A comprehensive model for the modal dynamics of vertical-cavitysurface-emitting lasers

We present a quasi-3-D dynamic model of vertical-cavity surface-emitting lasers (VCSELs). The interdependent processes of carrier transport, heat generation and dissipation, and optical fields are solved self-consistently for each point in time and space. An effective index model is adopted for the evaluation of the optical fields in the complex layer structure. The inclusion of a temperature- and carrier-density-dependent refractive index, and its time dependence, allows us to study the evolution of the transverse optical field distributions under dynamic conditions. The model is applied to a typical index-guided structure with a 7-μm oxide aperture. A direct comparison is made using "cold" cavity modes, which is a normal technique when modeling the dynamics of VCSELs. Significant discrepancies are demonstrated both at smalland large-signal modulation, which indicates the need of a more sophisticated model for accurately predicting and understanding the geometry-dependent modal evolution     

An improved time-domain traveling-wave model for vertical-cavitysurface-emitting lasers

The use of the time-dependent transfer matrix and wide-angle beam propagation method is proposed to improve the computational speed and accuracy of a recently developed time-domain traveling-wave model of vertical-cavity surface-emitting lasers. With suitable utilization of the transfer matrix, significant reduction of the total execution time of the traveling-wave model can be obtained. In addition, the use of the wide-angle beam propagation method can minimize the calculation error of the traveling-wave model due to the diffraction of light from the small aperture of the laser cavity     

Spectrally-filtered electroluminescence of vertical-cavitysurface-emitting lasers

We show that spontaneous emission from the mirror layers (λ=780 nm) of a vertical cavity surface emitting laser (VCSEL) is a significant component of the spectrum. By using bandpass filters, we are able to distinguish the electroluminescence (or “near-field”) pattern of the mirror layers from the active region pattern. We show that in some lasers, these patterns are irregular, possibly due to the presence of absorbing doping or defect clusters in the p-mirror that absorb light from the active region, and re-radiate the light at the shorter wavelength characteristic of the mirror layers. In addition, we show that dark areas appear, both in the active regions and the mirrors, as the device degrades     

Electrical characteristics of proton-implanted vertical-cavitysurface-emitting lasers

The electrical characteristics of proton-implanted GaAs quantum-well vertical-cavity surface-emitting semiconductor lasers (VCSELs) have been studied. We show that the 2 kT current, observed over many decades in these VCSELs, is primarily due to nonradiative recombination mechanisms. These include surface recombination at the edges of the proton-implanted region and bulk recombination at defects and heterojunction interface traps. The contribution of these mechanisms to the total nonradiative current and the threshold current density has been calculated. Lateral spontaneous emission measurements have been used to prove that the radiative current has a kT behavior in the subthreshold region. Electrical derivative measurements have been used to identify leakage current paths through the proton-implanted region in the low-bias regions. In addition, electrical derivative measurements have been used to measure the variation of series resistance with current near the lasing threshold. From a consideration of the various current paths in the VCSEL, a lumped circuit equivalent model for the VCSEL has been developed     

High-speed high-temperature operation of vertical-cavitysurface-emitting lasers

Vertical-cavity surface-emitting lasers emitting at 850 nm have been developed that are capable of 10-Gb/s operation at high temperatures. Measurements are made at 10 and 12.5 Gb/s at temperatures up to 150°C     

Noise characteristics of oxide-confined vertical-cavitysurface-emitting lasers

We demonstrate the possibility of generating intensity squeezed light with free-running or injected multimode vertical-cavity surface-emitting laser. Sub-shot-noise operation results from very strong anticorrelations between the transverse modes. The influence of the active media diameter on the amount of squeezing is analyzed     

Modal characteristics of ARROW-type vertical-cavitysurface-emitting lasers

Antiresonant reflecting optical waveguide (ARROW-type) vertical-cavity surface-emitting lasers are designed for high-power single-mode operation. A detailed full-vector finite-difference time-domain (FDTD) study shows strong modal discrimination in favor of the fundamental mode for large aperture (>6 μm), large index-step (Δn>0.025) simplified ARROW-type devices. The FDTD model identifies the polarization-dependent radiation losses of the higher order modes, which prevent them from reaching laser threshold     

Spectral linewidth in oxide-confined vertical-cavitysurface-emitting lasers

We present a model to compute the linewidth in vertical-cavity surface-emitting lasers (VCSELs), by accounting for the 3-D structure of real devices. To this aim, we include the noise source in the field equations and treat both the noise and the structural characteristics by means of coupled-mode theory. In this way, we obtain an expression for the linewidth that is given as the standard relation, modified by two correction factors that account for spatial effects and modal dispersion of the resonator. In the numerical results, we study for oxide-confined VCSELs the transition from index to gain-guided regime, where the standard linewidth theory does not hold, and we give some guidelines for narrow-line emission devices     

Relative intensity noise of multitransverse-mode vertical-cavitysurface-emitting lasers

Relative intensity noise (RIN) spectra of weakly index guided vertical-cavity surface-emitting lasers (VCSELs) in a multitransverse-mode regime are analyzed by using a model that takes into account all the transverse modes supported by the waveguide. Several resonance peaks are obtained in the noise spectra that correspond to the relaxation oscillation frequencies of the transverse modes. It is shown that for low spatially overlapping transverse modes, low RIN operation can be maintained. However, the excitation of transverse modes with a significant spatial overlap leads to a clear enhancement of the RIN at low frequencies     

High efficiency AlGaInP-based 650 nm vertical-cavitysurface-emitting lasers

Record high continuous-wave output power of 3.1 mW and peak wall-plug efficiency of 14% at the wavelength of 650 nm have been achieved from oxide-confined AlGaInP-AlGaAs vertical-cavity surface-emitting lasers. At a wavelength of 657 nm laser emission is detected up to 60°C     

Pitchfork bifurcation polarisation bistability in vertical-cavitysurface-emitting lasers

Pitchfork bifurcation polarisation bistability has been observed experimentally in a vertical-cavity surface-emitting laser for the first time. All-optical flipflop operation has been successfully demonstrated by injecting the trigger light inputs having the two orthogonal polarisations     

Aperture placement effects in oxide-defined vertical-cavitysurface-emitting lasers

A study of the effects of aperture placement on the properties of vertical-cavity surface-emitting lasers (VCSELs) is presented. When thin apertures are placed at the peak of the electric field standing wave optical losses are very high for small apertures. The threshold current increases with decreasing aperture size and two-dimensional diffraction like patterns are evident in the far field. For apertures placed at a node, optical losses appear to be negligible, and loss of optical confinement is apparent for apertures below 2 πm     

Observation of bistability in GaAs quantum-well vertical-cavitysurface-emitting lasers

Two different types of bistability in proton-implanted GaAs quantum-well (QW) vertical-cavity surface-emitting lasers (VCSELs) have been observed. The first type of bistability has a small hysteresis width (~50 μA) in the light versus current and voltage versus current characteristics. Light-induced large negative differential resistance, random fluctuations, and self-pulsations are observed at the switching point. The emission patterns show that the bistability occurs at a spatially localized area under the output facet that covers only a small fraction of the N1S-μm-diameter aperture. The bistability stems from spatially localized saturable absorption. The second type of bistability has a large hysteresis width (~1 μA) in the L-1 characteristics and is observed well above the threshold current. In this case, no observable bistable loop exists in the voltage versus current characteristics, and the bistability is associated with transverse mode-hopping     

Polarization stability of phase-locked arrays of vertical-cavitysurface-emitting lasers

The polarization stability of the fundamental lasing super-mode obtained from coherently coupled arrays of vertical-cavity surface-emitting lasers has been investigated. Various devices have been analyzed and none showed the abrupt change of the polarization direction (flip) often observed in solitary devices. This polarization stability is due to a current independent dichroism of 0.5 GHz     

Aperture dependent loss analysis in vertical-cavitysurface-emitting lasers

A study of the influence of oxide apertures on the internal loss in vertical-cavity surface-emitting lasers (VCSEL's) is performed for two different aperture placements within the VCSEL cavity. It is found that when apertures are placed at a node in the standing wave of a VCSEL cavity there are negligible aperture dependent losses. However, when apertures are placed at an antinode there is a clear relationship between aperture dimension and internal loss     

Effect of strong optical feedback on vertical-cavitysurface-emitting lasers

An analysis is performed of the effects of strong optical feedback on the characteristics of single-transverse mode VCSEL's. Consideration is given to the cases of short (1.5 cm) and long (15 cm) external cavities. When the laser is operated well above threshold in a short external cavity with high reflectivity, a strong dependence on the accumulated external cavity phase is observed. Stable operation is found for an optimum phase while for other values of the phase, chaotic dynamics is observed. Such behavior is not seen near threshold where the laser output is stable for any accumulated phase. For the longer external cavity the influence of the phase term is found to be insignificant: chaotic behavior is seen in the output over a wide range of operating currents     

Measurement of differential carrier lifetime in vertical-cavitysurface-emitting lasers

Measurements of differential carrier lifetimes on gain-guided proton-implanted vertical-cavity surface-emitting lasers with device size as a parameter are reported. The lifetimes were obtained from laser impedance measurements and from small-signal modulation optical response at subthreshold currents. A simple small-signal equivalent circuit was used to correct the optical data and to extract the carrier lifetimes from the impedance data. Carrier lifetimes ranged from 4.2 ns at 0.04 mA, to about 0.6 ns at a bias close to threshold. The measured carrier lifetimes were used to calculate the corresponding threshold carrier density (n_th~6×10¹⁸ cm^-3) and recombination parameters     

Small-signal modulation of multitransverse modes vertical-cavitysurface-emitting semiconductor lasers

The small-signal modulation response of multi-transverse modes, proton-implanted vertical-cavity semiconductor lasers was studied experimentally and theoretically. Multiresonance frequencies and notches in the modulation response were obtained and the detailed characteristics varied for different overlap levels between the lasing modes. The theoretical modeling matched the experimental results and revealed the coupled oscillators manifestation for highly overlapping transverse modes     

Modulation response of multiple transverse modes in vertical-cavitysurface-emitting lasers

The small-signal modulation response of multiple transverse modes in a vertical-cavity surface-emitting laser was studied numerically. The overlap between the modal distribution of the field and the carrier distribution in the active region is fundamental to determining the modulation response, According to the injection current level, the modulation response curve in several configurations and parameters used can display peaks and notches that may impair the frequency response of the device. These features reflect the competition of carrier by the operating modes in a way that can be described as interference. Therefore, the total modulation response curve cannot be evaluated from the modulation response of the individual modes