Waveguide Confinement Research Articles

Characteristics of thermal drift of the emission frequency of a stripe-geometry semiconductor laser

An investigation was made of tuning of the emission frequency of a stripe-geometry semiconductor laser as a result of heating of the active region during a pump pulse or when the pump current was varied. It was found that the rate of thermal drift of the emission frequency of a stripe-geometry laser changes abruptly on transition from lasing in one transverse mode to lasing in another. It is shown that as the pump current increases, the frequency can either increase or decrease and, for a certain current, the rate of frequency tuning may fall to zero. These characteristics are due to the waveguide confinement of the field in the active region of a semiconductor laser.

Mode-stabilized separated multiclad layer stripe geometry GaAlAs double heterostructure laser

A new stripe geometry GaAlAs double heterostructure laser with built-in optical waveguide to stabilize the transverse mode parallel to the junction plane is developed. A novel optical waveguide and internal current confinement structure are realized in the structure. Lasers with strip width 4.7 μm and cavity length 200 μm showed cw threshold currents of 45–70 mA and highly stable transverse and longitudinal single-mode lasing.

Room-temperature threshold-current dependence of GaAs-AlxGa1−xAs double-heterostructure lasers on x and active-layer thickness

The known properties of GaAs and AlxGa1−xAs have been used to calculate the threshold-current density of double-heterostructure (DH) lasers at room temperature without adjustable parameters. In the absence of leakage currents due to unconfined carriers, the room-temperature threshold-current density for broad-area DH lasers may be repesented by Jth (A/cm2) =4.5×103d+(20d/Γ)[αi+(1/L) ln(1/R)], where d is the active-layer thickness in microns, Γ is the waveguide confinement factor, αi is the internal loss, L is the cavity length, and R is the facet reflectivity. The experimentally observed increase of Jth for x<0.2 given by Rode is shown to be due to the diffusive electron and hole leakage currents, and a best fit to the data was obtained with an electron minority-carrier diffusion length in AlxGa1−xAs (x≲0.3) of ∼1 μm. The above expression for Jth fits Kressel and Ettenberg’s Jth versus active-layer-thickness data at x=0.65, while for x=0.3, the experimental Jth is 300 A/cm2 larger than the calculated Jth at d=0.1 μm. This difference appears to be due to greater scattering loss at x=0.3 than x=0.6.

Distributed-feedback coupling in Ga-_1−XAlXAs double-heterostructure lasers: effect of aluminum concentration

The variation of the feedback coupling coefficient in Ga(1-x)Al(x)As distributed-feedback (DFB) lasers as a function of the Al concentration surrounding the GaAs optical confinement waveguide is considered. An optimum thickness for which the feedback coupling is maximum is determined for each transverse mode. The largest such maximum occurs for the lowest order mode. Fractional Al concentrations that yield symmetrical optical waveguides are found to be most effective in minimizing threshold current density, with the maximum Al concentrations being limited by doping and lattice mismatch considerations.