Design optimization for high-brightness surface-emitting photonic-crystal distributed-feedback lasers

A new time-domain Fourier-Galerkin (TDFG) theory is developed to simulate the near-field, far-field and spectral characteristics of surface-emitting photonic-crystal distributed-feedback (SE PCDFB) lasers. It is found that a properly-designed two-dimensional hexagonal or square-lattice grating should efficiently couple the output into a single SE mode that retains coherence for aperture diameters of up to /spl ap/1 mm. We identify lattice structures and precise conditions under which all components of the transverse electric or transverse magnetic polarized optical fields constructively interfere to produce a single-lobed, near-diffraction-limited circular output beam. The TDFG simulations predict that quantum efficiencies as high as 30% (60% if reflectors are built into the waveguide structure) should be attainable. A surprising conclusion is that diffractive coupling into the surface-emitting direction must be relatively weak, in order to assure selection of the desired symmetric in-phase mode. Furthermore, gain media with a moderate linewidth enhancement factor should produce the best SE PCDFB performance, whereas edge emitters nearly always benefit from a very small value.     

Linewidth enhancement in distributed-feedback semiconductor lasers

It is demonstrated that the linewidth enhancement in distributed-feedback (DFB) laser diodes can differ significantly from (1+ alpha /sup 2/), where alpha is Henry's linewidth enhancement factor. The influence of the relevant laser parameters, the detuning of the gain peak wavelength, a pi /2 phase shift and a reflecting end facet on the linewidth enhancement is discussed with respect to an improved DFB laser design.<>     

Coupled phase-shift distributed-feedback semiconductor lasers fornarrow linewidth operation

Mode properties of a coupled phase-shift distributed-feedback (DFB) structure are analyzed and the feasibility of narrow-linewidth emission is shown theoretically. The structure consists of a multiple number of phase-shift DFB laser units which are arranged in tandem and coupled with each other through additional phase shift of corrugation. Optimum structure parameters were determined for two coupled laser units so that the frequency detuning is zero and the mode pattern is the flattest. The mode analysis shows that the intensity distribution is flatter and the normalized coupling constant can be larger than those for the conventional DFB laser with a single phase shift. This indicates that the cavity length can be extended with less influence from the longitudinal spatial hole burning effect     

Heat-source distribution in etched-well surface-emitting semiconductor lasers

The authors report on the development of a comprehensive self-consistent thermal-electrical model of etched-well vertical-cavity surface-emitting lasers. The analysis provides valuable insight into distribution of heat sources in these devices. Two-dimensional current- and heat-spreading analysis is used to determine in a self-consistent manner a realistic distribution of heat sources in etched-well vertical-cavity surface-emitting lasers. Strong nonuniformities of heat-source and temperature distributions are revealed. The relative contributions of various heat sources are evaluated. The Joule heating of the p-AlGaAs cladding layer is identified as a major cause of intense heating above threshold.<>     

Analysis and design of vertical-cavity surface-emitting lasers forself-sustained pulsation operation

The generation mechanism of self-sustained pulsation in vertical-cavity surface-emitting lasers (VCSELs) is analyzed with the influence of lateral loss effects, such as self-focusing, lateral diffraction loss, and spatial hole burning, taken into consideration. The condition for self-sustained pulsation is also derived in an analytical form. It is shown that the lateral loss effects have significant influence on the excitation of self-sustained pulsation, especially for devices with small size. Furthermore, the possibility of using diffused quantum-well (QW) structures in VCSELs to enhance self-sustained pulsation is studied. It is found that by using diffused QW structures, the range of core area to obtain self-sustained pulsation is increased. In addition, peak power and repetition frequency of the pulses can also be improved     

光泵垂直扩展腔面发射半导体激光器的研究进展

近年来，光泵垂直扩展腔面发射半导体激光器由于其光束质量好、可实现大功率输出，受到了广泛的关注。在介绍其基本工作原理的基础上，综述了不同波段光泵垂直扩展腔面发射半导体激光器的研究现状与进展，并分析、讨论了实现高功率光泵垂直扩展腔面发射半导体激光器面临的主要问题及解决方案。     

Integrated semiconductor vertical-cavity surface-emitting lasers and PIN photodetectors for biomedical fluorescence sensing

Vertical-cavity surface-emitting lasers (VCSELs), optical emission filters, and PIN photodetectors were fabricated as part of a monolithically integrated near-infrared fluorescence detection system. The integration of these micro-fabricated components with micro-arrays, flow channel arrays, and biochips can drastically reduce cost and enable parallel sensing architectures. An optoelectronic design is presented that integrates VCSELs, optical filters, and photodetectors through a modification to a typical VCSEL structure. System designs were simulated and compared, leading to several innovative approaches for integrated sensors. The laser and detector modules were characterized independently and subsequently integrated to form a complete sensor. VCSELs with oxidation apertures measuring 4, 7, 14, and 20 /spl mu/m showed a lasing wavelength of /spl lambda/=773 nm, threshold current densities from 6400 to 1300 A/spl middot/cm/sup -2/, and maximum output powers of 0.6-4 mW, with transverse single-mode and multimode operation. PIN photodetectors were fabricated with integrated emission filters. Quantum efficiencies above 85% were observed with a dark current of 500 fA/(mm detector diameter). Complete sensor units were tested and near-infrared fluorescent molecules (IR-800) were detected. A theoretical detection limit of 10/sup 5/ fluorophores//spl mu/m/sup 2/ was determined. The compact parallel architecture, high-power laser, and low-noise photodetector make this sensor a good candidate for biomedical fluorescence-based sensing applications.     

Novel wavelength-resonant optoelectronic structure and itsapplication to surface-emitting semiconductor lasers

An optimised design for optoelectronic devices which depends on the interaction between an electromagnetic standing wave and the carrier population is described. The structure consists of quantum well layers spaced at one-half the wavelength of a selected optical transition in quantum wells. This spatial periodicity allows the amplifying or absorbing medium (quantum wells) to coincide with the peaks of the standing wave optical field in the Fabry-Perot cavity. In such a periodic medium, the gain or absorption for the selected wavelength is enhanced by a factor of two compared to a uniform medium. This concept was applied to fabricate a surface-emitting semiconductor laser in the GaAs/AlGaAs system. Lasing was achieved with the shortest gain medium length (320 nm) ever reported     

Low-threshold-current distributed-feedback InGaAsP/InP CW lasers

Distributed-feedback buried-heterostructure InGaAsP/InP lasers with room temperature CW threshold current as low as 50 mA, corresponding to a current density of 2.3 kA/cm2, are presented. CW operation in the temperature range from ?20°C to 58°C was confirmed.     

Analysis of distributed-feedback lasers using a recursive Green'sfunctional approach

A method is presented for obtaining the exact propagation constants (resonance wavelengths and threshold gains) for distributed-feedback lasers. The method is based on computing the exact Green's function for resonant cavities using a recursive Green's function approach. The net threshold gains of distributed-feedback lasers are calculated and compared with the results obtained using conventional coupled-mode theory. The comparison reveals that coupled-mode theory is weakest for aperiodic structures     

垂直腔面发射激光器DBR结构参数的优化设计

采用光学传递矩阵法 ,研究了生长偏差对分布布拉格反射 (DBR)结构反射特性的影响 ,并探讨了两种DBR结构改进方案。结果表明 ,周期厚度偏差将使DBR反射谱发生较大偏移 ,在相位匹配条件下减小高折射层厚度可以降低DBR吸收损耗、提高反射率 ,反向改变顶层和底层DBR周期厚度可以提高垂直腔面发射激光器边模抑制比     

Vertical-external-cavity surface-emitting lasers and quantum dot lasers

The use of cavity to manipulate photon emission of quantum dots (QDs) has been opening unprecedented opportunities for realizing quantum functional nanophotonic devices and quantum information devices....     

Rate-equation model for coupled-cavity surface-emitting lasers

We present a detailed theoretical study of a vertical-cavity surface-emitting laser (VCSEL) with two optically coupled, active cavities. The study is based on a rate-equation model written for carriers and photons under steady-state conditions. The model allows one to determine all the relevant parameters-carrier densities, gains, and output powers-starting from two input parameters: the injection currents in each cavity. The system of equations is solved for different operating regimes of the device and the results provided by the model are shown to be in very good qualitative and quantitative agreement with the experimental data.     

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     

垂直腔面发射激光器驻波图样与特性分析

根据电场在激光器腔镜反射的相位特性,研究了在不同腔镜组合情况下垂直腔面发射半导体激光器(VCSEL)几种可能的驻波图样。结果表明,驻波图样与两端反射镜顶层折射率的选择密切相关,有源层中心与驻波波腹的相对位置对VCSEL的限制因子以及阈值特性等有很大的影响。     

Few-mode vertical-cavity surface-emitting lasers for space-division multiplexing

In order to choose the proper radius of oxide aperture for few-mode vertical-cavity surface-emitting lasers (VCSELs), the influences of oxide aperture size on the multi-transverse-mode behaviors are investigated in detail. By establishing the effective refractive index model to simulate VCSELs with different radii of oxide apertures, the wavelength and corresponding order of different modes are obtained. VCSELs with three kinds of oxide apertures are manufactured. Then the multi-transverse-mode spectra and near-field are measured. It is found that when the radius is between 1.5 and 4.5 μm, few-mode VCSELs can be implemented. The 2.5 μm VCSEL manufactured in this paper only emits LP01 mode and LP21 mode. Since the space distance between the two modes is 2 μm, it is expected to realize direct-modulation few-mode VCSELs by channel etching or ion implantation between the two modes.     

Intracavity contacts for low-threshold oxide-confinedvertical-cavity surface-emitting lasers

Very low threshold vertical-cavity surface-emitting lasers are demonstrated using intracavity contacts, an upper dielectric Bragg reflector, and an undoped lower AlAs-GaAs Bragg reflector. The undoped lower mirror allows the demonstration of the highest differential efficiency yet achieved for sub-100-μA threshold, which is 60% for a 67-μA threshold. Devices with smaller output coupling show threshold current densities as low 98 A/cm², and a minimum threshold current of 23 μA for a small aperture     

High-power (>0.5-W CW) diode-pumped vertical-external-cavity surface-emitting semiconductor lasers with circular TEM/sub 00/ beams

We report demonstration of a new high-power semiconductor laser technology, the optically pumped semiconductor (OPS) vertical-external-cavity surface-emitting laser (VECSEL). Using diode laser pump, an OPS-VECSEL laser with a strain-compensated InGaAs-GaAsP-GaAs multiquantum-well (MQW) structure operated continuous-wave (CW) near /spl lambda//spl sim/1004 nm with record output power of 0.69 W in a TEM/sub 11/ mode, 0.52 W in a TEM/sub 00/ mode, and 0.37 W coupled to a single-mode fiber. It is feasible to produce greater than 1 W of power in a diffraction-limited circular beam from an efficient, compact, manufacturable and reliable OPS-VECSEL laser.     

A model for the above-threshold spectra of truncated-well distributed-feedback lasers

A detailed model for the above-threshold spectra of truncated-well distributed-feedback lasers is presented. Techniques are reported for fitting the model to experimental data. Using these techniques, the above threshold model is shown to predict correctly the evolution of below-threshold spectra to above threshold spectra. Key differences between below- and above-threshold spectra are identified and are shown to be a result of spatial hole burning. Estimations are obtained for the distribution of carriers longitudinally, for the longitudinal refractive index profile and for the longitudinally variant spontaneous emission rate in a laser by fitting the model to spectral data. Finally, the role of the standing wave in truncated-well distributed-feedback lasers is examined and is shown to be significant.     

GaInAsP/InP surface-emitting lasers with current confining structure

In order to reduce the threshold current of GaInAsP/InP surface-emitting (SE) lasers, we search for an effective current confining structure and examined several types; round-low-mesa, round-high-mesa/polyimide-buried, buried-heterostructure (BH), and planar-buried-heterostructure (PBH). The minimum threshold current was reduced down to 18 mA at 77 K and the threshold current density was estimated to be reduced to 3 kA/cm². The operating temperature has been raised to -10°C (263 K). The longitudinal-mode hopping was first observed for GaInAsP/InP SE lasers. The effective refractive index for GaInAsP/InP SE lasers was 4-5, that was almost the same as conventional edge-emitting lasers.