Kimitaka Shibata

Selective-area MOCVD growth for 1.3 μm laser diodes with a monolithically integrated waveguide lens

A tapered thickness profile and a high thickness enhancement ratio of 3.5 in the waveguide which are necessary for a narrow beam have been realized by selective-area metalorganic chemical vapor deposition (MOCVD) growth using a tapered shape twin mask. A multiple quantum well (MQW) active layer with high strain of 0.9% which is effective for a low threshold current has also been successfully grown by the control of the compositional modulation of InGaAsP in the selective-area growth. Using these techniques, a narrow beam and a low threshold current have been realized for a 1.3 μm laser diode monolithically integrated with a tapered thickness waveguide lens.

Master-oscillator power-amplifier scheme for efficient green-light generation in a planar MgO:PPLN waveguide

We developed a new master-oscillator power-amplifier scheme consisting of a tapered semiconductor amplifier and a fiber-grating-stabilized laser diode for efficient green-light generation in a planar MgO:PPLN waveguide, and demonstrated cw green-light generation of 346 mW.

640-nm laser diode for small laser display

Short wavelength and highly efficient AlGaInP quantum-well laser diode is promising as a red light source for small laser display application. Two kinds of the laser diodes are presented in this paper. A narrow ridge laser diode was designed for single lateral mode. In addition, a broad area laser diode was optimized for the higher power operation. To suppress a carrier leakage from an active layer, AlInP cladding layers were adopted to both of the lasers. Evaluation tests of the fabricated lasers were performed under CW operation. The wavelength of the narrow ridge laser was 636.0 nm under the condition of 25°C and 100 mW. Single lateral mode oscillation and the high wall plug efficiency of 29% were obtained. The beam divergences were 16° and 8° in fast and slow axes, respectively. The broad area laser showed lasing wavelength of 636.9 nm at 25°C for 200 mW output. The wall plug efficiency was 30% under this condition. Both of the lasers showed both high luminance and high wall plug efficiency. These lasers are suitable for small laser display applications.

Metalorganic vapor-phase epitaxial regrowth of InP on reactive ion-etched mesa structures for p-substrate buried heterostructure laser application

Growth behavior of sulfur-doped n-InP around reactive ion-etched (RIE) mesas has been investigated for realization of p-substrate buried heterostructure laser utilizing metalorganic vapor phase epitaxy. It is found that the growth of n-InP layer on the sidewall of the mesa ((1 1 0) plane) is significantly suppressed, as the flow rate of hydrogen sulfide (H2S) which is used for n-type doping, increased. This phenomenon of growth suppression was also observed for growth of highly S-doped n-InP on narrow (0 0 1) facets. Taking account of both, these phenomena can be explained by migration enhancement of indium atoms on sulfur-terminated surfaces caused by excess H2S supply. Consequently, the shape of the regrown embedding layer was found to be exactly controlled by the H2S flow rate. Using this technique, a p-substrate 1.3 μm buried heterostructure laser with pnp current-blocking structure has been successfully fabricated around the RIE mesa and excellent lasing characteristics with high reliability has been realized for the first time.

12W CW operation of 640nm-band laser diode array

A high-power and short-wavelength GaInP/AlGaInP quantum-well laser diode array was designed and fabricated. Because a conduction band offset of this material system is small, a carrier leakage from an active layer is an important limiting factor of the maximum light output. In this work, long cavity length of 1.5 mm, high front facet reflectivity of 18% and AlInP cladding layers were adopted to reduce the leakage. An evaluation test of the fabricated array was performed under CW operation. At 15°C, high light output of 12W was obtained with injection current of 16A. The lasing wavelength was 643.3 nm. Moreover, high wall-plug efficiency of 34% was achieved. These excellent characteristics are considered to be due to the effective suppression of the carrier leakage.

Uncooled DFB lasers for CATV

Strained-layer MQW-DFB lasers at a wavelength of 1.3 micrometers operating from -40 degree(s)C to 85 degree(s)C without any coolers are demonstrated. On the basis of the leakage current analysis, a laser structure including the active layer and the current blocking layer is chosen to achieve low distortion over wide-temperature-range. Extremely low threshold current of 17 mA at 85 degree(s)C and operation current of 37 mA at 5 mW and 85 degree(s)C are obtained. The lasers realize low distortion of less than -50 dBc at 65 degree(s)C in 78-channel CSO measurements. Furthermore, a fabricated laser module with a coaxial package also achieved low CSO values of -55 dBc under 16-channel loading in the temperature range from -40 degree(s)C to 85 degree(s)C. This uncooled DFB laser module is very useful for return path application in CATV systems.

Fine-pitch control in EB lithography for semiconductor laser grating formation

Grating-pitch accuracy is studied from minimum pitch variation point of view. The pitches of the gratings delineated at the focus range from -50micrometers to +50micrometers and stitching errors between subfields are evaluated using an EB machine which features a long distance between the deflector and the wafer stage. The grating pitch variation is realized by using a deflection amplitude control. It is confirmed that errors of the pitches due to defocus are less than 0.05 nm, and the deviations from nominal setting of the pitch are also less than 0.1 nm when the pitches are varied from -6 percent to +6 percent at 0.1 percent step.