Wavelength-selectable lasers with Bragg-wavelength-detuned sampled grating reflectors

Wavelength-selectable lasers (WSLs) with a novel type of grating reflectors are proposed for realizing fast tunable lasers that can cover a wide range of wavelengths. Each WSL includes an array of distributed-Bragg-reflection (DBR)-type lasers that are combined with a multimode-interference (MMI) coupler. In order to cover different wavelength bands with simple fabrication, the grating reflector is formed of two sampled-grating (SG) subsections on waveguides of different thicknesses. The resultant Bragg-wavelength detuning from the thickness difference between the two SG subsections causes the maximal refection shift to the high-order reflection peaks. A laser array where each laser covers a different wavelength band is realized by varying the corresponding wavelength position of the second-order peak from laser to laser. Each laser has one-side SGs for allowing one-electrode fast tuning. It can also allow high-reflection facet coating to increase output power. Four-laser WSLs, where each laser can be tuned to cover at least 3.5 nm of wavelength span with a side-mode suppression ratio that is better than 30 dB, are designed and demonstrated. Forty 50-GHz-spaced channels can be covered with the four-laser array