Observation Changes of Laser in Aged ide - Define arr

Aged oxide-defined narrow-stripe lasers sometimes exhibit beam narrowing in both the near-field and far-field light distributions, accompanied by the development of sustained pulsations. The beam narrowing is found to correlate with the presence of a darkened area under the stripe viewed by cathodoluminescence imaging. We propose an explanation based on a thermal waveguiding effect resulting from increasing heat dissipation in the darkened area. HIS paper reports a study on changes of laser beam characteristics in aged oxide-defined narrow-stripe AlCaAs lasers. The changes are characterized by laser beam narrowing in both the near-field and far-field light distributions in some aged lasers, accompanied by the development of self-sustained pulsations. We have found a correlation between beam narrowing and the presence of a darkened area under the stripe in cathodoluminescence images viewed through the p-AlGaAs cladding layers. We propose an explanation based on a thermal waveguiding effect resulting from increasing heat dissipation in the center of the stripe. The fact that material defects cause sustained pulsations in semiconductor lasers is well established [ 11, [ 2 ] . However, changes in laser beam characteristics related to material degradation have not been reported before. The oxide-defined narrow-stripe lasers we have studied are grown by liquid phase epitaxy. The lasing wavelength is around 8200 A. The current isolation is provided by a 0.1-pm-thick Si02 film, and the stripe contact is made through 5-pm-wide openings in the oxide film. The wafer is cleaved into 250-pmlong bars and diced into chips which are indium-soldered onto a copper block heat sink. Before aging, the lasers are free from kinks and pulsations up to 15 mW, as expected for narrowstripe lasers. The aging is carried out in a 70°C ambient at a constant light output of 7 mW/facet. Fig. 1 shows an example of the CW near-field and far-field light distributions of a laser before and after aging. This laser has been under life test over 4000 h and has developed beam narrowing and sustained pulsations. The threshold current has risen from 100 to 130 mA. In most lasers, the far-field narrowing is more pronounced than the near-field narrowing. We note that the beam after narrowing, as shown in Fig. 1, remains symmetrical and well behaved, and the narrowing effect is not a result of kinks or bends in the light-current ( L I ) characteristics, even though nonlinear L-1 characteristics and beam movements often occur at high powers. The narrowed far field is not caused by wavefront distortion or multifilaFAR F IELD