CN115184960A - Pulse type coherent wind lidar based on non-polarization-maintaining light path - Google Patents

Pulse type coherent wind lidar based on non-polarization-maintaining light path Download PDF

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CN115184960A
CN115184960A CN202210671897.5A CN202210671897A CN115184960A CN 115184960 A CN115184960 A CN 115184960A CN 202210671897 A CN202210671897 A CN 202210671897A CN 115184960 A CN115184960 A CN 115184960A
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polarization
beam splitter
light
polarized light
coupler
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李五一
罗浩
肖增利
卢立武
乔乃燕
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Nanjing Movelaser Technology Co ltd
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Nanjing Movelaser Technology Co ltd
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S17/00—Systems using the reflection or reradiation of electromagnetic waves other than radio waves, e.g. lidar systems
    • G01S17/88—Lidar systems specially adapted for specific applications
    • G01S17/95—Lidar systems specially adapted for specific applications for meteorological use
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S7/00—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00
    • G01S7/48—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S17/00
    • G01S7/483—Details of pulse systems
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S7/00—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00
    • G01S7/48—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S17/00
    • G01S7/483—Details of pulse systems
    • G01S7/486—Receivers
    • 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 provides a pulse type coherent wind lidar based on a non-polarization-maintaining light path, which comprises a seed source, a beam splitter, a modulator, an optical fiber amplifier, a circulator, a telescope, a first polarization beam splitter, a second polarization beam splitter, a first coupler, a second coupler, a first balance detector, a second balance detector and a signal processing module. According to the pulse type coherent wind lidar based on the non-polarization-maintaining light path, the polarization-maintaining device is replaced by the non-polarization-maintaining device, the cost of an optical device is reduced, a shaft does not need to be aligned when tail fibers of the non-polarization-maintaining device are welded, the welding working time can be shortened, and the cost of the wind lidar is reduced; meanwhile, the balance detector based on the radio frequency amplification principle is used, so that the output power range is large and the saturation is not easy to occur.

Description

Pulse type coherent wind lidar based on non-polarization-maintaining light path
Technical Field
The invention belongs to the technical field of laser radars, and particularly relates to a pulse type coherent wind lidar based on a non-polarization-maintaining light path.
Background
The pulse type wind lidar transmits laser to aerosol particles in the atmosphere, receives a scattered echo signal, demodulates Doppler frequency shift information contained in the scattered echo signal, and further calculates to obtain wind field information, and is widely applied to the fields of wind speed measurement and wind resource assessment in the wind energy field, wind shear measurement in airports, climatological research, aerometeorological guarantee and the like. The common technology for demodulating Doppler frequency shift information is coherent detection, and the principle is that echo signal light interferes with local oscillation light of a radar laser, signal processing is carried out on the coherent signal intensity of two beams of light, and the Doppler frequency shift is calculated after a difference frequency signal is extracted.
The coherent efficiency is used as an important index of the wind lidar, the strength of coherent signals and the signal-to-noise ratio of a system are influenced, and the larger the coherent efficiency is, the larger the signal-to-noise ratio is. The coherence efficiency is related to the matching degree between the local oscillator light and the signal light, and the polarization state difference is one of the influencing factors, and the polarization states of the local oscillator light and the signal light need to be consistent to maximize the coherence efficiency. However, in the process of transmitting the two beams of light, if there is a birefringence effect, such as a defect of the optical fiber itself and a stress change caused by an external environment, the polarization state will change randomly, and when the polarization states of the local oscillation light and the signal light are orthogonal, the coherence efficiency will be reduced to zero. At present, in order to reduce the influence of polarization state difference on coherence efficiency, a wind lidar generally adopts a full polarization-maintaining optical path method, the initial polarization states of a local oscillator path and a signal path are consistent, and polarization-maintaining optical devices are selected according to technical requirements, so that the stability of the polarization states of local oscillator light and signal light is improved.
Fig. 1 is a schematic structural diagram of a coherent doppler wind lidar based on a full polarization-maintaining optical path. The laser emitted by the seed source 101 is linearly polarized light, and is divided into two linearly polarized lights with consistent vibration directions through the beam splitter 102. One beam is used as local oscillator light; the other beam is chopped and frequency-shifted by the modulator 103, amplified by the optical fiber amplifier 104, transmitted from the 1 port to the 2 port of the circulator 105, and transmitted to the atmosphere through the telescope 106. The movement of aerosol particles can cause the scattered light signals to generate Doppler frequency shift, echo signal light carrying frequency shift information is received by the telescope 106, transmitted from the 2 port of the circulator 105 to the 3 port, mixed with the local oscillation light by the 3dB coupler 106 and then enters the balance detector 107, and optical devices through which the signal light and the local oscillation light pass are polarization maintaining devices. The two beams interfere in the balanced detector 108, outputting a coherent signal intensity. The signal processing module 109 extracts the difference frequency information of the local oscillation light and the signal light to obtain the doppler shift information, so that the wind velocity information can be calculated.
The existing pulse type coherent wind lidar has the following problems: firstly, the existing general adopted polarization-maintaining optical path is a polarization-maintaining device, optical devices of all component modules of the polarization-maintaining optical path are polarization-maintaining devices, the stability of the polarization states of signal light and local oscillator light can be improved, and the influence of the difference of the polarization states on the coherence efficiency is reduced, but the structure of the polarization-maintaining device is more complex than that of a non-polarization-maintaining device, the manufacturing difficulty is high, the requirements on processing technology and equipment are high, the cost of the device is high, and in addition, the working shaft of a tail fiber needs to be aligned during welding, the welding operation time is long, and the production cost is increased; secondly, a transimpedance amplification mode is generally adopted in a balance detector in the existing radar, peak power which can be borne is small, when the return light power of the end face is large, the detector can be saturated, the recovery time of the detector after saturation can increase a radar measurement blind area, and the detector can not work normally due to the fact that the recovery time is too long.
Disclosure of Invention
The technical problem is as follows: in order to solve the problems of the prior art, the invention provides a pulse type coherent wind lidar based on a non-polarization-preserving light path.
The technical scheme is as follows: the invention provides a pulse type coherent wind lidar based on a non-polarization-maintaining light path, which comprises a seed source, a beam splitter, a modulator, an optical fiber amplifier, a circulator, a telescope, a first polarization beam splitter, a second polarization beam splitter, a first coupler, a second coupler, a first balanced detector, a second balanced detector and a signal processing module, wherein the seed source is connected with the first polarization beam splitter; the beam splitter receives light from a seed source and splits the light into two beams of P polarized light; the first polarization beam splitter receives a beam of P-polarized light from the beam splitter; the modulator receives the other beam of P polarized light from the beam splitter, and outputs the beam to the optical fiber amplifier after frequency shift; the optical fiber amplifier amplifies the optical signal after frequency shift and outputs the amplified optical signal to the telescope through the circulator; the telescope transmits light beams into the atmosphere and receives scattered echo signals from the atmosphere; the scattered echo signal is output to a second polarization beam splitter through a circulator; the first polarization beam splitter splits an input beam of P polarized light into P polarized light and S polarized light with mutually vertical vibration directions; the second polarization beam splitter divides the input scattering echo signal into S polarized light and P polarized light with mutually vertical vibration directions; the first coupler receives the P polarized light from the first polarization beam splitter and the P polarized light from the second polarization beam splitter, and outputs the P polarized light and the P polarized light after frequency mixing to a first balanced detector for interference; the second coupler receives the S polarized light from the first polarization beam splitter and the S polarized light from the second polarization beam splitter, and outputs the S polarized light and the S polarized light to the second balanced detector for interference after frequency mixing; the signal processing module receives coherent signals from the first balanced detector and the second balanced detector, eliminates the frequency modulated by the modulator, obtains Doppler frequency shift containing positive and negative information, and calculates wind speed information.
As an improvement, the modulator is a non-polarization-maintaining device; the optical fiber amplifier is a non-polarization-maintaining device; the circulator is a non-polarization-maintaining device.
As another improvement, the first polarization beam splitter is a polarization maintaining device; the incident end of the second polarization beam splitter is a non-polarization-maintaining optical fiber, and the emergent end of the second polarization beam splitter is a polarization-maintaining optical fiber.
As another improvement, the first coupler is a polarization-maintaining device; the second coupler is a polarization maintaining device.
As another improvement, the seed source and the beam splitter are polarization maintaining devices.
As another improvement, the first coupler is a 3dB coupler; the second coupler is a 3dB coupler.
The invention also provides a pulse type coherent wind lidar based on a non-polarization-maintaining light path, which comprises a seed source, a beam splitter, a modulator, an optical fiber amplifier, a circulator, a telescope, a first polarization beam splitter, a second polarization beam splitter, a first coupler, a second coupler, a first balanced detector, a second balanced detector and a signal processing module, wherein the seed source is connected with the first coupler; the beam splitter receives light from a seed source and splits the light into two beams of P polarized light; the first polarization beam splitter receives a beam of P-polarized light from the beam splitter; the modulator receives another beam of P polarized light from the beam splitter; the modulator, the optical fiber amplifier, the circulator and the telescope are sequentially connected through optical fibers; and the second polarization beam splitter is connected with the 3 ports of the circulator through optical fibers. The first coupler is connected with the first polarization beam splitter and the second polarization beam splitter through optical fibers respectively; the second coupler is respectively connected with the first polarization beam splitter and the second polarization beam splitter through optical fibers; the signal processing module is connected with the first balanced detector and the second balanced detector. As an improvement, the modulator is a non-polarization-maintaining device; the optical fiber amplifier is a non-polarization maintaining device; the circulator is a non-polarization-maintaining device; the first polarization beam splitter is a polarization maintaining device; the incident end of the second polarization beam splitter is a non-polarization-maintaining optical fiber, and the emergent end of the second polarization beam splitter is a polarization-maintaining optical fiber; the first coupler is a polarization maintaining device; the second coupler is a polarization maintaining device; the seed source and the beam splitter are polarization maintaining devices.
The invention also provides a wind speed measuring method based on the non-polarization-maintaining light path, which comprises the following steps:
(1) The beam splitter receives light from a seed source and splits the light into two beams of P polarized light, wherein one beam of P polarized light is output to the first polarization beam splitter to be used as local oscillation light, and the other beam of P polarized light is output to the modulator;
(2) The modulator chops and shifts the input P polarized light, and a fixed frequency difference is generated between the light after frequency shift and local oscillation light; the light after frequency shift is amplified by the optical fiber amplifier, transmitted to the No. 2 port through the No. 1 port of the circulator and then transmitted to the atmosphere through the telescope; the scattering echo signal on the surface of the aerosol particle is received by the telescope, transmitted to the No. 3 port through the No. 2 port of the circulator and output to the second polarization beam splitter; the modulator, the optical fiber amplifier and the circulator are all non-polarization-maintaining devices, P polarized light passing through a non-polarization-maintaining light path is changed into elliptical polarized light, the elliptical polarized light comprises P polarized light and S polarized light, and the vibration direction is not fixed; the scattered light is elliptically polarized light, and the influence of atmospheric depolarization exists, so that the echo signal light is elliptically polarized light, comprises P polarized light and S polarized light, and the vibration direction is not fixed;
(3) The local oscillation light and the signal light of the non-polarization-maintaining light path have different polarization states, and the polarization state of the signal light is not fixed, so that the two beams of light respectively pass through the first polarization beam splitter and the second polarization beam splitter and are divided into S-polarized light and P-polarized light with mutually vertical vibration directions, and the coherence efficiency can be improved; the first polarization beam splitter is a polarization maintaining device and divides the local oscillation light into two linearly polarized light beams with equal power, the incident end of the second polarization beam splitter is a non-polarization maintaining optical fiber, the emergent end of the second polarization beam splitter is a polarization maintaining optical fiber, and the sum of the power of the two linearly polarized light beams after beam splitting is ensured to be unchanged when the signal light polarization states are different;
(4) The polarization states of the P polarized light after the local oscillation beam splitting and the P polarized light after the scattering echo signal splitting are the same, and the P polarized light after the frequency mixing by the first coupler interferes in the first balanced detector; the polarization states of the S polarized light after the local oscillation beam splitting and the S polarized light after the scattering echo signal splitting are the same, and the S polarized light are subjected to frequency mixing by a second coupler and then are interfered in a second balanced detector;
(5) The first balanced detector and the second balanced detector respectively output the coherent signal intensity of the local oscillation light and the signal light to the signal processing module; after the signal processing module extracts the difference frequency signal, the frequency modulated by the modulator is removed, the Doppler frequency shift containing positive and negative information is obtained, and the wind speed information is calculated.
Considering only shot noise, the radar system signal-to-noise ratio can be expressed as:
Figure BDA0003694972050000041
wherein (eta) q For the quantum efficiency of the detector, S is the detector sensitivity, e is the electron charge 1.6X 10 -19 c，P LO Is the local oscillator optical power, P S As the power of the scattered signal light), η h The coherent efficiency is related to the degree of polarization state matching of the local oscillator light and the signal light, and when other conditions are consistent, the larger the polarization state difference of the two beams of light is, the lower the coherent efficiency is, so that the lower the signal-to-noise ratio is, the lower the signal-to-noise ratio isWhen the polarization state of the signal light is orthogonal to the local oscillation light, the coherence efficiency is zero.
The voltage signals output by the first balance detector (11) and the second balance detector (12) are respectively as follows:
Figure BDA0003694972050000042
Figure BDA0003694972050000043
in the formula K P Is the gain, S, of the first balanced detector (11) 1 、S 2 Is the response rate of the photodiode in the first balanced detector (11); k S Is the gain, S, of the second balanced detector (12) 3 、S 4 The responsivity of the photodiode in the detector (12) is balanced by the second. P LO Is local oscillation optical power, and epsilon/(1-epsilon) is the splitting ratio of the polarization beam splitter (8), P S In order to scatter the power of the signal light, Δ ν is a frequency difference between the local oscillation light and the signal light,
Figure BDA0003694972050000044
is the phase difference between the local oscillation light and the signal light.
Has the beneficial effects that: according to the pulse type coherent wind lidar based on the non-polarization-maintaining light path, the non-polarization-maintaining device is used for replacing the polarization-maintaining device, the cost of an optical device is reduced, a shaft does not need to be aligned when the tail fiber of the non-polarization-maintaining device is welded, the welding working time can be shortened, and the cost of the wind lidar is reduced; meanwhile, by using the balance detector based on the radio frequency amplification principle, the output power range is large, and the saturation is not easy to occur.
Specifically, the present invention has the following outstanding advantages over the prior art:
(1) The pulse type coherent wind lidar based on the non-polarization-maintaining light path adopts a non-polarization-maintaining device, reduces the device cost and reduces the optical fiber welding working hour. The non-polarization-maintaining device is used for replacing a polarization-maintaining device in a full-polarization-maintaining light path, the non-polarization-maintaining device is simple in structure and small in process complexity, requirements for manufacturing processes and production equipment are lower than those of the polarization-maintaining device, cost is low, the whole cost of the radar is reduced, and meanwhile, due to the fact that the non-polarization-maintaining optical fiber does not need to be aligned to a working shaft during welding, welding working hours are reduced.
(2) By adopting a polarization diversity receiving scheme, the local oscillator light and the signal light with different polarization states are subjected to polarization beam splitting, two beams of light with the same polarization state are respectively interfered, the coherence efficiency is improved, and the influence of polarization state change and atmospheric depolarization in a non-polarization-maintaining light path is reduced.
(3) By enabling the responsivity of the photodiodes to be consistent and adjusting the gains of the two balanced detectors to be consistent, the stability of the signal-to-noise ratio of the radar is ensured under different polarization states of signal light.
(4) By improving the laser output power behind the circulator, the signal light power is further improved, and the signal-to-noise ratio of a non-polarization-maintaining light path is improved.
(5) The amplification scheme of the balanced detector based on radio frequency amplification increases the output power range, and the detector is not easy to saturate. The traditional trans-impedance amplification mode is replaced by the radio frequency amplification mode, the output power range of the balanced detector is enlarged, the balanced detector is not easy to saturate, and the problem of saturation of the balanced detector caused by large return light power of the end face of the radar is solved.
Drawings
Fig. 1 is a schematic structural diagram of a pulsed coherent wind lidar system based on a full polarization-maintaining light path.
Fig. 2 is a block diagram of a pulsed coherent wind lidar system based on a non-polarization-maintaining optical path. The sequence numbers and their names in the figure:
the device comprises a seed source 1, a beam splitter 2, a modulator 3, a fiber amplifier 4, a circulator 5, a telescope 6, a polarization beam splitter 7, a polarization beam splitter 8, a coupler 9-3dB, a coupler 10-3dB, a balanced detector 11, a balanced detector 12 and a signal processing module 13.
Fig. 3 is a schematic diagram of a balanced detector structure.
Detailed Description
The present invention is further described below.
The pulse type coherent wind lidar based on the non-polarization-maintaining light path comprises a seed source 1, a beam splitter 2, a modulator 3, an optical fiber amplifier 4, a circulator 5, a telescope 6, a first polarization beam splitter 7, a second polarization beam splitter 8, a first coupler 9, a second coupler 10, a first balanced detector 11, a second balanced detector 12 and a signal processing module 13; the beam splitter 2 receives the light from the seed source 1 and splits the light into two beams of P polarized light; the first polarization beam splitter 7 receives a beam of P-polarized light from the beam splitter 2; the modulator 3 receives another beam of P-polarized light from the beam splitter 2; the modulator 3, the optical fiber amplifier 4, the circulator 5 and the telescope 6 are connected in sequence through optical fibers; the second polarization beam splitter 8 is connected to the 3-port of the circulator 3. The first coupler 9 is respectively connected with the first polarization beam splitter 7 and the second polarization beam splitter 8 through optical fibers; the second coupler 10 is respectively connected with the first polarization beam splitter 7 and the second polarization beam splitter 8 through optical fibers; the signal processing module 13 is respectively connected with the first balanced detector (11) and the second balanced detector 12.
The beam splitter 2 receives the light from the seed source 1 and splits the light into two beams of P polarized light; the first polarization beam splitter 7 receives a beam of P-polarized light from the beam splitter 2; the modulator 3 receives the other beam of P polarized light from the beam splitter 2, shifts the frequency of the beam and outputs the shifted beam to the optical fiber amplifier 4; the optical fiber amplifier 4 amplifies the optical signal after frequency shift and outputs the amplified optical signal to the telescope 6 through the circulator 5; the telescope 6 transmits light beams into the atmosphere and receives scattered echo signals from the atmosphere; the scattered echo signal is output to a second polarization beam splitter 8 through a circulator 5; the first polarization beam splitter 7 splits an input beam of P-polarized light into P-polarized light and S-polarized light with mutually perpendicular vibration directions; the second polarization beam splitter 8 splits the input scattering echo signal into S-polarized light and P-polarized light whose vibration directions are perpendicular to each other; the first coupler 9 receives the P-polarized light from the first polarization beam splitter 7 and the P-polarized light from the second polarization beam splitter 8, mixes the P-polarized light and the P-polarized light, and outputs the mixed light to the first balanced detector 11 for interference; the second coupler 10 receives the S-polarized light from the first polarization beam splitter 7 and the S-polarized light from the second polarization beam splitter 8, mixes the S-polarized light and the S-polarized light, and outputs the mixed light to the second balanced detector 12 for interference; the signal processing module 13 receives coherent signals from the first balanced detector 11 and the second balanced detector 12, eliminates the frequency modulated by the modulator 3, obtains the doppler shift including positive and negative information, and calculates the wind speed information.
The modulator 3 is a non-polarization-maintaining device; the optical fiber amplifier 4 is a non-polarization-maintaining device; the circulator 5 is a non-polarization maintaining device.
The first polarization beam splitter 7 is a polarization maintaining device; the incident end of the second polarization beam splitter 8 is a non-polarization-maintaining fiber, and the emergent end is a polarization-maintaining fiber.
The first coupler 9 is a polarization-maintaining device; the second coupler 10 is a polarization maintaining device. The seed source 1 and the beam splitter 2 are polarization maintaining devices.
The first coupler 9 is a 3dB coupler; the second coupler 10 is a 3dB coupler.
The method for measuring the wind speed by adopting the radar comprises the following steps:
the first beam splitter 2 receives light from the seed source 1 and splits the light into two beams of P polarized light, wherein one beam of P polarized light is output to the first polarization beam splitter 7 to be used as local oscillation light, and the other beam of P polarized light is output to the modulator 3;
the modulator 3 chops and shifts the input P polarized light, and a fixed frequency difference is generated between the light after frequency shift and local oscillation light; the light after frequency shift is amplified by the optical fiber amplifier 4, then transmitted to the No. 2 port through the No. 1 port of the ring (5) and then transmitted to the atmosphere through the telescope, the scattering echo signal on the surface of the aerosol particle is received by the telescope 6, transmitted to the No. 3 port through the No. 2 port of the ring 5 and output to the second polarization beam splitter 8, the modulator 3, the optical fiber amplifier 4 and the ring 5 are all non polarization-maintaining devices, the P polarized light passing through a non polarization-maintaining light path is changed into elliptical polarized light, the elliptical polarized light comprises P polarized light and S polarized light, the vibration direction is not fixed, the scattered light is elliptical polarized light, the influence of atmosphere depolarization exists, the echo signal light is elliptical polarized light, the P polarized light and the S polarized light are included, and the vibration direction is not fixed;
the local oscillation light and the signal light of the non-polarization-maintaining light path have different polarization states, and the polarization state of the signal light is not fixed, so that the two beams of light respectively pass through the first polarization beam splitter 7 and the second polarization beam splitter 8 and are divided into S polarized light and P polarized light with mutually vertical vibration directions, and the coherence efficiency can be improved; the first polarization beam splitter 7 is a polarization maintaining device and divides local oscillation light into two linearly polarized light beams with equal power, the incident end of the second polarization beam splitter 8 is a non-polarization maintaining optical fiber, the emergent end of the second polarization beam splitter is a polarization maintaining optical fiber, and the sum of the power of the two linearly polarized light beams after beam splitting is not changed when signal light polarization states are different;
(IV) the polarization states of the P polarized light after the local oscillation beam splitting and the P polarized light after the scattering echo signal splitting are the same, and the P polarized light after the frequency mixing by the first coupler 9 interferes in the first balanced detector 11; the polarization states of the S polarized light after the local oscillation beam splitting and the S polarized light after the scattering echo signal splitting are the same, and the S polarized light after the scattering echo signal splitting are subjected to frequency mixing by a second coupler 10 and then subjected to interference in a second balanced detector 12;
fifthly, the first balanced detector 11 and the second balanced detector 12 output the coherent signal intensity of the local oscillation light and the signal light to the signal processing module 13 respectively; after the difference frequency signal is extracted by the signal processing module 13, the frequency modulated by the modulator is removed to obtain the doppler frequency shift containing the positive and negative information, and the wind speed information is calculated.
Considering only shot noise, the radar system signal-to-noise ratio can be expressed as:
Figure BDA0003694972050000071
wherein (eta) q For the quantum efficiency of the detector, S is the detector sensitivity, e is the electron charge 1.6X 10 -19 c，P LO Is the local oscillator optical power, P S As the power of the scattered signal light), η h The coherence efficiency is related to the degree of polarization state matching between the local oscillator light and the signal light, and when other conditions are consistent, the larger the polarization state difference between the two beams of light is, the lower the coherence efficiency is, so that the lower the signal-to-noise ratio is, and when the polarization state of the signal light is orthogonal to the local oscillator light, the coherence efficiency is zero. The voltage signals output by the first balanced detector 11 and the second balanced detector 12 are respectively:
Figure BDA0003694972050000072
Figure BDA0003694972050000073
in the formula K P Is the gain, S, of the first balanced detector (11) 1 、S 2 The responsivity of the photodiode in the first balanced detector (11); k S Is the gain, S, of the second balanced detector (12) 3 、S 4 The responsivity of the photodiode in the detector (12) is balanced by the second.
K P Is the gain, S, of the first balanced detector (11) 1 、S 2 Is the response rate of the photodiode in the first balanced detector (11); k is S Is the gain, S, of the second balanced detector (12) 3 、S 4 The responsivity of the photodiode in the detector (12) is balanced by the second. P is LO Is local oscillation optical power, and epsilon/(1-epsilon) is the splitting ratio of the polarization beam splitter (8), P S In order to scatter the signal light power, Δ ν is a frequency difference between the local oscillation light and the signal light,
Figure BDA0003694972050000082
is the phase difference between the local oscillation light and the signal light.
The data processing adopts a scalar addition algorithm, and the final output average signal power is as follows:
Figure BDA0003694972050000081
in order to ensure that the average signal power is not influenced by the splitting ratio epsilon/(1-epsilon) of the second polarization beam splitter (8) when the polarization state of the scattered echo signal changes and further ensure the stability of the signal to noise ratio of the radar, the responsivities of 4 photodiodes in the first balanced detector (11) and the second balanced detector (12) need to be consistent, and the gains of the two balanced detectors need to be adjusted to be consistent. According to the average signal power calculation formula, because polarization diversity reception divides the local oscillator light into 50/50 of light and then beat frequencies of the local oscillator light and the signal light respectively, compared with a polarization-maintaining optical path, when the local oscillator light power and the signal light power are the same, the average signal power output by a non-polarization-maintaining optical path finally is reduced by 3dB. If only shot noise is considered, the noise power of the two is equal, so that the signal-to-noise ratio is reduced by 3dB. The signal-to-noise ratio can be improved by increasing the output power.
When output power increases, increased terminal surface return optical power simultaneously, in order to avoid the balanced detector saturation, adopt the balanced detector structure as shown in fig. 3, specifically include balanced detector, resistance Rg, high pass filter HPF, radio frequency amplifier RFA and low pass filter LPF, the output of balanced detector divides two tunnel: one path is grounded through a resistor Rg, and the other path is connected with the input end of a high-pass filter HPF; the output end of the high-pass filter HPF is connected with the input end of the radio-frequency amplifier RFA, the output end of the radio-frequency amplifier RFA is connected with the input end of the low-pass filter LPF, and the output end of the low-pass filter LPF is connected with the output Vout. The primary amplification adopts a radio frequency amplifier to replace the traditional trans-impedance amplification mode, the output power range is enlarged, 39dbm can be reached, and the saturation is not easy to occur. The structure has a simple feedback structure, and the saturation recovery time can be very short even after saturation, so that the saturation oscillation phenomenon can not occur. Therefore, the defects of small input power and easy saturation in the traditional mode are overcome.
The above-mentioned embodiments only express several embodiments of the present invention, and the description thereof is more specific and detailed, but not construed as limiting the scope of the invention. It should be noted that, for a person skilled in the art, several variations and modifications can be made without departing from the inventive concept, which falls within the scope of the present invention. Therefore, the protection scope of the present patent shall be subject to the appended claims.

Claims (9)

1. The utility model provides a pulsed coherent wind lidar based on non-polarization maintaining light path which characterized in that: the device comprises a seed source (1), a beam splitter (2), a modulator (3), an optical fiber amplifier (4), a circulator (5), a telescope (6), a first polarization beam splitter (7), a second polarization beam splitter (8), a first coupler (9), a second coupler (10), a first balanced detector (11), a second balanced detector (12) and a signal processing module (13); the beam splitter (2) receives light from the seed source (1) and splits the light into two beams of P polarized light; the first polarization beam splitter (7) receives a beam of P-polarized light from the beam splitter (2); the modulator (3) receives another beam of P polarized light from the beam splitter (2), shifts the frequency of the beam and outputs the beam to the optical fiber amplifier (4); the optical fiber amplifier (4) amplifies the optical signal after frequency shift and outputs the amplified optical signal to the telescope (6) through the circulator (5); the telescope (6) transmits the light beam into the atmosphere and receives scattered echo signals from the atmosphere; the scattered echo signals are output to a second polarization beam splitter (8) through a circulator (5); the first polarization beam splitter (7) splits an input beam of P polarized light into P polarized light and S polarized light with mutually vertical vibration directions; the second polarization beam splitter (8) splits the input scattering echo signal into S polarized light and P polarized light with mutually perpendicular vibration directions; the first coupler (9) receives the P polarized light from the first polarization beam splitter (7) and the P polarized light from the second polarization beam splitter (8), and outputs the P polarized light and the P polarized light after mixing to the first balanced detector (11) for interference; the second coupler (10) receives the S polarized light from the first polarization beam splitter (7) and the S polarized light from the second polarization beam splitter (8), mixes the S polarized light and the S polarized light, and outputs the S polarized light and the S polarized light to the second balanced detector (12) for interference; the signal processing module (13) receives coherent signals from the first balanced detector (11) and the second balanced detector (12), eliminates the frequency modulated by the modulator (3), obtains Doppler frequency shift containing positive and negative information, and calculates wind speed information.
2. The pulsed coherent wind lidar based on a non-polarization-maintaining optical path according to claim 1, wherein: the modulator (3) is a non-polarization-maintaining device; the optical fiber amplifier (4) is a non-polarization-maintaining device; the circulator (5) is a non-polarization-maintaining device.
3. The pulsed coherent wind lidar according to claim 1, wherein the pulsed coherent wind lidar comprises: the first polarization beam splitter (7) is a polarization maintaining device; and the incident end of the second polarization beam splitter (8) is a non-polarization-maintaining optical fiber, and the emergent end of the second polarization beam splitter is a polarization-maintaining optical fiber.
4. The pulsed coherent wind lidar according to claim 1, wherein the pulsed coherent wind lidar comprises: the first coupler (9) is a polarization-maintaining device; the second coupler (10) is a polarization maintaining device.
5. The pulsed coherent wind lidar according to claim 1, wherein the pulsed coherent wind lidar comprises: the seed source (1) and the beam splitter (2) are polarization maintaining devices.
6. The pulsed coherent wind lidar according to claim 1, wherein the pulsed coherent wind lidar comprises: the first coupler (9) is a 3dB coupler; the second coupler (10) is a 3dB coupler.
7. The utility model provides a pulsed coherent wind lidar based on non-polarization maintaining light path which characterized in that: the device comprises a seed source (1), a beam splitter (2), a modulator (3), an optical fiber amplifier (4), a circulator (5), a telescope (6), a first polarization beam splitter (7), a second polarization beam splitter (8), a first coupler (9), a second coupler (10), a first balanced detector (11), a second balanced detector (12) and a signal processing module (13); the beam splitter (2) receives light from the seed source (1) and splits the light into two beams of P polarized light; the first polarization beam splitter (7) receives a beam of P polarized light from the beam splitter (2); the modulator (3) receives another beam of P-polarized light from the beam splitter (2); the modulator (3), the optical fiber amplifier (4), the circulator (5) and the telescope (6) are sequentially connected through optical fibers; the second polarization beam splitter (8) is connected with the 3 ports of the circulator (3) through optical fibers; the first coupler (9) is respectively connected with the first polarization beam splitter (7) and the second polarization beam splitter (8) through optical fibers; the second coupler (10) is respectively connected with the first polarization beam splitter (7) and the second polarization beam splitter (8) through optical fibers; the signal processing module (13) is respectively connected with the first balanced detector (11) and the second balanced detector (12).
8. The pulsed coherent wind lidar according to claim 7, wherein the pulsed coherent wind lidar further comprises: the modulator (3) is a non-polarization-maintaining device; the optical fiber amplifier (4) is a non-polarization-maintaining device; the circulator (5) is a non-polarization-maintaining device; the first polarization beam splitter (7) is a polarization maintaining device; the incident end of the second polarization beam splitter (8) is a non-polarization-maintaining optical fiber, and the emergent end of the second polarization beam splitter is a polarization-maintaining optical fiber; the first coupler (9) is a polarization maintaining device; the second coupler (10) is a polarization maintaining device; the seed source (1) and the beam splitter (2) are polarization maintaining devices.
9. The wind speed measurement method based on the non-polarization-preserving light path is characterized by comprising the following steps: the method comprises the following steps:
the first beam splitter (2) receives light from the seed source (1) and splits the light into two beams of P polarized light, wherein one beam of P polarized light is output to the first polarization beam splitter (7) to be used as local oscillation light, and the other beam of P polarized light is output to the modulator (3);
the modulator (3) chops and shifts the input P polarized light, and a fixed frequency difference is generated between the light after frequency shift and local oscillation light; the light after frequency shift is amplified by the optical fiber amplifier (4), transmitted to the No. 2 port through the No. 1 port of the circulator (5) and transmitted to the atmosphere through the telescope; scattered echo signals on the surfaces of the aerosol particles are received by the telescope (6), transmitted to the port No. 3 through the port No. 2 of the circulator (5) and output to the second polarization beam splitter (8);
the local oscillation light and the signal light of the non-polarization-maintaining light path have different polarization states, and the polarization state of the signal light is not fixed, so that the two beams of light respectively pass through a first polarization beam splitter (7) and a second polarization beam splitter (8) and are divided into S-polarized light and P-polarized light with mutually vertical vibration directions;
(IV) the polarization states of the P polarized light after the local oscillation beam splitting and the P polarized light after the scattering echo signal splitting are the same, and the P polarized light after the frequency mixing by the first coupler (9) interferes in the first balanced detector (11); the S polarized light after the local oscillation beam splitting has the same polarization state as the S polarized light after the scattering echo signal splitting, and the S polarized light after the frequency mixing by the second coupler (10) interferes in the second balanced detector (12);
the first balance detector (11) and the second balance detector (12) respectively output the coherent signal intensity of the local oscillation light and the coherent signal intensity of the signal light to the signal processing module (13); after the signal processing module (13) extracts the difference frequency signal, the frequency modulated by the modulator is removed, the Doppler frequency shift containing positive and negative information is obtained, and wind speed information is calculated.
CN202210671897.5A 2022-06-15 2022-06-15 Pulse type coherent wind lidar based on non-polarization-maintaining light path Pending CN115184960A (en)

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Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN116068584A (en) * 2023-03-13 2023-05-05 武汉聚合光子技术有限公司 Non-blind area coherent laser radar
CN117092662A (en) * 2023-10-17 2023-11-21 中国科学技术大学 Quantum interference laser radar system and method for wind field detection

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN116068584A (en) * 2023-03-13 2023-05-05 武汉聚合光子技术有限公司 Non-blind area coherent laser radar
CN117092662A (en) * 2023-10-17 2023-11-21 中国科学技术大学 Quantum interference laser radar system and method for wind field detection
CN117092662B (en) * 2023-10-17 2024-02-23 中国科学技术大学 Quantum interference laser radar system and method for wind field detection

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