Polarization modulation dynamics of vertical-cavitysurface-emitting lasers with an extended cavity

Vertical-cavity surface-emitting lasers (VCSELs) are known to exhibit a small birefringence and dichroism whose axes are directed along the crystal axes of the quantum wells and which fix the polarization of the oscillating light. In this paper, we consider the dynamics of the polarization of light in such a laser, extended by means of a quarter-wavelength plate in an external cavity. Periodic variations are experimentally observed. A theoretical analysis and numerical results are proposed, using a recent model which includes the carriers' spin interaction. A good match is found between experimental and numerical results     

The dynamic properties and stability analysis for vertical-cavitysurface-emitting lasers

In this paper, a phenomenal analysis on the wavelength dependence of the gain temperature coefficient is presented. Based on this model, the relation between the dynamic properties and the lasing wavelength within the gain regime are investigated using the rate equations, including the wavelength dependence of both the differential gain and linewidth enhancement factor. Our calculation shows that when the lasing mode occurs in the negative damping rate regime, the relative intensity noise (RIN) is more than 43 dB higher, and the linewidth is broadened out more than 30 dB, which indicates laser being in a chaotic state. The stability of the vertical-cavity surface-emitting lasers with distant external optical feedback is analyzed numerically. The results for different cavity designs are compared. The effects of the nonlinear gain coefficient on RIN and spectral linewidth of the VCSEL's with external optical feedback is investigated     

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     

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     

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     

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     

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     

A comprehensive circuit-level model of vertical-cavitysurface-emitting lasers

The increasing interest in vertical-cavity surface-emitting lasers (VCSEL's) requires the corresponding development of circuit-level VCSEL models for use in the design and simulation of optoelectronic applications. Unfortunately, existing models lack either the computational efficiency or the comprehensiveness warranted by circuit-level simulation. Thus, in this paper we present a comprehensive circuit-level model that accounts for the thermal and spatial dependence of a VCSEL's behavior. The model is based on multimode rate equations and empirical expressions for the thermal dependence of the active-layer gain and carrier leakage, thereby facilitating the simulation of VCSEL's in the context of an optoelectronic system. To confirm that our model is valid, we present sample simulations that demonstrate its ability to replicate typical dc, small-signal, and transient operation, including temperature-dependent light-current (LI) curves and modulation responses, multimode behavior, and diffusive turn-off transients. Furthermore, we verify our model against experimental data from four devices reported in the literature. As the results will show, we obtained excellent agreement between simulation and experiment     

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     

RF crosstalk in multiple-wavelength vertical-cavitysurface-emitting laser arrays

We present the crosstalk measured in multiple-wavelength vertical-cavity surface-emitting laser (VCSEL) arrays under RF modulation. The array consists of eight bottom-emitting VCSEL's arranged with a “pie”-like configuration within a 60-μm-diameter circle with a 3-μm spacing for coupling into a multimode fiber. The crosstalk is investigated by measuring a cross-modulation response of two VCSEL's in the array using a monochromator in an optical spectrum analyzer as a receiver. Excess crosstalk is minimized by flip-chip mounting the array and introducing a proper bias condition. The crosstalk observed In the adjacent VCSEL's is less than -40 dB at the modulation frequency below 700 MHz and it Increases at 20 dB/decade above this frequency when both VCSEL's are biased at 5.0 mA     

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     

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     

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     

Modal properties of two-dimensional antiguided vertical-cavitysurface-emitting laser arrays

We present a detailed analysis on 2-D (4 × 4 square-lattice) antiguided vertical-cavity surface-emitting laser (VCSEL) arrays based on the effective-index model. The calculation shows that the array can operate under 2-D resonant coupling, provided that the resonance condition in both the horizontal and vertical directions is satisfied. Consequently, the resonant-mode edge radiation loss is inversely proportional to the number of array elements along one direction for a N × N array. Low-edge-loss out-of-phase and adjacent array modes are found to compete with the in-phase resonant mode. While the 3-D gain overlap is not a significant factor in modal discrimination, the introduction of inter-element loss allows the in-phase mode to exhibit the lowest threshold gain for a wide range of inter-element width, s (Δ₈ ≈ 0.5 μm for 980-nm wavelength devices). The 2-D antiguided array results from shifting the cavity resonance between the element and inter-element regions and is fabricated by selective chemical etching and two-step metalorganic chemical vapor deposition growth. Diffraction-limited in-phase and out-of-phase array mode operation is observed from top-emitting arrays, depending on the inter-element width. Substrate-emitting array structures are investigated as a means to lower heating and increase the coherent output power     

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