Receiving optical system with unlimited incident light angle of optical filter

Abstract

The utility model discloses a receiving optical system with an unlimited incident light angle of an optical filter, belongs to the technical field of detection imaging, and aims to solve the problem that the performance of a narrow-band interference optical filter of the conventional receiving optical system is influenced by the incident angle of the incident light. Comprising a first lens group, an aperture diaphragm, a second lens group, a first micro-lens array, a narrow-band interference filter and a second micro-lens array which are coaxially and sequentially arranged from front to back, a micro-lens unit of the second micro-lens array is a positive lens, the aperture diaphragm is located on an object space focal plane of the second lens group, an image space telecentric imaging lens group is imaged on a primary image plane, and the image space telecentric imaging lens group is located on a secondary image plane. The primary image plane coincides with the image space focal plane of the first micro-lens array, and the micro-mirror units of the first micro-lens array and the micro-mirror units of the second micro-lens array are in one-to-one correspondence and are aligned front and back. The image space telecentric imaging lens group can modulate the main light of each imaging view field to be parallel to the optical axis, thereby preventing the performance of the narrow-band interference optical filter from being affected by the incident angle of the incident light.

Description

Technical Field

[0001] This invention belongs to the field of detection and imaging technology, and particularly relates to a receiving optical system in which the angle of incident light from the filter is not limited. Background Technology

[0002] Narrowband interference filters are physical filtering devices that use the principle of multi-beam interference to allow light within a specific wavelength range to pass through. Due to their advantages over ordinary narrowband pass filters, such as narrower bandwidth and higher peak transmittance, they are now widely used in optical displays, optical communications, and optical instruments, playing a particularly crucial role in narrowband spectral imaging and laser imaging radar.

[0003] Narrowband spectral imaging refers to imaging light only at a specific wavelength or within a small spectral range centered on a specific wavelength, such as filter-based hyperspectral cameras. Hyperspectral cameras, also known as hyperspectral imaging spectrometers, are detection devices that integrate spectral acquisition and target imaging. Utilizing imaging spectroscopy technology, they can perform spectral imaging of the same target across a continuous spectral band, integrating spatial, radiometric, and spectral information about the target. Currently, hyperspectral cameras are widely used in resource surveys, environmental monitoring, national defense, and many other fields. Among different spectral principles, filter-based hyperspectral cameras offer advantages such as simple system structure, small size, light weight, high spatial resolution, and good flexibility. Whether using a filter wheel or a linearly graded filter, both achieve discrete or continuous narrowband spectral imaging within a certain spectral range through narrowband interference filters.

[0004] Laser imaging radar is a product of the combination of traditional radar and laser technology. It is an active detection imaging device that uses lasers to acquire depth and intensity information of a target's three-dimensional scene. It is currently widely used in environmental monitoring, autonomous driving, satellite ranging, and national defense, such as single-photon laser imaging radar based on the Time-of-Flight (ToF) ranging principle. Single-photon laser imaging radar is a novel laser imaging radar technology based on a Gm-APD area array detector for weak light detection, enabling the detection and counting of echo signal light at the single-photon level. Narrow-band interference filters play a crucial role in single-photon laser imaging radar based on the ToF ranging principle. Their passband width directly affects the background noise and image signal-to-noise ratio of the single-photon laser imaging radar, while the passband width and transmittance directly affect performance such as the upper limit of the detection range.

[0005] Narrow-band interference filters are physical filtering devices made using the principle of multi-beam interference. They can filter out monochromatic light with a nanometer-wide bandwidth, allowing only light within a specific wavelength range to pass through, from polychromatic light. The filtering function of narrow-band interference filters is achieved through the design of the optical film structure. When polychromatic light passes through a multilayer film system consisting of alternating high- and low-refractive-index films, light of different wavelengths is reflected and interfered between the films. This results in the superposition and enhancement of light waves of specific wavelengths, while light waves of other wavelengths cancel each other out, thereby achieving high transmittance for specific wavelengths and a high cutoff depth for other wavelengths.

[0006] Narrow-band interference filters are generally used when light is incident normally, i.e., the incident light is parallel to the filter normal. When light is incident obliquely on a narrow-band interference filter, as the angle between the incident light and the filter normal increases, the center wavelength of its passband will shift towards shorter wavelengths. The blue-shifted center wavelength can be obtained from equation (1):

[0007]

[0008] Where θ is the incident angle of the filter, and λ θ λ is the center wavelength of the filter corresponding to the incident angle θ, λ0 is the center wavelength of the filter at zero incident angle, and n eff This represents the overall refractive index of the filter. Increasing the incident angle of light also leads to a decrease in the peak transmittance of the narrowband interference filter, resulting in a wider bandwidth.

[0009] Narrowband interferometric filters play a crucial role in single-photon laser imaging radar based on the Time-of-Flight (ToF) ranging principle. Typically, a narrowband interferometric filter is added to the receiving optical system to cut off light outside the laser wavelength of the signal source, preventing stray light from triggering the Gm-APD focal plane detector; this achieves the purpose of suppressing background noise, improving the signal-to-noise ratio, and increasing the probability of target detection.

[0010] When light rays are incident obliquely on a narrowband interference filter, its filtering performance can severely impact the receiving efficiency of a single-photon laser imaging radar. The operating wavelength of the laser imaging radar is the same as the wavelength of the laser emitted from the laser. When the incident angle of the narrowband interference filter is too large, resulting in an excessive blue shift of its passband center wavelength, such as... Figure 3 As shown, this may affect the laser wavelength (λ in the figure). laser It is cut off because it exceeds the passband of the filter.

[0011] The effects of this phenomenon on single-photon lidar include, but are not limited to: decreased light transmission efficiency of the receiving optical system, vignetting, and reduced imaging field of view. In addition, decreased filter transmittance also leads to decreased light transmission efficiency of the receiving optical system, and passband broadening further reduces the detection probability and upper limit of the detection range of the single-photon lidar.

[0012] Because the performance of narrowband interference filters, such as center wavelength, transmittance, and passband bandwidth, is easily affected by the angle of incident light, in the design of receiving optical systems that require narrowband interference filters, it is necessary to make the incident angle of light on all incident filters as small as possible or not exceeding a certain value, so that the performance of the filters remains relatively unchanged. However, for various fixed-focus, zoom, or complex optical systems with different imaging field of view requirements, it is usually difficult to find a suitable position in the optical path to place the filters so that the incident angle of light on all incident filters is as small as possible. Therefore, a receiving optical system design with unrestricted incident light angle of the filters is needed to meet the requirement of unrestricted incident light angle of the filters.

[0013] Therefore, based on the technical requirements, this utility model patent designs a receiving optical system with an unrestricted incident angle of the filter. It features that the performance of the narrowband interference filter is not affected by the incident light angle of any aperture in any field of view, and it is suitable for fixed-focus and zoom receiving optical imaging systems in any field of view. Utility Model Content

[0014] The purpose of this invention is to provide a receiving optical system with an unrestricted incident light angle, thereby solving the problem that the performance of narrowband interference filters in existing receiving optical systems is affected by the incident light angle. The technical solution adopted by this invention is as follows:

[0015] A receiving optical system with an unrestricted incident light angle via a filter includes an image-side telecentric imaging lens group and a microlens array-filter lens group. The image-side telecentric imaging lens group includes a first lens group, an aperture stop, and a second lens group. The microlens array-filter lens group includes a first microlens array, a narrowband interference filter, and a second microlens array. The first lens group, aperture stop, second lens group, first microlens array, narrowband interference filter, and second microlens array are coaxially arranged from front to back. The microlens units of the second microlens array are positive lenses. The aperture stop is located on the object-side focal plane of the second lens group. The image-side telecentric imaging lens group images onto a primary image plane, which coincides with the image-side focal plane of the first microlens array. Each microlens unit of the first microlens array corresponds to and is aligned with each microlens unit of the second microlens array.

[0016] Furthermore, the first lens group is composed of several convex lenses arranged coaxially in sequence.

[0017] Furthermore, the second lens group is composed of several convex lenses arranged coaxially in sequence.

[0018] Furthermore, the micromirror units of the first microlens array are either positive lenses or negative lenses.

[0019] Furthermore, each micromirror unit of the first microlens array is aligned front to back with each pixel of the detector.

[0020] Compared with existing technologies, this utility model is closely integrated with practical applications, taking into account both the rationality and feasibility of the design, and has the following advantages:

[0021] 1. The receiving optical system consists of an image-side telecentric imaging lens group and a microlens array-filter lens group, which avoids the influence of the incident angle of the incident light on the performance of the narrowband interference filter.

[0022] 2. The first microlens array modulates the light rays of each imaging field of the receiving optical system into parallel or nearly parallel light incident on the narrowband interference filter, so that the incident angle of all light rays incident on the narrowband interference filter is zero or close to zero degrees.

[0023] 3. The second microlens array converges the light rays from each imaging field of view that have passed through the narrowband interference filter onto the focal plane of the detector, which can then be used for detector detection. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of the structure of the present invention when the micromirror unit of the first microlens array is a positive lens;

[0025] Figure 2 This is a schematic diagram of the structure of the present invention when the micromirror unit of the first microlens array is a negative lens;

[0026] Figure 3 This is a wavelength curve diagram showing that the excessive blue shift of the center wavelength of the passband caused by the excessive incident angle of the narrowband interference filter.

[0027] In the figure, 1. Image-side telecentric imaging mirror group, 11. First lens group, 12. Aperture stop, 13. Second lens group, 14. Combustion chamber, 2. Microlens array-filter mirror group, 21. First microlens array, 22. Narrowband interference filter, 23. Second microlens array, 3. Detector focal plane, 4. Primary image plane. Detailed Implementation

[0028] To make the objectives, technical solutions, and advantages of this utility model clearer, the present utility model is described below with reference to specific embodiments shown in the accompanying drawings. However, it should be understood that these descriptions are merely exemplary and not intended to limit the scope of the present utility model. Furthermore, descriptions of well-known structures and technologies are omitted in the following description to avoid unnecessarily obscuring the concept of the present utility model.

[0029] The connections mentioned in this utility model are divided into fixed connections and detachable connections. Fixed connections, also known as non-detachable connections, include but are not limited to conventional fixed connection methods such as folded connections, riveted connections, adhesive connections, and welded connections. Detachable connections include but are not limited to conventional disassembly methods such as bolt connections, snap-fit ​​connections, pin connections, and hinge connections. When a specific connection method is not explicitly defined, it is assumed that at least one existing connection method can be found to achieve this function, and those skilled in the art can choose according to their needs. For example, a welded connection can be chosen for a fixed connection, and a bolted connection can be chosen for a detachable connection.

[0030] The present invention will be further described in detail below with reference to the accompanying drawings. The following embodiments are explanations of the present invention, but the present invention is not limited to the following embodiments.

[0031] Example: Figures 1-3 As shown, a receiving optical system with an unrestricted incident light angle via a filter includes an image-side telecentric imaging lens group 1 and a microlens array-filter lens group 2. The image-side telecentric imaging lens group 1 includes a first lens group 11, an aperture stop 12, and a second lens group 13. The microlens array-filter lens group 2 includes a first microlens array 21, a narrowband interference filter 22, and a second microlens array 23. The first lens group 11, the aperture stop 12, the second lens group 13, the first microlens array 21, the narrowband interference filter 22, and the second microlens array 23 are arranged coaxially from front to back. The microlens units of the second microlens array 23 are positive lenses. The aperture stop 12 is located on the object-side focal plane of the second lens group 13. The image-side telecentric imaging lens group 1 images onto a primary image plane 4, which coincides with the image-side focal plane of the first microlens array 21. Each microlens unit of the first microlens array 21 corresponds to and is aligned with each microlens unit of the second microlens array 23.

[0032] The first lens group 11 is composed of several convex lenses arranged coaxially in sequence.

[0033] The second lens group 13 is composed of several convex lenses arranged coaxially in sequence.

[0034] The microlens units of the first microlens array 21 are either positive lenses or negative lenses.

[0035] Each microlens unit of the first microlens array 21 is aligned front to back with each pixel of the detector.

[0036] The target echo light in each imaging field of view is first focused by the first lens group 11, then limited by the aperture stop 12, and then focused again by the second lens group 13, forming an image on the primary image plane 4. By constraining the aperture stop 12 to be located on the object-side focal plane of the second lens group 13, the image-side telecentric condition is formed. After being modulated by the image-side telecentric imaging lens group 1, the different target echo lights are then collimated by the first microlens array 21 to form parallel light, filtered by the narrowband interference filter 22, and finally focused by the second microlens array 23, forming images on the detector focal plane 3 for detector detection.

[0037] This invention comprises an image-side telecentric imaging mirror group 1 and a microlens array-filter mirror group 2. The image-side telecentric imaging mirror group 1 enables imaging of multiple target echo beams, while ensuring that the principal rays of the multiple target echo beams in each imaging field of view are parallel to the optical axis, and the size of the primary image plane 4 is the same as the size of the detector focal plane 3; the first microlens array 21 is placed after the image-side telecentric imaging mirror group 1, so that the object-side focal plane of the first microlens array 21 coincides with the primary image plane 4; Figure 1 and Figure 2 Schematic diagrams illustrating the implementation of this invention using two different first microlens arrays 21 are provided. Colored lines represent target echo light incident from different angles. The micromirror units of the first microlens array 21 can be positive lenses, such as... Figure 1 As shown, it can also be a negative lens, such as... Figure 2 As shown, when the micromirror unit of the first microlens array 21 is a positive lens, the object-side focal plane of the first microlens array 21 is located between the second lens group 13 and the first microlens array 21. When the micromirror unit of the first microlens array 21 is a negative lens, the object-side focal plane of the first microlens array 21 is located between the first microlens array 21 and the narrowband interference filter 22.

[0038] The number of micromirror units in the first microlens array 21 along the horizontal and vertical directions is the same as the number of pixels in the detector along the horizontal and vertical directions. The spacing between the micromirror units in the first microlens array 21 is the same as the pixel spacing of the detector. The radial position of the center of each micromirror unit in the first microlens array 21 corresponds one-to-one with the position of each pixel in the detector. The imaging field rays converging at the first image plane are collimated by the first microlens array 21 and become rays parallel to the optical axis. The narrowband interference filter 22 is set in the first microlens array 21. After the lens array 21 and perpendicular to the optical axis, the light rays from each aperture in each field of view will enter the narrowband interference filter 22 at an incident angle of zero degrees or close to zero degrees. This avoids phenomena such as blue shift of the transmission band and decrease in transmittance caused by the incident light angle not being parallel to the filter normal, or controls them within the acceptable range of the receiving optical system. The micromirror units of the second microlens array 23 are positive lenses, and the number of micromirror units, the unit spacing, and the radial position of each unit in the second microlens array 23 are the same as those in the first microlens array 21. When the second microlens array 23 is placed after the narrowband interference filter 22, and the image-side focal plane of the second microlens array 23 coincides with the detector focal plane 3, the light rays from each field of view will converge again on the detector focal plane 3 to achieve imaging.

[0039] The main function of the telecentric imaging lens group 1 is to achieve imaging of the target under test with the required field of view, and to make the principal rays of each field of view parallel to the optical axis.

[0040] The main function of the first microlens array 21 is to modulate the main rays converging from each field of view of the image-side telecentric imaging lens group 1 into parallel rays, that is, the rays from each aperture of each field of view are parallel to the optical axis.

[0041] The main function of the second microlens array 23 is to refocus the parallel or near-parallel light rays from each field of view that have passed through the narrowband interference filter 22 onto the focal plane 3 of the detector, thereby achieving imaging for the detector to use for detection.

[0042] This utility model is closely integrated with practical applications, taking into account both the rationality and feasibility of the design, and has the following advantages:

[0043] 1. The receiving optical system consists of an image-side telecentric imaging mirror group 1 and a microlens array-filter mirror group 2, which avoids the performance of the narrowband interference filter 22 being affected by the incident angle of the incident light.

[0044] 2. The first microlens array 21 modulates the light rays of each imaging field of the receiving optical system into parallel or nearly parallel light rays incident on the narrowband interference filter 22, so that the incident angle of all light rays incident on the narrowband interference filter 22 is zero or close to zero degrees.

[0045] 3. The second microlens array 23 converges the light rays from each imaging field of view that have passed through the narrowband interference filter 22 onto the focal plane 3 of the detector, which can then be used for detector detection.

[0046] The above embodiments are merely illustrative examples of the present utility model and do not limit its scope of protection. Those skilled in the art can make partial changes to it, as long as they do not exceed the spirit and essence of the present utility model, they are all within the scope of protection of the present utility model.

Claims

1. An optical system for receiving light from an optical filter, the optical system being free of a restriction on the angle of incidence of light rays, characterized in that: The application relates to an imaging lens, which comprises a like-side telecentric imaging lens (1) and a microlens array-filter lens (2); the like-side telecentric imaging lens (1) comprises a first lens group (11), an aperture diaphragm (12) and a second lens group (13), the microlens array-filter lens (2) comprises a first microlens array (21), a narrow-band interference filter (22) and a second microlens array (23), the first lens group (11), the aperture diaphragm (12), the second lens group (13), the first microlens array (21), the narrow-band interference filter (22) and the second microlens array (23) are coaxially arranged in sequence from front to back, the microlens units of the second microlens array (23) are positive lenses, the aperture diaphragm (12) is located on the object-side focal plane of the second lens group (13), the like-side telecentric imaging lens (1) is imaged on a primary image plane (4), the primary image plane (4) is coincident with the image-side focal plane of the first microlens array (21), and each microlens unit of the first microlens array (21) is aligned with each microlens unit of the second microlens array (23) in front and back.

2. The receiving optical system with an unrestricted incident light angle according to claim 1, characterized in that: The first lens group (11) is composed of coaxially arranged convex lenses in sequence.

3. The optical system according to claim 2, wherein the optical system is capable of receiving light from an optical filter having an incident light ray angle of 0° to 90°. The second lens group (13) is composed of coaxially arranged convex lenses in sequence.

4. The optical system according to any one of claims 1 to 3, wherein the optical system is not limited in the angle of the incident light. The microlens units of the first microlens array (21) are positive lenses or negative lenses.

5. The optical system according to claim 4, wherein the optical system is capable of receiving light from an optical filter having an incident light ray angle of 0° to 90°. Each microlens unit of the first microlens array (21) is aligned with each image element of a detector in front and back.

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