Triple coding empowered FDMA-CDMA mode high-security CAOS camera
Abstract:
For the first time, to the best of our knowledge, the hybrid triple coding empowered frequency division multiple access (FDMA)-code division multiple access (CDMA) mode of the coded access optical sensor (CAOS) camera is demonstrated. Compared to the independent FDMA and CDMA modes, the FDMA-CDMA mode has a novel high-security space-time-frequency triple signal encoding design for robust, faster, linear irradiance extraction at a moderately high dynamic range (HDR). Specifically, this hybrid mode simultaneously combines the linear HDR strength of the FDMA-mode fast Fourier transform (FFT) digital signal processing (DSP)-based spectrum analysis with the high signal-to-noise ratio (SNR) provided by the many simultaneous CAOS pixels' photodetection of the CDMA mode. In particular, the demonstrated FDMA-CDMA mode with P FDMA channels provides a P times faster camera operation versus the equivalent linear HDR frequency modulation (FM)-CDMA mode. Visible band imaging experiments using a digital-micromirror-device-based CAOS camera operating in its passive light mode demonstrates a P=4 channels FDMA-CDMA mode, illustrating high-quality image recovery of a calibrated 64 dB six-patch HDR target versus the CDMA and FM-CDMA CAOS modes, which limit dynamic range and speed, respectively. For the first time to our knowledge, we demonstrate the simultaneous dual image capture capability of the FDMA-CDMA mode using silicon (Si) and germanium (Ge) large-area point photodetectors, allowing the capture of the ultraviolet-near-infrared 350-1,800 nm full spectrum. The active FDMA-CDMA mode CAOS camera operation is also demonstrated using P=3 LED light sources, each with its unique optical spectral content driven by its independent FDMA frequency. This illuminated target spectral signature matched active CAOS mode allows simultaneous capture of P images without the use of P time-multiplexed slot operation tunable optical filters. Applications for such a FDMA-CDMA camera includes controlled light illumination food inspection to bright light exposure security systems.
