Development And Key Technologies Of Coded Aperture Spectrometer

In traditional spectrometer, there is a contradiction between the spectral resolution and signal-to-noise(SNR). Based on MEMS(Micro Electro Mechanical System) technology, our group use coded aperture curved in a silicon wafer to replace the traditional single slit in a grating spectrometer. Modulated by the coded aperture and the grating system, the encoded signal can be obtained by the imaging detector. After the denoising and decoding process, the SNR of the decoded spectrum is enhanced by the coded aperture while realizing a proper resolution. This paper is mainly focused on the principle of the SNR enhancement brought by the coded aperture, the accurate decoding method, accurate wavelength scan and calibration method and spectrometer hardware and decoding software design.The SNR enhancement of the spectrometer presented in this paper mainly comes from the Hadamard Transform and multi-channel detection. Based on the Hadamrd Transform theory, theoretical analysis and experimental verification have been made to find out the best design of the coded aperture which can maximum the SNR of the spectrometer. The non-uniform illumination on the apertures, the Point Spread Function(PSF) of the optical system and the smear noise of the detector will bring in system decoded errors in the decoded spectrum. Through the analysis on the influence of these system errors on the encoding process, we modified the encoding equation based on the calibration of the non-uniform illumination and aperture spread function caused by the PSF to correct the corresponding decoded errors. We have proposed an algorithm based on wavelet transform to remove the smear noise with even distribution as well as an algorithm based on deconvolution to remove the non-uniform smear noise. To realize high resolution in a broadband spectral detection, we use a rotator with high precision to drive the grating to implement wavelength scan. To solve the calibration problem caused by the non-linear dispersion of the grating, we proposed a piecewise linear calibration algorithm. With this algorithm, the wavelength calibration error in the region from ultraviolet to near infrared is less than 0.03 nm. During the wavelength scan process, the filter in the coded aperture system is changed according to the spectral band on the detector plane, which can both remove the secondary spectrum and reduce the level of stray light in the system. Compared with the single slit spectrometer, the coded aperture spectrometer needs to deal with larger amount of data and more complicated algorithm. Therefore the multi-thread technology is used to in the software development process to make the software run as fast as possible.