Focusing and focal length measuring device and method

Abstract

The present invention relates to the field of optical detection technology, and in particular to a focusing and focal length measuring device and method, wherein the focusing and focal length measuring device comprises: a collimator, an optical path extension system, a lens and a beam receiving system arranged in sequence; the optical path extension system comprises: an incident mirror, an optical path extension mirror group and an exit mirror; when focusing, the optical axis of the Gaussian beam emitted by the collimator coincides with the optical axis of the lens, the Gaussian beam emitted by the collimator is reflected to the optical path extension mirror group by the incident mirror, the Gaussian beam is incident to the exit mirror after multiple reflections by the optical path extension mirror group, and is reflected to the lens by the exit mirror, and the optical axis of the Gaussian beam emitted by the exit mirror coincides with the optical axis of the lens; the Gaussian beam forms a light spot on a target surface through the lens; wherein the incident angle of the Gaussian beam reflected by the incident mirror is adjusted to adjust the object side beam waist distance of the Gaussian beam. The present invention is at least conducive to optimizing space utilization and reducing the overall volume of the measurement system, and improving the detection efficiency and accuracy of the system.

Description

Technical Field

[0001] The present invention belongs to the technical field of optical detection, and in particular relates to a focusing and focal length measuring device and method. Background Art

[0002] In the development of optical technology, infrared cameras are widely used in laser processing, additive manufacturing, semiconductors, life sciences and communications due to their unique advantages. Among them, 1550nm infrared cameras are ideally suitable for beam positioning and alignment of lasers, transmitters and communication bands.

[0003] As application demands continue to increase, the requirements for infrared camera imaging quality are also increasing. The key to achieving high-quality camera imaging is whether the camera target surface is accurately located on the focal plane of the camera lens. Therefore, focusing is an essential assembly and adjustment process for infrared cameras, and the precise focusing of infrared cameras and the precise measurement of the focal length of the camera lens are the determining factors for imaging quality. However, due to external factors such as ambient temperature and platform vibration, the focal length of the lens may change slightly, which in turn affects the imaging quality. Therefore, a method that can accurately measure the focal length and achieve focusing in the actual use environment is needed to improve the imaging quality of the camera. Summary of the invention

[0004] In view of this, the present invention aims to provide a focusing and focal length measuring device and method to improve the measurement accuracy and reduce the overall volume of the measuring device.

[0005] To achieve the above object, the technical solution created by the present invention is implemented as follows:

[0006] The invention provides a focusing and focal length measuring device, comprising: a collimator, an optical path extension system, a lens and a beam receiving system arranged in sequence; the collimator is used to emit a Gaussian beam; the optical path extension system comprises: an incident mirror, an optical path extension mirror group and an exit mirror; when focusing is performed, the optical axis of the Gaussian beam emitted by the collimator coincides with the optical axis of the lens, the Gaussian beam emitted by the collimator is reflected to the optical path extension mirror group by the incident mirror, the Gaussian beam is incident to the exit mirror after multiple reflections by the optical path extension mirror group, and is reflected to the lens by the exit mirror, and the optical axis of the Gaussian beam emitted by the exit mirror coincides with the optical axis of the lens; the beam receiving system has a target surface, and the Gaussian beam forms a light spot on the target surface through the lens; wherein the beam receiving system is movable in a direction parallel to the optical axis of the lens, and when focusing is performed, the incident angle of the Gaussian beam reflected by the incident mirror to the Gaussian beam is adjusted to adjust the object waist distance of the Gaussian beam.

[0007] Furthermore, the device also includes: a high-precision rotating displacement stage and an adjustment frame; the collimator is fixed on the adjustment frame, and the high-precision rotating displacement stage carries the adjustment frame and the collimator; when measuring the focal length, the high-precision rotating displacement stage is used to drive the collimator to rotate a preset angle so that the angle between the optical axis of the Gaussian light beam emitted by the collimator and the optical axis of the lens is a preset angle.

[0008] Furthermore, the high-precision rotation stage has an angle feedback module, and the angle feedback module is used to obtain the rotation angle of the collimator.

[0009] Furthermore, the optical path extension system also includes a shell, the shell has a accommodating cavity and an opening, the accommodating cavity is connected to the outside through the opening, the optical path extension mirror group is arranged in the accommodating cavity, the incident mirror and the exit mirror are arranged outside the shell, the Gaussian light beam is reflected by the incident mirror and then incident on the optical path extension mirror group from the opening, and the Gaussian light beam emitted by the optical path extension mirror group is incident on the exit mirror from the opening.

[0010] Furthermore, the optical path extension mirror group includes: a first reflector, a second reflector and a folding mirror. The reflective surface of the first reflector is opposite to and parallel to the reflective surface of the second reflector. The Gaussian light beam emitted from the incident mirror is reflected multiple times between the first reflector and the second reflector, and then is incident on the folding mirror. The folding mirror reflects the Gaussian light beam to the output mirror.

[0011] Furthermore, the beam receiving system includes: a first translation stage and a camera, the first translation stage carries the camera, the camera includes a target surface, and the first translation stage is used to drive the camera to move in a direction parallel to the optical axis of the lens; the device also includes: a computer, and the camera is connected to the computer.

[0012] Furthermore, the first translation stage has a position feedback module, and the position feedback module is used to obtain the distance between the camera and the lens.

[0013] On the other hand, the invention also provides a focusing and focal length measurement method, comprising: providing a focusing and focal length measurement device as described above, the device comprising: a collimator, an optical path extension system, a lens and a beam receiving system, the optical path extension system comprising an incident mirror, an optical path extension mirror group and an exit mirror, and the beam receiving system having a target surface; focusing, the focusing comprising: step S1: a Gaussian beam emitted by the collimator forms a light spot on the target surface through the optical path extension system and the lens, setting the incident angle of the Gaussian beam reflected by the incident mirror to a first angle, adjusting the optical path extension mirror group so that the optical axis of the Gaussian beam emitted by the exit mirror coincides with the optical axis of the Gaussian beam emitted by the collimator; step S2: moving the beam receiving system to N different positions along a direction parallel to the optical axis of the lens, obtaining the image distance between the beam receiving system and the lens at each position and the corresponding light spot radius, wherein N is an integer greater than or equal to 10; step S3: using curve fitting to obtain a first curve representing the relationship between the image distance and the spot radius when the incident angle is a first angle; step S4: setting the incident angle of the incident mirror to reflect the Gaussian light beam to a second angle, repeating step S2, and using curve fitting to obtain a second curve representing the relationship between the image distance and the spot radius when the incident angle is the second angle; step S5: setting the incident angle of the incident mirror to reflect the Gaussian light beam to a third angle, repeating step S2, and using curve fitting to obtain a third curve representing the relationship between the image distance and the spot radius when the incident angle is the third angle; step S6: obtaining the intersection of the first curve, the second curve and the third curve, determining the focal plane position according to the image distance corresponding to the intersection, and moving the beam receiving system to the focal plane position to achieve fixed focus.

[0014] Furthermore, the focus and focal length measurement device also includes: a high-precision rotary displacement stage and an adjustment frame, and the collimator is fixed on the adjustment frame; the method also includes: focal length measurement, and the focal length measurement includes: moving the beam receiving system to the focal plane position; removing the optical path extension system, and the Gaussian beam emitted by the collimator passes through the lens to form a light spot on the target surface; adjusting the high-precision rotary displacement stage to rotate the collimator by a preset angle, so that the light spot is displaced by a first length on the target surface; based on the preset angle and the first length, the focal length is obtained by a focal length calculation formula; the focal length calculation formula is: ; Wherein, Δr is the first length, f is the focal length, and α is the preset angle.

[0015] Furthermore, the curve fitting formula is: ; where z is the image distance, w is the spot radius, A, B and C are all unknown coefficients.

[0016] Compared with the prior art, the invention can achieve the following beneficial effects:

[0017] The present invention provides a focusing and focal length measuring device, and provides a method for focusing a camera and measuring the focal length of a camera lens based on curve fitting. In the focusing and focal length measuring device, an optical path extension system is used to reflect a Gaussian beam multiple times, thereby extending the transmission optical path of the Gaussian beam when the distance between a collimator and a lens is small, thereby reducing the overall volume of the device, thereby reducing the space occupied by the device and improving space utilization. In addition, the posture of an incident mirror in the optical path extension system is adjusted to change the incident angle of the incident mirror reflecting the Gaussian beam, thereby adjusting the object side beam waist distance. The object side beam waist distance is the length of the transmission path of the Gaussian light beam emitted from the collimator to the lens. The object side beam waist distance is changed by changing the incident angle of the incident mirror, thereby avoiding the need to move the collimator to change the object side beam waist distance. This overcomes the dependence of the mobile collimator operation on experience and manual operation accuracy, solves the problem of difficulty in ensuring high-precision measurement, and solves the problem of difficulty in ensuring the consistency of the optical axis of the Gaussian light beam before and after the mobile collimator. It also solves the problem of the mobile collimator causing the device to occupy too much space, making the measuring device more compact and portable, which is conducive to improving detection efficiency and accuracy, and has high practical value and broad application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] The drawings constituting part of the present invention are used to provide a further understanding of the present invention. The exemplary embodiments and descriptions of the present invention are used to explain the present invention and do not constitute an improper limitation on the present invention. In the drawings:

[0019] Figure 1 A schematic diagram of the structure of the focus setting and focal length measurement device according to an embodiment of the present invention;

[0020] Figure 2 Schematic diagram of the transmission of a Gaussian beam through a camera lens;

[0021] Figure 3 A schematic diagram of the structure of a focus fixing and focal length measuring device without an optical path extension system according to an embodiment of the present invention;

[0022] Figure 4 A flowchart of the method for focusing and measuring focal length as described in Example 1 of the present invention is created;

[0023] Figure 5 A simulation curve diagram of the spot radius with respect to distance at different object-side beam waist distances described in an embodiment of the present invention;

[0024] Figure 6 For the present invention to create the embodiment of the Figure 5 Simulation curve near the middle focus and partial enlargement diagram within the double focal depth;

[0025] Figure 7 This is a simulation curve diagram of the constant spot radius at the focus under different object waist distances described in the embodiment of the present invention.

[0026] Explanation of the accompanying drawings: 1. high-precision rotating translation stage; 2. adjustment frame; 3. collimator; 4. housing; 5. incident mirror; 6. first reflecting mirror; 7. second reflecting mirror; 8. folding mirror; 9. output mirror; 10. lens holder; 11. lens; 12. first translation stage; 13. camera; 14. computer. DETAILED DESCRIPTION

[0027] As can be seen from the background technology, there is an urgent need to provide a method for accurately measuring focal length and achieving fixed focus, so as to improve the imaging quality of the camera.

[0028] After analysis, it was found that the relevant technology involves an experimental device for measuring Raman beam parameters, which can be used for fixed focus. The experimental device includes: placing a beam expander, a lens and a beam quality analyzer on a scaled guide rail. The length of the entire device can reach about 2.4 meters. Since the spot size at the focal plane of the lens does not change with the change of the distance between the beam expander and the lens, the beam expander is placed at three different positions on the guide rail. For each position of the beam expander, the size of the spot diameter at 10 different distances from the beam quality analyzer to the lens is measured. For each position of the beam expander, a curve can be fitted according to the distance from the beam quality analyzer to the lens and the spot diameter. Three different beam expander positions can be fitted to obtain three curves, and then the intersection of the three curves can be obtained. According to the intersection, the focal plane position of the lens in the experiment can be determined. However, the disadvantages of this method include: large volume, changing the object waist distance by moving the beam expander, and the beam expander may be offset during the movement process, thereby causing a change in the beam direction and an offset of the optical axis.

[0029] In addition, during the installation and adjustment of infrared cameras, large-diameter collimators are often used to simulate parallel light emitted from infinity, and then the infrared cameras are installed and adjusted, with the clarity and size of the camera target light spot imaging and the number of pixels occupied by the light spot as the basis for judgment, or the infrared cameras are installed and adjusted through image algorithms and clarity evaluation. If collimators are used for focusing and focal length measurement, a large-diameter collimator is usually required, which has the disadvantages of large equipment size, high cost, poor flexibility, difficult maintenance, and strong environmental dependence.

[0030] In order to solve the above problems, the present invention provides a focusing and focal length measuring device and method, which are beneficial to improving the measurement accuracy and reducing the overall volume of the measuring device.

[0031] In order to make the purpose, technical solution and advantages of the invention more clear, the invention is further described in detail below in conjunction with the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described here are only used to explain the invention and do not constitute a limitation of the invention.

[0032] It should be noted that, in the absence of conflict, the embodiments of the present invention and the features in the embodiments may be combined with each other.

[0033] In the description of the invention, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise", etc., indicating the orientation or position relationship, are based on the orientation or position relationship shown in the drawings, and are only for the convenience of describing the invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the invention. In addition, the terms "first", "second", etc. are only used for descriptive purposes, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Therefore, the features defined as "first", "second", etc. may explicitly or implicitly include one or more of the features. In the description of the invention, unless otherwise specified, the meaning of "multiple" is two or more.

[0034] In the description of the invention, it should be noted that, unless otherwise clearly specified and limited, the terms "installation", "connection" and "connection" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in the invention can be understood according to specific circumstances.

[0035] The present invention will be described in detail below with reference to the accompanying drawings and in combination with embodiments.

[0036] Figure 1 The present invention is a schematic structural diagram of a focus setting and focal length measurement device according to an embodiment of the present invention.

[0037] refer to Figure 1The focus setting and focal length measuring device provided by the invention comprises: a collimator 3, an optical path extension system, a lens 11 and a beam receiving system which are arranged in sequence; the collimator 3 is used to emit a Gaussian beam; the optical path extension system comprises: an incident mirror 5, an optical path extension mirror group and an exit mirror 9; when focusing, the optical axis of the Gaussian beam emitted by the collimator 3 coincides with the optical axis of the lens 11, the Gaussian beam emitted by the collimator 3 is reflected to the optical path extension mirror group by the incident mirror 5, the Gaussian beam is incident to the exit mirror 9 after multiple reflections by the optical path extension mirror group, and is reflected to the lens 11 by the exit mirror 9, and the optical axis of the Gaussian beam emitted by the exit mirror 9 coincides with the optical axis of the lens 11; the beam receiving system has a target surface, and the Gaussian beam forms a light spot on the target surface through the lens 11; wherein the beam receiving system is movable in a direction parallel to the optical axis of the lens 11, and when focusing, the incident angle of the Gaussian beam reflected by the incident mirror 5 is adjusted to adjust the object waist distance of the Gaussian beam.

[0038] It should be noted that the collimator 3 may be a fiber collimator, and the object-side beam waist distance is the length of the Gaussian beam transmission path during the process of the Gaussian beam emitted from the collimator 3 being transmitted to the lens 11 .

[0039] The Gaussian light beam is reflected multiple times by using the optical path extension system, thereby extending the transmission optical path of the Gaussian light beam when the distance between the collimator 3 and the lens 11 is small, which is beneficial to reducing the overall volume of the device. The object waist distance is changed by changing the incident angle of the incident mirror 5, thereby avoiding changing the object waist distance by moving the collimator 3, overcoming the dependence of the operation of moving the collimator 3 on experience and manual operation accuracy, solving the problem of difficulty in ensuring high-precision measurement, and solving the problem of difficulty in ensuring the consistency of the optical axis of the Gaussian light beam before and after moving the collimator 3, and solving the problem of the device occupying too much space due to moving the collimator 3, making the device more compact and portable.

[0040] In other embodiments of the present invention, the focus setting and focal length measuring device may further include: a lens holder 10 , and the lens holder 10 is used to fix and support the lens 11 .

[0041] The specific method of using the focusing and focal length measuring device provided by the embodiment of the present invention is as follows: Figure 1, the Gaussian beam is output by the collimator 3. Since the spot size formed by the Gaussian beam at the focal plane of the lens 11 is unchanged and has nothing to do with the object waist distance, the Gaussian light emitted from the collimator 3 enters the optical path extension system. The incident mirror 5 changes the incident angle for reflecting the Gaussian beam, thereby changing the object waist distance, which is equivalent to changing the distance between the collimator 3 and the lens 11. After each adjustment of the object waist distance, the Gaussian beam adjusted by the optical path extension system passes through the lens 11 and finally enters the beam receiving system to form a spot on the target surface. The radius of the spot formed on the target surface is measured, and by measuring the change of the spot radius with the position of the beam receiving system, the spot radius corresponding to different positions on the imaging side of the lens 11 is accurately measured, and three curves of the spot radius corresponding to different object waist distances with respect to the position of the beam receiving system are fitted. The position of the beam receiving system corresponding to the intersection of the three curves is the focal plane position or the focus position, and the focal plane position or the focus position is also the fixed focus position of the camera 13. The light beam receiving system is adjusted to a fixed focus position, the light path extension system is removed, and the collimator 3 is rotated by a preset angle. The displacement of the light spot on the target surface before and after the collimator 3 is rotated can be obtained. If the displacement amount is defined as the first length, the focal length of the lens 11 can be calculated based on the preset angle and the first length.

[0042] The analysis of the Gaussian beam spot size at the focal plane of lens 11 being constant and independent of the object waist distance is as follows:

[0043] The ABCD matrix of the Gaussian beam can be used to obtain the complex parameter q at the position where the imaging side of the lens 11 is at a distance z from the lens 11: z Satisfies the following formula:

[0044] ;

[0045] ;

[0046] Figure 2 This is a schematic diagram of a Gaussian beam passing through a camera lens. Figure 2 In the above formula, z is the distance from the imaging side of lens 11 to lens 11, and λ is the wavelength. is the focal length of lens 11, w 0 is the object waist radius, L is the object waist distance, R z is the constant phase curvature radius of the Gaussian beam at a distance z from the lens 11 on the imaging side, w z is the Gaussian beam radius at a position where the imaging side is at a distance z from the lens 11, and i is an imaginary number. Compared with not setting up an optical path extension system, adding an optical path extension system can change the object side beam waist distance L.

[0047] when At this time, the radius of the light spot formed on the target surface at a distance F from the lens 11 on the imaging side is , it can be seen that the spot radius Only with laser wavelength , focal length F, object-space beam waist radius Related to the spot radius It is independent of the object waist distance L, that is, the spot radius at the focal plane position The spot radius at the focal plane does not change with the change of the object waist distance L. Is a fixed value.

[0048] For further reference, Figure 1 The focusing and focal length measuring device also includes: a high-precision rotation displacement stage 1 and an adjustment frame 2; the collimator 3 is fixed on the adjustment frame 2, and the high-precision rotation displacement stage 1 is used to carry the adjustment frame 2 and the collimator 3; when measuring the focal length, the high-precision rotation displacement stage 1 is used to drive the collimator 3 to rotate a preset angle so that the angle between the optical axis of the Gaussian light beam emitted by the collimator 3 and the optical axis of the lens 11 is a preset angle.

[0049] Furthermore, the high-precision rotational translation stage 1 has an angle feedback module, and the angle feedback module is used to obtain the rotation angle of the collimator 3 .

[0050] In this way, the rotation angle of the collimator 3 can be directly obtained through the high-precision rotation stage 1, accurate angle adjustment can be achieved, and more intuitive feedback of the rotation angle can be obtained through the high-precision rotation stage 1. Specifically, when measuring the focal length, the light beam receiving system is adjusted to a fixed focus position, the optical path extension system is removed, and the collimator 3 is driven by the high-precision rotation stage 1 to produce a precise rotation angle. Compared with before the collimator 3 is rotated, the light spot on the target surface is displaced after the collimator 3 is rotated. If the displacement amount is defined as a first length, the rotation angle of the collimator 3 can be obtained as a preset angle through the angle feedback module, and the focal length of the lens 11 can be calculated based on the preset angle and the first length.

[0051] It can be understood that the high-precision rotational translation stage can drive the collimator 3 to rotate at a precise angle. Therefore, the high-precision rotational translation stage can provide precise rotational angle adjustment and precise angle readings. In addition, the adjustment frame 2 is used to fix and adjust the collimator 3, and the adjustment frame 2 and the high-precision rotational translation stage 1 are used to align the collimator 3 with the optical axis of the lens 11.

[0052] For further reference, Figure 1The optical path extension system also includes a shell 4, which has a accommodating cavity and an opening. The accommodating cavity is connected to the outside through the opening. The optical path extension mirror group is arranged in the accommodating cavity, and the incident mirror 5 and the exit mirror 9 are arranged outside the shell 4. After being reflected by the incident mirror 5, the Gaussian beam is incident on the optical path extension mirror group from the opening, and the Gaussian beam emitted by the optical path extension mirror group is incident on the exit mirror 9 from the opening.

[0053] In other embodiments of the present invention, the housing 4 is a mechanical shell.

[0054] In some embodiments of the present invention, the optical path extension mirror group may include at least two plane mirrors. In other embodiments of the present invention, the optical path extension mirror group may also include: a first reflector 6, a second reflector 7 and a folding mirror 8, wherein the reflection surface of the first reflector 6 and the reflection surface of the second reflector 7 are arranged opposite and parallel to each other, and the Gaussian beam emitted by the incident mirror 5 is reflected multiple times between the first reflector 6 and the second reflector 7, and then incident on the folding mirror 8, and the folding mirror 8 reflects the Gaussian beam to the exit mirror 9. In this way, the optical path extension mirror group can effectively extend the optical path, making the overall volume of the focus and focal length measurement device smaller.

[0055] It should be noted that the reference Figure 1 The smaller the incident angle of the Gaussian beam incident on the incident mirror 5, the longer the optical path of the Gaussian beam after being transmitted through the optical path extension system, and the longer the object waist distance, which is equivalent to changing the distance between the collimator 3 and the lens 11. The Gaussian beam adjusted by the optical path extension system passes through the lens 11 and finally forms a spot on the target surface of the beam receiving system, and then the spot size on the target surface is measured.

[0056] The incident mirror 5, the first reflector 6, the second reflector 7, the folding mirror 8 and the exit mirror 9 are all plane mirrors, and the reflection path is constructed by the first reflector 6 and the second reflector 7. The light beam reflects back and forth between the first reflector 6 and the second reflector 7, which increases the propagation distance of the light in the optical path extension system. This multiple reflection configuration effectively extends the optical path length. The folding mirror 8 and the exit mirror 9 form a periscope folding optical path, so that the direction of the light beam emitted by the exit mirror 9 is consistent with the direction of the light beam incident on the incident mirror 5, that is, the original optical axis direction of the Gaussian beam is maintained.

[0057] For further reference, Figure 1 The light beam receiving system includes: a first translation stage 12 and a camera 13. The first translation stage 12 carries the camera 13. The camera 13 includes a target surface. The first translation stage 12 is used to drive the camera 13 to move in a direction parallel to the optical axis of the lens 11. The device also includes: a computer 14. The camera 13 is connected to the computer 14. The computer 14 is used to calculate the radius of the light spot.

[0058] Furthermore, the first translation stage 12 has a position feedback module, and the position feedback module is used to obtain the distance between the camera 13 and the lens 11 .

[0059] The target surface of the camera 13 can receive the light spot and transmit the data representing the light spot size to the computer 14. The computer 14 can calculate the light spot radius according to the method for measuring the light spot radius specified in the international standard ISO11146. That is to say, the light spot sizes corresponding to different positions on the imaging side of the lens 11 can be accurately measured through the camera 13, the computer 14 and the first translation stage 12 with a position feedback function. In this way, the change of the light spot size with the position of the camera 13 can be accurately measured through the camera 13, the computer 14 and the first translation stage 12 with a position feedback function, and then the computer 14 can be used to fit the curves of the light spot size corresponding to three different object waist distances with respect to the position of the camera 13.

[0060] The first displacement stage 12 with position feedback function can also be used to drive the camera 13 to make a small displacement, so as to facilitate precise focusing.

[0061] On the other hand, the present invention also provides a focusing and focal length measuring method, including: providing a focusing and focal length measuring device as described above. It should be noted that the parts that are the same as or corresponding to the above-mentioned embodiments can refer to the above-mentioned embodiments and will not be described in detail below.

[0062] The focusing and focal length measuring device comprises: a collimator 3, an optical path extension system, a lens 11 and a beam receiving system. The optical path extension system comprises an incident mirror 5, an optical path extension mirror group and an output mirror 9. The beam receiving system has a target surface.

[0063] The method for focusing and measuring focal length includes: performing focusing, and focusing includes:

[0064] Step S1: The Gaussian light beam emitted by the collimator 3 forms a light spot on the target surface through the optical path extension system and the lens 11, the incident angle of the incident mirror 5 to reflect the Gaussian light beam is set to a first angle, and the optical path extension mirror group is adjusted to make the optical axis of the Gaussian light beam emitted by the exit mirror 9 coincide with the optical axis of the Gaussian light beam emitted by the collimator 3; Step S2: Move the light beam receiving system to N different positions along a direction parallel to the optical axis of the lens 11, the distance between any two adjacent positions may be the same or different, and obtain the image distance between the light beam receiving system and the lens 11 at each position and the corresponding light spot radius, wherein N is an integer greater than or equal to 10; Step S3: When the incident angle is the first angle, obtained by curve fitting, A first curve representing the relationship between the image-side distance and the spot radius; step S4: setting the incident angle of the incident mirror 5 to reflect the Gaussian light beam to a second angle, repeating step S2, and using curve fitting to obtain a second curve representing the relationship between the image-side distance and the spot radius when the incident angle is the second angle; step S5: setting the incident angle of the incident mirror 5 to reflect the Gaussian light beam to a third angle, repeating step S2, and using curve fitting to obtain a third curve representing the relationship between the image-side distance and the spot radius when the incident angle is the third angle; step S6: obtaining the intersection of the first curve, the second curve and the third curve, determining the focal plane position according to the image-side distance corresponding to the intersection, and moving the beam receiving system to the focal plane position to achieve fixed focus.

[0065] Figure 3 The present invention is a schematic structural diagram of a focus fixing and focal length measuring device without an optical path extension system as described in an embodiment of the present invention.

[0066] Furthermore, the focusing and focal length measurement device further comprises: a high-precision rotation displacement stage 1 and an adjustment frame 2, and a collimator 3 is fixed on the adjustment frame 2; the method further comprises: focal length measurement, and the focal length measurement comprises: referring to Figure 3 , move the beam receiving system to the focal plane position; remove the optical path extension system, and the Gaussian beam emitted by the collimator 3 forms a light spot on the target surface through the lens 11; adjust the high-precision rotation stage 1 to rotate the collimator 3 by a preset angle, so that the light spot is displaced by a first length on the target surface; based on the preset angle and the first length, the focal length is obtained by the focal length calculation formula; the focal length calculation formula is: ; Wherein, Δr is the first length, f is the focal length, and α is the preset angle.

[0067] Furthermore, the curve fitting formula is: ; where z is the image distance, w is the spot radius, A, B and C are all unknown coefficients.

[0068] The position of the camera 13 can be adjusted by adjusting the first translation stage 12 , the curve can be fitted by using the computer 14 , and the angle of the collimator 3 can be adjusted by using the high-precision rotation translation stage 1 .

[0069] Figure 4 The present invention creates a flow chart of the method for focusing and focal length measurement described in Example 1.

[0070] Example 1

[0071] refer to Figure 4 , focus setting, focus setting includes:

[0072] Step S1: adjust the incident mirror 5 and the folding mirror 8 so that the incident angle of the incident mirror 5 is θ1, the object waist distance is L1, and the optical axis direction of the Gaussian beam emitted by the output mirror 9 is consistent with the optical axis direction of the Gaussian beam emitted by the collimator 3;

[0073] Step S2: Taking the machined focal plane position of the lens 11 as a reference, the camera 13 is moved N times by a fixed distance L0 within the effective position interval on the image side of the lens 11, and the radius of the light spot is recorded each time;

[0074] Step S3: Based on the distance between the camera 13 and the lens 11 and the light spot radius information corresponding to the distance, curve fitting is performed according to a curve fitting formula to obtain a first curve;

[0075] Step S4: adjust the incident mirror 5 and the folding mirror 8 so that the incident angle of the incident mirror 5 is θ2, and the optical axis direction of the Gaussian beam emitted by the output mirror 9 is consistent with the optical axis direction of the Gaussian beam emitted by the collimator 3. At this time, the object waist distance is L2. Repeat steps S2 and S3 to obtain the second curve.

[0076] Step S5: adjust the incident mirror 5 and the folding mirror 8 so that the incident angle of the incident mirror 5 is θ3, and the optical axis direction of the Gaussian beam emitted by the output mirror 9 is consistent with the optical axis direction of the Gaussian beam emitted by the collimator 3. At this time, the object waist distance is L3. Repeat steps S2 and S3 to obtain the third curve.

[0077] Step S6: according to the three curves obtained by fitting, the intersection of the three curves is found, and then the distance corresponding to the intersection is obtained as L4, and the camera 13 is moved to a position at a distance L4 from the lens 11, so that the camera 13 is focused.

[0078] After the focus is set, the focal length is measured. The steps are as follows:

[0079] The camera 13 is at a fixed focus position, the optical path extension system is removed, and the collimator 3 is rotated by an angle α using a high-precision rotation stage. The light spot will be displaced on the target surface of the camera 13, and the length of the displacement is , the focal length of lens 11 can be calculated using the focal length formula .

[0080] It should be noted that the significance of focal length measurement lies in that after moving the camera 13 to the fixed focus position, although the distance between the camera 13 and the lens 11 can be obtained, in practice, due to the influence of the camera 13 housing, there is still a certain distance between the camera 13 housing and the target surface. Only the fixed focus position where the camera 13 should be positioned is known, but the focal length of the lens 11 cannot be accurately obtained, so focal length measurement is required.

[0081] Figure 5 A simulation curve diagram of the spot radius with respect to distance at different object-side beam waist distances described in an embodiment of the present invention; Figure 6 For the present invention to create the embodiment of the Figure 5 Simulation curve near the middle focus and partial enlargement diagram within the double focal depth; Figure 7 This is a simulation curve diagram of the constant spot radius at the focus under different object waist distances described in the embodiment of the present invention.

[0082] Example 2

[0083] refer to Figures 5 to 7 , focus setting, focus setting includes:

[0084] Step S1: adjust the incident mirror 5 and the folding mirror 8 so that the incident angle of the incident mirror 5 is θ1, the object waist distance is in the range of 50 mm to 150 mm, and the optical axis direction of the Gaussian beam emitted by the output mirror 9 is consistent with the optical axis direction of the Gaussian beam emitted by the collimator 3;

[0085] Step S2: Taking the machined focal plane position of the lens 11 as a reference, the camera 13 is moved 20 times at a fixed distance within the effective position interval on the image side of the lens 11, and the radius of the light spot is recorded each time, wherein the fixed distance is in the range of 0.4 mm to 0.5 mm;

[0086] Step S3: Based on the distance between the camera 13 and the lens 11 and the light spot radius information corresponding to the distance, curve fitting is performed according to a curve fitting formula to obtain a first curve;

[0087] Step S4, adjust the incident mirror 5 and the folding mirror 8, so that the incident angle of the incident mirror 5 is θ2, and the optical axis direction of the Gaussian beam emitted by the output mirror 9 is consistent with the optical axis direction of the Gaussian beam emitted by the collimator 3. At this time, the object waist distance is in the range of 1400mm~1600mm, and repeat steps S2 and S3 to obtain the second curve;

[0088] Step S5, adjust the incident mirror 5 and the folding mirror 8, so that the incident angle of the incident mirror 5 is θ3, and the optical axis direction of the Gaussian beam emitted by the output mirror 9 is consistent with the optical axis direction of the Gaussian beam emitted by the collimator 3. At this time, the object waist distance is in the range of 2900 mm to 3100 mm, and repeat steps S2 and S3 to obtain the third curve;

[0089] Step S6: Find the intersection of the three curves obtained by fitting. Figure 5 and Figure 6 , the distance corresponding to the intersection is 500 mm, and the camera 13 is moved to a position 500 mm away from the lens 11, thus completing the focus setting of the camera 13.

[0090] After the focus is set, the focal length is measured. The steps are as follows:

[0091] The camera 13 is at a fixed focus position, the optical path extension system is removed, and the collimator 3 is rotated by an angle α using a high-precision rotation stage. The light spot will be displaced on the target surface of the camera 13, and the length of the displacement is , the focal length of lens 11 can be calculated using the focal length formula .

[0092] It should be noted that in Example 2, the aperture of the lens 11 is 50.8 mm, the focal depth of the lens 11 is 300.31 μm, and the spot size simulation curve at ±5 mm near the focus and the local magnification within 2 times the focal depth can be as follows: Figure 6 As shown in FIG. 1 , the distance corresponding to the intersection point is found to be 500 mm, and the camera 13 is moved to a position 500 mm away from the lens 11, and the focus of the camera 13 is completed. The focal plane spot simulation corresponding to different object waist distances can be as follows: Figure 7 As shown by Figure 7 It can be seen that the spot radius at the focal plane is a constant value of 0.375 mm.

[0093] In the embodiment of the present invention, the pixel size of the infrared camera 13 is 15 μm; the subdivision rate is 1 / 10, and the resolution after subdivision is 1.5 μm; and the focus accuracy is 0.8 μm.

[0094] In the embodiment of the present invention, the collimator 3 may be an APS05-1550 type optical fiber fixed focal length collimator 3 , the working wavelength of the collimator 3 is 1550 nm, and the beam divergence angle is 1.5 mrad.

[0095] The simulation shows that the method is practical and effective, and can achieve the focus of the camera 13. In the embodiment of the present invention, the focus accuracy can reach about 0.8 μm.

[0096] The advantages of the present invention over the prior art are that it can achieve high-precision focusing of the camera and accurate measurement of the focal length of the lens when the focal length of the lens is unknown. The present invention overcomes the problems of large equipment size, high cost, poor flexibility, and difficult maintenance during camera assembly or maintenance using the method of focusing and measuring focal length using a collimator. The present invention optimizes space utilization and reduces the overall volume of the detection device through precise component arrangement and path optimization, making the device more compact and portable, significantly reducing the physical space required for the device, and improving the efficiency of detection. In addition, the present method is suitable for complex optical detection environments, is easy to operate, and can achieve high-precision focusing of the camera and accurate measurement of the focal length of the camera lens.

[0097] It should be understood that the various forms of processes shown above can be used to reorder, add or delete steps. For example, the steps described in the disclosure of the present invention can be performed in parallel, sequentially or in different orders, as long as the desired results of the technical solution disclosed in the present invention can be achieved, and this document does not limit this.

[0098] The above specific implementations do not constitute a limitation on the protection scope of the present invention. It should be understood by those skilled in the art that various modifications, combinations, sub-combinations and substitutions can be made according to design requirements and other factors. Any modification, equivalent substitution and improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A focusing and focal length measuring device, characterized in that: include: A collimator, an optical path extension system, a lens and a beam receiving system are arranged in sequence; The collimator is used to emit a Gaussian beam; The optical path extension system comprises: an incident mirror, an optical path extension mirror group and an exit mirror; When focusing is performed, the optical axis of the Gaussian beam emitted by the collimator coincides with the optical axis of the lens, the Gaussian beam emitted by the collimator is reflected by the incident mirror to the optical path extension mirror group, the Gaussian beam is reflected by the optical path extension mirror group for multiple times and then is incident to the exit mirror, and is reflected by the exit mirror to the lens, and the optical axis of the Gaussian beam emitted by the exit mirror coincides with the optical axis of the lens; The beam receiving system has a target surface, and the Gaussian beam passes through the lens to form a light spot on the target surface; The light beam receiving system is movable in a direction parallel to the optical axis of the lens. When focusing is performed, the incident angle of the incident mirror reflecting the Gaussian light beam is adjusted to adjust the object-side beam waist distance of the Gaussian light beam.

2. The focusing and focal length measuring device according to claim 1, characterized in that: The device also includes: a high-precision rotation displacement stage and an adjustment frame; The collimator is fixed on the adjustment frame, and the high-precision rotation displacement stage carries the adjustment frame and the collimator; When measuring the focal length, the high-precision rotary translation stage is used to drive the collimator to rotate by a preset angle, so that the angle between the optical axis of the Gaussian light beam emitted by the collimator and the optical axis of the lens is the preset angle.

3. The focusing and focal length measuring device according to claim 2, characterized in that: The high-precision rotational translation stage has an angle feedback module, and the angle feedback module is used to obtain the rotation angle of the collimator.

4. The focusing and focal length measuring device according to claim 1, characterized in that: The optical path extension system also includes a shell, the shell has a accommodating cavity and an opening, the accommodating cavity is connected to the outside through the opening, the optical path extension mirror group is arranged in the accommodating cavity, the incident mirror and the exit mirror are arranged outside the shell, the Gaussian light beam is reflected by the incident mirror and is incident from the opening to the optical path extension mirror group, and the Gaussian light beam emitted from the optical path extension mirror group is incident from the opening to the exit mirror.

5. The focusing and focal length measuring device according to any one of claims 1 to 4, characterized in that: The optical path extension mirror group includes: a first reflector, a second reflector and a folding mirror. The reflective surface of the first reflector is opposite to and parallel to the reflective surface of the second reflector. The Gaussian light beam emitted from the incident mirror is reflected multiple times between the first reflector and the second reflector, and then is incident on the folding mirror. The folding mirror reflects the Gaussian light beam to the output mirror.

6. The focus setting and focal length measuring device according to claim 1, characterized in that: The beam receiving system comprises: a first translation stage and a camera, the first translation stage carries the camera, the camera comprises the target surface, and the first translation stage is used to drive the camera to move in a direction parallel to the optical axis of the lens; The device also includes: a computer, and the camera is connected to the computer.

7. The focus setting and focal length measuring device according to claim 6, characterized in that: The first translation stage has a position feedback module, and the position feedback module is used to obtain the distance between the camera and the lens.

8. A method for focusing and focal length measurement, characterized in that: include: A focus setting and focal length measuring device according to any one of claims 1 to 7 is provided, the device comprising: a collimator, an optical path extension system, a lens and a beam receiving system, the optical path extension system comprising an incident mirror, an optical path extension mirror group and an exit mirror, the beam receiving system having a target surface; Performing focus setting, the focus setting comprising: Step S1: The Gaussian beam emitted by the collimator forms a light spot on the target surface through the optical path extension system and the lens, the incident angle of the incident mirror to reflect the Gaussian beam is set to a first angle, and the optical path extension mirror group is adjusted so that the optical axis of the Gaussian beam emitted by the output mirror coincides with the optical axis of the Gaussian beam emitted by the collimator; Step S2: moving the light beam receiving system to N different positions along a direction parallel to the optical axis of the lens, and obtaining the image distance between the light beam receiving system and the lens and the corresponding spot radius at each position, wherein N is an integer greater than or equal to 10; Step S3: using curve fitting to obtain a first curve representing the relationship between the image-side distance and the spot radius when the incident angle is the first angle; Step S4: setting the incident angle of the incident mirror to reflect the Gaussian beam to a second angle, repeating step S2, and using curve fitting to obtain a second curve representing the relationship between the image-side distance and the spot radius when the incident angle is the second angle; Step S5: setting the incident angle of the incident mirror to reflect the Gaussian beam to a third angle, repeating step S2, and using curve fitting to obtain a third curve representing the relationship between the image distance and the spot radius when the incident angle is the third angle; Step S6: Obtain the intersection of the first curve, the second curve and the third curve, determine the focal plane position according to the image distance corresponding to the intersection, and move the light beam receiving system to the focal plane position to achieve fixed focus.

9. The method for focusing and focal length measurement according to claim 8, characterized in that: The focus setting and focal length measuring device further comprises: a high-precision rotary displacement stage and an adjustment frame, and the collimator is fixed on the adjustment frame; The method further includes: focal length measurement, wherein the focal length measurement includes: moving the beam receiving system to the focal plane position; The optical path extension system is removed, and the Gaussian light beam emitted by the collimator passes through the lens to form a light spot on the target surface; Adjusting the high-precision rotation stage to rotate the collimator by a preset angle, so that the light spot is displaced by a first length on the target surface; Obtaining a focal length by using a focal length formula based on the preset angle and the first length; The focal length formula is: ; Wherein, Δr is the first length, f is the focal length, and α is the preset angle.

10. The method for focusing and focal length measurement according to claim 8, characterized in that: The curve fitting formula is: ; Among them, z is the image distance, w is the spot radius, A, B and C are all unknown coefficients.

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