Kiyoshi Hanamitsu

Catastrophic degradation level of visible and infrared GaAlAs lasers

Burn‐off output powers of catastrophic failures have been studied for GaAlAs double heterostructure (DH) lasers with facet coatings in the wavelength range of 750–870 nm. It was found that the burn‐off power density does not depend on the lasing wavelength when the laser is operated under pulsed condition, whereas it decreases slightly as the wavelength becomes shorter under cw condition.

Mode-stabilized separated multiclad layer stripe geometry GaAlAs double heterostructure laser

A new stripe geometry GaAlAs double heterostructure laser with built‐in optical waveguide to stabilize the transverse mode parallel to the junction plane is developed. A novel optical waveguide and internal current confinement structure are realized in the structure. Lasers with strip width 4.7 μm and cavity length 200 μm showed cw threshold currents of 45–70 mA and highly stable transverse and longitudinal single‐mode lasing.

Repetitive pulsating stripe geometry GaAlAs double-heterostructure lasers with a stripe by a shallow Zn diffusion

We have fabricated a repetitively pulsating stripe geometry GaAlAs double‐heterostructure laser with a stripe by a shallow Zn‐diffusion into n‐GaAs top layer, generating high‐power fundamental transverse‐mode optical pulse trains. Spatially inhomogeneous current injection for exciting pulsations is achieved by a nonuniform breakover in space‐charge region under the Zn‐diffused stripe. These generated optical pulses have a peak power of more than 10 mW, a width of 0.4 ns, and a repetition frequency of 200 MHz–1 GHz.

Buried convex waveguide structure (GaAl) As injection lasers

A new channeled substrate (GaAl)As double‐heterostructure laser with mode control as well as internal current confinement is described. The narrow active region (3–3.5 mm) surrounded by GaAlAs is buried in the etched channel, around which a reverse‐biased heterojunction is formed. The threshold current is as low as 20 mA cw, and highly stable fundamental‐mode lasing is observed.

Lasing-Induced Change in the Differential Resistance of Stripe Geometry Ga1-xAlxAs DH Lasers

The lasing-induced change in the differential resistance is measured for various types of stripe geometry laser, and a model is given that explains the lasing induced change quantitatively to some extent. The amount of the lasing-induced reduction in the differential resistance is mainly determined by a parameter that limits the carrier supply into the active layer. The exsistence of a non-lasing region at the edge of the stripe and lateral carrier diffusion also decrease the amount of the reduction. In narrow-stripe lasers the amount of the reduction is small due to lateral carrier diffusion. From the moderate change in the differential resistance near the threshold, the spontaneous emission factor representing the contribution of the spontaneous emission to the lasing mode is estimated for various types of stripe laser.

Visible GaAlAs Laser with a Buried-Convex Waveguide Structure

A new buried-heterostructure visible GaAlAs laser, called a buried-convex waveguide structure (BCS) laser, has been developed. BCS lasers exhibit a highly stable transverse and single longitudinal mode operation in the 750 to 870 nm wavelength range. Very low threshold currents of 10–20 mA are obtained for the wavelength at about 750 nm. The output beam of BCS lasers has an aspect ratio of 2.0–2.5 and has no astigmatism. The relative intensity noise of BCS laser is very low at a level below -150 dB/Hz and is constant in the temperature range between 10 and 50°C. The maximum output power ofBCS lasers with facet coating is almost independent of the lasing wavelength between 750 and 870 nm.

AGING CHARACTERISTICS OF InGaAsP DFB LASER

Distributed feedback (DFB) lasers have been applied to wideband and long-haul optical transmission systems. For the applications, the long term performance on transmission characteristics is important. Some life-test results have been reported [1,2], however, the reliability of DFB lasers have not been clear yet. This paper presents the high temperature aging results including 1.8 Gbit/s transmission experiments. This is the first report which describes transmission characterisites as well as lasing characteristics of long aged DFB lasers.

Transient spectra in transverse-mode stabilized GaAlAs double-heterostructure lasers

We investigated the dynamic characteristics related to the transient spectra of two types of transverse‐mode stabilized GaAlAs double‐heterostructure lasers: internally‐striped‐planar (ISP) and channeled‐substrate‐planar (CSP) lasers. These lasers exhibited a linear light‐current relation, stable transverse‐mode oscillation, and dynamic response with suppressed relaxation oscillations. Several differences in their spectral behavior have been observed. The dc spectrum of the CSP laser shows a single longitudinal mode, whereas the dc spectrum of the ISP laser shows multilongitudinal modes. In the ISP laser, the transient spectrum under fast pulse modulation is nearly identical to its dc spectrum. The CSP laser shows a transient spectrum that is broader than that in cw operation. The experimental results may be explained from the differences of their device structure and waveguiding mechanisms.