Polarization Switching in Quantum-Dot Vertical-Cavity Surface-Emitting Lasers

We demonstrate experimental evidence of polarization switching accompanied by polarization-mode hopping in quantum-dot vertical-cavity surface-emitting lasers. In our case, the polarization switching is associated with a change of linearly polarized light to elliptically polarized one, hence switching takes place between elliptically polarized states. Current-modulation measurements show that the polarization switching is of thermal origin.      

High-Speed Quantum-Dot Vertical-Cavity Surface-Emitting Lasers

We report on recent progress in high-speed quantum-dot (QD) vertical-cavity surface-emitting lasers (VCSELs). Advanced types of QD media allow an ultrahigh modal gain, avoid temperature depletion, and gain saturation effects. Temperature robustness up to 100degC for 0.96-1.25 mum range devices is realized in the continuous wave (cw) regime. An open eye 20 Gb/s operation with bit error rates better than 10^-12 has been achieved in a temperature range 25degC - 85degC without current adjustment. A different approach for ultrahigh-speed operation is based on a combination of the VCSEL section, operating in the CW mode with an additional section of the device, which is electrooptically modulated under a reverse bias. The tuning of a resonance wavelength of the second section, caused by the electrooptic effect, affects the transmission of the system. The approach enables ultrahigh-speed signal modulation. 60 GHz electrical and ~35 GHz optical (limited by the photodetector response) bandwidths are realized.     

Characteristics of InGaAs Submonolayer Quantum-Dot and InAs Quantum-Dot Photonic-Crystal Vertical-Cavity Surface-Emitting Lasers

We have made InGaAs submonolayer (SML) quantum-dot (QD) and InAs QD photonic-crystal vertical-cavity surface-emitting lasers (PhC-VCSELs) for fiber-optic communications in the 990 and 1300 nm ranges, respectively. The active region of the InGaAs SML QD PhC-VCSEL contains three InGaAs SML QD layers, with each of the SML QD layer formed by alternating depositions of InAs and GaAs. The active region of the InAs QD PhC-VCSEL contains 17 undoped InAs-InGaAs QD layers. Both types of QD PhC-VCSELs exhibit single-mode characteristics throughout the current range, with side-mode suppression ratio (SMSR) larger than 35 dB. A maximum output power of 5.7 mW has been achieved for the InGaAs SML QD PhC-VCSEL. The near-field image study of the QD PhC-VCSELs indicates that the laser beam is well confined by the photonic-crystal structure of the device.     

Polarization Switching in Vertical-Cavity Surface-Emitting Lasers by Asymmetrical Current Injection

Polarization switching between two orthogonal linear polarizations was experimentally demonstrated in newly designed 980-nm vertical-cavity surface-emitting lasers ( VCSELs ). A square-shaped mesa structure was prepared in a p-type distributed Bragg reflector mirror. Four p-side electrodes were placed in contact with the four sides of the square mesa. When the same current was injected into the four electrodes, the VCSEL oscillated with 0$^{circ}$ or 90$^{circ}$ linear polarizations. When the current was asymmetrically injected (the same current for two electrodes on the opposite sides of the square, but different for neighboring electrodes), the direction of the linear polarization became perpendicular to the direction of the line connecting the two electrodes injected with the larger current. It was confirmed that the VCSELs oscillated with a single frequency and the lowest order transverse mode in all cases.      

纳米孔径垂直腔面发射激光器的制备及特性

在850 nm波长垂直腔面发射激光器的基础上制备了纳米孔径垂直腔面发射激光器.当小孔尺寸为400 nm×400 nm时,在25 mA驱动电流下,其最大输出光功率达到了0.3 mW,功率密度约为2 mW/μm2.文中介绍了纳米孔径垂直腔面发射激光器的制备工艺,并对它的光谱特性和寿命特性进行了分析.     

纳米孔径垂直腔面发射激光器的制备及特性

在850 nm波长垂直腔面发射激光器的基础上制备了纳米孔径垂直腔面发射激光器.当小孔尺寸为400 nm×400 nm时,在25 mA驱动电流下,其最大输出光功率达到了0.3 mW,功率密度约为2 mW/μm2.文中介绍了纳米孔径垂直腔面发射激光器的制备工艺,并对它的光谱特性和寿命特性进行了分析.     

Red Light Vertical-Cavity Surface-Emitting Lasers

Vertical-cavity surface-emitting lasers (VCSELs) have entered into commercial market over the last few years. The paper describes the progress of visible (red) VCSELs in particular. The Basic experimental structures are reviewed, with emphasis on distributed Bragg reflectors, gain media, as well as detuning.lt also points out some technical issues that must still be resolved. Finally, the polarization of VCSELs devices is discussed.     

Polarization Dynamics of Current-Modulated Vertical-Cavity Surface-Emitting Lasers

We study the dynamics of vertical-cavity surface-emitting lasers (VCSELs) with direct current modulation in the framework of a model for index-guided VCSELs that takes into account two orthogonal linear polarizations. We analyze the effect of current modulation near the polarization switching (PS) of type I, from the high to the low frequency polarization, and near the PS of type II, from the low to the high frequency polarization. We find that the oscillations of the total power are as those of a single-mode laser, unaffected by the underlaying polarization coexistence or polarization competition. We also study the small-signal modulation response in the Fourier domain, for modulation dc values near the PS point. Close to type I PS the response of the total power as well as the response of the orthogonal polarizations has the same functional dependency on the modulation frequency, and can be fitted by the response function of a single-mode laser. Close to type II PS, polarization competition is a significant process at low modulation frequencies. The polarization-resolved modulation response displays features at low frequencies that are not present in the response of the total power, which is as that of a single-mode laser. The dynamics becomes increasingly complex as the modulation amplitude grows, and there is multistability of solutions.     

795nm单模垂直腔面发射激光器

针对铷原予能级跃迁对光谱的特殊需求,设计并制备了795 nm单模垂直腔面发射激光器(VCSEL).根据对VCSEL的光场和模式的分析和计算结果,设计了单模VCSEL芯片结构.采用MOCVD技术生长了外延结构,制备了不同有源区直径的氧化限制型VCSEL芯片并进行了测试.当有源区直径从6 μm减小到3μm时,VCSEL芯片的边模抑制比(SMSR)由8.76 dB增加到34.05 dB,阈值电流由0.77 mA减小到0.35 mA.有源区直径为6,5,4和3μm的VCSEL芯片的输出功率分别为0.37,0.46,0.58和0.44 mW,有源区直径为4μm的VCSEL芯片的远场为圆形光束,发散角为15°.85℃时3.5 μm有源区直径的VCSEL芯片输出功率为0.125 mW,激射波长为795.3 nm.室温3 dB带宽大于8 GHz,满足了铷原子传感器对VCSEL单模光谱、输出功率及调制速率的要求.     

Characteristics of Laser Cavity Solitons in a Vertical-Cavity Surface-Emitting Laser With Feedback From a Volume Bragg Grating

In this paper, the properties of laser cavity solitons (CS) in a vertical-cavity surface-emitting laser with feedback from a volume Bragg grating (VBG) are experimentally characterized. Independent optical manipulation of all eight possible bit states of three CS is demonstrated. Tilting the VBG provides evidence for different trapping states due to device disorder. The CS are found to “split” from a single peak to two peaks with increasing current, then to more complex arrangements, which are strongly governed by the spatial inhomogeneities. Due to the lack of any dominant polarizing elements, the system shows complex polarization behavior; however, each stage of the CS evolution has an approximately constant polarization angle unique for each CS. The polarization state of the CS can be controlled by adding polarization-selective or changing optics into the cavity.      

新型结构垂直腔面发射激光器的研制

为改善垂直腔面发射半导体激光器(VCSEL)的热特性.提高其光电性能,研制了新型辐射桥结构的VCSEL,即采用辐射桥状的电流注入通道取代以往传统结构VCSEL的环形电流注入通道.研究表明辐射桥结构可以降低VCSEL器件的体电阻和热阻,改善器件的模式特性.在同一外延片上,采用相同的工艺制备了辐射桥结构与传统结构两种VCSEL器件,并对两种器件的光电性能进行了对比测试.结果表明,辐射桥结构VCSEL比传统结构的VCSEL微分电阻降低25%,输出功率提高到1.6倍;辐射桥结构的VCSEL具有良好的温度特性与模式特性,80℃时仍能正常激射,60℃时最大输出功率可达17 mW,器件的热阻可达1.95℃/mW;器件单模工作,其总体性能远优于传统结构的VCSEL器件.     

A Vertical-Cavity Surface-Emitting Laser at Threshold

Linewidth is measured over the threshold transition of a vertical-cavity surface-emitting laser and results are compared to a FokkerPlanck semiconductor laser model. The linewidth shows nonmonotonous behavior at threshold similar to that previously observed in distributed feedback lasers. The behavior agrees with the FokkerPlanck model if the linewidth enhancement factor $alpha approx 5.0$. Measurement of the relaxation oscillation frequency and the damping rate using an injected optical probe allows, together with the FokkerPlanck model, the extraction of major laser parameters.      

Coherence of Photonic Crystal Vertical-Cavity Surface-Emitting Laser Arrays

We measure and compare the coherence properties of 2 times 1 arrays of photonic crystal vertical-cavity surface-emitting lasers. Antenna array theory applied to the measured far field intensity patterns is used to determine the phase of the complex degree of coherence, which is found to vary with current injection. The amplitude of the complex degree of coherence is determined by calculating the visibility from the far field patterns and making near field measurements of the relative intensities between lasing defects. We find that the amplitude and phase of the complex degree of coherence are correlated, such that coherence is maximized near in-phase and out-of-phase coupling conditions, and controllable by independent current injection to each array element     

利用边发射光致发光谱研究垂直腔面发射激光器材料的特性

在室温下测量了GaInP/AlGaInP垂直腔面发射激光器(VCSEL)的光致发光谱和反射谱.通过反射谱测量可以很容易得到激光器的腔模波长.但是用通常的背散射配置不能测得与有源区中量子阱有关的光致发光信号.用边激发配置可以测到量子阱的光致发光谱,但这样测得的光谱已经受到激光器中的分布布拉格反射镜(DBR)的调制.采用腐蚀去上DBR层的方法可以在背散射配置下测得量子阱的光致发光谱,但仍无法避免下DBR层对发光谱的调制作用.从而只有采用边激发-边发射模式才能测得VCSEL中量子阱的真实的光致发光谱.     

微小孔阵列垂直腔面发射激光器的研究

在980nm波长的大功率垂直腔面发射激光器(VCSEL)的基础上制备了高输出功率的微小孔阵列半导体激光器,其最大输出光功率达到了1mW。介绍了针对微小孔阵垂直腔面发射激光器的特殊制备工艺,并对其特性进行了分析。     

具有金属纳米颗粒结构的微小孔面发射激光器

在普通850nm垂直腔面发射激光器基础上制备出带有金属纳米颗粒结构的微小孔径垂直腔面发射激光器。当小孔和金属颗粒的直径分别为400nm和100nm时,其最大输出光功率达到0.5mW。介绍了该器件的制备工艺,从实验和理论两方面验证了金属纳米颗粒结构激发局域表面等离子体,从而使输出光功率得到提高。     

利用边发射光致发光谱研究垂直腔面发射激光器材料的特性

在室温下测量了GaInP/AlGaInP垂直腔面发射激光器(VCSEL)的光致发光谱和反射谱.通过反射谱测量可以很容易得到激光器的腔模波长.但是用通常的背散射配置不能测得与有源区中量子阱有关的光致发光信号.用边激发配置可以测到量子阱的光致发光谱,但这样测得的光谱已经受到激光器中的分布布拉格反射镜(DBR)的调制.采用腐蚀去上DBR层的方法可以在背散射配置下测得量子阱的光致发光谱,但仍无法避免下DBR层对发光谱的调制作用.从而只有采用边激发 边发射模式才能测得VCSEL中量子阱的真实的光致发光谱.     

808nm InGaAlAs垂直腔面发射激光器的结构设计

为实现垂直腔面发射半导体激光器(VCSEL)在808 nm波长的激射,对VCSEL芯片的整体结构进行了设计。基于应变量子阱的能带理论、固体模型理论、克龙尼克-潘纳模型和光学传输矩阵方法,计算了压应变InGaAlAs量子阱的带隙、带阶、量子化子能级以及分布布拉格反射镜(DBR)的反射谱,从而确定了量子阱的组分、厚度以及反射镜的对数。数值模拟的结果表明,阱宽为6 nm的In0.14Ga0.74Al0.12As/Al0.3Ga0.7As量子阱,在室温下激射波长在800 nm左右,其峰值材料增益在工作温度下达到4000 cm-1;渐变层为20 nm的Al0.9Ga0.1As/Al0.2Ga0.8As DBR,出光p面为23对时反射率为99.57%,全反射n面为39.5对时反射率为99.94%。设计的顶发射VCSEL结构通过光电集成专业软件(PICS3D)验证,得到室温下的光谱中心波长在800 nm处,证实了结构设计的正确性。     

Irregular Pulsating Polarization Dynamics in Gain-Switched Vertical-Cavity Surface-Emitting Lasers

In this paper, we report on experimental and theoretical investigation on the nonlinear dynamics of the two orthogonal linearly polarized fundamental transverse modes of vertical-cavity surface-emitting lasers (VCSELs) under sinusoidal current modulation. Irregular pulses of the power of individual polarizations are measured with a period equal to twice the modulation period. In contrast with individual polarizations, total power displays regular pulsing at twice the modulation period. The variability of pulse streams is characterized by using residence times distributions. We show that the residence time distributions for individual linear polarizations display an exponential decay for large values of that time. Those results are well reproduced by using a theoretical model that includes spontaneous emission fluctuations. However the previous qualitative features remain even in the absence of spontaneous emission noise. Our results therefore suggest that the irregular polarization dynamics have a deterministic origin and can be defined as deterministic chaos.     

Polarization Control of Vertical-Cavity Surface-Emitting Lasers by Utilizing Surface Plasmon Resonance

We demonstrate polarization control of vertical-cavity surface-emitting lasers (VCSELs) to any desired directions by utilizing surface plasmon resonance at a metal nanohole array. A silver nanohole array is integrated on the p-type distributed Bragg reflector of an 850-nm AlGaAs-GaAs-based VCSEL. The metal nanohole array placed at rectangular lattices with orthogonally different two periods, one of which meets the resonaint condition, exhibits strong polarization preference in optical transmission. Integrated four VCSELs with different directions of the rectangular arrays of nanoholes demonstrate successful control of the polarization angles. The VCSELs are closely located onto a one chip so that the optical outputs are easily coupled to one optical fiber. The presented VCSEL array will open a new horizon of multi-input multi-output communication systems by using polarization multiplexing.