Isamu Sakuma

A GaAs-AlxGa1-xAs Double Heterostructure Planar Stripe Laser

A stripe laser structure called a planar stripe was developed. The edge blurring of the current path is improved by the fact that the current spreads only in the thin p-AlxGa1-xAs layer with relatively high resistance. The planar stripe laser has a small threshold current resulting from the small current spreading effect and a good thermal contact. It also shows finely controlled transverse modes, compared with a usual contact stripe laser, and relatively high external differential quantum efficiency. The threshold current density is comparable to that of the proton bombarded stripe laser. The transverse mode shows an approximate Hermite-Gaussian distribution.

High optical power density emission from a ’’window‐stripe’’ AlGaAs double‐heterostructure laser

Extremely high optical power density emission (107 W/cm2) was achieved with a new Zn‐diffused ’’window‐stripe’’ laser by eliminating the restriction of the catastrophic optical mirror damage (COMD). The maximum available optical power was at least one order of magnitude higher than the COMD threshold in conventional structures. Furthermore, gradual degradation due to the mirror oxidation has been reduced significantly under cw operation.

Unstable horizontal transverse modes and their stabilization with a new stripe structure

Kinks in the light output and other anomalous characteristics in stripe-geometry lasers were studied. It was found that these anomalies were caused by unstable horizontal, parallel to the junction, transverse modes. Introduction of a refractive-index guiding by Zn-diffusion stabilized the horizontal mode and removed the kink and other anomalies completely.

CW Optical Power from (Al・Ga)As Double Heterostructure Lasers

CW optical output power was investigated in (AlGa)As double heterostructure lasers. An analysis on CW optical power is presented, and parameters related to device characteristics and heat-sinking are analyzed in order to obtain laser operation with high CW optical power. 20–30 mW CW optical power was obtained routinely from each mirror of lasers with a 15 µm wide stripe and a 250 µm long cavity at a typical operating current of 200 mA. Lasers with a Si heat sink can deliver comparably high CW optical power under proper choice of design parameters. Several lasers delivered 85 mW in CW with a Si heat sink from each mirror at 310 mA, before the catastrophic optical mirror damage occurred. Conditions for long life operation are also discussed.

Rapid degradation of InGaAsP/InP double heterostructure lasers due to 〈110〉 dark line defect formation

Rapid degradation has been observed for InGaAsP/InP double heterostructure lasers. It has been found that the rapid degradation is due to 〈110〉 dark line defects generated parallel to the stripe and its occurrence depends on the thickness of the InGaAsP contact layer. It has been shown that formation of a InGaAsP contact layer of more than 0.5‐μm thickness is necessary in order to realize high reliability of the lasers.

Transverse mode stabilized InGaAsP/InP (λ = 1.3 µm) piano-convex waveguide lasers

Guiding mechanisms and lasing characteristics of an InGaAsP/InP 1.3 μm band piano-convex waveguide (PCW) laser are described. The laser structure is fabricated by a single-step liquid phase epitaxial (LPE) growth on a grooved substrate. The refractive index guiding caused by the lateral thickness variations of a waveguide layer adjacent to the active layer is investigated both theoretically and experimentally. Lasers with an adequate refractive index difference and groove width showed stable fundamental mode operation up to two times the threshold current level.

Transverse mode stabilized AlGaAs/GaAs plano‐convex waveguide laser made by a single‐step liquid phase epitaxy

A new laser structure, the plano‐convex waveguide (PCW) laser is described. A thickness‐varied waveguide layer used for transverse mode stabilization was formed adjacent to the planar active layer. The laser structure was fabricated by a single‐step liquid phase epitaxial growth on a grooved substrate. With pulsed injection, stable fundamental transverse mode operation was observed up to 3.5 times threshold current, where power output was 36 mW/facet. At zero dc bias, single longitudinal mode was attained after 10 ns of the leading edge of the optical pulse. Far‐field beam divergences of about 10° and 50° were obtained in directions parallel and perpendicular to the junction plane, respectively.

Internal second harmonic generation in InGaAsP DH lasers

Abstract Self induced second harmonic generation (SHG) accompanying 1.3 μm lasing radiation was first observed in fundamental transverse mode InGaAsP DH lasers. Sum frequency generation by two lasing longitudinal modes was observed, which has a conversion factor of four times greater than that for SHG by a single lasing longitudinal mode and predicts the simultaneous laser oscillation of the several longitudinal modes. The estimated second order nonlinear susceptibility of In 0.76 Ga 0.24 As 0.55 P 0.45 was about 5 × 10 -20 in rotationalized MKS unit, which is at least an order of magnitude greater than that of GaAs.

Reliability of Light Emitters and Detectors for Optical Fiber Communication Systems

Life test results on light emitters and detectors showed promisingly long lifetimes for short and long wavelength optical fiber communication systems. Data are presented on 0.85 μm AIGaAs LDs and LEDs, Si APDs and p-i-n-PDs, 1.3 μm InGaAsP LDs and LEDs, and Ge APDs and PDs. Degradation mechanisms and counteractions are also discussed.

Threshold Current Density and Lasing Transverse Mode in a GaAs-AlxGa1-xAs Double Heterostructure Laser

The relation between threshold current density Jth and the lasing transverse mode is obtained analytically as a function of the active layer thickness for GaAs-AlxGa1-xAs three layer double heterostructure lasers. The experimental results for lasers with x0.43 and x0.3 are in good agreement with the calculated results, assuming that the fractional differences of refractive index are 5% and 3.5%, respectively, and the absorption coefficient in all the layers is 10 cm-1. Jth of lasers with a very thin active layer is influenced markedly by the dependence of the gain on the injected carrier density. The gain must depend on the current raised to some power larger than 1 in order to reduce Jth in a very thin active layer. Another method to reduce Jth is also discussed using the calculated results.