Compact and Low-Loss Coherent Mixer Based on High Δ ZrO2-SiO2 PLC

In this paper, we report design and characteristics of a compact coherent mixer based on high Δ planar lightwave circuit (PLC) which consists of ZrO₂-doped silica glass. The PLC with 5% or more Δ is realized by employing ZrO₂ as a dopant. Propagation loss of the fabricated 5.5%-Δ ZrO₂ -SiO₂ PLC is reduced to 0.02 dB/cm by an optimized fabrication process. A coherent mixer is designed and fabricated by using ZrO₂-SiO₂ PLC and size of the mixer chip is reduced to 4 mm × 2 mm. Coupling loss between standard single-mode fiber and ZrO₂-SiO₂ PLC is reduced to less than 0.31 dB/facet by an optimized spot-size converter.

I. Introduction

PLANAR lightwave circuit (PLC) devices are used practically in optical communication systems, and various products have been already commercially available. In recent years, dual-polarization quadrature phase-shift keying signals combined with digital coherent detection schemes are started to introduce for 100 Gbit/s systems and demands for the systems expected to be rise. Thus, research and development of PLC based coherent mixers for the systems have been reported [1] .