垂直腔激光器中弛豫振荡频率的优化控制

从垂直腔面发射的半导体激光器（VCSELs）的结构出发，利用增益与载流子密度的广义对数关系，借助小信号分析法，推出了直接调制情形下驰豫振荡频率的严格解析关系。分析指出，量子阱器件的光子寿命并非越短越好，欲提高VCSELs的驰豫振荡频率，除了增加注入电流，提高微分增益等基本途径外，控制器件的结构参数可使驰豫振荡频率达到极大值。同时，自发辐射因子的可控性，以及降低稳态载流子密度，也都是提高VCSELs驰豫振荡频率和拓宽调制带宽的有效措施。     

微波模拟信号调制下VCSEL腔结构参数的优化设计

以垂直腔面发射半导体激光器(VCSEL)为研究对象,采用Volterra方法结合速率方程理论,从器件设计角度,分析了在5 GHz微波信号模拟调制情况下出射面反射镜的反射率、有源区厚度和光限制因子对其二阶谐波失真、三阶谐波失真和三阶互调失真的影响.结果表明,对于垂直腔面发射半导体激光器,采取大反射率、小有源区厚度和小光限制因子有利于降低器件的谐波和互调失真.     

湿法腐蚀和干法刻蚀工艺对850 nmVCSEL高速调制性能的影响

垂直腔面发射激光器(VCSEL)以其低功耗、低阈值电流、高调制速率和易制作二维阵列器件等特点,广泛应用于短距离光互连领域.湿法腐蚀和干法刻蚀作为高速VCSEL台面结构制备的两种工艺,影响VCSEL氧化层的大小.文章研究了氧化层面积对寄生电容的影响,并计算得到7 μm氧化孔径下采用干法刻蚀工艺的垂直腔面发射激光器,相比较湿法腐蚀工艺,氧化层电容由902.23 fF减小至581.32 fF,谐振腔电容由320.72 fF减小至206.65 fF.通过对采用湿法腐蚀和干法刻蚀工艺制备的GaAs量子阱结构高速VCSEL进行小信号调制响应测试,结果表明,7μm氧化孔径下干法刻蚀VCSEL小信号调制带宽提高至16.1 GHz.     

外部光反馈对980nm垂直腔面发射激光器振荡特性的影响

研究了外部光反馈对980nm垂直腔面发射激光器(VCSEL)振荡特性的影响.计算了垂直腔面发射激光器及边发射半导体激光器的光反馈灵敏因子.基于复合腔理论,分析了外部光反馈对垂直腔面发射激光器的阈值电流及微分量子效率等振荡特性参数的影响.实验结果表明,当反馈率为10%时,垂直腔面发射激光器的阈值电流由0.63A下降至0.59A,同时斜率效率和输出功率也有所下降.实验结果和理论分析符合得较好.     

基于速率方程的垂直腔表面发射半导体激光器温度模型与仿真

建立了一个基于速率方程、考虑了热效应、可以模拟非直流 (即小信号和瞬态调制下 )特性 ,且适用于通用电路仿真器的垂直腔表面发射半导体激光器 (VCSEL)的简单等效电路模型。并通过PSPICE仿真结果与实验对比验证了模型的适用性     

聚合物热光相移器件的研究及其应用

给出了垂直腔面发射激光器的小信号电路模型和调制特性 ,调制特性用解析计算和电路模型模拟两种方法得到 ,解析计算和电路模型模拟的结果一致 ,实验证实了电路模型的正确性     

垂直腔面发射激光器的小信号电路模型和调制特性

给出了垂直腔面发射激光器的小信号电路模型和调制特性,调制特性用解析计算和电路模型模拟两种方法得到,解析计算和电路模型模拟的结果一致,实验证实了电路模型的正确性.     

垂直腔面发射激光器的小信号电路模型和调制特性

给出了垂直腔面发射激光器的小信号电路模型和调制特性,调制特性用解析计算和电路模型模拟两种方法得到,解析计算和电路模型模拟的结果一致,实验证实了电路模型的正确性.     

DBR微腔激光器典型参数的开关调制响应及控制

以微腔激光器的典型代表垂直腔面发射半导体激光器(VCSEL)为例，选择自发辐射因子为控制参数，数值模拟了大信号深度调制情形下VCSEL的非线性动力学特性，实现了类似于边缘发射激光器的分岔，周期加倍分岔，多稳和混沌状态的稳定控制，得到分岔点位置和周期轨道与控制参数的变化关系，以及相应地调制参量和自发辐射因子的取值范围，计算结果较好地拟合了文献实验结果。     

双区共腔双稳态激光器在光注入下的计算机模拟

本文对双区共腔半导体双稳态激光器在从吸收区背面及沿轴向外部光注入下的稳态及瞬态特性进行了计算机模拟,得到稳态光开关及光放大特性,瞬态情况下随着注入光的增强输出由近混沌状脉动到单峰快衰减张弛振荡而更强光注入时则仅存在一延迟过程.     

Large- and small-signal modulation properties of red (670 nm) VCSELs

The large- and small-signal properties of red GaInP-AlGaInP triple QW VCSELs (670 nm) were measured. For the fundamental mode the small signal bandwidth is 2 GHz. Large-signal modulation up to 1.5 Gb/s is achievable with a prebias. The turn-on delay of unbiased devices is found to saturate due to heating from the average of the data signal.     

Equivalent circuit for vertical cavity top surface emitting lasers

A small signal equivalent circuit for VCSELs is developed which provides an excellent fit to measured S-parameter data. Equivalent circuits were obtained for 6 mu m diameter, 780nm, gain guided VCSELs with 14GHz modulation bandwidth, the highest yet reported.<>     

Analysis of bit-error rate of vertical-cavity surface-emitting lasers modulated at high speed

A theoretical study of single and multimode vertical-cavity surface-emitting lasers (VCSELs) subject to pseudorandom modulation of the current at a rate of 10 Gb/s is performed. Eye diagrams, probability density functions of the power at the decision time, averaged turn-on delay, and timing jitter are analyzed for different values of the on- and off-state currents. Bit sequences where errors occur are identified. Extensive simulations have been performed to obtain the bit-error rate (BER) for the back-to-back configuration. We find that the BER performance of single-mode VCSELs is better than the one obtained with multimode VCSELs when the off-state current is smaller than the threshold current. The same result is obtained when the off-state current is larger than the threshold value, providing that the on-state current is large enough. However, BER in single-mode VCSELs is greater than in multimode VCSELs when the off-state current is equal to the threshold current. BER performance is also better for multimode VCSELs when the off-state current is larger than the threshold value, if the on-state current is small enough.     

Fabrication and characteristics of high-speed implant-confined index-guided lateral-current 850-nm vertical cavity surface-emitting lasers

Process technology of high-speed implant-apertured index-guide lateral-current-injection top dielectric-mirror quantum-well 850-nm vertical cavity surface-emitting lasers (VCSELs) has been developed. Oxygen and helium implantation for aperture definition and extrinsic capacitance reduction, dielectric mirror formation, p- and n-ohmic contact formation, VCSEL resistance, and thermal analysis were investigated. Employing this technology, GaAs/AlGaAs-based 850-nm VCSELs with small signal modulation bandwidths up to 11.5 Gb/s and an eye diagram generated at 12 Gb/s by a pseudorandom bit sequence of 2/sup 31/-1 were achieved. The bit-error rates were below 10/sup -13/. The threshold current is as low as 0.8 mA for 7-/spl mu/m-diameter current apertures and typical slope efficiencies of 0.45-0.5 mA/mW were obtained.     

Effects of the spatial nonuniformity of optical transverse modes on the modulation response of vertical-cavity surface-emitting lasers

We present detailed numerical simulations to clarify the important role that the nonuniformity of the transverse optical mode plays for the high-speed response of oxide-confined vertical-cavity surface-emitting lasers (VCSELs). The comprehensive laser diode simulator, Minilase, as well as a one-dimensional rate equation model are used as simulation tools. It is demonstrated that, due to the nonuniform optical intensity, carriers at different locations in the quantum well have different stimulated recombination rates, and therefore exhibit different dynamic responses to small signal modulation. This nonuniformity causes an overdamping of the relaxation oscillation, as well as a low-frequency roll-off of the modulation response. Due to this nonlinear effect, the intrinsic maximum bandwidth of VCSELs with oxide confined apertures is shown to be much smaller than predicted by the conventional rate equation model which assumes uniform optical intensity. We further demonstrate that this damping effect can be greatly reduced by restricting the current injection to be well within the transverse optical field. This is achievable by using tapered oxides to make the electrical aperture smaller than the optical aperture, which thereby improves the modulation bandwidth significantly.     

Dynamic coherence measurements of index- and gain-guided VCSELs

Coherence properties of several different types of VCSELs are examined with constant and modulated injection current with a bandwidth typical of that used in telecommunications. Large signal modulation of index-guided single transverse-mode VCSELs is found to reduce the coherence length by more than a factor of ten relative to the direct current configuration. Multiple transverse-mode index-guided VCSELs have similar coherence lengths when operated dc and modulated, and shorter than that of the single transverse-mode VCSELs. Gain-guided multiple transverse-mode VCSELs also have shorter coherence lengths than single transverse-mode VCSELs and under modulation can have coherence lengths as low as 0.5 cm.     

120°C 20 Gbit/s operation of 980 nm VCSEL

980 nm VCSELs show under 20 Gbit/s large signal modulation clearly open eyes without adjustment of the driving conditions between 0 and 120°C.     

High performance selectively oxidized VCSELs and arrays forparallel high-speed optical interconnects

High-bandwidth single-mode selectively oxidized vertical-cavity surface-emitting laser (VCSEL) arrays operate at 980 nm or 850 nm emission wavelength for substrate or epitaxial side emission. Coplanar feeding lines and polyimide passivation are used to reduce electrical parasitics in top-emitting GaAs and bottom-emitting InGaAs VCSELs. To enhance fundamental single-mode emission for larger devices of reduced series resistance a surface relief transverse mode filter is employed. Fabricated VCSELs are applied in various interconnect schemes. InGaAs quantum-well based VCSELs at 935 nm emission wavelength are investigated for use in perfluorinated graded-index plastic-optical fiber (GI-POF) links. We obtain a 7 Gb/s pseudo random bit sequence (PRBS) nonreturn-to-zero (NRZ) data transmission over 80 m long 155 μm diameter GI-POF. We investigate data transmission over standard 1300 nm, 9 μm core diameter single-mode fiber with selectively oxidized single-mode GaAs and InGaAs VCSELs. We achieve biased 3 Gb/s and bias-free 1 Gb/s pseudo-random data transmission over 4.3 km at 830 nm emission wavelength where a simple fiber mode filter is used to suppress intermodal dispersion caused by the second order fiber mode. For the first time, we demonstrate 12.5 Gb/s data rate transmission of PRBS signals over 100 m graded-index multimode fiber or 1 km single-mode fiber using high performance single-mode GaAs VCSELs of 12.3 GHz modulation bandwidth emitting at λ=850 nm     

Frequency response of polarization switching in vertical-cavity surface-emitting lasers

We present an experimental study of the current-driven polarization modulation properties of VCSELs. In some VCSELs, abrupt polarization switching (PS) between two polarization modes is observed at a particular value of the pump current. We investigate the dynamics and the associated dominating time scales of PS as these features are strongly linked with the underlying physical mechanism causing the PS. To this end, we measure both for gain- and index-guided VCSELs the critical modulation amplitude necessary to steadily force PS back and forth across the PS point as a function of the modulation frequency. This yields the current-driven polarization modulation frequency response, which we compare with the thermal frequency response of the studied devices. The dynamic behavior turns out to be strikingly different for the different VCSEL types. Thermal effects only play a minor role in the PS in our index-guided VCSELs, while they really seem to lie at the origin of PS in the gain-guided VCSELs. By implementing this in a rate-equation based theoretical model, we are able to explain the peculiarities of the measured response curves and to reproduce the experimental findings.     

Dynamic behavior of fundamental-mode stabilized VCSELs using a shallow surface relief

An extensive theoretical study was performed on the dynamic behavior of 850-nm-wavelength oxide-confined fundamental-mode stabilized vertical-cavity surface-emitting lasers (VCSELs), using a shallow surface relief. The surface relief is used to provide lower mirror loss for the fundamental mode, thus acting as a mode discriminator. In this way, single-mode operation at high power levels can be obtained. We utilized a comprehensive model that includes the detailed epitaxial layer structure and device geometry when calculating the optical fields and that accurately accounts for the dynamic effects of carrier density and temperature on the modal distributions. Modulation response, eye diagrams, bit error rate (BER), and relative intensity noise (RIN) were simulated and compared to the performance of VCSELs without a mode discriminator, i.e., conventional multimode VCSELs. The fundamental-mode stabilized VCSELs are associated with a higher out-coupling, which lowers the relaxation oscillation frequency and damping, and strong spatial hole burning, which induces a low-frequency roll-off in the modulation response and contributes to the damping of the relaxation oscillation at low bias. However, their dynamics is fully competitive with conventional multimode VCSELs at both 2.5 and 10 Gb/s although they exhibit a slightly higher eye closure. We only found a 0.5-dB power penalty in the BER. The RIN is enhanced, with a peak that is about 10-15 dB higher, caused by the lower damping of the relaxation oscillation. It should be noted that in the comparison we assume that all modes are equally captured from the multimode VCSEL. A mode-selective loss can severely degrade its performance.