Light polarization fingerprints on nonlinear dynamics of vertical-cavity surface-emitting lasers

In this paper we summarize the recent results on nonlinear dynamics of vertical-cavity surface-emitting lasers (VCSELs) which are bearing the fingerprints of the particular polarization properties of VCSELs. Due to the surface emission and cylindrical symmetry, VCSELs lack strong polarization anisotropy and may undergo polarization switching and polarization mode-hopping. This provides new specificities to the rich nonlinear dynamics induced in VCSELs by an external perturbation. We unveil both experimentally and theoretically these new specificities for the case of optical feedback, optical injection, and unidirectional synchronization between VCSELs.     

Chaos synchronization and communication of the polarization modes for two unidirectionally coupled vertical-cavity surface-emitting lasers

We theoretically investigate the synchronization performance of the polarization modes of two unidirectionally coupled vertical-cavity surface-emitting lasers (VCSELs), where the master VCSEL subjects to polarization-preserved optical feedback and the slave VCSEL subjects to polarization-preserved optical injection. We demonstrate that high synchronization can be achieved between corresponding polarization components of the master laser and the slave laser. We also analyze the influence of the internal mismatched parameters on the synchronization performance. Furthermore, this system is used to dual-channel communication and the different transmitted digital information is respectively recovered at each polarization branch of the slaver laser successfully with the encryption scheme of chaos masking (CM). The results open an opportunity for multichannel chaotic communication by utilizing different polarization components in single-mode or multi-transverse-mode VCSELs.     

双波长垂直腔面发射激光器及特性研究

基于光子晶体技术在一维光子晶体带隙内引入缺陷态模式,并对激光器谐振腔内部电磁场分布和共振波长进行调制,从而将单一波长分裂为双波长输出.最终制备出了一种新的具有双波长光谱输出特性的垂直腔面发射激光器,缺陷层为Al_0.8Ga_0.2As材料,厚度为5λ/4.所得到的双波长输出光谱具有低吸收损耗、输出波长容易控制及同方向垂直输出特性.同时,通过调整一维光子晶体的折射率差和缺陷层厚度可以有效调谐双波长的间距及输出波段.所设计的双波长垂直腔面发射激光器结构同样 关键词： 垂直腔面发射激光器 光子带隙 双波长     

垂直腔面发射激光器的电路模拟

通过分析垂直腔面发射激光器的速率方程,并结合电子电路的特点,建立了等效电路模型。采用数值计算和电路模拟两种方法给出了垂直腔面发射激光器的频率响应特性。通过分析,证明了电路模型的正确性。通过电路模拟得出了脉冲调制的响应特性,验证了激光器固有的电光延迟和张驰振荡现象。     

Suppressing nonlinear dynamics induced by external optical feedback in vertical-cavity surface-emitting lasers

A numerical study of using external optical injection to suppress the nonlinear dynamics introduced by external optical feedback in vertical-cavity surface-emitting lasers (VCSELs) has been undertaken. The model under consideration is a master–slave configuration where the master VCSEL provides the continuous wave to control the nonlinear behaviors arising in the slave VCSEL. Simulation results indicate that the feedback-induced nonlinear dynamics (e.g. chaotic, single-periodic, and multi-periodic oscillations), relative intensity noise (RIN) as well as the coherence collapse can be suppressed effectively as long as the injection is strong enough to overcome the nonlinear effects of the feedback.     

Transverse-mode selectivity in possible nitride vertical-cavity surface-emitting lasers

Excitation of various transverse modes in possible nitride vertical-cavity surface-emitting lasers (VCSELs) is investigated and compared using the effective frequency optical model. In the comparative analysis of laser mode selectivity, two distinctly different configurations of possible nitride VCSELs are considered: the traditional VCSEL design with both (n-side and p-side) ring contacts as well as the uniform-current-injection (UCI) VCSEL design. Our simulation reveals that, during the continuous-wave device operation at room temperature, a multi-mode operation dominated by higher-order transverse modes is typical for traditional nitride VCSEL configurations whereas a desirable single-mode (based on the fundamental LP₀₁ mode) operation turns out to be characteristic for the wide current range in UCI ones. The above different threshold device behaviours are an immediate consequence of essentially different current-spreading phenomena in both VCSEL designs, resulting in completely different not only gain profiles but also temperature distributions within the laser active regions of both VCSELs. Seemingly similar behaviour has been also reported in arsenide VCSELs but it is expected to be much more severe in the case of nitride ones as a result of much higher both electrical resistivities of p-type nitrides and their temperature derivatives of refractive indices.     

Bistable polarization switching in mutually coupled vertical-cavity surface-emitting lasers

We theoretically investigate the polarization-resolved dynamics of two vertical-cavity surface-emitting semiconductor lasers that are mutually coupled through coherent optical injection. We find a sequence of bistable polarization switchings that can be induced by changing either the coupling strength or the optical propagation phase. The successive polarization switchings are correlated with the creation of new compoundcavity modes when these parameters are continuously varied.     

Scaling effects on the dynamic characteristics of long-wavelength vertical-cavity surface-emitting lasers (VCSELs)

The influence of the oxide aperture radius on the characteristics of a long-wavelength vertical-cavity surface-emitting laser (VCSEL) lasing at 1550 nm is presented in this paper. While previous works in the literature mostly investigate the scaling effects of short-wavelength VCSELs. The importance of studying the effects of long-wavelength operation should not be underestimated, as it could be used in fiber optics communication to mitigate dispersion and attenuation of the channel. Using the oxide-confined VCSEL model, the dynamic operations were examined taking into account the carrier-noise, photon-noise and phase-noise, including feedback of the external cavity. Our simulations show that by reducing the oxide aperture up to a given optimal radius, an improvement in the device's characteristics can be demonstrated. Below this value, performance degradation is expected due to increased diffraction losses, reduced confinement factor and enhanced spontaneous emission.     

Diode pumped 850 nm vertical-cavity surface-emitting laser

Very little, if any, has been published on optically pumped 850 nm vertical-cavity surface-emitting lasers (VCSELs), particularly for doped structures. This paper investigates GaAs-based VCSELs which have not been optimized for optical pumping work. Characterisation was carried out for both pulsed and continuous wave (CW). Pulsed operation causes a lower rise in temperature, thus postponing the onset of thermal rollover, and allowing the device to be operated at higher powers. A threshold of ∼160 kW/cm², and single mode output with incident power density of up to 225 kW/cm² were obtained. From the simulation work done, it has been observed that for optically pumped VCSELs, at higher pump density, there was faster turn on and higher output power, and that dilute nitride active material give better output performance compared to GaAs.     

长波长垂直腔面发射激光器研究

垂直腔面发射激光器（简称VCSEL）近年来受到了国内外科技界和企业界的高度关注，它在光通信领域具有潜在的应用．文章主要介绍了长波长垂直腔面发射激光器的发展历史、基本应用、器件结构、材料和制备工艺，最后分析了研制长波长VCSEL所遇到的问题及相应解决方法，并进行了展望．     

长波长垂直腔面发射激光器研究

垂直腔面发射激光器（简称VCSEL）近年来受到了国内外科技界和企业界的高度关注,它在光通信领域具有潜在的应用.文章主要介绍了长波长垂直腔面发射激光器的发展历史、基本应用、器件结构、材料和制备工艺,最后分析了研制长波长VCSEL所遇到的问题及相应解决方法,并进行了展望.     

Polarization and transverse-mode dynamics of gain-guided vertical-cavity surface-emitting lasers

Transverse-mode competition and polarization selection in gain-guided vertical-cavity surface-emitting lasers are studied by use of a transverse continuous model that incorporates basic physical mechanisms of polarization dynamics. Polarization stability and polarization switching within the fundamental Gaussian mode are described. The first-order transverse mode always starts lasing orthogonally polarized to the fundamental one. At larger currents polarization coexists with several active transverse modes. These results are shown to be sensitive to the carrier spin-flip relaxation rate.     

Radiation fields from whispering-gallery modes of oxide-confined vertical-cavity surface-emitting lasers

Near- and far-field radiation patterns are analyzed for whispering-gallery-mode lasing in native-oxide-confined vertical-cavity surface-emitting lasers. Calculations from classical antenna theory based on the higher-order Bessel functions are compared with experiment and shown to be a useful predictor of the measured radiation fields. The most interesting features of the lasing modes are the multiple and uniformly distributed intensity spots in the near and far fields.     

Polarization switching and synchronization of mutually coupled vertical-cavity surface-emitting semiconductor lasers

Polarization switching (PS) dynamics and synchronization performances of two mutually coupled vertical-cavity surface-emitting lasers (VCSELs) are studied theoretically in this paper. A group of dimensionless rate equations is derived to describe our model. While analysing the PS characteristics, we focus on the effects of coupling rate and frequency detuning regarding different mutual injection types. The results indicate that the x-mode injection defers the occurrence of PS, while the y-mode injection leads the PS to occur at a lower current. Strong enough polarization-selective injection can suppress the PS. Moreover, if frequency detuning is considered, the effects of polarization-selective mutual injection will be weakened. To evaluate the synchronization performance, the correlation coefficients and output dynamics of VCSELs with both pure mode and mixed mode polarizations are given. It is found that performance of complete synchronization is sensitive to the frequency mismatch but it is little affected by mixed mode polarizations, which is opposite to the case of injection-locking synchronization.     

Oxide aperture scaling effect on high-speed (>16 GHz) vertical-cavity surface-emitting lasers performance

High-speed, oxide-confined, polyimide-planarized 850 nm vertical-cavity surface-emitting lasers (VCSELs) with oxide aperture diameters of 9, 10, 12, 15, 20, and 30 μm have been fabricated and characterized. For a 9 μm oxide aperture diameter, the lasers exhibit a resonance frequency, a 3-dB modulation frequency, and a modulation current efficiency factor (MCEF) up to 12.4, 16.5 GHz, and 10.9 GHz/mA^1/2, respectively, at only 7.9 kA/cm². Threshold voltage and current were 1.45 V and 0.7 mA, respectively. It is demonstrated that increasing the resonance frequency with bias does not guarantee a higher modulation bandwidth. The influence of oxide aperture scaling effect on VCSEL performance is presented.     

Mechanisms of polarization switching in single-transverse-mode vertical-cavity surface-emitting lasers: thermal shift and nonlinear semiconductor dynamics

We analyze polarization switching in vertical-cavity surface-emitting lasers, taking into account a proper semiconductor frequency-dependent complex susceptibility and spin-flip processes. Thermal effects are included as a varying detuning, and gain differences arise from birefringence splitting. We find that, for large birefringence, gain differences between the two linearly polarized modes are preponderant, and switching occurs owing to thermal shift. For small birefringence polarization switching from the high- to the low-gain mode occurs owing to the combined effect of birefringence and semiconductor phase-amplitude-coupled dynamics for a finite value of the carrier spin-flip rate.     

增益导波垂直腔激光器注入电流空间分布及其对激光近场模式影响的理论分析和表征

依据导电介质的稳态电场理论建立了一种对增益导波型垂直腔半导体激光器注入电流矢量分析的三维解析模型. 计算研究了电流密度空间分布及其与顶面电注入环参量之间的相互关联性. 结果显示在两极之间存在一个载流子径向分布中心极大的区域. 由于激光功率与注入电流之间存在线性关系,因此,要使器件能够获得基模或中心均匀的光强输出以及尽可能低的阈值,应使激光有源层与载流子均匀分布的临界层重合. 计算结果对顶发射与底发射结构以及不同环参数下的载流子分布情况及对近场模式形成的影响进行了分析和讨论. 关键词： 垂直谐振腔激光器 注入电流 激光模式     

Micromechanical tunable vertical-cavity surface-emitting lasers

We report the study on a short wavelength-tunable vertical-cavity surface-emitting laser utilizing a monolithically integrated bridge tuning microelectromechanical system. A deformable-bridge top mirror suspended above an active region is utilized. Applied bridge-substrate bias produces an electrostatic force which reduces the spacing of air-gap and tunes the resonant wavelength toward a shorter wavelength (blue-shift). Good laser characteristics are obtained: such as continuous tuning ranges over 11 nm near 940 nm for 0--9 V tuning bias, the peak output power near 1 mW and the full-width-half-maximum limited to approximately 3.2--6.8 nm. A detailed simulation of the micromechanical and optical characteristics of these devices is performed, and the ratio of bridge displacement to wavelength shift has been found to be 3:1.     

Experimental study of polarization switching of vertical-cavity surface-emitting lasers as a dynamical bifurcation

We study the role of the bias current sweep rate in measurements of polarization switching (PS) of vertical-cavity surface-emitting lasers (VCSELs). We show that the polarization-resolved L-I (light-intensity) curve depends on the current sweep rate. As the current sweep rate increases, the PS occurs at higher bias currents for upward scans and at lower bias currents for downward scans. We also show that the delay of the dynamical bifurcation follows a power law relationship with the frequency of the ramp, in good agreement with recent theoretical predictions.