Hironobu Narui

Room-temperature continuous-wave operation of GaN-based vertical-cavity surface-emitting lasers fabricated using epitaxial lateral overgrowth

We have successfully demonstrated the room-temperature continuous-wave operation of GaN-based vertical-cavity surface-emitting lasers (VCSELs) with all-dielectric reflectors, which were fabricated using epitaxial lateral overgrowth. The VCSELs exhibited a threshold current of 8 mA and a threshold voltage of 4.5 V at a lasing wavelength of 446 nm. The maximum output power was 0.9 mW for an 8-µm-diameter current aperture, which was made possible because of the high thermal conductivity of the GaN substrate.

A submilliampere-threshold multiquantum-well AlGaAs laser without facet coating using single-step MOCVD

An extremely low threshold current, of 0.88 mA under continuous wave (CW) operation was obtained for a three-quantum-well AlGaAs-GaAs laser without facet coating at room temperature. This laser was fabricated using only single-step metalorganic chemical vapor deposition (MOCVD) on a nonplanar GaAs substrate. The energy conversion efficiency from input electric power to light output power was 42% at 1 mW/facet, which is the highest value for all types of lasers. The laser beam shape was nearly round with an aspect ratio of 0.86. >

1.30-/spl mu/m GaInNAs laser diode with lifetime over 1000 hours grown by MOCVD

We performed epitaxial growth of GaInNAs laser diodes under various growth rates by metal-organic chemical vapor deposition. A strong correlation was found between the growth rate and the photoluminescence (PL) characteristics. At the optimum growth rate, PL peak intensity and full-width at half-maximum of the PL peak were at a maximum and minimum, respectively. As a result of processing on a GaInNAs narrow-ridge waveguide laser device, a strong correlation was found between the growth rate and the device characteristics. At the optimum growth rate, which was the same optimum growth rate for the PL characteristics, the threshold current and characteristic temperature were also at their optimum values. It is clear that the growth rate is an important parameter for crystal quality and device characteristics. As a result of the optimization of the growth rate and the other growth conditions, a high characteristic temperature of 180 K and a long device lifetime over 1000 h were obtained.

Monolithic-integrated two-wavelength laser diodes for digital-versatile-disk/compact-disk playback

We have developed a monolithic two-wavelength laser diode, which emits 650 and 780 nm wavelengths. This device, which has a separated-confinement-heterostructure multi-quantum-well active region and a gain-guiding tapered-stripe structure, is fabricated using only two steps of metal organic chemical vapor deposition. The operating currents at 5 mW are 57.0 and 61.5 mA for the 650 and 780 nm elements, respectively. The relative intensity noise of the 650 and 780 nm elements was below −130 dB/Hz up to 70 °C without high-frequency superposition circuits.

140-fs duration and 60-W peak power blue-violet optical pulses generated by a dispersion-compensated GaInN mode-locked semiconductor laser diode using a nonlinear pulse compressor

Blue-violet optical pulses of 140-fs duration and 60-W peak power were obtained from a dispersion-compensated GaInN mode-locked semiconductor laser diode using a nonlinear pulse compression technique. Wavelength-dependent group velocity dispersion expressed by third-order phase dispersion was applied to the optical pulses using a pulse compressor with a spatial light modulator. The obtained optical pulses had the shortest duration ever obtained for a mode-locked semiconductor laser diode using edge-emitting type devices.

Generation of a 2.2 nJ picosecond optical pulse with blue-violet wavelength using a GaInN master oscillator power amplifier

We report the generation of a picosecond optical pulse with 2.2 nJ pulse energy at blue-violet wavelengths using a GaN-based mode-locked laser diode (MLLD) and a semiconductor optical amplifier (SOA). The picosecond optical pulse generated by MLLD at a frequency of 812 MHz was amplified effectively by SOA. We optimized SOA with a widely flared waveguide structure to generate a high optical pulse energy.

Lateral optical confinement of GaN-based VCSEL using an atomically smooth monolithic curved mirror

We demonstrate the lateral optical confinement of GaN-based vertical-cavity surface-emitting lasers (GaN-VCSELs) with a cavity containing a curved mirror that is formed monolithically on a GaN wafer. The output wavelength of the devices is 441–455 nm. The threshold current is 40 mA (Jth = 141 kA/cm2) under pulsed current injection (Wp = 100 ns; duty = 0.2%) at room temperature. We confirm the lateral optical confinement by recording near-field images and investigating the dependence of threshold current on aperture size. The beam profile can be fitted with a Gaussian having a theoretical standard deviation of σ = 0.723 µm, which is significantly smaller than previously reported values for GaN-VCSELs with plane mirrors. Lateral optical confinement with this structure theoretically allows aperture miniaturization to the diffraction limit, resulting in threshold currents far lower than sub-milliamperes. The proposed structure enabled GaN-based VCSELs to be constructed with cavities as long as 28.3 µm, which greatly simplifies the fabrication process owing to longitudinal mode spacings of less than a few nanometers and should help the implementation of these devices in practice.

9-kW peak power and 150-fs duration blue-violet optical pulses generated by GaInN master oscillator power amplifier

Blue-violet optical pulses of 9-kW peak power and 150-fs duration were obtained from a GaInN master oscillator power amplifier system using a nonlinear dispersion compensator. Seed pulses from a dispersion-compensated GaInN mode-locked semiconductor laser diode were stretched to 3-ps duration using a nonlinear dispersion compensator with a spatial light modulator that added second-order phase dispersion to an optimized nonlinear phase dispersion compensating the higher-order dispersion of the optical pulses. The stretched phase-optimized pulses were efficiently amplified to 3.0 nJ by a GaInN semiconductor optical amplifier. The amplified pulses were subsequently compressed using a linear pulse compressor, yielding 1.4-nJ femtosecond pulses. The obtained results show the highest peak-power ever reported for an electrically-pumped semiconductor gain medium.

Continuous wave operation of high power GaN-based blue vertical-cavity surface-emitting lasers using epitaxial lateral overgrowth

We have succeeded in achieving continuous-wave operation of gallium nitride (GaN) based vertical-cavity surfaceemitting lasers (VCSELs), which was fabricated by epitaxial lateral overgrowth (ELO) using dielectric distributed Bragg reflectors(DBRs) as masks for selective growth. The device exhibited CW operation at a wavelength of 453.9nm. The maximum output power was 1.1 mW, which is the highest value reported in previously published articles. The ELO process used for this study represents a breakthrough for challenges which were indicated by other former reports for GaN-based VCSELs and is suitable for mass production.

Nonlinear compression of optical pulses at 400 nm from a GaInN mode-locked semiconductor laser diode yielding 140-fs duration and 60-W peak-power optical pulses

Ultrashort optical pulses of 140-fs duration and 60-W peak power were obtained at 400 nm from a dispersion-compensated GaInN mode-locked semiconductor laser diode using a nonlinear pulse compressor consisted of a spatial light modulator.