Vertical-cavity Surface-emitting Semiconductor Lasers Research Articles

Photonic reservoir computing for parallel task processing based on a feedback-free spin-polarized VCSEL

Time delayed reservoir computing (RC) is a novel artificial neural network that is easy to implement in hardware due to its extremely simple structure. Because of its time-division multiplexed information processing, laser-based photonic time-delayed RCs usually realize parallel processing with polarization/wavelength multiplexing. However, the performance of two different tasks is difficult to regulate separately and simultaneously in the time delayed RC system, especially for the chip-scale configuration. Here, we propose a feedback-free RC system based on a spin-polarized vertical-cavity surface-emitting semiconductor laser (VCSEL), which simplifies the whole system structure and can process time series prediction and waveform recognition tasks in parallel, with employing the input and output coding to provide the effect from past states. By separately setting the number of past states introduced by the coding for the two tasks, the performance of the two tasks can be adjusted respectively. Furthermore, by appropriately tuning the pump polarization ellipticity which is the unique feature for the spin-polarized VCSEL, the computational ability of the proposed RC can be focused on one of the two parallel tasks. Therefore, the proposed RC system is capable of dealing with different tasks with high performance, and also expected to provide a viable solution for integrated neuromorphic computing systems due to its compact, feedback-free structure.

Nonlinear Dynamics Tailored by Spin-Polarized Carriers in Semiconductor Vertical-Cavity Surface-Emitting Lasers

Nonlinear Dynamics Tailored by Spin-Polarized Carriers in Semiconductor Vertical-Cavity Surface-Emitting Lasers

Suppression of modulation instability in VCSEL by external optical injection.

The dynamics of a broad area semiconductor vertical-cavity surface-emitting laser (VCSEL) is analytically and numerically investigated considering the linewidth enhancement factor resulting in the modulation instability of a spatially homogeneous generation mode. We find the aperture width depends on the parameters of the laser system, above which the modulation instability leads to chaotic filamentalization of the optical field and complicates the practical application of such lasers. We show that using the external optical injection of small amplitude, it is possible both to transform chaotic filaments into regular stationary spatial optical structures (stripes and hexagons) and to stabilize the broad-area VCSELs.

Topological semiconductor laser solitons with polarization singularities

We predict a wide class of two-dimensional vector dissipative solitons in wide-aperture semiconductor vertical-cavity surface-emitting lasers with a saturable absorber. For them, polarization structure varies over the laser cross section and includes singularities: $\mathsf{V}$ points with zero total intensity, $\mathsf{C}$ points with purely circular polarization, and $L$ lines with purely linear polarization. We show that the transverse motion of these solitons obeys the Eulerian mechanics dictated by soliton symmetry, taking into account the vector nature of laser solitons; presented are scenarios of soliton transverse rotation and ``lunar motion.''

Ubiquity of ring structures in the control space of complex oscillators.

We report the discovery of two types of stability rings in the control parameter space of a vertical-cavity surface-emitting semiconductor laser. Stability rings are closed parameter paths in the laser control space. Inside such rings, laser stability thrives even in the presence of small parameter fluctuations. Stability rings were also found in rather distinct contexts, namely, in the way that cancerous, normal, and effector cells interact under ionizing radiation and in oscillations of an electronic circuit with a junction-gate field-effect transistor (JFET) diode. We argue that stability-enhancing rings are generic structures present in the control parameter space of many complex systems.

Synchronization of polarization chaos in mutually coupled free-running VCSELs.

We numerically demonstrate and analyze polarization chaos synchronization between two free-running vertical cavity surface emitting semiconductor lasers (VCSELs) in the mutual coupling configuration under two scenarios: parallel injection and orthogonal injection. Specifically, we investigate the effect of external parameters (the bias current, frequency detuning and coupling coefficient) and internal parameters (the linewidth enhancement factor, spin-flip relaxation rate, field decay rate, carrier decay rate, birefringence and dichroism) on the synchronization quality. Finally simulation results confirm that in the parallel injection, chaotic synchronization can reach a cross-correlation coefficient of 0.99 within a range of parameter mismatch ±12%. On the other hand, the chaos synchronization for orthogonal injection only reaches a cross-correlation coefficient of 0.95 within a range of parameter mismatch ±3%.

Impact of the active area position in a nitride tunnel junction vertical-cavity surface-emitting laser on its emission characteristics

This paper presents results of numerical simulations of a nitride semiconductor vertical-cavity surface-emitting laser (VCSEL) with a tunnel junction. The modeled laser is based on a structure created at the University of California in Santa Barbara. The analysis concerns the impact of the position of laser’s active area on the emitted power. Both small detunings from the standing wave anti-node, and positioning of the active area at different anti-nodes are considered.

Analysis of Effect of Singlet-Triplet Annihilation in a Low-Threshold Optically Pumped Organic Semiconductor Laser

We investigate the impact of optical excitation in a low-threshold organic semiconductor vertical-cavity surface-emitting laser (OVCSEL) to achieve lasing. We study the threshold behavior and the dynamics of the optimized OVCSEL structure when pumped by both picosecond and nanosecond pulses. The boundary between pulsed and continuous wave lasing is analyzed for the study of annihilation quenching losses in the proposed OVCSEL. Results from numerical simulation show that, for the picosecond pulses excitation case, the singlet–triplet annihilation is not effective and a lasing threshold of about 0.75 μJ cm−2 can be obtained. We show that for the nanosecond pulses pumping case, triplet excitons largely quench singlet excitons and lasing is sustained for a short time following turn-on of the pump.

Quantum dot vertical-cavity surface-emitting lasers covering the \u2018green gap\u2019

Semiconductor vertical-cavity surface-emitting lasers (VCSELs) with wavelengths from 491.8 to 565.7 nm, covering most of the ‘green gap’, are demonstrated. For these lasers, the same quantum dot (QD) active region was used, whereas the wavelength was controlled by adjusting the cavity length, which is difficult for edge-emitting lasers. Compared with reports in the literature for green VCSELs, our lasers have set a few world records for the lowest threshold, longest wavelength and continuous-wave (CW) lasing at room temperature. The nanoscale QDs contribute dominantly to the low threshold. The emitting wavelength depends on the electron–photon interaction or the coupling between the active layer and the optical field, which is modulated by the cavity length. The green VCSELs exhibit a low-thermal resistance of 915 kW−1, which benefits the CW lasing. Such VCSELs are important for small-size, low power consumption full-color displays and projectors.

Integrated plasmonic circuitry on a vertical-cavity surface-emitting semiconductor laser platform.

Integrated plasmonic sources and detectors are imperative in the practical development of plasmonic circuitry for bio- and chemical sensing, nanoscale optical information processing, as well as transducers for high-density optical data storage. Here we show that vertical-cavity surface-emitting lasers (VCSELs) can be employed as an on-chip, electrically pumped source or detector of plasmonic signals, when operated in forward or reverse bias, respectively. To this end, we experimentally demonstrate surface plasmon polariton excitation, waveguiding, frequency conversion and detection on a VCSEL-based plasmonic platform. The coupling efficiency of the VCSEL emission to waveguided surface plasmon polariton modes has been optimized using asymmetric plasmonic nanostructures. The plasmonic VCSEL platform validated here is a viable solution for practical realizations of plasmonic functionalities for various applications, such as those requiring sub-wavelength field confinement, refractive index sensitivity or optical near-field transduction with electrically driven sources, thus enabling the realization of on-chip optical communication and lab-on-a-chip devices.

Central wavelength adjustment of light emitting source in interferometric sensors based on fiber-optic Bragg gratings

The paper is focused on the investigation of fiber-optic interferometric sensor based on the array of fiber Bragg gratings. Reflection spectra displacement mechanism of the fiber Bragg gratings under the external temperature effects and the static pressure is described. The experiment has shown that reflection spectra displacement of Bragg gratings reduces the visibility of the interference pattern. A method of center wavelength adjustment is proposed for the optical radiation source in accord ance with the current Bragg gratings reflection spectra based on the impulse relative modulation of control signal for the Peltier element controller. The semiconductor vertical-cavity surface-emitting laser controlled by a pump driver is used as a light source. The method is implemented by the Peltier element controller regulating and stabilizing the light source temperature, and a programmable logic-integrated circuit monitoring the Peltier element controller. The experiment has proved that the proposed method rendered possible to regulate the light source temperature at a pitch of 0.05 K and adjust the optical radiation source center wavelength at a pitch of 0.05 nm. Experimental results have revealed that the central wavelength of the radiation adjustment at a pitch of 0.005 nm gives the possibility for the capacity of the array consisting of four opticalfiber sensors based on the fiber Bragg gratings. They are formed in one optical fiber under the Bragg grating temperature change from 0° C to 300° C and by the optical fiber mechanical stretching by the force up to 2 N.

Study of high-speed semiconductor VCSELs based on AlInGaAs heterostructures with large gain-cavity detuning

The effect of the spectral detuning between the spectral gain maximum of an active region based on AlInGaAs nanoheterostructures and vertical microcavity resonance (gain-cavity detuning) on the steady-state- and dynamic characteristics of high-speed vertical-cavity surface-emitting lasers (VCSELs) for the 850-nm spectral range with two selectively oxidized current apertures is studied. For multimode devices with gain-cavity detuning exceeding 20 nm and a comparatively large current aperture (>6 μm), anomalous lasing onset via higher order modes is observed, with subsequent switching to lower order modes at high currents. Simultaneous lasing via both types of transverse modes, observed at intermediate pumping levels, leads to a nonclassical dependence of the maximum effective-modulation frequency on the pump current. An increase in the working temperature, as well as a decrease in the size of the current aperture of a VCSEL, leads to classical multimode lasing behavior. The observed phenomena are to be taken into account when optimizing the design of high-speed VCSELs.

Single-spatial-mode semiconductor VCSELs with a nonplanar upper dielectric DBR

Single-spatial-mode semiconductor vertical-cavity surface-emitting lasers (VCSELs) with a non-planar upper (output) dielectric distributed Bragg reflector (DBR) for the 850 nm spectral region are fabricated. The suggested design provides stable single-mode generation in the entire range of working currents, limited by overheating of the active region. Devices with intracavity contacts and a comparatively large current-aperture diameter (5–6 μm) exhibit single-mode lasing at a wavelength of 840–845 nm in the continuous-wave mode at room temperature with threshold currents of 1.2–1.3 mA, a differential efficiency of 0.5–0.55 mW mA−1, and anoutput power of up to 2 mW.

Stochastically sustained population oscillations in high-β nanolasers

Nonlinear dynamical systems involving small populations of individuals may sustain oscillations in the population densities arising from discrete changes in population numbers due to random events. By applying these ideas to nanolasers operating with small numbers of emitting dipoles and photons at threshold, we show that such lasers should display photon and dipole population cycles above threshold, which should be observable as a periodic modulation in the second-order correlation function of the nanolaser output. Such a modulation was recently reported in a single-mode vertical-cavity surface-emitting semiconductor laser.

Continuous sensing of tumor-targeted molecular probes with a vertical cavity surface emitting laser-based biosensor

Molecular optical imaging is a widespread technique for interrogating molecular events in living subjects. However, current approaches preclude long-term, continuous measurements in awake, mobile subjects, a strategy crucial in several medical conditions. Consequently, we designed a novel, lightweight miniature biosensor for in vivo continuous optical sensing. The biosensor contains an enclosed vertical-cavity surface-emitting semiconductor laser and an adjacent pair of near-infrared optically filtered detectors. We employed two sensors (dual sensing) to simultaneously interrogate normal and diseased tumor sites. Having established the sensors are precise with phantom and in vivo studies, we performed dual, continuous sensing in tumor (human glioblastoma cells) bearing mice using the targeted molecular probe cRGD-Cy5.5, which targets αVβ3 cell surface integrins in both tumor neovasculature and tumor. The sensors capture the dynamic time-activity curve of the targeted molecular probe. The average tumor to background ratio after signal calibration for cRGD-Cy5.5 injection is approximately 2.43±0.95 at 1 h and 3.64±1.38 at 2 h (N=5 mice), consistent with data obtained with a cooled charge coupled device camera. We conclude that our novel, portable, precise biosensor can be used to evaluate both kinetics and steady state levels of molecular probes in various disease applications.

Chaos dynamics in vertical-cavity surface-emitting semiconductor lasers with polarization-selected optical feedback

We study experimentally and numerically the dynamic states of chaotic oscillations in vertical-cavity surface-emitting semiconductor lasers (VCSELs) with polarization-selected optical feedback. We identify the regimes of fully-developed chaotic states, low-frequency fluctuations (LFFs), and coexistent states of LFFs and stable oscillation for the variations of the bias injection current and the optical feedback ratio. In particular, coexistent states of LFFs and stable oscillations are observed at higher optical feedback ratio and lower bias injection current. We draw maps of dynamic states in the space of the bias injection current and the optical feedback ratio. The qualitative agreement between the theory and the experiment is found.

Single-mode vertical-cavity surface emitting lasers for 87Rb-based chip-scale atomic clock

The results of numerical simulation and study of lasing characteristics of semiconductor verticalcavity surface-emitting lasers based on Al x Ga1 − x As alloys are presented. Lasers exhibit stable single-mode lasing at a wavelength of 795 nm at low operating currents ∼1.5 mA and an output power of 350 μW, which offers prospects of their applications in next-generation chip-scale atomic clocks

基于AlN膜结构VCSEL热特性的研究

In this paper,the internal thermal field and heat flow vector distributions of high power vertical-cavity surface-emitting semiconductor lasers(VCSELs),which is based on AlN film and SiO2 film passivation layers,were analyzed using ANSYS finite-element software.The simulation results proved that the AlN film passivation layer has better features than the SiO2 film passivation layers,and can make the device work in a more stable status,which also improves the device characteristics.Through the simulation,it was found that the Rthjc of VCSEL in AlN film was 3.12 K/W and the Rthjc of VCSEL in SiO2 film was 4.77 K/W.Comparison with the experimental values that the AlN film of 3.59 K/W and the SiO2 film of 4.82 K/W shows that simulation results are in good agreement with the experimental results.The proposed research works prove that the AlN film passivation layer has better thermal features than SiO2 film passivation layer.

Experimental study of resonant activation in a noisy bistable vertical-cavity surface-emitting laser with strong periodic excitation

An experimental evidence of the phenomenon of resonance activation (RA) in bistable semiconductor vertical-cavity surface-emitting laser (VCSEL) with a high level of internal noise under strong periodic excitation is presented. It is shown that the mean switching period (MSP) between polarization states passes through a minimum depending on the modulation frequency. From comparing frequency dependencies of the MSP and the coefficient of variation it is demonstrated for different conditions that resonance activation and stochastic resonance (SR) occur at different optimal values of the modulation frequency. The influence of the signal amplitude, the level of noise in VCSEL and asymmetry of bistable quasipotential are also experimentally studied. For large enough modulation amplitudes, RA and SR are accompanied by the phenomenon of the mean switching frequency locking.

Generation of π modes in semiconductor vertical-cavity surface-emitting lasers

We have theoretically and experimentally studied optical emission from the side faces of mesa structures for vertical-cavity surface-emitting lasers (VCSELs). The results of spatially resolved spectral measurements show that a new type of lasing modes is found in VCSELs with circular mesa structures, which corresponds to the π mode propagation along the mesa diameter with reflection from the sloped walls and the bottom Bragg mirror.