Temperature-dependent polarization characteristics of composite-resonator vertical-cavity lasers

We investigate the output characteristics from 10/spl deg/C to 160/spl deg/C of a monolithic dual-resonator vertical-cavity laser composed of three distributed Bragg reflector mirrors that separate two nominally identical optical cavities. The light output from the top ion-implanted cavity under forward bias is partitioned into two orthogonal polarizations of the fundamental transverse mode. A reverse bias of sufficient magnitude applied to the bottom oxide cavity causes the abrupt suppression of the dominant polarization and simultaneous emergence of the orthogonal polarization, consistent with wavelength dependent electroabsorptive loss in the reverse biased quantum wells of the oxide-confined cavity. We calculate the internal loss as a function of reverse bias and temperature, and characterize the polarization properties of the device based on the temperature dependence of the laser output. The polarization switching is consistent with increasing absorption with increasing temperature and decreasing absorption at longer wavelengths.     

Gain-switching in a vertical-cavity laser with high-contrastmirrors

Gain-switched operation of an optically pumped vertical-cavity surface-emitting laser with high-contrast Al_xO_y/GaAs distributed Bragg reflectors is characterised. A pulse width of less than 8 ps is obtained. The far-field radiation patterns at different pump levels are found to depend on the temporal response     

Dynamic properties of vertical-cavity surface-emitting lasers with improved polarization stability

We describe dynamic properties of rectangular etched post vertical-cavity surface-emitting lasers designed for increased polarization stability. These lasers show polarization extinction ratios higher than 20 dB in CW and under high-speed large signal modulation. The high degree of polarization stability allows for error-free transmission in polarization selective free space optical links.     

High-speed vertical-cavity surface emitting laser

Planar, gain-guided vertical-cavity surface-emitting lasers (VCSELs) with a modulation bandwidth of 14 GHz are described. This bandwidth is reached at a drive current of only 8 mA. The intrinsic bandwidth of these devices is estimated to be greater than 50 GHz. Nonlinear light-current characteristics of these lasers may lead to a high level of nonlinear harmonic distortion of the high-frequency output. It is shown that the relative intensity of the second-harmonic response decreases rapidly at higher drive currents, in agreement with a phenomenological model based on the DC characteristics of the laser     

Ultralow-threshold cryogenic vertical-cavity surface-emitting laser

Data are presented characterizing a low-threshold vertical-cavity surface-emitting laser designed for cryogenic operation. A threshold current of 12 μA and current density of 25 A/cm² are obtained at 77 K with the low-loss cavity design. From 77 K to 160 K, the threshold increases linearly with temperature, but only approximately tracks the detuning of the cavity resonance from the minimum energy transition of the quantum well. At 77 K, we estimate that the 25-A/cm² threshold current density is about twice that required for transparency     

Three-terminal dual-stage vertical-cavity surface-emitting laser

A three-terminal dual-stage VCSEL, operating continuous-wave at room temperature has been fabricated. Independent biasing of the two active stages leads to an extended singlemode regime compared to conventional VCSELs. The parallel configuration reveals singlemode operation with a differential series resistance <35 Ω     

Elliptical polarization emission from GaAlAs laser diodes in anexternal cavity configuration

We report the experimental operation of an external-cavity laser capable of oscillating in TE, TM, and elliptical-polarization states. An intracavity polarizer is used to force the laser to emit polarized radiation with TE and TM components whose wavelength can be changed by rotating the polarizer, a simple model based on the Jones matrix and steady-stale rate equations is used to explain experimental data. Theoretical results for near threshold operation accurately predict the TE and TM power as a function of polarizer angle as well as the polarization dependence of wavelength     

Analysis of vertical-cavity surface-emitting laser multimodebehavior

This paper investigates problems associated with multimode oscillation in vertical-cavity surface-emitting lasers (VCSELs). The multimode rate equations for transverse mode were formulated. These equations take into account carrier diffusion and gain nonuniformity in the lateral direction. It was shown that multimode transverse mode excitation is due to carrier spatial hole burning, but many factors affect the number of lasing modes. The role of gain nonuniformity distribution, carrier diffusion, and modal loss compared with mirror loss in a cavity were demonstrated by numerical solution of the multimode rate equations     

Effects of built-in polarization on InGaN-GaN vertical-cavity surface-emitting lasers

We investigate the effect of built-in spontaneous and piezoelectric polarization on the internal device physics of current-injected GaN-based vertical-cavity surface-emitting lasers (VCSELs) with strained InGaN quantum wells. Advanced device simulation is applied to a previously manufactured device design featuring dielectric mirrors and an indium-tin-oxide current injection layer. Contrary to common perception, we show: 1) that only a small fraction of the built-in quantum-well polarization is screened at typical injection current densities and 2) that the polarization of the AlGaN electron stopper layer has a strong effect on the VCSEL threshold current which can be partly compensated for by higher p-doping.     

High-power vertical-cavity surface-emitting laser with an extra Au layer

We report the performance of a high-power vertical-cavity surface-emitting laser (VCSEL) with an extra Au layer. By using the extra Au layer, the far-field divergence angle from a 600-/spl mu/m diameter VCSEL device is suppressed from 30/spl deg/ to 15/spl deg/, and no strong sidelobe is observed in far-field pattern. There is a slight drop in optical output power due to the introduction of the extra Au layer. By improving the device packaging method, the VCSEL device produces the maximum continuous-wave optical output power of 1.95 W with lasing wavelength of 981.5 nm. The aging test is carried out under constant current mode at 60/spl deg/C, and the preliminary result shows that the total degradation of output power is less than 10% after 800 h.     

Frequency response of polarization switching in vertical-cavity surface-emitting lasers

We present an experimental study of the current-driven polarization modulation properties of VCSELs. In some VCSELs, abrupt polarization switching (PS) between two polarization modes is observed at a particular value of the pump current. We investigate the dynamics and the associated dominating time scales of PS as these features are strongly linked with the underlying physical mechanism causing the PS. To this end, we measure both for gain- and index-guided VCSELs the critical modulation amplitude necessary to steadily force PS back and forth across the PS point as a function of the modulation frequency. This yields the current-driven polarization modulation frequency response, which we compare with the thermal frequency response of the studied devices. The dynamic behavior turns out to be strikingly different for the different VCSEL types. Thermal effects only play a minor role in the PS in our index-guided VCSELs, while they really seem to lie at the origin of PS in the gain-guided VCSELs. By implementing this in a rate-equation based theoretical model, we are able to explain the peculiarities of the measured response curves and to reproduce the experimental findings.     

A high-efficiency vertical-cavity surface-emitting switching laserfabricated with post-growth cavity mode positioning

The first room-temperature continuous-wave (CW) operation of the double heterostructure optoelectronic switching laser implemented as a vertical-cavity laser is described. A deposited dielectric top reflector of SiO₂/TiO₂ allowed the use of a cavity etch back technique after the sample was grown, to position the cavity mode at the desired wavelength. Room temperature CW threshold currents as low as 4.8 mA for a 14-μm-diameter device were obtained with slope efficiencies of 0.45 mW/mA. The maximum CW output power was 2.5 mW and the resistivity was 4×10^-4 Ωcm²     

Pixels consisting of a single vertical-cavity laser thyristor and adouble vertical-cavity phototransistor

Bidirectionally cascadable optical pixels that consist of a single-vertical-cavity surface-emitting laser (VCSEL) thyristor and a double-vertical-cavity phototransistor are proposed. Despite almost identical layer structures, each device characteristic can be independently optimized by introducing a λ/2-spacer layer into the phototransistor section. A lasing threshold of 0.8 mA and a slope efficiency of 0.25 W/A are obtained for the laser thyristor, and a flat-topped photocurrent spectrum over 30 A and a photocurrent gain of 70 A/W are obtained for the phototransistor at the resonant wavelength. This work demonstrates the possibility of monolithic integration using thermal desorption and a regrowth technique and the suitability of these devices for massively parallel optical interconnections     

Cascadability of optically latching vertical-cavity surface-emitting laser

The cascadability of an optically latching vertical-cavity surface-emitting laser is investigated through the use of a wavelength-tunable optical probe. The bistable vertical cavity laser emits at a wavelength of 0.98 mu m, and shows a sensitivity peak to probe light generated from a grating-tunable edge-emitting laser in the 0.98 mu m wavelength range. The sensitivity peak occurs in a window of approximately 50 AA around the vertical-cavity lasing wavelength, and corresponds to the Fabry-Perot transmission window of the surface-emitter.<>     

A proposal of broad-bandwidth vertical-cavity laser amplifier

We propose a generic vertical-cavity amplifier (VCA) using a coupled-cavity design to broaden the bandwidth. Calculations are made for cavities with GaAs-AlAs and GaAs-Al_xO₂ distributed Bragg reflectors (DBR). We found that at reasonable pumping levels the VCA increased the bandwidth by 85% (GaAs-AlAs) to 500% (GaAs-Al_xO₂) as compared to a simple two-mirror structure similar to vertical-cavity surface-emitting lasers. In particular, the GaAs-AlAs VCA shows a bandwidth of 2 nm at 6-dB signal gain, while the GaAs-Al_xO₂ VCA demonstrates a 5-nm bandwidth at 6-dB signal gain with no ripple at required single-pass power gain of ~2-2.5%. Furthermore, as large as 30-nm bandwidth in a lossless bandpass filter can be obtained     

Green-emitting organic vertical-cavity laser pumped by InGaN-based laser diode

An organic vertical-cavity surface-emitting laser is demonstrated, which is pumped by an InGaN-based blue laser diode. The vertical-cavity laser structure consists of a poly-N-vinylcarbazole film doped with Coumarin 540A and two Bragg reflectors made of TiO₂/SiO₂ quarter-wave thin films. By driving the pump laser diode with a pulse width of 3.5 ns, singlemode lasing was achieved at a wavelength of 540 nm for a threshold pump power of 137 mW/pulse.     

Multiple-wavelength vertical-cavity surface-emitting laser arrays with a record wavelength span

Multiple-wavelength vertical-cavity surface-emitting laser (VCSEL) arrays are fabricated using a modified patterned-substrate growth technique in a molecular beam epitaxy (MBE) system. We achieved a large lasing wavelength span of 62.7 nm and highly uniform threshold currents with an average of 2.16/spl plusmn/0.81 mA. High repeatibility of wavelength spacing between 15 arrays with sharp wavelength shift rate 117.14 nm/mm is achieved.     

Tunable extremely low threshold vertical-cavity laser diodes

Submilliampere-threshold wavelength-tunable three-terminal vertical-cavity laser diodes have been fabricated by proton implantation and wet chemical etching. Laser diodes of 8-μm active diameter exhibit record low threshold currents of 650 μA and emit upto 170-μW output power under CW conditions and 0.4 mW under pulsed excitation. Slightly larger devices of about 12-μm diameter emit up to 1.85 mW in a single mode under pulsed conditions. The emission wavelength is about 970 nm and matched to the spectral gain of the three active InGaAs quantum wells. Individual elements in a two-dimensional array can be continuously tuned over 2.2 nm by applying separate tuning currents of 70 μA to the corresponding top mesa electrodes. Tuning and laser currents are controlled independently     

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.     

An InGaAs-GaAs vertical-cavity surface-emitting laser grown on GaAs(311)A substrate having low threshold and stable polarization

We have fabricated an InGaAs-GaAs vertical-cavity surface-emitting laser (VCSEL) grown on a GaAs(311)A substrate by molecular beam epitaxy (MBE) and demonstrated continuous wave operation at room temperature. A threshold current density of 80 A/cm/sup 2//well and very stable polarization characteristics up to 2.7 times the threshold were achieved. The polarization state with the highest optical intensity was oriented along the [2~33] direction, which is the crystallographic axis exhibiting the maximum gain. An extinction ratio of more than 12.7 dB was obtained between two orthogonal polarization states. The high and anisotropic gain of a (311)A-oriented VCSEL will drastically improve the device performance by optimization and process engineering.