Shigeo Yamashita

Low-noise AlGaAs lasers grown by organometallic vapor phase epitaxy

The noise behavior of self-pulsation lasers is investigated. It is shown that the pulsation frequency is an important factor in achieving low-noise characteristics under optical feedback. To obtain low-noise lasers, an AlGaAs laser which has a ridge-waveguide self-aligned structure grown by OMVPE (organometallic vapor-phase epitaxy) has been developed. Low-noise characteristics (relative intensity noise >

Low-threshold (3.2 mA per element) 1.3 mu m InGaAsP MQW laser array on a p-type substrate

A low-threshold 1.3- mu m InGaAsP MQW laser array was fabricated on a p-type InP substrate taking compatibility with n/p/n-type laser-driver circuits into account. The laser has a p/n-type current-blocking structure and is made entirely by metal-organic chemical vapor deposition (MOCVD). A 10-channel laser array with a threshold current as low as 3.2+or-0.2 mA (per element) and a slope efficiency of 0.27+or-0.01 W/A is obtained.<<ETX>>

Transverse-mode stabilized Ga 1− xAlxAs visible diode lasers

Transverse-mode stabilized visible diode lasers in the 0.7-microm wavelength region are fabricated by growing a Ga(1-x)Al(x)As double heterostructure on a grooved GaAs substrate (channeled-substrate-planar structure). The diodes operate stably in the fundamental transverse mode and provide nonstigmatic laser beams. They can be collimated with a 0.5-1-mrad beam divergence using a simple graded-index fiber lens. Corresponding to single-longitudinal-mode operation at current levels above 1.1 times the threshold, a coherence length as long as 14 m is obtained in Michelson interference experiments.

Channeled‐substrate‐planar structure distributed‐feedback semiconductor lasers

Distributed‐feedback Ga1−xAlxAs lasers with a channeled‐substrate‐planar structure are fabricated. They operate in single transverse and longitudinal modes. No spectral broadening or excess noise is observed under high‐frequency modulation as a result of mode stabilization.

High-power 780 nm AlGaAs quantum-well lasers and their reliable operation

A high-power laser in the 780-nm wavelength region was realized by introducing an AlGaAs ternary alloy quantum-well structure. Since there is no axial structure, high reproducibility is expected. By applying the quantum-well structure to the AlGaAs ternary alloy wells, a reduction in the operation current of a laser which oscillates in the 780-nm wavelength region can be achieved. A reduction of the optical power density in the direction perpendicular to the junction plane is examined to lessen facet degradation. Investigations focus on the characteristic temperature and catastrophic optical damage (COD) level. It is found that a triple quantum-well (TQW) active layer structure has superior characteristics for high-power operation. Stable operation for over 1000 h under 50 degrees C and 60 mW conditions was achieved. A relatively high characteristic temperature of around 150 K was also obtained. The results of an aging test are provided. >

Degradation of Ga1−xAlxAs visible diode lasers

It is shown that Ga1−xAlxAs visible lasers degrade faster at shorter lasing wavelengths. The degradation in the wavelength region below 730 nm can mainly be attributed to the rapid formation of macroscopic defects in the active region. A notable improvement in life is obtained for these shorter wavelength lasers by Te‐doping of the active layer. On the other hand, degradation at above 740‐nm results from enhanced facet oxidation due to high AlAs mole fractions in the layers. Facet coatings using SiO2 films effectively suppress facet oxidation. As a result, room‐temperature extrapolated lives exceeding 10 000 h are achieved in the wavelength region above 740 nm.

GaAlAs gain‐guided semiconductor lasers with a curved facet

GaAlAs gain‐guided semiconductor lasers having a curved facet are fabricated by employing reactive ion beam etching. The use of the curved facet permits stabilization of transverse mode in the direction parallel to the junction plane, reduction of astigmatism, and multilongitudinal mode oscillation.

Monolithic Integration of a Laser and Driving Circuits in GaAs/GaAlAs System for High Speed Optical Transmission

The monolithic integration of a GaAlAs/GaAs multiquantum well laser with a FET driving circuit on a semi-insulating substrate is described. The circuit operates at more than 2 Gbit/sec.

Degradation Characteristics of Ga1-xAlxAs Visible Diode Lasers

A marked dependence of life on lasing wavelength is found in Ga1-xAlxAs visible lasers. The lasers degrade faster for shorter lasing wavelengths. Degradation in the wavelength region below 730 nm can be mainly attributed to the rapid formation of macroscopic defects in the active region. A notable improvement in life is obtained for these shorter wavelength lasers by Te-doping of the active layer. On the other hand, enhanced facet oxidation is the main degradation mechanism in lasers operating above 740 nm. Facet coatings using SiO2 films effectively suppress facet oxidation. As a result, room temperature extrapolated lives exceeding 10000 hours are achieved by facet coated lasers operating at wavelengths above 740 nm.