MBE growth and characteristics of periodic index separate confinement heterostructure InGaAs quantum-well lasers

We have used solid-source molecular beam epitaxy (MBE) to grow InGaAs quantum-well lasers emitting at 980nm in a novel configuration of periodic index separate confinement heterostructure (PINSCH). Periodic multilayers (GaAs/AlGaAs) are utilized as optical confinement layers to reduce the transverse beam divergence as well as to increase the maximum output power. The multilayers are grown by temperature modulation MBE without any shutter operation. The heterointerfaces in the multilayers are linearly graded such that the energy barrier heights are greatly decreased. This has led to a drastic reduction in the series resistance which is essential in the performance of high output power. The 5μm × 750μm device has far-field angles of 10° by 20°, a threshold current of 45 mA, an external differential quantum efficiency of 1.15 mW/mA (90%), and an output power of 620 mW, all measured at room temperature under CW operation. A record high fiber coupling efficiency of 51% has been achieved and more than 130 mW of power is coupled into a 5μm-core single mode fiber.     

940 nm高功率半导体激光器研究

报道了一种采用大光学腔结构的InGaAs/GaAs/AlGaAs应变量子阱高功率半导体激光器。在量子阱能级本征值方程的数值求解基础上 ,优化了InGaAs阱层材料的In组份含量 ;采用大光学腔结构以有效降低垂直于结平面方向的光束发散角及腔面的光功率密度 ,实现器件的高功率、低发散角光。设计的激光器外延结构采用分子束外延 (MBE)方法生长 ,成功获得具有较低激射阈值的 94 0nm波长激光器外延片。对 10 0 μm条形 ,10 0 0 μm腔长的制备器件测试表明 ,器件的最大连续输出功率达到 2W ,峰值波长为 939.4nm ,远场水平发散角为 10° ,垂直发散角为 30°。器件的阈值电流为 30 0mA。     

980-nm aluminum-free InGaAs/InGaAsP/InGaP GRIN-SCH SL-QW lasers

The design of 980-nm InGaAs/InGaAsP/InGaP GRIN-SCH lasers with aluminium-free GaAs-based materials is discussed. The first approach was successful MOCVD growth of InGaAsP alloy lattice matched to GaAs. It was found that an immiscible region existed, as determined by photoluminescence measurements. The main approach was to introduce the graded bandgap structure consisting of InGaAsP layers lattice matched to GaAs into GaAs/InGaP interfaces. The graded structure suppresses the heterojunction spikes, especially of the valence band at these interfaces. As a result, series resistance of GRIN-SCH lasers with the graded bandgap structure was reduced compared with simple SCH lasers with abrupt bandgap interfaces due to improved hole injection. Furthermore, the optimum graded structures for optical confinement region were investigated to improve the carrier injection efficiency, especially electron injection efficiency into a single quantum well active layer. Also, this graded bandgap structure formed the graded refractive index profile in an active region, which is the so-called GRIN-SCH waveguide. The GRIN-SCH profile could be controlled to narrow the transverse beam divergence for high coupling efficiency into a single-mode fiber and to reduce the optical power density at facets for high reliability. Finally the results of a life-test of GRIN-SCH lasers was shown, and the lifetime of GRIN-SCH lasers with immiscible InGaAsP layers was discussed     

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.     

High-Power Low Vertical Beam Divergence 800-nm-Band Double-Barrier-SCH GaAsP–(AlGa)As Laser Diodes

High-power double-barrier separate confinement heterostructure (SCH) GaAsP–AlGaAs–GaAs laser diodes designed for low vertical beam divergence emission at 800-nm band are presented. Insertion of thin wide-gap (low refractive index) barrier layers at the interfaces between the waveguide and cladding layers of an initial SCH causes an optical confinement weakening. As a result, the vertical divergences down to 16$^circ$and 13$^circ$have been obtained, depending on the design version. Similar threshold current densities, higher characteristic temperatures T$_0$compared to the high-power large optical cavity (LOC) lasers of comparable beam divergences and promising high-power performance make this design an alternative to LOC solution.     

High-Power Low Vertical Beam Divergence 800-nm-Band Double-Barrier-SCH GaAsP–(AlGa)As Laser Diodes

High-power double-barrier separate confinement heterostructure (SCH) GaAsP–AlGaAs–GaAs laser diodes designed for low vertical beam divergence emission at 800-nm band are presented. Insertion of thin wide-gap (low refractive index) barrier layers at the interfaces between the waveguide and cladding layers of an initial SCH causes an optical confinement weakening. As a result, the vertical divergences down to 16$^circ$and 13$^circ$have been obtained, depending on the design version. Similar threshold current densities, higher characteristic temperatures T$_0$compared to the high-power large optical cavity (LOC) lasers of comparable beam divergences and promising high-power performance make this design an alternative to LOC solution.     

Operating Characteristics of Semiconductor Quantum Well Lasers as Functions of the Waveguide Region Thickness

The performance characteristics of semiconductor lasers based on quantum wells (QWs) are theoretically studied as functions of the thickness of the waveguide region [optical confinement layer (OCL)]. The maximum modal gain, optical-confinement factor (in QWs, OCLs, and emitters), threshold current density, electron and hole densities (in QWs and OCLs), internal optical loss (in QWs, OCLs, and cladding layers), internal differential quantum efficiency, currents of stimulated and spontaneous recombination and the output optical power of the laser are calculated as functions of the OCL thickness. It is shown that up to pump current densities of 50 kA/cm² the dependence of the output power of the considered lasers on the OCL thickness is weak in the thickness range of 1.5–2.8 μm. This result is important for the development of high-brightness lasers, since such lasers use a wide waveguide to ensure low radiation divergence. It is shown that, at very high pump-current densities, the output power has a maximum as a function of the OCL width.

     

808 nm大功率无铝有源区非对称波导结构激光器

采用分别限制非对称波导结构,将光场从对称分布变为非对称分布,降低了载流子光吸收损耗,并允许p型区具有更高的掺杂水平,从而使器件电阻降低.对GaAsP/GaInP张应变单量子阱(SQW)非对称波导结构激光器的光场特性进行了理论分析,设计了波导层厚度,并制作了波长为808 nm的无铝有源区大功率半导体激光器.器件综合特性测试结果为:腔长900μm器件的阈值电流密度典型值为400 A/cm2,内损耗低至1.0 cm-1;连续工作条件下,150μm条宽器件输出功率达到6 W,最大斜率效率为1.25 W/A.器件激射波长为807.5 nm,平行和垂直结的发散角分别为3.0°和34.8°.20~70℃范围内特征温度达到133 K.结果表明,分别限制非对称波导结构是降低内损耗,提高大功率半导体激光器特性的有效措施.     

Influence of the confinement factor on the wavelength-dependentoutput properties of a tapered traveling-wave semiconductor amplifier

We analyze the influence of the confinement factor on the output properties of a tapered traveling-wave semiconductor amplifier as a function of the wavelength of the input field and current injected into the amplifier. The interaction of the optical field with the amplifying medium is described by means of a susceptibility function taking into account both the gain and the carrier-induced antiguiding effect, while the beam propagation method is used to describe the evolution of the field along the amplifier. We find that, for the same input power, devices with lower optical confinement factors allow for the same output optical power with better beam quality and higher saturation power than devices with higher optical confinement factor, in agreement with the available experimental results     

Performance of Ar/sup +/-milled Ti:sapphire rib waveguides as single transverse-mode broadband fluorescence sources

Rib waveguides have been fabricated in pulsed-laser-deposited Ti:sapphire layers using photolithographic patterning and subsequent Ar/sup +/-beam milling. Fluorescence output powers up to 300 /spl mu/W have been observed from the ribs following excitation by a 3-W multiline argon laser. Mode intensity profiles show high optical confinement and the measured beam propagation factors M/sub x//sup 2/ and M/sub y//sup 2/ of 1.12 and 1.16, respectively, indicate single transverse-mode fluorescence emission. Loss measurements using the self-pumped phase conjugation technique have yielded comparable values (1.7 dB/cm) for the ribs and the unstructured planar waveguide counterparts. The combination of optimum modal properties and strong optical confinement, together with sufficient levels of fluorescence output, make the single-moded Ti:sapphire rib waveguides a very interesting candidate as a fluorescence source for optical coherence tomography applications.     

Output coupling for closely confined Pb1-xSnxTe double-heterostructure lasers

The output coupling of an idealized, symmetric model of a double-heterostructure (DH) laser is analyzed theoretically using parameters suitable to Pb1-xSnxTe. For the TEOmode incident at the laser mirror and for thin optical guiding regions such that only the TEO, TE1, TMO, and TM1modes may propagate, an exact formulation of the coupling problem is obtained including mode coupling at the mirror into the continuum of unguided radiation modes. Using this formulation, the power reflection and transmission coefficients, the fraction of incident power coupled into the radiation modes, the mirror illumination, and the far-field pattern are calculated for typical parameters. Significant mode coupling can occur, limiting the maximum external efficiency of such lasers. This and other potentially undesirable characteristics resulting from close optical confinement, such as large output beam divergence, must be considered in design criteria for DH structures in this alloy system.     

High-power and low-divergence 980-nm InGaAs-GaAsP-AlGaAs strain-compensated quantum-well diode laser grown by MOCVD

High-power InGaAs-GaAsP-AlGaAs strain-compensated separate-confinement heterostructure double quantum-well lasers emitting at 980-nm wavelength have been grown by low-pressure metal-organic epitaxial chemical vapor deposition. Fabricated with a ridge waveguide, the lasers achieved an output power of 386 mW in the fundamental lateral mode without any kink being observed. By optimizing the laser structure parameters, a very low transverse beam divergence of 22.1/spl deg/ and a high slope efficiency of up to 0.89 mW/mA were obtained. The narrow transverse far field enables an output power of over 290 mW to be coupled into a single-mode fiber with a high coupling efficiency of 83.2% at 430 mA. Life testing at various powers shows excellent long-term reliability after 3500 h.     

VCSEL beam waists from optical spectra

We relate the optical beam waist of a vertical-cavity surface-emitting laser (VCSEL) to a measurement of the transverse mode splitting found in the device's optical output spectra and to a measurement of beam divergence. We show experimentally that the results are in good agreement. Accurate knowledge of beam waists is useful for tailoring devices for single-mode or for high-speed operation and to better understand and interpret the mode spectrum     

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.     

含热透镜多元件谐振腔的动态工作特性

由于光泵浦热效应,高功率固体激光器的输出参数如光束远场发散角、输出功率等会发生变化。本文使用g-参数等价腔详细研究了各种类型稳定腔、临界腔的动态工作特性,例如g-参数图上工作点的运动规律、临界光焦度、临界g参数以及光斑半径、远场发散角等。文中还对理论的实验验证和应用进行了讨论。     

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.     

高功率单高阶模倒置表面浮雕结构垂直腔面发射激光器

提出并研究了一种带有环形出光孔的倒置表面浮雕结构垂直腔面发射激光器.该器件最突出的结构特点在于,支持稳定的单高阶横向模式激射.在输入电流为六倍阈值电流时,输出功率高达9.8 m W,边模抑制比将近30 d B.在外界为360 K高温时,输出功率仍可达4 m W.且其远场表现出的高斯光束发散角较小.     

The heteroepitaxial ridge-overgrown distributed feedback laser

A new distributed feedback laser, the heteroepitaxial ridge-overgrown distributed feedback (HRO-DFB) laser, is proposed and demonstrated. The growth steps permit post-active-layer growth determination of the grating period, and the fabrication of this laser is simple with an automatic alignment of the current confinement to the ridge-overgrowths, which form the strip-loaded waveguide of the laser. The lateral overgrowth extending over the oxide films on both sides of the window stripe enhances the effect of grating feedback. Both LPE and MO-CVD have been employed successfully for the ridge overgrowth. The HRO-DFB laser was shown to operate in stable single-longitudinal mode with no observable mode partition events under 2 Gbit/s pseudorandom pulse modulation. The dynamic spectral width under 2 Gbit/s modulation was typically 0.5-2 Å. Other characteristics of these 1.5 μm HRO-DFB lasers include ∼8 mW/facet of single-longitudinal mode output power, and narrow beam divergence of 10° operating in the fundamental transverse mode in the junction plane. The CW thresholds were usually 50-100 mA. Transmission experiments with dispersive fibers (17 ps/km-nm) atsim1.55 mum at 2 Gbits/s over 82 km and at 420 Mbits/s over 203 km confirmed that the HRO-DFB laser is an excellent a single-frequency optical source for use in optical communication applications.     

高功率850 nm宽光谱大光腔超辐射发光二极管

超辐射发光二极管(SLD)具有不同于半导体激光器和普通发光二极管的优异性能。为提高半导体超辐射发光管的光谱宽度,采用非均匀阱宽多量子阱(MQW)材料拓宽超辐射器件的输出光谱。优化设计器件的波导结构,利用大光腔结构设计出高功率、低发散角850 nm超辐射发光二极管。采用直波导吸收区而后在器件的出光腔面上镀制抗反射膜的方法制作超辐射发光二极管。器件在140 mA时器件半峰全宽(FWHM)可以达到26 nm,室温下连续输出功率达到7 mW。器件的垂直发散角为28°,水平发散角为10°。由于器件具有比较小的发散角,与光纤耦合时具有比较高的耦合效率,单模保偏光纤耦合输出功率达到1.5 mW。     

输出平均功率达200W的板状激光器

脉冲运转的“之”字形Nd:YAG板状激光器,在工作频率为50pps时,最高输出激光平均功率达230W。由于采用了“之”字形光路,使热畸变得到补偿,输出激光束的发散角得到改善,一般为3×4mrad。