Theoretical Studies of Polarization Bistability in Birefringent ARROW VCSELs

The polarization bistable characteristics of birefringent antiresonant reflection optical waveguide (ARROW) vertical-cavity surface-emitting lasers (VCSELs) under external optical injection is studied and juxtaposed theoretically with an equivalent index-guided device. The simulation results show that ARROW VCSELs exhibit bistable behaviour and have wider hytheresis loops. The wider hytheresis loop in ARROW VCSEL is attributed to the difference in the lateral profiles of the two polarization modes, resulting in the accentuation of the optical gain difference between the two polarizations. This is because the introduction of a birefringent ARROW has an equivalent effect of creating an anisotropic geometrical cavity in the laser structure. Our theoretical studies also show that the polarization bistability characteristics of ARROW VCSELS are not sensitive to small values of birefringence and can be easily tailored by varying the cladding thicknesses, an option that is not available to index-guided VCSELs     

Polarization selection in VCSELs due to current carrier heating

The problem of polarization switching of light from a vertical cavity surface emitting laser (VCSEL) is discussed. It is shown that heating of holes in the p-type distributed Bragg reflector and of electrons and holes in the quantum wells of the active region lead to switching of the polarization of the VCSEL. The model developed here makes it possible to explain the results of experiments on switching of the polarization of VCSELs at fixed active region temperatures. Fiz. Tekh. Poluprovodn. 33, 887–893 (July 1999)     

Polarization dependence of photo-detection in strained multiplequantum-well semiconductor lasers

We investigated polarization dependence of photo-detection in strained layer multiple quantum-well (SL-MQW) lasers for time compressive multiplex (TCM) application. The polarization dependence of SL-MQW lasers is larger than that of bulk lasers because of the quantum effect. To improve the polarization dependence of photo-detection, we theoretically and experimentally analyzed the effect of strain quantity on the polarization dependence, and found that large tensile strained quantum-well structure is suitable for the small polarization independence of 0.8 dB and low threshold current characteristics. Moreover, we achieved smaller polarization dependence less than 0.5 dB by applying reverse bias voltage in the photo-detection mode     

Transverse mode control in long-monolithic-cavity VCSELs with temperature-profile control

Transverse mode control by using temperature-profile control in VCSELs with a large active area of more than 10 /spl mu/m diameter is demonstrated. From spectrum measurement, higher-order mode suppression was observed as power increased for a heater introduced for temperature-profile control. The far-field pattern without heating had two peaks and it changed to a Gaussian shape with heating.     

Polarization properties of four-wave mixing in strained semiconductor optical amplifiers

We present a theoretical and experimental study of the polarization properties of the four-wave mixing susceptibility of highly-strained multiquantum-well optical amplifiers and show how the intensity and polarization of the four-wave mixing signal depend on the polarization of the input waves. We demonstrate the validity of our model by generating a wavelength-converted signal having a polarization orthogonal to that of the pump wave at the output of the amplifier. In addition, we discuss the possibility of making the conversion efficiency independent of the input signal polarization by proper selection of the pump polarization.     

Polarisation control in VCSELs by elliptic surface etching

850 nm-wavelength vertical-cavity surface-emitting lasers (VCSELs) with an elliptical shallow surface relief having various aspect ratios and orientations have been fabricated. Using appropriate etch dimensions, VCSELs of up to 12.5 μm active diameter are forced to operate on the fundamental mode for a certain current range. By aligning the longer axis of the etched ellipse with the [011] or [011¯] crystal axis, the polarisation of the fundamental mode is pinned accordingly with a polarisation suppression ratio of ~30 dB     

Threshold control in VCSELs by proton implanted depth

The proton implantation is one of key procedures to confine the current diffusion in vertical cavity surface emitting lasers(VCSELs),in which the proton implanted depth and profile are main parameters.Threshold characteristics of VCSELs with various proton implanted depths are studied after optical,electrical and thermal fields have been simulated self-consistently in three dimensions.It is found that for VCSELs with confinement radius of 2 mm,increasing proton implanted depth can reduce the injected curren...     

Influence of Low-Frequency Modulation on Polarization Switching of VCSELs Subject to Optical Feedback

The influence of low-frequency modulation on the polarization switching (PS) properties of vertical-cavity surface-emitting lasers (VCSELs) under optical feedback has been investigated experimentally. The current modulation frequency has a large impact on the PS of VCSELs even in the low-frequency range between 1 and 100 kHz. Thermal effects play an important role in this phenomenon.     

Polarization Control in Buried Tunnel Junction VCSELs Using a Birefringent Semiconductor/Dielectric Subwavelength Grating

We present long-wavelength InGaAlAs-InP vertical-cavity surface-emitting lasers (VCSELs) with a buried tunnel junction (BTJ) and a well-defined polarization accomplished by a semiconductor/dielectric subwavelength grating (SWG). The grating is incorporated in the inner VCSEL cavity and exhibits an effective birefringence for polarizations parallel and perpendicular to the grating grooves. Theoretical modeling leads to distinct design rules for VCSELs with grating structure that deviate from the conventional design without grating. Due to the large polarization-mode separation, lasing activity is enabled only for one polarization mode. BTJ-VCSELs with properly chosen SWG parameters show predictable and full polarization stability. In addition, the relevant device parameters such as threshold current are comparable to conventional BTJ-VCSELs.     

Single-mode operation and transverse-mode control in VCSELs induced by frequency-selective feedback

An experimental study of a vertical-cavity surface-emitting laser with frequency-selective feedback is reported. We show that we can force the laser to emit in its fundamental transverse mode or in a higher order transverse mode and that we can also control the polarization emitted in the fundamental one. We obtain single fundamental-mode operation within a large range of injection current values (almost /spl ap/2.5 I/sub th/) and a maximum optical power of 2.7 mW. In this current range, the output is found to be stable.     

Unstable waveguiding in VCSELs

It has been known for a long time that unstable waveguiding can occur in planar, gain guided stripe lasers. The possible existence of instabilities can be demonstrated by a very simple waveguide calculation. In this letter the demonstration of possible instabilities is extended to structures with cylindrical geometry. On the basis of these results it is concluded that unstable waveguiding may exist in cylindrical vertical cavity surface emitting lasers     

Polarization control for coherent communications

Two practical implementations of endless polarization control are described. The first approach uses polarization maintaining fiber transducer, while the second uses an integrated optic lithium niobate device. In order to characterize the lithium niobate device in detail, a technique for analyzing the birefringence as a function of the applied voltages was developed, and the measured performance of the devices is presented. Fractional-wave controllers for both static and endless control applications are considered, and design rules for maximum wavelength-window and minimum loss fiber-loop polarization adjusters are given. Endless control using various configurations of the three types of transducers is discussed, and it is shown how apparently different schemes are closely related     

Continuous-wave mid-infrared VCSELs

We report the continuous-wave operation of an optically pumped mid-infrared (mid-IR) vertical-cavity surface-emitting laser (VCSEL). The active region consisting of type-II antimonide quantum wells with a “W” configuration occupies a cavity formed by a semiconductor bottom mirror and dielectric top mirror. The emission wavelength of 2.9 μm is nearly independent of temperature (dλ/dT≈0.09 nm/K) compared to type-II edge-emitters and the multimode linewidth is narrow (2.9 nm). At T=78 K, the threshold pump intensity is ≈940 W/cm², the peak output power from a 50-μm spot is 45 mW, and the differential power conversion efficiency is 4.5%. Lasing is observed up to T=160 K     

Bistability in bipolar cascade VCSELs

Measurement results on the formation of bistability loops in light versus current and current versus voltage characteristics of two-stage bipolar cascade vertical-cavity surface-emitting lasers (VCSELs) are presented. It is observed that the bistable behaviour is the more pronounced the more the cavity resonance is blueshifted with respect to the gain maximum of the quantum wells. In addition, the slope efficiency increases by more than a factor of 1.5 compared to conventional VCSELs owing to carrier recycling     

相干光检测系统中的偏振控制

相干光检测可以提高光通信系统的接收灵敏度,改善系统的性能;但大气的退偏效应使光信号通过大气传输后偏振状态随机变化,难以实现两束光偏振态一致的要求,直接影响该系统的检测效率。文中讨论了相干光通信系统偏振控制的新方法,在此基础上建立了偏振控制数学模型。选择挤压光纤偏振控制器作为该方案的偏振控制器件,选择模拟退火算法为该系统控制算法,并利用改进后的模拟退火算法实现偏振态的自动控制,整个控制过程采用盲搜索,没有具体参量的变化。仿真结果表明:该方法适合相干光通信,达到了偏振控制的目的。     

垂直腔面发射激光器的热学特性

通过求泊松方程、电流密度方程、载流子扩散方程以及有源层结压降方程自洽解的方法,计算了垂直腔面发射激光器(VCSEL)的电势分布,进而求解热传导方程,得到VCSEL的温度分布.详细分析了注入电流密度小于或等于阈值电流密度时,晶片键合结构垂直腔面发射激光器的键合界面阻抗、氧化层限制孔径、外加电压以及分布布拉格反射镜的热导率的大小对VCSEL内部温度分布的影响.     

VCSEL技术及其在光互连中的应用

垂直腔表面发射激光器（VCSELs）是并行光互连、高速光交换系统中最合适的光源。它具有易耦合、易封装和测试的优点。由于其独特的性能，可以较为方便地制作二维激光器阵列。基于VCSEL阵列的光电混合集成及并行光互连是当前的研究热点。本文介绍了VCSEL基本结构及设计中的关键技术，并对VCSEL在光互连中的应用进行了研究。