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.     

Self-Aligned Microlens-Integrated Vertical-Cavity Surface-Emitting Lasers

A novel method for fabricating microlens-integrated vertical-cavity surface-emitting lasers (VCSELs) by selective oxidation of composition-graded digital alloy AlGaAs was developed. Due to the simultaneous formation of a microlens and oxide aperture via single-step oxidation, self-aligned microlens-integrated VCSELs could be fabricated using standard intracavity-contacted VCSEL processing without additional process steps. The output beam from the oxide-buried and oxide-removed AlGaAs microlens-integrated VCSELs was strongly focused to a beam radius of 3.7 and 3.5 mum at a distance of about 25 and 15mum, respectively, from the surface of the VCSEL     

Design of Stable Single-Mode Chaotic Light Source Using Antiresonant Reflecting Optical Waveguide Vertical-Cavity Surface-Emitting Lasers

The influence of external optical feedback (EOFB) on the lasing characteristics of 1.55-mum antiresonant reflecting optical waveguide (ARROW) vertical-cavity surface-emitting lasers (VCSELs) with various core radii are analyzed theoretically. It is found that ARROW VCSELs with large core radii (i.e., > 4 mum) respond more sensitively to EOFB than that with small core radii (i.e., les 4 mum). Furthermore, strong EOFB-driven ARROW VCSELs with large radii show more difficult to sustain single-mode chaotic oscillation than those with small radii. This is because radiation loss margin of ARROW reduces with the increase of core radii so that the presence of carrier spatial-hole burning deteriorates the stable single-mode operation of VCSELs. However, if the dimensions of ARROW as well as the radius of injection current aperture can be selected appropriately, stable single-mode chaotic light sources can be obtained from EOFB-driven ARROW VCSELs with large core radius.     

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.     

Ultralow Threshold Red Vertical-Cavity Surface-Emitting Lasers

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Ultralow Threshold Red Vertical-Cavity Surface-Emitting Lasers

Visible Vertical-cavity Surface-emitting Lasers (VCSELs) have been designed and fabricated by using metalorganic vapor phase epitaxy. Using the 8λ optical cavities with 3 quan tum wells in A1GaInP/AlGaAs VCSEL's to reduce the drift leakage current and enhance the model gain, the device can operate continuous wave at wavelength of 670nm. For better performance, a misoriented (100) substrate (6～10° to (110)) has been used to reduce the ordering of AlGaInP. However, as the angle of misorientation increased, the symmetry of the structure became worse. This made it difficult to achieve little aperture device. By using 45° rotated selective oxidation method, a little aperture (1 × 1μm2) device with low threshold of 0.25mA can operate continuous wave at room temperature.     

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.     

Loss-Induced Confinement in Photonic Crystal Vertical-Cavity Surface-Emitting Lasers

Through calculations and comparison with experimental results, we verify that loss introduced by an etched photonic crystal in a vertical-cavity surface-emitting laser (VCSEL) contributes significantly to the transverse optical confinement and supported modes. The optical loss is examined theoretically using a simple waveguide model from the scalar Helmholtz equation. The modal loss of fabricated lasers is extracted from the observed spectral-mode splitting. The effect of modal loss on the slope efficiency and modal behavior is examined. The model is found to be consistent with experimental measurements, and provides a means of accurate design of single-mode photonic crystal VCSELs.      

Optimal Parameters of Photonic-Crystal Vertical-Cavity Surface-Emitting Diode Lasers

We investigate the modal characteristics of a 1300-nm InP-based photonic-crystal (PC) vertical-cavity surface- emitting diode laser. To this aim, we apply the plane-wave admittance method and analyze a broad range of PC parameters such as hole etching depth, distance between the holes, and their diameters. We determine a range of technologically feasible PC parameters providing an optimal laser performance.     

Polarization-Resolved Modulation Response of Single-Transverse-Mode Vertical-Cavity Surface-Emitting Lasers

The small-signal modulation response of vertical-cavity surface-emitting lasers (VCSELs) is studied numerically, based on the spin-flip model. A detailed characterization of the influence of various parameters, such as the dichroism, the birefringence, the spin-flip rate and the noise level is done. The analysis is performed in regions of the parameter space where the operating conditions, in the absence of modulation, are such that there is either stable single linear polarization, or bistability of two orthogonal linear polarizations or polarization instability. In the instability region the intensities of the orthogonal polarizations display anticorrelated self-sustained oscillations that result in a complex small-signal modulation response, exhibiting multiple resonance peaks with frequencies that vary with the injection current and the spin-flip rate. In contrast, in parameter regions where there is stable single polarization the modulation response of the total intensity is as that of a single-mode laser, exhibiting a conventional single-resonance peak, and is almost not influenced by the value of the spin-flip rate. Polarization mode-hopping results in a distortion of the polarization-resolved modulation response at low frequencies.      

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.      

光子晶体垂直腔表面发射激光器及最佳化设计

单基模垂直腔表面发射激光器(VCSEL)在光网络数据传输、光互连、光存储和激光打印中有潜在的应用前景。光子晶体垂直腔表面发射激光器(PC-VCSEL)已成为备受关注的研究课题。介绍了PC-VCSEL的结构、最佳化设计及特性。     

Single-Mode Emission From Vertical-Cavity Surface-Emitting Lasers With Low-Index Defects

Mode confinement to low-index "defect" regions of a two-dimensional square photonic lattice has been studied as a means to realize single-spatial-mode vertical-cavity surface-emitting lasers (VCSELs). A selective etching process with two-step metal-organic chemical vapor deposition is used to fabricate the low-index defect VCSELs. A device with a 9-mum-wide aperture demonstrates 2.9-mW continuous-wave (CW) output power. The near diffraction-limited single-lobe far-field and high-resolution spectral analyses confirm single fundamental defect mode emission. Comparison studies between pulsed and CW operation indicate that thermal effects have a significant impact on the modal performance of the devices. Single-mode emission with more than 8 mW of peak pulsed power has been observed with short pulsewidth operation (0.1 mus, 2%). Improvements in thermal management are required to achieve higher CW single-mode emission in these devices     

Accurate Nonlinear Volterra Series Analysis for Vertical-Cavity Surface-Emitting Lasers

In this letter, an accurate nonlinear Volterra series analysis for vertical-cavity surface-emitting lasers (VCSELs) is presented. Closed-form expressions for the modulation response, harmonic distortions, and second- and third-order intermodulation distortions are derived. Moreover, the suggested nonlinear model avoids the numerical solution of laser rate equations and provides in-depth insight of a distortion analysis of VCSEL.     

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.      

Full-Vectorial Three-Dimensional Finite Element Optical Simulation of Vertical-Cavity Surface-Emitting Lasers

The electromagnetic problem of modeling vertical-cavity surface-emitting lasers with their full 3D structure is analyzed. The vectorial Helmholtz equation is discretized on prism elements, and the resulting complex symmetric generalized eigen- problem is solved by an efficient numerical technique. The full-vectorial treatment enables one to determine the polarization characteristics of these lasers. The model is compared to 2D calculations and is demonstrated for advanced laser diodes incorporating surface reliefs and photonic crystal patterns.     

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.     

980nm高功率垂直腔面发射激光器的理论分析

理论分析了980nm高功率垂直腔面发射激光器(VCSEL)的器件特性与其分布布拉格反射镜(DBR)反射率的依赖关系,并计算了具有不同有源区直径的VCSEL的输出特性.分析了具有不同有源区直径的VCSEL在不同DBR反射率条件下的连续输出特性曲线,发现DBR反射率的改变会对有源区直径不同的VCSEL产生不同程度的影响.为了验证理论分析的结果,进行了器件测试实验.实验结果表明,有源区直径为500μm的VCSEL,当其N-DBR反射率分别为99.7%及99.2%时,在连续注入电流为6A时,其输出功率分别为2.01W和2.09W;而有源区直径为200μm的VCSEL,当N-DBR反射率为99.7%及99.2%时,连续注入电流为3A时,其输出功率分别为0.64W及1.12W.器件测试结果有效验证了理论分析的结论.     

氧化限制型垂直腔面发射激光器串联电阻分析

含氧化限制孔的VCSEL具有低的阈值电流,但氧化孔的存在也会加大串联电阻.本文采用理论模型,详细计算了氧化限制型VCSEL的串联电阻.把串联电阻分解为垂直方向电阻和横向电阻,分析了串联电阻与氧化孔半径的关系,提出了降低VCSEL串联电阻的具体方法.     

Loss and Index Guiding in Single-Mode Proton-Implanted Holey Vertical-Cavity Surface-Emitting Lasers

Wedge-shaped holes are fabricated in the top mirror of proton-implanted vertical-cavity surface-emitting lasers (VCSELs). A radially symmetric fill factor approach is used to calculate the resulting transverse index profile. To investigate both the index confinement provided by the etched pattern and its effect on optical loss, continuous-wave (CW) and pulsed experiments are performed. Under CW operation, we show proper wedge design leads to improved fundamental-mode output power, decreased threshold, and increased efficiency. We report a significant decrease in threshold under pulsed operation for the etched device compared to an unetched device, indicating a significant reduction in diffraction loss to the fundamental mode due to strong index guiding. Single-mode output is maintained over the entire operating range of the VCSEL due to increased loss for the higher order modes.