CAOS Spectral Imager Design and Advanced High Dynamic Range FDMA-TDMA CAOS Mode

TL;DR

This paper introduces a novel CAOS spectral imager capable of line and 2D spectral imaging with high spectral resolution and demonstrates its HDR operation in FDMA-TDMA mode, enabling faster imaging with improved SNR.

Contribution

It presents the first implementation of a CAOS spectral camera with line and 2D spectral imaging capabilities and demonstrates HDR operation in FDMA-TDMA mode.

Findings

Achieved spectral resolution of ~6.2 nm across 412-732 nm range.

Demonstrated line spectral imaging with a 38x52 pixel grid.

Showed HDR imaging with FDMA-TDMA mode at higher speed and SNR.

Abstract

In the first part of the paper, a CAOS line camera is introduced for spectral imaging of one dimensional (1-D) 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 transforming operations in the orthogonal direction to provide line pixels optical spectrum analysis. The imager incorporates the Digital Micro-mirror Device (DMD)-based Coded Access Optical Sensor (CAOS) structure. The design includes a line-by-line scan option to enable two dimensional (2-D) spectral imaging. For the first time, demonstrated is 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 to simulate a line target with individual pixels along 1-D that have unique spectral content. A ~412 nm to ~732 nm input target spectrum is measured using a 38 by 52 CAOS pixels spatial sampling grid providing a test image line of 38 pixels with each pixel providing a designed spectral resolution of ~6.2 nm. The spectral image is generated using the robust Code Division Multiple Access (CDMA) mode of the camera. The second part of the paper demonstrates for the first time the High Dynamic Range (HDR) operation of the Frequency Division Multiple Access (FDMA)-Time Division Multiple Access (TDMA) mode of the CAOS camera. The FDMA-TDMA mode also feature HDR recovery like the Frequency Modulation (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.