Tetsuya Yagi

Photoluminescence and Lattice Mismatch in InGaAs/InP

A new photoluminescence (PL) band in LPE InGaAs layers nearly lattice-matched to InP has been observed at 0.69 eV at 77 K. This PL band has a strong correlation with the degree of the lattice mismatch between InGaAs and InP, and the intensity shows the minimum at the lattice mismatch of -0.08~-0.07%. The in-depth profile of the PL intensity has been also measured, the result showing that the intensity slightly increases in the interface region of InGaAs and InP, though the PL intensity of the InGaAs edge emission is nearly constant in the InGaAs layer. These results are well explained by considering the difference of the lattice parameters of InGaAs and InP at both the LPE growth and room temperature, and might suggest the existence of some defects introduced during the epitaxial growth by the lattice mismatch between InGaAs and InP.

Highly Reliable 637-639 nm Red High-Power LDs for Displays

Higher power laser diodes (LDs) with a wavelength of 637-639nm are strongly demanded as a light source of display applications because luminosity factor of laser light is relatively high. In order to realize reliable high power operation, we have optimized LD structure, focusing on improvement of power saturation and sudden degradation. As a result, 40μm-wide broad-area (BA) LDs with window-mirror structure have been designed. We fabricated two kinds of single emitter LDs of 1.0mm cavity and 1.5mm cavity. The single LD is installed in conventional φ5.6 mm TO-CAN package. The 1.0mm LD showed very high wall plug efficiency (WPE) of 33% at 25 ºC (23% at 45 ºC) in the power range of around 300mW (30 lm). High output power of 600mW (60 lm) is realized by the 1.5mm LD. Both LDs have operated for over 1,000 hours without any degradation. Estimated mean time to failure (MTTF) is 10,000 hours. In addition, we fabricated an array LD consisting of 20 emitters (BA-LD structure), which shows reliable CW operation of 8W (at junction temperature of 50 ºC) for 10,000 hours.

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.

High Performance Micro Green Laser for Laser TV

Ultra-compact, highly efficient and high-power micro green laser is newly developed for light source of laser TV. Usage of planar-waveguide devices improves efficiency, power, size, and cost of the intra-cavity SHG green laser dramatically.

Optical and thermal properties of Si-O-C films grown by organic catalytic chemical vapor deposition using organic silicon

Optical, thermal and mechanical properties of Si–O–C ternary alloy films grown by organic catalytic chemical vapor deposition (CVD) were studied in comparison with those of Si–O films grown by electron-beam evaporation and AlN grown by electron cyclotron resonance sputtering. Si–O–C with Si: 36 at.%, O: 46 at.%, and C: 18 at.%, grown using TEOS, shows a relatively high refractive index of around 1.9 and a small extinction coefficient of less than 0.01 at wavelengths between 500 nm and 1000 nm. The value of the extinction coefficient is roughly five times smaller than that of SiO films grown by electron-beam evaporation. The thermal conductivity of 0.64 W/mK and the stress of the film are comparable with those of SiO. The results indicate that Si–O–C grown by organic catalytic CVD using TEOS is a promising material for optical applications such as laser diodes and semiconductor optical amplifiers.

Short wavelength limitation in high power AlGaInP laser diodes

In wavelength region of red color, luminous efficacy rapidly increases as wavelength shortens. In that sense, red laser diode (LD) with shorter wavelength is required for display applications. Experimental results for short wavelength limitation in AlGaInP LDs are shown and discussed in this paper. Broad area LDs with 625, 630, and 638 nm are successfully fabricated. Operation current versus output power (P-I) characteristics and its temperature dependence of 625 nm LD are inferior to that of 630 and 638 nm ones. The main reason might be carrier leakage, and the results indicate that additional countermeasures to carrier leakage should be adopted to realize a 625 nm LD with the same temperature characteristics as 630 and 638 nm LDs. Conversion efficiencies from input electrical power to luminous flux output of the LDs are also studied. 625 nm LD has low efficiency, though brightness of 625 nm light is 1.7 times of 638nm one with the same output power. And 630 nm LD shows better conversion efficiency at high luminous flux region than 638 nm one, though the P-I characteristics of 630 nm is worse than that of 638 nm one. The tendency is inverted at low flux region, indicating that the lasing wavelength of red LD for laser display should be chosen carefully.

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.

100-mW cw operation of 650- to 685-nm red lasers with window-mirror-structure

We have investigated dependence of the saturation output power on the wavelength and the cavity length of red laser diodes (LDs) with the wavelength range of 646 - 689 nm. In the 60 degree(s)C CW operation of 650 micrometers -long-cavity LDs, the saturation powers of the 659 nm-LD and the 687 nm-LD were 90 mW and 124 mW, respectively. As a result of extension of the cavity lengths from 650 micrometers to 900 micrometers , the saturation output powers of the 659-nm LD and the 687 nm-LD are increased to 121 mW and 165 mW, respectively. This improvement has led to the first realization of 1000-hour, 100 mW CW operation of the 659 nm-LDs. Also, the 900 micrometers - long 687 nm-LDs have shown the reliable 120 mW CW operation at 40 degree(s)C for 1800-hour, for the first time.

63.5L: Late‐News Paper: Planar‐Waveguide Green Laser for Laser TV

We have newly developed an ultra-compact, highly efficient and high-power green laser for a light source of laser TV. A planar-waveguide configuration improves performance of solid-state green laser dramatically. The laser consists of essential minimum three devices (a pump LD, a planar-waveguide Nd:YVO4 and a planar-waveguide PPMgLN). Output green peak power of 11.4-W with the corresponding electrical efficiency of 21% is demonstrated. In addition, temperature insensitive features are also proved. The size of developed laser module is as small as 5cc. We believe this laser is the most suitable green laser light source for laser TV at present.