Yuanhe Tang

Partially light-controlled imaging system based on High Temperature Poly-Silicon Thin Film Transistor-Liquid Crystal Display.

A partially light-controlled imaging system is proposed as a novel device. It is used to improve the imaging quality at the illumination of 1.979 x 10(5)lx by means of mitigating image contrast. It consists of a High Temperature Poly-Silicon Thin Film Transistor-Liquid Crystal Display (HTPS TFT-LCD), which is set between the lens and CCD and is coupled with CCD by the optical fiber taper. The transmittance of pixelated LCD can be controlled by Field-Programmable Gate Array to realize the partially light-controlled and thus dynamic range of the imaging system can be extended. Samples of indoor objects and outdoor license plate are photographed by the prototype imaging system under strong light. The imaging results of this novel system are satisfactory with better restored details, compared with the photos taken by normal CCD camera (WAT-231S2) which uses aperture and shutter to control the overall light intensity.

Study on the wide-angle Michelson interferometer with large air gap

A wide-angle Michelson interferometer with large air gap is proposed to effectively reduce the size of the glass arms and constraint on material. It provides a novel and practical instrument for ground based wind measurement of the upper atmosphere. The field widening conditions for the large air gap are calculated in theory. For the five spectral lines of 557.7 nm, 630.0 nm, 732.0 nm, 834.6 nm, and 865.7 nm, the optimal results under ideal condition are obtained with air gaps of 1.0 cm, 1.5 cm, and 2.0 cm, respectively. With the fixed optical path difference (OPD) of 7.495 cm, three pairs of glass arms are optimized. The pair with length of 1.5 cm for air gap, 5.765 cm for H-ZF12, and 2.956 cm for H-ZLaF54, has better effect of field widening than the other two pairs and its OPD variation is only within 0.30 wavelengths at incident angle of 3°. For developing a more practical wide-angle Michelson interferometer, the H-K9L glass with size of 4.445 cm is employed as the arm material of solid interferometer. The experiment for field of view of 3° is designed and the data processing and analysis for 60 images show the agreement between experimental results and theoretical simulation. The OPD variations are only within 0.27 wavelengths for image edge. The feasibility and practicality of the wide-angle Michelson interferometer with large air gap is proved by means of theory and experiment.

Partially light-controlled imager based on liquid crystal plate and image intensifier for aurora and airglow measurement

In order to obtain information both of aurora and airglow in one image by the same detector, a PLCI based on liquid crystal plate LCP and super second-generation image intensifier SSGII is proposed in this research. The detection thresholds of the CCD for aurora and airglow are calculated. For the detectable illumination range of 10(4)-10(-2) lx, the corresponding electron count is 1.57×10(5) - 0.2 for every pixel of CCD. The structure and work principle of the PLCI are described. An LC is introduced in the front of CCD to decrease the intensities of aurora in overexposure areas by means of controlling transmittances pixel by pixel, while an image intensifier is set between the LC and CCD to increase the intensity of the weak airglow. The modulation transfer function MTF of this system is calculated as 0.391 at a Nyquist frequency of 15 lp/mm. The curve of transmittance with regard to gray level for the LC is obtained by calibration experiment. Based on the design principle, the prototype is made and used to take photos of objects under strong light greater than 2×10(5) lx. The clear details of [symbols: see text] presented in the image indicate that the PLCI can greatly improve the imaging quality. The theoretical calculations and experiment results prove that this device can extend the dynamic range and it provides a more effective method for upper atmospheric wind measurement.

Modulation transfer function of partial gating detector by liquid crystal auto-controlling light intensity

Based on the electro-optical properties of liquid crystal, we have designed a novel partial gating detector. Liquid crystal can be taken to change its own transmission according to the light intensity outside. Every single pixel of the image is real-time modulated by liquid crystal, thus the strong light is weakened and low light goes through the detector normally .The purpose of partial-gating strong light (>105lx) can be achieved by this detector. The modulation transfer function (MTF) equations of the main optical sub-systems are calculated in this paper, they are liquid crystal panels, linear fiber panel and CCD array detector. According to the relevant size, the MTF value of this system is fitted out. The result is MTF= 0.518 at Nyquist frequency.

Circuit design of partial gating image based on Cyclone II and HTPS

In order to enhance the dynamic range of digital imaging system, we have brought forward processing image by the Cyclone II chip and controlling HTPSs high-density liquid crystal unit. The system in this paper proposed a kind of low cost solution, the luminous intensity entering each pixel of CCD can be adjusted directly accurately. Meanwhile, the attenuation luminance coefficients set by system algorithm and precision parameters can be adjusted artificially on the physical level to satisfy different needs. It is proving that the function of partial gating image is realized by the image processing experiment in which the details of the final image are more obvious and clear than the original. Then the system latitude problem is solved fundamentally. The image of partial gating is obtained through the experiment, and then the anticipated goal has achieved successfully.

Study of the precision of upper atmospheric wind field measurement

The passive optical methods to observe the earthly upper atmospheric wind field by satellite remote sensing is to measure the parameters including atmospheric wind velocities, temperature, pressure and volume emission rates of airglow (aurora). WINDII is the first image interferometer for upper atmospheric wind measurement in 1991 made by Canada and France loaded on NASAs UARS. The precision of wind speed is 10m/s for WINDII and its temperature precision is 10K. The second wind measurement instrument of SWIFT is launched at 2011 based on the same principle as WINDII. SWIFTs wind speed precision is 3m/s, and its temperature precision is 2K. According to the development of the photoelectron technology and CCD, the wind fields detected precision is enhanced continuously. In this paper, the theory of detected precision of wind speed and temperature is analyzed firstly; the factors between the higher precision of wind field and CCD detector parameter are made sure. And then the precision equation is deduced. The wind speed and temperature precision expression includes of optical path difference (OPD), phase, aurora wavelength, visibility, CCDs responsibility, signal-to-noise, view of field (VOF) etc. The precision of 1m/s wind speed and 1K temperature need fixed OPD 24.28cm with O+ 732.0nm aurora. This research can provide the theory for advance upper atmospheric wind field detecting precision.

Study of liquid crystal based on auto-controlling light intensity

A liquid crystal panel module coupled in the image intensifier which has been coupled the magnetic mirror has been proposed. The normal imaging under strong light and the part gating of light intensity control can be achieved by changing the transmittance of these pixel points which is changed by the voltage imposed on pixel points. Influence of the response time and transmittance of the liquid crystal to the entire system have been researched, that liquid crystal can achieve part gating function has been confirmed through experiments. Liquid crystal display module (LCP)s response time is 22ms by using the 650nm, 4mw SZ-04 laser and the transmittance of LCP ranges from 1.28 to 25.60%.It has been proved that the liquid crystal selected in this article fit for the entire LCP. Photography effect graphs achieved by part gating of light intensity have been got.

Correction of charge packet transfer rate in CCD

The charge packet transfer rate is one of the most important factors of charge transfer losing (CTL) in Charge Coupled Devices (CCD). It is important to build up a model of CCD structure parameters, charge transfer efficiency (CTE), transfer frequency of charge packet and work temperature etc. But it is very hard to build up an exact theoretical model and find the analytical solution neither math nor physics. The traditional discussion of the working principle of CCD build up a nonlinear partial differential equation, but it just consider the remainder electrons concentration while integer k=0. In this paper, we increase the result of the electrons concentration while k=1, 2,..., n, and discuss the result. A more accreted result of the charge packet rate had been got. The result is 81 percent of the CTL which is traditionally discussed about of CCD. Then the CTE in low temperature is discussed using the result. And the optimum frequency of the CCD is corrected also. The correction of the charge packet rate in CCD can enhance the performance of CCD.

The electron's velocity direction through the magnetic mirror field for the low-light imaging system

In order to improve the detectability of low-light imaging CCD (charge coupled devices), we have brought forward a magnetic mirror device to apply to microchannel electron vase plate ((MEVP)) of low-light imaging system at room temperature. After introduced the principle of restricted electron in magnetic mirror field to accumulate enough time for low-light CCD imaging, magnetic intensity has been calculated discretionary position in the mirror, the formula of electrons velocity direction has been given through the throat of magnetic mirror in this paper. The educed electrons angle distribution between velocity direction and magnetic mirror axis has been simulated at 7-10 degree. This answers for the design needs of microchannel vase plate now. The electrons loop speckle imaging has been obtained by experiment; the result is same as theoretical value. It is proved that if the electrons educed by the magnetic mirror field at the same cone angle and approximate speed, the gain of microchannel plate will be more stable, so that it is favorable to reduce the noise of photoelectronic imaging.