1.5-µm λ/4-shifted InGaAsP/InP DFB lasers

A single wavelength light source in 1.5-μm range was developed using InGaAsP/InP -shifted distributed feedback (DFB) semiconductor heterostructures. Superiority of the -shifted DFB structure in terms of stability of the main mode at the Bragg wavelength was shown theoretically, in which the threshold, the output, and the polarization characteristics were taken into account. A -shifted corrugated grating was made by a newly developed negative and positive photoresists technique. Buried heterostructure (BH) diode lasers with nonreflective window ends were fabricated and highly stable single-mode operation with a low threshold was obtained reproducibly. Direct modulation properties and life-tests results indicated that the -shifted DFB lasers could be a reliable single-mode light source in a long span lightwave transmission system in 1.5-μm range.