Uniform and high-power characteristics of 780-nm AlGaAs TQW laserdiodes fabricated by large-scale MOCVD

An approach to large-scale fabrication of high-power laser diodes lasing at a wavelength of around 780 nm is described. Heterostructures with AlGaAs triple quantum well (TQW) active layers are grown by using a metalorganic chemical vapor deposition (MOCVD) system which has a capacity of more than 12 2-in φ wafers. Taking the limitations of uniformity and the controllability of the MOCVD growth into account, we have designed the TQW-SCH (separate confinement heterostructure) structure which is suitable for high-power operation. The designed TQW-SCH structures are formed with sufficient controllability by the MOCVD. In the lasers sampled from ten epitaxial wafers grown at one time, the various room temperature characteristics exhibited excellent uniformity. The linear CW light output power versus current characteristics up to 100 mW even at 60°C are uniformly obtained over each epitaxial wafer. In preliminary aging tests at 60°C and 50 mW, a highly stable operation over 500 h has been realized. A maximum CW output power of 170 mW and a fundamental transverse mode up to 100 mW are realized at room temperature. Even at 95°C, a CW light output power of 100 mW is obtained     

A 780 nm high-power and highly reliable laser diode with a longcavity and a thin tapered-thickness active layer

Conventional AlGaAs laser diodes with uniform thickness active layers of various cavity lengths are investigated. It is recognized that the extension of the cavity length is effective in the improvement of the maximum output power, the temperature characteristics, and the operating life in high-temperature conditions. A 780-nm, high-power laser diode having a 350-μm-long cavity with a thin tapered-thickness active layer was fabricated. The optical power density near the mirror facets, the thermal resistance, the current density, and the carrier density were reduced by this structure. The laser emitted over 100 mW of CW (continuous-wave) output power at temperatures up to 80°C. A maximum output power level of 160 mW was achieved at room temperature. The fundamental transverse mode was confirmed at least up to 120 mW     

Terraced substrate inner stripe visible semiconductor laser and itsarrays

Lasers emitting in the range of 7500-7800 Å, which have average current thresholds of 30-40 mA and maintain single transverse mode operation up to 20 mW, are reported. Life tests show that the lasers have almost no threshold change after 3000 h of aging at 4-mW CW operation. The terraced substrate inner stripe laser arrays have clean single-lobe far-field patterns with full width at half power of 6° in CW operation and 2.4° in pulsed operation     

Single transverse mode operation of 1.55-μm buriedheterostructure vertical-cavity surface-emitting lasers

In this letter, we report the single-mode operation of 1.55-μm buried heterostructure vertical-cavity surface-emitting lasers (VCSELs) fabricated on a GaAs-AlAs distributed Bragg reflector using thin-film wafer fusion. A 7-μm VCSEL exhibits a single transverse mode at up to about 0.1-mW maximum optical output power and 75°C maximum operation temperature under continuous-wave operation     

Low threshold current high-temperature operation of InGaAs/AlGaAsstrained-quantum-well lasers

The authors report improved high-temperature characteristics for In_0.2Ga_0.8As strained-quantum-well ridge waveguide lasers with an optimized cavity design. They have fabricated In_0.2 Ga_0.8As lasers that operate CW at up to 220°C with over 9-mW output power. At 200°C the threshold current is as low as 15.9 mA for a 400-μm-long laser with 35/98% reflectivity facets. Optimization of the laser cavity also improves the high-temperature operation of quantum-well lasers in other material systems; GaAs quantum well lasers that operate at up to 220°C CW have been fabricated     

Dry-etched 650 nm AlGaInP visible-light laser diodes with operatingtime of over 3000 h

The authors have achieved CW operation of 650 nm GaInP/AlGaInP index waveguide-type visible-light laser diodes (LDs) with dry-etched mesa stripes fabricated by Cl₂ reactive ion beam etching. The threshold current of 47 mA and slope efficiency of 0.40 W/A are almost the same as those of a wet-etched LD fabricated from the same wafer (L=500 μm). The cross-sectional scanning electron microscope view of the buried mesa stripe shows that the dry-etched LD has a symmetric mesa shape resulting in a small focusing spot and stable mode operation. The wet-etched mesa, however, is asymmetric because a 6° misoriented substrate is used for this wavelength operation. An aging test with light output power of 3 mW at 50°C has revealed that these LDs have an operating time of over 3000 h, which represents a sufficient reliability for conventional uses     

Low-noise 650-nm-band AlGaInP visible laser diodes with a highlydoped saturable absorbing layer

Stable self-sustained pulsating and low-noise 650-nm-band AlGaInP visible laser diodes were demonstrated by adopting a novel structure, which has a highly doped saturable absorbing (SA) layer. Short carrier lifetime, which is indispensable for self-pulsation, was realized by applying high doping concentration to the p-type SA layer. 500-μm-long devices with 51%/51% coated facets were fabricated, resulting in the threshold current of 75 mA at 20°C. The temporal output power was measured at the average output power of 5 mW and the stable self-pulsation was observed up to an ambient temperature of 60°C. Therefore, the relative intensity noise (RIN) was kept about -140 dB/Hz in temperature ranging from 20°C to 60°C. Since the refractive index difference could be kept large and the optical mode could be confined effectively, the astigmatism in this work was below 3 μm at 5 mW against dc injection current. The lasers operated over 1350 h under the average output power of 5 mW at 60°C     

InGaAsP/InP buried crescent laser diode emitting at 1.3 µm wavelength

The fabrication procedure, designing of an active region and a p-n-p-n current blocking structure, characteristics and the aging results of an InGaAsP/InP buried crescent (BC) laser diode are described. The BC laser diodes exhibit high laser performances, such as a low-threshold current, a fundamental transverse mode oscillation with linear light output-current characteristics. CW operation at as high as 100°C is achieved with a junction up configuration as a result of the improvement in the current blocking structure. A stable CW operation at 80°C has been realized with a constant optical output power of 5 mW.     

Greater than 500-mW CW kink-free single transverse-mode operation of weakly index guided buried-stripe type 980-nm laser diodes

This is the first report of greater than 500-mW CW kink-free single transverse-mode operation of 980-nm laser diodes with a weakly index guided buried-stripe type structure. The device exhibited a kink-free level of 545 mW and maximum optical output power of over 650 mW limited by thermal saturation and showed no catastrophic optical damage, in addition, a currently on-going aging test at 350 mW optical output power at 50/spl deg/C has shown stable operation. Using a can-sealed LD, we also fabricated a co-axial type module with a two-lens system and a lensed-fiber. The coupling efficiency between the LD and a single-mode fiber was calculated to be approximately 78% and we have confirmed 300 mW kink-free fiber output operation. These figures are also the highest reported operation levels for 980-nm co-axial type modules.     

Continuous-wave operation of single-transverse-mode 1310-nm VCSELsup to 115°C

Long-wavelength vertical cavity surface emitting lasers (VCSELs) have thus far not provided substantial continuous-wave (CW) output power above 70°C. We describe recent advances using a vertically integrated 850 nm optical pump with a 1310-nm VCSEL. Using this approach, the devices described demonstrate record high temperature performance. We show single-transverse mode CW operation from -40 to +115°C, 0.5 mw optical power up to +85°C, and excellent device uniformity     

High-power temperature-insensitive gain-offset InGaAs/GaAsvertical-cavity surface-emitting lasers

The authors have grown 997 nm vertical-cavity surface-emitting lasers with an offset between the wavelength of the cavity mode and the quantum well gain peak to improve high temperature operation, and with higher aluminum-content barriers around the active region to improve the carrier confinement. They fabricated lasers of 8-15 and 20-μm diameters. The 8-μm-diameter devices exhibited CW operation up to 140°C with little change in threshold current from 15°C to 100°C, and the 20-μm-diameter devices showed CW output power of 11 mW at 25°C without significant heat sinking     

Room-temperature, continuous-wave operation for mode-stabilisedAlGaInP visible-light semiconductor laser with a multiquantum-wellactive layer

646 nm continuous-wave operation at room temperature (25°C) has been achieved by a transverse mode stabilised AlGaInP laser diode with a (multi-)quantum-well structure. The laser structure was grown by metalorganic vapour phase epitaxy. The threshold current (density) is 55 mA (4.4 kA/cm²) and maximum light output power is 19 mW. Stable fundamental transverse-mode operation was obtained, at least up to 15 mW     

900-mW high brightness buried ridge lasers by selective areaepitaxy

A study has been made of high power single lateral mode buried ridge lasers fabricated by selective area epitaxy. Several ridge thicknesses have been evaluated simultaneously in a single fabrication run. These lasers operate purely in the fundamental mode to output powers in excess of 450 mW, after which they are subject to beam steering or higher order mode operation. For weakly guided lasers, the output remains in a narrow lobe [full-width at half-maximum (FWHM)] = 4°-6°, stable at a given current value, up to output powers of 900 mW in CW tests     

High-power output over 200 mW of 1.3 µm GaInAsP VIPS lasers

Maximum CW output power was investigated in GaInAsP 1.3μm V-grooved inner stripe on P-substrate (VIPS) lasers considering both cavity length and facet reflectivity. Long-cavity lasers show a strong dependence of maximum output power on front reflectivity. A CW light output over 200 mW was obtained at room temperature using a 700 μm long cavity laser with 5 and 98 percent reflectivity of the front and rear facets, respectively. The fundamental transverse mode operation was confirmed up to 170 mW. A coupled power over 110 mW into a single-mode fiber was achieved with a coupling efficiency of 58 percent. We have verified the high reliability under high power levels, as high as 75 percent of the maximum CW output powers at room temperature.     

High-power 780 nm window diffusion stripe laser diodes fabricatedby an open-tube two-step diffusion technique

High-power and low-threshold-current GaAlAs lasers with a simple window structure fabricated by controllable open-tube two-step diffusion and single-step metalorganic chemical vapor deposition are discussed. The window structure and the waveguide with a narrow width around 2 μm are formed by diffusion of zinc, which just passes through an n-type active layer. CW output power up to 134 mW without catastrophic damage and a threshold current of 17 mA have been achieved. A maximum output power density of 16 MW/cm² is estimated. A stable fundamental transverse mode of up to 100 mV in the wavelength range of 780 nm is obtained. Excellent uniformity of device characteristics is confirmed     

Design optimization of ARROW-type diode lasers

Antiresonant reflecting optical wavelength (ARROW)-type diode lasers have been optimized for high-power, single-spatial-mode operation. Calculated modal behavior predicts strong intermodal discrimination with low loss for the fundamental ARROW mode. Single-lobe far-field operation is obtained only when the high-index reflecting (antiresonant) cladding layers correspond to an optical thickness of λ₁ (m+3/4), where λ is the lateral (projected) wavelength of the leaky wave in the high-index layers, and m is an integer (m=0, 1,. . .). Experimental results include stable, single-spatial mode operation to 500-mW peak pulsed power and 300-mW CW power at an emission wavelength of 0.98 μm     

InGaAsP/InP separated multiclad layer stripe geometry lasers emitting at 1.5 ?m

InGaAsP/InP separated multiclad layer stripe geometry lasers emitting at 1.5 ?m are reported. The CW threshold current at 25°C is only 82 mA and the maximum temperature where CW lasing is obtained is 65°C. The characteristic temperature of the pulsed threshold current is 60 K. The transverse mode is fundamental and the longitudinal mode is single up to 1.5 times the threshold under CW operation. A few samples operated for over 1000 h at 50°C under constant optical power operation of 5 mW/facet.     

High-Performance Blue InGaN Laser Diodes With Single-Quantum-Well Active Layers

The authors report on the high-performance blue laser diodes (LDs) with an emission wavelength of ~448 nm employing InGaN single-quantum-well (QW) active layers. At 100-mW continuous-wave (CW) output power, operation current and voltage are, respectively, 150 mA and 5.3 V, corresponding to the wall plug efficiency of >12%, a record value for the single-mode InGaN LDs with blue wavelengths. The single QW blue LD showed normal temperature dependence of light output-current curves with the characteristic temperature of 170 K. In addition, we demonstrate a high level of catastrophic optical damage of >300 mW and long device lifetime under CW operation condition at room temperature.     

100-mW kink-free blue-violet laser diodes with low aspect ratio

400-nm-band GaN-based laser diodes (LDs) operating with a kink-free output power of over 100 mW and having a low aspect ratio of 2.3 have been successfully fabricated for the first time. A new ridge structure, in which the outside of the ridge is covered with a stacked layer of Si on SiO/sub 2/ and the ridge width is as narrow as 1.5 /spl mu/m, is applied to realize high kink-free output power with a wide beam divergence angle parallel to the junction plane. A new layer structure around the active layer is demonstrated to be quite effective for obtaining a narrow beam divergence angle perpendicular to the junction plane, maintaining low threshold current. Ten LDs with low aspect ratio have been operated stably for over 1000 h under 30-mW continuous-wave operation at 60/spl deg/C. Relative intensity noise measured under optical feedback with high-frequency modulation is as low as -125 dB/Hz. These results indicate that this LD is suitable for next-generation high-density optical storage systems.     

Single-mode blue-violet laser diodes with low beam divergence and high COD level

We demonstrate GaN-based high-power single transverse-mode laser diodes (LDs) emitting at 405 nm. LD structures are designed to exhibit a high level of catastrophic optical damage and small beam divergence angle. By the control of refractive index profiles, we achieved a vertical beam divergence angle of as low as 17.5/spl deg/ and maximum output power of as high as 470 mW under continuous-wave operation condition. In addition, nearly fundamental transverse-mode operation is demonstrated up to 500-mW pulsed output power by far-field investigation.