单向耦合VCSEL偏振模的同步与编码

为了研究单向耦合垂直腔面发射激光器系统的混沌动力学及其在通信中的应用,采用数值仿真的方法,理论研究了两个单向耦合的垂直腔面发射激光器偏振模的同步特性,并通过对发射激光器偏振态相位的调制实现了该系统的编码。结果表明,主激光器和从激光器相应模式间可以获得高性能的同步,而且存在两个明显的同步区域——完全同步和注入锁定同步。加载的数字信息也可以在从激光器每个偏振分量中还原,这表明可以利用单模或多横模垂直腔面发射激光器进行多信道混沌通信。     

Data transparent reconfigurable optical interconnections usingpolarization switching in VCSEL's induced by optical injection

We demonstrate a data transparent reconfigurable optical interconnection system based on optical injection controlled polarization switching in a master-slave vertical-cavity surface-emitting laser (VCSEL) configuration. A 140-Mb/s data stream generated by the slave VCSEL is redirected by an anisotropic diffractive optical element depending on the polarization state of the emitted light. The polarization of the slave laser is controlled by injecting an orthogonally polarized optical signal from a master laser. The current modulation of the master VCSEL and the subsequent polarization switching of the slave VCSEL occur at 40 MHz. In our setup, both the data rate and the optical interconnection reconfiguration rate are limited by the electronic drive circuitry and could in principle attain the gigahertz range     

Transverse Mode Switching and Locking in Vertical-Cavity Surface-Emitting Lasers Subject to Orthogonal Optical Injection

In this paper, we report on theoretical and experimental investigation on polarization and transverse mode behavior of vertical-cavity surface-emitting lasers (VCSELs) under orthogonal optical injection as a function of the injection strength and of the detuning between the injection frequency and the free-running frequency of the solitary laser. As the injection strength increases the VCSEL switches to the master laser polarization. We find that the injection power necessary to obtain such polarization switching is minimum at two different values of the frequency detuning: the first one corresponds to the frequency splitting between the two linearly polarized fundamental transverse modes, and the second one appears at a larger positive frequency detuning, close to the frequency difference between the first-order and the fundamental transverse modes of the solitary VCSEL. We show theoretically that both the depth and the frequency corresponding to the second minimum increase when the relative losses between the two transverse modes decrease. Bistability of the polarization switching is obtained for the whole frequency detuning range. Such a bistability is found for the fundamental mode only or for both transverse modes, depending on the value of the detuning. The theoretical and experimental optical spectra are in good agreement showing that the first-order transverse mode appears locked to the external injection     

Polarization behavior of birefringent multitransverse mode vertical-cavity surface-emitting lasers

An analysis has been undertaken of the effect of birefringence on the selection of polarization states of a weakly index guided vertical-cavity surface-emitting laser (VCSEL) supporting both a fundamental and a first-order transverse mode. It is shown that for small index steps polarization switching due to spatial-hole burning effects can occur. For larger index steps it is found that higher order modes can emerge which are orthogonally polarized to the dominant polarization of the fundamental mode.     

外加电场下垂直腔面发射激光器的偏振转换电流

电光效应双折射可以控制垂直腔面发射激光器的偏振特性。本文计算了作用在垂直腔面发射激光器（VCSEL）的上面的分布格反射镜（DBR）上的外加电场产生的双折射,并在此基础上通过对自旋反转模型（SFM）的修正,得到面发射激光器在外加电场存在时的偏振转换电流。     

高功率垂直腔底发射激光器的偏振特性

在垂直腔面发射激光器(VCSEL)作为显示光源的应用中,为了获得高功率的偏振激光,研究了980nm大口径底发射VCSEL的偏振特性。通过刻蚀矩形台面和矩形出光口径,制备矩形VCSEL。在连续条件下,出光口径为550μm×300μm的底发射矩形VCSEL最大输出功率为660mW,微分电阻为0.09Ω。实验中,矩形VCSEL在工作电流下,同时存在稳定的水平偏振光和竖直偏振光,并且沿着矩形长边出射的水平偏振光一直占据主导地位。而圆形VCSEL在水平和竖直方向的激射情况几乎相同。水平偏振光的激射光谱相对于竖直偏振光出现蓝移,并且用对称三层波导模型解释了蓝移现象。研究了矩形VCSEL的正交偏振比与矩形口径长宽比的关系。实验结果表明,矩形柱结构能够有效地稳定VCSEL的偏振方向,使大口径器件激射高功率的偏振激光。     

Mapping of the dynamics induced by orthogonal optical injection in vertical-cavity surface-emitting lasers

In this paper, the output characteristics of an oxide-confined AlGaAs-As quantum well vertical-cavity surface-emitting laser (VCSEL) under orthogonal optical injection are mapped as a function of the strength of the optical injection and the detuning between the injection frequency and the free-running frequency of the solitary laser, for a very large range of frequency detuning (from -82 to 89 GHz). The injection light is polarized orthogonally with respect to the solitary VCSEL output light. As the injection strength increases the VCSEL switches to the master laser polarization. Polarization switching is accompanied by a rich nonlinear dynamics, including limit cycle, wave mixing, subharmonic resonance and period doubling route to chaos. Polarization switching is found with but also without injection locking. Injection locking occurs with the slave fundamental transverse mode or, for large positive detunings, with the first-order transverse mode.     

Subwavelength Grating-Mirror VCSEL With a Thin Oxide Gap

A new vertical-cavity surface-emitting laser (VCSEL) structure based on a subwavelength grating mirror and a thin oxide gap is suggested and numerically investigated. The structure is shown to exhibit similar threshold gain, suppression of higher order transverse modes, and polarization stability as a grating-mirror VCSEL reported in the literature based on a thick air gap. The thin oxide gap structure has a number of advantages including easier fabrication, better mechanical stability, and very strong single-mode properties.     

Picosecond polarization dynamics and noise in pulsed vertical-cavity surface-emitting lasers

We have measured on picosecond time scales the polarization behavior of vertical-cavity surface-emitting lasers (VCSELs) pumped with short optical pulses. Our data describe the temporal properties of the intensity and intensity noise for orthogonally polarized modes as well as noise correlations between the modes in both the circular and the linear detection bases. A variety of behavior is observed that depends on the polarization of the pump, the strength of the pump, the VCSEL operating temperature which determines the carrier spin-flip rates, and the degree of birefringence and dichroism in the laser. We develop an extension of the "split density" model which includes carrier relaxation processes that are important on picosecond time scales. Our numerical simulations illustrate how spin-flip processes lead to anti-correlated fluctuations in the circularly polarized modes and how anti-correlated noise can arise between the linearly polarized modes without switching between two "preferred" modes, as is commonly seen on longer time scales.     

表面光栅垂直腔面发射激光器偏振特性研究

研究了表面光栅结构对垂直腔面发射激光器(VCSEL)的偏振控制作用。引入表面光栅后,对不同刻蚀深度下的偏振相关的镜面损耗进行了仿真,结果表明表面光栅刻蚀深度在44~130 nm范围内均可实现稳定偏振,具有较大的工艺容差。表面光栅VCSEL在基横模工作状态下偏振抑制比(Orthogonal Polarization Suppression Ratio, OPSR)超过20 dB,偏振光谱峰间偏振抑制比达到40 dB,且在多横模状态也实现了有效的偏振控制。为了进一步验证光栅对偏振控制的效果,制作了方向互相垂直的两种表面光栅,具有这两种方向光栅的VCSEL的OPSR均达20 dB以上。测试分析表明表面光栅是VCSEL实现稳定偏振的一种有效手段。     

互注入VCSEL非线性及同步特性的理论研究

考虑到瓦注入耦合特有的非线性效应,建立了互注入式垂直腔面发射激光器（VCSEL）的理论模型,推导了系统注入锁定范围的解析表达式,理论研究了互注入的同步类型以及注入延时对系统非线性行为的影响。结果表明：在激光器参数相同的理想情况下,系统能实现完全同步,此时注入延时会影响VCSEL的运行状态;当存在参数偏差或噪声时,系统能实现延时同步,此时注入延时对同步质量的影响呈阶梯状。仿真结果验证了所推导的锁定范围表达式的正确性,发现注入锁定范围与注入量的平方根成难比。     

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     

An 850-nm InAlGaAs strained quantum-well vertical-cavitysurface-emitting laser grown on GaAs (311)B substrate withhigh-polarization stability

The polarization stability of 850-nm InAlGaAs strained quantum-well (QW) vertical-cavity surface-emitting laser (VCSEL) grown on GaAs (311)B substrate was investigated by comparing it with that of GaAs unstrained QW VCSEL grown on GaAs (311)B substrate. Photoluminescence measurement showed that strained QWs grown on GaAs (311)B substrate had larger anisotropy in optical gain than unstrained QWs. The VCSEL with strained QWs showed an orthogonal polarization suppression ratio (OPSR) as high as 21 dB under CW operation. Time-dependent OPSR measurement indicated that the strained QW VCSEL had higher polarization stability than the unstrained QW VCSEL under zero-bias modulation     

Polarization-Controlled Surface Grating VCSELs Under Unpolarized and Polarized Optical Feedback

The polarization control of a surface grating vertical-cavity surface-emitting laser (VCSEL) and of a nominally identical standard VCSEL without a surface grating are compared for unpolarized and polarized optical feedback with different feedback levels in the long external cavity regime. While the polarization of the standard VCSEL is strongly influenced by isotropic feedback with a feedback level of just 1% and can even be controlled by polarized feedback, the surface grating VCSEL remains polarization-stable under isotropic feedback. Its polarization can only be disturbed by optical feedback polarized orthogonal to the polarization of the solitary surface grating VCSEL for feedback levels exceeding 18%.     

A low-threshold polarization-controlled vertical-cavitysurface-emitting laser grown on GaAs (311)B substrate

We have demonstrated a GaAs (311)B vertical-cavity surface-emitting laser (VCSEL) with a threshold current as low as 250 μA, which is the lowest value ever reported for that on non-(100) oriented substrates. Also, the fabricated VCSEL shows a stable polarization state for wide during current ranges and a large polarization-mode suppression ratio over 30 dB between the [2¯33] and [011¯] axis modes at 5 mA. The electrical specific resistance of 1.2×10^-4 Ω·cm^-2 at the threshold was reasonably low due to carbon autodoping to AlAs in a p-type distributed Bragg reflector (DBR)     

Polarization-Controlled Surface Grating VCSELs Under Externally Induced Anisotropic Strain

The polarization control of surface grating vertical-cavity surface-emitting lasers (VCSELs) is tested under externally applied anisotropic stress and is compared to that of a nominally identical standard VCSEL without a surface grating. This is done by bending the VCSEL chip in a well-defined way. The anisotropic in-plane strain thus induced in the VCSELs leads to a polarization switch of the standard VCSEL for rather moderate strain. In contrast, the polarization of the surface grating VCSELs is fixed by the grating and remains unchanged despite a high strain which causes a wavelength splitting of the two polarization modes of about 130 pm. Such a result is of high practical relevance, since strain is unavoidably induced during VCSEL fabrication and mounting and counteracts any method applied for polarization control.     

Injection locking dynamics of vertical cavity semiconductor lasersunder conventional and phase conjugate injection

Stable phase locking of an electrically pumped vertical cavity surface-emitting semiconductor laser (VCSEL) was demonstrated experimentally by injecting light from an edge-emitting master laser into the slave laser VCSEL cavity within a large detuning range (~80 GHz). By varying the injected power and frequency detuning, a variety of interesting nonlinear behavior was observed. A theoretical model based on two-field rate equations is presented and compared with experiment, showing good agreement     

Polarization-resolved relative intensity noise measurements of a vertical-cavity surface-emitting laser subjected to strong optical feedback

We experimentally measure the polarization-resolved relative intensity noise (RIN) in two orthogonal polarization states of a vertical-cavity surface-emitting laser (VCSEL) subjected to strong optical feedback. A comparison is made with the RIN of solitary VCSEL. Optical feedback is shown to enhance the RIN in one polarization direction while suppressing the RIN in the orthogonal polarization. The RIN in the dominant polarization mode exhibits complementary behavior to the RIN in the suppressed polarization mode.     

Vertical-Cavity Surface-Emitting Lasers With Integrated Excitation of Surface Plasmon Polariton Modes

We report the excitation of surface plasmon polaritons (SPPs) on a thin Au layer integrated on top of the mirror of a vertical-cavity surface-emitting laser (VCSEL) along with their subsequent extraction to air. Gratings etched into the Au layer are used to couple the light in to and out of the metal film. The polarization properties of the optical emission from out-coupling gratings placed 5 $mu$ m away from the central optical aperture are used to confirm the coupling of the VCSEL light into and out of the SPP modes. The result paves the way to compact integrated plasmonic devices.      

Phase tuning of injection-locked VCSELs

Phase tuning of injection-locked single-mode vertical-cavity surface-emitting laser diodes (VCSELs) is investigated experimentally with two slave VCSELs being locked by a master VCSEL. By slightly varying the laser current and thereby the frequency within the locking range, a maximum phase shift of more than 0.8 π is achieved. The method is applicable to large injection-locked VCSEL arrays