Toshiki Hijikata

Reduction in Threshold Current Density of Quantum Well Lasers Grown by Molecular Beam Epitaxy on 0.5° Misoriented (111)B Substrates

GaAs/AlGaAs graded-index, separate confinement heterostructure quantum-well lasers with an extremely low threshold current density (Jth) were grown by molecular beam epitaxy on 0.5° misoriented (111)B substrates. The Jth of these lasers was reduced by 20 A/cm2 compared with that of (100)-oriented devices, which results from the quantization along the direction. The minimum Jth of 158 A/cm2 was achieved for a 490 µm long device.

Near‐ideal low threshold behavior in (111) oriented GaAs/AlGaAs quantum well lasers

Fundamental characteristics of (111) oriented GaAs/AlGaAs graded‐index separate‐confinement‐heterostructure single quantum well lasers have been compared with conventional (100) oriented lasers. In particular, the threshold current density Jth of (111) oriented lasers does not change with the well width Lz in the range of Lz=30–100 A, which corresponds to an ideal extreme. The lowest Jth of 145 A/cm2 together with a high characteristic temperature T0 of 186 K in the threshold‐temperature dependence has been achieved for an Lz of 40 A and a cavity length of 490 μm. The dependence of T0 on Lz showed that T0 is maximum at Lz∼60 A for both (111) and (100) oriented lasers.

Visible GaAlAs V‐channeled substrate inner stripe laser with stabilized mode using p‐GaAs substrate

A new visible laser, the V channeled substrate inner stripe laser, is developed. This laser can internally confine the current into the V‐channel by using a thin n‐GaAs layer grown on the p‐GaAs substrate. cw threshold currents were 35–45 mA in the visible spectral range of 770–790 nm. And highly stable transverse and single longitudinal mode operation were observed because the built‐in optical waveguide was formed within the V channel.

Suppression of feedback-induced noise in short-cavity V-channeled substrate inner stripe lasers with self-oscillation

Self‐oscillations of V‐channeled substrate inner stripe (VSIS) lasers with index guiding and the influence of external feedback on low‐frequency noise generation are presented. The self‐oscillation is induced by means of shortening a cavity length of VSIS laser to 110 μm. VSIS lasers with self‐oscillation have the fundamental linewidth of 0.56 A below 3 mW and are not sensitive to both phase and amplitude of the externally reflected light. Signal to noise ratio of short‐cavity VSIS laser at 1 MHz with a 10‐KHz bandwidth was 97 dB at 0.05% optical feedback.

Interface disorder in GaAs/AlGaAs quantum wells grown by molecular beam epitaxy at high substrate temperature

The interface disorder of quantum wells grown by molecular beam epitaxy at high substrate temperature is investigated by low‐temperature photoluminescence. The excitonic emission from a single quantum well is a single sharp peak, and the well width precisely determined from the emission peak energy does not equal to integral multiples of one‐monolayer width in almost all samples. These results indicate that the lateral size of growth islands with a one‐monolayer height is much smaller than the exciton diameter and a one‐monolayer interface acts as a layer with smaller AlAs mole fraction than the barrier layer.

GaInP/AlInP Quantum Well Structures and Double Heterostructure Lasers Grown by Molecular Beam Epitaxy on (100) GaAs

GaInP/AlInP single quantum well structures and double heterostructure lasers have been grown by molecular beam epitaxy at 510°C with the dimetric phosphorus beam. The peak energy and linewidth of the photoluminescence spectrum at 10 K from quantum wells as a function of well width have been studied. A 10- µm wide stripe-geometry GaInP/AlInP laser diode has shown a room temperature CW operation with a threshold current of 93 mA and an emission wavelength of 671 nm.

0° phase mode operation in phased‐array laser diode with symmetrically branching waveguide

An AlGaAs phased‐array laser with a novel index waveguide structure like the letter ‘‘Y’’ is described. In all arrays with such a structure, controllable selection of only 0° phase mode and complete suppression of 180° phase shift mode is achieved up to ∼65 mW in 2%–96% coated devices. The far‐field patterns, near‐field patterns, and spectra of the array are in good agreement with the theoretical results. The cw threshold currents are ∼100 mA, and the external differential quantum efficiencies are 57% per facet.

Room‐temperature cw operation in the visible spectral range of 680–700 nm by AlGaAs double heterojunction lasers

Room‐temperature cw operation at the wavelength below 700 nm has been achieved by AlGaAs double heterojunction (DH) lasers with a novel structure, in which a thick buffer layer is grown and the substrate is removed. Continuous‐wave threshold currents were 60–120 mA in the visible spectral range of 680–700 nm. Also the fundamental transverse and single longitudinal mode were obtained under cw operation. The shortest cw wavelength is 683 nm at the present time.

Single-lobed far-field pattern operation in a phased array with an integrated phase shifter

A phased array with an integrated phase shifter which can convert a 180° phase mode into an in‐phase mode was demonstrated. An Al2O3 facet coating with a different thickness on each array element was performed. It should act as the phase shifter. A stable single‐lobed far‐field pattern was obtained from the array with the phase shifter.

Highly reliable and mode‐stabilized operation in v‐channeled substrate inner stripe lasers on p‐GaAs substrate emitting in the visible wavelength region

Highly reliable and mode‐stabilized operation is realized in v‐channeled substrate inner stripe (VSIS) lasers emitting in the visible wavelength region. The VSIS lasers with emission wavelengths of 725–790 nm have low threshold currents of 40±5 mA and reproducibly provide fundamental transverse and single longitudinal mode operation up to 20 mW/facet cw. These performances result from the transverse‐mode stabilization by a built‐in optical waveguide which is self‐aligned with an internal current confining channel. Accelerated lifetests and the statistical characterization of reliability were performed on VSIS lasers emitting at 780 nm. The median lifetimes are estimated to be 1.1×106 h for 5 mW/facet, 4.8×104 h for 10 mW/facet, and 1.3×104 h for 15 mW/facet operations at 25 °C. In addition, almost no degradation in modal characteristics has been observed in the devices operated at 5 mW/facet at 50 °C for 4000 h, up to the present. Photoluminescence study was performed in order to clarify the effects of th...