We propose an integrated waveguide depolarizer for use in interferometric fiber optic gyroscopes (IFOGs) with single-mode fiber coils. The integrated waveguide depolarizer is based on a Mach-Zender interferometer with polarizing beamsplitters. A waveguide polarizing beamsplitter is designed using multiple air trench structures oriented at the Brewster angle. We also analyze the effect of component imperfections on the degree of polarization achievable with an integrated waveguide depolarizer.
The ability to make small-area bends and splitters in low index contrast waveguide materials is a critical enabler to realize densely integrated planar lightwave circuits (PLCs) in such materials. We discuss two approaches, the first based on photonic crystal (PhC) structures of limited spatial extent and the second on single air trenches. In each case, PhC or air trench regions are used to augment conventional waveguides (CWGs) to permit drastic reductions in overall device size while preserving the traditional advantages of CWGs such as straightforward design for single mode operation, low propagation loss, low fiber coupling loss, low dispersion, and mature microfabrication processes. We show how these approaches can be used to realize example devices having a very small footprint, including Mach-Zender interferometers and ring resonators.
We discuss the use of multiple layer air trench and silicon strip structures to realize high efficiency 90° bends for low index contrast waveguides. We use a micro-genetic algorithm (mGA) coupled with a 2-D finite difference time domain method to perform rigorous electromagnetic optimization of multi-layer structures for single mode waveguides. We find that a 3-layer air trench structure can be designed for a 90° waveguide bend that exhibits 97.2% efficiency for TM polarized light at a wavelength of 1.55 μm. We are also able to design five- and six-layer silicon strip bends that have high efficiency for both TE and TM polarizations. For example, simulation results for a six-layer design show 95.2% and 97.2% for TE and TM polarizations, respectively. Moreover, the bend efficiency for each polarization state is greater than 90% over a broad wavelength range (1.5 μm to 1.7 μm).