Nobuyuki Miyauchi

Room‐temperature cw operation in the visible spectral range of 680–700 nm by AlGaAs double heterojunction lasers

Room‐temperature cw operation at the wavelength below 700 nm has been achieved by AlGaAs double heterojunction (DH) lasers with a novel structure, in which a thick buffer layer is grown and the substrate is removed. Continuous‐wave threshold currents were 60–120 mA in the visible spectral range of 680–700 nm. Also the fundamental transverse and single longitudinal mode were obtained under cw operation. The shortest cw wavelength is 683 nm at the present time.

Highly reliable and mode‐stabilized operation in v‐channeled substrate inner stripe lasers on p‐GaAs substrate emitting in the visible wavelength region

Highly reliable and mode‐stabilized operation is realized in v‐channeled substrate inner stripe (VSIS) lasers emitting in the visible wavelength region. The VSIS lasers with emission wavelengths of 725–790 nm have low threshold currents of 40±5 mA and reproducibly provide fundamental transverse and single longitudinal mode operation up to 20 mW/facet cw. These performances result from the transverse‐mode stabilization by a built‐in optical waveguide which is self‐aligned with an internal current confining channel. Accelerated lifetests and the statistical characterization of reliability were performed on VSIS lasers emitting at 780 nm. The median lifetimes are estimated to be 1.1×106 h for 5 mW/facet, 4.8×104 h for 10 mW/facet, and 1.3×104 h for 15 mW/facet operations at 25 °C. In addition, almost no degradation in modal characteristics has been observed in the devices operated at 5 mW/facet at 50 °C for 4000 h, up to the present. Photoluminescence study was performed in order to clarify the effects of th...

High optical power cw operation in visible spectral range by window V‐channeled substrate inner stripe lasers

High optical power cw operation has been achieved at the wavelength range of 780 nm by newly developed window V‐channeled substrate inner stripe lasers. This laser consists of a waveguiding window region with a plane active layer and a stimulated region with a crescent active layer. These two regions are coupled to each other. cw optical power over 70 mW and low cw threshold current of 30 mA were obtained. Moreover, the fundamental transverse mode was observed up to 60 mW, and it was found that the beam waist along the junction existed at the mirror.

High output power characteristics in broad‐channeled substrate inner stripe lasers

A high output power AlGaAs laser is newly developed in the spectral range of 770–780 nm. The laser has a double‐depth channel on the p‐GaAs substrate which forms a built‐in optical waveguide having a double effective refractive index/loss step. This novel waveguide is effective to make the fundamental lateral mode extremely stable; that is, up to 60 mW when the reflectivity of the front facet (Rf) is 0.12, and 100 mW when Rf is 0.04. cw threshold currents are 35–45 mA and external differential efficiencies are 0.6–0.8 mW/mA. Also, an astigmatic distance below 3 μm is obtained when Rf is more than 0.10.

Influences of thin active layer in (GaAl)As double-heterostructure lasers grown by liquid-phase epitaxy

Studies have been carried out on the influences of thinning the active layer in (GaAl)As double‐heterostructure (DH) lasers grown by liquid‐phase epitaxy (LPE). The measured peak gain varies sublinearly with current in the laser with a thin active layer of d∼0.05 μm while it varies linearly for d≲0.07 μm. This sublinear gain‐current relationship results from the rather wide graded‐band‐gap interface region formed by LPE and increases the lasing threshold. The photoluminescence (PL) peak of a DH sample with a thin active layer shifts to higher energies with the excitation due to the wide interface width, which agrees with the calculated results. High‐energy bumps observed in the PL spectra are more noticeable in the sample with the thinner active layer, which demonstrates that carriers recombine at the high‐energy portion of the interface region. The excitation dependence of PL intensity has shown that the nonradiative recombination rate is higher for the thinner active layer. Discussion is given concernin...

Improvement of high-power characteristics of 780-nm AlGaAs laser diode by (NH4)2S facet treatment

Coherent cw operation has been obtained with a 10x4 array of Grating Surface Emitting (GSE) lasers consisting of 40 lasers and 50 emitting sections. The array is a GaAs quantum well device, grown on an A1GaAs substrate, operating at 861 nm to which the substrate is transparent. It is mounted p-down to metallized traces on a BeO slab to provide isolated electrical contacts and thermal contact to a simple chilled-water cooler. A single spectral line 0.5 A wide indicates coupling of the 40 laser sections. More detailed measurements on a section of an array containing ten laterally coupled lasers, 20 outputs, show that it is operating at a junction temperature of 30°C, has a line width of 0.1 5A, and a measured coherence of >75%. The expected wavelength stabilization with temperature due to the DBR grating is found, with a value of =0.6A/°C. An array of 4 longitudinally coupled lasers produced a line width of 130MHz and evidence of high coherence.

Improved lifetimes of (GaAl)As visible (740 nm) lasers by reducing bonding stress

It is shown that the active layer stress caused by the bonding process can be reduced by setting the thicknesses of the cap layer and the substrate at the appropriate values. The life test of the (GaAl)As V‐channeled substrate inner stripe lasers emitting at 740 nm, 50 °C demonstrated that the lifetime is considerably improved by the introduction of the thick cap layer (∼40 μm) and the thinned substrate (∼80 μm).

High-Power CW Operation in V-Channeled Substrate Inner-Stripe Lasers with “Torch”-Shaped Waveguide

High-power AlGaAs lasers with a waveguide pattern like a torch have been grown by a two-step liquid-phase epitaxy process. The waveguide pattern consists of a 6 µm-wide region about 220 µm long and a 10 µ-wide region about 20 µm long connected by a tapered region about 10 µm long. A stable fundamental transverse mode has been obtained of up to more than 200 mW output power in a 4%–95% coated device in the wavelength range of 830 nm. The lasers have extremely high reliability, and stable continuous operation for over 4000 hours has been confirmed at 50°C, 50 mW with no obvious degradation.

Stable single-longitudinal-mode operation in visible (AlGa)As semiconductor lasers coupled with a short external cavity

High stability of single longitudinal mode has been achieved in visible wavelength regions using V‐channeled substrate inner‐stripe lasers coupled with a short external cavity. The temperature dependence of the coupled‐gain peak coincided entirely with that of one longitudinal mode for lasers with external‐cavity lengths of 50–60 μm. As a result, a wide longitudinal‐mode locking range of 31 °C was obtained over 8 mW. This result is in good agreement with the theoretical calculation, in which the effect of the thermal expansion of the external‐cavity length is taken into account.

Stable Single-Longitudinal-Mode Operation over Wide Temperature Range on Semiconductor Lasers with a Short External Cavity

V-channeled Substrate Inner Stripe lasers coupled with a Short External Cavity maintain one single longitudinal mode over wide temperature ranges without mode hopping. Temperature stability is obtained when the thermal shift of the modulated spectrum envelope coincides with that of the longitudinal modes. We enhanced the stability by using a Si submount in place of a Cu submount for the laser. The temperature dependence of the gain maximum is compensated by the small thermal expansion of Si. The laser shows a longitudinal mode locking range of more than 46°C. The data are consistent with theoretical calculations.