Fabrication of distributed Bragg reflectors to reduce coupling losses of photonic circuits

Inhalt:
In moving away from the SOI platform to a variety of substrates such as quartz glass or lithium niobate, the coupling efficiency generally reduces significantly. The coupling efficiency can be improved by introducing a reflecting layer below the photonic systems, which reduces the losses towards the substrate. In this work, a distributed Bragg reflector consisting of 2, 4 and 6 layers is designed using the transfer matrix method. The designs are fabricated on top of a silicon and quartz glass substrate and the layer characteristics are determined using ellipsometry. The reflection of the 6-layer DBR on top of silicon and quartz glass is measured using FTIR to be >98% and >96%, respectively. The designs are elaborately tested in a FEM model including a grating coupler, where a reflection improvement from 51% to 86% was observed for the 6-layer DBR with respect to an SOI substrate.