Narrow-linewidth three-electrode regrowth-free semiconductor DFB lasers with uniform surface grating

Abstract

There has been much interest in developing low-cost laser sources for applications such as photonics integrated circuits and advanced coherent optical communications. The ultimate objectives in this development include wide wavelength tunability, a narrow linewidth, and an ease of integration with other devices. For this purpose, semiconductor surface grating distributed feedback (SG-DFB) lasers have been introduced. SG-DFB manufacturing consists of a unique sequence of planar epitaxial growth resulting in a major simplification to the fabrication process. SG-DFB lasers are highly monolithically integrate-able with other devices due to their small footprint. The segmentation of the built-in top electrode helps to alleviate the adverse spatial-hole burning effects encountered in single-electrode devices and brings hence significant enhancements to the laser performance. For the first time, we report here on the design, fabrication, and characterization of InGaAsP/InP multiple-quantum-well (MQW) SG-DFB lasers with uniform third-order surface grating etched by means of stepper lithography and inductively-coupled reactive-ion. The uncoated device reported here is 750 μm-long SG-DFB laser whose central and lateral top electrodes are 244 μmlongs each, separated by two 9 μm-long grooves. The experimental characterization shows stable single mode operation at room temperature under uniform and non-uniform injection. High side mode suppression ratios (SMSRs) (50-55dB) under a wide range of injection current have been discerned as well. A relatively broad wavelength tuning (<4nm) has also been observed. Moreover, a narrow linewidth (<300 kHz) has been recorded for different injection currents.