Optical signal processing with MEMS technology: Applications in optical communication systems

During the last decade we have seen a considerable increase in the capacity of communication networks. The growth of the capacity is mainly supported by the advance of photonics technology such as wavelength division multiplexing. Signal processing in the optical domain, such as optical filtering and wavelength multiplexing/demultiplexing, becomes progressively more important to obtain better system performance and to reduce the burden of the electronics.; In this dissertation, we discuss the use of optical signal processing techniques for applications in optical communication systems. We have shown that tunable optical transversal filters can be made with a relatively simple configuration based on the geometry of a Gires Tournois interferometer. The back reflection plane of the interferometer is replaced with a one-dimensional array of MEMS phase shifters for spatial light modulation. Optical signals are processed at the speed of light in the time domain, and the optical filter characteristics can be modified within tens of microseconds by MEMS devices. A bulk-micromachining fabrication process is used to make movable micromirrors with surface roughness of less than 10 nanometers over the entire range of motion of approximately one micrometer.; Using Gaussian beam optics, we show that the transfer function of the device has the form of the transversal filter in digital signal processing. The design and analysis techniques of conventional digital filters can therefore be adapted to tunable optical filters without many modifications. Both the magnitude and phase of the transfer function can be controlled by reconfiguring the MEMS spatial light modulators. However, there is an inevitable trade off between the filtering complexity and the averaged power throughput of the optical transversal filter. Applications in chromatic dispersion compensation, variable-bandwidth optical bandpass filtering, and reconfigurable wavelength multiplexing/demultiplexing are discussed in detail with experimental results.; The flexibility and wide range of applications, combined with fast tuning speeds of MEMS, make the tunable optical transversal filters very attractive for multi-functional all-optical filtering elements in advanced optical communication systems.