Ultra compact bend-less Mach-Zehnder modulator based on GSST phase change material

Abstract

Optical phase change materials (O-PCMs) are emerging as promising active materials for exploitation in silicon photonics platforms, due to their compatibility with CMOS fabrication technology and the tunability of their optical characteristics via external excitation. Despite their advantages, O-PCMs suffer from relatively high insertion loss hindering efficient modulation. Also, the change of the imaginary part of the refractive index in O-PCMs is large and the realization of a Mach-Zehnder modulator (MZM) based on O-PCM materials becomes challenging. To overcome these issues, we consider the variation of both real and imaginary parts of the refractive index, facilitated by a GSST-based MZM design. To achieve this, we design an active waveguide that is constructed via depositing an ITO layer (as the microheater) surrounding the pre-fabricated GSST layer on a silicon rib-waveguide. The active length of the proposed MZM is designed ∼4.3 µm at the wavelength of 1.55 µm. The simulations indicate that a compact MZM can be achieved by eliminating the S-bends in the MZM structure without affecting the modulation. The proposed bend-less MZM demonstrates an insertion loss less than 1.7 dB and an extinction ratio greater than 35 dB over the entire optical C-band.