CN111007526B - System and method for suppressing optical noise of continuous wave all-fiber coherent Doppler laser speed measurement radar - Google Patents
System and method for suppressing optical noise of continuous wave all-fiber coherent Doppler laser speed measurement radar Download PDFInfo
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- CN111007526B CN111007526B CN201911265988.3A CN201911265988A CN111007526B CN 111007526 B CN111007526 B CN 111007526B CN 201911265988 A CN201911265988 A CN 201911265988A CN 111007526 B CN111007526 B CN 111007526B
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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
- G01S17/02—Systems using the reflection of electromagnetic waves other than radio waves
- G01S17/50—Systems of measurement based on relative movement of target
- G01S17/58—Velocity or trajectory determination systems; Sense-of-movement determination systems
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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
- 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
- G01S7/481—Constructional features, e.g. arrangements of optical elements
- G01S7/4818—Constructional features, e.g. arrangements of optical elements using optical fibres
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- 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 speed measuring radars, in particular to a suppression system of optical noise of a continuous wave all-fiber coherent Doppler laser speed measuring radar, which adopts a 1/4 wave plate and a fiber polarization beam splitter to realize rotation and screening of the light polarization state of an echo signal; the APC end face of the second port of the optical fiber circulator or the polarization beam splitter is coated with a film to reduce the end face reflection, thereby reducing the interference; the invention also provides a suppression method based on the system, thereby reducing additional noise caused by light leakage at the end face of the optical fiber and the port of the circulator in the continuous wave all-fiber laser coherent Doppler velocity radar, improving the signal-to-noise ratio and ensuring the detection precision of the system.
Description
Technical Field
The invention belongs to the technical field of laser speed measuring radars, and particularly relates to a system and a method for inhibiting optical noise of a continuous wave all-fiber coherent Doppler laser speed measuring radar.
Background
In recent years, the laser speed measuring radar technology has great development, and the specific application fields comprise laser wind measurement, laser liquid speed measurement, unmanned laser radar and the like. In order to realize the above functions, widely used technical bases include a doppler velocity measurement technique, an optical coherence measurement technique, and an all-fiber optical path structure. The Doppler velocity measurement technology is based on the principle that a light source and a target move relatively to generate laser frequency shift, and the relative movement velocity of the target and the light source is obtained by measuring the movement amount of the laser frequency and performing reverse extrapolation; the optical coherence measurement is a method for acquiring specific Doppler frequency shift amount, coherent detection is carried out by using local oscillator light and signal light carrying Doppler frequency shift information, and the Doppler frequency shift amount is acquired by measuring difference frequency information; finally, all-fiber structures have also been widely used in such devices due to the significant advantage of structural stability.
As a typical example of weak signal light detection, a laser wind radar, including a continuous light and pulse light laser wind radar, measures the size and direction of a wind field by detecting doppler information carried in backward scattering of probe light by aerosol particles in the atmosphere. The backscattering coefficient caused by the atmospheric aerosol particles is extremely low, so that the system is particularly critical in the extraction capability of the Doppler information of weak signal light. The key to solving the above problem is to improve the signal-to-noise ratio of the signal. At present, two aspects are generally considered, one of which is to increase the optical power of the signal, and the other is to reduce the noise in the measurement process. Besides the above mentioned local oscillator light relative intensity noise, the coherent doppler laser velocity measurement radar, especially the continuous wave all-fiber laser coherent doppler velocity measurement radar, also faces an important noise source, such as coherent noise introduced by reflected light from the end face of the optical fiber of the system and leakage light from part of the optical path.
In the prior art, the fiber laser radar consists of an MOPA-SL light source coupled by optical fibers, a circulator, an inline polarization controller and a photoelectric detector. The PC end of the port of the circulator 2 is coated with an anti-reflection coating (< 0.25%) to obtain local oscillator light with proper power, and because the local oscillator light is mixed with the signal light in advance and returns from the same optical path in the scheme, the optical intensity noise caused by strong local oscillator light is difficult to reduce by adopting a balanced detection scheme, and the further improvement of the signal-to-noise ratio of the system is influenced.
Disclosure of Invention
Aiming at the defects, the invention provides a system and a method for inhibiting the optical noise of a continuous wave all-fiber coherent Doppler laser speed measurement radar.
In order to achieve the technical purpose, one technical scheme of the invention is as follows:
full optical fiber continuous coherent Doppler laser speed measuring radar optical noise suppression system, including narrow linewidth laser, first coupler, polarization beam splitter, second coupler, collimator, 1/4 wave plate, beam expanding system, detection target and signal processing unit, narrow linewidth laser connects the input of first coupler, the first output of first coupler pass through the amplifier with the first port of polarization beam splitter links to each other, polarization beam splitter with set gradually between the detection target the collimator 1/4 wave plate with beam expanding system, the APC terminal surface of the second port of polarization beam splitter has plated the antireflection film, the third port of polarization beam splitter with the second coupler links to each other, the fast axle of 1/4 wave plate is 45 degrees contained angles with the polarization direction and sets up, the second output of first coupler also with the second coupler links to each other, the second coupler passes through balanced detector and connects signal processing unit.
Further, the narrow linewidth laser is one of a distributed feedback laser, a distributed bragg reflector laser and an external cavity semiconductor laser.
Further, the amplifier is an erbium-doped fiber amplifier, the first coupler is a high-ratio fiber coupler, and the second coupler is a 3dB fiber coupler.
Based on the system, the invention correspondingly provides a method for inhibiting the optical noise of the all-fiber continuous coherent Doppler laser velocity measurement radar, which comprises the following specific steps:
s1, narrow-linewidth continuous laser emitted by a narrow-linewidth laser is divided into local oscillation light and seed light by a first coupler,
s2, the seed light in the step S1 is amplified by an amplifier and is injected into a first port of a polarization beam splitter as detection light, the APC end face of a second port of the polarization beam splitter is coated with an antireflection film,
s3, the circularly polarized light is converted into circularly polarized light through a 1/4 wave plate with the fast axis and the polarization direction forming an included angle of 45 degrees, the circularly polarized light is emitted to the target to be detected through a beam expanding system and then returns,
s4, the back scattered light carrying the information of the detection target is converted into linearly polarized light through the 1/4 wave plate again, the polarization direction of the linearly polarized light is vertical to the polarization direction of the detection light,
s5, injecting the linearly polarized light in the step S4 from a second port of the polarization beam splitter, and emitting the linearly polarized light from a third port of the polarization beam splitter to obtain signal light,
and S6, mixing the signal light and the local oscillator light in the step S5 and sending the mixture to a balance detector for detection, and sending a difference frequency signal output by the balance detector to a signal processing unit for processing.
In order to achieve the technical purpose, the other technical scheme of the invention is as follows:
the suppression system of the optical noise of the all-fiber continuous coherent Doppler laser velocimetry radar comprises a narrow linewidth laser, a first coupler, an optical fiber circulator, a polarization beam splitter, a second coupler, a collimator, a 1/4 wave plate and a beam expanding system, a detection target and a signal processing unit, wherein the narrow linewidth laser is connected with the input end of the first coupler, the first output end of the first coupler is connected with the first port of the optical fiber circulator through an amplifier, the optical fiber circulator and the detection target are sequentially provided with the collimator, the 1/4 wave plate and the beam expanding system, the APC end face of the second port of the optical fiber circulator is plated with an antireflection film, the third port of the optical fiber circulator is connected with the second coupler through the polarization beam splitter, and the fast axis of the 1/4 wave plate and the polarization direction are arranged at an included angle of 45 degrees,
and the second output end of the first coupler is also connected with the second coupler, and the second coupler is connected with the signal processing unit through a balance detector.
Further, the narrow linewidth laser is one of a distributed feedback laser, a distributed bragg reflector laser and an external cavity semiconductor laser.
Further, the amplifier is an erbium-doped fiber amplifier, the first coupler is a high-ratio optical fiber coupler, and the second coupler is a 3dB optical fiber coupler.
Based on the system, the invention correspondingly provides a method for inhibiting optical noise of an all-fiber continuous coherent Doppler laser velocity measurement radar, which comprises the following specific steps:
s1, narrow-linewidth continuous laser emitted by a narrow-linewidth laser is divided into local oscillation light and seed light by a first coupler,
s2, the seed light in the step S1 is amplified by an amplifier and is injected as probe light to pass through a first port of an optical fiber circulator, the APC end face of a second port of the optical fiber circulator is coated with an antireflection film,
s3, the circularly polarized light is converted into circularly polarized light through a 1/4 wave plate with the fast axis and the polarization direction forming an included angle of 45 degrees, the circularly polarized light is emitted to a target to be detected through a beam expanding system 7 and then returns,
s4, the back scattered light carrying the information of the detection target is converted into linearly polarized light through the 1/4 wave plate again, the polarization direction of the linearly polarized light is vertical to the polarization direction of the detection light,
s5, injecting the linearly polarized light in the step S4 from a second port of the optical fiber circulator, and emitting the linearly polarized light from a third port of the optical fiber circulator to obtain signal light,
and S6, mixing the signal light in the step S5 with the local oscillation light through the polarization beam splitter, sending the mixture to a balance detector for detection, and sending a difference frequency signal output by the balance detector to a signal processing unit for processing.
The invention has the following beneficial effects:
1. the polarization state of echo signal light and the polarization state of probe light are adjusted to be an included angle of 90 degrees by adopting a 1/4 wave plate, and the signal light and interference light are separated by using an optical fiber polarization beam splitter, so that the influence of the interference light is reduced;
2. the end face reflection is reduced by the film coating of the end face of the second port of the circulator or the optical fiber polarization beam splitter, so that the interference is reduced;
3. and reducing the relative intensity noise of the local oscillation light by adopting a balance detector.
Drawings
FIG. 1 is a schematic diagram of a system for suppressing optical noise of a continuous wave all-fiber laser coherent Doppler velocity measurement radar in the prior art;
FIG. 2 is a schematic structural diagram of a system for suppressing optical noise of the continuous wave all-fiber laser coherent Doppler velocity measurement radar in embodiment 1;
FIG. 3 is a noise measurement spectrum diagram of example 1;
FIG. 4 is a schematic structural diagram of a system for suppressing optical noise of the continuous wave all-fiber laser coherent Doppler velocity measurement radar in embodiment 2;
FIG. 5 is a graph of the noise measurement spectrum of example 2;
FIG. 6 is a schematic structural view of a comparative example;
fig. 7 is a graph of a noise measurement spectrum of the comparative example.
Detailed Description
The invention aims to reduce additional noise caused by light leakage at the end face of an optical fiber and the port of a circulator in a continuous wave all-fiber laser coherent Doppler velocity radar by utilizing the polarization characteristic, the end face coating technology and the balance detection technology, thereby improving the signal-to-noise ratio and ensuring the detection precision of a system. Based on the above theory and method, two implementation devices can be provided, and two technical solutions of the present invention are described in detail below with reference to the accompanying drawings.
The following describes embodiment 1 of the present invention in detail with reference to fig. 2, but the present invention is not limited to the claims.
The suppression system for the optical noise of the continuous wave all-fiber laser coherent Doppler velocity measurement radar provided in the embodiment comprises a narrow-line-width laser 1-1, a first coupler 1-2, a polarization beam splitter 1-4, a second coupler 1-9, a collimator 1-5, a 1/4 wave plate 1-6, a beam expanding system 1-7, a detection target 1-8 and a signal processing unit 1-11.
The narrow linewidth laser 1-1 is used for emitting narrow linewidth continuous laser, the narrow linewidth laser 1-1 is a distributed feedback laser, a distributed Bragg reflection laser and an external cavity semiconductor laser, the narrow linewidth laser 1-1 is connected with the input end of a first coupler 1-2, and the first coupler 1-2 is a high-ratio optical fiber coupler and used for dividing passing output light into two paths. The polarizing beam splitter 1-4 has three ports: the device comprises a first port, a second port and a third port, wherein optical signals enter from the first port and are output from the second port, the second port is also connected with back scattering optical signals returned from the detection targets 1-8, and the back scattering optical signals are output from the third port. The first output end of the first coupler 1-2 is connected with the first port of the polarization beam splitter 1-4 through an amplifier 1-3, and the amplifier 1-3 is an erbium-doped fiber amplifier 1-3 for amplifying an incoming optical signal. A collimator 1-5, a 1/4 wave plate 1-6 and a beam expanding system 1-7 are sequentially arranged between a polarization beam splitter 1-4 and a detection target 1-8, and an anti-reflection film is plated on an APC end face of a second port of the polarization beam splitter 1-4, so that the intensity of reflected light on the end face is reduced as much as possible, and the influence of the reflected light is further reduced. And the third port of the polarization beam splitter 1-4 is connected with a second coupler 1-9, and the second coupler 1-9 is a 3dB optical fiber coupler. The fast axis of the 1/4 wave plate 1-6 and the polarization direction form an included angle of 45 degrees, and the 1/4 wave plate 1-6 converts the circularly polarized light and the linearly polarized light mutually. The second output end of the first coupler 1-2 and the third port of the polarization beam splitter 1-4 are connected with the second coupler 1-9, and the second coupler 1-9 is connected with the signal processing unit 1-11 through the balance detector 1-10.
Based on the above system, the method for suppressing optical noise of the continuous wave all-fiber laser coherent doppler velocity measurement radar provided in this embodiment includes the following specific steps:
s1, a narrow linewidth laser 1-1 emits narrow linewidth continuous laser which is linearly polarized light and is output through an optical fiber, and output light is divided into local oscillation light and seed light through a first coupler 1-2. Wherein, one path of weaker light is used as local oscillator light, and the other path of weaker light is seed light;
s2, injecting the seed light serving as detection light into a first port of an optical fiber polarization beam splitter 1-4 after being amplified by an optical fiber amplifier 1-3, wherein an anti-reflection film is plated on an APC end face of a second port of the polarization beam splitter 1-4;
s3, the detection light sequentially passes through the polarization beam splitter 1-4 and the light collimator 1-5, then reaches a 1/4 wave plate 1-6 with a fast axis and a polarization direction forming an included angle of 45 degrees to become circularly polarized light, and finally is emitted to a target space through the beam expanding system 1-7;
s4, the detection light is caused to generate weak backscattering carrying speed signals by the detection targets 1-8 in the space, the backscattering carrying the information of the detection targets 1-8 returns to the optical system through the beam expanding system 1-7 along the original path, the 1/4 wave plate 1-6 converts the circularly polarized light into linearly polarized light again, the polarization direction of the linearly polarized light obtained at the moment is vertical to the polarization direction of the original linearly polarized light,
s5, injecting the linearly polarized light in the step S4 from a second port of the polarization beam splitter 1-4, and emitting the linearly polarized light from a third port of the polarization beam splitter 1-4 to obtain signal light;
and S5, the signal light and the local oscillator light are mixed through the second coupler 1-9 and sent to the balance detector 1-10 for detection, and the difference frequency signals output by the balance detector 1-10 are processed by the signal processing unit 1-11 through subsequent analog-to-digital conversion, fast Fourier transform, frequency spectrum accumulation, peak searching calculation and the like.
As shown in fig. 3, the spectrometer bandwidth is set to 1KHz with an average number of 30. After the system provided by the embodiment is used for processing, the background noise is about-80 dBm, and the fluctuation range is less than 3dB. The system can be stably in a high signal-to-noise ratio state, so that a weak return light signal can be stably measured.
The suppression system for the optical noise of the continuous wave all-fiber laser coherent Doppler velocity measurement radar provided in the embodiment comprises a narrow-linewidth laser 2-1, a first coupler 2-2, a fiber circulator 2-4, a polarization beam splitter 2-9, a second coupler 2-10, a collimator 2-5, a 1/4 wave plate 2-6, a beam expanding system 2-7, a detection target 2-8 and a signal processing unit 2-12.
The narrow linewidth laser 2-1 is used for emitting narrow linewidth continuous laser, the narrow linewidth laser 2-1 is a distributed feedback laser, a distributed Bragg reflection laser and an external cavity semiconductor laser, the narrow linewidth laser 2-1 is connected with the input end of the first coupler 2-2, and the first coupler 2-2 is a high-ratio optical fiber coupler and used for dividing passing output light into two paths. The fiber optic circulators 2-4 have three ports: the optical signal enters from the first port and is output from the second port, the second port is also connected with the back scattering optical signal returned from the detection target 2-8, and the back scattering optical signal is output from the third port. The first output end of the first coupler 2-2 is connected with the first port of the optical fiber circulator 2-4 through an amplifier 2-3, and the amplifier 2-3 is an erbium-doped optical fiber amplifier 2-3 for amplifying an incoming optical signal. A collimator 2-5, a 1/4 wave plate 2-6 and a beam expanding system 2-7 are sequentially arranged between the optical fiber circulator 2-4 and a detection target 2-8, and an anti-reflection film is plated on the APC end face of the second port of the optical fiber circulator 2-4, so that the intensity of reflected light on the end face is reduced as much as possible, and the influence of the reflected light is further reduced. And a third port of the optical fiber circulator 2-4 is connected with a second coupler 2-10 through a polarization beam splitter 2-9, and the second coupler 2-10 is a 3dB optical fiber coupler. The fast axis of the 1/4 wave plate 2-6 and the polarization direction form an included angle of 45 degrees, and the 1/4 wave plate 2-6 converts the circularly polarized light and the linearly polarized light mutually. The second output end of the first coupler 2-2 and the polarization beam splitter 2-9 are connected with the second coupler 2-10, and the second coupler 2-10 is connected with the signal processing unit 2-12 through the balance detector 2-11.
Based on the above system, the method for suppressing optical noise of a continuous wave all-fiber laser coherent doppler velocity measurement radar provided by this embodiment includes the following specific steps:
s1, a narrow linewidth laser 2-1 emits narrow linewidth continuous laser which is linearly polarized light and is output through an optical fiber, output light is divided into local oscillation light and seed light through a first coupler 2-2, wherein one path which is weaker is used as the local oscillation light, and the other path is used as the seed light;
s2, the seed light is amplified by the optical fiber amplifier 2-3 and then injected into a first port of the optical fiber circulator 2-4 as detection light, and an anti-reflection film is plated on the APC end face of a second port of the optical fiber circulator 2-4;
s3, the detection light sequentially passes through the optical fiber circulator 2-4 and the collimator 2-5, then reaches the 1/4 wave plate 2-6 with the fast axis and the polarization direction forming an included angle of 45 degrees to become circularly polarized light, and finally is emitted to a target space through the beam expanding system 2-7;
s4, the detection light is caused to generate weak backscattering carrying speed signals by the detection targets 2-8 in the space, the backscattering carrying the information of the detection targets 2-8 returns to the optical system through the beam expanding system 2-7 along the original path, the 1/4 wave plate 2-6 converts the circularly polarized light into linearly polarized light again, the polarization direction of the linearly polarized light obtained at the moment is vertical to the polarization direction of the original linearly polarized light,
s5, injecting the linearly polarized light in the step S4 from a second port of the optical fiber circulator 2-4, and emitting the linearly polarized light from a third port of the optical circulator to obtain signal light;
and S5, the signal light and the local oscillator light are mixed through the polarization beam splitters 2-9 and the second couplers 2-10 and sent to the balance detectors 2-11 for detection, and the difference frequency signals output by the balance detectors 2-11 are processed by the signal processing units 2-12 in a follow-up mode of analog-to-digital conversion, fast Fourier transform, frequency spectrum accumulation, peak searching calculation and the like.
As shown in fig. 5, the spectrometer bandwidth is set to 1KHz with an average number of 30. After the system provided by the embodiment is used for processing, the background noise is about-80 dBm, and the fluctuation range is less than 3dB. The system can be in a high signal-to-noise ratio state stably, so that a weak return light signal can be measured stably.
The comparative example will be described with reference to fig. 6.
Compared with embodiment 2, in the system provided by the comparative example, the narrow linewidth laser 3-1 is connected to the input end of the first coupler 3-2, the first output end of the first coupler 3-2 is connected to the first port of the optical fiber circulator 3-4 through the amplifier 3-3, only the collimator 3-5 and the beam expanding system 3-6 are arranged between the optical fiber circulator 3-4 and the detection target 3-7, the third port of the optical fiber circulator 3-4 is directly connected to the second coupler 3-8, the second output end of the first coupler 3-2 is also connected to the second coupler 3-8, and the second coupler 3-8 is connected to the signal processing unit 3-10 through the balanced detector 3-9. The second port of the optical fiber circulator 3-4 is not provided with an antireflection film, and the front end of the beam expanding system 3-6 is not provided with a 1/4 wave plate, meanwhile, a polarization beam splitter is not arranged between the optical fiber circulator 3-4 and the second coupler 3-8.
As shown in fig. 7, the spectrometer bandwidth is set to 1KHz with an average number of 30. The fluctuation range of the background noise is about 20dB after the system provided by the comparative example is processed. The system noise fluctuation range is large, and a part of moments can cover a weak return light signal, so that the measurement cannot be stably carried out.
In conclusion, the invention has the following beneficial effects:
1. the polarization state of echo signal light and the polarization state of detection light are adjusted to be an included angle of 90 degrees by adopting a 1/4 wave plate, and the signal light and interference light are separated by using a polarization beam splitter, so that the influence of the interference light is reduced;
2. the end surface reflection is reduced by the coating of the APC end surface of the second port of the circulator or the polarization beam splitter, so that the interference is reduced;
3. and reducing the relative intensity noise of the local oscillator light by adopting a balance detector.
By using the technical scheme of the invention, the additional noise caused by light leakage on the end face of the optical fiber and the port of the circulator in the continuous wave all-fiber laser coherent Doppler velocity radar can be reduced; meanwhile, relative intensity noise introduced by local oscillation light can be reduced compared with the existing reference scheme, so that the signal-to-noise ratio of the system is improved.
The above description is only for the purpose of illustrating preferred embodiments of the present invention and is not to be construed as limiting the invention, and the present invention is not limited to the above examples, and those skilled in the art should also be able to make various changes, modifications, additions or substitutions within the spirit and scope of the present invention.
Claims (8)
1. The utility model provides an inhibition system of continuous coherent Doppler laser speed measuring radar optical noise of full optical fiber, its characterized in that, includes narrow linewidth laser, first coupler, polarization beam splitter, second coupler, collimater, 1/4 wave plate, beam expanding system, surveys target and signal processing unit, the narrow linewidth laser is connected the input of first coupler, the first output of first coupler pass through the amplifier with the first port of polarization beam splitter links to each other, polarization beam splitter with survey and set gradually between the target the collimater 1/4 wave plate with beam expanding system, the APC terminal surface of the second port of polarization beam splitter has plated the antireflection film, the third port of polarization beam splitter with the second coupler links to each other, the fast axle of 1/4 wave plate is 45 degrees contained angles with the polarization direction and sets up, the second output of first coupler also with the second coupler links to each other, the second coupler passes through balanced detector and connects signal processing unit.
2. The system of claim 1, wherein the narrow linewidth laser is one of a distributed feedback laser, a distributed bragg reflector laser, and an external cavity semiconductor laser.
3. The system of claim 1, wherein the amplifier is an erbium-doped fiber amplifier, the first coupler is a high-ratio fiber coupler, and the second coupler is a 3dB fiber coupler.
4. A method for suppressing the optical noise of the all-fiber continuous coherent doppler laser velocimetry radar according to any one of claims 1 to 3, comprising the following steps:
s1, narrow-linewidth continuous laser emitted by a narrow-linewidth laser is divided into local oscillation light and seed light by a first coupler,
s2, amplifying the seed light in the step S1 by an amplifier to be used as detection light to be injected into a first port of a polarization beam splitter, wherein the APC end face of a second port of the polarization beam splitter is coated with an anti-reflection film,
s3, the circularly polarized light is converted into circularly polarized light through a 1/4 wave plate with the fast axis and the polarization direction forming an included angle of 45 degrees, the circularly polarized light is emitted to a target to be detected through a beam expanding system 7 and then returns,
s4, the back scattered light carrying the information of the detection target is converted into linearly polarized light through the 1/4 wave plate again, the polarization direction of the linearly polarized light is vertical to the polarization direction of the detection light,
s5, injecting the linearly polarized light in the step S4 from a second port of the polarization beam splitter, and emitting the linearly polarized light from a third port of the polarization beam splitter to obtain signal light,
and S6, mixing the signal light and the local oscillator light in the step S5 and sending the mixture to a balance detector for detection, and sending a difference frequency signal output by the balance detector to a signal processing unit for processing.
5. The utility model provides an inhibition system of continuous coherent Doppler laser speed measuring radar optical noise of full optical fiber, its characterized in that, includes narrow linewidth laser instrument, first coupler, optical fiber circulator, polarization beam splitter, second coupler, collimater, 1/4 wave plate, beam expanding system, surveys target and signal processing unit, narrow linewidth laser instrument is connected the input of first coupler, the first output of first coupler pass through the amplifier with the first port of optical fiber circulator links to each other, optical fiber circulator with survey and set gradually between the target the collimater 1/4 wave plate with beam expanding system, the APC terminal surface of the second port of optical fiber circulator has plated the antireflection film, the third port of optical fiber circulator passes through polarization beam splitter with the second coupler links to each other, the fast axis of 1/4 wave plate is 45 degrees contained angles with the polarization direction and sets up, the second output of first coupler also with the second coupler links to each other, the second coupler passes through balanced detector and connects signal processing unit.
6. The system as claimed in claim 5, wherein the narrow linewidth laser is one of a distributed feedback laser, a distributed Bragg reflector laser, and an external cavity semiconductor laser.
7. The system of claim 5, wherein the amplifier is an erbium-doped fiber amplifier, the first coupler is a high-ratio fiber coupler, and the second coupler is a 3dB fiber coupler.
8. The method for suppressing the optical noise of the all-fiber continuous coherent Doppler laser velocimetry radar according to any one of claims 5 to 7, wherein the specific steps include:
s1, narrow-linewidth continuous laser emitted by a narrow-linewidth laser is divided into local oscillation light and seed light by a first coupler,
s2, the seed light in the step S1 is amplified by an amplifier and is injected as probe light to pass through a first port of an optical fiber circulator, the APC end face of a second port of the optical fiber circulator is coated with an antireflection film,
s3, the circularly polarized light is converted into circularly polarized light through a 1/4 wave plate with the fast axis and the polarization direction forming an included angle of 45 degrees, the circularly polarized light is emitted to a target to be detected through a beam expanding system 7 and then returns,
s4, the back scattered light carrying the information of the detection target is converted into linearly polarized light through the 1/4 wave plate again, the polarization direction of the linearly polarized light is vertical to the polarization direction of the detection light,
s5, injecting the linearly polarized light in the step S4 from a second port of the optical fiber circulator, and emitting the linearly polarized light from a third port of the optical fiber circulator to obtain signal light,
and S6, mixing the signal light in the step S5 with the local oscillation light through the polarization beam splitter, sending the mixture to a balance detector for detection, and sending a difference frequency signal output by the balance detector to a signal processing unit for processing.
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