Polarization Beam Splitter With Different Core Widths and Its Application to Dual-Polarization Optical Hybrid

We investigated the core-width dependence of the birefringence of silica-based waveguides with different relative refractive index differences (Δ), namely a 0.75%-Δ GeO₂-doped waveguide and a 5%-Δ Ta₂O₅-doped waveguide. We revealed that the birefringence of the 0.75%-Δ GeO₂-doped waveguide is almost the same as the stress-induced birefringence and that the 5%-Δ Ta₂O₅-doped waveguide has a large geometrical birefringence. By utilizing the core-width dependence of the birefringence, we have successfully demonstrated a 0.75%-Δ polarization beam splitter (PBS) with an operating wavelength range of more than 150 nm and a dual-polarization optical hybrid including a compact 5%-Δ PBS with a polarization extinction ratio of more than 20 dB over the C-band.

I. Introduction

A coherent detection technique for a polarization-division multiplexed multi-level modulation format is indispensable for next generation photonics networks [1]– [3]. Polarization-division multiplexing, in which two orthogonal polarizations are used as two independent optical carriers, is an important technology for doubling the spectral efficiency. A polarization beam splitter/combiner (PBS/PBC) for splitting/combining the two orthogonal polarizations is an essential device for realizing a polarization-division multiplexing function. A PBS using silica-based planar lightwave circuits (PLCs) is particularly attractive, because many silica-based waveguide optical components, such as arrayed waveguide gratings (AWG) [4], [5] , dual polarization optical hybrids (DPOH) [6]– [9], optical variable attenuators (VOA) [10] and optical splitters [11], have been commercialized, and further integration of the PBS with these optical components can be expected for future compact multi-function devices.