Model Of Vertical-cavity Surface-emitting Lasers Research Articles

Design and analysis of high-temperature operating 795 nm VCSELs for chip-scale atomic clocks

We propose a new structure design and analysis of high-temperature (>350 K) operating 795 nm vertical-cavity surface-emitting lasers (VCSELs) for 87Rb based chip-scale atomic clocks (CSACs). Compositions and thicknesses of the InAlGaAs/AlGaAs multiple quantum wells (MQWs) are optimized for high optical gain at elevated temperatures. The temperature sensitivity of the threshold current is estimated by calculating the temperature dependence of the cavity-mode gain. A self-consistent VCSEL model based on quasi-3D finite element analysis is employed to investigate the temperature distribution and output of the proposed structure. An output of 1 mW with a 3 dB bandwidth of 6 GHz is obtained from a 3 μm aperture VCSEL under 2.4 mA current at temperature higher than 340 K. These findings indicate that high-gain QWs and gain-offset consideration are especially crucial to make high-performance VCSELs at elevated temperatures.

Comprehensive large-signal analyses of RF modulation of vertical cavity surface emitting lasers

This paper introduces comprehensive numerical simulations of the static and dynamic characteristics of vertical cavity surface emitting lasers (VCSELs) under both continuous-wave (CW) operation and sinusoidal modulation. Both cases of single and two-tone modulations are studied. The VCSEL is assumed to oscillate in two modes, and the obtained results are compared to those of single mode VCSELs. The study is based on a multimode rate equation model of VCSELs, which describes the time evolution of number of the emitted photons and the density of injected electrons in the active and cladding layers. The higher and half harmonic distortions of the single-tone modulated signals as well as the intermodulated distortion of the two-tone modulated signals are investigated and correlated to the characteristics of the signal waveform.

Fabrication and performance of bottom-emitting flip-chip bonded 980 nm vertical-cavity lasers with copper- and indium-plated heat-sinks

Bottom-emitting, flip-chip bonded, oxide-confined, 980 nm vertical-cavity surface-emitting lasers (VCSELs) with improved performance were fabricated and characterized. Flip-chip bonding, bottom-emitting VCSELs with 20 µm active area diameter on copper- and indium-plated heat spreaders reduced the devices’ thermal resistance by 35% and increased the bias current density at which the output optical power saturates by 19%, which increased the maximum output optical power achieved by 26%. Bonded VCSELs with active area diameters of 20 µm demonstrated an ∼30% decrease in the active region temperature at the maximum output optical power. A 10% improvement in the devices’ modulation bandwidth is calculated due to reduced temperature and increased power. Devices with different active area diameters exhibited a threshold current density and differential quantum efficiency of (0.88 ± 10%) kA cm−2 and 0.57 ± 8%, respectively, implying good active area scaling. A simple rate-equation-based thermal VCSEL model was used to extract different VCSELs’ parameters, which enabled the estimation of internal temperature for different device sizes at different bias currents. A genetic algorithm was utilized in model parameter extraction and optimization. Good agreement between measured and simulated characteristics for different device sizes was obtained. Detailed protocols for critical fabrication steps are presented.

Modeling and Simulation of VCSEL’s Turn-on Delay Based on Rate-Equations

Vertical-Cavity Surface-Emitting Lasers (VCSELs) are a new generation of semiconductor lasers that have many advantages. In this paper, we present a comprehensive circuit-level VCSEL model that addresses the spatial and thermal behavior of VCSELs including turn on delay based on the rate equations without sacrificing the numerical efficiency demanded by the circuit-level simulation of optoelectronic systems. It is implemented into SPICE-like simulators to simulate the dc, ac and transient features (including turn-on delay and turn-off effect) of VCSELs. The simulated results exhibit good agreements with references.

Structure modifications of oxide‐confined GaInNAs VCSELs for the second‐generation optical‐fibre communication

AbstractFor the second‐generation optical‐fibre communication, lasing sources emitting stable single‐fundamental‐mode (SFM) 1.3‐μm radiation are required. Then oxide‐confined GaAs‐based GaInNAs quantum‐well (QW) vertical‐cavity surface‐emitting lasers (VCSELs) seem to be the best solution. But possibility to reach their efficient 1.3‐μm low‐threshold SFM operation is usually questionable. Therefore the comprehensive fully self‐consistent simulation VCSEL model is used to find the most promising VCSEL structure for this application. It has been concluded from our analysis, that the best performance may be reached in the VCSEL structure in which the proper detuning of the cavity mode towards longer wavelengths and the proper step‐like active‐region QW structure are simultaneously applied. Then the stable 1.3‐μm SFM operation is reached for temperatures exceeding 305 K in the relatively large VCSEL with the 12‐μm diameter activity region. Its threshold current is only somewhat higher than 6 mA at the ambient temperature of 350 K. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

High-order circuit-level thermal model of vertical-cavity surface-emitting lasers

A high-order equivalent circuit model of vertical-cavity surface-emitting lasers (VCSEL) is introduced by virtue of the rate equations. This model accounts for both thermal and spatial dependences of VCSEL characteristics. A four-term Bessel-series expansion for the VCSEL carrier number is utilised to achieve good accuracy. A zero-order Laguerre–Gaussian beam is utilised for describing the photo distribution to simplify the computation. A general diode sub-circuit, instead of a complicated polynomial expression, is adopted to model the current–voltage relationship. This model is fast, accurate and scalable. Moreover, it can be readily used in SPICE-like circuit simulators. Numerical examples are included to validate this model and show that this model exhibits much improved accuracy than the previously published models.

Dynamical Hysteresis and Thermal Effects in Vertical-Cavity Surface-Emitting Lasers

We study numerically the polarization-resolved light-output characteristic of vertical-cavity surface-emitting lasers (VCSELs) using the spin-flip model for VCSELs extended to take into account thermal effects via a dynamical equation for the active region temperature, including heat dissipation, heating due to nonradiative carrier recombination, and Joule effect. The temperature dynamics is coupled to the carrier and optical field dynamics via a frequency and temperature-dependent gain coefficient. We show that the interplay of thermal effects and injection current variation can result in turn-on and turn-off hysteresis cycles that can be, depending on various model parameters, positive or negative. In the first case, the turn-on occurs at a higher value of the bias current than the turn-off; in a negative hysteresis cycle, the laser turns-on at a lower value of the bias current than the turn-off. These results are interpreted in terms of the interplay of the two time-scales determined by the injection current swept rate and the thermal relaxation rate.

Nonlinear localized modes in bandgap microcavities

We study experimentally an electrically pumped GaAs-based bandgap structure based on a vertical cavity surface emitting laser (VCSEL). We demonstrate that a microcavity embedded into this bandgap VCSEL structure supports localized optical modes without any holding beam. We propose a model of surface-structured VCSELs based on a reduced dissipative wave equation for describing electromagnetic modes in such semiconductor cavities and analyze a crossover between linear and nonlinear solitonlike cavity modes.

径向桥电极高功率垂直腔面发射激光器

The novel high-power vertical-cavity surface-emitting lasers(VCSEL) with radial bridge electrode is fabricated in order to improve the thermal characteristics and increase the out power of high power VCSEL.The analysis on the model of the high-power VCSEL shows the radial bridge electrode can reduce the electric and thermal resistance and the Joule heat of VCSEL.The radial brigde electrode and the conventional electrode high power VCSEL both with 200μm aperture are made and tested comparatively. The testing results show that the differential resistance of the VCSEL is 0.43Ωand the out power is 340 mW,1.7 times higher than the conventional device,which can operate at higher up to 80℃,and its thermal resistance is 0.95℃/mW.The temperature and opto-electric characteristics of radial bridge electrode high power VCSEL are much better than those of the conventional electrode high power VCSEL.

Drifting instabilities of cavity solitons in vertical-cavity surface-emitting lasers with frequency-selective feedback

In this paper we study the formation and dynamics of self-propelled cavity solitons (CSs) in a model for vertical-cavity surface-emitting lasers (VCSELs) subjected to external frequency-selective feedback and build their bifurcation diagram for the case where carrier dynamics is eliminated. For low pump currents, we find that they emerge from the modulational instability point of the trivial solution, where traveling waves with a critical wave number are formed. For large currents, the branch of self-propelled solitons merges with the branch of resting solitons via a pitchfork bifurcation. We also show that a feedback phase variation of (2) can transform a CS (whether resting or moving) into a different one associated to an adjacent longitudinal external cavity mode. Finally, we investigate the influence of the carrier dynamics, relevant for VCSELs. We find and analyze qualitative changes in the stability properties of resting CSs when increasing the carrier relaxation time. In addition to a drifting instability of resting CSs, a distinctive kind of instability appears for certain ranges of carrier lifetime, leading to a swinging motion of the CS center position. Furthermore, for carrier relaxation times typical of VCSELs the system can display multistability of CSs.

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.

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.

Low current density, inverted polarity, high-speed, top-emitting 850 nm vertical-cavity surface-emitting lasers

High-speed, oxide-confined, inverted polarity (n-up), polyimide-planarised 850 nm vertical-cavity surface-emitting lasers (VCSELs) were fabricated and characterised. The lasers exhibit a 23 dB frequency modulation bandwidth (f3dB) up to 15.2 GHz with a 10 mm oxide aperture diameter, at the lowest current density (Jbias) ever reported of 6.4 kA/cm 2 . The ratio f3dB 2 /Jbias ¼ 36.1 (GHz 2 /kA/cm 2 ) represents a 21% increase when compared with the highest pre- viously reported ratio. The threshold voltage and current were as low as 1.45 V and 0.9 mA, respectively, with a series resistance of 65 V. A rate-equation-based thermal VCSEL model was used to predict the device performance at different temperatures. Good agreements between measured and simulated DC characteristics were obtained.

Influences of the Current Transverse Profile on the Transverse Mode Competition of VCSELs Diodes

A spatially independent model of vertical-cavity surface-emitting lasers (VCSELs) is derived by integrating the spatially dependent rate equations over the cross section of the cavity of a VCSEL. The angular and radial non-uniformities of the injection current are taken into account. The well-known LP modes of a weakly-guiding cylindrical waveguide are employed to describe the transverse modal structure in the VCSEL cavity. This model is solved in a self-consistent way by using the 4th order Runge-Kutta method. The dependence of transverse mode competition on the current intensity, the angular and radial non-uniformities of the injection current, and the geometrical parameters of the electrical contact are thoroughly investigated and analyzed. The results are useful to the optimum design of the optical transverse modal structure of VCSELs.

Localized traveling waves in vertical-cavity surface-emitting lasers with frequency-selective optical feedback

Spatially self-localized states have been found in a model of vertical-cavity surface-emitting lasers with frequency-selective optical feedback. The structures obtained differ from most known dissipative solitons in optics in that they are localized traveling waves. The results suggest a route to realization of a cavity soliton laser using standard semiconductor laser designs.

Numerical analysis of high Q-factor photonic-crystal VCSELs with plane-wave admittance method

The paper presents the application of a novel plane-wave admittance method (PWAM) to the three-dimensional and fully vectorial modeling of vertical-cavity surface-emitting lasers with incorporated photonic crystal. The basic mathematical details of the method are given and its convergence is verified for a sample structure. Then the simulations performed with PWAM are used to determine the optimal photonic crystal parameters for low-loss, high-Q-factor regime.

Input and intrinsic device modeling of VCSELs

An efficient model scheme that combines the non-linear behavior of the input parasitics with the intrinsic fundamental device rate equations of the Vertical Cavity Surface Emitting Lasers (VCSELs) is proposed. A systematic methodology for the model parameter extraction from dc and ac, electrical and optical measurements, is also presented and simulation results are compared with the experimental measurements. Extraction and simulation procedures are implemented in commercial integrated circuit design tools and they are proved to be very fast while they preserve adequate accuracy.

Rate-equation-based VCSEL thermal model and simulation

In this paper, we present a simple thermal model of Vertical-Cavity Surface-Emitting Laser (VCSEL) light-current (LI) characteristics based on the rate-equation. The model can be implemented in conventional SPICE-like circuit simulators, including HSPICE, and be used to simulate the key features of VCSEL. The results compare favorably with experimental data from a device reported in the literature. The simple empirical model is especially suitable for Computer Aided Design (CAD), and greatly simplifies the design of optical communication systems.

Investigation of Polarization Properties of VCSELs Subject to Optical Feedback From an Extremely Short External Cavity—Part I: Theoretical Analysis

A two modes rate equation model for vertical-cavity surface-emitting lasers (VCSELs) subject to optical feedback from an extremely short external cavity (ESEC) is presented. By making use of it we develop a map of bistability to investigate the parametric dependence of polarization properties of VCSELs in such configuration, finding out a periodic dependence of the polarization switching (PS) currents on the ESEC length. By increasing the external mirror reflectivity we can make this periodic dependence stronger and strongly asymmetric providing the possibility to prevent PS for any injection current achieving polarization stabilization in VCSELs. Further numerical simulations with isotropic and non isotropic feedback show how parameters as the compression coefficients, the frequency splitting between the linearly polarized (LP) modes, the differential gain and the top mirror reflection coefficient, affect the map of bistability.

Design of low-power fast VCSEL drivers for high-density links in 90-nm SOI CMOS

The continuous decrease of the supply voltage to 1 V and below in CMOS makes the design of laser drivers a challenging task. Hence, a detailed comparison of three basic driver architectures, namely, common source (CS), CS with source degeneration, and source follower (SF) is presented using transistor models including short channel effects. Based on this comparison, two power-optimized driver topologies are implemented in a 90-nm silicon-on-insulator CMOS technology. The SF driver features a bandwidth of 18 GHz on a 50-/spl Omega/ load. The required chip area is only 140 /spl mu/m/spl times/140 /spl mu/m, which is very beneficial for high-density short-distance optical interconnects. This allows a data rate of 12.5 Gb/s at a bit error ratio of less than 10/sup -12/ to be achieved even with a 10-Gb/s oxide confined vertical-cavity surface-emitting laser (VCSEL). The power consumption is 27 mW. The drivers were optimized for maximal eye opening by applying a fast and accurate VCSEL model.