Analysis and optimization of Q-switched operation of a Tm/sup 3+/-doped silica fiber laser operating at 2 /spl mu/m

Analysis and operation of a Q-switched Tm/sup 3+/-doped silica fiber laser in the wavelength region of 2 /spl mu/m is described when pumped with a Nd:YAG laser operating at 1.319 /spl mu/m. A large core of 17-/spl mu/m diameter was used to increase the laser gain volume, allowing high pump-power absorption and an output of high pulse energy and peak power. An acoustooptic modulator was used as Q-switching element and operated at repetition rates up to 30 kHz. A maximum peak output power of greater than 4 kW and a pulse duration at full-width at half-maximum of 150 ns has been obtained. This is the first report of high peak-power operation of the thulium-doped silica fiber laser.     

Directional light output from photonic-wire microcavity semiconductor lasers

We have obtained directional light output from a recently realized InGaAsP photonic-wire microcavity ring lasers. The output was achieved by fabricating a 0.45-/spl mu/m-wide U-shape waveguide next to a 10-/spl mu/m diameter microcavity ring laser. The laser has a threshold pump power of around 124 /spl mu/W when optically pumped at 514 nm. It is comparable to the former structure without output coupling. The output coupling efficiency can be controlled carefully by choosing the spacing between the laser cavity and the waveguide.     

High-power vertical cavity surface emitting laser with good performances

Fabrication and performance of a high-power bottom-emitting InGaAs/GaAsP vertical cavity surface emitting laser with 430 /spl mu/m diameter are described. The device realises the maximum room temperature CW output power 1.52 W at 987.6 nm with FWHM 0.8 nm. The far-field divergence angle is below 20/spl deg/. Reliability test shows at 70/spl deg/C an output power 0.35 W over 500 h.     

High-power single-mode selectively oxidized vertical-cavity surface-emitting lasers

Single-mode vertical-cavity top-surface-emitting lasers with maximum output power of 2.7 mW and side-mode suppression of 50 dB have been fabricated using solid source MBE for growth and selective oxidation to define the 3-/spl mu/m diameter active area. Threshold current is 290 /spl mu/A and a maximum wallplug efficiency of 27% is obtained at an output power of 1 mW.     

Short wavelength (/spl lambda//spl sim/4.3 /spl mu/m) high-performance continuous-wave quantum-cascade lasers

We report continuous-wave (CW) operation of a 4.3-/spl mu/m quantum-cascade laser from 80 K to 313 K. For a high-reflectivity-coated 11-/spl mu/m-wide and 4-mm-long laser, CW output powers of 1.34 W at 80 K and 26 mW at 313 K are achieved. At 298 K, the CW threshold current density of 1.5 kA/cm/sup 2/ is observed with a CW output power of 166 mW and maximum wall-plug efficiency of 1.47%. The CW emission wavelength varies from 4.15 /spl mu/m at 80 K to 4.34 /spl mu/m at 298 K, corresponding to a temperature-tuning rate of 0.87 nm/K. The beam full-width at half-maximum values for the parallel and the perpendicular far-field patterns are 26/spl deg/ and 49/spl deg/ in CW mode, respectively.     

Midinfrared holmium fiber lasers

The use of the high-power Tm/sup 3+/-doped silica fiber laser as a pump source for Ho/sup 3+/-doped silica and Ho/sup 3+/-doped fluoride fiber lasers for the generation of 2.1-/spl mu/m radiation is demonstrated. The Ho/sup 3+/-doped silica fiber laser produced a maximum output power of 1.5 W at a slope efficiency of /spl sim/82%; one of the highest slope efficiencies measured for a fiber laser. In a nonoptimized but similar fiber laser arrangement, a Ho/sup 3+/-doped fluoride fiber laser produced an output power of 0.38 W at 2.08 /spl mu/m at a slope efficiency of /spl sim/50%. A Raman fiber laser operating at 1160 nm was also used to pump a Ho/sup 3+/-doped fluoride fiber laser operating at a wavelength of 2.86 /spl mu/m. An output power of 0.31W was produced at a slope efficiency of 10%. The energy transfer upconversion process that depopulates the lower laser level in this case operates at a higher efficiency when the pump wavelength is closer to the absorption peak of the /sup 5/I/sub 6/ energy level, however, this energy transfer process does not impede to a great extent the performance of the Ho/sup 3+/-doped fluoride fiber laser based on the /spl sim/2.1/spl mu/m laser transition.     

High-power vertical-cavity surface-emitting laser with an extra Au layer

We report the performance of a high-power vertical-cavity surface-emitting laser (VCSEL) with an extra Au layer. By using the extra Au layer, the far-field divergence angle from a 600-/spl mu/m diameter VCSEL device is suppressed from 30/spl deg/ to 15/spl deg/, and no strong sidelobe is observed in far-field pattern. There is a slight drop in optical output power due to the introduction of the extra Au layer. By improving the device packaging method, the VCSEL device produces the maximum continuous-wave optical output power of 1.95 W with lasing wavelength of 981.5 nm. The aging test is carried out under constant current mode at 60/spl deg/C, and the preliminary result shows that the total degradation of output power is less than 10% after 800 h.     

High-power highly reliable 1.02-1.06-/spl mu/m InGaAs strained-quantum-well laser diodes

By growing the InGaAs active layer at temperatures lower than in conventional growth, we extended the lasing wavelength and presented the high reliability in InGaAs strained-quantum-well laser diodes. Equivalent I-L characteristics were obtained for 1.02-, 1.05-, and 1.06-/spl mu/m laser diodes with a cavity length of 1200 /spl mu/m. Maximum output power as high as 800 mW and fundamental transverse mode operation at up to 400 mW were obtained at 1.06 /spl mu/m and an 1800-/spl mu/m cavity. Stable operation was observed for over 14 000 h under auto-power-control of 225 mW at 50/spl deg/C for the 1.02-, 1.05-, and 1.06-/spl mu/m lasers with a 900-/spl mu/m cavity.     

Electrically pumped room temperature CW VCSELs with 2.3 /spl mu/m emission wavelength

Continuous wave (CW) operation at room temperature of electrically pumped InGaAlAs/InP vertical-cavity surface-emitting lasers (VCSELs) at emission wavelengths as high as 2.3 /spl mu/m is demonstrated for the first time. Devices with 15 /spl mu/m active region diameter show a maximum output power of 0.75 mW at 20/spl deg/C and a maximum CW operating temperature of 45/spl deg/C.     

Multi-watt, high efficiency, diffraction-limited Nd:YAG planar waveguide laser

An efficient, longitudinally diode-pumped, diffraction-limited, Nd:YAG double-clad planar waveguide laser was operated on four transitions of the Nd/sup 3+/ ion. Optimized output powers of 4.3, 3.5, and 2.7 W were obtained for absorbed pump powers of /spl sim/7 W, for the transitions at the lasing wavelengths of 1.064 /spl mu/m, 946 nm, and 1.3 /spl mu/m, respectively. Operation of the weak /sup 4/F/sub 3/2//spl rarr//sup 4/I/sub 5/2/ transition, lasing at 1.833 /spl mu/m, was demonstrated at an absorbed pump power threshold of 300 mW and an output power of 400 mW, with a nonoptimized output coupling. Diffraction-limited performance was obtained in both the guided and nonguided axes.     

Ridge-width dependence on high-temperature continuous-wave quantum-cascade laser operation

We report continuous-wave (CW) operation of quantum-cascade lasers (/spl lambda/=6 /spl mu/m) up to a temperature of 313 K (40/spl deg/C). The maximum CW optical output powers range from 212 mW at 288 K to 22 mW at 313 K and are achieved with threshold current densities of 2.21 and 3.11 kA/cm/sup 2/, respectively, for a high-reflectivity-coated 12-/spl mu/m-wide and 2-mm-long laser. At room temperature (298 K), the power output is 145 mW at 0.87 A, corresponding to a power conversion efficiency of 1.68%. The maximum CW operating temperature of double-channel ridge waveguide lasers mounted epilayer-up on copper heatsinks is analyzed in terms of the ridge width, which is varied between 12 and 40 /spl mu/m. A clear trend of improved performance is observed as the ridge narrows.     

High-power continuous-wave operation of quantum-cascade lasers up to 60/spl deg/C

High-temperature high-power continuous-wave (CW) operation of high-reflectivity-coated 12-/spl mu/m-wide quantum-cascade lasers emitting at /spl lambda/ = 6 /spl mu/m with a thick electroplated Au top contact layer is reported for different cavity lengths. For a 3-mm-long laser, the CW optical output powers of 381 mW at 293 K and 22 mW at maximum operating temperature of 333 K (60/spl deg/C) are achieved with threshold current densities of 1.93 and 3.09 kA/cm/sup 2/, respectively. At 298 K, the same cavity gives a maximum wall plug efficiency of 3.17% at 1.07 A. An even higher CW optical output power of 424 mW at 293 K is obtained for a 4-mm-long laser and the device also operates up to 332 K with an output power of 14 mW. Thermal resistance is also analyzed at threshold as a function of cavity length.     

Neodymium-doped cladding-pumped aluminosilicate fiber laser tunable in the 0.9-/spl mu/m wavelength range

A tunable high-power cladding-pumped neodymium-doped aluminosilicate fiber laser is demonstrated. The maximum power reached was 2.4 W with a slope efficiency of 41% and a threshold pump power of 1.68 W, both with respect to launched pump power, when cladding pumped by two 808-nm diode pump sources at both fiber ends. The dependence of the tuning range on the fiber length is investigated. The tuning range changed from 922 to 942 nm for a 25-m-long fiber to 908-938 nm with a 14-m-long fiber, because of reabsorption effects. The output linewidth was 0.26 nm in a diffraction-limited beam. Operation on the challenging 0.9-/spl mu/m three-level transition in neodymium-doped double-clad fiber laser was facilitated by a W-type core refractive index profile. This filtered out the unwanted and competing strong transition at 1.06 /spl mu/m while guidance of 0.9 /spl mu/m remained intact.     

Self-heating and trapping effects on the RF performance of GaN MESFETs

RF power performances of GaN MESFETs incorporating self-heating and trapping effects are reported. A physics-based large-signal model is used, which includes temperature dependences of transport and trapping parameters. Current collapse and dc-to-RF dispersion of output resistance and transconductance due to traps have been accounted for in the formulation. Calculated dc and pulsed I-V characteristics are in excellent agreement with the measured data. At 2 GHz, calculated maximum output power of a 0.3 /spl mu/m/spl times/100 /spl mu/m GaN MESFET is 22.8 dBm at the power gain of 6.1 dB and power-added efficiency of 28.5% are in excellent agreement with the corresponding measured values of 23 dBm, 5.8 dB, and 27.5%, respectively. Better thermal stability is observed for longer gate-length devices due to lower dissipation power density. At 2 GHz, gain compressions due to self-heating are 2.2, 1.9, and 0.75 dB for 0.30 /spl mu/m/spl times/100 /spl mu/m, 0.50 /spl mu/m/spl times/100 /spl mu/m, and 0.75 /spl mu/m/spl times/100 /spl mu/m GaN MESFETs, respectively. Significant increase in gain compression due to thermal effects is reported at elevated frequencies. At 2-GHz and 10-dBm output power, calculated third-order intermodulations (IM3s) of 0.30 /spl mu/m/spl times/100 /spl mu/m, 0.50 /spl mu/m/spl times/100 /spl mu/m, and 0.75 /spl mu/m/spl times/100 /spl mu/m GaN MESFETs are -61, -54, and - 45 dBc, respectively. For the same devices, the IM3 increases by 9, 6, and 3 dBc due to self-heating effects, respectively. Due to self-heating effects, the output referred third-order intercept point decreases by 4 dBm in a 0.30 /spl mu/m/spl times/100 /spl mu/m device.     

Type-II interband cascade lasers in the 4.3-4.7-/spl mu/m wavelength region

Operation of type-II interband cascade lasers in the 4.3-4.7-/spl mu/m wavelength region has been demonstrated at temperatures up to 240 K in pulsed mode. These lasers fabricated with 150-/spl mu/m-wide mesa stripes operated in continuous-wave (CW) mode up to a maximum temperature of 110 K, with an output power exceeding 30 mW/f and a threshold current density of about 41 A/cm/sup 2/ at 90 K. The maximum CW operation temperature of 110 K is largely limited by the high specific thermal resistance of the 150-/spl mu/m-wide broad area lasers. A 20-/spl mu/m-wide mesa stripe laser was able to operate in CW mode at higher temperatures up to 125 K as a result of the reduced specific thermal resistance of a smaller device.     

Double-pass copper vapor laser master-oscillator power-amplifier systems: generation of flat-top focused beams for fiber coupling and percussion drilling

In this paper, a compact master-oscillator power-amplifier laser system incorporating telescopic beam expansion in a high-gain double-pass amplifier is presented. A miniature (0.5 W) master-oscillator copper vapor laser is used to efficiently extract over 37 W of high-beam-quality (full transverse coherence) output power from a kinetically enhanced nominally 35-W copper vapor laser at 12-kHz pulse repetition frequency. By configuring the oscillator for low coherence output and using a multimode optical fiber between the oscillator and the double-pass amplifier, a high-power (34 W) low-divergence output beam having a well-defined flat-top far-field beam profile was also produced. The flat-top farfield beam profile arises from control of the spatial coherence of a flat-top near-field beam, rather than the usual techniques for producing flattened Gaussian beams from coherent Gaussian beams. Use of the flat-top focused beam for high-speed percussion drilling of high quality 100-/spl mu/m diameter holes in metals was demonstrated, as well as high-power (34-W average power, 80-kW peak power) damage-free power transmission through 100-/spl mu/m core diameter step-index optical fibers.     

Low-threshold high-T/sub 0/ 1.3-/spl mu/m InAs quantum-dot lasers due to p-type modulation doping of the active region

P-type doping is used to demonstrate high-To, low-threshold 1-3 /spl mu/m InAs quantum-dot lasers. A 5-/spl mu/m-wide oxide confined stripe laser with a 700-/spl mu/m-long cavity exhibits a pulsed T/sub 0/ = 213 K (196 K CW) from 0/spl deg/C to 80/spl deg/C. At room temperature, the devices have a CW threshold current of /spl sim/4.4 mA with an output power over 15 mW. The threshold at 100/spl deg/C is 8.4 mA with an output power over 8 mW.     

Tunable twin-guide distributed feedback laser diodes with over 9 nm continuous electro-optic tuning range

Tunable twin-guide laser diodes at 1.55 /spl mu/m with a record electro-optic tuning range are presented. Employing an optimised device design, continuous tuning ranges of 9.3 and 11.0 nm are achieved in continuous-wave (CW) and pulsed operation, respectively. In CW operation, the output power of 300 /spl mu/m-long devices remains above 1 mW throughout the whole tuning range.     

1.47 /spl mu/m Tm/sup 3+/:ZBLAN fibre laser pumped at 1.064 /spl mu/m

A large core area (1257 /spl mu/m/sup 2/) Tm/sup 3+/-doped ZBLAN fibre laser operated at 1.47 /spl mu/m is demonstrated. The pump source is a Nd:YAG laser operated at 1.064 /spl mu/m. A laser output power of 1.56 W continuous wave was obtained for 5.2 W of launched pump power. The slope efficiency with respect to the launched pump power was measured to be 33%.     

Continuous-wave operation of GaInAsSb-GaSb type-II ridge waveguide lasers emitting at 2.8 /spl mu/m

We have realized compressively strained GaInAsSb-GaSb type-II double quantum-well lasers with an emission wavelength of 2.8 /spl mu/m. Using broad area devices, an internal absorption of 9.8 cm/sup -1/ and an internal quantum efficiency of 0.57 is determined. For the increase of the threshold current with temperature, a T/sub 0/ of 44 K is obtained. Narrow ridge waveguide lasers show continuous-wave laser operation at temperatures up to 45 /spl deg/C, with room-temperature (RT) threshold current of 37 mA. At RT, the maximum optical output power per facet of an uncoated 800/spl times/7 /spl mu/m/sup 2/ ridge waveguide laser exceeds 8 mW.