Integrated polarization focal plane detection imaging has the advantages of small size, high system integration, high mechanical stability and real-time polarization imaging in multiple polarization directions. We have developed a simulation model for back-illuminated mid-wave InAs/GaSb Type-II superlattices (T2SLs) infrared focal plane arrays (FPAs) on-chip integrated polarization grating. The polarization grating is an Al-ZnS double-layer subwavelength grating with antireflection coating, which has a better polarization transmission than a single-layer Al grating with the same deep slot. The effect of different grating parameters on the detector is simulated and optimized by the finite-difference time-domain (FDTD) method, and the results obtained are qualitatively interpreted in a physical sense by the Fabry-Perot-like (F-P-like) resonance theory. The optimized grating has a TM polarization transmittance higher than 92% and extinction ratios greater than 32 dB for wavelengths from 3-5 μm, and is suitable for infrared polarization imaging in the 0°-50° field-of-view range. The simulation results can provide theoretical basis and guidance for the design of polarization gratings for mid-infrared monolithic integrated polarization InAs/GaSb T2SLs FPAs.
The infrared spectra of the Sun include numerous absorption lines, among which He I 10830 Å is one of the most representative spectral lines in the near-infrared band formed in the high-temperature region of the upper chromosphere. The observation of the spectral lines is important for the solar physics research. In this paper, the monochromatic images of sunspots in the He I 10830 Å spectral line was obtained by the one-meter new vacuum solar telescope at the Fuxian Lake solar observation base. The infrared detector using the domestic InGaAs 640×512 focal plane array device can reach a low dark current of 62e-/s/pixel and readout noise of 25.4 e- at 78K by Stirling cooler. The laboratory tests and actual astronomical observations were completed. In the case of large detector readout noise and dark current, a method of extracting the observation target by effectively calculating the flat field was proposed. A monochromatic image of sunspots with He I 10830 Å is obtained for the first time in China using the self-developed detector.
This paper describes the significance of infrared astronomy and the development of infrared detectors for astronomical telescope applications. First, the requirements of astronomical observations on infrared focal plane detector indicators such as dark current, readout noise, and image element size are analyzed, and the infrared detector performance parameters of major domestic and foreign astronomical telescopes in recent decades are summarized. Compared with foreign countries, the performance of domestic infrared astronomical telescopes, especially dedicated astronomical infrared detectors, is still very backward. For example, the readout noise is two orders of magnitude higher than the Webb telescope's 5.9e-, and the dark current is four orders of magnitude higher than the Webb telescope's 0.001e− / pixel∙s. Based on the NIR spectroscopic observation requirements of the 1-meter infrared solar telescope at Yunnan Observatory, we developed a low dark current and low noise 640×512 InGaAs NIR focal plane detector module and a dedicated imaging circuit for sunspot imaging and spectroscopic testing. Measurements using the photon curve transfer method showed that the dark current of the InGaAs NIR focal plane camera was as low as 64e−/ pixel∙s, and the average readout noise of the image elements was 25.4e−.Finally, the research direction of special infrared detectors for astronomical observation is discussed, and this paper has implications for the research of next-generation astronomical infrared telescopes in China.
A zoom system named liquid-filled micro-cylindrical lenses integrating a capillary and a biconvex micro-cylindrical lens in a polydimethylsiloxane (PDMS) substrate is designed, which can achieve continuous changed focal length from 2.675 to 9.012 mm by injecting variable concentrations of glycerol aqueous solution into the capillary. The aberration fan diagrams, root mean square spot radius, peak-to-valley wavefront aberration, and modulation transfer function curves at different zoom configurations of the liquid-filled micro-cylindrical lenses are all analyzed, showing good imaging quality over the whole focal length range. And an anamorphic zoom system for uniform collimated beam is designed putting such two PDMS substrates similar as the Kepler telescope structure. The anamorphic system can realize the zoom shaping function with 1:2 to 2:1 aspect ratio beam conversion without machine movement along optical axis and with no significant aberration. The introduced zoom system is characterized by high image quality, small volume, and a simple and stable structure, providing a design idea for cylindrical lenses with variable focal length.
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