阅读说明：本技术 一种提高spad阵列相机探测效率的方法 (Method for improving detection efficiency of SPAD array camera ) 是由 唐建伟 陈学文 龚道和 王星泽 于 2019-09-10 设计创作，主要内容包括：本发明涉及一种利用微透镜阵列提高单光子雪崩二极管(SPAD)阵列相机探测效率的方法。该方法首先通过一个微透镜阵列将信号光聚焦成光斑阵列,然后通过一个缩放系统将所述光斑阵列的周期缩放到和SPAD阵列相机的感光阵列的周期相等,当缩放后的光斑阵列和所述SPAD阵列相机的感光阵列对准时,所述SPAD阵列相机的探测效率得到最大幅度的提高。本发明解决了SPAD阵列相机感光区填充因子过低的问题导致相机探测效率较低的问题,通过简单添加外部光路就可以直接对SPAD阵列相机进行探测效率的提升。(The invention relates to a method for improving the detection efficiency of a Single Photon Avalanche Diode (SPAD) array camera by utilizing a micro lens array. The method comprises the steps of firstly focusing signal light into a light spot array through a micro lens array, then zooming the period of the light spot array to be equal to the period of a photosensitive array of an SPAD array camera through a zooming system, and when the zoomed light spot array is aligned with the photosensitive array of the SPAD array camera, the detection efficiency of the SPAD array camera is improved to the greatest extent. The invention solves the problem of low detection efficiency of the camera caused by the low filling factor of the photosensitive area of the SPAD array camera, and can directly improve the detection efficiency of the SPAD array camera by simply adding an external light path.)

1. A method for improving the detection efficiency of an SPAD array camera is characterized in that signal light is focused into a light spot array through a micro-lens array, then the period of the light spot array is zoomed to be equal to that of a photosensitive array of the SPAD array camera through a zooming system, and when the zoomed light spot array is aligned with the photosensitive array of the SPAD array camera, the detection efficiency of the SPAD array camera is greatly improved.

2. The method of claim 1, wherein the microlens array is a two-dimensional microlens array having a period equal to or not equal to a SPAD array period of the SPAD camera.

3. The method of claim 1, wherein the magnification of the zoom system is:

in the formula, P_APDIs the period of the SPAD array, P_MLIs the period of the microlens array; the zooming system selects any optical path system capable of realizing the zooming multipleOr a device.

4. The method of claim 1 or 3, wherein the zoom system is a single lens imaging system or a 4f imaging system.

5. The method of claim 1, wherein the camera is a SPAD array camera with 32 x 32 pixels or more, each pixel of the camera capable of fast responding to single photon events with time dependent photon counting.

6. The method of claim 1, wherein the microlens array is carried on a frame that is translatable and rotatable, such that the microlens array is capable of translation and rotation in a plane perpendicular to the optical axis.

7. The method of claim 1, wherein the image plane of the microscope system or the telescope system is placed at the front focal plane of the microlens array for high efficiency time resolved single photon microscopy or telescope imaging.

Technical Field

The invention relates to the field of photon counting imaging, in particular to a method for improving detection efficiency of an SPAD array camera.

Background

Each pixel of the SPAD array camera based on the Geiger mode is equivalent to an SPAD detector, time-resolved photon counting imaging can be carried out, light intensity information and photon arrival time information can be provided, the SPAD array camera has remarkable advantages compared with a common camera, and the SPAD array camera has wide application prospects in the field of three-dimensional real-time imaging. Both Photon Force corporation and MPD corporation in italy in the uk currently have introduced 32 x 32 pixel commercial SPAD array cameras. However, since the SPAD array camera needs to integrate a TDC (time-to-digital conversion) circuit, the effective photosensitive area of each pixel only occupies a small part of the pixel area (for example, the photosensitive area fill factors of the SPAD array camera proposed by the present Photon Force and MPD companies are only 1.5% and 3.14%, respectively), which results in low effective detection efficiency of the camera. Therefore, it is highly desirable to improve the detection efficiency of SPAD array cameras.

In China, a research team proposes to place a matched micro-lens array in front of a detector to improve the detection efficiency of a laser radar echo signal (Wangji and the like, a laser radar receiving system and a laser radar receiving method), but the periods of the detector array and the micro-lens array are required to be the same. In order to improve the detection efficiency of the SPAD array camera by using the method, a micro-nano processing technology is needed to directly integrate the micro-lens array on a chip of the SPAD array camera. No effective method for improving the detection efficiency of SPAD array cameras is currently available.

Disclosure of Invention

The invention provides a method for improving the detection efficiency of an SPAD array camera by utilizing a micro-lens array and an optical zoom system, aiming at solving the problem that the detection efficiency of the camera is low due to the fact that the filling factor of a photosensitive area of the current SPAD array camera is too low. For the SPAD array camera with low filling factor of the photosensitive area, the invention can greatly improve the detection efficiency.

The technical scheme for realizing the invention is that signal light is focused into a light spot array through a micro-lens array, then the period of the light spot array is zoomed to be equal to the pixel period of an SPAD array camera through an optical zooming system, and the light spot array and the photosensitive areas of the SPAD array camera are aligned one by one.

Optionally, the microlens array is a two-dimensional microlens array, the array period of which may not be equal to the SPAD array period of the SPAD camera.

Optionally, the magnification of the zoom system is:

in the formula, P_APDIs the period of the SPAD array, P_MLIs the period of the microlens array. The scaling system may be any optical path system or device capable of achieving the scaling factor.

Optionally, the zoom system is a 4f system, consisting of two lenses, the focal length ratio of which is the desired magnification.

Optionally, the camera is a SPAD array camera with 32 × 32 pixels or more, each pixel of the camera can respond to single photon events quickly, and has both time resolution and photon counting functions.

Optionally, the microlens array is mounted on a frame that can translate and rotate, so that the microlens array can translate and rotate in a plane perpendicular to the optical axis, thereby achieving alignment of the zoomed light spot array and the photosensitive array of the SPAD array camera.

Optionally, an image plane of the microscope system or the telescope system is arranged at a front focal plane of the microlens array, so that high-efficiency time-resolved single photon microscopic imaging or telescope imaging can be realized.

The invention has the beneficial effects of solving the problem of low fill factor of the photosensitive area of the SPAD array camera and greatly improving the detection efficiency.

The invention utilizes the gathered optical signal of the micro lens array and adopts the optical zooming method to realize the matching of the micro lens array and the camera photosensitive array, can solve the problem of low filling factor of the photosensitive area of the SPAD array camera, greatly improves the detection efficiency and has the following advantages:

first, although the pixel period of the SPAD array camera is small, the size of the used microlens array can be relatively large because the invention adopts the optical zooming method for matching, and the microlens is directly matched and aligned to the photosensitive array of the camera without a complex integration process. Compared with the development and manufacture of a micro-lens array which is tiny in size and integrated on a chip, the development and manufacture of discrete micro-lens array components and parts with common sizes are greatly reduced in difficulty, and the development and manufacture of high-performance micro-lens arrays are facilitated, such as higher duty ratio, higher transmittance, larger numerical aperture, smaller aberration and the like.

Secondly, by using the method provided by the invention, the detection efficiency of the current commercial SPAD array camera can be directly improved by simply adding an external optical path.

Drawings

The technical solution of the present invention will be further specifically described with reference to the accompanying drawings and the detailed description.

FIG. 1 is a schematic diagram of the system for improving the detection efficiency of the SPAD array camera according to the invention. In the figure: 1, a micro-lens array; 2, an optical zoom system; 3, SPAD array camera; 4, SPAD array camera chips; 5, front focal plane of the micro lens array; 6, forming a light spot array at the rear focal plane of the micro-lens array; and 7, signal light to be detected.

FIG. 2 is a schematic diagram of the detection path of the 4f system selected for the zoom system in one embodiment. In the figure: 8, lens L1; 9, lens L2.

FIG. 3 is a schematic diagram of a photosensitive chip of the SPAD array camera of the present invention. In the figure: 32 x 32 pixels of a SPAD array camera chip; 11, the photosensitive area of the pixel.

Figure 4 is an illustration of the effect of improving SPAD detection efficiency using the present invention. The graph (a) in fig. 4 is an imaging effect graph after the detection efficiency is improved; the graph (b) is an imaging effect graph before the detection efficiency is improved.

Detailed Description

It should be understood that the following specific examples are only for illustrating the present application and are not to be construed as limiting the present application. It should be noted that the drawings provided in the embodiments are only for illustrative purposes and are not drawn to completely comply with the actual implementation, and the shapes, features, size ratios, spatial layouts and the like of the components in the drawings may be different from those in the actual implementation.

The invention provides a method for improving the detection efficiency of an SPAD array camera by utilizing a micro-lens array and an optical zoom system, aiming at solving the problem that the detection efficiency of the camera is low due to the fact that the filling factor of a photosensitive area of the current SPAD array camera is too low. The schematic diagram of the invention is shown in fig. 1, and the invention is composed of a micro lens array 1, a zooming system 2, a SPAD array camera 3 and the like in sequence. The signal light 7 is focused into the light spot array 6 through the micro lens array 1, then the period of the light spot array 6 is zoomed to be equal to the pixel period of the SPAD array camera chip 4 through the zooming system 2, and when the zoomed light spot array is aligned with the photosensitive array of the SPAD array camera chip 4, the detection efficiency of the SPAD array camera 3 is improved to the maximum extent.

Fig. 2 is a schematic diagram of a system optical path according to an embodiment of the present invention, in which a signal light 7 sequentially passes through a micro lens array 1, a lens 8, and a lens 9, and finally reaches the SPAD array camera chip 4 to be detected. In the light path, the lens 8 and the lens 9 constitute a 4f zoom system.

In this embodiment, the microlens array 1 used is a two-dimensional microlens array of N x N with an array period P_MLFocal length of the microlens is f_ML. Lens 8 having focal length f_L1Focal length of lens 9 is f_L2. As shown in fig. 3, the SPAD array camera chip 4 is a two-dimensional SPAD array 10 of 32 x 32 pixels, the period of the array 10 being P_APDEach pixel consists of a geiger mode SPAD photosensitive area 11 and a corresponding TDC circuit. The distance between the micro-lens array 1 and the lens 8 is equal to f_ML+f_L1The distance between lens 8 and lens 9 being equal to f_L1+f_L2The distance between the lens 9 and the SPAD array camera chip 4 is equal to f_L2The focal lengths of the lens 8 and the lens 9 satisfy f_L2/f_L1＝P_APD/P_ML。

The signal light 7 is converged on the focal plane of the micro lens array to form a light spot array 6 after passing through the micro lens array 1, and the period of the light spot array 6 is equal to the period P of the micro lens array_ML. Since the distance between the micro-lens array 1 and the lens 8 is equal to f_ML+f_L1The array of spots 6 is exactly in the focal plane of the lens 8. Therefore, the light spot array 6 is just imaged on the SPAD array camera chip 4 through the 4f zoom system formed by the lens 8 and the lens 9. F is satisfied due to the focal lengths of the lens 8 and the lens 9_L2/f_L1＝P_APD/P_MLI.e. the magnification of the 4f zoom system is P_APD/P_MLSo that the period of the array of spots imaged onto the surface of the SPAD array camera chip 4 is equal to the period P of the SPAD array_APD. In order to align the scaled array of spots with the photosensitive area of the SPAD array, translation and rotation of the array of spots is required. In an embodiment, the micro lens array 1 is mounted on a frame capable of translating and rotating, so that the micro lens array 1 can translate and rotate in a plane perpendicular to the optical axis, thereby realizing the alignment of the zoomed light spot array and the photosensitive array of the SPAD array camera. When the specific alignment operation is carried out, the optimal alignment can be realized only by adjusting the translation dimension and the rotation dimension to maximize the photon counting value on the SPAD array camera.

It should be noted that the signal light has different meanings at the front focal plane 5 (shown by a dotted line) of the microlens array 1 according to different application scenarios. It may be a light emitting entity, a cross section of a light beam, or an image plane of an optical imaging system, such as an image plane of a microscopic imaging system or an image plane of a telescopic imaging system. The smaller the divergence angle of the signal light emitted therefrom, the smaller the spot size of the spot array obtained after passing through the microlens array. For the SPAD array camera with a particularly small photosensitive area filling factor, the smaller the divergence angle of the signal light, the larger the detection efficiency improvement multiple can be obtained by using the invention.

In this embodiment, to demonstrate the effect of the present invention, a transparent glass plate printed with "MARK" opaque words is placed on the front focal plane 5 of the microlens array 1, and is illuminated vertically from the left side of the glass plate by a halogen lamp light with a low divergence angle, so that a photon counting image shown in the left side of fig. 4 can be obtained on the SPAD array camera 3. In contrast, the right image of fig. 4 shows a photon counting imaging under the same illumination condition before the detection efficiency is improved. Comparing the left image and the right image of fig. 4, it can be seen that the detection efficiency can be significantly improved by using the method of the present invention, so as to significantly improve the signal-to-noise ratio of photon counting imaging under the same illumination condition. In this embodiment, the detection efficiency of the SPAD array camera is improved by more than 20 times.

Finally, it should be noted that the above specific embodiments are only used for explaining the present invention, and have a more concrete description, but should not be construed as limiting the scope of the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted without departing from the spirit and scope of the invention as defined in the appended claims.