CAOS module designs and imaging

Mazhar, Mohsin A.

CAOS module designs and imaging

cbnd

Date

2021

Authors

Mazhar, Mohsin A.

Publisher

University College Cork

Abstract

In this dissertation, proposed and demonstrated are the various novel CAOS module designs and imaging modes that offer a wide range of imaging capabilities suited to various imaging scenarios. The CAOS modules designs include the use of several commercially available electrical and optical components that are controlled through custom in-lab built software for image capture, reconstruction, and post-processing. The first chapter introduces the novel Code Division Multiple Access (CDMA) mode of the camera that is best suited for high Signal-to-Noise (SNR) imaging of bright light targets in minimal acquisition time. Theoretical and experimental comparisons of CDMA mode to the previously well-known Hadamard Transform imaging are also presented, showcasing the advantages of the CAOS-CDMA mode. The next part of this dissertation introduces several novel hybrid CAOS Camera imaging modes, which include Time Division Multiple Access (TDMA), CDMA-TDMA, Frequency Modulation (FM)-TDMA, Frequency Division Multiple Access (FDMA)-TDMA, and FM-CDMA-TDMA. A thorough explanation of the workings of each of these modes with their performance trade-offs has been included as well. Experimental demonstrations include the use of the CAOS camera for laser beam spot size measurement using different imaging modes. To demonstrate the power of CAOS, FM-TDMA mode is used to capture the oscillatory behavior of a Gaussian beam up to a Dynamic Range (DR) of 94.9 dB. This oscillatory behavior is also predicted and confirmed by the Huygens-Fresnel diffraction theory. The performance limits of these modes are further tested and evaluated against a commercially produced Image Engineering custom made uniformly lit 160 dB High Dynamic Range (HDR) target. DR recovery limit and SNR performance are also evaluated for a Quantalux HDR sCMOS sensor which is incorporated within a new Digital Single Lens Reflex (DSLR) design of the CAOS camera. Experiments confirming the superior HDR linear performance of CDMA and FM-TDMA mode in comparison to the sCMOS are also presented. A record 177 dB linear DR response using a controlled laser pixel using electronic amplification and Digital Signal Processing (DSP) is also reported. In addition, a 48 Pixels of Interest frames per second video sample is also recorded for tracking a moving laser beam spot. Another key aspect of any imaging camera is the ability to resolve a low contrast image over an HDR target. Such targets are ever-present in daily life and hence for robust operation, a high-end sensor must be capable of imaging such scenes. Two CMOS sensors, namely the 2.1 MP Quantalux sCMOS sensor, and the EMVA1288 compliant Photonfocus CMOS HDR sensor are tested against an in-house built 90 dB HDR target. This target has 16 discrete irradiance levels while maintaining a 2:1 relative irradiance across the entire DR of the target. Inspection of the experimentally measured target data reveals partial linear recovery up to 42 dB, whereas the weaker target regions were also registered by the Quantalux CMOS sensor but for these, recovery was non-linear. Highly accurate, linear HDR performance was recorded when engaging CAOS FM-TDMA mode. Thus, the proposed operation of the CAOS camera ensures accurate recovery of a low contrast HDR target which might be critical in applications related to imaging and display testing. The previously mentioned designs of the CAOS camera rely on passive imaging of targets, where the target emits/reflects light, and this light is imaged via an imaging lens onto the imaging sensor. Alternatively, a design variant of the CAOS camera uses a hybrid method of combining optical device engagement and time-frequency CAOS operations whereby the SLM and the illuminating source work in unison to deliver the FM-CDMA mode of the camera. Specifically, the illuminating source must-have modulation capabilities that allow frequency modulation of the light source providing FM encoding whereas the SLM is used to implement CDMA Walsh codes for pixel irradiances. Indeed this mode of operation preserves the linear high DR imaging capabilities of CAOS and experiments conducted with a calibrated target indicate a near 60 dB linear DR using a white light imaging target. The last part of this dissertation covers the CAOS line camera, a linear HDR CAOS spectrometer, and a 2-D spectral imager. The CAOS line camera design relies on the use of a 1-D SLM for time-frequency modulation instead of the previously demonstrated 2-D SLM based CAOS camera. The line camera design incorporates the use of a Galvo system with a feedback control system for precise image translation over the 1-D SLM. The introduction of a Galvo system mitigates the need for a mechanical motion of the camera thereby reducing imaging artifacts. An increase in the Field-of-View (FOV) is also recorded. Potential applications involve broadband operation from Ultra-Violet to Infrared regimes, high linear dynamic range target recovery, and robust low contrast imaging. Next, a design of the CAOS spectrometer utilizing a dispersive grating is introduced for spectral content analysis. The advantages of the CAOS platform in spectrometry are two-fold (i) it delivers linear HDR spectral measurements, and (ii) high SNR performance due to simultaneous encoding of multiple spatial-spectral regions. The highly adaptive and programmable nature of the CAOS platform allows inspection of any spectral band, UV, Visible, and Infrared. This design of the CAOS spectrometer is further modified to enable 2-D spectral imaging. The design relies on line scan mechanism to sequentially image the target. Experiments conducted include imaging of a vertical slit, which mimics a line target. Additionally, a frequency channel criterion to choose FDMA frequencies, which minimize inter-channel crosstalk, is also presented. In comparison to FM-TDMA, this criterion allows minimization of imaging times significantly while ensuring no compromise on the complete recovery of an HDR scene.

Keywords

Camera , CAOS , Imaging , Camera linearity , High dynamic range , Broadband , TDMA , CDMA , FM-TDMA

Citation

Mazhar, M. A. 2021. CAOS module designs and imaging. PhD Thesis, University College Cork.