Three transducers for one photodetector: essays for optical communications

Dissertation presented to obtain the PhD degree in Electrical and Computer Engineering - Electronics

Optical processing devices based on a- SiC:H multilayer architectures are expected to become reconfigurable to perform WDM optoelectronic logic functions and provide as well complex photonic functions such as signal amplification and switching. This thesis, entitled ”Three Transducers for One Photodetector: essays for optical communications”, reports the main work areas to design, control, validate and evaluate the research of a voltage-controllable wavelength selective optical switching based on shifting between positive and negative electrically bias and a photodetector, which enables the filtering function with the detector itself and has the potential to be rapidly optically biasing tuned: System Architecture – In this work area it is defined the basic requirements of the device: light-to-dark sensitivity, colour recognition, selective optical and electrical output response, amplification and opto-electronic conversion to transmit, receive, and/or process intelligence(data).The output multiplexed signals should have a strong nonlinear dependence on the light absorption profile, i.e., on the incident light wavelength, bit rate and intensity under unbalanced light generation of carriers. Experimental Design – This test activities work area allows the evaluation of the results. Multiple monochromatic pulsed communication channels were transmitted together, each one with a specific bit sequence. The combined optical signal was analyzed by reading out, under different applied voltages and optical bias, the generated photocurrent across the device. Depending on the wavelength of the external background and irradiation side, it acts either as a short- or a long- pass band filter or as a band-stop filter Optoelectronic Algorithm Interface – To help improve our understanding of the output multiplexed signal, computer models of monolithic photodetectors are developed. Following control theoretic methods we derive state-space representation and an equivalent circuit optoelectronic simulator. We validate each model and calibrate the spectral gain model by background–probe experiments and truth tables lookup that perform 8-to-1 multiplexer (MUX) and 1-to-8 demultiplexer (DEMUX) functions. Applications – The purpose of this work area is to present a new optical logic architecture that offers considerable improvements in reconfigurability. Tunable WDM converters based on amorphous SiC multilayer photonic active filters are used to build blocks to perform standard digital system operations. The transducers combine the simultaneous demultiplexing operation with the photodetection and self amplification. They are optimized for provide the high-sensitivity needed for low-light applications, such as medicine, lighting, sensing and measurement, and manufacturing. The migration to next generation packet based networks can be much easier and smoother than previously thought, using the emerging a-Si solutions and its integration with plastic optical fiber. It will push the limits of functionality, cost/performance and integration level.