Kunio Aiki

Transverse mode stabilized Al x Ga 1-x As injection lasers with channeled-substrate-planar structure

A built-in passive waveguide mechanism is introduced in Al x Ga 1-x As injection lasers by growing planar double heterostructure (DH) layers on a grooved GaAs substrate. The lasing mode is confined to the channel region due to excess absorption loss outside the channel. Stable fundamental mode oscillation is achieved up to twice the threshold current for a channel width of 5-8 \mu . Undesirable lasing behavior usually induced by transverse mode instability, such as nonlinear kinks in the light output versus current characteristics, are significantly reduced in the present lasers. The dc threshold current is 40-90 mA at room temperature. Median lifetime of 780 hours has been obtained during preliminary aging tests at a heat sink temperature of 70°C.

Longitudinal‐mode behaviors of mode‐stabilized AlxGa1−xAs injection lasers

Lasing spectra of a transverse‐mode‐stabilized AlGaAs laser of a channeled‐substrate planar structure have been investigated. These lasers, which oscillate in the fundamental transverse mode, reproducibly operate in a single longitudinal mode. In addition, their linewidth is as narrow as or smaller than 30 MHz when the injection current is ∼1.2 times above threshold. The intensity distribution and excitation dependence of a nonlasing longitudinal mode have been found to be more complicated than expected from a simple theory: sizable dips have been observed in the envelope function, and nonlasing modes have been found to decrease as the injection current is increased above threshold. Furthermore, hysteresis has invariably been observed in the lasing‐wavelength–vs–device‐temperature (or dc current) characteristics. These behaviors are believed to reflect a slightly inhomogeneous nature of the gain spectrum because of a finite thermalization time of injected carriers, as discussed recently by Yamada and Suem...

Channeled‐substrate planar structure (AlGa)As injection lasers

Undesirable nonlinear ’’kinks’’ in light‐output–vs–current characteristics of stripe geometry double‐heterostructure (DH) injection lasers are significantly reduced by stabilizing the transverse modes along the junction plane. Built‐in passive guiding mechanism is introduced by growing planar (AlGa)As/GaAs DH layers on a grooved GaAs substrate.

Fabrication and characterization of narrow stripe InGaAsP/InP buried heterostructure lasers

InGaAsP/InP buried‐heterostructure lasers with a stripe width of 1–2 μm have been fabricated by two‐step liquid phase epitaxy and preferential chemical etching. They operate in the fundamental transverse mode at wavelengths of ∼1.3 μm with threshold current as low as 22 mA. The temperature limit for cw operation is 80 °C.

Temperature distribution along the striped active region in high-power GaAlAs visible lasers

Catastrophic degradation related to local heating in GaAlAs visible lasers occasionally occurs under relatively low optical output power. To develop highly reliable lasers, we used laser Raman spectroscope with an argon ion laser focused at about 1 μm≂ to evaluate the local operating temperature rise not only at the facet surface, but also along the striped active region. The local operating temperature rise in the vicinity of the facet’s active region increased exponentially up to 200 °C when the optical output power was 30 mW/facet. This high temperature causes the rapid formation of a dark region and final catastrophic degradation. The calculated temperature rise along the striped active region is about one‐half of that of the facet. The internal operating temperature is far higher than the average temperature measured by the thermal resistance method, which is considered to be a large influence on the lifetime and activation energy of lasers in practical applications.

cw operation of distributed-feedback GaAs--GaAlAs diode lasers at temperatures up to 300 K

Distributed‐feedback GaAs‐GaAlAs diode lasers with separate optical and carrier confinement have been successfully operated under dc bias up to room temperature. They lased in a single longitudinal mode with a threshold current density of 0.94 kA/cm2 at 170 K and 3.5 kA/cm2 at 300 K.

Effects of lateral mode and carrier density profile on dynamic behaviors of semiconductor lasers

Dynamic behaviors of the semiconductor lasers have been investigated both theoretically and experimentally. A single-mode rate equation, which takes account of the lateral mode profile and the carrier density profile, has been solved numerically. Effects of the carrier and lateral mode confinement have been clarified. The lateral mode deformation in lasers without a built-in mode confinement structure greatly enhances the relaxation oscillations. In lasers whose stripe width is narrower than \sim10 \mu m, the carrier diffusion is found to play an important role in suppressing the relaxation oscillations, especially for lasers without a lateral carrier confinement structure. On the other hand, the fraction of the spontaneous emission going into the lasing mode is significant for lasers with a lateral carrier confinement structure. The slow increase of the laser output at the transient is confirmed to be due to the carrier diffusion.

Frequency multiplexing light source with monolithically integrated distributed‐feedback diode lasers

The details of the fabrication and performances of a monolithically integrated frequency-multiplexing light source are presented. The light source consists of six GaAs-GaAlAs distributed-feedback (DFB) diode lasers with different grating periods and passive GaAlAs waveguides. By changing the grating periods by ∼9 Å, the lasers lase with different wavelengths with a separation of ∼20 Å. Laser output beams are guided and collected into a single launching waveguide through bends and confluence regions. The overall differential quantum efficiency of about 0.3 percent is obtained at the launching output terminal.

GaAs--GaAlAs distributed-feedback diode lasers with separate optical and carrier confinement

Remarkable reduction of the threshold current density is achieved in GaAs‐GaAlAs distributed‐feedback diode lasers by adopting a separate‐confinement heterostructure. The diodes are lased successfully at temperatures up to 340 °K under pulsed operation. The lowest threshold current density is 3 kA/cm2 at 300 °K.

GaAs–Ga1−xAlxAs double‐heterostructure distributed‐feedback diode lasers

We report laser oscillation at 80–100°K in electrically pumped GaAs–Ga1−xAlxAs double‐heterostructure distributed‐feedback diode lasers. The feedback for laser oscillation was provided by a corrugated interface between the active GaAs layer and the p‐Ga1−xAlxAs layer. The lowest threshold current density was 2.5 kA/cm2 in pulsed operation. The wavelength of laser emission was 8112 A at 82°K with a half‐width of less than 0.3 A. The temperature dependence of the laser wavelength was found to be smaller than that of the conventional Fabry‐Perot laser.