Binary superimposed gratings for tunable and multiwavelength semiconductor lasers

Abstract

Tunable distributed Bragg reflectors with comb-like reflection spectrum have been shown to allow semiconductor lasers tuning over about 100 nm wavelength range. Recently we proposed a concept of BSG as a multiwavelength reflector and looked into a number of key design issues for widely tunable lasers. In this paper we analyze the technical aspects of designing and implementing the BSG. We show that the calculated performance of the binary grating is at least as good as that of the existing approaches. However, BSG offers additional design freedoms in positions and amplitudes of reflectance peaks, which in turn allows extension of the tuning range of the laser or relaxing the tuning current requirements. The principles of widely tunable lasers have been adapted to a practical design which should significantly simplify the control requirements for the tuning. We show that a BSG reflector for 1.55 micrometers tunable laser can be successfully implemented with the smallest feature size as large as 0.12 micrometers , which is well within the capacity of electron beam lithography. A simulated tuning curve for a BSG laser predicts a high side- mode suppression ratio (> 35 dB).