Laser vibrometry optical device based on a cassegrain system

Abstract

The application relates to a laser vibration measurement optical device based on a Cassegrain system, which comprises a return light receiving optical system, a laser emission optical system and a heterodyne interference optical fiber system. The return light receiving optical system comprises a Cassegrain system and a receiving light interface arranged at the back side of the Cassegrain system. The laser emission optical system comprises an emission optical fiber interface and an optical path adjusting assembly, and the optical path adjusting assembly is arranged at the front side of the Cassegrain system and used for adjusting the emission optical path of the emission optical fiber interface so that the adjusted emission optical path is coaxial with the receiving optical path of the Cassegrain system. The heterodyne interference optical fiber system is connected to the receiving optical fiber interface and the emission optical fiber interface through optical fibers respectively, is used for emitting measurement light through the emission optical fiber interface, and performs differential signal detection according to reference light and return light received through the receiving optical fiber interface, so that the detection distance of laser vibration measurement is greatly improved.

Description

Technical Field

[0001] This invention relates to the field of laser vibration measurement technology, and in particular to a laser vibration measurement optical device based on the Cassegrain system. Background Technology

[0002] Laser vibration measurement is closely related to people's production and daily life. Due to its advantages such as non-contact measurement and high precision, it has been widely used in material flaw detection, mechanical system fault diagnosis, noise elimination, dynamic characteristic analysis of structural components, and verification of finite element calculation results of vibration.

[0003] However, existing laser vibrometer techniques that combine laser heterodyne interferometry and Doppler frequency shift have limitations. Firstly, they are difficult to use for long-distance detection due to optical path constraints. Secondly, parasitic reflections between the output measurement beam and the reference beam significantly affect the demodulation difficulty and signal-to-noise ratio of the Doppler vibration signal. For example, Chinese invention patent CN208458872U discloses a fiber-optic heterodyne interferometry optical path structure and a laser vibrometer. This uses an all-fiber structure to connect various optical components to form a heterodyne interferometry loop, thereby achieving laser vibrometer measurement. Although it features small size, high signal-to-noise ratio, and strong anti-interference capability, making it suitable for precision measurement, it still struggles to achieve long-distance vibration detection. Summary of the Invention

[0004] One advantage of this invention is that it provides a laser vibratory optical device based on the Cassegrain system, which can significantly increase the detection distance of laser vibratory measurement while ensuring high detection accuracy.

[0005] Another advantage of the present invention is that it provides a laser vibration measurement optical device based on a Cassegrain system. In one embodiment of the present invention, the laser vibration measurement optical device can utilize the Cassegrain system to achieve a transceiver optical system without shared lenses, thereby eliminating the influence of end-face parasitic reflections caused by lenses and helping to significantly improve the detection range of laser vibration measurement.

[0006] Another advantage of the present invention is that it provides a laser vibratory optical device based on a Cassegrain system. In one embodiment of the present invention, the laser vibratory optical device can achieve small spot focusing of laser beam energy over long distances, and after being scattered by the surface of the object being measured, it can receive more energy in the optical axis direction, which helps to improve the detection distance.

[0007] Another advantage of the present invention is that it provides a laser vibrometric optical device based on a Cassegrain system. In one embodiment of the present invention, the laser vibrometric optical device can reduce the difficulty of overall assembly by increasing the size of the secondary mirror of the Cassegrain system. At the same time, an anti-reflection coating or an anti-reflective coating is deposited at an appropriate position on the surface of the secondary mirror to reduce light loss and reduce the obstruction of the secondary mirror to the received light.

[0008] Another advantage of the present invention is that it provides a laser vibration measurement optical device based on the Cassegrain system. In one embodiment of the present invention, the laser vibration measurement optical device can receive the measurement light and the reference light into two optical fibers respectively, so as to eliminate the signal demodulation difficulties caused by parasitic reflection, which helps to improve the signal-to-noise ratio of the vibration signal, optimize the vibration signal, and improve the detection accuracy.

[0009] Another advantage of the present invention is that it provides a laser vibrometric optical device based on a Cassegrain system. In one embodiment of the present invention, the laser vibrometric optical device can adopt a dual-channel transceiver integration to simplify the overall structure and help improve fiber coupling efficiency.

[0010] Another advantage of the present invention is that it provides a laser vibratory optical device based on a Cassegrain system. In one embodiment of the present invention, the laser vibratory optical device can use a combined differential frequency-shifting heterodyne interferometry system to significantly reduce the extinction ratio, so that the parasitic frequency of the system at the carrier frequency is reduced to below the noise level, thereby eliminating parasitic frequency interference caused by the device.

[0011] Another advantage of the present invention is that it provides a laser vibrometric optical device based on a Cassegrain system. In one embodiment of the present invention, the laser vibrometric optical device can use a symmetrical focusing structure to adjust the primary mirror of the Cassegrain system with high precision, so that the scattered light signal can be stably received, which helps to achieve stable signal measurement.

[0012] Another advantage of this invention is that it provides a Cassegrain-based laser vibrometric optical device, wherein, to achieve the above-mentioned objectives, expensive materials or complex structures are not required. Therefore, this invention successfully and effectively provides a solution that not only offers a simple Cassegrain-based laser vibrometric optical device, but also increases the practicality and reliability of the Cassegrain-based laser vibrometric optical device.

[0013] To achieve at least one of the above-mentioned advantages or other advantages and objectives of the present invention, the present invention provides a laser vibrometer optical device based on a Cassegrain system, comprising:

[0014] An echo receiving optical system, wherein the echo receiving optical system includes a Cassegrain system and a receiving optical fiber interface correspondingly disposed on the rear side of the Cassegrain system, and the Cassegrain system is used to receive an echo signal for propagation to the receiving optical fiber interface;

[0015] A laser emitting optical system, wherein the laser emitting optical system includes a transmitting fiber interface and an optical path adjustment component correspondingly disposed on the transmitting side of the transmitting fiber interface, and the optical path adjustment component is located on the front side of the Cassegrain system for adjusting the transmitting optical path of the transmitting fiber interface so that the adjusted transmitting optical path is coaxial with the receiving optical path of the Cassegrain system; and

[0016] A heterodyne interferometric fiber optic system, wherein the heterodyne interferometric fiber optic system is connected to the receiving fiber optic interface and the transmitting fiber optic interface respectively via optical fibers, for transmitting measurement light through the transmitting fiber optic interface and performing differential signal detection based on the reference light and the echo light received via the receiving fiber optic interface.

[0017] According to one embodiment of this application, the echo receiving optical system further includes a beam splitter and an image sensor, wherein the beam splitter is correspondingly disposed in the optical path between the Cassegrain system and the receiving fiber optic interface, and the beam splitter is used to split the echo signal received via the Cassegrain system into two beams of echo light, so as to propagate to the receiving fiber optic interface and the image sensor respectively.

[0018] According to one embodiment of this application, the Cassegrain system includes a primary receiving mirror and a secondary receiving mirror arranged coaxially, with the primary receiving mirror located behind the secondary receiving mirror. The radial dimension of the secondary receiving mirror is greater than or equal to the radial dimension of the primary receiving mirror, and the central region of the rear surface of the secondary receiving mirror is coated with an anti-reflective coating.

[0019] According to one embodiment of this application, both the edge region of the rear surface of the receiving secondary mirror and the front surface of the receiving secondary mirror are coated with an anti-reflection film.

[0020] According to one embodiment of this application, the Cassegrain system further includes a focusing mechanism, wherein the focusing mechanism is correspondingly disposed on the primary receiving mirror, and the focusing mechanism has a symmetrical fine-tuning screw structure for adjusting the relative position between the primary receiving mirror and the secondary receiving mirror.

[0021] According to one embodiment of this application, the focusing mechanism includes a pitch adjustment mechanism, a linear guide mechanism, and a fine-tuning screw mechanism, wherein the pitch adjustment mechanism is correspondingly disposed on the periphery of the receiving primary mirror, and the linear guide mechanism and the fine-tuning screw mechanism are correspondingly disposed on the rear side of the receiving primary mirror.

[0022] According to one embodiment of this application, the beam splitter is a dichroic mirror, used to reflect one echo signal received via the Cassegrain system into one reflected echo light and one transmitted echo light, so as to propagate to the receiving fiber optic interface and the image sensor respectively.

[0023] According to one embodiment of this application, the echo receiving optical system further includes an achromatic system correspondingly disposed in the optical path between the beam splitter and the receiving fiber interface, for shaping one echo beam split by the beam splitter to propagate to the receiving fiber interface.

[0024] According to one embodiment of this application, the achromatic system includes a biconvex lens, a biconcave lens, and a quadrature surface mirror sequentially disposed in the optical path between the beam splitter and the receiving fiber interface.

[0025] According to one embodiment of this application, the optical path adjustment component of the laser emitting optical system includes a first reflector correspondingly disposed in front of the Cassegrain system for reflectively bending the emitting optical path of the emitting fiber interface so that the emitting optical path after being bent by the first reflector is coaxial with the receiving optical path of the Cassegrain system.

[0026] According to one embodiment of this application, the optical path adjustment component further includes a second reflector correspondingly disposed on the light-incident side of the first reflector, and both the first reflector and the second reflector are cylindrical 45° reflectors.

[0027] According to one embodiment of this application, the laser emitting optical system further includes a beam shaping component correspondingly disposed in the optical path between the emitting fiber interface and the optical path adjustment component, for shaping the laser beam emitted via the emitting fiber interface to propagate to the optical path adjustment component.

[0028] According to one embodiment of this application, the beam shaping assembly includes a plano-convex aspherical lens, a biconcave spherical lens, a first biconvex spherical lens, and a second biconvex spherical lens, which are sequentially disposed in the optical path between the transmitting fiber interface and the optical path adjustment assembly.

[0029] According to one embodiment of this application, the heterodyne interferometric fiber optic system includes a laser transmitter, a laser beam splitter, a frequency shifter assembly, a fiber optic combiner / splitter, and a detector. The input end of the laser beam splitter is connected to the laser transmitter via the optical fiber, and the output end of the laser beam splitter is connected to the transmitting fiber interface and the frequency shifter assembly via the optical fiber, respectively. The combining end of the fiber optic combiner / splitter is connected to the detector via the optical fiber, and the splitting end of the fiber optic combiner / splitter is connected to the receiving fiber interface and the frequency shifter assembly via the optical fiber, respectively.

[0030] According to one embodiment of this application, the frequency shifter assembly includes a first frequency shifter and a second frequency shifter in the optical fiber sequentially disposed between the laser beam splitter and the optical fiber combining and splitting device, and the frequency shift difference between the first frequency shifter and the second frequency shifter is neither equal to the frequency shift frequency of the first frequency shifter nor equal to the frequency shift frequency of the second frequency shifter.

[0031] According to one embodiment of this application, the detector is a balanced photodetector, and the balanced photodetector has at least two photodiodes.

[0032] According to one embodiment of this application, the heterodyne interferometric fiber system further includes a fiber attenuator correspondingly disposed in the fiber between the laser beam splitter and the frequency shifter assembly for attenuating and fine-tuning the reference light split by the laser beam splitter.

[0033] According to one embodiment of this application, the heterodyne interferometric fiber system further includes an indicator laser for emitting indicator light and a fiber wavelength division multiplexing device, wherein the fiber wavelength division multiplexing device is correspondingly disposed in the fiber between the laser beam splitter and the transmitting fiber interface, and the indicator laser is connected to the fiber wavelength division multiplexing device through the fiber.

[0034] According to one embodiment of this application, the laser emitter is an infrared narrow linewidth laser for emitting infrared laser, and the indicator laser is for emitting visible laser. Attached Figure Description

[0035] Figure 1 This is a block diagram of a laser vibrometer optical device based on a Cassegrain system according to an embodiment of the present invention.

[0036] Figure 2 A schematic diagram of the structure of the laser vibrometer optical device based on the Cassegrain system according to the above embodiment of the present invention is shown;

[0037] Figure 3An example of the echo receiving optical system and the laser emitting optical system in the Cassegrain system-based laser vibrometer optical device according to the above embodiments of the present invention is shown.

[0038] Key component symbols: 1. Laser vibrometer optical device based on Cassegrain system; 10. Echo receiving optical system; 11. Cassegrain system; 110. Receiving optical path; 111. Primary receiving mirror; 1110. Plano-concave mirror; 112. Secondary receiving mirror; 1120. Meniscus lens; 1121. Rear surface; 1122. Front surface; 113. Focusing mechanism; 1131. Pitch adjustment mechanism; 1132. Linear guide mechanism; 1133. Fine-tuning screw mechanism; 12. Fiber optic interface; 13. Beam splitter; 131. Dichroic mirror; 14. Image sensor; 141. Camera; 15. Achromatic system; 151. Biconvex lens; 152. Biconcave lens; 153. Quadratic surface mirror; 20. Laser emitting optical system; 21. 1. Transmitting fiber optic interface; 210. Transmitting optical path; 22. Optical path adjustment assembly; 221. First reflector; 222. Second reflector; 220. Cylindrical 45° reflector; 23. Beam shaping assembly; 231. Plano-convex aspherical lens; 232. Biconcave spherical lens; 233. First biconvex spherical lens; 234. Second biconvex spherical lens; 30. Heterodyne interference fiber optic system; 300. Optical fiber; 31. Laser transmitter; 311. Infrared narrow linewidth laser; 32. Laser beam splitter; 33. Frequency shifter assembly; 331. First frequency shifter; 332. Second frequency shifter; 34. Fiber optic combining and splitting device; 35. Detector; 351. Balanced photodetector; 36. Fiber optic attenuator; 37. Indicator laser; 38. Fiber optic wavelength division multiplexer.

[0039] The above description of the main component symbols, together with the accompanying drawings and specific embodiments, provides a more detailed explanation of the present invention. Detailed Implementation

[0040] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0041] It should be noted that when a component is said to be "installed on" another component, it can be directly on the other component or it may be in a component that is centered on it. When a component is said to be "set on" another component, it can be directly set on the other component or it may also be in a component that is centered on it. When a component is said to be "fixed to" another component, it can be directly fixed to the other component or it may also be in a component that is centered on it.

[0042] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the specification of this invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The term "or / and" as used herein includes any and all combinations of one or more of the associated listed items.

[0043] To address the problem that existing heterodyne interferometric laser vibrometer technology is difficult to achieve long-distance detection, this application provides a laser vibrometer optical device based on a Cassegrain system. By combining the Cassegrain telescope system and the optical path of heterodyne interferometric laser vibrometer, the transceiver optical system does not share a common lens, thereby eliminating end-face parasitic reflections caused by the lens and significantly improving the detection distance of laser vibrometer.

[0044] Specifically, see the attached document. Figure 1 and Figure 2 As shown, an embodiment of the present invention provides a laser vibratory optical device 1 based on a Cassegrain system, which may include an echo receiving optical system 10, a laser emitting optical system 20, and a heterodyne interferometric fiber system 30. The echo receiving optical system 10 may include a Cassegrain system 11 and a receiving fiber interface 12, wherein the receiving fiber interface 12 is correspondingly disposed on the rear side of the Cassegrain system 11, and the Cassegrain system 11 is used to receive echo signals for propagation to the receiving fiber interface 12. The laser emitting optical system 20 may include a transmitting fiber interface 21 and an optical path adjustment component 22, wherein the optical path adjustment component 22 is correspondingly disposed on the transmitting side of the transmitting fiber interface 21, and the optical path adjustment component 22 is located on the front side of the Cassegrain system 11, used to adjust the transmitting optical path 210 of the transmitting fiber interface 21 so that the adjusted transmitting optical path 210 is coaxial with the receiving optical path 110 of the Cassegrain system 11. The heterodyne interferometric fiber system 30 can be connected to the receiving fiber interface 12 and the transmitting fiber interface 21 via fiber 300, respectively, for transmitting measurement light through the transmitting fiber interface 21 and performing differential signal detection based on the reference light and the echo light received via the receiving fiber interface 12.

[0045] It is worth noting that the Cassegrain-based laser vibrometer optical device 1 of this application utilizes the cooperation between the Cassegrain system 11 and the optical path adjustment component 22 to separate the optical path of the echo receiving optical system 10 from the optical path of the laser emitting optical system 20, preventing interference between them. In other words, there are no shared lenses between the echo receiving optical system 10 and the laser emitting optical system 20, ensuring that no end-face reflection light is transmitted back to the interferometer system, thereby eliminating end-face parasitic reflections caused by lenses and significantly improving the detection range of laser vibrometers. Simultaneously, the emission optical path 210, adjusted by the optical path adjustment component 22, is coaxial with the receiving optical path 110 of the Cassegrain system 11. This allows the measurement light emitted by the laser emitting optical system 20 to receive more echo signals along the optical axis after being scattered by the surface of the object being measured, further enhancing the detection range of laser detection.

[0046] It is understandable that parasitic reflection is a beam of light without actual detection information caused by reflected light from multiple media end faces in a single lens that transmits and receives simultaneously returning to the interference optical path system. This often occurs at fiber end faces, lens surfaces, and structural components where stray light is coupled into the interference optical path. The presence of parasitic reflection results in a signal carrier frequency that always contains a large amplitude signal without detection surface information, which significantly limits the detection distance, especially in the case of weak signal transmission. The laser vibrometer optical device 1 based on the Cassegrain system described in this application eliminates parasitic reflection at the transceiver end through dual-path transceiver integration, thereby enabling effective detection of weak signals over long distances.

[0047] More specifically, such as Figure 1 and Figure 2As shown, the echo receiving optical system 10 may further include a beam splitter 13 and an image sensor 14. The beam splitter 13 is correspondingly disposed in the optical path between the Cassegrain system 11 and the receiving fiber optic interface 12. The beam splitter 13 is used to split the echo signal received via the Cassegrain system 11 into two beams of echo light, which are then propagated to the receiving fiber optic interface 12 and the image sensor 14, respectively. In other words, the beam splitter 13 of this application splits the echo signal received via the Cassegrain system 11 into two beams of echo light. One beam of echo light is propagated to the receiving fiber optic interface 12 and transmitted through an optical fiber to the heterodyne interferometer fiber optic system 30 for signal detection; the other beam of echo light is propagated to the image sensor 14 for image reception and imaging, in order to determine whether the measurement light illuminates the surface of the object being measured. It is understood that, since the Cassegrain-based laser vibration optical device 1 of this application can achieve long-distance (such as 300 meters) laser detection, it is difficult to determine whether the emitted measurement light has irradiated the surface of the object being measured by the human eye alone. Therefore, the Cassegrain-based laser vibration optical device 1 of this application can directly acquire the surface image information of the object being measured by means of the echo receiving optical system 10, so as to determine the position of the light spot formed by the measurement light on the surface of the object being measured from a distance, and to perform laser vibration measurement in a convenient and accurate manner.

[0048] For example, such as Figure 3 As shown, the Cassegrain system 11 in the echo receiving optical system 10 may include, but is not limited to, a primary receiving mirror 111 and a secondary receiving mirror 112 arranged coaxially, with the primary receiving mirror 111 located behind the secondary receiving mirror 112. This allows the echo signal propagating along the receiving optical path 110 to be first reflected by the primary receiving mirror 111 to propagate to the secondary receiving mirror 112, and then reflected back by the secondary receiving mirror 112 to pass through the primary receiving mirror 111 and propagate to the beam splitter 13. It is understood that in the Cassegrain-based laser vibrometer optical device 1 of this application, the optical path adjustment assembly 22 is located in front of the secondary receiving mirror 112, and the beam splitter 13 is located behind the primary receiving mirror 111.

[0049] Optionally, the primary receiving mirror 111 in the Cassegrain system 11 may be, but is not limited to, a plano-concave mirror 1110 with a central through-hole, wherein the concave surface of the plano-concave mirror 1110 faces the secondary receiving mirror 112, and the concave surface of the plano-concave mirror 1110 is coated with an anti-reflection film, such that the echo signal propagating along the receiving optical path 110 is first reflected by the concave surface of the plano-concave mirror 1110 to propagate to the secondary receiving mirror 112, and then reflected back by the secondary receiving mirror 112 to pass through the central through-hole of the plano-concave mirror 1110 and propagate to the beam splitter 13. It is understood that in other examples of this application, the concave surface of the plano-concave mirror 1110 may also be coated with a metal reflective film or other types of reflective film systems; or, the primary receiving mirror 111 may also be implemented as other types of mirrors, which will not be elaborated further in this application.

[0050] Optionally, the receiving secondary mirror 112 in the Cassegrain system 11 may, but is not limited to, be implemented as a meniscus lens 1120, wherein the convex surface of the meniscus lens 1120 faces the receiving primary mirror 111, and the convex surface of the meniscus lens 1120 is coated with a metallic reflective film for reflecting the echo signal reflected by the plano-concave mirror 1110 back to the plano-concave mirror 1110. It is understood that the convex surface of the meniscus lens 1120 may also be coated with other types of reflective films; or, the receiving secondary mirror 112 may also be implemented as other types of mirrors, which will not be elaborated further in this application.

[0051] Preferably, the radial dimension of the secondary receiving mirror 112 is greater than or equal to the radial dimension of the primary receiving mirror 111, and the central region of the rear surface 1121 of the secondary receiving mirror 112 is coated with an anti-reflective film, such that the echo signal propagating along the receiving optical path 110 first passes through the secondary receiving mirror 112 and then propagates to the primary receiving mirror 111 for reflection. It is understood that the rear surface 1121 of the secondary receiving mirror 112 can be implemented as the convex surface of the meniscus lens 1120, and the anti-reflective film is preferably implemented as a metallic reflective film.

[0052] It is worth noting that, compared to existing Cassegrain telescopes, the radial dimension of the receiving secondary mirror 112 in the Cassegrain system 11 of this application is increased. This not only facilitates overall assembly but also allows the echo signal propagating along the receiving optical path 110 to be modulated or focused by the receiving secondary mirror 112 before being reflected by the receiving primary mirror 111. This helps to shorten the subsequent focusing distance and facilitates a reduction in the overall size of the echo receiving optical system 10. It is understood that in other examples of this application, the radial dimension of the receiving secondary mirror 112 may also be smaller than that of the receiving primary mirror 111, meaning that the detection range can still be improved to some extent using a conventional Cassegrain system.

[0053] More preferably, such as Figure 3 As shown, both the edge region of the rear surface 1121 and the front surface 1122 of the receiving secondary mirror 112 are coated with anti-reflection films to increase the transmittance of the echo signal, thereby reducing the obstruction of the echo signal by the receiving secondary mirror 112 and helping to reduce the energy loss of the echo signal. In other words, the concave surface of the meniscus lens 1120 is coated with an anti-reflection film, the central region of the convex surface of the meniscus lens 1120 is coated with a metallic reflective film, and the edge region of the convex surface of the meniscus lens 1120 is coated with an anti-reflection film. It is understood that the edge region in this application refers to the region located around the central region, and the extent of the central region is determined according to the actual operating requirements of the Cassegrain system 11.

[0054] Most preferably, the antireflective coating deposited on the receiving secondary mirror 112 of this application is an antireflective coating within a specific wavelength spectral range, used to increase the transmittance of the echo signal without increasing the transmittance of light of other wavelengths. That is, the antireflective wavelength range of the antireflective coating covers the effective wavelength of the echo signal, reducing the energy loss of the echo signal and improving the signal-to-noise ratio of the echo signal.

[0055] According to the above embodiments of this application, as Figure 3 As shown, the Cassegrain system 11 of this application may further include a focusing mechanism 113, wherein the focusing mechanism 113 is correspondingly disposed on the receiving primary mirror 111, for adjusting the relative position of the receiving primary mirror 111 and the receiving secondary mirror 112, so as to adjust the focal length of the Cassegrain system 11.

[0056] It is worth noting that existing Cassegrain telescopes are typically used in telescope systems, and their focusing mechanisms are designed as single-sided hinge mechanisms. When using screw adjustment, torsional torque is generated, and due to the error gap between the screw focusing mechanisms, field of view shift occurs before and after the primary mirror is focused. Although this can be received in telescope systems, laser vibrometer systems are extremely sensitive to coupling angle and position deviations because they require the echo signal to be coupled into the optical fiber. Therefore, the existing single-sided screw side focusing structure cannot meet the accuracy requirements of laser vibrometers.

[0057] To solve this problem, such as Figure 3As shown, the focusing mechanism 113 of the Cassegrain system 11 of this application preferably includes a pitch adjustment mechanism 1131, a linear guide mechanism 1132, and a fine-tuning screw mechanism 1133. The pitch adjustment mechanism 1131 is symmetrically arranged around the periphery of the primary receiving mirror 111 and is used to adjust the pitch angle of the primary receiving mirror 111. The linear guide mechanism 1132 and the fine-tuning screw mechanism 1133 are correspondingly arranged on the rear side of the primary receiving mirror 111 and are used to drive the primary receiving mirror 111 to move along the linear guide mechanism 1132 via the fine-tuning screw mechanism 1133, thereby adjusting the center distance between the primary receiving mirror 111 and the secondary receiving mirror 112. In other words, the focusing mechanism 113 of this application has a symmetrical fine-tuning screw structure, which can adjust the center distance between the primary receiving mirror 111 and the secondary receiving mirror 112 with high precision to achieve stable signal measurement.

[0058] For example, the pitch adjustment mechanism 1131 adjusts the pitch receiving angle of the receiving main mirror 111 by screwing in and out three sets of precision adjusters evenly distributed around the circumference and mounted on the main mirror mounting bracket; the fine adjustment screw mechanism 1133 and the pitch adjustment mechanism 1131 are paired with a high-precision linear guide rail, which can achieve a linear travel accuracy of 2µm when moving back and forth to focus, so as to stably receive the scattered echo signal and achieve stable signal measurement.

[0059] According to the above embodiments of this application, the receiving fiber optic interface 12 in the echo receiving optical system 10 is implemented as a connector that couples the echo signal (i.e., laser echo) propagating in space into the fiber optic cable, such as a coupling fiber optic connector suitable for connecting the fiber optic cable 300.

[0060] In addition, such as Figure 3 As shown, the beam splitter 13 in the echo receiving optical system 10 may, but is not limited to, be implemented as a dichroic mirror 131, wherein the dichroic mirror 131 is correspondingly disposed on the rear side of the Cassegrain system 11, for reflecting one echo signal received via the Cassegrain system 11 into one reflected echo light and one transmitted echo light, so as to propagate to the receiving fiber optic interface 12 and the image sensor 14 respectively.

[0061] For example, such as Figure 3As shown, the receiving fiber optic interface 12 and the image sensor 14 are respectively located on the reflection side and transmission side of the dichroic mirror 131. The dichroic mirror 131 is used to reflect one echo signal received via the Cassegrain system 11, splitting it into a reflected echo light to propagate to the receiving fiber optic interface 12 and a transmitted echo light to propagate to the image sensor 14 for imaging. It is understood that in other examples of this application, the receiving fiber optic interface 12 and the image sensor 14 may also be located on the transmission side and reflection side of the dichroic mirror 131, respectively, such that one reflected echo light split by the dichroic mirror 131 is propagated to the image sensor 14 for imaging, and one transmitted echo light split by the dichroic mirror 131 is propagated to the receiving fiber optic interface 12.

[0062] According to the above embodiments of this application, as Figure 2 and Figure 3 As shown, the echo receiving optical system 10 may further include an achromatic system 15, wherein the achromatic system 15 is disposed in the optical path between the beam splitter 13 and the receiving fiber interface 12, for shaping the echo light beam split by the beam splitter 13 to propagate to the receiving fiber interface 12.

[0063] Specifically, such as Figure 3 As shown, the achromatic system 15 may include a biconvex lens 151, a biconcave lens 152, and a quadrature surface mirror 153 sequentially disposed between the beam splitter 13 and the receiving fiber interface 12. This allows the echo light, split by the beam splitter 13, to first pass through the biconvex lens 151 and the biconcave lens 152 sequentially, and then be reflected by the quadrature surface mirror 153, so that it is shaped and propagated to the receiving fiber interface 12 and coupled into the optical fiber 300. In other words, the achromatic system 15 of this application uses transmission and reflection to shape and couple the echo light into the optical fiber, which helps to achieve the highest fiber coupling efficiency and best imaging quality confocal adjustment function at the receiving primary mirror 111, making it practical, simple, and convenient.

[0064] It is worth noting that the biconvex lens 151 and biconcave lens 152 in the achromatic system 15 can, but are not limited to, be spherical or aspherical lenses. Furthermore, the image sensor 14 in the echo-receiving optical system 10 can, but is not limited to, be implemented as a camera 141. Preferably, the camera 141 is a visible light camera, used to acquire image information of the probe spot on the surface of the object being measured using the echo-receiving optical system 10, in order to determine the position illuminated by the measurement light emitted by the laser-emitting optical system 20.

[0065] It is understood that the Cassegrain system 11 and the achromatic system 15 in the echo receiving optical system 10 of this application can achieve an echo signal energy reception of not less than 70%, and the achromatic system 15 can be, but is not limited to, implemented as the optical system utilizing refraction and reflection described above.

[0066] According to the above embodiments of this application, the transmitting fiber interface 21 in the laser emitting optical system 20 can be implemented as a connector that emits measurement light (i.e., laser signal) propagating in the fiber into space, i.e., a coupling fiber connector suitable for connecting the fiber 300.

[0067] In addition, such as Figure 2 and Figure 3 As shown, the optical path adjustment component 22 in the laser emitting optical system 20 may include a first reflector 221 correspondingly disposed in front of the Cassegrain system 11, for reflectively bending the emitting optical path 210 of the emitting fiber interface 21, such that the emitting optical path 210 bent by the first reflector 221 is coaxial with the receiving optical path 110 of the Cassegrain system 11. That is, the measurement light emitted through the emitting fiber interface 21, after being reflected by the first reflector 221, can propagate forward along the optical axis of the Cassegrain system 11.

[0068] Optionally, the optical path adjustment assembly 22 may further include a second reflector 222 correspondingly disposed on the light-incident side of the first reflector 221, for reflectively bending the transmitting optical path 210 of the transmitting fiber interface 21, so that the transmitting optical path 210, after being bent by the second reflector 222, extends to the first reflector 221 and is reflected and bent by the second reflector 222. In other words, the second reflector 222 is located in the optical path between the first reflector 221 and the transmitting fiber interface 21, for reflectively bending the transmitting optical path 210 of the transmitting fiber interface 21 twice, so that the transmitting optical path 210 after the two bends is coaxial with the receiving optical path 110 of the Cassegrain system 11, which helps to more rationally arrange the position of the transmitting fiber interface 21 and reduce the size of the device.

[0069] Preferably, such as Figure 3 As shown, both the first reflector 221 and the second reflector 222 are implemented as cylindrical 45° reflectors 220, which helps to achieve the effect of coaxial adjustment between the transmitting optical path 210 and the receiving optical path 110. It is understood that in other examples of this application, the first reflector 221 and the second reflector 222 can also be implemented as plane reflectors or total internal reflection prisms arranged at 45°, as long as the required optical path adjustment effect can be achieved; this application will not elaborate further on this.

[0070] Optionally, such as Figure 2 and Figure 3 As shown, the laser emitting optical system 20 may further include a beam shaping component 23, wherein the beam shaping component 23 is correspondingly disposed in the optical path between the emitting fiber interface 21 and the optical path adjustment component 22, for shaping the laser beam emitted via the emitting fiber interface 21 to propagate to the optical path adjustment component 22, which helps to realize long-distance measurement of vibration signals without focusing at the emitting end.

[0071] It is worth noting that, since the first reflector 221 and the second reflector 222 bend the emitting optical path 210 at right angles twice, and the emitting optical path 210 after the two bends is coaxial with the receiving optical path 110, the emitting optical path 210 of the emitting fiber interface 21 is parallel to the receiving optical path 110 of the Cassegrain system 11 before bending. This allows the beam shaping component 23 to be arranged in parallel on the side of the Cassegrain system 11, which helps to increase the compactness of the device structure.

[0072] Preferably, such as Figure 3 As shown, the beam shaping assembly 23 includes a plano-convex aspherical lens 231, a biconcave spherical lens 232, a first biconvex spherical lens 233, and a second biconvex spherical lens 234, sequentially disposed in the optical path between the transmitting fiber interface 21 and the optical path adjustment assembly 22. These components are used to focus or collimate the measurement light emitted via the transmitting fiber interface 21, thereby shaping the laser beam and making it suitable for long-distance laser vibration measurement. It is understood that the beam shaping assembly 23 of this application can also achieve beam focusing or collimation at different distances by adjusting the lens spacing to meet the laser vibration measurement requirements at different distances. Furthermore, the various lenses in the beam shaping assembly 23 of this application can be, but are not limited to, spherical or aspherical lenses, and their materials can also be glass or plastic; these details will not be elaborated further in this application.

[0073] It is worth mentioning that, generally, the laser beam emitted via the transmitting fiber interface 21 includes not only measuring light for measuring vibration signals, but also indicating light for indicating the vibration measurement position. The measuring light may include, but is not limited to, infrared light with wavelengths of 1550 nm, 1310 nm, or 850 nm; while the indicating light may include, but is not limited to, visible light with wavelengths of 635 nm or 520 nm. Therefore, the laser emitting optical system 20 of this application preferably employs a dual-spectrum shaping system to achieve focusing or collimation of the measuring light and the indicating light at a specific distance, which helps to reduce energy loss during beam propagation in air.

[0074] According to the above embodiments of this application, as Figure 1 and Figure 2 As shown, the heterodyne interferometric fiber optic system 30 of this application may include, but is not limited to, a laser transmitter 31, a laser beam splitter 32, a frequency shifter assembly 33, a fiber optic combiner / splitter 34, and a detector 35. The input end of the laser beam splitter 32 is connected to the laser transmitter 31 via the fiber optic cable 300, and the output end of the laser beam splitter 32 is connected to the transmitting fiber optic interface 21 and the frequency shifter assembly 33 via the fiber optic cable 300, respectively. The combining end of the fiber optic combiner / splitter 34 is connected to the detector 35 via the fiber optic cable 300, and the splitting end of the fiber optic combiner / splitter 34 is connected to the receiving fiber optic interface 12 and the frequency shifter assembly 33 via the fiber optic cable 300, respectively. Thus, the laser emitted by the laser emitter 31 is first split into a measurement beam and a reference beam by the laser beam splitter 32. The measurement beam is transmitted through the optical fiber 300 to the transmitting optical fiber interface 21 for emission into space, while the reference beam is transmitted through the optical fiber 300 to the frequency shifter assembly 33 for heterodyne adjustment. Simultaneously, the echo light received through the receiving optical fiber interface 12 is transmitted through the optical fiber 300 and the reference beam adjusted by the frequency shifter assembly 33 to the optical fiber combining and splitting device 34, so that it is synchronously transmitted through the optical fiber 300 to the detector 35, thereby realizing the detection of balanced differential optical signals at the detector 35 to obtain laser vibration information.

[0075] Preferably, such as Figure 2 As shown, the frequency shifter assembly 33 of the heterodyne interferometric fiber system 30 includes a first frequency shifter 331 and a second frequency shifter 332 sequentially disposed in the fiber 300 between the laser beam splitter 32 and the fiber combiner / splitter 34. The frequency shift difference between the first frequency shifter 331 and the second frequency shifter 332 is neither equal to the frequency shifting frequency of the first frequency shifter 331 nor equal to the frequency shifting frequency of the second frequency shifter 332. This helps to obtain an equal transmission extinction ratio, so that the interference signal of the mixing is below the noise floor, thereby greatly improving the detection distance.

[0076] It is worth noting that, since the frequency shifter is a diffractive optical device, when used alone in a heterodyne interference optical path, crosstalk of the diffraction orders will result in mixed interference signals. These mixed interference signals will interfere with the conditioning of subsequent effective detection signals. Therefore, the frequency shifter component 33 of the heterodyne interference fiber system 30 of this application adopts a combined frequency shift, and the frequency shift of the combined output is not equal to the frequency shift value of any single device. That is, the frequency shift difference Δf between the first frequency shifter 331 and the second frequency shifter 332 is not equal to the frequency shift frequency f1 of the first frequency shifter 331, and is not equal to the frequency shift frequency f2 of the second frequency shifter 332, i.e., Δf = (f1 - f2) ≠ f1 and Δf = (f1 - f2) ≠ f2. It can be understood that the heterodyne interference fiber system 30 of this application adopts a combined differential frequency shift method, which greatly reduces the extinction ratio, thereby reducing the parasitic frequency of the system below the noise at the carrier frequency, thus eliminating parasitic frequency interference caused by the devices.

[0077] For example, the frequency shifter assembly 33 may be implemented, but is not limited to, an 80MHz difference frequency of 150MHz and 70MHz, or an 80MHz difference frequency of 320MHz and 240MHz, etc.

[0078] Furthermore, the detector 35 of this application is implemented as a balanced photodetector 351, and the balanced photodetector 351 has at least two photodiodes. It is understood that, compared to ordinary photodetectors, the balanced photodetector 351 of this application can achieve excellent common-mode rejection ratio (CMRR), thereby better reducing noise, so as to obtain minute changes in the signal optical path from interference noise and improve the accuracy of laser vibration measurement.

[0079] According to the above embodiments of this application, the beam splitting ratio of the laser beam splitter 32 can be, but is not limited to, 99:1, 90:10, 80:20, or 70:30. To achieve beam distribution under different detection requirements, the heterodyne interferometric fiber system 30 can further include a fiber attenuator 36, which is correspondingly disposed in the fiber 300 between the laser beam splitter 32 and the frequency shifter assembly 33. This allows the reference light split by the laser beam splitter 32 to first be transmitted to the fiber attenuator 36 for attenuation fine-tuning, and then transmitted to the frequency shifter assembly 33 for heterodyne adjustment.

[0080] It is worth noting that the laser emitter 31 may, but is not limited to, be implemented as an infrared narrow linewidth laser 311 for emitting infrared laser with a specific wavelength, such as infrared light with a wavelength of 1550nm.

[0081] In addition, to ensure that the human eye can see the location of the emitted measuring light, such as Figure 2 As shown, the heterodyne interferometric fiber optic system 30 of this application may further include an indicator laser 37 and a fiber wavelength division multiplexer 38, wherein the fiber wavelength division multiplexer 38 is correspondingly disposed in the fiber optic cable 300 between the laser beam splitter 32 and the transmitting fiber optic interface 21, and the indicator laser 37 is connected to the fiber wavelength division multiplexer 38 through the fiber optic cable 300, such that the indicator light emitted by the indicator laser 37 and the measurement light split by the laser beam splitter 32 are first coupled through the fiber wavelength division multiplexer 38 and then transmitted to the transmitting fiber optic interface 21 for transmission.

[0082] It is understood that the indicator laser 37 of this application is used to emit visible laser light, that is, the wavelength of the indicator light is within the visible light band, so that the laser beam emitted through the transmitting fiber interface 21 is a dual-band laser, that is, including invisible measurement light and visible indicator light. In this way, when performing laser vibration measurement, people can directly see the illumination spot formed by the indicator light on the surface of the object being measured, that is, the position illuminated by the measurement light, which is the actual position of the laser vibration measurement at this time.

[0083] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0084] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A laser vibrometer optical device based on the Cassegrain system, characterized in that, include: An echo receiving optical system, wherein the echo receiving optical system includes a Cassegrain system and a receiving optical fiber interface correspondingly disposed on the rear side of the Cassegrain system, and the Cassegrain system is used to receive an echo signal for propagation to the receiving optical fiber interface; A laser emitting optical system, comprising a transmitting fiber interface and an optical path adjustment component correspondingly disposed on the transmitting side of the transmitting fiber interface, wherein the optical path adjustment component is located in front of the Cassegrain system and is used to adjust the transmitting optical path of the transmitting fiber interface so that the adjusted transmitting optical path is coaxial with the receiving optical path of the Cassegrain system; and a heterodyne interferometry fiber system, wherein the heterodyne interferometry fiber system is connected to the receiving fiber interface and the transmitting fiber interface respectively via optical fibers, and is used to emit measurement light through the transmitting fiber interface and perform differential signal detection based on reference light and echo light received via the receiving fiber interface.

2. The laser vibrometer optical device based on the Cassegrain system as described in claim 1, characterized in that, The echo receiving optical system further includes a beam splitter and an image sensor, wherein the beam splitter is correspondingly disposed in the optical path between the Cassegrain system and the receiving fiber optic interface, and the beam splitter is used to split the echo signal received via the Cassegrain system into two echo beams, which are then propagated to the receiving fiber optic interface and the image sensor, respectively.

3. The laser vibrometer optical device based on the Cassegrain system as described in claim 2, characterized in that, The Cassegrain system includes a primary receiving mirror and a secondary receiving mirror arranged coaxially, with the primary receiving mirror located behind the secondary receiving mirror. The radial dimension of the secondary receiving mirror is greater than or equal to the radial dimension of the primary receiving mirror, and the central region of the rear surface of the secondary receiving mirror is coated with an anti-reflective coating.

4. The laser vibrometer optical device based on the Cassegrain system as described in claim 3, characterized in that, The edge region of the rear surface of the receiving secondary mirror and the front surface of the receiving secondary mirror are both coated with an anti-reflection film.

5. The laser vibrometer optical device based on the Cassegrain system as described in claim 3, characterized in that, The Cassegrain system further includes a focusing mechanism, wherein the focusing mechanism is correspondingly disposed on the primary receiving mirror, and the focusing mechanism has a symmetrical fine-tuning screw structure for adjusting the relative position between the primary receiving mirror and the secondary receiving mirror.

6. The laser vibrometer optical device based on the Cassegrain system as described in claim 5, characterized in that, The focusing mechanism includes a pitch adjustment mechanism, a linear guide mechanism, and a fine-tuning screw mechanism, wherein the pitch adjustment mechanism is correspondingly disposed on the periphery of the receiving primary mirror, and the linear guide mechanism and the fine-tuning screw mechanism are correspondingly disposed on the rear side of the receiving primary mirror.

7. The laser vibrometer optical device based on the Cassegrain system as described in claim 2, characterized in that, The beam splitter is a dichroic mirror, used to reflect one echo signal received by the Cassegrain system into one reflected echo light and one transmitted echo light, so that they can be propagated to the receiving fiber optic interface and the image sensor, respectively.

8. The laser vibrometer optical device based on the Cassegrain system as described in claim 2, characterized in that, The echo receiving optical system further includes an achromatic system correspondingly disposed in the optical path between the beam splitter and the receiving fiber interface, for shaping the echo light beam split by the beam splitter to propagate to the receiving fiber interface.

9. The laser vibrometer optical device based on the Cassegrain system as described in claim 8, characterized in that, The achromatic system includes a biconvex lens, a biconcave lens, and a quadrature surface mirror, which are sequentially arranged in the optical path between the beam splitter and the receiving fiber interface.

10. The laser vibrometer optical device based on the Cassegrain system as described in any one of claims 1 to 9, characterized in that, The optical path adjustment component of the laser emitting optical system includes a first reflector correspondingly disposed in front of the Cassegrain system, used to reflectively bend the emitting optical path of the emitting fiber interface so that the emitting optical path after being bent by the first reflector is coaxial with the receiving optical path of the Cassegrain system.

11. The laser vibrometer optical device based on the Cassegrain system as described in claim 10, characterized in that, The optical path adjustment assembly further includes a second reflector correspondingly disposed on the light-incident side of the first reflector, and both the first reflector and the second reflector are cylindrical 45° reflectors.

12. The laser vibrometer optical device based on the Cassegrain system as described in claim 11, characterized in that, The laser emitting optical system further includes a beam shaping component correspondingly disposed in the optical path between the emitting fiber interface and the optical path adjustment component, for shaping the laser beam emitted via the emitting fiber interface to propagate to the optical path adjustment component.

13. The laser vibrometer optical device based on the Cassegrain system as described in claim 12, characterized in that, The beam shaping assembly includes a plano-convex aspherical lens, a biconcave spherical lens, a first biconvex spherical lens, and a second biconvex spherical lens, which are sequentially disposed in the optical path between the transmitting fiber interface and the optical path adjustment assembly.

14. The laser vibrometer optical device based on the Cassegrain system as described in any one of claims 1 to 9, characterized in that, The heterodyne interferometric fiber optic system includes a laser transmitter, a laser beam splitter, a frequency shifter assembly, a fiber combiner / splitter, and a detector. The input end of the laser beam splitter is connected to the laser transmitter via an optical fiber, and the output end of the laser beam splitter is connected to the transmitting fiber interface and the frequency shifter assembly via optical fibers, respectively. The combining end of the fiber combiner / splitter is connected to the detector via an optical fiber, and the splitting end of the fiber combiner / splitter is connected to the receiving fiber interface and the frequency shifter assembly via optical fibers, respectively.

15. The laser vibrometer optical device based on the Cassegrain system as described in claim 14, characterized in that, The frequency shifter assembly includes a first frequency shifter and a second frequency shifter in the optical fiber sequentially disposed between the laser beam splitter and the optical fiber combining and splitting device, wherein the frequency shift difference between the first frequency shifter and the second frequency shifter is neither equal to the frequency shift frequency of the first frequency shifter nor equal to the frequency shift frequency of the second frequency shifter.

16. The laser vibrometer optical device based on the Cassegrain system as described in claim 15, characterized in that, The detector is a balanced photodetector, and the balanced photodetector has at least two photodiodes.

17. The laser vibrometer optical device based on the Cassegrain system as described in claim 14, characterized in that, The heterodyne interferometric fiber system further includes a fiber attenuator correspondingly disposed in the fiber between the laser beam splitter and the frequency shifter assembly for attenuating and fine-tuning the reference light split by the laser beam splitter.

18. The laser vibrometer optical device based on the Cassegrain system as described in claim 14, characterized in that, The heterodyne interferometric fiber system further includes an indicator laser for emitting indicator light and a fiber wavelength division multiplexing device, wherein the fiber wavelength division multiplexing device is correspondingly disposed in the fiber between the laser beam splitter and the transmitting fiber interface, and the indicator laser is connected to the fiber wavelength division multiplexing device through the fiber.

19. The laser vibrometer optical device based on the Cassegrain system as described in claim 18, characterized in that, The laser emitter is an infrared narrow-linewidth laser for emitting infrared laser, and the indicator laser is for emitting visible laser.

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