Parasitic noise suppression laser frequency shift feedback device

Abstract

The present application relates to a parasitic noise suppression laser frequency shift feedback device, comprising: a laser, a collimating lens, a beamsplitter, a Faraday rotator, a half-wave plate, an acousto-optic frequency shifting unit, a focusing lens unit, and a quarter-wave plate, arranged sequentially along a first direction, the first direction being the direction of the laser's output light; backscattered light from a target to be measured can be sequentially returned to the laser cavity via the quarter-wave plate, focusing lens unit, acousto-optic frequency shifting unit, half-wave plate, Faraday rotator, beamsplitter, and collimating lens, where it is modulated by the laser frequency shift feedback effect and then output by the laser. The aforementioned parasitic noise suppression laser frequency shift feedback device achieves parasitic noise suppression and normal amplification of signal light by adding a Faraday rotator, a half-wave plate, and a quarter-wave plate to the optical path, with minimal impact on the device's complexity and no restrictions on the device's use when the target to be measured is at close or long distances.

Description

Technical Field

[0001] The present application relates to the field of laser measurement technology, and in particular to a parasitic noise suppression type laser frequency shift feedback device. Background Art

[0002] Weak-light detection is crucial in many fields, including astronomy, medical imaging, and precision manufacturing. Currently, most low-light detection applications require sophisticated and expensive detectors, such as PMTs (photomultiplier tubes). These detectors are inherently very sensitive, requiring complex stray light shielding devices, which severely limits their application scenarios.

[0003] Therefore, laser frequency shift feedback technology is often used to measure weak light signals. Laser frequency shift feedback technology can amplify and modulate the optical signal returned by the target in the laser cavity and then output it again. The laser cavity itself is equivalent to a signal amplifier, and its signal amplification factor can reach 10 6 Moreover, the laser frequency shift feedback technology belongs to coherent detection, which makes it have good anti-interference ability to external ambient light, so it can be used to measure weak light signals.

[0004] In laser frequency-shift feedback technology, after emitting from the laser, the laser is modulated by a frequency-shifting device (such as an acousto-optic frequency shifter) and then shaped by other optical devices such as lenses before it reaches the target. The surfaces of these devices also reflect light signals, which can be considered parasitic noise in the laser frequency-shift feedback device.

[0005] Due to the high sensitivity of the laser frequency shift feedback effect, the parasitic noise is also amplified by the feedback effect when it returns to the laser cavity, causing the signal light returned by the target to be submerged in these parasitic noises. This greatly limits the laser frequency shift feedback device's ability to detect weaker targets.

[0006] Existing methods for suppressing parasitic noise in laser frequency-shift feedback devices are limited. For example, a rotating mirror is introduced to separate parasitic noise from signal light, but this significantly increases the complexity of the laser frequency-shift feedback device. Alternatively, a spatial separation of parasitic noise and signal light is employed. However, this requires strict beam alignment, increases debugging difficulty, complicates the device, and limits its use when the target is moving over long distances. Summary of the Invention

[0007] Based on this, it is necessary to provide a parasitic noise suppression laser frequency shift feedback device to address the technical problems in the existing technology that the parasitic noise suppression methods of the laser frequency shift feedback device result in greater complexity of the laser frequency shift feedback device and limited working distance.

[0008] A parasitic noise suppression laser frequency shift feedback device, comprising: a laser, a collimating lens, a beam splitter, a Faraday rotator, a half-wave plate, an acousto-optic frequency shifting unit, a focusing lens unit, and a quarter-wave plate arranged in sequence along a first direction, wherein the first direction is the direction of light emitted by the laser;

[0009] The laser is used to output linearly polarized laser light, wherein the polarization state of the linearly polarized laser light is along a first polarization direction;

[0010] The collimating lens is used to collimate the laser beam output by the laser;

[0011] The beam splitter is used to split the collimated laser beam into a transmitted beam and a reflected beam;

[0012] The Faraday rotator is used to rotate the polarization state of the transmitted light beam by 45 degrees before emitting the polarization state to the half-wave plate;

[0013] The half-wave plate is used to rotate the polarization state of the light beam emitted from the Faraday rotator again by a specific angle θ in the same direction, and then emit it to the acousto-optic frequency shifting unit, so that the polarization state of the light beam emitted from the half-wave plate to the acousto-optic frequency shifting unit is a second polarization direction, and the second polarization direction is consistent with the polarization direction of the acousto-optic frequency shifting unit, wherein θ is the angle difference between the polarization direction of the light beam emitted from the Faraday rotator to the half-wave plate and the second polarization direction;

[0014] The acousto-optic frequency shifting unit is used to differentially shift the frequency of the light beam emitted by the 1 / 2 wave plate, and emit the light beam after differential frequency shifting to the focusing lens unit;

[0015] The focusing lens unit is used to focus the light beam emitted by the acousto-optic frequency shifting unit;

[0016] The quarter wave plate is used to rotate the light beam focused by the focusing lens unit from a linear polarization state to a circular polarization state and then irradiate the light beam to the target to be measured;

[0017] The backscattered light of the target to be measured can be returned to the laser cavity of the laser through a 1 / 4 wave plate, a focusing lens unit, an acousto-optic frequency shifting unit, a 1 / 2 wave plate, a Faraday rotator, a beam splitter, and a collimating lens in sequence, and then output by the laser after being modulated under the laser frequency shift feedback effect.

[0018] In one embodiment, the parasitic noise suppression type laser frequency shift feedback device further includes a photodetector and a signal processor; the photodetector is used to detect the laser beam output by the laser after the laser frequency shift feedback effect, so as to detect the optical signal and convert the optical signal into an electrical signal; the signal processor is electrically connected to the photodetector, and is used to demodulate the electrical signal to obtain information about the target to be measured.

[0019] In one embodiment, the photodetector is disposed in the direction of the reflected light of the beam splitter, and is configured to receive the reflected light beam.

[0020] In one embodiment, the photodetector is disposed in the tail light output direction of the laser.

[0021] In one embodiment, the signal processor is configured to output the demodulation result to a computer, so that the computer can calculate and display information of the target to be measured based on the demodulation result.

[0022] In one embodiment, the modes of the laser are a fundamental transverse mode and a single longitudinal mode.

[0023] In one embodiment, the acousto-optic frequency shifting unit includes a first acousto-optic frequency shifter and a second acousto-optic frequency shifter, and the first acousto-optic frequency shifter and the second acousto-optic frequency shifter are used to perform differential frequency shifting on the light beam emitted by the half-wave plate.

[0024] In one embodiment, the focusing lens unit includes a concave lens and a convex lens.

[0025] In one embodiment, the number of the concave lenses is not limited to one, and may be one or more. The number of the convex lenses is not limited to one, and may be one or more.

[0026] In one embodiment, the laser is a solid-state laser or a semiconductor laser.

[0027] The above-mentioned parasitic noise suppression laser frequency shift feedback device, based on the principle of laser polarization feedback, performs different polarization modulation on the parasitic noise and signal light, so that the two are respectively transformed into the insensitive state and sensitive state of the intra-cavity light field when returning to the laser cavity. This achieves the effect that the parasitic noise does not undergo frequency shift feedback amplification, while the signal light undergoes frequency shift feedback amplification and is output. In other words, the parasitic noise intensity is reduced without affecting the return signal intensity of the target to be measured, thereby accurately obtaining information about the target to be measured.

[0028] The aforementioned parasitic noise suppression laser frequency shift feedback device can reduce the intensity of parasitic noise to near zero, while allowing the signal light to be properly amplified through the laser frequency shift feedback effect, significantly improving the device's actual response to weak signals (preventing the signal light from being drowned in parasitic noise). Compared to traditional laser frequency shift feedback devices, the parasitic noise suppression laser frequency shift feedback device of the present application adds a Faraday rotator, a half-wave plate, and a quarter-wave plate to the optical path to achieve parasitic noise suppression and normal signal light amplification. This virtually unaffects the complexity of the device, and its use is unrestricted or unaffected when the target to be measured is at close or long distances (i.e., it does not affect the device's operating distance). BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 Schematic diagram of a traditional laser frequency shift feedback device (without parasitic noise suppression function).

[0030] Figure 2 FIG. 1 is a schematic diagram of a parasitic noise suppression laser frequency shift feedback device according to an embodiment of the present application.

[0031] Figure 3 FIG. 1 is a schematic diagram of an acousto-optic frequency shifting unit according to an embodiment of the present application.

[0032] Reference numerals: 1. laser; 2. collimating lens; 3. spectroscope; 4. photodetector; 5. Faraday rotator; 6. half-wave plate; 7. first acousto-optic frequency shifter; 8. second acousto-optic frequency shifter; 9. concave lens; 10. convex lens; 11. quarter-wave plate; 12. target to be measured; 13. acousto-optic frequency shifting unit; 14. focusing lens unit; 15. signal processor; X, first direction. DETAILED DESCRIPTION

[0033] To make the above-mentioned objects, features, and advantages of the present application more clearly understood, the specific embodiments of the present application are described in detail below with reference to the accompanying drawings. The following description sets forth many specific details to facilitate a full understanding of the present application. However, the present application can be implemented in many other ways than those described herein, and those skilled in the art can make similar improvements without violating the scope of the present application. Therefore, the present application is not limited to the specific embodiments disclosed below.

[0034] In the description of this application, it should be understood that if the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise", "axial", "radial", "circumferential", etc. appear, the orientation or position relationship indicated by these terms is based on the orientation or position relationship shown in the accompanying drawings, which is only for the convenience of describing this application and simplifying the description, and does not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on this application.

[0035] In addition, if the terms "first" or "second" appear, these terms are used for descriptive purposes only and should not be understood to indicate or imply relative importance or implicitly specify the number of technical features indicated. Therefore, a feature specified as "first" or "second" may explicitly or implicitly include at least one of such features. In the description of this application, if the term "plurality" appears, "plurality" means at least two, for example, two, three, etc., unless otherwise specifically defined.

[0036] In this application, unless otherwise specified or limited, the terms "mounted," "connected," "connected," "fixed," etc., should be interpreted broadly. For example, these terms may refer to fixed connections, removable connections, or integration; mechanical connections or electrical connections; direct connections or indirect connections through an intermediary; and internal communication between two components or interaction between two components, unless otherwise specified. Those skilled in the art will understand the specific meanings of these terms in this application based on the specific circumstances.

[0037] In this application, unless otherwise expressly specified or limited, if a first feature is described as being "above" or "below" a second feature, or similar descriptions, this may mean that the first and second features are in direct contact, or that the first and second features are in indirect contact through an intermediate medium. Furthermore, when a first feature is described as being "above," "above," or "above" a second feature, it may mean that the first feature is directly above or diagonally above the second feature, or simply means that the first feature is at a higher level than the second feature. When a first feature is described as being "below," "below," or "below" a second feature, it may mean that the first feature is directly below or diagonally below the second feature, or simply means that the first feature is at a lower level than the second feature.

[0038] It should be noted that if an element is referred to as being "fixed to" or "disposed on" another element, it may be directly on the other element or there may be an intermediate element. If an element is considered to be "connected to" another element, it may be directly connected to the other element or there may be an intermediate element. If any, the terms "vertical", "horizontal", "upper", "lower", "left", "right" and similar expressions used in this application are for illustrative purposes only and do not represent the only embodiment.

[0039] Please refer to Figure 1 , Figure 1 The figure shows a schematic diagram of a conventional laser frequency shift feedback device (without parasitic noise suppression function). The conventional laser frequency shift feedback device includes: a laser 1, a collimating lens 2, a beam splitter 3, an acousto-optic frequency shifting unit 13, and a focusing lens unit 14.

[0040] Please refer to Figure 2 , Figure 2 A schematic diagram of a parasitic noise suppression laser frequency shift feedback device according to one embodiment of the present application is shown. The parasitic noise suppression laser frequency shift feedback device according to the present application comprises: a laser 1, a collimating lens 2, a beam splitter 3, a Faraday rotator 5, a half-wave plate 6, an acousto-optic frequency shifting unit 13, a focusing lens unit 14, and a quarter-wave plate 11, arranged in sequence along a first direction X. The first direction X represents the direction of light emitted from the laser 1. In actual use, the target 12 to be measured is located on the side of the quarter-wave plate 11 facing away from the focusing lens unit 14. The first direction X can be, but is not limited to, a horizontal direction. The laser beam output by the laser 1 passes through the collimating lens 2, the beam splitter 3, the Faraday rotator 5, the half-wave plate 6, the acousto-optic frequency shifting unit 13, the focusing lens unit 14, and the quarter-wave plate 11 in sequence before being irradiated onto the surface of the target 12 to be measured.

[0041] Laser 1 is used to output linearly polarized laser light, with the polarization state of the linearly polarized laser light along a first polarization direction. Collimating lens 2 is used to collimate the laser beam output by laser 1. Beam splitter 3 is used to split the collimated laser beam into a transmitted beam and a reflected beam. Faraday rotator 5 is used to rotate the polarization state of the transmitted beam by 45° before emitting it to half-wave plate 6. Half-wave plate 6 is used to rotate the polarization state of the light beam emitted by Faraday rotator 5 again by a specific angle θ in the same direction before emitting it to acousto-optic frequency shifting unit 13, so that the polarization state of the light beam emitted by half-wave plate 6 to acousto-optic frequency shifting unit 13 is in a second polarization direction, which is consistent with the polarization direction of acousto-optic frequency shifting unit 13. θ is the angle difference between the polarization direction of the light beam emitted by Faraday rotator 5 and the second polarization direction. The acousto-optic frequency shifting unit 13 is used to differentially frequency-shift the light beam emitted by the half-wave plate 6 and then transmit the differentially frequency-shifted light beam to the focusing lens unit 14. The focusing lens unit 14 is used to focus the light beam emitted by the acousto-optic frequency shifting unit 13. The quarter-wave plate 11 is used to rotate the light beam focused by the focusing lens unit 14 from a linear polarization state to a circular polarization state before irradiating it onto the target 12 to be measured. The backscattered light from the target 12 is then returned to the laser cavity of the laser 1 through the quarter-wave plate 11, the focusing lens unit 14, the acousto-optic frequency shifting unit 13, the half-wave plate 6, the Faraday rotator 5, the beam splitter 3, and the collimating lens 2. After being modulated by the laser frequency shift feedback effect, it is then output by the laser 1. Therefore, information about the target 12 can be obtained based on the laser beam output by the laser 1 after the laser frequency shift feedback effect.

[0042] A first clockwise direction and a second clockwise direction are defined, and they are opposite, i.e., when one is clockwise, the other is counterclockwise. When the transmitted light beam passes through the beam splitter 3 and enters the Faraday rotator 5, the direction in which the polarization state of the transmitted light beam is rotated by 45° is defined as the first clockwise direction. Specifically, the Faraday rotator 5 rotates the polarization state of the transmitted light beam by 45° along the first clockwise direction before exiting the beam to the half-wave plate 6. The half-wave plate 6 further rotates the polarization state of the light beam exiting the Faraday rotator 5 by a specific angle θ along the same direction (i.e., the first clockwise direction). This results in the polarization state of the light beam exiting the half-wave plate 6 and exiting the acousto-optic frequency shifting unit 13 being in the second polarization direction, i.e., the same direction as the principal axis of the acousto-optic crystal in the acousto-optic frequency shifting unit 13, and thus, consistent with the polarization direction of the acousto-optic frequency shifting unit 13.

[0043] The quarter wave plate 11 is used to adjust the phase of the light beam focused by the focusing lens unit 14 , so that the light beam focused by the focusing lens unit 14 is rotated from a linear polarization state to a circular polarization state before being irradiated onto the target 12 .

[0044] The parasitic noise suppression-type laser frequency shift feedback device described above operates on the following principle: the light beam emitted from the half-wave plate 6 is divided into two parts when passing through the acousto-optic frequency shifting unit 13 and the focusing lens unit 14. The first part directly passes through the acousto-optic frequency shifting unit 13 for differential frequency shifting, is focused by the focusing lens unit 14, and then passes through the quarter-wave plate to illuminate the target 12 to be measured. The backscattered light from the target 12 then returns to the laser cavity. This part can be called signal light. The second part does not enter the quarter-wave plate 11, but is reflected from the surfaces of the acousto-optic frequency shifting unit 13 and the focusing lens unit 14 and returns to the laser cavity. It is amplified by the laser frequency shift feedback effect and this part can be called parasitic noise. It can be seen that in the parasitic noise suppression laser frequency shift feedback device, the signal light travels twice in the optical path through the Faraday rotator 5, the half-wave plate 6, and the quarter-wave plate, while the parasitic noise travels twice in the optical path through the Faraday rotator 5 and the half-wave plate 6, but does not pass through the quarter-wave plate.

[0045] The first time the parasitic noise passes through Faraday rotator 5, its polarization state rotates by 45° in the first clockwise direction. The first time it passes through half-wave plate 6, its polarization state rotates again by a specific angle θ in the same direction (i.e., the first clockwise direction). The second time (i.e., the return process) it passes through half-wave plate 6, its polarization state rotates by the same specific angle θ in the opposite direction (i.e., the second clockwise direction). The second time (i.e., the return process) it passes through Faraday rotator 5, its polarization state rotates by 45° in the first clockwise direction. This shows that the polarization states of the parasitic noise before and after the first and second passes through Faraday rotator 5 in the optical path are orthogonal, thus reducing the intensity of the parasitic noise to zero.

[0046] When the signal light passes through Faraday rotator 5 for the first time, its polarization state rotates by 45° in the first clockwise direction. When it passes through half-wave plate 6 for the first time, its polarization state rotates by a specific angle θ in the same direction (i.e., the first clockwise direction). When it passes through quarter-wave plate 6 for the first time, its polarization state rotates from linear polarization to circular polarization. After the signal light passes through quarter-wave plate 6 for the second time (i.e., the return process), its polarization state rotates from circular polarization to linear polarization, and is also rotated by 90° in the second clockwise direction compared to the polarization state before the first pass through quarter-wave plate. When the signal light passes through half-wave plate 6 for the second time (i.e., the return process), its polarization state rotates by an equivalent angle θ in the second clockwise direction. When it passes through Faraday rotator 5 for the second time (i.e., the return process), its polarization state rotates by 45° in the first clockwise direction. This shows that the polarization state of the signal light before and after the first pass through Faraday rotator 5 in the optical path is the same, indicating that the signal light can still be amplified normally through the laser frequency shift feedback effect.

[0047] The aforementioned parasitic noise suppression laser frequency shift feedback device can reduce the intensity of parasitic noise to zero, while allowing the signal light to be normally amplified through the laser frequency shift feedback effect, significantly improving the device's actual response to weak signals (preventing the signal light from being drowned out by the parasitic noise). Compared to traditional laser frequency shift feedback devices, the parasitic noise suppression laser frequency shift feedback device of the present application adds a Faraday rotator 5, a half-wave plate 6, and a quarter-wave plate 11 to the optical path to achieve parasitic noise suppression and normal signal light amplification. This virtually unaffects the complexity of the device, and its use is unrestricted or unaffected when the target 12 is at close or long distances (i.e., it does not affect the device's operating distance).

[0048] The following further illustrates the principle of the parasitic noise suppression of the above-mentioned parasitic noise suppression laser frequency shift feedback device through the expression:

[0049] The Jones matrices of the Faraday rotator 5, the half-wave plate 6, and the quarter-wave plate 11 are Q1, Q2, and Q3, respectively. The specific expressions are as follows:

[0050]

[0051] The parasitic noise travels twice in the optical path, passing through the Faraday rotator 5 and the half-wave plate 6, but not the quarter-wave plate. Therefore, the demodulation result after the laser frequency shift feedback effect is:

[0052] (1)

[0053] In formula (1), is the output fluctuation of laser 1 caused by parasitic noise; is the steady-state output power of laser 1; is the polarization filter matrix inside the laser cavity; is the polarization state of the laser emitted by laser 1; is the light feedback coefficient, which is related to the reflectivity of the target 12 to be measured; is the amplification factor of the feedback light from laser 1, which is related to the beam frequency shift 2 Correlation, value can reach 10 6 , the weak feedback light scattered by the weak scattering surface can be greatly amplified; It is the phase quantity introduced by parasitic noise feedback.

[0054] The signal light travels back and forth twice in the optical path, passing through the Faraday rotator 5, the half-wave plate 6, and the quarter-wave plate. Therefore, the demodulation result is:

[0055] (2)

[0056] Since the direction of the emitted light from laser 1 is the first direction X, the final demodulation result is the result of the first direction X represented by equation (2), which is expressed as:

[0057] (3)

[0058] In formula (3), The output fluctuation of the laser 1 is caused by the signal light returned from the target 12. is the fixed phase of the system, is the phase quantity introduced by the signal light feedback, and the other parameters have the same representative meanings as those mentioned in formula (1).

[0059] From the demodulation results of the parasitic noise (i.e., formula (1)) and the demodulation results of the signal light (i.e., formula (3)), it can be seen that the parasitic noise intensity is reduced to 0, while the signal light can still be amplified normally by the laser frequency shift feedback effect, with G (about 10 6 ) without being affected by parasitic noise.

[0060] In summary, the above-mentioned parasitic noise suppression type laser frequency shift feedback device, based on the principle of laser polarization feedback, performs different polarization modulation on the parasitic noise and signal light, so that the two are respectively converted into the insensitive state and sensitive state of the intra-cavity light field when returning to the laser cavity, thereby achieving the effect that the parasitic noise does not undergo frequency shift feedback amplification, while the signal light undergoes frequency shift feedback amplification and is output, that is, the parasitic noise intensity is reduced without affecting the return signal intensity of the target 12 to be measured, and thus the information of the target 12 to be measured can be accurately obtained.

[0061] In one embodiment, the second polarization direction is perpendicular to the first polarization direction, and in this case, θ is 45°.

[0062] In other embodiments, the second polarization direction is not limited to being perpendicular to the first polarization direction, and θ is not limited to being 45°.

[0063] In one embodiment, the first polarization direction is along a horizontal direction, and the second polarization direction is along a vertical direction.

[0064] In other embodiments, the first polarization direction may be along other directions, and the second polarization direction may be along other directions.

[0065] refer to Figure 2 In one embodiment, the parasitic noise suppression laser frequency shift feedback device further includes a photodetector 4 and a signal processor 15. The photodetector 4 is configured to detect the laser beam output by the laser 1 after the laser frequency shift feedback effect, thereby detecting the optical signal and converting the optical signal into an electrical signal. The signal processor 15 is electrically connected to the photodetector 4 and configured to demodulate the electrical signal, thereby obtaining information about the target 12 to be measured based on the demodulation result.

[0066] Furthermore, the signal processor 15 performs synchronous phase demodulation and outputs the demodulation result to the computer, and the computer can calculate and display the information (such as displacement, etc.) of the target 12 to be measured in real time based on the demodulation result.

[0067] refer to Figure 2 In one embodiment, the photodetector 4 is arranged in the reflected light direction of the spectrometer 3 to receive the reflected light beam, that is, the laser beam output by the laser 1 after the laser frequency shift feedback effect is reflected by the spectrometer 3 and then detected by the photodetector 4.

[0068] In one embodiment, the photodetector 4 may be disposed in the tail light output direction of the laser 1 to detect the output light intensity of the laser 1 through the tail light.

[0069] In one embodiment, the modes of the laser 1 are a fundamental transverse mode and a single longitudinal mode.

[0070] refer to Figure 3 , Figure 3 Schematic diagram of an acousto-optic frequency shifting unit according to an embodiment of the present application. The acousto-optic frequency shifting unit 13 includes a first acousto-optic frequency shifter 7 and a second acousto-optic frequency shifter 8. The frequency shift amount of the light beam emitted from the 1 / 2 wave plate 6 to the acousto-optic frequency shifting unit 13 when it passes through the first acousto-optic frequency shifter 7 and the second acousto-optic frequency shifter 8 in sequence is The frequency shift of the backscattered light from the target 12 when it returns to the laser cavity through the second acousto-optic frequency shifter 8 and the first acousto-optic frequency shifter 7 is , so the round-trip frequency shift of the signal light is 2 .

[0071] refer to Figure 2 In one embodiment, the focusing lens unit 14 includes a concave lens 9 and a convex lens 10 .

[0072] In one embodiment, the number of the concave lenses 9 is not limited to one, and can be one or more.

[0073] In one embodiment, the number of the convex lenses 10 is not limited to one, and can be one or more.

[0074] The number and focal length of the concave lenses 9 and the convex lenses 10 can be set according to the specific use requirements of the light beam.

[0075] In one embodiment, the laser 1 is a solid-state laser or a semiconductor laser.

[0076] The technical features of the above-mentioned embodiments can be combined arbitrarily. In order to make the description concise, not all possible combinations of the technical features in the above-mentioned embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0077] The above-described embodiments merely represent several implementation methods of the present application. While the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the patent application. It should be noted that a person of ordinary skill in the art may make various modifications and improvements without departing from the spirit of the present application, and these modifications and improvements fall within the scope of protection of the present application. Therefore, the scope of protection of the present patent application shall be determined by the appended claims.

Claims

1. A parasitic noise suppression laser frequency shift feedback device, characterized in that: The parasitic noise suppression laser frequency shift feedback device comprises: a laser, a collimating lens, a beam splitter, a Faraday rotator, a half-wave plate, an acousto-optic frequency shifting unit, a focusing lens unit, and a quarter-wave plate arranged in sequence along a first direction, wherein the first direction is the direction of the output light of the laser; The laser is used to output linearly polarized laser light, wherein the polarization state of the linearly polarized laser light is along a first polarization direction; The collimating lens is used to collimate the laser beam output by the laser; The beam splitter is used to split the collimated laser beam into a transmitted beam and a reflected beam; The Faraday rotator is used to rotate the polarization state of the transmitted light beam by 45 degrees before emitting the polarization state to the half-wave plate; The half-wave plate is used to rotate the polarization state of the light beam emitted from the Faraday rotator again by a specific angle θ in the same direction before emitting the light beam to the acousto-optic frequency shifting unit, so that the polarization state of the light beam emitted from the half-wave plate to the acousto-optic frequency shifting unit is a second polarization direction, and the second polarization direction is consistent with the polarization direction of the acousto-optic frequency shifting unit, wherein θ is the angle difference between the polarization direction of the light beam emitted from the half-wave plate through the Faraday rotator and the second polarization direction, and the same direction is a first clockwise direction, which is the rotation direction of the Faraday rotator when the polarization state of the transmitted light beam is rotated by 45° when the transmitted light beam is transmitted from the beam splitter to the Faraday rotator; The acousto-optic frequency shifting unit is used to differentially shift the frequency of the light beam emitted by the 1 / 2 wave plate, and emit the light beam after differential frequency shifting to the focusing lens unit; The focusing lens unit is used to focus the light beam emitted by the acousto-optic frequency shifting unit; The quarter wave plate is used to rotate the light beam focused by the focusing lens unit from a linear polarization state to a circular polarization state and then irradiate the light beam to the target to be measured; The backscattered light of the target to be measured can be returned to the laser cavity of the laser through a 1 / 4 wave plate, a focusing lens unit, an acousto-optic frequency shifting unit, a 1 / 2 wave plate, a Faraday rotator, a beam splitter, and a collimating lens in sequence, and then output by the laser after being modulated under the laser frequency shift feedback effect.

2. The parasitic noise suppression laser frequency shift feedback device according to claim 1, wherein: The parasitic noise suppression laser frequency shift feedback device also includes a photodetector and a signal processor; the photodetector is used to detect the laser beam output by the laser after the laser frequency shift feedback effect, so as to detect the optical signal and convert the optical signal into an electrical signal; the signal processor is electrically connected to the photodetector and is used to demodulate the electrical signal to obtain information about the target to be measured.

3. The parasitic noise suppression laser frequency shift feedback device according to claim 2, wherein: The photoelectric detector is arranged in the direction of the reflected light of the spectroscope, and is used to receive the reflected light beam.

4. The parasitic noise suppression laser frequency shift feedback device according to claim 2, wherein: The photoelectric detector is arranged in the tail light output direction of the laser.

5. The parasitic noise suppression laser frequency shift feedback device according to claim 2, wherein: The signal processor is used to output the demodulation result to the computer, so that the computer can calculate and display the information of the target to be measured according to the demodulation result.

6. The parasitic noise suppression laser frequency shift feedback device according to claim 1, wherein: The modes of the laser are fundamental transverse mode and single longitudinal mode.

7. The parasitic noise suppression laser frequency shift feedback device according to claim 1, wherein: The acousto-optic frequency shifting unit includes a first acousto-optic frequency shifter and a second acousto-optic frequency shifter, and the first acousto-optic frequency shifter and the second acousto-optic frequency shifter are used to perform differential frequency shifting on the light beam emitted by the 1 / 2 wave plate.

8. The parasitic noise suppression laser frequency shift feedback device according to claim 1, wherein: The focusing lens assembly unit includes a concave lens and a convex lens.

9. The parasitic noise suppression type laser frequency shift feedback device according to claim 8, characterized in that: The number of the concave lenses is one or more, and the number of the convex lenses is one or more.

10. The parasitic noise suppression laser frequency shift feedback device according to claim 1, wherein: The laser is a solid-state laser or a semiconductor laser.

Images