Design and fabrication of Bragg reflectors based on SU-8

We report the design and fabrication of two kinds of distributed Bragg reflectors (DBRs). One is a Bragg filter which introduces a periodic height modulation in part of a waveguide, and the other is a horizontal DBR with a deeply patterned grating structure in a waveguide at a freespace wavelength of 1.55 um (the propagation loss of quartz fiber used in optical communication is lowest around 1.55 um wavelength) based on a Si/SiO2/SU8/air structure. The transfer matrix theory was used to calculate the spectral response of the Bragg filter and its dependence on the height modulation and the grating length. In addition, a multilayer film reflection theory was applied to simulate reflection spectrum of the DBR and estimate the least number of pairs of DBR mirrors needed for almost 100% (¿ 99.6%) reflection. Based on the simulation results, we designed and successfully fabricated these two types of DBRs with Si/SiO2/SU8/air structures.