Yoshiro Takiguchi

High-Power (over 100 mW) Green Laser Diodes on Semipolar

Continuous-wave operation of InGaN green laser diodes (LDs) on semipolar {2021} GaN substrates with output powers of over 100 mW in the spectral region beyond 530 nm is demonstrated. Wall plug efficiencies (WPEs) as high as 7.0–8.9% are realized in the wavelength range of 525–532 nm, which exceed those reported for c-plane LDs. The longest lasing wavelength has reached 536.6 nm under cw operation. These results suggest that the InGaN green LDs on the {2021} plane are better suited as light sources for applications requiring wavelengths over 525 nm.

\{20\bar{2}1\}

True green GaInN laser diodes with a lasing wavelength above 525 nm under continuous wave operation have been successfully fabricated on semipolar {2021} GaN substrates by improving both the diode structure and epitaxial growth conditions. At a case temperature of 55 °C, their lifetime was estimated to be over 5000 h for an optical output power of 50 mW and over 2000 h at 70 mW.

GaN Substrates Operating at Wavelengths beyond 530 nm

We report the growth of BeZnCdSe quantum-well laser diode (LD) structures with a short-period superlattice cladding layer and demonstrate continuous-wave lasing in the pure-green spectral region (545 nm) at room temperature. The threshold current density and voltage of a 5-?m-wide gain-guided laser were found to be 1.7 kA/cm2 and 10.4 V, respectively. This threshold current density is sufficiently low compared with that of InGaN/GaN green LDs.

Long-Lifetime True Green Laser Diodes with Output Power over 50 mW above 525 nm Grown on Semipolar \{20\bar{2}1\} GaN Substrates

We experimentally and theoretically studied degradation phenomena and their mechanism in broad-area semiconductor lasers (BA-LDs) with optical feedback (OFB). We made two types of BA-LDs (one is consisted of AlGaAs emitting at 808nm in TE mode, and another one is consisted of AlGaInP emitting at 642nm in TM mode), and investigated conditions of the degradations caused by an optical feedback. The both types of BA-LDs showed degradations depending on feedback rate and output power. For example, both BA-LDs were damaged with about 20% of intensity feedback rate at half of an output power of a catastrophic optical mirror damage (COMD) levels. To describe a theoretical model for the degradation, the optical power at a front facet of the BA-LDs was calculated and compared with the COMD level of the solitary BA-LDs. In the theoretical model, we included a threshold reduction caused by the OFB. We found that the degradation was explained by a constructive interference between internal and the feedback optical fields. The BA-LDs are damaged when a coherent sum of those fields exceeds the solitary COMD level. We found that the threshold reduction decreases a critical value of the feedback rate corresponding to the damage at low output power regime, and also found that there is an optimum reflectivity of the front facet. The theoretical results show a good agreement with experimental results. According to this model, we can avoid the damages induced by the OFB in the various applications.

545 nm Room-Temperature Continuous-Wave Operation of BeZnCdSe Quantum-Well Green Laser Diodes with Low Threshold Current Density

A 0.3 W operation for a single emitter broad area red laser at 45degC was achieved, for the first time, and a highly reliable 25 emitter array operation of 6.6 W at 25degC. The laser array is composed of 25 broad stripe lasers with a stripe pitch of 400 mum. The operation current, operation voltage, slope efficiency, emission wavelength and the energy conversion efficiency of the laser diode were obtained. Lifetime test was performed under constant current mode.

Effect of the threshold reduction on a catastrophic optical mirror damage in broad-area semiconductor lasers with optical feedback

Room temperature continuous-wave operation at 540 nm was demonstrated with a BeZnCdSe quantum-well laser-diode. Threshold current density of the narrow stripe, 800 µm cavity laser was as low as ∼1.7 kA/cm²