Behavior Of Vertical-cavity Surface-emitting Lasers Research Articles

Particle swarm optimization-assisted approach for the extraction of VCSEL model parameters.

We propose a direct particle swarm optimization (PSO) method for extracting the parameters of a physical model describing the behavior of vertical-cavity surface-emitting lasers (VCSELs), starting from the light-current (L-I) characteristics and the small signal modulation (S21) responses, at different currents and temperatures. With an optimal choice of hyperparameters of the algorithm, the method is able to predict parameters that accurately reproduce the behavior of the device. Its prediction capabilities are compared to those of two commonly used nonlinear optimizers (Interior Point and Levenberg-Marquardt), to benchmark its performances.

Annealing effects of 850 nm vertical-cavity surface-emitting lasers after proton irradiation

A long-term annealing experiment was performed using 850 nm vertical-cavity surface-emitting lasers (VCSELs) irradiated with 10 MeV protons. Static parameters such as the threshold current, slope efficiency, and light output power were tested using annealing currents above and below the threshold. The experimental results indicated that these parameters gradually recovered with annealing time, and the degree of recovery was proportional to the annealing current. In addition, curve fitting was performed to obtain the direct relationship between the slope efficiency and annealing current. A comprehensive investigation of the annealing behavior of VCSELs is crucial for device applications in harsh radiation environments.

Mode Behavior of VCSELs With Impurity-Induced Disordering

This letter explores the modal behavior of oxide-confined vertical-cavity surface-emitting lasers (VCSELs) with varying emission apertures defined by impurity-induced disordering (IID) via closed ampoule zinc diffusion. A 1-D plane wave propagation method is used to calculate the mirror loss as a function of IID strength and depth. The devices are fabricated with masked areas ranging from approximately 70%-110% of the oxide aperture defining an unmodified emission aperture designed to overlap mainly with the fundamental mode. An analysis of the transverse mode lasing characteristics and mode-dependent thermal characteristics demonstrates a decrease in thermal performance associated with the increasing overlap between the IID ring and supported optical modes of the VCSEL cavity. A single-mode output power of 1.6 mW with over 30 dBm side-mode suppression ration is achieved from a 3 μm device with an IID-defined output aperture of approximately 1.3 μm. The optimal IID emission aperture to oxide aperture ratio for maximizing the single-fundamental-mode output power is experimentally measured.

Stokes vector characterization of the polarization behavior of vertical-cavity surface-emitting lasers

We demonstrate that a full polarization analysis in terms of the Stokes vector parameters is necessary to determine the polarization state of light emitted by vertical-cavity surface-emitting lasers (VCSELs). For three selected representative VCSEL devices, we measured the injection current dependence of the three Stokes parameters and compared these results with linearly selected polarization P-I curves, clearly demonstrating that a complete polarization analysis is required to unveil the full polarization behavior.

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.

Optimum Biasing of VCSEL Diodes for All-Optical Up-Conversion of OFDM Signals

Nonlinear behavior of vertical-cavity surface-emitting laser (VCSEL) diodes is exploited to perform all-optical up-conversion by second- and third-order mixing. We investigate and explain conditions for optimum frequency mixing with a common WLAN IEEE 802.11a signal. Then, we apply these findings to the transmission of an ultra-wideband (UWB) multiband-OFDM ECMA-368 signal over a fiber-optic link. We demonstrate direct modulation with the UWB signal up to 10.3 GHz and perform up-conversion to frequencies as high as 16 GHz, far beyond the cutoff frequency of the VCSEL diode.

Simplified Model of the Dynamic Thermal Tuning Behavior of VCSELs

In this letter, a simplified thermal model is used to derive a closed-form expression for the frequency dependency of the current-to-wavelength tuning coefficient (FM response) of vertical-cavity surface-emitting lasers (VCSELs). It explains the experimentally observed square root law and shows very good agreement with measured FM responses of two different VCSEL types. It yields significantly improved accuracy compared to the usually assumed first-order low-pass model.

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 dynamics of vertical-cavity surface-emitting lasers with optical feedback

The standard two-mode rate equations are extended to discuss polarization behavior of vertical-cavity surface-emitting lasers (VCSELs) with optical feedback. In the rate equations, a logarithmic gain formula and unit step function are used to simulate the experimental conditions more truly. Our simulation results show that weak polarization-preserving feedback will cause multiple polarization switches (PSs) with increasing bias current; strong feedback can suppress PSs and make the VCSEL work in a single polarized mode. The case is similar when y-polarized feedback is considered. The PS point does not disappear even under strong x-polarized feedback. Bifurcation diagrams show that the interplay of PSs and delayed feedback makes the nonlinear dynamics of the two polarized modes more complex. If the feedback is large enough, both chaotic pulses due to feedback and low-frequency fluctuations due to gain competition emerge in the time traces of the two modes. Polarization modulation is also demonstrated when a quarterwave plate is added to the external cavity, which agrees with the experimental observations.

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.

Characteristics of GaAs/AlGaAs vertical-cavity surface-emitting lasers irradiated with gamma rays

The effects of gamma radiation on vertical-cavity surface-emitting laser (VCSEL) characteristics are investigated experimentally. Three groups (batches) of oxide-confined VCSELs are investigated. It is found that radiation can change (increase or decrease) the quantum efficiency of VCSELs considerably, depending on their production batch. Small changes in the threshold current are observed for some devices. Shifts to a longer wavelength in the peak-emission profile are noticed after irradiation, which is found to be reversible in some VCSELs by simply increasing the radiation dose. It is also discovered that gamma radiation affects the total number of competing transverse modes depending on the radiation dose. Self-pulsation characteristics in some devices are not affected by the radiation exposure. Knowledge of the behavior of VCSELs under gamma exposure would be useful for their applications in hostile environment.

Rate equations for vertical-cavity surface-emitting lasers

By applying a multiple time scale perturbation method, we simplify the spin-flip model equations [San Miguel et al., Phys. Rev. A $52,$ 1728 (1995)] describing the polarization behavior of vertical-cavity surface-emitting lasers. The reduced problem consists of three rate equations for a two-mode semiconductor laser. The asymptotic theory is based on the natural values of the laser parameters and considers the case of large values of the spin-flip rate and birefringence with respect to the relaxation oscillation frequency. Our analysis corrects and complements previous derivations of rate equations from the spin-flip model equations. We find that the cross-gain saturation coefficients due to spin-flip processes are not symmetric and may become negative. As a result, a new physical interpretation of polarization switching from the high-frequency mode to the low-frequency mode and for high values of the birefringence is possible.

Oxide-confined vertical-cavity surface-emitting laser pumped Nd:YVO4 microchip lasers

In this letter, we demonstrate an experimental study of using a large area oxide-confined vertical-cavity surface-emitting laser (VCSEL) to pump a Nd:YVO/sub 4/ microchip laser. The maximum output power of 1.2 mW in TEM/sub 00/ mode is obtained with a pump power of 8.2 mW. Experimental results show that the complex transverse modal behavior of VCSELs in the higher injection current may cause an impediment of power scaling.

Impact of in-plane anisotropic strain on the polarization behavior of vertical-cavity surface-emitting lasers

We experimentally demonstrate that the presence of switching between two fundamental modes with orthogonal linear polarization in vertical-cavity surface-emitting lasers and the current at which this phenomenon occurs depend on both the magnitude and the orientation of an externally induced in-plane anisotropic strain. We interpret this behavior by considering the anisotropy in gain and in refractive index, both induced by the in-plane strain, and by accounting for a redshift of the two gain curves as a result of current-induced heating.

Effect of photon-energy-dependent loss and gain mechanisms on polarization switching in vertical-cavity surface-emitting lasers

We have analyzed the effect of the photon energy and temperature dependence of both the gain and the total losses inside the cavity to understand the polarization behavior of vertical-cavity surface-emitting lasers. The assumption that the losses are dominated by free-carrier absorption in the p-doped mirror is made. Developing a new theoretical approach, we are able to predict different polarization switching regimes in which switching occurs from the high- to the low-frequency mode, from the low- to the high-frequency mode, or both consecutively. All these predictions have been experimentally verified by our measurements on GaAs/AlGaAs proton-implanted vertical-cavity surface-emitting lasers.

Transverse modes under external feedback and fiber coupling efficiencies of VCSEL's

We report a detailed study on the transverse mode behavior of vertical-cavity surface-emitting lasers (VCSEL's) under strong external feedback. Backreflections from a glass facet result, periodically depending on the feedback phase, in variations of the transverse mode pattern of strongly index guided multitransverse-mode-emitting lasers. As a result, butt-coupling efficiencies of these lasers strongly depend on laser-fiber distance. For typical active VCSEL diameters around 15-/spl mu/m fiber-coupled powers into standard 50 /spl mu/m-core diameter graded-index (GI) silica fibers vary by nearly 10 dB. Even for high-numerical aperture 100-/spl mu/m-core diameter fibers, power variations of up to 2 dB are observed.

Multilayer analysis of anisotropic heat flux in vertical cavity-surface emitting lasers with quarter-wave semiconducting mirrors

Monolithic arrays of vertical cavity-surface emitting lasers (VCSELs) have the potential to be used in microwave systems based on opto-electronic technologies. However, the temperature has a strong influence over several characteristics of VCSELs. Self-heating may restrain the gain inside the device cavity and it is responsible for an increase in the laser threshold current as well as a decrease of its output power. In this paper, the thermal behavior of VCSELs was evaluated by means of a procedure that takes into account the multilayer aspects of the heat-flux propagation. The method has the advantage of dealing with the heat propagation inside each layer of the periodic structures of the device. Thus, the different characteristics and influence of the materials employed in the chip manufacturing can he considered and the device temperature profile can be predicted. From the method assumptions and simulations, the thermal resistances of typical devices were calculated. The results were shown to be in good agreement with experimental values reported in the literature.

Effects of a thermal-dependent electric field penetration depth on threshold behavior of surface-emitting lasers

A theoretical model including the electric field penetration analysis and its dependence on temperature were derived in order to study the threshold behavior of vertical-cavity surface-emitting lasers. The longitudinal mode of oscillation is found by adopting a conveniently chosen reference plane, and considering the complex reflection coefficients for traveling waves at this plane. The influence of thermal effects on laser wavelength, linear gain, carrier density, and threshold current density are evaluated. Agreement with experimental results from the open literature was achieved. © 1998 John Wiley & Sons, Inc. Microwave Opt Technol Lett 17: 94–97, 1998.

Dynamic behavior of vertical-cavity surface-emitting lasers

A quasi-three-dimensional dynamic model of index-guided vertical-cavity surface-emitting lasers is developed. Detailed structure of Bragg reflectors and lateral optical confinement are considered into the model. A three-dimensional waveguide problem is reduced to one dimension by using the effective-index method. The dynamic response of optical field is solved by the time-domain algorithm. In addition, the lateral variation of carrier concentration, refractive index, and spontaneous-emission profile are also determined in a self consistent manner. Using this model, the influence of carrier transport and hot carriers on the dynamic behavior of vertical-cavity surface emitting lasers is studied. It is found that these nonlinearities have significant influence on the relaxation-oscillation frequency and modulation bandwidth of the devices.

Thermal effects on the threshold of vertical-cavity surface-emitting lasers: first- and second-order phase transitions

We investigate the threshold behavior of vertical-cavity surface-emitting lasers (VCSEL's) by solving the set of coupled equations for carrier density, field amplitude, and plasma and lattice temperatures. We show that, because of plasma heating and lattice heating, the threshold of VCSEL's can be continuous or discontinuous with bistability between lasing and nonlasing states (correspondingly second- or f irst-order phase transition), depending on the relative position of the cavity frequency to the gain bandwidth and on the ambient (substrate) temperature of the device.