Takaaki Hirata

Fabrication and characteristics of GaAs-AlGaAs tunable laser diodes with DBR and phase-control sections integrated by compositional disordering of a quantum well

GaAs-AlGaAs rib-waveguide graded-index separate-confinement heterostructure (GRINSCH) single-quantum-well (SQW) tunable distributed Bragg reflector (DBR) laser diodes were fabricated by EB lithography, ion implantation, and two-step metalorganic vapor phase epitaxy (MOVPE) growth. Active and passive waveguides were monolithically integrated by the compositional disordering of quantum-well heterostructures using silicon ion implantation. First-order gratings and rib waveguides were adopted with EB lithography to improve lasing characteristics, and they have wide application to photonic integrated circuits (PICs). Waveguide losses of partially disordered GRINSCH-SQW passive waveguides were as low as 4.4 cm/sup -1/ at the lasing wavelength. A narrow linewidth as low as 560 kHz and a frequency tuning of more than 2.9 THz were obtained. The results show that this fabrication process is useful for PICs. >

Photonic Integrated Circuit Combining Two GaAs Distributed Bragg Reflector Laser Diodes for Generation of the Beat Signal

We have fabricated a photonic integrated circuit (PIC) that had two GaAs distributed Bragg reflector (DBR) laser diodes (LD) and a Y-branch coupler integrated by means of the compositional disordering of a quantum well. Using this PIC as an optical heterodyne sweeper, frequency characteristics of a GaAs Schottky photodiode were measured.

GaAs/AlGaAs first-order gratings fabricated with electron beam lithography and very-narrow-linewidth long-cavity DBR laser diodes

A technique for fabricating GaAs/AlGaAs first-order gratings using electron beam (EB) lithography and its application to long-cavity distributed-Bragg-reflector (DBR) laser diodes are presented. The field stitching error, which limits the application of EB lithography to optical devices, was reduced to 5 nm by deflection amplitude calibration using marks on the samples. A technique for controlling the coupling coefficient using partially corrugated gratings is also proposed. These techniques were applied to fabrication of GaAs/AlGaAs first-order gratings of graded-index, separate-confinement-heterostructure, single-quantum-well (GRIN-SCH-SQW) distributed-Bragg-reflector (DBR) laser diodes. The resulting stitching error did not influence the single-mode lasing characteristics, and a very narrow linewidth of 237 kHz was achieved. The results show that EB lithography using the above techniques is useful in the fabrication of various optical devices with gratings. >

A Study of an Absolute Determination of the Magnetic Flux Quantum Using a Superconducting Levitation System

A study on a new method of determining the magnetic flux quantum 0 possibly at subppm level using a superconducting levitation system is described with some data from a preliminary experiment. The method employs a superconducting levitation system to substitute the gravitational potential energy of the floating body for the magnetic energy. The estimation of the expected accuracy and methods of improving the experiment are discussed.

Monolithic integration of waveguide gratings and quantum-well distributed-feedback laser for implementation of subminiature optical-disc pickup head

We propose a subminiature optical-disc pickup head implementation by monolithic integration of wave- guide grating components, a graded-index separate-confinement heterostructure single-quantum-well distributed-feedback laser and photodiodes. Fabrication of a prototype device and the results of a preliminary experiment are presented.

Fabrication of First-Order Gratings for GaAs/AlGaAs LD's by EB Lithography

High-precision first-order gratings, 110 nm pitch, for GaAs/AlGaAs LDs were successfully fabricated using EB lithography. The field stitching error of EB lithography caused by height difference between reference marks for calibration and the samples, was reduced to 5 nm by controlling the EB deflection voltage calibrated by the detection of the position of the marks on the samples. We also investigated the effect of field stitching error on lasing characteristics using measurement and calculation. We found that a 20 nm stitching error is sufficiently small for single-mode LD operation.

A Novel GRIN-SCH-SQW Laser Diode Monolithically Integrated with Low-Loss Passive Waveguides

We propose a novel fabrication process for monolithic multielement laser diodes and demonstrate the performance of a monolithically integrated passive waveguide laser as compared with a conventional laser fabricated under the same procedures. This process, which is based on silicon ion implantation and two-step MOVPE growth, is suitable for integrating optical elements like gratings and rib waveguides. We also demonstrate that the COD level of the window structure laser fabricated by this process is more than 1.3 W in pulsed operation.

Basic Properties, Linewidth Enhancement Factor and Spectral Linewidth of SQW Laser Diodes Emitting in the 780 nm Region

GRIN-SCH-SQW laser diodes with quite a narrow well width of 3 nm were successfully fabricated by MOVPE. Oscillation wavelength and dispersion of linewidth enhancement factor α were found to be greatly dependent on cavity length i.e. threshold level. α measured at oscillation wavelength was 2.1 in the 300 µm-long laser, and 3.7 in the 1000 µm-long laser. This dependence was roughly explained by taking account of bandgap shrinkage and broadening of the gain spectrum. The narrowest spectral linewidth obtained was 1.5 MHz at an output power of 8.7 mW with a linewidth-power product of 5.7 MHzmW in the 1000 µm-long laser.

Improvement of the Superconducting Magnetic Levitation System for an Absolute Determination of the Magnetic Flux Quantum

The superconducting magnetic levitation system for the absolute determination of the magnetic flux quantum 0 is improved. Resolution of the vertical position of the floating body with laser interferometer becomes 1/100 µm order, which corresponds to 1 ppm of the gravitational potential energy of the floating body. An outline of this system and some temporary results are described.

GaAs/AlGaAs GRIN-SCH-SQW DBR Laser Diodes with Passive Waveguides Integrated by Compositional Disordering of the Quantum Well Using Ion Implantation

GaAs/AlGaAs GRIN-SCH-SQW DBR laser diodes are fabricated by ion implantation and two-step MOVPE growth. Passive waveguides are monolithically integrated by compositional disordering of quantum well heterostructures using silicon ion implantation. Waveguide losses of partially disordered GRIN-SCH-SQW passive waveguides are measured, and propagation losses as low as 4.4 cm-1 are observed at the lasing wavelength. Stable single mode operation is obtained, and the narrowest linewidth achieved is 840 kHz. The results show that this fabrication process is useful for photonic integrated circuits.