Measurement and modeling of distributed-feedback lasers with spatial hole burning

Longitudinal spatial hole burning (SHB) in semiconductor lasers is examined theoretically and experimentally in index-coupled distributed-feedback (DFB) lasers. The amplified spontaneous emission (ASE), or facet light, below threshold is measured and fitted by a theoretical model in order to extract the parameters such as the phases of optical field reflection at the facets. The ASE spectrum above threshold is also measured and compared with theoretical results using the same parameters. The photon density profile of the dominant lasing mode and the carrier density profile at a bias current above threshold are then calculated. The theoretical results are compared to the experimentally measured change in the spontaneous emission (SE) (or carrier density) profile along the laser stripe using an optical fiber setup with careful calibration between the below and above threshold SE longitudinal profiles. By fitting the experimental ASE spectra from the facet both below and above threshold and the SHB profile from the side of the laser as a function of position to our theoretical results, we show that our procedure is a promising and systematic approach for understanding DFB lasers, especially the SHB effects. It is also shown that the facet reflectivities, phases, and the coupling coefficient have a large impact on the SHB of DFB lasers.