Characterization of fiber distributed-feedback lasers with an index-perturbation method

We demonstrate the characterization of fiber distributed-feedback lasers by scanning a heat-induced index perturbation along the cavity and by measuri ng the induced laser frequency shift. The measured shift is shown to be a g ood indicator for the intensity distribution in the cavity, and the experim ental results reveal that the sensitivity of fiber distributed-feedback las er sensors with frequency readout is highly localized near the grating phas e-shift position. Use of the characterization data to determine the grating coupling parameter kappa, the polarization dependence of kappa, and birefr ingence nonuniformities as well as for identification of the order of longi tudinal mode operation are discussed and demonstrated experimentally. Asymm etrically phase-shifted lasers with highly directional output are also inve stigated. (C) 1999 Optical Society of America. OCIS codes: 140.3430, 140.35 10, 140.4780, 230.1480, 050.2770, 060.2370.