Keizo Takemasa

1.3-μm AlGaInAs-AlGaInAs strained multiple-quantum-well lasers with a p-AlInAs electron stopper layer

1.3-/spl mu/m AlGaInAs-AlGaInAs strained multiple-quantum-well (MQW) lasers with a p-AlInAs electron stopper layer have been fabricated. The electron stopper layer was inserted between the MQW and p-side separate confinement heterostructure (SCH) layers to suppress the electron overflow from the MQW to p-SCH. The characteristic temperatures of the threshold currents and slope efficiencies were improved in the lasers with the stopper layers, especially at higher temperatures. As a result, a maximum operating temperature of 155/spl deg/C was achieved, which was 20/spl deg/C higher than that without the stopper layer.

Confirmation of AlGaAs Crystal Domain Inversion Using Asymmetric Wet Etching and Optical Second-Harmonic Generation Methods

The occurrence of crystal domain inversion on a (001) GaAs substrate was confirmed by a direct observation method based on asymmetric wet etching of AlGaAs and an optical method based on second-harmonic generation. Direct evidence of crystalline inversion was exhibited in samples with a periodic structure prepared by wafer bonding, selective removal of the bonded GaAs, and metal-organic vapor phase epitaxial regrowth on the patterned template.

AlGaAs Semiconductor Quasiphase-Matched Wavelength Converters

Wavelength conversion based on sum frequency generation (SFG) using a semiconductor quasiphase-matched (QPM) waveguide with a periodically crystal domain inverted structure has been studied both theoretically and experimentally. Mathematical expressions with clear physical insight into QPM SFG are derived, taking into account waveguide propagation loss. SFG from AlGaAs QPM waveguides fabricated by a direct wafer bonding technique have been characterized. Nearly polarization insensitive wavelength conversion is demonstrated, and a normalized conversion efficiency of 810%/(W cm2) is obtained for a 0.5-mm-long waveguide with a propagation loss of over -100 dB/cm. The dependence of conversion efficiency and polarization sensitivity on device length is also discussed, and it is shown that the experimental results agree well with the theoretical simulations.

High Temperature Operation of AlGaInAs Ridge Waveguide Lasers with a p-AlInAs Electron Stopper Layer

1.3 µm AlGaInAs/InP ridge waveguide lasers with a p-AlInAs electron stopper layer (ESL) were fabricated and the effect of the ESL was investigated. By inserting an ESL between active and separate confinement heterostructure (SCH) layers, the characteristic temperature of threshold current and slope efficiency were improved, especially in the higher operating temperature range, and the maximum operating temperature under CW operation was improved by 20°C. An excellent CW characteristic temperature of 111 K was obtained with operating temperatures between 20 and 80°C and the record high operating temperature of 210°C was achieved with the 700-µm-long laser under pulse operation. Power reductions at a constant current with increasing temperature were determined at 80°C as -1.27 dB and -1.67 dB under pulse and CW operations, respectively.

Effects of well number on temperature characteristics in 1.3-/spl mu/m AlGaInAs/InP quantum well lasers

Effects of well number on temperature characteristics have been investigated in 1.3-/spl mu/m AlGaInAs-InP multiple-quantum-well (MQW) lasers. A record high pulsed operating temperature of 220/spl deg/C has been achieved in lasers with 10 QWs and a small power reduction of -1.68 dB between 20 and 80/spl deg/C has been obtained in lasers with 4 QWs.

Wavelength Router Using Bridged Planar Spectrographs

We propose a device which has the same wavelength routing function as a conventional arrayed-waveguide-grating and consists of two planar waveguide spectrographs connected by waveguide array of equal-length. We fabricate the device using compound semiconductor for future integration of many functions. The fabricated device shows a filter width of 1.7 nm and a sidelobe level of -8 dB which is limited by the power distribution in the waveguide array. A device using the whispering gallery mode is also demonstrated. The whispering gallery mode is expected to reduce the phase error. The sidelobe level is reduced by over 5 dB as compared to a device using the conventional channel waveguide. Finally, a design for compensating the effect of the radius of curvature on the propagation constant is proposed.

Semiconductor Quasiphase Matched Wavelength Converters

the fundamental wavelength. Figure 2 shows an example of an etched Y-face cross-sectional micrograph showing the domain structure of the LN thin-film grown on the periodically grooved Mg: LN substrate. Spontaneous polarization of the LN thin-film is opposite to that of the substrate, and a periodically inverted domain structure is realized by the overlapping of the inverted and noninverted regions. Figure 3 shows the measured second-harmonic tuning curve as a function of the fundamental wavelength for the planar waveguide device with a firstorder modulation period of 3.6 pm. Generation of a second-harmonic blue light of about 441 nm wavelength was achieved. Though the output power of the second-harmonic wave is insufficient due not only to the small overlap between the inverted and noninverted regions but also to the optical absorption of the film in the blue wavelength; further improvement is in progress for practical applications. In summary, a new fabrication process of a QPM-SHG device by formation of a periodic groove structure on a Mg:LN substrate using proton-exchange and selective etching techniques followed by groove-filling domain-inverted LPE of a LN thin-film optical waveguide was proposed. Second-harmonic blue light generation of about 441 nm wavelength was demonstrated by first-order quasi-phasematching. *Matsushifa Electric Industrial Co., Ltd., 3-1-1 Yagumo-Nakamachi, Moviguchi, Osaka 570, JAPAN *institute for Materials Research, Tohoku University, Katahira 2-1-1, Aoba-ku, Sendai

High-temperature operation of 1.3-/spl mu/m AlGaInAs/InP strained multiple quantum well lasers with an AlInAs electron stopper layer

Summary form only given. Recently, AlGaInAs-InP lasers have been demonstrated to show superior temperature characteristics as compared to conventional GaInAsP/InP lasers, which is due to a larger conduction band offset of the AlGaInAs-InP systems and the resultant decrease in the electron overflow out of the multiple quantum well (MQW) active layers. In this study, we investigated the effect of the electron stopper layer (ESL) and observed a considerable improvement in the characteristic temperatures of the threshold current and slope efficiency, especially at higher temperatures, resulting in a higher operation temperature in the lasers with the ESL.

A novel gain measurement technique for design of long-wavelength vertical cavity lasers

We have developed a novel gain measurement technique based on a surface-normal optical pump-probe arrangement. The sample is optically pumped at 1.48 µ m, and single-pass optical gain is obtained from the transmitted power of a 1.55-µ m probe beam. Using this technique, gain can be measured accurately up to high excitation levels. In addition, the technique allows gain to be measured from as-grown wafers and can be used to optimize the active-layer parameters more conveniently by circumventing complicated device fabrication. The measured gain can also predict the minimum mirror reflectivity for laser oscillation in vertical cavity lasers.

Photoreflectance Study of Interface Roughness in Ge/SiGe Strained-Layer Heterostructures.

Ge/SiGe strained-layer heterostructures have been investigated using photoreflectance (PR) spectroscopy. On the basis of the comparison between the experimental and calculated quantum well-related transition energies formed at the Γ point, band discontinuities at the Ge/SiGe heterojunction are determined and found to vary linearly with Ge content in the SiGe layer. Conduction band offset ratio Q c (= ΔE c/(ΔE c+ΔE v HH )) at the Γ point is evaluated to be 0.68 ±0.08 . From the intrinsic linewidth of the quantum well-related transitions, roughness at the Ge/SiGe heterointerface has been characterized for the first time and is estimated to be ±1 monolayer (ML). In addition, the splittings in the PR spectra are observed in some samples at low temperatures. These splittings are due to the difference in the well width and correspond to the height (or depth) of about 10 ML.