Seiki Yano

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.

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...

High optical power cw operation in visible spectral range by window V‐channeled substrate inner stripe lasers

High optical power cw operation has been achieved at the wavelength range of 780 nm by newly developed window V‐channeled substrate inner stripe lasers. This laser consists of a waveguiding window region with a plane active layer and a stimulated region with a crescent active layer. These two regions are coupled to each other. cw optical power over 70 mW and low cw threshold current of 30 mA were obtained. Moreover, the fundamental transverse mode was observed up to 60 mW, and it was found that the beam waist along the junction existed at the mirror.

High output power characteristics in broad‐channeled substrate inner stripe lasers

A high output power AlGaAs laser is newly developed in the spectral range of 770–780 nm. The laser has a double‐depth channel on the p‐GaAs substrate which forms a built‐in optical waveguide having a double effective refractive index/loss step. This novel waveguide is effective to make the fundamental lateral mode extremely stable; that is, up to 60 mW when the reflectivity of the front facet (Rf) is 0.12, and 100 mW when Rf is 0.04. cw threshold currents are 35–45 mA and external differential efficiencies are 0.6–0.8 mW/mA. Also, an astigmatic distance below 3 μm is obtained when Rf is more than 0.10.

Effect of group V/III flux ratio on deep electron traps in AlxGa1−xAs (x=0.7) grown by molecular beam epitaxy

The effect of group V/III flux ratio γ on deep electron traps in AlxGa1−xAs (x=0.7) grown by molecular beam epitaxy at 720 °C has been studied by deep level transient spectroscopy. The photoluminescence characteristics of a GaAs single quantum well sandwiched by Al0.7Ga0.3As are determined by the electron traps denoted as E4–E6(E6’) in Al0.7Ga0.3As with the activation energies of 0.77 eV (E4), 0.72 eV (E5), 0.90 eV (E6), and 1.00 eV (E6’). The concentrations of these traps are minimized to the order of 1013 cm−3 at γ∼2 in spite of high Al content.