High-power double-clad fiber lasers

Rare-earth doped, laser-diode-pumped, single-mode, double-clad fiber lasers are studied in detail, experimentally and theoretically, with particular attention to properties of scaling to higher output powers. Gain saturation, spontaneous emission, fiber propagation loss, and the optimum output coupler are considered for oscillator design and laser performance. Thermal properties are investigated, including the thermal fracture limit, the decrease of quantum efficiency with increasing pump power through the temperature dependence of multiphonon decay and ion-ion energy transfer, and thermal lensing. Self-focusing and Raman effects are briefly considered. It is shown that output powers in the tens of watts range are readily feasible with available double-clad fiber lasers     

High-power terahertz quantum-cascade lasers

Demonstration of quantum-cascade lasers at /spl sim/4.4 THz (/spl lambda//spl sim/68 /spl mu/m), which are measured to emit 248 mW peak power in pulsed mode, and 138 mW continuous-wave power at heatsink temperatures of 10 K, is reported. These lasers are based on a resonant-phonon depopulation scheme, and use a semi-insulating surface-plasmon waveguide.     

High-power pulsed xenon ion lasers

Output and threshold characteristics of small-bore pulsed xenon ion lasers are presented in detail as a function of current and gas pressure for ranges of these parameters that are consistent with high optical power output in the green-blue spectral region. It has been found that six wavelengths characteristic of xenon exhibit peak output powers greater than 100 watts, from a 5-foot laser tube over a limited (8-24 mtorr) range of xenon tube pressure. Laser action has also been obtained at high peak powers for longer current pulse (5-50 mus) operation of the tube. In addition, observation of three new laser wavelengths 5340, 5501, and 5590 Å is reported. These lines are only observed at very low tube pressures and very high peak currents.     

High-power continuous-wave quantum cascade lasers

High-power continuous-wave (CW) laser action is reported for a GaInAs-AlInAs quantum cascade structure operating in the mid-infrared (λ≃5 μm). Gain optimization and reduced heating effects have been achieved by employing a modulation-doped funnel injector with a three-well vertical-transition active region and by adopting InP as the waveguide cladding material to improve thermal dissipation and lateral conductance. A CW optical power as high as 0.7 W per facet has been obtained at 20 K with a slope efficiency of 582 mW/A, which corresponds to a value of the differential quantum efficiency η_d=4.78 much larger than unity, proving that each electron injected above threshold contributes to the optical field a number of photons equal to the number of periods in the structure. The lasers have been operated CW up to 110 K and more than 200 mW per facet have still been measured at liquid nitrogen temperature. The high overall performance of the lasers is also attested by the large “wall plug” efficiency, which, for the best device, has been computed to be more than 8.5% at 20 K. The spectral analysis has shown finally that the emission is single-mode for some devices up to more than 300 mW at low temperature     

High-power passively mode-locked semiconductor lasers

We have developed optically pumped passively mode-locked vertical-external-cavity surface-emitting lasers. We achieved as much as 950 mW of mode-locked average power in chirped 15-ps pulses, or 530 mW in 3.9-ps pulses with moderate chirp. Both lasers operate at a repetition rate of 6 GHz and have a diffraction-limited output beam near 950 nm. In continuous-wave operation, we demonstrate an average output power as high as 2.2 W. Device designs with a low thermal impedance and a smooth gain spectrum are the key to such performance. We discuss design and fabrication of the gain structures and, particularly, their thermal properties     

High-power single-mode ZnO thin-film random lasers

The possibilities to realize high-power single-mode ultraviolet lasing in highly disordered zinc oxide (ZnO) thin films are investigated. An effective one-dimensional time-domain traveling-wave model is developed to simulate random laser action in ZnO thin-film waveguides with ridge structure. Spectral and spatial redistributions of lasing modes, due to lasing mode localization and repulsion, are shown in highly disordered media. Hence, by controlling the photon density distribution, selective excitation of lasing modes can be achieved. A coupled-cavity ZnO thin-film random laser is also proposed to achieve high-power single-mode operation under nonuniform pumping. Preliminary experimental results have verified the possibility to realize high-power single-mode emission by the use of the proposed coupled-cavity design.     

High-power buried coarctate mesa-structure AlGaAs lasers

A high-power mode-stabilised AlGaAs laser with a buried coarctate mesa-structure (BCM) has been developed. The threshold current and the differential quantum efficiency are typically 40 mA and 56% per front facet, respectively. Fundamental-transverse-mode single-longitudinal-mode CW operation has been achieved at up to 80 mW.     

小发散角高功率半导体激光器研究

在量子阱半导体激光器中,量子尺寸引起的衍射效应使半导体激光器的光束质量很差。分别限制结构的垂直结平面发散角在40°左右,使得光束整形系统比较复杂,限制了半导体激光器的直接应用。为解决这一问题,提出了降低垂直结平面发散角的要求。回顾了小发散角半导体激光器的技术发展及应用,对具有小发散角的模式扩展波导结构进行了理论模拟和实验验证,获得了优化的结构。采用MOCVD外延技术生长了外延片,制作了高峰值功率脉冲激光器,获得了快轴发散角小于25,°峰值功率大于80W的半导体激光器,在激光引信应用中获得良好效果。     

高光束质量大功率垂直腔面发射激光

大功率垂直腔面发射激光器(VCSEL)在激光泵浦、激光测距、激光雷达等领域有广泛的应用前景,但目前的常规激光器材料结构尚未针对大功率激光输出进行优化设计。特别是为获得大功率激光输出所采用的大出光窗口导致的激光光束质量劣化成为限制其应用发展的核心问题之一。针对上述问题对激光器材料结构与器件结构进行了两方面的新结构设计和研制:(1)以实现大功率激光输出为目标,材料结构设计上对出光窗口一侧的N-DBR反射率进行了调整,以具有99.3%反射率的n-DBR替代常规结构中所采用的99.7%以上反射率。与常规材料结构相比,采用优化后的材料结构制备的直径500μm出光孔径的单管器件在注入电流110 A时激光输出功率达到102 W,而单元出光窗口直径100μm的5×5阵列在100 A电流下的激光输出功率为103 W,单元直径为140μm的8×8阵列在130 A注入电流下的激光输出功率达到115 W;(2)针对大出光窗口导致的光束质量劣化,通过湿法化学刻蚀研制了直接集成在出光窗口表面的微透镜结构,单元出光窗口直径为90μm的6×6阵列器件在4 A注入电流下的激光光束发散角压缩到6.6°,与未集成微透镜时的14.8°相比有了大幅改善。实验结果表明:降低n-DBR反射率及集成微透镜结构有效地改善提高了大功率垂直腔面发射激光的输出功率和激光光束质量。     

High-power, high-temperature InGaAs-AlGaAs strained-layerquantum-well diode lasers

Output power of 2.26 W and maximum power conversion efficiency of 57% were obtained for InGaAs-AlGaAs strained-layer quantum-well lasers (25°C, λ≃1 μm). Output powers were 2.35 W (-55°C) and 1.79 W (75°C) with maximum power efficiencies of 51% (-55°C) and 46% (75°C)     

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.     

High-power multiple-stripe injection lasers with channel guides

A new type of injection laser, the channel-guide (CG) structure, has been developed for use in multiple-stripe laser configurations. Leaky-mode operation of single-stripe CG lasers has been observed, and these devices produce "kink-free" outputs to pulsed powers of 180 mW (40 ns). Ten-stripe lasers fabricated using the channel-guide structure show strong leaky-mode coupling between stripes. Linear outputs to 2.8 W (40 ns) with stable far fields have been measured. Our results indicate that a real index antiguide is formed by the crowding of carriers into the channel region. The simple fabrication procedure makes the CG structure desirable for use in multiple-stripe high-power lasers.     

High-power 1.06 mu m GaInAsP DCPBH lasers

High-power 1.06 mu m double channel planar buried-heterostructure (DCPBH) lasers have been fabricated by liquid-phase epitaxy. AT 20 degrees C, the threshold current is 80 mA and CW output powers of 20 mW can be obtained. Under pulsed operation, quantum efficiencies of 0.37 W/A per facet and maximum pulse output powers of 150 mW are realised, while maintaining the lowest-order spatial mode and a symmetrical far-field distribution.<>     

High-power wavelength-tunable cladding-pumped rare-earth-doped silica fiber lasers

We describe the design and performance of cladding-pumped silica fiber lasers with high continuous-wave output powers and broad wavelength tunability in the 1, 1.5, and 2 μm spectral ranges. An ytterbium-doped fiber laser was tuned via wavelength dependent feedback provided by an external cavity containing a diffraction grating from 1027 to 1105 nm at multi-watt power levels. Similarly, high output power and wide wavelength tunability from 1540 to 1600 nm and from 1860 to 2090 nm at multi-watt output power levels has been achieved in Er-Yb co-doped and Tm-doped silica fiber lasers, respectively. A neodymium doped fiber laser was tuned from 1057 to 1118 nm at a lower power level. Limiting factors and the prospects for further improvements in performance are considered.     

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     

High-power (AlGa)As strip-buried heterostructure lasers

The characteristics of index-guided strip-buried heterostructure lasers are described. The lasers are grown by a two-step process, consisting of the initial 5-layer planar growth by MOCVD, and after etching to define the strip buried wave guide, recovery by Al0.65Ga0.35As using LPE. The devices are highly uniform, having 20 mA thresholds, quantum efficiencies of 0.65, and T0of 163°C. The TE polarized emission was in the lowest order transverse mode and consisted of ∼ 6 longitudinal modes. CW output powers of 50 mW per facet were obtained from lasers with reduced output reflectivity, and pulsed powers of 95 mW per facet from uncoated lasers have been obtained. The far-field angular widths weresim 23degandsim 50degin, and perpendicular to the junction plane, respectively. The total optical conversion efficiency of the coated laser emitting 50 mW CW was 41.5 percent.     

High-power 980 nm quantum dot broad area lasers

High-power quantum dot broad area lasers emitting at 980 nm are presented. Continuous-wave output powers of 4.3 W from a 50 /spl mu/m stripe width laser and of 6.3 W from a 100 /spl mu/m stripe width laser were achieved at 15/spl deg/C     

High-power, strained-layer amplifiers and lasers with tapered gainregions

Laterally tapered gain regions designed to accommodate the diffraction of narrow single-lobe beams that have been used in both optical amplifiers and lasers are described. Amplifier output power of 3.5 W with 3.1 W in a 1.05 times diffraction-limited lobe and laser output power of over 4 W with approximately half the power in a 1.7 times diffraction-limited lobe have been achieved     

High-power high-Modulation-speed 1060-nm DBR lasers for Green-light emission

We report on the static and dynamic performance of high-power and high-modulation-speed 1060-nm distributed Bragg reflector (DBR) lasers for green-light emission by second-harmonic generation. Single-wavelength power of 387 mW at 1060-nm wavelength and green power as high as 99.5 mW were achieved. A thermally induced wavelength tuning of 2.4 nm and a carrier-induced wavelength tuning of -0.85 nm were obtained by injecting current into the DBR section. Measured rise-fall times of 0.2 ns for direct intensity modulation and 0.6 ns for wavelength modulation make the lasers suitable for >50-MHz green-light modulation applications.     

High-power distributed Bragg reflector lasers operating at 1065nm

A report is presented on distributed Bragg reflector lasers emitting in excess of 700 mW in a single-spatial and single-spectral mode at 1065 nm. The threshold current of these devices is ~30 mA, there is an L-I slope of 0.74 W/A, and a sidemode suppression ratio greater than 30 dB. The current and thermal tuning are 0.016 A/mA and 0.7 A/degC, respectively.