Lens group center thickness and air gap measuring device and measuring method thereof

Abstract

This invention discloses a device and method for measuring the center thickness and air gap of a lens group. The device includes a light source module, a coaxial detection module, an optical delay line module, and a detection module. It employs broadband low-coherence light for multi-interface tomography positioning, introduces narrow-band high-coherence light as an optical path scale to correct nonlinear errors during scanning in real time, and constructs upper and lower coaxial optical paths. Combined with a segmented optimization strategy for local signal-to-noise ratio, deep penetration is transformed into bilateral shallow layer detection. This invention overcomes the difficulty of weak signal extraction from multi-layered structures, thereby improving measurement accuracy. As a device and method for measuring the center thickness and air gap of a lens group, this invention can be widely applied in the field of lens parameter measurement technology.

Description

Technical Field

[0001] This invention relates to the field of lens parameter measurement technology, and in particular to a device and method for measuring the center thickness and air gap of a lens group. Background Technology

[0002] With the continuous development of modern optical manufacturing technology, optical systems are evolving towards higher precision, miniaturization, and greater complexity. In the design, manufacturing, and testing of complex optical lens groups, accurate measurement of their internal geometric parameters is crucial for ensuring the overall performance of the system. In particular, the center thickness of the lens and the air gap between lens layers are key geometric parameters that directly affect the refraction path of light in the medium, determining the effective focal length, sharpness, and final image quality of the optical system. Simultaneously, with consumption upgrades and technological advancements, the market demand for precision optical instruments is showing a trend towards extremely high precision. The geometric dimensions of the lens group directly relate to the structural stability and optical assembly accuracy of the system; therefore, accurate measurement of these core geometric parameters is a crucial aspect of quality control and assembly optimization for complex optical components.

[0003] Currently, the main methods for measuring optical lens parameters include mechanical contact measurement, optical image capture, and conventional interferometry. Mechanical contact methods typically rely on micrometers or reference rods for comparison, which is not only cumbersome and prone to scratching the surface of precision lenses, but also cannot directly measure the air gaps inside encapsulated or multi-layered lens groups. While non-contact conventional measurement techniques improve detection accuracy to some extent, they generally suffer from difficulties in opto-mechanical integration, limited measurement range, or inability to adapt to complex multi-layered structures. Especially when dealing with complex multi-layered lens groups, existing technologies reveal several bottlenecks: First, the measurement beam must penetrate multiple interfaces, leading to severe attenuation of deep echo signals and susceptibility to noise interference; second, traditional scanning structures struggle to balance large-stroke measurement with high-precision optical path calibration, easily introducing nonlinear scanning errors; furthermore, in continuous multi-layered interface structures, as the detection depth increases, the location of deep interfaces is easily affected by the cumulative effects of machining tolerances and optical path drift in previous layers, making it difficult for existing conventional technologies to achieve stable and accurate calculations of the internal multi-layer center thickness and air gaps. Summary of the Invention

[0004] To address the aforementioned technical problems, the present invention aims to provide a lens group center thickness and air gap measuring device and method, which can overcome the difficulty of weak signal extraction in multi-layer structures and thus improve measurement accuracy.

[0005] The first technical solution adopted in this invention is: a lens group center thickness and air gap measuring device, comprising a light source module, a counter-coaxial detection module, an optical delay line module, and a detection module, wherein the optical path output terminal of the light source module is connected to the optical path input terminals of the counter-coaxial detection module, the optical delay line module, and the detection module, respectively, wherein: The light source module is used to output the original light signal according to the drive control command; The opposing coaxial detection module is used to switch the upper and lower measurement optical paths by optical switch, and extract the reflected light signals of each optical interface of the lens group from the upper and lower directions; The optical delay line module is used to continuously adjust the optical path length of the reference arm. Through a large-stroke time-domain dynamic scan, the reference light and the measurement return light from each interface of the lens group will interfere sequentially. The detection module is used to generate two analog electrical signals and calculate the position of the interference peak and the scale displacement information through an algorithm.

[0006] Furthermore, the measuring device also includes a 1×2 coupler, a first circulator, a second circulator, a first 2×2 coupler, a second optical switch, a second 2×2 coupler, a wavelength division multiplexer, and an end-face mirror. The first output terminal of the first circulator is connected to the input terminal of the opposing coaxial detection module, the second output terminal of the first circulator is connected to the input terminal of the detection module through the first 2×2 coupler, and the output terminal of the wavelength division multiplexer is connected to the input terminal of the optical delay line module, wherein: The 1×2 coupler is used to split the broadband raw optical signal to obtain a first broadband split optical signal and a second broadband split optical signal. The first circulator is used to receive the first broadband beam splitting optical signal and transmit it unidirectionally to the first optical switch, and at the same time receive the reflected optical signal carrying sample interface information returned from the opposing coaxial detection module and transmit it unidirectionally to the first 2×2 coupler. The second circulator is used to receive the second broadband beam splitting optical signal and transmit it unidirectionally to the second optical switch, and at the same time receive the broadband reference optical signal with time delay information returned from the optical delay line module and transmit it unidirectionally to the first 2×2 coupler. The first 2×2 coupler is used to receive the reflected light signal from the first circulator and the broadband reference light signal from the second circulator, perform interference, and output the first interference light signal to the first photodetector; The second optical switch is used to switch the input optical signal channel of the optical delay line module. When switched to the lower path, the broadband reference optical signal output by the second circulator is transmitted to the wavelength division multiplexer. The second 2×2 coupler is used to split the narrowband original optical signal to obtain a first narrowband split optical signal and a second narrowband split optical signal. At the same time, it receives the narrowband reference optical signal returned from the optical delay line module and the narrowband reference optical signal returned from the end face mirror, so that the two beams interfere and output the second interference optical signal to the second photodetector. The wavelength division multiplexer is used to combine the second broadband split optical signal and the first narrowband split optical signal and couple them to the same optical fiber for transmission to the optical delay line module. At the same time, the mixed optical signal returned from the optical delay line module is separated according to wavelength. The end face reflector is used to receive the second narrowband split beam signal output from the second 2×2 coupler and reflect it back along the original path.

[0007] Furthermore, the light source module specifically includes a broadband light source and a narrowband light source, wherein the center wavelength of the broadband light source is 1310nm and the center wavelength of the narrowband light source is 1550nm, wherein: The broadband light source is used to output broadband raw optical signals; The narrowband light source is used to output narrowband raw optical signals.

[0008] Furthermore, the opposing coaxial detection module specifically includes a first optical switch, a first collimator, a dichroic mirror, an upper reference plane, a measurement sample, a stage, a lower reference plane, and a second collimator, wherein: The first optical switch is used to switch the measurement optical path channel of the opposing coaxial detection module, and transmit the first broadband beam splitting optical signal output by the first circulator to the first collimator or the second collimator respectively. The first collimator is used to convert the optical fiber transmission diverging light signal output by the first optical switch into parallel light output, and at the same time receive the parallel reflected light signal returned from the dichroic mirror and couple it back into the optical fiber; The dichroic mirror is used to split the parallel light emitted from the first collimator. The first part of the parallel light is reflected to the upper reference plane, and the second part of the parallel light is transmitted to the measurement sample. At the same time, it receives the reflected light signal returned from the measurement sample and transmits it to the first collimator. The upper reference surface is used as a reference surface for the measurement above, receiving the light signal reflected by the dichroic mirror and reflecting it back along the original path; The measurement sample is used as the object to be measured, and the transmitted light is sequentially incident on the optical interface. The reflected light generated by the optical interface carries geometric information about the thickness of the lens center and the air gap. The stage is used to fix the measurement sample; The lower reference plane is used as a reference plane for the measurement below, receiving the transmitted light signal that penetrates the measurement sample or the parallel light signal emitted from the second collimator and reflecting it back along the original path. The second collimator is used to convert the optical fiber transmission diverging light signal output by the first optical switch into parallel light output, and at the same time receive the parallel reflected light signal returned from the lower optical path and couple it back into the optical fiber.

[0009] Furthermore, the optical delay line module specifically includes a third collimator, a right-angle prism, and a reflector, wherein: The third collimator is used to collimate the output light of the wavelength division multiplexer into a spatial parallel beam and efficiently couple the returned parallel beam back into the optical fiber. The right-angle prism is used to change the propagation direction of the parallel light beam; The reflector is used to reflect the parallel beam of light, after it has been deflected by the right-angle prism, back along its original path to the third collimator.

[0010] Furthermore, the detection module specifically includes a first photodetector, a second photodetector, and a terminal device, wherein: The first photodetector is used to receive the first interference light signal output by the first 2×2 fiber coupler and convert the reflected light carrying geometric information of the lens center thickness and air gap into a first analog electrical signal; The second photodetector is used to receive the second interference optical signal output from the second 2×2 fiber coupler and convert it into a second analog electrical signal; The terminal device is used to calculate the interference peak position and scale displacement information of the first and second analog electrical signals through an algorithm, and to calculate the center thickness of each lens in the lens group under test and the air gap between the lenses.

[0011] The second technical solution adopted in this invention is: a method for measuring the center thickness and air gap of a lens group, comprising: The output includes broadband low-coherence light for multi-interface tomographic positioning and narrowband high-coherence scale light for optical path nonlinearity error correction. The broadband low-coherence light is divided into measurement light and reference light. The measurement light is transmitted to the opposing coaxial detection module, and the reference light and narrowband high-coherence scale light are combined and transmitted to the optical delay line module. The first optical switch switches to the upper measurement optical path. The measurement light is collimated into parallel light by the first collimator and then split by the dichroic mirror. The first part of the light is reflected to the upper reference surface to form a reference reflection signal. The second part of the light is transmitted to the lens group under test, and reflection signals carrying geometric information are generated sequentially at the optical interfaces of each lens and the lower reference surface. All reflection signals are returned to the first circulator. The first optical switch switches to the lower measurement optical path. The measurement light is collimated into parallel light by the second collimator and then incident upwards. It generates reflection signals at the optical interfaces of each lens and the upper reference surface in sequence and returns to the second circulator. The right-angle prism driving the optical delay line module performs a long-stroke linear scan, continuously adjusting the optical path length of the reference arm so that the reference light interferes sequentially with the measurement light returned from each interface of the lens group at the first 2×2 coupler, forming a broadband interference signal carrying interface position information. At the same time, the narrowband light interferes at the second 2×2 coupler, forming a narrowband scale light signal with standard cosine oscillation. The first and second photodetectors respectively collect broadband interference signals and narrowband scale light signals and convert them into analog electrical signals, which are then transmitted to the terminal equipment for calculation to obtain the center thickness of each lens in the lens group under test and the air gap between the lenses.

[0012] The beneficial effects of the method and system of this invention are as follows: By constructing an upper and lower coaxial optical path and combining it with a local signal-to-noise ratio segment optimization strategy, this invention transforms deep penetration into bilateral shallow detection, overcomes the problem of weak signal extraction in multi-layer structures, and then uses broadband low-coherence light to achieve multi-interface tomography positioning. It also introduces narrowband high-coherence light as an optical path scale to correct nonlinear errors in the scanning process in real time, thereby improving measurement accuracy at the system level. Attached Figure Description

[0013] Figure 1 This is a schematic diagram of the structure of a lens group center thickness and air gap measuring device according to the present invention; Figure 2 This is a schematic diagram of the measurement method of a lens group center thickness and air gap measuring device according to the present invention; Figure 3 This is a schematic diagram illustrating the principle of measuring the center thickness and air gap of the lens assembly according to a specific embodiment of the present invention; Figure 4 This is a schematic diagram illustrating the principle of measuring the inter-peak optical path length of interference provided in a specific embodiment of the present invention; Figure 5 This is a schematic diagram of the signal-to-noise ratio distribution and preferred range of the dual-path detection signal provided in a specific embodiment of the present invention.

[0014] Figure descriptions: 1. 1310nm broadband light source; 2. 1×2 coupler; 3. First circulator; 4. First optical switch; 5. First collimator; 6. Dichroic mirror; 7. Upper reference plane; 8. Sample to be tested; 9. Stage; 10. Lower reference plane; 11. Second collimator; 12. Second circulator; 13. First 2×2 coupler; 14. Second optical switch; 15. First photodetector; 16. 1550nm narrowband light source; 17. Second 2×2 coupler; 18. Second photodetector; 19. Wavelength division multiplexer; 20. Third collimator; 21. Right-angle prism; 22. Mirror; 23. End face mirror; 24. Terminal equipment. Detailed Implementation

[0015] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments. The step numbers in the following embodiments are only for ease of explanation and do not limit the order of the steps. The execution order of each step in the embodiments can be adapted according to the understanding of those skilled in the art.

[0016] First, it should be noted that the relevant technology has the following shortcomings, for example: 1) For example, an automatic measurement device and detection method for the center thickness of a lens. This scheme combines a spectral confocal system and a Fizeau interferometer system. First, the initial value of the lens center thickness is measured by the spectral confocal system. Then, an interferogram is acquired through Fizeau interferometry. The translation and tilt errors of the lens are obtained through phase extraction, unwrapping, and Zernike fitting. Finally, the thickness result is corrected. This method has a high degree of automation and can reduce the influence of assembly and adjustment errors. However, the system structure is complex, it relies on high-precision interferometry and image processing modules, has a high cost, and has high requirements for environmental stability and calibration accuracy.

[0017] 2) Another example is a laser triangulation method for measuring the center thickness of a lens. This method integrates a laser source, a reticle, and a dual-CCD imaging system. After monitoring and adjusting the lens's eccentricity and tilt errors, it uses the triangulation principle to collect scattered light from the upper and lower surfaces to calculate the center thickness. This method has the advantages of being non-contact, highly accurate, and having strong anti-interference capabilities. However, its system is highly dependent on the dual-CCD architecture and complex mechanical adjustment mechanisms. The optical path adjustment steps are complicated, and the precise calibration and mechanical adjustment requirements of the imaging system are high, increasing the practical operation threshold and implementation difficulty.

[0018] 3) Alternatively, a high-precision lens gap measurement device can be used. This device integrates mechanical linkage components such as knobs, gears, and sliders to achieve synchronous clamping and precise center positioning of the lens under test. A digital height gauge probe then contacts the center of the lens to complete the gap measurement. This device effectively solves the problem of traditional equipment's difficulty in accurately locating the lens center and reduces human error. However, it still relies on contact measurement, has numerous mechanical transmission components, a cumbersome adjustment process, and its measurement accuracy is easily affected by hardware assembly errors, long-term mechanical wear, and the consistency of manual operation, thus limiting its application in actual high-frequency testing.

[0019] Based on this, the present invention addresses the shortcomings of existing non-contact optical measurement methods when measuring complex multilayer lens groups, such as difficulty in identifying weak signals in deep layers, nonlinear distortion of optical paths during large-stroke scanning, and tolerance accumulation in multilayer continuous structures. It provides a method for measuring the center thickness and air gap of complex lens groups. First, it combines wide and narrow dual light sources, using narrow-band scale light to correct the nonlinear scanning error of broadband positioning light, balancing large stroke and high precision. Then, it employs opposing coaxial detection and signal optimization, transforming deep-layer detection into shallow-layer detection, significantly improving the resolution of weak signals. Finally, it uses low-coherence light non-contact detection, eliminating physical scratches on the surface and achieving non-destructive testing of the lens group under test. This method, based on low-coherence light interferometry, enables the measurement of the center thickness and air gap of the lens group.

[0020] Reference Figure 1 This invention provides a device for measuring the center thickness and air gap of a lens group, comprising a light source module, a counter-coaxial detection module, an optical delay line module, and a detection module. The optical path output terminal of the light source module is connected to the optical path input terminals of the counter-coaxial detection module, the optical delay line module, and the detection module, respectively. The light source module is used to output the original light signal according to the drive control command; Specifically, the light source module includes a broadband light source and a narrowband light source. The center wavelength of the broadband light source is 1310nm, and the center wavelength of the narrowband light source is 1550nm. The broadband light source is used to output broadband raw optical signals, and the narrowband light source is used to output narrowband raw optical signals.

[0021] In this embodiment, the light source module includes a 1310nm broadband light source 1 and a 1550nm narrowband light source 16. This module receives drive and control command signals from the computer in the detection module and outputs raw optical signals at 1310nm and 1550nm. After emission from the two light sources, the signals are combined and enter a wavelength division multiplexer 19, which outputs the optical signals to the optical delay line module. This is primarily used to provide broadband low-coherence positioning light and narrowband high-coherence scale light.

[0022] The opposing coaxial detection module is used to switch the upper and lower measurement optical paths by optical switch, and extract the reflected light signals of each optical interface of the lens group from the upper and lower directions; Specifically, the opposing coaxial detection module includes a first optical switch 4, a first collimator 5, a dichroic mirror 6, an upper reference surface 7, a measurement sample, a stage 9, a lower reference surface 10, and a second collimator 11. The first optical switch is used to switch the measurement optical path channel of the opposing coaxial detection module, transmitting the first broadband beam-splitting optical signal output from the first circulator 3 to either the first collimator or the second collimator. The first collimator converts the fiber-optic transmission diverging optical signal output from the first optical switch into parallel light emission, while simultaneously receiving the parallel reflected optical signal returned from the dichroic mirror and coupling it back into the fiber. The dichroic mirror splits the parallel light emitted from the first collimator; a first portion of the parallel light is reflected to the upper reference surface, and a second portion of the parallel light is transmitted to the measurement sample, while simultaneously receiving… The reflected light signal returned from the measurement sample is transmitted to the first collimator; the upper reference surface serves as a reference surface for the measurement above, receives the light signal reflected by the dichroic mirror and reflects it back along the original path; the measurement sample serves as the object to be measured, allowing transmitted light to be incident sequentially onto the optical interface, and the reflected light generated by the optical interface carries geometric information about the lens center thickness and air gap; the stage is used to fix the measurement sample; the lower reference surface serves as a reference surface for the measurement below, receives the transmitted light signal penetrating the measurement sample or the parallel light signal emitted from the second collimator and reflects it back along the original path; the second collimator converts the fiber-optic transmission diverging light signal output from the first optical switch into parallel light emission, and simultaneously receives the parallel reflected light signal returned from the lower optical path and couples it back into the optical fiber.

[0023] In this embodiment, the opposing coaxial detection module includes a first optical switch, a first collimator, a dichroic mirror, an upper reference surface, a measurement sample, a stage, a lower reference surface, and a second collimator. This module receives the detection beam transmitted after being split by a 1×2 fiber coupler. After reflection from each interface of the sample, the measurement beam carries optical path information about the internal geometric thickness of the lens group and the air gap. These reflected light signals are transmitted in reverse along the original path to the circulator, and then output by the circulator to the 2×2 fiber coupler. It is mainly used to extract interference signals from each interface of the lens group from both upper and lower directions, effectively overcoming the problem of deep signal attenuation caused by single-sided penetration through bilateral shallow detection.

[0024] The optical delay line module is used to continuously adjust the optical path length of the reference arm. Through a large-stroke time-domain dynamic scan, the reference light and the measurement return light from each interface of the lens group will interfere sequentially. Specifically, the optical delay line module includes a third collimator 20, a right-angle prism 21, and a reflector 22. The third collimator is used to collimate the output light of the wavelength division multiplexer into a spatial parallel beam and efficiently couple the returned parallel beam back into the optical fiber. The right-angle prism is used to change the propagation direction of the parallel beam. The reflector is used to reflect the parallel beam after it has been turned by the right-angle prism back to the third collimator along the original path.

[0025] In this embodiment, the optical delay line module includes a third collimator, a right-angle prism, and a reflector. This module receives a reference beam after it has been combined by a wavelength division multiplexer. After the reference beam undergoes refracting and dynamic optical path delay between the right-angle prism and the reflector, it returns along its original path with a time-varying delayed optical signal, and is output to a 2×2 fiber coupler via a circulator. It is mainly used to continuously adjust the optical path length of the reference arm. Through large-stroke time-domain dynamic scanning, the reference beam interferes sequentially with the measurement return light from each interface of the lens group, achieving precise spatial positioning.

[0026] The detection module is used to generate two analog electrical signals and calculate the position of the interference peak and the scale displacement information through an algorithm.

[0027] Specifically, the detection module includes a first photodetector 15, a second photodetector 18, and a terminal device 24. The first photodetector receives the first interference light signal output from the first 2×2 fiber coupler and converts the reflected light carrying geometric information about the lens center thickness and air gap into a first analog electrical signal. The second photodetector receives the second interference light signal output from the second 2×2 fiber coupler and converts it into a second analog electrical signal. The terminal device uses an algorithm to calculate the interference peak position and scale displacement information of the first and second analog electrical signals, and calculates the center thickness of each lens in the lens group under test and the air gap between the lenses.

[0028] In this embodiment, the detection module includes a first photodetector, a second photodetector, and a terminal device, namely a computer. This module receives dual-channel interference light signals from a 2×2 fiber coupler and their combined output. The photodetector converts the light signals into analog electrical signals, which are then output to the computer's data acquisition card for digital quantization. The computer then calculates the geometric parameters of the multilayer lens group using an algorithm. The module is primarily used to receive interference light signals, convert them into electrical signals, and then perform data acquisition and algorithm processing via the computer to ultimately calculate the center thickness and air gap of the lens group.

[0029] Additionally, it should be noted that the measuring device in this embodiment of the invention further includes a 1×2 coupler 2, a first circulator, a second circulator 12, a first 2×2 coupler 13, a second optical switch 14, a second 2×2 coupler 17, a wavelength division multiplexer, and an end-face reflector 23. The first output terminal of the first circulator is connected to the input terminal of the opposing coaxial detection module, and the second output terminal of the first circulator is connected to the input terminal of the detection module through the first 2×2 coupler. The output terminal of the wavelength division multiplexer is connected to the input terminal of the optical delay line module. The 1×2 coupler is used to perform beam splitting processing on the broadband raw optical signal to obtain a first broadband split optical signal and a second broadband split optical signal. The first circulator is used to receive the first broadband split optical signal and transmit it unidirectionally to the first optical switch, while simultaneously receiving the reflected optical signal carrying sample interface information returned from the opposing coaxial detection module and transmitting it unidirectionally to the first 2×2 coupler 17. Coupler; the second circulator is used to receive the second broadband beam-splitting optical signal and transmit it unidirectionally to the second optical switch, while simultaneously receiving the broadband reference optical signal with time delay information returned from the optical delay line module and transmitting it unidirectionally to the first 2×2 The system comprises the following components: a coupler; a first 2×2 coupler receiving a reflected optical signal from a first circulator and a broadband reference optical signal from a second circulator, interfering with the signal and outputting a first interference optical signal to a first photodetector; a second optical switch switching the input optical signal channel of the optical delay line module, transmitting the broadband reference optical signal output from the second circulator to a wavelength division multiplexer when switched to the lower path; a second 2×2 coupler splitting the narrowband original optical signal to obtain a first narrowband split optical signal and a second narrowband split optical signal, while simultaneously receiving the narrowband reference optical signal returned from the optical delay line module and the narrowband reference optical signal returned from the end face mirror, causing the two beams to interfere and outputting a second interference optical signal to a second photodetector; a wavelength division multiplexer combining the second broadband split optical signal and the first narrowband split optical signal and coupling them to the same optical fiber for transmission to the optical delay line module, while simultaneously separating the mixed optical signal returned from the optical delay line module according to wavelength; and an end face mirror receiving the second narrowband split optical signal output from the second 2×2 coupler and reflecting it back along the original path.

[0030] In summary, compared with the prior art, the embodiments of the present invention have the following distinguishing technical features: 1) Opposing coaxial detection and signal optimization mechanism: Constructing an upper and lower opposing coaxial optical path, combined with a local signal-to-noise ratio segment optimization strategy, transforming deep penetration into bilateral shallow detection, overcoming the problem of weak signal extraction in multi-layer structures.

[0031] 2) Wideband and narrowband dual-source collaborative calibration technology: Wideband low-coherence light is used to achieve multi-interface tomographic positioning, and narrowband high-coherence light is introduced as an optical path scale to correct nonlinear errors in the scanning process in real time, thereby improving measurement accuracy at the system level.

[0032] Therefore, compared with the prior art, the embodiments of the present invention have the following advantages: 1) By adopting a bidirectional coaxial opposing detection structure and a signal segmentation optimization strategy, the traditional single-sided deep penetration is transformed into double-sided shallow detection, which greatly improves the ability to resolve weak signals at the bottom of multi-layer complex structures.

[0033] 2) The entire optical path adopts non-contact low-coherence light illumination detection, which fundamentally eliminates the physical scratches and damage to the surface of the precision lens caused by traditional mechanical clamping.

[0034] 3) The introduction of narrowband scale light to correct the nonlinear scanning error of the rotation delay line in real time enables high-precision interface tomography positioning at the micron level while ensuring continuous and rapid scanning with a large stroke.

[0035] In summary, the optical path system of this invention is based on a fiber-optic Michelson interferometer structure. Light emitted from a 1310nm broadband light source is split via an optical fiber into a 1×2 coupler. One beam enters the first circulator and then the first optical switch. When the optical switch is switched to the upper path, the beam enters the first collimator and exits as parallel light. After passing through a dichroic mirror, it is split again. One beam hits the upper reference plane and then reflects back, while the other beam hits the sample under test (8) and the lower reference plane sequentially before reflecting back. When the optical switch is switched to the lower path, the beam enters the second collimator and exits as parallel light, hitting the lower reference plane and the sample under test sequentially before reflecting back. The reflected light returns to the first circulator and then enters the first 2×2 coupler. Another beam of light, split from the 1×2 coupler, enters the second circulator and then the second optical switch. When the optical switch switches to the lower path, the beam enters the 1310nm end of the wavelength division multiplexer. After passing through the third collimator and exiting as parallel light, it strikes the right-angle prism and the reflector in sequence and is reflected back. The reflected light returns to the second circulator and then enters the first 2×2 coupler. The two broadband beams split from the 1×2 coupler interfere after being reflected back at the first 2×2 coupler, forming an interference peak. The interference signal is converted into an electrical signal by the first photodetector and then processed by the computer. Simultaneously, light emitted from a 1550nm narrowband source enters the second 2×2 coupler via optical fiber for beam splitting. One beam enters the 1550nm end of the wavelength division multiplexer, passes through the third collimator and exits as parallel light, then strikes the right-angle prism and the reflector in sequence and is reflected back. The reflected light returns to the second 2×2 coupler; the other beam enters the end face reflector via optical fiber and is reflected back. The two narrowband beams split from the second 2×2 coupler interfere with each other after being refracted back, forming a standard cosine oscillation function. The interference signal is converted into an electrical signal by the second photodetector and then processed by the computer.

[0036] Reference Figure 2 A method for measuring the center thickness and air gap of a lens group, comprising the following steps: S100 outputs broadband low-coherence light for multi-interface tomographic positioning and narrowband high-coherence scale light for optical path nonlinearity error correction. The broadband low-coherence light is divided into measurement light and reference light. The measurement light is transmitted to the opposing coaxial detection module, and the reference light and narrowband high-coherence scale light are combined and transmitted to the optical delay line module. S200: Switch to the upper measurement optical path through the first optical switch. The measurement light is collimated into parallel light by the first collimator and then split by the dichroic mirror. The first part of the light is reflected to the upper reference surface to form a reference reflection signal. The second part of the light is transmitted to the lens group under test and sequentially generates reflection signals carrying geometric information at the optical interfaces of each lens and the lower reference surface. All reflection signals return to the first circulator. S300: Switch to the lower measurement optical path through the first optical switch. The measurement light is collimated into parallel light by the second collimator and then incident upwards. Reflection signals are generated sequentially at the optical interfaces of each lens and the upper reference surface and then return to the second circulator. S400 drives the right-angle prism of the optical delay line module to perform a long-stroke linear scan, continuously adjusting the optical path length of the reference arm so that the reference light interferes with the measurement light returned from each interface of the lens group in sequence at the first 2×2 coupler, forming a broadband interference signal carrying interface position information. At the same time, the narrowband light interferes at the second 2×2 coupler, forming a standard cosine oscillating narrowband scale light signal. S500, the first photodetector, and the second photodetector respectively collect broadband interference signals and narrowband scale light signals and convert them into analog electrical signals, which are then transmitted to the terminal equipment for calculation to obtain the center thickness of each lens in the lens group under test and the air gap between the lenses.

[0037] In this embodiment, since the complex lens group consists of multiple layers of lenses with different refractive indices and air gaps, its interference signal has the characteristics of multiple interfaces and multiple peaks. The system introduces a dynamic compensation peak-finding strategy combined with design parameters. Before the measurement begins, the operator needs to pre-input the material number of each layer of the lens group to be measured into the software. The system will automatically look up the refractive index of the corresponding material in the 1310nm band from its built-in material library.

[0038] like Figure 3 As shown, taking the first and second lenses of the lens group under test as examples, the backlight from the front and rear surfaces of the first lens under test and the front surface of the second lens under test interfere with the backlight from the reference arm module. Three interference peaks are generated between the interference peak generated on the upper reference plane and the interference peak generated on the lower reference plane. The optical path between the first two interference peaks is the optical path of the lens under test, denoted as . The refractive index is denoted as The optical path length between the last two interference peaks is the same as the optical path length of the air gap, denoted as . The refractive index is denoted as Under standard conditions, the refractive index of air is 1, that is... .

[0039] ; ; Narrowband optical interferometry is used to measure the optical path between interference peaks produced by broadband optical interferometry. The principle is as follows: Figure 4 As shown, the optical path length between broadband optical interference peaks It can be represented as: ; in, For the wavelength of a narrowband light source, Let be the number of periods of the cosine function between the two interference peaks. For air to wavelength The refractive index of light waves.

[0040] The narrowband light source used in this system has a wavelength of 1550nm. The refractive index of air for 1550nm light is 1. By combining this with the narrowband optical ranging system, the optical path can be determined. and Its expression is: ; ; This allows us to determine the center thickness of the lens group under test. Space from air Its expression is: ; ; For complex lens groups containing more than ten physical interfaces, the cumulative effect of reflection and absorption at multiple interfaces causes the reflected light signal to exhibit a significant energy attenuation trend with increasing detection depth. It is difficult for the probe light incident from one side to maintain a high signal-to-noise ratio throughout the entire lens group. To improve the stability of the thickness of each interface, this system adopts a segmented optimization and logical splicing signal processing strategy.

[0041] like Figure 5 As shown, when processing data, the system no longer relies solely on a single signal to measure the entire distance. Instead, it employs a signal selection strategy based on signal-to-noise ratio (SNR), calculating the local SNR of the upper and lower detection signals at corresponding depths, as shown below. Figure 5 (a) and Figure 5 As shown in (b), the ratio of the peak amplitude of the interference envelope to the root mean square of the adjacent background noise is used as the criterion. When probing each lens interface, the system simultaneously compares the signal-to-noise ratio of the interference peaks generated by the upper and lower probe beams at that location. The program automatically selects the path with better signal quality and less interference as the original calculation benchmark for that interface.

[0042] The content of the above method embodiments is applicable to this system embodiment. The specific functions implemented in this system embodiment are the same as those in the above method embodiments, and the beneficial effects achieved are also the same as those achieved in the above method embodiments.

[0043] The preferred embodiments of the present application have been described above with reference to the accompanying drawings, but this is not intended to limit the scope of the embodiments of the present application. Any modifications, equivalent substitutions, and improvements made by those skilled in the art without departing from the scope and substance of the embodiments of the present application shall be within the scope of the embodiments of the present application.

Claims

1. A device for measuring the center thickness and air gap of a lens group, characterized in that, The system includes a light source module, a counter-coaxial detection module, an optical delay line module, and a detection module. The optical path output terminal of the light source module is connected to the optical path input terminals of the counter-coaxial detection module, the optical delay line module, and the detection module, respectively. The light source module is used to output the original light signal according to the drive control command; The opposing coaxial detection module is used to switch the upper and lower measurement optical paths by optical switch, and extract the reflected light signals of each optical interface of the lens group from the upper and lower directions; The optical delay line module is used to continuously adjust the optical path length of the reference arm. Through a large-stroke time-domain dynamic scan, the reference light and the measurement return light from each interface of the lens group will interfere sequentially. The detection module is used to generate two analog electrical signals and calculate the position of the interference peak and the scale displacement information through an algorithm.

2. The lens group center thickness and air gap measuring device according to claim 1, characterized in that, The measuring device further includes a 1×2 coupler, a first circulator, a second circulator, a first 2×2 coupler, a second optical switch, a second 2×2 coupler, a wavelength division multiplexer, and an end-face reflector. The first output terminal of the first circulator is connected to the input terminal of the opposing coaxial detection module, the second output terminal of the first circulator is connected to the input terminal of the detection module through the first 2×2 coupler, and the output terminal of the wavelength division multiplexer is connected to the input terminal of the optical delay line module. The 1×2 coupler is used to split the broadband raw optical signal to obtain a first broadband split optical signal and a second broadband split optical signal. The first circulator is used to receive the first broadband beam splitting optical signal and transmit it unidirectionally to the first optical switch, and at the same time receive the reflected optical signal carrying sample interface information returned from the opposing coaxial detection module and transmit it unidirectionally to the first 2×2 coupler. The second circulator is used to receive the second broadband beam splitting optical signal and transmit it unidirectionally to the second optical switch, while receiving the broadband reference optical signal with time delay information returned from the optical delay line module and transmitting it unidirectionally to the first 2×2 coupler. The first 2×2 coupler is used to receive the reflected light signal from the first circulator and the broadband reference light signal from the second circulator, perform interference, and output the first interference light signal to the first photodetector; The second optical switch is used to switch the input optical signal channel of the optical delay line module. When switched to the lower path, the broadband reference optical signal output by the second circulator is transmitted to the wavelength division multiplexer. The second 2×2 coupler is used to split the narrowband original optical signal to obtain a first narrowband split optical signal and a second narrowband split optical signal. At the same time, it receives the narrowband reference optical signal returned from the optical delay line module and the narrowband reference optical signal returned from the end face mirror, so that the two beams interfere and output the second interference optical signal to the second photodetector. The wavelength division multiplexer is used to combine the second broadband split optical signal and the first narrowband split optical signal and couple them to the same optical fiber for transmission to the optical delay line module. At the same time, the mixed optical signal returned from the optical delay line module is separated according to wavelength. The end face reflector is used to receive the second narrowband split beam signal output from the second 2×2 coupler and reflect it back along the original path.

3. The lens group center thickness and air gap measuring device according to claim 2, characterized in that, The light source module specifically includes a broadband light source and a narrowband light source. The center wavelength of the broadband light source is 1310nm, and the center wavelength of the narrowband light source is 1550nm. The broadband light source is used to output broadband raw optical signals; The narrowband light source is used to output narrowband raw optical signals.

4. The lens group center thickness and air gap measuring device according to claim 3, characterized in that, The opposing coaxial detection module specifically includes a first optical switch, a first collimator, a dichroic mirror, an upper reference plane, a measurement sample, a stage, a lower reference plane, and a second collimator, wherein: The first optical switch is used to switch the measurement optical path channel of the opposing coaxial detection module, and transmit the first broadband beam splitting optical signal output by the first circulator to the first collimator or the second collimator respectively. The first collimator is used to convert the optical fiber transmission diverging light signal output by the first optical switch into parallel light output, and at the same time receive the parallel reflected light signal returned from the dichroic mirror and couple it back into the optical fiber; The dichroic mirror is used to split the parallel light emitted from the first collimator. The first part of the parallel light is reflected to the upper reference plane, and the second part of the parallel light is transmitted to the measurement sample. At the same time, it receives the reflected light signal returned from the measurement sample and transmits it to the first collimator. The upper reference surface is used as a reference surface for the measurement above, receiving the light signal reflected by the dichroic mirror and reflecting it back along the original path; The measurement sample is used as the object to be measured, and the transmitted light is sequentially incident on the optical interface. The reflected light generated by the optical interface carries geometric information about the thickness of the lens center and the air gap. The stage is used to fix the measurement sample; The lower reference plane is used as a reference plane for the measurement below, receiving the transmitted light signal that penetrates the measurement sample or the parallel light signal emitted from the second collimator and reflecting it back along the original path. The second collimator is used to convert the optical fiber transmission diverging light signal output by the first optical switch into parallel light output, and at the same time receive the parallel reflected light signal returned from the lower optical path and couple it back into the optical fiber.

5. The lens group center thickness and air gap measuring device according to claim 4, characterized in that, The optical delay line module specifically includes a third collimator, a right-angle prism, and a reflector, wherein: The third collimator is used to collimate the output light of the wavelength division multiplexer into a spatial parallel beam and efficiently couple the returned parallel beam back into the optical fiber. The right-angle prism is used to change the propagation direction of the parallel light beam; The reflector is used to reflect the parallel beam of light, after it has been deflected by the right-angle prism, back along its original path to the third collimator.

6. The lens group center thickness and air gap measuring device according to claim 5, characterized in that, The detection module specifically includes a first photodetector, a second photodetector, and a terminal device, wherein: The first photodetector is used to receive the first interference light signal output by the first 2×2 fiber coupler and convert the reflected light carrying geometric information of the lens center thickness and air gap into a first analog electrical signal; The second photodetector is used to receive the second interference optical signal output from the second 2×2 fiber coupler and convert it into a second analog electrical signal; The terminal device is used to calculate the interference peak position and scale displacement information of the first and second analog electrical signals through an algorithm, and to calculate the center thickness of each lens in the lens group under test and the air gap between the lenses.

7. A method for measuring the center thickness and air gap of a lens group, characterized in that, Includes the following steps: The output includes broadband low-coherence light for multi-interface tomographic positioning and narrowband high-coherence scale light for optical path nonlinearity error correction. The broadband low-coherence light is divided into measurement light and reference light. The measurement light is transmitted to the opposing coaxial detection module, and the reference light and narrowband high-coherence scale light are combined and transmitted to the optical delay line module. The first optical switch switches to the upper measurement optical path. The measurement light is collimated into parallel light by the first collimator and then split by the dichroic mirror. The first part of the light is reflected to the upper reference surface to form a reference reflection signal. The second part of the light is transmitted to the lens group under test, and reflection signals carrying geometric information are generated sequentially at the optical interfaces of each lens and the lower reference surface. All reflection signals are returned to the first circulator. The first optical switch switches to the lower measurement optical path. The measurement light is collimated into parallel light by the second collimator and then incident upwards. It generates reflection signals at the optical interfaces of each lens and the upper reference surface in sequence and returns to the second circulator. The right-angle prism driving the optical delay line module performs a long-stroke linear scan, continuously adjusting the optical path length of the reference arm so that the reference light interferes sequentially with the measurement light returned from each interface of the lens group at the first 2×2 coupler, forming a broadband interference signal carrying interface position information. At the same time, the narrowband light interferes at the second 2×2 coupler, forming a narrowband scale light signal with standard cosine oscillation. The first and second photodetectors respectively collect broadband interference signals and narrowband scale light signals and convert them into analog electrical signals, which are then transmitted to the terminal equipment for calculation to obtain the center thickness of each lens in the lens group under test and the air gap between the lenses.

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