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The recent progress of GaN-based vertical-cavity surface-emitting lasers (VCSELs) with incorporated curved mirrors at one end of their cavities is reviewed. GaN-VCSELs consisting of 3 InGaN/GaN quantum wells, current apertures formed by boron ion implantation, and curved mirrors at one end of the cavities were fabricated. The near-field and far-field patterns exhibited Gaussian-like profiles, and their divergences agreed well with the theoretical values calculated from the radius of curvature of the curved mirror and the cavity length. The near-field beam waist for a GaNVCSEL with a 6-μm current aperture was as small as 1.4 μm (half width at 1/e2), which indicated that the light was laterally confined by the incorporated curved mirror and that the current aperture could be made smaller than 6 μm. For a GaN-VCSEL with a current aperture of 4μm, a threshold current of as low as 0.56 mA (Jth = 4.5 kA/cm2) was obtained at room temperature under CW operation at a wavelength of 451.8 nm. To the best of our knowledge, this is the lowest threshold current reported among all-dielectric DBR type GaN-VCSELs and is comparable with the lowest value reported for GaN-VCSELs that have a two-dimensional quantum well structure. The authors believe this result to be a milestone for the realization of GaN-VCSELs with extremely low power consumption.

We investigated the spectral and temporal characteristics of blue-violetfemtosecond optical pulses generated by a passively mode-locked GaInN laser diode ina dispersion-compensated external cavity. The output optical pulses at 400 nm wereanalyzed in detail by intensity auto- and cross-correlation measurements using secondharmonic generation on the surface of a β-BaB2O4 crystal. The obtained results clarifiedwavelength-dependent chirp characteristics of the optical pulses. The analysis suggestedthat a large frequency shift due to saturation in the saturable absorber and gain sectionsplayed an important role in the generation of femtosecond optical pulses.

We report single transverse mode operation of a blue GaN-based vertical-cavity surface-emitting laser (GaN-VCSEL) with a monolithically incorporated curved mirror. For a device with a 4 μm current aperture diameter and a curved mirror with a radius of curvature (ROC) of 51 μm, single transverse mode operation was confirmed up to an output power of 3.2 mW under continuous wave operation at 20 °C. For a device with a smaller ROC of 31 μm, multi transverse mode operation was confirmed, indicating that the transverse mode can be controlled by the cavity design of such GaN-VCSELs.

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.

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.

We present optical pulse generation with 100 W peak power, 3 ps temporal duration, and 1 GHz repetition from a GaInN master oscillator power amplifier (MOPA). An external cavity GaInN laser diode is passively mode-locked to generate 4 W peak power optical pulses as a master oscillator, and a semiconductor optical amplifier (SOA) effectively amplified these to a high peak power of more than 100 W. Two major factors that contributed to effective amplification of optical pulses were the generation of clean optical pulses without sub-pulse components by the GaInN mode-locked laser diode and suppression of amplified spontaneous emission in the SOA. This novel high-peak-power pulse source is used to induce multi-photon absorption to create sub-micrometer recording marks in a bulk plastic recording media. The realization of an all-semiconductor pulse source is a significant breakthrough towards a practical 3D optical data storage system.

We demonstrate the generation of 20W peak power, 3ps optical pulses using a combination of a GaInN-based, mode-locked laser diode and an optical amplifier. A strong nonlinear phase shift over 4π has also been observed.

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.

Femtosecond optical pulses with a duration of 200 fs were generated using a GaInN bisectional laser diode passively mode-locked in a dispersion-compensated external cavity with spectral filtering performed outside the cavity. The fact that the femtosecond pulses were obtained with a negative intracavity group-velocity dispersion and a saturable absorber recovery time of about 15 ps indicates that the mechanism involved was soliton mode-locking. The spectro-temporal investigation of the output pulses directly emitted after the mode-locked laser diode revealed that the spectral broadening was due to self-phase modulation in the gain section.

We have demonstrated passively mode-locked operation of a GaInN bisectional laser diode in a dispersion-compensated external cavity. With negative group velocity dispersion in the external cavity, we obtained femtosecond optical pulses after spectral filtering with a bandpass filter. The pulse duration was as short as 200 fs with a time-bandwidth product of 0.41. This is the shortest pulse ever reported for a mode-locked GaInN laser diode.

We have generated picosecond optical pulses with a peak power greater than 300 W at 1 GHz repetition at a blue-violet wavelength using a GaInN-based master oscillator power amplifier. The optical pulses were generated by a mode-locked laser diode incorporating the flared waveguide structure for the increased active region volume to obtain higher output power. The pulses were effectively amplified by the semiconductor optical amplifier with reduced optical confinement factor to high peak power.

We directly generated 1.6-ps optical pulses with a peak power of 20 W at a repetition of 1 GHz using a blue-violet GaInN mode-locked laser diode incorporating a flared waveguide operating in single transverse mode. The flared waveguide enabled optical pulses to be generated with peak powers of over six times higher than those produced using a straight waveguide while preserving the pulse duration.

We have generated single-transverse-mode optical pulses with 100 W peak power and 3 ps duration at 1 GHz repetition from a blue-violet GaInN mode-locked laser diode (MLLD) and a semiconductor optical amplifier (SOA) without the use of any pulse compression. The generation of clean optical pulses without subpulse components from the MLLD and the reduction in amplified spontaneous emission in the SOA by incorporating a flare waveguide structure resulted in effective amplification of optical pulses to produce over 100 W peak power.