Comparison of Usability of Oxide Apertures and Photonic Crystals Used to Create Radial Optical Confinements in 650-nm GaInP VCSELs

Threshold characteristics of GaAs-based 650-nm gallium indium phosphide (GalnP) vertical-cavity surface-emitting diode lasers (VCSELs) with two different optical confinement structures are investigated with the aid of a self-consistent, fully-physical VCSEL model. Efficacy of the optical confinement introduced by the oxide aperture is compared with an alternative single-defect photonic-crystal design with holes etched throughout the whole VCSEL. Initially, photonic-crystal VCSEL reveals 10% lower threshold electrical power than that of the analogous oxide-confined VCSEL. Further optimization of the current injection allows for an additional 20% threshold reduction. The photonic-crystal confinement concept appears to be a very prospective solution for VCSEL configurations, for which oxidation is unfeasible, e.g., for possible nitride or phosphide VCSELs.     

980nm垂直腔面发射激光器的研制

采用低压金属有机化合物气相外延生长技术,应用AlAs/AlGaAs选择性湿氮氧化工艺实现光、电限制，制备出具有一定性能的980nm内腔接触式氧化物限制型顶发射980nm垂直腔面发射激光器(VCSEL). 通过制备不同氧化孔径尺寸的VCSEL，分析了氧化孔径尺寸大小对器件的阈值电流和串联电阻的影响. 获得的最小阈值电流为0.8mA，最大光输出功率达8mW.     

Vertical-cavity surface emitting lasers: moving from research tomanufacturing

After more than a decade of research, vertical-cavity surface emitting lasers (VCSELs) are making the transition into the manufacturing arena. We review unique VCSEL properties found in their structure, growth, fabrication, and performance, which have precipitated their commercial acceptance. The short optical cavity that is formed between two distributed Bragg reflector mirrors is a distinctive VCSEL attribute. The spectral alignment between the resonance of the optical cavity formed by these mirrors and the laser gain bandwidth is shown to influence the VCSEL performance. Thus, epitaxial VCSEL growth by metalorganic vapor-phase epitaxy aided by in situ reflectance monitoring is discussed with an emphasis on uniformity and reproducibility. We also describe the fabrication techniques and VCSEL structures used to obtain transverse electrical and optical confinement, including etched air-post, ion-implanted, and selectively oxidized VCSELs. For the latter, wet oxidation of AlGaAs to form buried-oxide apertures has enabled record laser performance, such as ultralow threshold current and high efficiency. Numerous applications for VCSELs have been identified that leverage their manufacturing and performance advantages     

Design, fabrication, and performance of infrared and visiblevertical-cavity surface-emitting lasers

This paper discusses the issues involving the design and fabrication of vertical-cavity surface-emitting lasers (VCSELs). A review of the basic experimental structures is given, with emphasis on recent developments in distributed Bragg reflectors, gain media, as well as current and optical confinement techniques. The paper describes present VCSEL performance, in particular, those involving selective oxidation and visible wavelength operation     

Loss-Induced Confinement in Photonic Crystal Vertical-Cavity Surface-Emitting Lasers

Through calculations and comparison with experimental results, we verify that loss introduced by an etched photonic crystal in a vertical-cavity surface-emitting laser (VCSEL) contributes significantly to the transverse optical confinement and supported modes. The optical loss is examined theoretically using a simple waveguide model from the scalar Helmholtz equation. The modal loss of fabricated lasers is extracted from the observed spectral-mode splitting. The effect of modal loss on the slope efficiency and modal behavior is examined. The model is found to be consistent with experimental measurements, and provides a means of accurate design of single-mode photonic crystal VCSELs.      

High-speed digital modulation characteristics of oxide-confined vertical-cavity surface-emitting lasers-numerical simulations consistent with experimental results

The vertical-cavity surface-emitting laser (VCSEL) is a preferred light source for short-distance high-speed fiber-optic communication links. We simulate the digital modulation behavior of typical oxide-confined VCSELs under realistic working conditions with a comprehensive model that includes the detailed geometry when calculating the optical fields and that accurately accounts for the dynamic effects of carrier density and temperature on the modal distributions. The intrinsic output characteristics of single- and multimode VCSELs were studied as functions of bias and modulation depth under a 2/sup 7/-1 pseudorandom bit sequence current modulation at 2 and 10 Gb/s. The data were used to create numerical eye diagrams that show, e.g., the significant impact of the bit pattern history and the noise on the timing jitter in both single- and multimode VCSELs. For the single-mode VCSEL, the choice of the bias current and modulation depth was less critical due to its higher damping of the relaxation oscillations. The simulated VCSELs were fabricated and experimentally evaluated. The measured eye diagrams showed the same characteristic features as those in the simulations.     

High-yield flip-chip bonding and packaging of low-threshold VCSEL arrays on sapphire substrates

Oxide-confined top-emitting 850 nm and bottom-emitting 980 nm vertical-cavity surface-emitting laser (VCSEL) 8/spl times/8 arrays were designed and fabricated for applications of optical interconnects. The arrays were flip-chip bonded onto sapphire substrates that contain complimentary metal-oxide-semiconductor (CMOS) driver and fan-out circuitries. The off-sited bonding contacts and minimized bonding force produced very high yield of the hybridization process without causing damage to the VCSEL mesas. The hybridized devices were further mounted either on printed circuit board (PCB) or in 68-pin pin-grid-array (PGA) packages. The transparent sapphire substrate allowed optical outputs from the top-emitting VCSEL arrays to transmit directly through without additional substrate removal procedure. Lasing thresholds below 250 /spl mu/A for 850 nm VCSELs and 800 /spl mu/A for 980 nm VCSEL were found at room temperature. The oxide confinement apertures of VCSELs were measured to be around 6 /spl mu/m in diameter. High-speed data transmission demonstrated a bandwidth of up to 1 Gbits/s per channel for these hybridized VCSEL transmitters.     

Influences of the Current Transverse Profile on the Transverse Mode Competition of VCSELs Diodes

A spatially independent model of vertical-cavity surface-emitting lasers (VCSELs) is derived by integrating the spatially dependent rate equations over the cross section of the cavity of a VCSEL. The angular and radial non-uniformities of the injection current are taken into account. The well-known LP modes of a weakly-guiding cylindrical waveguide are employed to describe the transverse modal structure in the VCSEL cavity. This model is solved in a self-consistent way by using the 4th order Runge-Kutta method. The dependence of transverse mode competition on the current intensity, the angular and radial non-uniformities of the injection current, and the geometrical parameters of the electrical contact are thoroughly investigated and analyzed. The results are useful to the optimum design of the optical transverse modal structure of VCSELs.     

Antiresonant reflecting optical waveguide-type vertical-cavity surface emitting lasers: comparison of full-vector finite-difference time-domain and 3-D bidirectional beam propagation methods

The cold-cavity modal characteristics of an antiresonant optical waveguide-type cylindrical vertical-cavity surface-emitting laser (VCSEL) are investigated through numerical simulations using a three-dimensional (3-D) bidirectional beam propagation method (BD-BPM) and a full-vector axisymmetric finite-difference time-domain (FDTD) method. Good agreement between the BPM- and FDTD-computed radial mode profiles as well as the mode-dependent radiation losses is obtained. The results of this paper establish the accuracy of the BD-BPM technique for simulating this class of devices and confirm effective-index method predictions that antiresonance conditions for cylindrical geometry devices (i.e., VCSELs) differ from those of planar geometry devices (i.e., edge emitters).     

"Anti" up the aperture [antiguided VCSEL structures]

Coupled vertical cavity surface-emitting laser (VCSEL) arrays are an attractive means to increase the coherent output power of VCSELs. Single-mode VCSELs, with output powers greater than 10 mW, would be useful as telecommunication transmitters /spl lambda/=1.3-1.55 /spl mu/m) or sources for optical interconnects. Commercially available single-mode VCSELs, even at shorter wavelengths /spl lambda/=0.85 /spl mu/m), are generally limited to a few milliwatts of output power. The conventional VCSEL structure incorporates a built-in positive-index waveguide, designed to support a single fundamental mode. Promising results in the 3-5 mW range (/spl lambda/=0.85 /spl mu/m) have been obtained from wet-oxidized, positive-index-guided VCSELs with small emission apertures (less than 3.5 /spl mu/m-dia). The small aperture size leads to a high electrical resistance and high current density, which can impact device reliability. By contrast, antiguided VCSEL structures have shown promise for achieving larger aperture single-mode operation. To obtain high single-mode powers with a larger emitting aperture, the use of a negative-index guide (antiguide) is beneficial. This paper discusses antiguided structures and some of their advantages when incorporated in 2-D VCSEL array structures.     

Spatially dependent noise model for vertical-cavity surface-emitting lasers

We present a comprehensive noise model for vertical-cavity surface-emitting lasers (VCSELs). The time-domain model accounts for the stochastic fluctuations in the local carrier density in the separate confinement heterostructure and quantum wells, and in the modal intensity and phase of both the internal and the out-coupled optical field. In this work, we consider these fluctuations to be caused by the temporal uncertainty of the processes that supply or consume carriers and photons, such as carrier diffusion and photons escaping the cavity, and the processes that create or annihilate carriers and photons, such as stimulated emission and absorption. The noise model is based on a deterministic quasithree-dimensional dynamic model that treats the carrier transport, heat generation and dissipation, and optical fields in the device. Langevin noise terms are derived and added to the rate equations in the numerical solution. The noise model is applied to simulate the noise characteristics of fundamental-mode stabilized VCSELs with a shallow, mode discriminating, surface relief. The relative intensity noise and frequency noise of the output are calculated. From the latter, the linewidth of the VCSEL can be estimated. The results are compared with those of conventional multimode VCSELs.     

Reliability assessment of 1.55-μm vertical cavity surface emitting lasers with tunnel junction using high-temperature aging tests

In this paper, the long-term reliability of all monolithic 1.55-μm etched-mesa vertical cavity surface emitting lasers (VCSELs) with tunnel junction is investigated via high-temperature storage tests and accelerated life tests. Characteristic variations depend on the operating conditions are examined via the threshold current, the optical output power, and the dark current. The median device lifetime is extrapolated and the activation energy of the VCSELs is calculated based on the reliability testing results. In addition, the degradation mechanism of the tested VCSELs is analyzed using the correlation between the current-voltage characteristics (I-V) and the device lifetime. From these results, the long-term reliability of the VCSEL test structures for high-speed optical communication systems can be determined and the device parameters, such as dark current, can be used as a monitoring factor for estimating reliability of the VCSELs.     

Nonlinear dynamics of vertical-cavity surface-emitting lasers

The dependence of the transient response of a vertical-cavity surface-emitting laser (VCSEL) on its aperture size is investigated subject to direct current modulation and external optical feedback. It is shown that lasers with small aperture size suppress higher order bifurcations and chaos even under large-signal modulation and external optical feedback. Furthermore, the noise characteristics of VCSELs under the influence of external optical feedback are studied via the calculation of relative intensity noise. It is found that the level of external optical feedback for the onset of coherence collapse is high for devices with small aperture size. On the other hand, the small-signal response of lasers is also analyzed through the calculation of third-order harmonic distortion. It is shown that harmonic distortion is minimized in small devices. Therefore, VCSELs with small aperture size have better immunity to irregular response under direct current modulation and external optical feedback     

Ultralow-threshold sapphire substrate-bonded top-emitting 850-nm VCSEL array

Oxide-confined top-emitting vertical-cavity surface-emitting-laser (VCSEL) 8 /spl times/ 8 arrays were designed and fabricated with ultralow thresholds. The arrays were flip-chip bonded onto sapphire substrates and mounted in pin-grid-array packages as optical transmitter arrays. By using the offset-contact bonding process, we were able to obtain very high yield for hybridized devices without damaging the VCSEL mesas. Room-temperature lasing thresholds below 70 /spl mu/A were found from some of these packaged VCSELs with measured oxide apertures 2.6 /spl mu/m in diameter. The emission spectrum at an injection current of 70 /spl mu/A showed a full-width at half-maximum linewidth of less than 2.5 A. Polarization properties were also confirmed from the output of the device. The superior performance was attributed to the optimized size and placement of the confinement aperture and the precise alignment of the gain profile of the active region to the mode of the resonant cavity.     

Recent Advances of VCSEL Photonics

A vertical-cavity surface emitting laser (VCSEL) was invented 30 years ago. A lot of unique features can be expected, such as low-power consumption, wafer-level testing, small packaging capability, and so on. The market of VCSELs has been growing up rapidly in recent years, and they are now key devices in local area networks using multimode optical fibers. Also, long wavelength VCSELs are currently attracting much interest for use in single-mode fiber metropolitan area and wide area network applications. In addition, a VCSEL-based disruptive technology enables various consumer applications such as a laser mouse and laser printers. In this paper, the recent advance of VCSEL photonics will be reviewed, which include the wavelength extension of single-mode VCSELs and their wavelength integration/control. Also, this paper explores the potential and challenges for new functions of VCSELs toward optical signal processing     

Selectively etched tunnel junction for lateral current and optical confinement in InP-based vertical cavity lasers

We demonstrate a thin, selectively lateral-etched, AlIn(Ga)As tunnel-junction (TJ) layer as a current and optical confinement aperture in the InP-based long-wavelength vertical cavity surface-emitting lasers (VCSELs). A high etch selectivity was demonstrated by etching the aperture a distance of several microns without affecting the surrounding InP etch-resistant layer. Edgeemitting lasers enclosing the TJ aperture showed high injection efficiency and low current spreading underneath the aperature. Single-mode continuous-wave operation of a 1.55-μm VCSEL was demonstrated successfully with a room-temperature differential efficiency of 21% using a 6-μm-wide TJ aperature.     

质子注入对GaAs基器件隔离研究

质子注入参数对注入型垂直腔面发射激光器（Vertical cavity surface emitting laser, VCSEL）的电流限制孔径位置及电流限制效果具有较大影响。文中从质子注入的能量和剂量及其相互作用对VCSEL电流限制孔径的影响规律及机制出发,通过理论模拟分析了注入参数对质子分布及注入区电阻值的影响。在此基础上,采用VCSEL外延片进行了质子注入实验研究。实验结果和理论分析均表明:注入区电流隔离效果及质子分布受注入能量和剂量共同调控。当注入参数为320 keV、8×1014 cm?2时,经430 ℃、30 s退火后可得到结深约0.7 μm,平均射程距有源区约1.3 μm,电阻值达4.6×107 Ω?cm2的质子注入区。使用该参数制备的VCSEL器件实现了较好的激光激射,证明该质子分布不仅可避免VCSEL有源区损伤,而且能实现较好的电流隔离效果,满足VCSEL电流限制孔径的制备要求。研究结果对质子注入型VCSEL的芯片结构及工艺优化具有重要指导意义。     

Effect of proton implantation on the degradation of GaAs/AlGaAsvertical cavity surface emitting lasers

The electroluminescence (EL) technique is used to analyse the degradation mode of VCSELs with proton implantation for current confinement. Point defects generated by the implantation in the active layer are believed to affect the VCSEL long term reliability     

High performance of 1.55-μm buried-heterostructurevertical-cavity surface-emitting lasers

We report a record low threshold current of 1.55-μm vertical-cavity surface-emitting laser (VCSEL). Thin-film wafer-fusion technology enables InP-based buried heterostructure VCSELs to be fabricated on GaAs-AlAs distributed Bragg reflectors. Threshold current density is independent of mesa size, and a 5-μm VCSEL exhibits a threshold current as low as 380 μA at 20°C and a single transverse mode up to the maximum optical output power under continuous-wave operation     

单面键合面发射激光器的研制与分析

键合长波长垂直腔面发射激光器(VCSEL)的研制对于光通信的发展具有重要意义,可以有效克服传统外延生长方法的诸多难題.文章通过对布喇格反射镜、有源区和光学腔的设计,结合键合技术进行工艺设计,研制出单面键合长波长垂直腔面发射激光器,并对器件进行了光泵浦测试与分析.器件的光泵激射证明结构及工艺设计是合理的,键合后的界面可以承受腐蚀、剥离、氧化等后续工艺,且键合界面未对器件光学性能造成明显不良影响.