Polarization-independent and dispersion-free integrated optical MZI in SOI substrate for DWDM applications

Abstract

Polarization dependencies and dispersions are the two major bottlenecks in waveguide based silicon photonic devices for various applications – especially in DWDM systems. In this paper, we present the design and experimental demonstration of a 2×2 integrated optical MZI that shows both polarization-independent and dispersion-free response over a wide wavelength range (C+L optical band) in SOI platform - for the first time to our knowledge. The entire device footprint (W×L) is ~ 0.8 mm × 5.2 mm; which is comprised of optimally designed single-mode waveguides (for input/output and interferometer arms) and a pair of MMI based 3-dB power splitters. To monitor the wavelength dependent performance, unbalanced arm lengths (L ~ 3037 μm, L+ΔL ~ 3450 μm) were introduced to construct the MZI. The differential arm length (ΔL ~ 412 μm) has been specifically chosen to provide alternate ITU channel transmission peaks at both the output ports alternatively. Accordingly, the fabricated device separates 100 GHz DWDM channel wavelengths alternatively into two output ports and is nearly insensitive to the polarization of the guided light. We have observed a uniform channel extinction of ~ 10 dB (~ 6 dB) at both ports with a 3-dB bandwidth of ~ 110 GHz (~120 GHz) for TM (TE) polarization over the wavelength range of 1520 nm to 1600 nm. The lower extinction for TE polarization is due to its relatively higher bending loss in the longer arm of the MZI. This can be adjusted by introducing identical bends in both the arms.