An array-type focused laser differential interferometry system

Abstract

The present invention discloses an array-type focused laser differential interferometry measurement system, which relates to the technical field of fluid mechanics measurement and aims to solve the problem of how to improve FLDI measurement efficiency while ensuring measurement accuracy. The present invention utilizes a diffraction optical element in a transmitting optical path to generate a multi-path splitting pair. A multi-path optical fiber array receiving system is provided at the tail end of the receiving optical path, comprising multiple groups of receiving terminals, each group of receiving terminals comprising a three-dimensional coordinate frame, a photodetector and an optical fiber probe. A rigid connecting rod is fixedly connected to the moving part of the three-dimensional coordinate frame, the optical fiber probe is fixedly connected to the rigid connecting rod, and the receiving end faces parallel to the optical axis direction of a convex lens. The rigid connecting rods of the multiple groups of receiving terminals are respectively adjusted in position so that the receiving end positions of the multiple optical fiber probes respectively correspond one-to-one to the final imaging focus position of the multiple light paths in the receiving optical path. The present invention has a simple structure and an ingenious conception, can significantly improve measurement efficiency, and can simultaneously ensure the accurate reception of the multiple light signals, thereby ensuring measurement accuracy.

Description

Technical Field

[0001] The present invention relates to the technical field of fluid mechanics measurement, and in particular to an array-type focused laser differential interferometry measurement system. Background Art

[0002] Ground-based wind tunnel testing is an important tool for studying hypersonic aerodynamics and is of great significance to the study of hypersonic aerodynamics. However, due to the extreme environment of hypersonic wind tunnels, which often involve high inflow velocities, high total inflow temperatures, and even the risk of high-speed metal oxide particle impacts, hypersonic flow field testing technologies are relatively scarce, hindering research on related issues to a certain extent. As a measurement instrument based on the principle of optical interferometry, focused laser differential interferometry (FLDI) has the advantages of non-intrusiveness and high temporal resolution. It has been widely used to measure hypersonic flow fields (such as the hypersonic boundary layer transition, the hypersonic turbulent boundary layer, the hypersonic free stream disturbance, and the supersonic jet noise radiation).

[0003] Existing focused laser differential interferometry measurement systems all include a transmitting optical path and a receiving optical path. The transmitting optical path includes a coherent light source generator, a concave lens, a polarizer, a prism, and a convex lens arranged in sequence. The coherent light source generator is used to emit a beam of parallel laser light with the same phase and consistent polarization direction. The concave lens is used to diverge the parallel laser beams of each channel into conical laser beams. The polarizer is used to filter out the interference light of nonlinear polarization in the conical laser beams of each channel. The prism is used to separate the linearly polarized light of each channel into two beams of polarized light with the same intensity and perpendicular polarization directions according to the principle of birefringence. The convex lens is used to focus the two separated beams with perpendicular polarization directions in each channel into two separate focal points, and the two separated focal points of each channel are in the focusing area; the receiving optical path includes a convex lens, a prism, and a polarizer arranged in sequence. The convex lens is used to refocus the laser beam diverged after passing through the focusing area. The prism is used to merge the two separated beams of each splitting pair. The polarizer is used to mix the merged beams so that the mixed beams can undergo phase interference. Traditional methods acquire data through a single laser beam and interference pattern, but their efficiency and accuracy are limited when measurements of large areas or complex structures are required.

[0004] Currently, relevant research has been conducted to improve the measurement efficiency of FLDI. For example, the invention patent application with publication number CN111426446A, entitled "A Multi-channel Focused Laser Differential Interferometer," discloses the use of a beam splitter group and a corresponding reflector group to split a single laser beam emitted by a single laser into multiple laser beams, which are then focused at multiple measuring points. This allows density pulsation information from multiple measuring points in the flow field to be obtained simultaneously each time, greatly reducing the number of experiments, improving wind tunnel test efficiency, and saving test costs. However, this beam splitting method disperses the focus points into multiple points, requiring multiple sets of equipment to complete the measurement. Not only may optical components such as lenses introduce more errors, further reducing measurement accuracy, but the equipment footprint and cost will also increase exponentially.

[0005] Based on the above experience, further research shows that if the split beam control is completed in only one set of equipment, since the propagation directions of each beam pair in the convergence area are not parallel, the spacing and height of the receiving end signal will also have certain deviations, resulting in distorted measurement results. Therefore, an array-type focused laser differential interferometry measurement system is urgently needed to solve this problem. Summary of the Invention

[0006] A common solution in existing array-type focused laser differential interferometry systems is to use a diffraction optical element (DOE) to split the light in the transmitting optical path to multiply the amount of measurement performed simultaneously. However, multi-path light brings new problems. In the receiving optical path, since the multi-path light signals are ultimately focused on a spherical focal plane rather than a focal plane, this will cause the optical signal receiving device to be unable to accurately receive the multi-path light signals. In particular, it is difficult to achieve a good signal-to-noise ratio for the two outermost light signals, and the measurement accuracy is difficult to guarantee. The above problems are not solved by the current array-type focused differential interferometry measurement system.

[0007] The object of the present invention is to provide an array-type focused laser differential interferometry measurement system to solve the problem of how to improve the FLDI measurement efficiency while ensuring the measurement accuracy.

[0008] To achieve the above-mentioned purpose, the present invention provides the following technical solutions: an array-type focused laser differential interferometry measurement system, comprising an emitting optical path and a receiving optical path, wherein the emitting optical path first uses a diffraction optical element to generate a multi-path splitting pair after diverging the coherent light into a cone, and then filters out the nonlinearly polarized interference light in the cone-shaped light beam through a polarizer; a multi-path optical fiber array receiving system is provided at the tail end of the receiving optical path, which comprises multiple groups of receiving terminals, each group of receiving terminals comprises a three-dimensional coordinate frame, a photodetector and an optical fiber probe, a rigid connecting rod is fixedly connected to the moving part of the three-dimensional coordinate frame, the receiving end of the optical fiber probe is fixedly connected to the rigid connecting rod on the outside, and the receiving end is oriented parallel to the optical axis direction of the convex lens, the rigid connecting rods of the multiple groups of receiving terminals are adjusted in position respectively, so that the receiving end positions of the multiple optical fiber probes correspond one-to-one to the final imaging focus positions of the multiple lights in the receiving optical path, and the optical fiber probes of each group of receiving terminals are respectively connected to the photodetectors of each group.

[0009] Photodetectors are relatively large. If multiple photodetectors are used directly, the adjustment space is limited and it can only be applied to the multiple sets of equipment mentioned in the above background technology. However, after adopting the above typewriter-type connecting rod structure multi-channel optical fiber array receiving system of the present invention, since the optical fiber probes are respectively fixed on the rigid connecting rods connected to different three-dimensional coordinate frames, each optical fiber probe can be driven by the rigid connecting rod to accurately adjust the position individually, so that the receiving ends of all optical fiber probes fall on the spherical focal plane where the multiple optical signals are focused, thereby realizing accurate reception of each optical signal and ensuring measurement accuracy.

[0010] Preferably, the receiving optical path also includes a mounting seat, the upper end of which is provided with multiple slide rails, the direction of the slide rails being parallel to the optical axis direction of the convex lens of the receiving optical path, and the three-dimensional coordinate frame and photoelectric detector of each group of receiving terminals are positionably slidably connected to a slide rail.

[0011] Preferably, the emission light path includes a coherent light source generator, a concave lens, a diffractive optical element, a polarizer, a Wollaston prism, and a convex lens arranged in sequence, wherein the diffractive optical element divides the conical light beam diverged by the concave lens into multiple light paths, and then filters out the interference light through the polarizer. The Wollaston prism divides each linear polarization into two linear polarization beams with a certain separation angle, mutually perpendicular polarization directions and equal light intensity. The divergent light beams are converged in the observation area through the convex lens to form 6 pairs of separate focal points.

[0012] Preferably, the receiving optical path includes a convex lens, a Wollaston prism, a polarizer, a concave lens, and a multi-channel optical fiber array receiving system arranged in sequence, wherein the concave lens is used to adjust the actual focal length of the receiving end.

[0013] Another technical solution provided by the present invention is the application of an array-type focused laser differential interferometry measurement system in hypersonic flow field measurement, which is used to multiply the measurement efficiency while ensuring the measurement accuracy.

[0014] The present invention also provides a technical solution: a multi-path light receiving method for a focused laser differential interferometry measurement system, in which an equal number of fiber optic probes are set according to the number of light beams received by the receiving light path, and each fiber optic probe is fixed on a different position adjustment device. According to the specific imaging focus of each light beam, the receiving end position of each fiber optic probe is adjusted so that it corresponds one-to-one with each imaging focus position. Each fiber optic probe is connected to a photodetector for converting light intensity information into electrical signals and transmitting them to a data processing and analysis system.

[0015] Compared with the prior art, the present invention has the following beneficial effects:

[0016] 1. This array-type focused laser differential interferometry measurement system has a simple structure and ingenious design. By adopting array design and focused laser differential interferometry technology, it can achieve high-precision, synchronous measurement of multiple measuring points in a small area to meet the needs of accurate detection of complex structures or small changes. Through multi-point synchronous acquisition, it significantly improves measurement speed and efficiency, reduces the time consumption of single-point measurement, thereby improving the working efficiency of the entire system and indirectly saving measurement costs.

[0017] 2. This array-based focused laser differential interferometry measurement system effectively solves the spatial limitations in optical path layout and signal acquisition within an extremely small measurement area through an innovative fiber probe layout and three-dimensional control mechanism, ensuring the efficient operation of the measurement system in confined spaces.

[0018] 3. This array-type focused laser differential interferometry measurement system can be adjusted separately at multiple points to ensure that each light is received at the actual imaging focus, which can improve data reliability and system measurement accuracy. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 The principle comparison between the traditional solution and the array solution of Example 1 is shown;

[0020] Figure 2 Schematic diagram of the three-dimensional structure of the measurement system of Example 1 of the present invention;

[0021] Figure 3 This is a schematic diagram of the three-dimensional structure of a multi-channel optical fiber array receiving system according to embodiment 1 of the present invention;

[0022] Figure 4 Schematic diagram of the positional relationship of the optical elements of Example 1. The three-dimensional coordinate frame in the figure is only for positional indication.

[0023] In the figure: 1. Three-dimensional coordinate frame; 2. Rigid connecting rod; 3. Photoelectric detector; 4. Fiber optic probe; 5. Mounting base. DETAILED DESCRIPTION

[0024] See Figures 1 to 4 In the array-type focused laser differential interferometry measurement system of the present invention, after the coherent light is diverged into a cone, a diffraction optical element is first used to generate a multi-path splitting pair, and then the nonlinear polarization interference light in the cone beam is filtered out through a polarizer;

[0025] After proposing the above improvement plan, during the actual installation process of the array-type focused laser differential interferometer optical path, the spacing and height of the signals appearing at the receiving end also showed certain deviations due to the deviation of the lens installation, which would lead to inaccurate measurement results. Based on this, we continued to study how to solve the measurement accuracy problem;

[0026] In order to avoid distortion in the measurement results caused by the non-parallel propagation directions of the light beams in the convergence area, the spacing and height of the signals at the receiving end may also have certain deviations, which leads to distorted measurement results. The improvement idea of ​​the receiving end of the present invention is to find the position of the optical signal in real time. Therefore, the device receiving the optical signal needs to be able to achieve precise three-dimensional control to solve the problem of synchronous acquisition of multiple points.

[0027] To address the challenges of a small measurement range and minute signal spacing, we employed extremely delicate fiber optic probes, secured to a three-dimensional coordinate frame via rigid metal links, enabling precise three-dimensional control. This layout enabled efficient probe placement within a confined space and ensured accurate reception of optical signals. The in-line arrangement of photodetectors and independent connections to the fiber optic probes further ensured synchronized signal acquisition and accurate detection.

[0028] The specific method is to set up an equal number of fiber optic probes based on the number of received light beams, and each fiber optic probe is fixed to a different position adjustment device. According to the specific imaging focus of each beam, the receiving end position of each fiber optic probe is adjusted to correspond to the position of each imaging focus. Each fiber optic probe is connected to a photodetector, which converts the light intensity information into an electrical signal and transmits it to the data processing and analysis system. This innovation not only overcomes space limitations, but also optimizes the optical path design and improves the overall performance of the system.

[0029] See Figure 3 A multi-channel optical fiber array receiving system is provided at the tail end of the receiving optical path, which includes multiple groups of receiving terminals. Each group of receiving terminals includes a three-dimensional coordinate frame 1, a photodetector 3 and an optical fiber probe 4. A rigid connecting rod 2 is fixedly connected to the moving part of the three-dimensional coordinate frame 1. The receiving end of the optical fiber probe 4 is fixedly connected to the rigid connecting rod 2 on the outside, and the receiving end is oriented parallel to the optical axis direction of the convex lens. The rigid connecting rods 2 of the multiple groups of receiving terminals are adjusted in position respectively, so that the receiving end positions of the multiple optical fiber probes 4 correspond one-to-one to the final imaging focus positions of the multiple lights in the receiving optical path. The optical fiber probes 4 of each group of receiving terminals are respectively connected to the photodetectors 3 of each group.

[0030] like Figure 3 As shown, in order to facilitate fixation and adjustment, the receiving optical path may further include a mounting seat 5, the upper end of which is provided with a plurality of slide rails, the direction of the slide rails being parallel to the optical axis direction of the convex lens of the receiving optical path, and the three-dimensional coordinate frame 1 and the photoelectric detector 3 of each group of receiving terminals are positionably slidably connected with a slide rail. Specifically, tightening devices may be provided on both sides of the lower ends of the three-dimensional coordinate frame 1 and the photoelectric detector 3, and they can be positioned by tightening. After adopting the above structure, the complexity of adjustment can be effectively reduced, and the positioning of the three-dimensional coordinate frame can be facilitated.

[0031] The difference between the present invention and the ordinary focused laser differential interferometer system in terms of optical elements is that the emission light path of the present invention includes a coherent light source generator, a concave lens, a diffraction optical element (DOE), a polarizer, a Wollaston prism, and a convex lens arranged in sequence. The diffraction optical element divides the conical light beam diverged by the concave lens into multiple light paths, and then filters out the interference light through the polarizer. The Wollaston prism divides each linear polarization into two linear polarization beams with a certain separation angle, mutually perpendicular polarization directions and equal light intensity. The diverged light beams are converged in the observation area through the convex lens to form six pairs of separate focal points.

[0032] The receiving optical path differs from an ordinary focused laser differential interferometer system in that it includes a convex lens, a Wollaston prism, a polarizer, a concave lens arranged in sequence, and the above-mentioned multi-channel optical fiber array receiving system, wherein the concave lens is used to adjust the actual focal length of the receiving end.

[0033] In addition, some structures and devices in the present invention can be equivalently replaced while achieving the same function. For example, the above-mentioned Wollaston prism can also adopt other birefringent prisms with the same splitting angle, such as Sanderson prism, etc. The three-dimensional coordinate frame can also adopt a bracket that can also achieve independent multi-dimensional adjustment, such as a four-dimensional adjustment frame.

[0034] The present invention can be applied to hypersonic flow field measurements, capable of multiplying measurement efficiency while ensuring measurement accuracy. It plays a particularly important role in wind tunnel testing, primarily in the aerospace field. Based on traditional focused laser differential interferometry, it introduces array technology to achieve high-precision measurement of the aerodynamic characteristics of aircraft surfaces. By simulating the airflow environment under different flight conditions in a wind tunnel, the system can accurately observe and record the surface deformation and airflow distribution of an aircraft under various aerodynamic conditions, thereby providing key data for aircraft design optimization, aerodynamic performance evaluation, and structural improvement, ensuring that the aircraft achieves optimal performance during actual flight. The application of the measurement system of the present invention is conducive to improving the efficiency and accuracy of wind tunnel testing.

[0035] The present invention is further described below through examples. The following is only a reference example and not all examples or optimal solutions. The data and structures therein should not be used as specific limitations on the technical solutions of the present invention.

[0036] Example 1:

[0037] The array focused laser differential interferometry system consists of Figures 1 to 4 As shown, the emission light path ( Figure 2 Center left) and receiving optical path ( Figure 2 The diagram is composed of two parts (middle right).

[0038] 1) Emission light path. The helium-neon laser emits a parallel light beam with the same phase and polarization direction, which becomes a divergent conical light beam after passing through a concave lens. The light cone is divided into 6 light paths by the diffraction optical element (DOE). After passing through the polarizer, the interference light perpendicular to the polarization direction is filtered out, thereby improving the final interference effect. The light beam passes through the Wollaston prism. Based on the birefringence characteristics of the Wollaston prism, when the optical axis of the prism is 45° to the direction of polarization, each linear polarization is divided into 2 beams of linear polarization (o light and e light) with a certain separation angle, perpendicular polarization directions and equal light intensity. The convex lens then converges the divergent light beams in the observation area (interacting with the sample to be tested in the test chamber), forming 6 pairs of separate focal points.

[0039] 2) Receiving optical path. After passing through the focusing area, the light beam diverges again, converges after passing through the convex lens, and passes through the second Wollaston prism. At this time, the light beams with a certain separation angle are merged into a beam with the same propagation direction. The laser beam passes through the polarizer, and the light intensity component parallel to the polarization direction is retained, forming 6 terminal signals. The focal length is adjusted by the concave lens, and the 6 three-dimensional coordinate frames of the multi-channel fiber optic array receiving system are adjusted so that the receiving ends of the 6 fiber optic probes coincide with the imaging focus of the 6 optical signals. The 6 optical signals are accurately captured by the 6-channel fiber optic array and then transmitted to the photoelectric detector for photoelectric conversion to generate electrical signals. Subsequently, they are converted into digital signals by a high-frequency data acquisition card and analyzed and processed in real time by dedicated software to obtain the final measurement results.

[0040] In the transmitting light path, the optical focusing "probe" can be adjusted through a manual vertical lifting platform and a manual precision translation platform to ensure accurate positioning of the light path; in the receiving light path, the optical "probe" can be flexibly adjusted through an electric translation platform and the three-dimensional coordinate frame of the present invention to ensure high precision and stability of the system.

[0041] The array-based focused laser differential interferometry system of this embodiment requires minimal modifications to existing equipment, eliminates the need for multiple optical components, and is easy to implement. Its implementation has significantly improved measurement efficiency. Conventional single-point measurement systems are relatively slow. The new array-based measurement system, however, can measure multiple points simultaneously, significantly increasing data acquisition speed.

[0042] The specific measurement time required by a single-point measurement system depends on the complexity of the sample and the required measurement accuracy. For example, traditional single-point measurement takes approximately six minutes per sample, limiting measurement efficiency and data accuracy. However, the introduction of an array measurement system, thanks to the diffractive optical element's six optical paths, reduces measurement time to one-sixth of the original time, meaning each sample can be measured in just one minute, a sixfold increase in measurement efficiency.

[0043] This array-focused laser differential interferometry system utilizes a multi-channel fiber array with a typewriter-style linkage structure. This eliminates the problem of decreased measurement accuracy associated with multi-channel acquisition. Instead, the system adjusts the receiving position of each light channel individually to ensure it is at the actual focal point, reducing measurement errors and improving data reliability. Furthermore, by configuring a diffractive optical element and a multi-channel fiber array receiving system, it enables simultaneous monitoring of multiple areas, significantly improving measurement speed and spatial resolution. This advancement enables the system to more effectively acquire the aerodynamic characteristics of aircraft surfaces during wind tunnel testing, meeting the demands for high-precision and high-efficiency measurements.

[0044] This improvement reduces subsequent processing and adjustment costs associated with reduced precision, saving an average of 200,000 RMB annually in rework costs due to precision loss, while also reducing associated labor costs and material waste. The new system not only speeds up measurement but also improves accuracy, boosting overall production efficiency. This results in an estimated annual labor cost savings of approximately 300,000 RMB, and due to the reduction in errors, the overall annual cost reduction is expected to be approximately 500,000 RMB.

[0045] The above are merely preferred embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by a person skilled in the art within the technical scope disclosed in the present invention should be included in the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be based on the scope of protection defined by the claims.

[0046] Matters not described in detail in the present invention, such as the conformity of the lens position relationship with the imaging theorem and the focal length of the lens, are all well known to those skilled in the art.

Claims

1. An array-type focused laser differential interferometry system, comprising a transmitting optical path and a receiving optical path, characterized in that: After the coherent light is diverged into a cone, the emission light path first uses a diffraction optical element to generate a multi-path split light pair, and then passes through a polarizer to filter out nonlinearly polarized interference light in the cone beam; A multi-channel optical fiber array receiving system is provided at the tail end of the receiving optical path, which includes multiple groups of receiving terminals, each group of receiving terminals includes a three-dimensional coordinate frame (1), a photoelectric detector (3) and an optical fiber probe (4), a rigid connecting rod (2) is fixedly connected to the moving part of the three-dimensional coordinate frame (1), the receiving end of the optical fiber probe (4) is fixedly connected to the rigid connecting rod (2) on the outside, and the receiving end faces parallel to the optical axis direction of the convex lens, the rigid connecting rods (2) of the multiple groups of receiving terminals are respectively adjusted in position, so that the receiving end positions of the multiple optical fiber probes (4) correspond one-to-one to the final imaging focus position of the multiple light in the receiving optical path, and the optical fiber probes (4) of each group of receiving terminals are respectively connected to the photoelectric detectors (3) of each group.

2. The array-type focused laser differential interferometry system according to claim 1, characterized in that: The receiving optical path also includes a mounting seat (5), the upper end of which is provided with a plurality of slide rails, the direction of the slide rails being parallel to the optical axis direction of the convex lens of the receiving optical path, and the three-dimensional coordinate frame (1) and the photoelectric detector (3) of each group of receiving terminals are positionally slidably connected to a slide rail.

3. The array-type focused laser differential interferometry system according to claim 1, characterized in that: The emission light path includes a coherent light source generator, a concave lens, a diffractive optical element, a polarizer, a Wollaston prism, and a convex lens, which are arranged in sequence. The diffractive optical element divides the conical light beam diverged by the concave lens into multiple light paths, and then filters out interference light through the polarizer. The Wollaston prism divides each linear polarization into two linear polarization beams with a certain separation angle, mutually perpendicular polarization directions, and equal light intensity. The convex lens converges the diverged light beams in the observation area to form six pairs of separate focal points.

4. The array-type focused laser differential interferometry system according to claim 1, characterized in that: The receiving optical path includes a convex lens, a Wollaston prism, a polarizer, a concave lens, and a multi-channel optical fiber array receiving system arranged in sequence, wherein the concave lens is used to adjust the actual focal length of the receiving end.

5. Application of an array-type focused laser differential interferometry system according to any one of claims 1 to 4 in hypersonic flow field measurement, characterized in that: Used to multiply measurement efficiency while ensuring measurement accuracy.

6. The multi-path light receiving method of an array-type focused laser differential interferometry system according to any one of claims 1 to 4, characterized in that: According to the number of light beams received by the receiving optical path, an equal number of fiber optic probes are set, and each fiber optic probe is fixed on a different position adjustment device. According to the specific imaging focus of each light beam, the receiving end position of each fiber optic probe is adjusted so that it corresponds one-to-one with each imaging focus position. Each fiber optic probe is connected to a photodetector, which is used to convert light intensity information into electrical signals and transmit them to the data processing and analysis system.

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