Kunio Itoh

New heteroisolation stripe-geometry visible-light-emitting lasers

Visible-light-emitting lasers were fabricated, using a new stripe-geometry double heterostructure. The distinct feature of the geometry is the isolation of the contact stripe electrode to p-GaAs by the use of a layer of n-Ga 1-z Al z As epitaxially grown on top of p-GaAs. This geometry results in small internal strain, few crystal imperfections, and low thermal resistance in diodes so that high laser performance can be obtained. Lasing wavelengths as short as 7610 A and 6680 A have been attained in CW and pulsed operation, respectively, at room temperature. Various characteristic features of the lasers are described with regard to optical spectra, lasing thresholds, and external quantum efficiencies.

A 0.2 W CW laser with buried twin-ridge substrate structure

An extremely high output power has been obtained with a new structure laser named the buried twin-ridge substrate (BTRS) laser. The very thin active layer formed on a ridged substrate permitted high power output increasing the catastrophic damage level. The buried stripe formed with a blocking layer remarkably improved the current confinement lowering the threshold current. A multilayer coating technique was applied to both facets to increase the front facet output. Fundamental transverse mode is achieved at more than 100 mW in CW with an uncoated laser while the maximum output power attained is as high as 200 mW in CW operation with a multicoated laser.

600 mW CW single-mode GaAlAs triple-quantum-well laser with a new index guided structure

A very-high-power, single-mode GaAlAs triple-quantum-well (TQW) laser with a novel real refractive index guided structure has been developed. The maximum output power of 720 mW CW and single transverse- and longitudinal-mode operation up to 600 mW CW have been achieved in a single-element device. This excellent mode operation is attained by using the real refractive index guided structure with a GaAlAs current-blocking layer which gives a low effective refractive index step, suppressing the spatial hole-burning effect in the high-power range. >

A novel high-power laser structure with current-blocked regions near cavity facets

A novel high-power GaAlAs laser structure has been developed. In the new structure, current-blocked regions are formed near both facets for suppressing local temperature rise. Furthermore, the active layer is made thin only in the vicinity of the facets in order to enlarge the spot size without significant increase of the operating current. The experimentally fabricated laser with the new structure exhibited a COD power density 1.4 times higher and a degradation rate 1/2 times lower than those of the conventional structure lasers.

Improvement in operation lives of GaAlAs visible lasers by introducing GaAlAs buffer layers

It is shown that drastic reduction of the active-layer stress can be obtained by the introduction of a GaAlAs buffer layer in GaAlAs visible lasers. The life tests of the GaAlAs visible lasers with the optimally designed buffer layers were carried out at 50°C in a dry nitrogen ambient. The results indicate that the introduction of the optimal buffer layer leads to a reduction in the stress induced degradation of GaAlAs visible lasers.

Very low threshold visible TS lasers

Fundamental transverse mode lasers with very low threshold currents have been realized by use of the modified terraced substrate (TS) geometry. The threshold currents of 250 μm cavity length lasers at room temperature are typically 20-30 mA for wavelengths around 750 nm. In the 710 nm laser, which is the shortest lasing wavelength in this work, the threshold is as low as 70 mA in CW operation. The 726 nm laser was operated for only 150 h, while a lifetime longer than 10 000 h is expected for TS lasers with a lasing wavelength longer than 750 nm.

A new chemical etching technique for formation of cavity facets of (GaAl)As lasers

A new chemical etching technique which offers excellent cavity facets of Ga1-xAlxAs lasers is reported. This technique is based on our finding that the crystallographic anisotropy in the conventional etching process of Ga1-xAlxAs multilayers depends strongly on the AlAs mode fractionxin every layer. A suitable combination of the mole fractions in the multilayer is therefore a key factor for obtaining practically vertical walls with sufficient smoothness and flatness as laser cavity facets. In fact, the reflectivity of the etched facet obtained is 28 percent, being compatible to that in the conventional cleaved facets. As a result, a CW operation with threshold current as low as 28 mA and external quantum efficiency as high as 24 percent per facet has been attained with high reproducibility.

100-mW high-power angled-stripe superluminescent diodes with a new real refractive-index-guided self-aligned structure

We have developed 100-mW high-power angled-stripe superluminescent diodes with a new angled-stripe real refractive-index guided self-aligned structure. The structure has a GaAlAs optical confinement layer on a planar active layer and an inclined current injection stripe by 5/spl deg/ with respect to the facet normal. The structure gives small internal loss (/spl sim/10 cm/sup -1/) and facet power reflectivity less than the order of 10/sup -6/. As a result, the output power as high as 105 mW at a low operating current of 270 mA is obtained with less than 3% spectral modulation and 10.5 nm full width at half maximum (FWHM) spectral width.

Embedded-stripe GaAs-GaAlAs double-heterostructure lasers with polycrystalline GaAsP layers - I: Lasers with cleaved mirrors

We report a new type of embedded stripe laser in which low-order mode CW oscillation is successfully attained at room temperature. In order to achieve lateral current confinement, a high-resistivity polycrystalline GaAsP layer is formed around the mesa stripe by selective vapor-phase growth technology. It turns out that a stable single-mode operation is attained at an injected current up to several times the threshold value.

Noise and longitudinal mode characteristics of (GaAl)As TS lasers with reduced facet reflectivities

The AM noise in operation of index-guided (GaAl)As lasers is found to be strikingly reduced by the antireflection (AR) coating of cavity facets. This effect is shown to result from the longitudinal multi-mode operation due to the reduced facet reflectivity. It is observed that the width of the envelope of a laser spectrum depends on the facet reflectivity as well as the laser output power. The AM noise in the low-frequency range of the reduced reflectivity lasers is shown to be nearly constant with respect to temperature change. In contrast, the AM noise in a laser without the AR facet coating is characterized by a number of spikes occurring over a wide temperature range.