New high-resolution positive and negative photoresist method for λ/4-shifted DFB lasers

Abstract

High-resolution positive and negative photoresists were used to fabricate λ/4-phase-shifted corrugations by holographic exposure. To avoid mixing these photoresists, cyclised polyisoprene was used as a midlayer. The shape and depth of the corrugations on the positive and negative photoresist regions were almost the same. Single-mode operation at the Bragg wavelength was confirmed in lasers with the corrugation.