Design of Polarization-Independent Coarse Wavelength Splitters Based on Ridge-Waveguide Directional Couplers

Abstract

We present the first unique design of a polarization-independent dual-wavelength splitter for wavelengths around 1.3 μm and 1.55 μm that is potentially of great interest to passive optical network (PON) applications. The filter design is simple compared with the other architectures and is based on ridge-type lateral directional couplers that can be readily integrated with other planar waveguide devices. Two design examples, based on InP/InGaAsP and Si/SiGe waveguides, are given. This polarization-independent wavelength splitting is achieved by exploiting the polarization dependence of the waveguides to produce coupling lengths that are sensitive to polarization and wavelength. We show that, to split the wavelengths without splitting the polarizations, the coupling lengths must be sufficiently different for TE and TM and for the different wavelengths in order to give the correct required ratios between the TE and TM coupling lengths for the two wavelengths of interest. We also show that the same approach can be applied to the design of a polarization splitter. The crosstalk, optical bandwidth, and fabrication sensitivity for the wavelength filter are evaluated.

Subwavelength TE/TM grating coupler based on silicon-on-insulator

“…All of these are considered to a single mode because of grating couplers' polarization-dependent. Due to different effective refractive index for two orthogonal polarization, it is hard to fulfill with the phase match condition based on the same grating parameters [11].Some non-polarization structures [12][13][14][15] were improved. For example, an air-cladding apodized focusing subwavelength grating [12]overcome the limitation of the structure polarization insensitive and experimentally demonstrate an air cladding apodized focusing nanohole subwavelength grating(SWG) that can efficiently couple two polarizations into a single waveguide in the telecommunication band.…”

A novel wavelength multiplexer/demutiplexer based on side-port multimode interference coupler

“…Various structures, such as directional couplers [5], Mach-Zehnder interferometers [6], arrayed waveguide gratings [7] and multimode interference (MMI) couplers [8][9][10][11]15] have been proposed to realize MUX/DMUX in the 1.31/1.55-μm wavelength window. Among them, MMI couplers based on self-imaging are attractive for wavelength splitting due to their advantageous properties of compact size, low excess loss, large fabrication tolerance [12], etc.…”