Planar Waveguide Devices for Communication and Sensing Applications

Silicon photonics is widely regarded as a promising technology to meet the requirements of rapid bandwidth growth and energy-efficient on-chip communication while reducing cost per bit. In all potential application areas it is widely recognized that use of wavelength division multiplexing (WDM) techniques will be critical in achieving the required high levels of data transmission. Si photonics devices will have to deal with several tens of different wavelengths of light in the next-generation multi-core CMOS chips. There are mainly four kinds of devices capable of multi/ demultiplexing tens of WDM signals; they are ring resonators, lattice-form filters, arrayed waveguide gratings (AWG) and planar Echelle gratings. The former two are cascaded devices relying on temporal multi-beam interference effect and the latter two utilize spatial multi-beam interference effect. In order to achieve good crosstalk characteristics in the temporal and spatial multi-beam interference effects, uniformity of effective index ( ) / = c n k β , where β and k denote propagation constant and wave number, is critically important. Filter characteristics of four kinds of devices will be investigated and performance limitations of silicon photonics filters are discussed. In the latter part of the paper, an integrated-optic spectrometer based on Fourier-transform spectroscopy will be described. A novel planar waveguide spectrometer consists of interleaved Mach-Zehnder interferometer (MZI) array. Practical importance of Fourier-transform spectrometer is the ability to correct for interferometer defects caused by effective index fluctuations (phase errors) in data processing stage. Successful measurement results of the signal spectrum with 20-GHz resolution by the spectrometer implemented in silica-based planar waveguide will be presented.