High output power values of 15.7 mW at 20 °C and 2.7 mW at 110 °C were obtained from a blue GaN-based vertical-cavity surface-emitting laser (VCSEL) under continuous-wave operation as a result of introducing a long-cavity (10λ) structure. The threshold current and voltage at 20 °C were 4.5 mA and 5.1 V, respectively. Owing to the reduced thermal resistance provided by the long-cavity structure and the adjusted reflectivity of the front cavity mirror, this VCSEL also exhibited a high slope efficiency of 0.87 W/A, a differential quantum efficiency of 31%, and a wall-plug efficiency of 8.9%.

We have achieved a high output power of 6 mW from a 441 nm GaN-based vertical-cavity surface-emitting laser (VCSEL) under continuous wave (CW) operation, by reducing both the internal loss and the reflectivity of the front cavity mirror. A preliminary analysis of the internal loss revealed an enormously high transverse radiation loss in a conventional GaN-based VCSEL without lateral optical confinement (LOC). Introducing an LOC structure enhanced the slope efficiency by a factor of 4.7, with a further improvement to a factor of 6.7 upon reducing the front mirror reflectivity. The result was a slope efficiency of 0.87 W/A and an external differential quantum efficiency of 32% under pulsed operation. A flip-chip-bonded VCSEL also exhibited a high slope efficiency of 0.64 W/A and an external differential quantum efficiency of 23% for the front-side output under CW operation. The reflectivity of the cavity mirror was adjusted by varying the number of AlInN/GaN distributed Bragg reflector pairs from 46 to 42, corresponding to reflectivity values from 99.8% to 99.5%. These results demonstrate that a combination of internal loss reduction and cavity mirror control is a very effective way of obtaining a high output GaN-based VCSEL.

We have demonstrated successful two-photon excitation fluorescence bioimaging using a high-power pulsed all-semiconductor laser. Toward this purpose, we developed a pulsed light source consisting of a mode-locked laser diode and a two-stage diode laser amplifier. This pulsed light source provided optical pulses of 5 ps duration and having a maximum peak power of over 100 W at a wavelength of 800 nm and a repetition frequency of 500 MHz.

Continuous-wave operation at room-temperature has been demonstrated for InGaN multi-quantum-well (MQW) laser diodes (LDs) grown on low-dislocation-density n-GaN substrates with a backside n-contact. The current, current density and voltage at the lasing threshold were 144 mA, 10.9 kA/cm2 and 10.5 V, respectively, for a 3 µm wide ridge-geometry diode with high-reflection dielectric coated mirrors. Single-transverse-mode emission was observed in the far-field pattern of the LDs and the beam full width at half power in the parallel and perpendicular directions was 6° and 25°, respectively.

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.

The origin of the internal loss in ridge‐type laser diodes (LDs) fabricated using selective re‐growth is investigated through a systematic device characterization and additional optical measurements. We found that the internal loss of this LD is mainly caused by the absorptive layers at the re‐growth boundary and Mg‐doped GaN layer. The internal loss can be significantly reduced through a re‐design of the LD structure to avoid these absorptive regions by shifting the perpendicular optical field to the n‐cladding side. The re‐designed LDs had a very low threshold current of 10 mA and superior gain characteristics. These results indicate, that the InGaN‐quantum‐well (QW) active layer has a large differential gain and fewer non‐radiative defects. The fabrication method of this LD, i.e. epitaxial growth on low‐dislocation‐density GaN substrates combined with a process without dry‐etching, is responsible for the high quality of the QWs.

High-efficiency and high-power operation have been demonstrated for blue GaN-based vertical-cavity surface-emitting lasers (VCSELs) with AlInN/GaN distributed Bragg reflectors. The high-efficiency performance was achieved by introducing a novel SiO2-buried lateral index guide and adjusting the front mirror reflectivity. Lateral optical confinement has been shown to greatly lower the otherwise significant loss of transverse radiation exhibited by typical VCSELs based on GaN. Employing a long (10λ) cavity can also enhance the output power, by lowering the thermal resistance of the VCSEL and increasing the operating current associated with thermal rollover. This modification, in conjunction with optimized front mirror reflectivity and a buried SiO2 lateral index guide, results in a blue VCSEL (in the continuous wave mode with an 8 μm aperture at 20 °C) having a superior differential quantum efficiency value of 31% and an enhanced 15.7 mW output power. This unit also exhibits a relatively high output power of 2.7 mW at temperatures as high as 110 °C. Finally, a 5.5 μm aperture VCSEL was found to generate a narrow divergence (5.1°) single-lobe far field pattern when operating at an output power of approximately 5 mW.

We have successfully demonstrated a high output power of 1.19 W from a two-dimensional 16 × 16 blue GaN-based vertical-cavity surface-emitting laser (VCSEL) array under continuous wave operation at a lasing wavelength of 447 nm. A 256-element VCSEL array exhibited a high-quality far-field beam pattern with a circular shape and narrow divergence angle of around 7°. A very small shift of the lasing wavelength with a change in the dissipated power of 0.05 nm W−1 revealed a very low thermal resistance of 3.4 K W−1.