DFB laser arrays with precise channel separation and high coupling coefficient

Abstract

Distributed feedback (DFB) semiconductor laser arrays operating at precisely controlled wavelengths are important components for wavelength division multiplexing networks. Recently, precise wavelength control has been realized by the reconstruction-equivalent-chirp (REC) technique based on sampled Bragg gratings (SBGs) [1]. However, the effective coupling coefficient, κ, of a sampled grating is necessarily reduced substantially from that of a uniform grating, compromising the single longitudinal mode (SLM) performance of DFB lasers. To overcome this, designs of SBGs with phase shifted grating sections have been proposed and demonstrated in fibre lasers. In these structures, the (not required) zeroth-order mode is suppressed while the index modulation experienced by the nonzeroth-order channels is enhanced, the ±1st order channels being of particular interest [2]. Here, for the first time, we apply a combination of π-phase shifted gratings with the REC technique to DFB diode lasers. Using a single electron beam lithography (EBL) step we have demonstrated an increased effective coupling coefficient κ and have fabricated an eight-channel laser array with a spacing of 100 GHz (∼0.8 nm @1550 nm). For the same channel spacing using conventional 0th order gratings (Fig. 1(a)), a resolution of about 0.125 nm would be required, which is beyond the typical resolution limit of 0.5 nm of EBL machines.