INVESTIGATION ON THE SPECTRAL CHARACTERISTICS OF DFB LASERS WITH DIFFERENT GRATING CONFIGURATIONS MADE BY ELECTRON-BEAM LITHOGRAPHY

The single-mode stability for DFB lasers with various e-beam-written grating configurations has been investigated theoretically and experimentally, both for as-cleaved and AR-coated lasers. Other laser properties interesting for coherent and multichannel communications systems such as linewidth and tunability have also briefly been investigated. Lasers with more sophisticated grating structures, such as an optimized multiple phase-shifted or a corrugation-pitch-modulated grating, did not exhibit any performance significantly superior to lambda/4-shifted DFB lasers with an appropriate coupling coefficient. AR-coating of the end facets proved indispensable to obtain a high yield of lasers with single-mode operation at high output power and to reduce the large chip-to-chip variation seen for the as-cleaved lasers. A theoretical investigation dealing with the effect of end reflections on the stop-band and the problem to determine the coupling coefficient was also made.