The most significant shortage of the Dyson spectrometer is that the small clearance among the slit, image plane and the hemisphere lens makes the spectrometer difficult to assembly. To solve this problem, several approaches have been proposed. Such as inserting additional aspherical lenses in the optical path to enlarge the image distance, or using a fused silica lens and incorporates a built-in fold mirror to allow the detector sufficient clearance from the slit. In this paper, a Dyson imaging spectrometer with freeform surface has been designed. The freeform surface is used to enlarge clearance distance and compensate the large residual aberration without additional lenses. The design starts from a sphere Dyson system, and then the freeform surfaces are applied to optimize the initial configuration by the use of optical software. The design results show that the Dyson imaging spectrometer with freeform surfaces have great optical performance and easy to mounting which is crucial for development in the fields of aeronautics and astronautics remote sensing.
Hyperspectral imager can obtain both spatial information and spectral information at the same time, which is widely used in agriculture, biomedicine, environment monitoring. At present, hyperspectral imager is developing in the direction of lightweight, miniaturization and low power consumption. The miniaturization of hyperspectral imager includes the miniaturization of optical system and the miniaturization of detector system. In this paper, a miniaturization hyperspectral imager based on CMOS detector is proposed. The working range of is 400-1000nm, which contains 512 spectral bands. The field angle of hyperspectral imager is ±4 degree and the focal length is 99mm. The optical system consists of the telescope, the slit and the spectrometer. Considering the miniaturization of optical system, the spectrometer uses prism-grating spectroscopy. The CMOS sensor GSENSE400BSI is used in the detector system, whose pixel size is 11 micron*11 micron and pixel number is 2048*2048.The detector system consists of an imaging core board and an interface board, and the image output is Cameralink interface. Because of the high integration of CMOS sensor, the design of peripheral circuit can be greatly simplified. The total weight of the hyperspectral imager is not more than 2.5kg and the total power consumption is not more than 5W.The spectral imaging system has the advantages of lightweight, miniaturization and low power consumption. After testing, the spectrometer has good imaging quality.
Wide field of view (FOV) can provide the high efficiency of remote sensing. In this paper, the optical fiber array is used to connect the telescope and the spectrometer, which makes the configuration of the imaging spectrometer flexible and compact with large FOV. In the proposed system, the optical fiber array is coupled with slit, and relay the image of the slit into the several spectrometers with short field or several parallel fields in a single spectrometer. The optical fiber array can avoid the problems of linear array of imaging fiber bundles without slit, such as manufacture difficulty of the single row fiber bundles, breakage of fiber and the difficulty of alignment the fiber with the pixels of detector. The optical design of the telescope based on TMA and the imaging spectrometer based on Fery prism are detailed in this paper. Moreover, the pushbroom scan experiment demonstrates the feasibility of the optical fiber array in the imaging spectrometer.
The stereoscopic spectral imager combines the space technology and the spectrum technology, which can obtain the three-dimensional information and the spectral information of the target at the same time. A compact stereoscopic spectral imaging system is proposed in this paper. The stereoscopic spectral imaging system works at the wavelength range from 450 to 1000nm. The optical system consists of three telescopes and a spectrometer. The stereoscopic spectral imaging system uses the compact design of the shared spectrometer and detector, which effectively saves the volume weight and the cost of the system, and realizes the requirement of lightweight miniaturization. One of the three telescopes is perpendicular to the earth, the other two observe forward and rear along the direction of the flight. The side angle is 27 degree. The Offner-Chrisp imaging spectrometer based on curved surface prism is used in the system. Curved prism is a special optical element, which can effectively reduce the size of the system, reduce the spectral curvature and improve the performance of the system. The MTF values of all wavelengths at 46lp/mm are greater than 0.6 and the results demonstrated the good performance of the optical design. The stereoscopic spectral imaging system can achieve high-resolution imaging under the condition of wide spectral segment, has the high energy utilization efficiency and can obtain the spectral information in real time.
The prototype of compact light-weighted hyperspectral imager based on the compact Offnerspectrometer is introduced. Two curved prisms are designed to disperse the incident light in the optical system with the benefits of low smile, keystone and lateral distortion. It has 148 spectral bands covering spectral range from 420 to 1000nm, the ground sampling distance is 50m@700km, and the swath width is 100km. But the weight is only 12.8kg, the outer dimensions are 362mm (X)* 343mm (Z)*139 mm (Y). As prisms are used for imaging spectrometer, the spectral sampling distance varies with wavelength. The width of the spectral response function varies from 1nm to 12nm. The mean bandwidth is less than 5nm. The sensor has achieved high performance levels in terms of signal to noise ratio(SNR), spectral calibration and image quality. It can be used for environmental and disaster monitoring.
A non-contact heart rate detection method based on the dual-wavelength technique is proposed and demonstrated experimentally. The heart rate is obtained based on the PhotoPlethysmoGraphy (PPG). Each detection module uses the reflection detection probe which is composed of the LED and the photodiode. It is a well-known fact that the differences in the circuits of two detection modules result in different responses of two modules for motion artifacts. It will cause a time delay between the two signals. This poses a great challenge to compensate the motion artifacts during measurements. In order to solve this problem, we have firstly used the time registration and translated the signals to ensure that the two signals are consistent in time domain. Then the adaptive filter is used to compensate the motion artifacts. Moreover, the data obtained by using this non-contact detection system is compared with those of the conventional finger blood volume pulse (BVP) sensor by simultaneously measuring the heart rate of the subject. During the experiment, the left hand remains stationary and is detected by a conventional finger BVP sensor. Meanwhile, the moving palm of right hand is detected by the proposed system. The data obtained from the proposed non-contact system are consistent and comparable with that of the BVP sensor. This method can effectively suppress the interference caused by the two circuit differences and successfully compensate the motion artifacts. This technology can be used in medical and daily heart rate measurement.
The primary mirror is an important optical component of space camera. Its performance related to the optical image quality, and the weight directly affects the whole camera weight. The traditional design of primary mirror relies on much experience, lacking of precise theory, and many design parameters obtained by empirical formulas, thus the performance of the result is unstable. For this study, a primary mirror made of SiC with the diameter of 700mm was conceptual designed to get the optimized structure. Then sensitivity analysis was carried out to determine the optimum thickness of the back muscles. Finally, the optimum primary mirror fully satisfied the required was completed, with outstanding mechanical performance and light weight. A comparison between the optimum primary and traditional primary was performed and the results showed that the optimum primary has higher lightweight ratio increased by 5%, higher modal frequency increased by 81Hz.The maximum deformation under gravity reduced by 48nm, PV of the mirror surface reduced by 8.1nm and RMS reduced by 3.1nm. All the results indicated that the optimization method in the paper is reasonable and effective, which gives a reference to the primary mirror design in the future.