CN105588643B - Thermal infrared divides aperture polarization imaging optical system - Google Patents

Abstract

The invention discloses a sub-aperture polarization imaging optical system in the thermal infrared band, which includes a common-aperture pre-telescope group, a sub-aperture imaging mirror group, a common-aperture relay imaging mirror group and an infrared detector; the sub-aperture imaging mirror group includes Four polarization channels, where polarizing devices and a group of sub-lens groups are placed in sequence, their polarization directions are different, so that the polarization information of the target can be detected; the image formed by the sub-aperture imaging lens group is adjusted by the field lens, and is captured by the common aperture The secondary imaging of the relay imaging mirror group is on the focal plane of the infrared detector. Since the sub-apertures have the same optical characteristics, the simultaneous detection of different polarization state information is realized, and images are simultaneously imaged on different regions of the same infrared detector. The optical system provided by the invention has good imaging quality, high polarization measurement accuracy, is not affected by external disturbances, can be applied to fast moving platforms or detect fast changing targets, has a compact structure, has no moving parts, and has 100% cold aperture efficiency.

Description

Thermal Infrared Split Aperture Polarization Imaging Optical System

technical field

The invention relates to a thermal infrared sub-aperture polarization imaging optical system, which is suitable for a polarization sub-aperture multi-channel imaging system.

Background technique

The polarization imaging system can detect the reflection of the target object or the polarization information of its own radiation. The polarization information can provide various important physical information about the material surface properties, roughness, shape, etc. of the target object. It is used in astronomical observation, medical diagnosis, remote sensing applications and Military identification and other fields have broad application prospects.

The polarization state is generally represented by a Stokes vector. In order to obtain complete Stokes vector information, at least four images of different polarization states of the target need to be acquired. At present, the main polarization imaging systems include time-sharing detection system and simultaneous detection system. The time-sharing detection system realizes time-sharing measurement of different polarization states by introducing optical components such as rotating polarizers or wave plates, and phase-variable modulators. However, the time delay in the measurement process of the time-sharing detection system will inevitably introduce errors caused by the change of the target object or the rapid movement of the platform. At the same time, the multi-channel splitting technology used in the detection system mainly includes the amplitude splitting technology using a prism or a beam splitter, the focal plane splitting technology that places an integrated polarization element at the focal plane of the detector, and the split-aperture imaging that places a multi-channel subsystem on the aperture. technology. The sub-amplitude technology uses four optical systems and four infrared detectors. The performance difference between different optical systems and detectors will introduce measurement errors, and the sub-amplitude system is relatively large; the sub-focal plane technology is at the focal plane of the detector. Arranging micro-polarization devices is very difficult to process and produce, and there are spatial registration errors; since the sub-aperture system only uses one detector, the four-way sub-aperture system simultaneously images the polarization state information of the target on different surfaces of the detector It has the advantages of compact size, reliable performance, and no moving parts. In the existing thermal infrared sub-aperture imaging technology (reference J. Larry Pezzaniti and David B. Chenault. Proc. of SPIE58880. 2550.), the cold aperture is far away from the focal plane of the detector, and there are multiple relay lenses in the middle , not suitable for the current package molding infrared cooling photodetector.

Contents of the invention

Aiming at the deficiencies in the prior art, the present invention provides a sub-aperture imaging system for polarization imagers that is compact in size, high in imaging quality, convenient for data processing, works in the thermal infrared band, and accurately matches the exit pupil with the cold diaphragm of the detector. .

In order to achieve the above object, the technical solution of the present invention is to provide a thermal infrared sub-aperture polarization imaging optical system, which includes a common aperture front telescope group, a sub-aperture imaging mirror group, a common aperture relay imaging mirror group and an infrared detector; The sub-aperture imaging lens group includes four sub-channels arranged side by side, wherein the three sub-channels have the same structure, and a polarizer, a group of channel objective lenses and a group of channel field lenses are sequentially placed along the direction of the light path, and the three sub-channels The polarizing directions of the polarizers are 0°, 45° and 90° respectively; the fourth sub-channel is sequentially placed along the direction of the optical path with a glass plate of equal thickness and the same material, a group of channel objective lenses and a group of channel field lenses; in the common aperture The secondary imaging mirror group includes a common aperture relay field mirror and a common aperture relay imaging mirror; the common aperture relay imaging mirror performs secondary imaging of the target on the photosensitive surface of the infrared detector.

The ratio of the focal length to the total focal length of the optical system of the common-aperture front telescope group according to the present invention is 1.5:1˜2.5:1. The common-aperture forward telescope group can be a thermal infrared Galilean telescope or a thermal infrared Kepler telescope.

The ratio of the focal length of the channel objective lens in the sub-aperture imaging lens group of the present invention to the total focal length of the optical system is 0.5:1˜2:1. The channel objective lens in the sub-aperture imaging lens group can be a telephoto objective lens or a double split objective lens.

The common-aperture relay imaging lens group described in the present invention is a three-piece or double-Gauss objective lens.

Compared with the prior art, the present invention has the advantages of:

1. The sub-aperture optical system is used to obtain the polarization state information of the target at the same time, and image it on the same infrared detector, with compact structure and good stability.

2. The four sub-aperture optical systems have the same optical structure characteristics, are not disturbed by external environment and other factors, and have high measurement accuracy.

3. The optical system structure of secondary imaging is adopted, and the secondary imaging of the aperture diaphragm is at the position of the cold diaphragm, which has the advantage of sharing the cold diaphragm, ensures 100% efficiency of the cold diaphragm, and precisely matches the cold diaphragm of the detector.

4. After the four sub-apertures go through the image plane once, they are imaged on the detector through the common rear group of common-aperture lenses, which avoids the distortion of the image plane caused by the eccentricity of the sub-apertures, and the image quality is good.

5. The system lenses are made of commonly used infrared materials, which have low processing and manufacturing costs.

Description of drawings

Fig. 1 is a schematic structural diagram of a thermal infrared split aperture polarization imaging system provided by an embodiment of the present invention;

Fig. 2 is the modulation transfer function graph of the thermal infrared sub-aperture polarization imaging system provided by the embodiment of the present invention;

Fig. 3 is a spot diagram of the thermal infrared sub-aperture polarization imaging system provided by the embodiment of the present invention;

Fig. 4 is a grid distortion diagram of the thermal infrared sub-aperture polarization imaging system provided by the embodiment of the present invention;

Among them: 1. The first lens of the common aperture front telescope group, 2. The second lens of the common aperture front telescope group, 3. The third lens of the common aperture front telescope group, 4. The first lens of the common aperture front telescope group Four lenses, 5, polarizer, 6, the first lens of sub-aperture imaging mirror group, 7, the second lens of sub-aperture imaging mirror group, 8, sub-aperture field lens, 9, common aperture relay field lens, 10 1. The first lens of the common-aperture relay imaging mirror group, 11. The second lens of the common-aperture relay imaging mirror group, 12. The third lens of the common-aperture relay imaging mirror group, 13. The common-aperture relay imaging mirror group The fourth lens, 14, the fifth lens of the common-aperture relay imaging mirror group, 15, the detector cold diaphragm, 16, the infrared detector.

Detailed ways

The technical solutions of the present invention will be further described in detail below in conjunction with the accompanying drawings and embodiments.

Example 1

This embodiment provides a thermal infrared sub-aperture polarization imaging optical system, which includes a common-aperture pre-telescope group, a sub-aperture imaging mirror group, a common-aperture relay imaging mirror group and an infrared detector. The sub-aperture group includes four polarization channels, and each polarization channel is respectively placed with a polarization element and a group of aperture imaging mirror groups along the direction of the light path. Its working band is the thermal infrared band, the focal length of the lens is 68mm, the F/# is 2, and the full field of view is 3.2°×4°.

Referring to accompanying drawing 1, it is the structural representation of the optical lens that present embodiment provides, and common aperture pre-telescope group can adopt thermal infrared Galileo telescope or thermal infrared Kepler telescope, and a specific structure in the present embodiment comprises common aperture The first lens 1, the second lens 2, the third lens 3 and the fourth lens 4 of the front telescope group, the ratio of the focal length of the common aperture front telescope group to the total focal length of the optical system is 1.5:1～ 2.5:1.

The sub-aperture imaging lens group includes four sub-channels arranged side by side, wherein the three sub-channels have the same structure, and a polarizer 5 is placed in sequence along the optical path direction, and a group of channel objective lenses includes the first lens 6 and the sub-aperture imaging lens group. The second lens 7, a group of channel field mirrors 8, the polarization directions of the polarizers of the three sub-channels are respectively 0°, 45° and 90°, and the fourth sub-channel is placed one by one along the direction of the optical path—the same thickness as the polarizer 5 Material glass sheet, to compensate for the optical path difference to obtain the light intensity information of the target object, and a set of channel objective lens and a set of channel field lens; the ratio of the focal length of the channel objective lens in the sub-aperture imaging lens group to the total focal length of the optical system is 0.5 :1～2:1.

After the incident light passes through the common-aperture pre-telescope group, the width of the light is compressed and the field of view is limited, and enters the sub-aperture subsystem. After placing polarizers with different polarization directions, it is imaged in the common aperture by the sub-aperture imaging mirror group. Following the field mirror 9, the common-aperture relay imaging mirror group passes through the detector cold diaphragm 15, and is imaged twice on the infrared detector 16; the common-aperture relay imaging mirror group can be a three-piece or double-Gauss type objective lens. The embodiment specifically includes a first lens 10 , a second lens 11 , a third lens 12 , a fourth lens 13 and a fifth lens 14 . The infrared detector can be a staring infrared focal plane array detector.

The specific data and materials used for each lens of the split-aperture optical system for thermal infrared polarization imaging provided in this embodiment are shown in Table 1.

Table 1

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See Figure 2, which is the modulation transfer function (MTF) curve of the system. At the Nyquist frequency of 32 lp/mm, the MTF of the system is greater than 0.5, which is close to the diffraction limit.

Referring to accompanying drawing 3, it is a spot diagram on the ray tracing image plane, and the circle in the figure represents the system diffraction Airy disc. The spot diagram energy of each field of view is concentrated in the range of Airy disk, which has good imaging quality.

See attached figure 4, which is a system grid distortion map, the relative distortion is less than 1.13%, and the maximum distortion is 20um, which is slightly larger than 1 pixel. The distortion existing in the system can be corrected by image processing.

Claims (7)

1. a kind of thermal infrared divides aperture polarization imaging optical system, it is characterised in that：It includes the preposition microscope group of looking in the distance in aperture altogether, point Aperture imaging microscope group, common aperture relay imaging microscope group and infrared detector；Described divides aperture imaging microscope group to include four side by side The subchannel of arrangement, wherein, the structure of three subchannels is identical, and a polarizer, one group of passage are sequentially placed along optical path direction Object lens and one group of passage field lens, it is respectively 0 °, 45 ° and 90 ° that the polarizer of three subchannels, which is polarized direction,；4th subchannel edge Optical path direction is sequentially placed the identical material glass piece of a uniform thickness, one group of passage object lens and one group of passage field lens；In the aperture altogether Include aperture altogether after imaging microscope group and relay field lens and altogether aperture relay imaging mirror；Aperture relay imaging mirror is total to by target secondary imaging In on the photosurface of infrared detector.

2. a kind of thermal infrared according to claim 1 divides aperture polarization imaging optical system, it is characterised in that：Described is total to The ratio between total focal length of the preposition microscope group of looking in the distance in aperture, its focal length and optical system is 1.5:1~2.5:1.

3. a kind of thermal infrared according to claim 1 or 2 divides aperture polarization imaging optical system, it is characterised in that：It is described The preposition microscope group of looking in the distance in common aperture be thermal infrared Galilean telescope or thermal infrared Kepler telescope.

4. a kind of thermal infrared according to claim 1 divides aperture polarization imaging optical system, it is characterised in that：Described point The ratio between the focal length of passage object lens in aperture imaging microscope group and the total focal length of optical system are 0.5:1~2:1.

5. a kind of thermal infrared according to claim 1 or 4 divides aperture polarization imaging optical system, it is characterised in that：It is described The passage object lens divided in aperture imaging microscope group be telephoto objective, or double separation object lens.

6. a kind of thermal infrared according to claim 1 divides aperture polarization imaging optical system, it is characterised in that：Described is total to Aperture relay imaging microscope group is three-chip type or double-Gauss objective.

7. a kind of thermal infrared according to claim 1 divides aperture polarization imaging optical system, it is characterised in that：Described is red External detector is gazing type infrared focal plane array seeker.