InP-based photonic crystal electro-optic modulator

In this article, we designed a Mach – Zehnder Interferometer (MZI) based modulator based on photonic crystal at 1.55 μm wavelength. The layer stack of the slab waveguide consists of the InP/InGaAsP/InP clad/film/substrate layers. The geometry of photonic crystal is pillar-based in the air background with a square lattice. The radius of pillars is determined 110 nm at a lattice constant of 580 nm by determining the gap map and band diagram. Band diagram shows that only transverse magnetic (TM) mode can propagate through the waveguides. The designed Y-junction is based on the directional coupler. The optimized structure of the Y-junction power splitter shows a 40% shorter coupling length and about 10% improvement in spectral transmission at 1550 nm central wavelength.The MZI-based modulator is consisted of two optimized Y-junction splitter and combiner with two arms. The driving reverse bias voltage is applied on an arm of the MZI. The reverse bias voltage of 7 V creates a change in refractive index of about 1.1 × 10−3. This change is sufficient to obtain a total phase difference of π between both arms. The field distributions reveal that the wave from the output port can interfere constructively or destructively.