Self-consistent calculation of the lasing eigenmode of thedielectrically apertured Fabry-Perot microcavity with idealized ordistributed Bragg reflectors

Optical confinement in the dielectrically apertured Fabry-Perot microcavity is investigated theoretically. The apertured region is first treated as embedded in an idealized planar waveguide to show that the confined eigenmode's resonant frequency can cut off parasitic waveguide modes existing outside the aperture, and lead to three-dimensional optical confinement. For more realistic cavities with nonunity mirror reflectivities, self-consistent calculations of the eigenmode characteristics are performed for the limit of an optically thin aperture to derive the lowest order confined eigenmode frequency, threshold susceptibility, and mode profile. The analysis is then extended to treat dielectric cavities based on Bragg reflectors     

Ultralow internal optical loss in separate-confinement quantum-well laser heterostructures

Internal optical loss in separate-confinement laser heterostructures with an ultrawide (>1 smm) waveguide has been studied theoretically and experimentally. It is found that an asymmetric position of the active region in an ultrawide waveguide reduces the optical confinement factor for higher-order modes and raises the threshold electron density for these modes by 10–20%. It is shown that broadening the waveguide to above 1 μm results in a reduction of the internal optical loss only in asymmetric separate-confinement laser heterostructures. The calculated internal optical loss reaches ∼0.2 cm⁻¹ (for λ≈1.08 μm) in an asymmetric waveguide 4 μm thick. The minimum internal optical loss has a fundamental limitation, which is determined by the loss from scattering on free carriers at the transparency carrier density in the active region. An internal optical loss of 0.34 cm⁻¹ was attained in asymmetric separate-confinement laser heterostructures with an ultrawide (1.7 μm) waveguide, produced by MOCVD. Lasing in the fundamental transverse mode has been obtained owing to the significant difference in the threshold densities for the fundamental mode and higher-order modes. The record-breaking CW output optical power of 16 W and wallplug efficiency of 72% is obtained in 100-μm aperture lasers with a Fabry-Perot cavity length of ∼3 mm on the basis of the heterostructures produced. __________ Translated from Fizika i Tekhnika Poluprovodnikov, Vol. 38, No. 12, 2004, pp. 1477–1486. Original Russian Text Copyright ? 2004 by Slipchenko, Vinokurov, Pikhtin, Sokolova, Stankevich, Tarasov, Alferov.     

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.     

Current spreading and carrier diffusion in long-wavelengthvertical-cavity surface-emitting lasers

Current spreading and carrier diffusion in vertical cavity surface-emitting lasers (VCSELs) critically affect the threshold current density, transverse gain profile, and optical modal characteristics of the devices. We have numerically analyzed these effects for four popular long-wavelength VCSEL structures with wafer-bonded GaAs-AlGaAs Bragg bottom mirrors. The results show that current confinement for p-mirror VCSELs is approximately twice as effective as the corresponding n-mirror VCSEL's although the confinement factor for all practical VCSEL structures studied here is considerably lower than the “ideal” structure. Calculations also show a strong dependence of current confinement on device aperture size and a tradeoff between the optical modal property and the current confinement efficiency for different apertured devices     

Quenching of lasing in high power semiconductor laser

Emission characteristics of high-power semiconductor lasers with a mesa-stripe design based on heterostructures with separate confinement are studied. It is shown that, in high-power semiconductor lasers with a mesa-stripe design, divergence of emission increases with the pump current as a result of generation of high order lateral optical modes. It is demonstrated that scattered radiation of high order lateral optical modes affects the transparency of passive regions outside the mesa stripe that forms a waveguide of the Fabry-Perot resonator. It is established that the transparency of passive regions results in fulfillment of threshold conditions for the closed optical mode in the semiconductor laser’s chip. As a result of generation of the closed optical mode in a cavity formed by four cleaved faces quenching of lasing modes in the mesa-stripe waveguide of the Fabry-Perot resonator occurs.     

InGaAsP/InP separated multiclad layer stripe geometry laser emitting at 1.5 µm wavelength

We have developed an InGaAsP/InP separated multiclad layer (SML) stripe geometry laser emitting at 1.5 μm wavelength. In this laser, the optical confinement is done by the effective refractive index step owing to the formation of the coupled waveguide outside the stripe region. The current confinement is done by the p-n-p-n structure outside the stripe region. The CW threshold current at 25 °C is only 82 mA for the stripe width and the cavity length of 6 μm and 250 μm, respectively. The maximum temperature where the CW lasing is obtained is 65°C. The characteristic temperature of the threshold current is 60 K. The transverse mode is fundamental up to 1.8 times the threshold. Ten samples are operated at 50°C with constant optical output of 5 mW/facet. These samples are still operating at over 10 000 h with a slight increase in the driving current. The appreciable change in the characteristics due to aging is not observed.     

Analysis of microcavity VCSEL lasing modes using a full-vectorweighted index method

Presents a semi-analytic full-vector method for calculating the spatial profile, optical confinement factor resonant frequency, absorption loss, and mirror loss of lasing modes in cylindrically symmetric microcavity vertical-cavity surface-emitting lasers (VCSEL's). It can be shown that this method gives the best separable approximation for the electric and magnetic vector potentials. Our technique can model the entire VCSEL structure and can treat complex media. We apply the method to etched-post and oxide-apertured VCSEL's designed for 980-nm emission and find a blueshift in cavity resonance as the cavity radius shrinks. We also find a minimum optical cavity radius below which radially bound lasing modes cannot be supported. This radius depends on the device geometry and lies between 0.5 and 1 μm for the devices studied. Once this model is augmented to include diffraction losses-the dominant loss mechanism for conventional small aperture lasers-it will provide a complete picture of lasing eigenmodes in microcavity VCSEL's     

Quasi-exact optical analysis of oxide-apertured microcavity VCSELsusing vector finite elements

We report a new full vector finite element model for analyzing the optical properties of azimuthally symmetric oxide-apertured vertical-cavity surface emitting lasers (VCSELs). Our model allows for quasi-exact calculation of the lasing mode blueshift, threshold gain, and field profile. Through a detailed analysis of a sample VCSEL, we ascertain the physical effects which determine diffractive or parasitic mode loss. They are: 1) the background density of parasitic modes and 2) the coupling strength between the lasing mode and the parasitic mode continuum. The coupling strength is in turn determined by the relative alignment between the lasing and parasitic mode propagation vectors and the lasing mode penetration into the oxide region. This analysis improves our understanding of the optical physics of apertured VCSELs and should enable the next leap down in lasing threshold     

Narrow-core hollow optical waveguide with nanostructured SOI as ultra-low loss platform for efficient photodetection

A nanostructured hollow optical waveguide based on high-index contrast grating (HCG) embedded SOI is proposed. An ultra-low propagation loss of 1.22 dB/m even at narrow, 1-\(\upmu \)m thick, air-core is reported. A high-performance photodetection is realized by the introduction of hollow core in form of intrinsic region in the photodetection (PIN) layer within HCG-assisted narrow-core waveguide. A sufficiently high responsivity of 0.8 A/W and quantum efficiency of 64% are obtained at 1550-nm which is possible because of the presence of surface modes within HCG which get coupled in the photodetection layer leading to a strong optical confinement in that layer. High reflectivity, small penetration length and coupling of lateral surface modes in HCG make it possible to offer improved waveguiding and hence photodetection.     

AlInAs氧化物限制1.3μm低阈值边发射激光器

研究制作了一种利用AlInAs氧化物作为限制的1.3μm边发射AlGaInAs多量子阱激光器.有源层上方和下方的AlInAs波导层被氧化作为电流限制层.这种结构提供了良好的侧向电流限制和光场限制.当电流通道为5μm宽时,获得了12.9mA的阈值电流和0.47W/A的斜率效率.与具有相同宽度的脊条的脊波导结构的激光器相比,这种AlInAs氧化物限制的激光器的阈值电流降低了31.7%,斜率效率稍微有所提高.低阈值和高效率的特性表明,氧化AlInAs波导层能够提供良好的侧向电流限制.这种AlInAs氧化物限制的激光器垂直方向的远场半高全宽角为36.1°,而水平方向的是21.6°,表明AlInAs氧化物对侧向光场也有很强的限制能力.     

Low-threshold native-oxide confined narrow-stripe folded-cavity surface-emitting InGaAs-GaAs lasers

Narrow-stripe folded-cavity surface-emitting InGaAs-GaAs lasers are demonstrated, AlAs native-oxide layers above and below waveguide region are employed for current and optical confinement to form narrow-stripe InGaAs-GaAs quantum-well lasers. A low-temperature (400/spl deg/C) selective wet-oxidation technique and an ion-beam-etching technique are used to fabricate insulator confined narrow-stripes and internal 45/spl deg/ deflectors, respectively. Continuous-wave threshold currents as low as 4.5 mA and 59% surface-emitting quantum efficiencies are achieved on the devices with 2-/spl mu/m-wide aperture and a 420-/spl mu/m-long cavity.     

Coupling efficiency of waveguide laser resonators formed by flat mirrors: Analysis and experiment

We present a new and more efficient method of calculating the losses of a waveguide laser resonator consisting of a hollow circular dielectric waveguide and flat mirrors, taking into account the effects of waveguide modes up to order HE13. Both symmetric and asymmetric cavities are considered. We show that low cavity losses, only slightly exceeding the HE11waveguiding losses, are predicted to be possible for much larger mirror distances than had previously been suspected, provided that an optimum total cavity length is chosen. The low losses arise when the HE11and HE12modes emerge from the guide with relative amplitudes and phases such that the returning diffraction patterns interfere to produce a narrow beam with low aperture losses. The theoretical predictions were checked experimentally for CO2lasers having various waveguide dimensions. Good qualitative agreement was found, but the optimum total cavity lengths were typically 3-5 percent longer than predicted. Possible explanations of this discrepancy are discussed. We also predicted and experimentally verified that variations of the cavity length over a few centimeters can exert a coarse wavelength selectivity sufficient to determine the band and branch on which a CO2laser oscillates; conversely, that for a grating tuned laser, the cavity length must be varied by a similar amount as the wavelength is tuned in order to maintain low cavity losses over the entire wavelength range.     

Highly birefringent and monomode GaAlAs-GaAs planar optical waveguide

A novel optical waveguide exhibiting a layered core region is proposed. Owing to the original design of the core stack and form birefringence in the multilayer, a waveguide supporting both TE and TM lowest-order modes with high confinement has been obtained. It has been designed, fabricated, and characterized and presents a modal birefringence greater than 0.01, which is in good agreement with the calculated values.     

Comparison of vertical-cavity surface-emitting lasers with half-wave cavity spacers confined by single- or double-oxide apertures

Data are presented on vertical-cavity surface-emitting lasers (VCSEL's) laterally confined with either single- or double-oxide apertures in a half-wave cavity spacer. Despite a higher nonradiative recombination rate, double aperture as compared to single-aperture devices show lower threshold current density and higher differential quantum efficiency for smaller optical modes. The advantage of double apertures is attributed to the better optical confinement that results in a reduced lateral diffraction loss.     

TE/TM mode splitters on InGaAsP/InP

In a monolithic heterodyne polarization diversity receiver, mode splitters which effectively separate the TE and TM polarization of the optical wave are required. For this purpose, a directional coupler which utilizes a metal cladding on one of its branches to separate both polarizations was investigated. The polarization splitters can act in two distinct modes of operation, depending on the degree of lateral confinement of the optical rib waveguide before an asymmetric coupler. For weak confinement, the metallized waveguide is guiding for TE- but nonguiding for TM-polarization, and negligible TM-crosstalk results     

Subwavelength Nanopatch Cavities for Semiconductor Plasmon Lasers

We propose and analyze a family of nanoscale cavities for electrically pumped surface-emitting semiconductor lasers that use surface plasmons to provide optical mode confinement in cavities which have dimensions in the 100-300-nm range. The proposed laser cavities are in many ways nanoscale optical versions of micropatch antennas that are commonly used at microwave/RF frequencies. Surface plasmons are not only used for mode confinement but also for output beam shaping to realize single-lobe far-field radiation patterns with narrow beam waists from subwavelength size cavities. We identify the cavity modes with the largest quality factors and modal gain, and show that in the near-IR wavelength range (1.0-1.6 mum) cavity losses (including surface plasmon losses) can be compensated by the strong mode confinement in the gain region provided by the surface plasmons themselves and the required material threshold gain values can be smaller than 700 cm^-1.     

部分相干光通过多个硬边光阑ABCD光学系统传输的快速算法

部分相干光通过受光阑限制近轴ABCD光学系统传输是实际工作中一个十分有意义却是很困难的问题。虽然使用“Mathematia”编制的程序可对Collins公式作数值积分，但随着光阑数目的增加，计算变得非常繁琐和耗时。用有限个复高斯函数之和来逼近硬边光阑窗函数的方法，推导出了部分相干光通过多个硬边光阑ABCD光学系统传输的递推公式，提供了一种模拟部分相干光通过硬边光学系统传输的快速算法。计算示例表明，当离光阑不太近时，使用解析公式和直接对Collins公式作数值积分的结果符合甚好，并具有快速计算的主要优点，因此大为节约了机时。此外，由于将单光阑推广到多光阑的ABCD光学系统，并考虑了光束的部分空间相干性，因此所得结果更具一般性，且对多模部分相干激光是适用的。     

VCSEL稳态热特性分析

使用数值方法对氧化层限制型垂直腔面发射激光器(VCSEL)内部稳态热场分布进行了计算,结果显示其分布形式取决于DBR区热导率及其与高阻限制层热导率的差异,并指出在限制层孔径变化及外加电极电压变化时对热场分布的影响;器件中温度最高的部分处于中心氧化限制层附近。有源层中温度沿径向的分布情况表明,在氧化限制孔径下方形成明显的温度台阶是导致器件有源层中产生折射率台阶的主要原因。     

Computer model of a superluminescent LED with lateral confinement

We present a computer simulation of a strip-geometry superluminescent light emitting diode (SLD). One end of the strip waveguide has a finite reflectivity while the reflectivity vanishes at the other end because it is assumed that the strip waveguide terminates in a high-loss region. The gain of the structure is computed from the drive current and several intrinsic device parameters; gain saturation is taken into account. We discuss the dependence of the light power coupled into a fiber from an InGaAsP SLD at 1.3 μm as a function of the driving current, the reflectivity of one end of the strip waveguide, its numerical aperture (NA), and its length and width. A considerable improvement in power coupling efficiency can be realized when the waveguide NA equals the fiber NA or, in the absence of lateral confinement, when the fiber NA is much larger than the half-width to length ratio (times the refractive index) of the strip waveguide. Previous analyses have ignored lateral waveguiding effects.