Design of pseudo real-time hybrid-optical spectrographic processor as applied to speech signal processing

Compared to the electronics counterpart, optical spectrographic processor has several advantages in the sense of faster speed, free space interconnectivity and inherent parallel processing capability. With development and advance of spatial light modulators and CCD technologies, a hybrid-optical spectrographic processing system is thus proposed in this thesis and plays even more important roles in time-varying signal processing, owing to its real-time implementability and reconfigurability. This novel optical architecture takes advantage of the optical system and the digital computer, which exploits the parallelism, speed transformation of Fourier optics and the controllability, programmability and decision-making of the digital computer. In general, this thesis focuses on the design architectures of a hybrid-optical spectrographic processor to realize improved system performance through apodized window functions and relaxed dynamic range requirement for capturing devices, and to exploit new potential applications, particularly in speech signal processing.; The prototype of the hybrid-optical spectrographic processor proposed initially in this thesis consists of the programmable spatial light modulator and high-resolution CCD. The characteristics of optical devices such as SLM, CCD and transform lens etc. are well specified in terms of the response time, the spatial resolution, as well as the dynamic range requirement. The time-frequency resolution of spectrogram depends significantly upon the response time of a SLM whose spatial resolution limits the highest frequency component in the spectrogram. Due to the fact that the higher frequency components in speech signal usually have much less intensity than the lower frequency ones, the dynamic range required for the CCD is as large as up to 150 dB in some cases. The size of the transform lens has dual impacts on the spectrogram, i.e., both the resolution limit and longitudinal spherical aberration increases with the lens size. The processing capability of the optical system is generally superior to its electronics counterpart due to its inherent parallelism property and the speed can be significantly improved accordingly.; To compensate the high dynamic range requirement in the initial prototype, a non-bias hybrid-optical spectrographic processor architecture is proposed by cascading both amplitude a modulated SLM and a phase modulated SLM at the input plane. The new architecture can relax the stringent dynamic range requirement for CCD by about 15∼30 dB. The dynamic range can be further relaxed by including the apodized filter which is used to suppress the intensity of the lower frequency components. (Abstract shortened by UMI.)...