CAOS spectral imager design and advanced high dynamic range FDMA–TDMA CAOS mode

Abstract

A CAOS line camera is introduced for spectral imaging of one-dimensional (1D) or line targets. The proposed spectral camera uses both a diffraction grating as well as a cylindrical lens optics system to provide line imaging along the line pixels’ direction of the image axis and Fourier transform operations in the orthogonal direction to provide optical spectrum analysis of the line pixels. The imager incorporates a coded access optical sensor (CAOS) structure based on a digital micromirror device (DMD). The design includes a line-by-line scan option to enable 2D spectral imaging. Line style spectral imaging using a 2850 K color temperature white light target illumination source along with visible band color bandpass filters and a moving mechanical pinhole is demonstrated for the first time, to the best of our knowledge, to simulate a line target with individual pixels in 1D that have unique spectral content. A ∼ 412 to ∼ 732 n m input target spectrum is measured using a 38 × 52 CAOS pixel spatial sampling grid providing a test image line of 38 pixels, with each pixel providing a designed spectral resolution of ∼ 6.2 n m . The spectral image is generated using the robust code division multiple access (CDMA) mode of the camera. Then, for what we believe is the first time, the high dynamic range (HDR) operation of the frequency division multiple access–time division multiple access (FDMA–TDMA) mode of the CAOS camera is demonstrated. The FDMA–TDMA mode also features HDR recovery like the frequency modulation TDMA (FM–TDMA) mode, although at a much faster imaging rate and a higher signal-to-noise ratio (SNR), as more than one CAOS pixel is extracted at a time. Experiments successfully demonstrate 66 dB HDR target recovery using both FDMA–TDMA and FM–TDMA modes, with the FDMA–TDMA mode operating at an encoding speed eight times faster than the FM–TDMA mode, given that eight FM channels are used for the FDMA–TDMA mode. The CAOS spectral imager can be used to image both full spectrum stationary line targets as well as spectrally map 2D targets using line scanning methods. The demonstrated FDMA–TDMA CAOS mode is suited for improved speed and SNR linear HDR imaging.