CN108051908B - An imaging optical system - Google Patents

Abstract

The present invention relates to optical image technology fields, a kind of imaging optical system is disclosed, including the first off axis reflector mirror, the first lens group, DMD micro mirror array, the second off axis reflector mirror, imaging microscope group and detector, the light that target object issues is assembled through the first off axis reflector mirror, into first lens group, it images on the DMD micro mirror array, imaging beam again passes by first lens group after being reflected by the DMD micro mirror array, then after the second off axis reflector mirror collimation, into the imaging microscope group, then image on the detector.Above system is designed using the optical texture that DMD makees intermediate image plane and partial symmetry, DMD micro mirror array and detector pixel spatially one-to-one relationship is dexterously realized, to reach the processing to imaging system admission light.Using the corresponding imaging relations of DMD device and detector pixel, the gray scale of adjustable detector target surface, to expand the dynamic range of photo electric imaging system.

Description

An imaging optical system

technical field

The invention relates to the technical field of optical imaging, in particular to an imaging optical system.

Background technique

DMD is a popular spatial light modulator in recent years, mainly used in optical systems such as projectors and target generators. The DMD modulates the light intensity by controlling the flipping of millions of micromirrors on it, and each micromirror can be individually controlled. The state of the micromirror can be controlled by changing the data in the data unit corresponding to the micromirror.

As a main optoelectronic imaging device, the image sensor has a detectable dynamic range of 48-60dB, which is the main factor restricting the detection range of the optoelectronic imaging system. High dynamic range imaging technology has an urgent demand in deep space exploration, medical imaging, military observation and other fields. Usually, the software processing method of multiple exposures or the hardware method of increasing the number of detectors can be used to improve the dynamic range of the photoelectric system. However, the former multiple exposure technology based on time domain cannot detect high-speed dynamic targets, and the latter increases the detection The hardware method of the processor greatly increases the cost of the system and requires a lot of post-processing to complete the image fusion.

Contents of the invention

The present invention aims to overcome the limitation of the dynamic range of the existing image sensor on the detection dynamic range of the photoelectric system, and provides an imaging optical system that meets the requirements for scene measurement and observation of high dynamic radiation energy characteristics.

To achieve the above object, the present invention adopts the following technical solutions:

The present invention provides an imaging optical system, including a first off-axis reflector, a first lens group, a DMD micromirror array, a second off-axis reflector, an imaging mirror group and a detector. The light emitted by a target object passes through the first An off-axis reflector converges, enters the first lens group, and is imaged on the DMD micromirror array. After being reflected by the DMD micromirror array, the imaging beam passes through the first lens group again, and then passes through the second lens group. After the two off-axis mirrors are collimated, they enter the imaging mirror group, and then image on the detector;

The design of the imaging optical system follows the right-hand coordinate rule, the Z axis is the system optical axis, and coincides with the base normal of the DMD micromirror array, and the light incident direction is parallel to the Z axis and points to the positive direction;

The first off-axis reflector is offset along the Y direction with an aperture off-axis in the YOZ plane, and the offset amount is not less than the light aperture of the first off-axis reflector, and the second off-axis reflector The reflector is offset along the X direction in an off-axis manner in the XOZ plane, and the offset amount of the second off-axis reflector along the X direction is the same as the offset of the first off-axis reflector along the Y direction The amount is the same, the first off-axis reflector and the second off-axis reflector have the same surface parameters, and the optical path that the light passes between the two off-axis reflectors is about the DMD micromirror array The normal is symmetrical, and the second off-axis reflector coincides with the first off-axis reflector after rotating clockwise by 90° around the normal of the DMD micromirror array.

In some embodiments, the entrance pupil of the imaging optical system is located behind the first off-axis mirror in the incident direction of the light beam.

In some embodiments, both the first off-axis reflector and the second off-axis reflector are concave quadric surfaces with negative optical power.

In some embodiments, the surface expressions of the quadric surfaces of the first off-axis reflector and the second off-axis reflector are both:

Among them, Z is the surface sagittal height, C is the curvature radius of the vertex, K is the quadratic surface coefficient, and r is the radial coordinate.

In some embodiments, the first lens group is composed of 4 lenses arranged in sequence, and the 4 lenses are all spherical mirrors, and the first lens group has negative refractive power.

In some embodiments, the size of the DMD micromirror array is 2560×1600, 1920×1080 or 1024×768.

In some embodiments, the imaging mirror group is a catadioptric structure, including a third off-axis mirror and a second lens group arranged along the optical path, the third off-axis mirror and the first off-axis mirror have The same parameters, the second lens group and the first lens group have the same parameters.

In some embodiments, the imaging lens group is a coaxial catadioptric structure, including a first lens, a second lens, a first mirror, a third lens, a fourth lens, a fifth lens, and a sixth lens arranged in sequence and the second reflector.

In some embodiments, the materials of the first off-axis reflector and the second off-axis reflector are microcrystalline, fused silica or silicon carbide.

The beneficial effect of the present invention is that: the above-mentioned DMD micromirror array is used as the imaging optical system of the intermediate image plane, utilizes the working characteristics of the DMD micromirror array, realizes the one-to-one matching between the DMD micromirror array and the detector pixel, and achieves the adjustment of the detector The purpose of the image plane gray scale is to expand the detection dynamic range of the photoelectric imaging system and meet the needs of scene measurement and observation of high dynamic radiation energy characteristics. It can be applied to deep space detection, medical imaging, military observation and other fields. In the above-mentioned imaging optical system, on the primary image plane where the DMD micromirror array is located, the optical modulation transfer function of each field of view is greater than 0.70 at the Nyquist frequency, and the distortion is close to 0. In addition, the above-mentioned imaging optical system places the DMD micromirror array on the intermediate image plane and adopts a partially symmetrical structure, so that the beam emitted from the primary image plane is nearly collimated light, which realizes the replaceability of the imaging lens group and expands Considering the applicability of the above-mentioned imaging optical system, the user can choose the appropriate structural form of the imaging lens group according to actual needs. At the same time, the above-mentioned imaging optical system has the characteristics of good imaging quality, compact structure, and low difficulty in processing and assembly.

Description of drawings

FIG. 1 schematically shows a schematic diagram of the optical structure of an imaging optical system according to Embodiment 1 of the present invention.

FIG. 2 schematically shows a schematic view of light directions in the optical structure of the imaging optical system according to Embodiment 1 of the present invention.

3 is a schematic diagram of the optical structure of the first lens group in the imaging optical system according to Embodiment 1 of the present invention.

FIG. 4 is an optical modulation transfer function curve of the intermediate image plane of the imaging optical system according to Embodiment 1 of the present invention.

FIG. 5 is an optical modulation transfer function curve of the secondary image plane of the imaging optical system according to Embodiment 1 of the present invention.

FIG. 6 schematically shows the optical structure of the imaging optical system according to Embodiment 2 of the present invention.

FIG. 7 schematically shows the direction of light in the optical structure of the imaging optical system according to Embodiment 2 of the present invention.

FIG. 8 is a schematic diagram of the optical structure of the imaging lens group of the imaging optical system according to Embodiment 2 of the present invention.

9 is an optical modulation transfer function curve of the secondary image plane of the imaging optical system according to Embodiment 2 of the present invention.

Detailed ways

In order to make the object, technical solution and advantages of the present invention clearer, the present invention will be 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 present invention, but not to limit the present invention.

Referring first to Fig. 1 and Fig. 2, there is shown an imaging optical system 100 according to one embodiment of the present invention, comprising a first off-axis reflector 110, a first lens group 120, a DMD micromirror array 130, a second off-axis reflector 140. Imaging mirror group and detector 160. The light emitted by the target object is converged by the first off-axis reflector 110, enters the first lens group 120, and is imaged on the DMD micromirror array 130. After being reflected by the DMD micromirror array 130, the imaging beam passes through the first lens group 120 again, and then After being collimated by the second off-axis mirror 140 , it enters the imaging mirror group and is imaged on the detector 160 .

The design of the imaging optical system 100 follows the right-handed coordinate rule. The Z-axis is the system optical axis and coincides with the base normal of the DMD micromirror array 130. The incident direction of the light is parallel to the Z-axis and points to the positive direction.

The first off-axis reflector 110 is offset along the Y direction with an aperture off-axis in the YOZ plane, and the offset amount is not less than the light aperture of the first off-axis reflector 110 . The second off-axis reflector 140 is offset along the X direction in an off-axis manner in the XOZ plane, and the offset amount of the second off-axis reflector 140 along the X direction is the same as that of the first off-axis reflector 110 along the Y direction. The offset is the same. The first off-axis reflector 110 and the second off-axis reflector 140 have the same surface parameters, and the optical path of light between the two off-axis reflectors is symmetrical about the normal of the DMD micromirror array 130, and the second off-axis reflector The off-axis mirror 140 is rotated 90° clockwise around the normal of the DMD micromirror array 130 and coincides with the first off-axis mirror 110 .

The entrance pupil of the imaging optical system 100 is located behind the first off-axis mirror 110 in the incident direction of the light beam.

In one embodiment, both the first off-axis reflector 110 and the second off-axis reflector 140 are concave quadric surfaces with negative optical power. Further, the surface expressions of the quadric surfaces of the first off-axis reflector 110 and the second off-axis reflector 140 are both:

Among them, Z is the surface sagittal height, C is the curvature radius of the vertex, K is the quadratic surface coefficient, and r is the radial coordinate.

In one embodiment, the first lens group 120 is composed of four lenses arranged in sequence, and the four lenses are all spherical mirrors, and the first lens group 120 has a negative refractive power.

The units of the DMD micromirror array 130 correspond to the pixels of the detector 160 one by one in space. The size of the DMD micromirror array 130 can be 2560×1600, 1920×1080 or 1024×768 to achieve matching with the detector 160 pixel array.

Further, in the YOZ plane, after the light beam passes through the first lens group 120, the principal ray on the axis is incident on the DMD micromirror array 130 at an angle of about 17° with the optical axis of the system, and the light beam is reflected by the DMD micromirror array 130 , the chief ray on the axis emerges in the XOZ plane at an angle of about 17° with the optical axis of the system.

The imaging lens group is replaceable, and the user can select a suitable structural form of the imaging lens group according to actual needs, which expands the applicability of the imaging optical system 100 .

In the embodiment shown in FIG. 1, the imaging lens group is a catadioptric structure, including a third off-axis reflector 152 and a second lens group 154 arranged along the optical path, the third off-axis reflector 152 and the first off-axis reflector The mirror 110 has the same parameters, and the second lens group 154 and the first lens group 120 have the same parameters.

In the embodiment shown in FIG. 6 and FIG. 7 , the imaging lens group 250 is a coaxial catadioptric structure. Please refer to FIG. 8 at the same time, the imaging lens group 250 includes a first lens 251, a second lens 252, a first reflection mirror 253, a third lens 254, a fourth lens 255, a fifth lens 256, a sixth lens 257 and The second reflector 258 . The first lens 251 , the second lens 252 , the first reflecting mirror 253 , the third lens 254 , the fourth lens 255 , the fifth lens 256 , the sixth lens 257 and the second reflecting mirror 258 are all spherical mirrors.

Further, the materials of the first off-axis reflector 110 and the second off-axis reflector 140 may be commonly used reflector materials such as microcrystalline, fused silica, or silicon carbide. The materials of the lenses used in the first lens group 120 and the imaging lens group are all commonly used glass.

The following are specific examples.

Example 1

In this embodiment, the size of the DMD micromirror array 130 is selected to be 1920×1080, and the size of a single micromirror is 10.8 μm. The resolution of the detector 160 is selected to be 1920×1080, and the pixel size is 10.8 μm. A catadioptric imaging optical system 100 with a long focal length and a small relative aperture is designed, and the operating wavelength is the visible light band. The system parameters are shown in Table 1. This imaging optical system 100 can be regarded as being made up of two parts, and the first part is the telescopic system that magnification is-1, by the first off-axis mirror 110, the first lens group 120, the DMD micromirror array 130, the second off-axis The second part is a secondary imaging system, which is composed of an imaging mirror group and a detector 160.

The design of the imaging optical system in this embodiment is shown in FIG. 1 and FIG. 2 , following the right-handed coordinate rule, and the Z axis is the optical axis of the system, and coincides with the base normal of the DMD micromirror array 130 . The light incident direction is parallel to the Z axis and points in the positive direction.

The light emitted by the target object is converged by the first off-axis mirror 110 , enters the first lens group 120 , and is imaged on the DMD micromirror array 130 . The imaging beam is reflected by the DMD micromirror array 130 and passes through the first lens group 120 again, collimated by the second off-axis mirror 140 , enters the imaging mirror group, converges thereon, and finally forms an image on the detector 160 . The first off-axis mirror 110 is offset by 300 mm along the +Y direction in the YOZ plane in an aperture off-axis manner. The first lens group 120 is composed of 4 lenses, all of which are spherical mirrors. The structural layout is shown in FIG. 2 . After the light beam passes through the first lens group 120, in the YOZ plane, the on-axis chief ray is incident on the DMD micromirror array 130 at an angle of about 17° to the system optical axis. The included angle between the normal of the DMD micromirror array 130 and the optical axis of the system is 12°. After the light beam is reflected by the DMD micromirror array 130, the principal ray on the axis exits at an angle of about 17° with the optical axis of the system in the XOZ plane, and is collimated by the first lens group 120 and the second off-axis mirror 140 again, and enters the The imaging component is finally imaged on the detector 160 . The second off-axis mirror 140 is offset in the +X direction by 300mm in the XOZ plane in an off-axis manner. The first off-axis reflector 110 and the second off-axis reflector 140 have completely consistent surface parameters, and the light path between the two off-axis reflectors is symmetrical about the normal of the DMD micromirror array 130, and the second off-axis reflector The off-axis mirror 140 is rotated 90° clockwise around the normal of the DMD micromirror array 130 and coincides with the first off-axis mirror 110 . The imaging mirror group is a catadioptric structure, including a third off-axis mirror 152 and a second lens group 154 arranged along the optical path. The third off-axis mirror 152 has the same parameters as the first off-axis mirror 110 , and the second lens group 154 has the same parameters as the first lens group 120 .

In this embodiment, the optical modulation transfer function curve of the intermediate image plane (primary image plane) of the imaging optical system in which the DMD micromirror array 130 is used as the intermediate image plane is shown in FIG. 4 . The optical modulation transfer function curve of the secondary image plane of the imaging optical system of this embodiment is shown in FIG. 5 .

Imaging optical system parameters in Table 1 Embodiment 1

parameter Numerical value working band 0.46～0.65μm Field of view ±0.8° System focal length 1000mm F number 5

Example 2

In this embodiment and embodiment 1, the same DMD micromirror array 230 and detector 260 are selected, and the parameters of the imaging optical system 200 are the same as those in embodiment 1, see Table 1. The secondary imaging system uses a coaxial catadioptric structure, which is different from Embodiment 1. This shows that the DMD micromirror array is replaceable as the imaging mirror group in the imaging optical system of the intermediate image plane to meet different application requirements.

The design of the imaging optical system 200 in this embodiment is shown in FIG. 6 , following the right-handed coordinate rule, and the Z axis is the optical axis of the system, which coincides with the base normal of the DMD micromirror array 230 . The light incident direction is parallel to the Z axis and points in the positive direction.

The light emitted by the target object is converged by the first off-axis mirror 210 , enters the first lens group 220 , and is imaged on the DMD micromirror array 230 . The imaging beam is reflected by the DMD micromirror array 230 and passes through the first lens group 220 again, collimated by the second off-axis mirror 240 , enters the imaging mirror group 250 , converges there, and finally images on the detector 260 . The first off-axis mirror 210 is offset by 300 mm along the +Y direction in the YOZ plane in an aperture off-axis manner. The first lens group 220 is composed of 4 lenses, all of which are spherical mirrors. The structural layout is shown in FIG. 2 . After the light beam passes through the first lens group 220, in the YOZ plane, the on-axis chief ray is incident on the DMD micromirror array 230 at an angle of about 17° to the system optical axis. The included angle between the normal of the DMD micromirror array 230 and the optical axis of the system is 12°. After the light beam is reflected by the DMD micromirror array 230, the on-axis chief ray exits in the XOZ plane at an angle of about 17° with the system optical axis, and is collimated by the first lens group 220 and the second off-axis mirror 240 again, and enters the The imaging component 250 is finally imaged on the detector 260 . The second off-axis mirror 240 is offset by 300 mm along the +X direction in the XOZ plane in an off-axis manner. The first off-axis reflector 210 and the second off-axis reflector 240 have completely consistent surface parameters, and the light path between the two off-axis reflectors is symmetrical about the normal of the DMD micromirror array 230, and the second off-axis reflector The on-axis mirror 240 is rotated clockwise by 90° around the normal of the DMD micromirror array 230 and coincides with the first off-axis mirror 210 . The imaging mirror group 250 is a coaxial catadioptric structure. lens 255 , fifth lens 256 , sixth lens 257 and second mirror 258 . The first lens 251 , the second lens 252 , the first reflecting mirror 253 , the third lens 254 , the fourth lens 255 , the fifth lens 256 , the sixth lens 257 and the second reflecting mirror 258 are all spherical mirrors.

The optical modulation transfer function curve of the secondary image plane of the imaging optical system 200 of Embodiment 2 is shown in FIG. 9 .

The DMD micromirror array provided by the present invention is used as the imaging optical system of the intermediate image plane, and utilizes the working characteristics of the DMD micromirror array to realize the one-to-one matching between the DMD micromirror array and the detector pixel, so as to adjust the gray scale of the detector image plane The purpose of this is to expand the detection dynamic range of the photoelectric imaging system and meet the needs of scene measurement and observation of high dynamic radiation energy characteristics. It can be applied to deep space detection, medical imaging, military observation and other fields. In the above-mentioned imaging optical system, on the primary image plane where the DMD micromirror array is located, the optical modulation transfer function of each field of view is greater than 0.70 at the Nyquist frequency, and the distortion is close to 0. In addition, the above-mentioned imaging optical system places the DMD micromirror array on the intermediate image plane and adopts a partially symmetrical structure, so that the beam emitted from the primary image plane is nearly collimated light, which realizes the replaceability of the imaging lens group and expands Considering the applicability of the above-mentioned imaging optical system, the user can choose the appropriate structural form of the imaging lens group according to actual needs. At the same time, the above-mentioned imaging optical system has the advantages of good imaging quality, compact structure, and low difficulty in processing and assembly.

The specific embodiments of the present invention described above do not constitute a limitation to the protection scope of the present invention. Any other corresponding changes and modifications made according to the technical concept of the present invention shall be included in the protection scope of the claims of the present invention.

Claims (8)

1. an imaging optical system, is characterized in that, comprises the first off-axis reflector, the first lens group, DMD micromirror array, the second off-axis reflector, imaging mirror group and detector, and the light that target object sends passes through The first off-axis reflector converges, enters the first lens group, and is imaged on the DMD micromirror array, and the imaging beam passes through the first lens group again after being reflected by the DMD micromirror array, and then passes through the first lens group. After the second off-axis mirror is collimated, it enters the imaging mirror group, and then forms an image on the detector; The design of the imaging optical system follows the right-hand coordinate rule, the Z axis is the system optical axis, and coincides with the base normal of the DMD micromirror array, and the light incident direction is parallel to the Z axis and points to the positive direction; The first off-axis reflector is offset along the Y direction with an aperture off-axis in the YOZ plane, and the offset amount is not less than the light aperture of the first off-axis reflector, and the second off-axis reflector The reflector is offset along the X direction in an off-axis manner in the XOZ plane, and the offset amount of the second off-axis reflector along the X direction is the same as the offset of the first off-axis reflector along the Y direction The amount is the same, the first off-axis reflector and the second off-axis reflector have the same surface parameters, and the light path passed between the two off-axis reflectors is about the law of the DMD micromirror array. Line symmetry, the second off-axis reflector coincides with the first off-axis reflector after rotating 90° clockwise around the normal of the DMD micromirror array. 2 . The imaging optical system according to claim 1 , wherein an entrance pupil of the imaging optical system is located behind the first off-axis mirror in the incident direction of the light beam. 3 . 3 . The imaging optical system according to claim 1 , wherein both the first off-axis reflector and the second off-axis reflector are concave quadric surfaces with negative refractive power. 4 . 4. The imaging optical system according to claim 3, wherein the surface expressions of the quadric surfaces of the first off-axis mirror and the second off-axis mirror are:

Among them, Z is the surface sagittal height, C is the curvature radius of the vertex, K is the quadratic surface coefficient, and r is the radial coordinate. 5. The imaging optical system according to claim 1, wherein the first lens group is composed of 4 lenses arranged in sequence, and the 4 lenses are all spherical mirrors, and the first lens group has negative light Focus. 6. The imaging optical system according to claim 1, wherein the size of the DMD micromirror array is 2560×1600, 1920×1080 or 1024×768. 7. The imaging optical system according to claim 1, wherein the imaging mirror group is a catadioptric structure, comprising a third off-axis reflector and a second lens group arranged along the optical path, the third off-axis The on-axis mirror has the same parameters as the first off-axis mirror, and the second lens group has the same parameters as the first lens group. 8 . The imaging optical system according to claim 1 , wherein materials of the first off-axis reflector and the second off-axis reflector are both microcrystalline, fused silica or silicon carbide.

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