement system and method with self-adaptive local oscillation light |
-
2022
- 2022-11-11 CN CN202211410990.7A patent/CN115792861A/en active Pending
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN117074719A (en) * | 2023-05-17 | 2023-11-17 | 山东省科学院海洋仪器仪表研究所 | Photon counting coherent ocean flow field velocity measurement system and method with self-adaptive local oscillation light |
| CN117074719B (en) * | 2023-05-17 | 2024-01-09 | 山东省科学院海洋仪器仪表研究所 | Photon counting coherent ocean flow field velocity measurement system and method with self-adaptive local oscillation light |
Similar Documents
| Publication | Publication Date | Title |
|---|---|---|
| US8144334B2 (en) | Fiber-optic, digital system for laser Doppler vibrometers (LDVs) | |
| CN110780310B (en) | Polarization diversity dual-channel speed measuring and distance measuring coherent laser radar measuring method and device | |
| CN107835055B (en) | Microwave source phase noise measurement method and system | |
| CN111693988A (en) | Laser millimeter wave integrated distance and speed measuring radar method and device | |
| CN110632388B (en) | Frequency mixing-based photoelectric detector frequency response measuring method and device | |
| CN108303704B (en) | Laser measurement method based on polarization modulation and laser radar | |
| CA2800267A1 (en) | Method and apparatus for a pulsed coherent laser range finder | |
| US20190331796A1 (en) | Method for processing a signal from a coherent lidar in order to reduce noise and related lidar system | |
| CA3034765A1 (en) | Method for processing a signal arising from coherent lidar and associated lidar system | |
| RU191111U1 (en) | Fiber Coherent Doppler Lidar | |
| CN111999739A (en) | Coherent laser radar method and device for measuring distance and speed by phase modulation | |
| CN112363146B (en) | Distance and speed measuring method and device for dual-modulation common-path linear frequency modulation laser radar | |
| CN114035174A (en) | Double-channel double-chirp linear frequency modulation continuous wave laser radar method and device | |
| CN115015886A (en) | Double-channel pseudo-random code phase modulation distance measuring and speed measuring laser radar method and device | |
| CN115792861A (en) | Device and method for realizing coherent accumulation of pulse laser Doppler radar signals | |
| CN111983628A (en) | Speed and distance measuring system based on monolithic integrated linear frequency modulation dual-frequency DFB laser | |
| CA3100885C (en) | Wind field information measurement method and nacelle-based lidar | |
| CN104111450A (en) | Method and system for detecting object micro Doppler characteristics by use of double pulses | |
| JP7325669B2 (en) | Laser radar device | |
| CN114720998A (en) | Non-contact dynamic displacement measurement system based on modal decomposition | |
| CN115308715A (en) | Method and system for sparse modulation wind-measuring radar | |
| US11635518B2 (en) | Measurement apparatus and measurement method using a laser and beat signals | |
| CN113607277A (en) | Narrow linewidth laser linewidth measuring system and adjusting method thereof | |
| CN115902924A (en) | Doppler laser speed measurement radar device and method | |
| CN112147628A (en) | Remote displacement measuring device and measuring method based on photoelectric oscillator |
Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| PB01 | Publication | ||
| PB01 | Publication | ||
| SE01 | Entry into force of request for substantive examination | ||
| SE01 | Entry into force of request for substantive examination |