Quantum-well Vertical-cavity Surface-emitting Lasers Research Articles

Time-Multiplexed Spiking Convolutional Neural Network Based on VCSELs for Unsupervised Image Classification

In this work, we present numerical results concerning a multilayer “deep” photonic spiking convolutional neural network, arranged so as to tackle a 2D image classification task. The spiking neurons used are typical two-section quantum-well vertical-cavity surface-emitting lasers that exhibit isomorphic behavior to biological neurons, such as integrate-and-fire excitability and timing encoding. The isomorphism of the proposed scheme to biological networks is extended by replicating the retina ganglion cell for contrast detection in the photonic domain and by utilizing unsupervised spike dependent plasticity as the main training technique. Finally, in this work we also investigate the possibility of exploiting the fast carrier dynamics of lasers so as to time-multiplex spatial information and reduce the number of physical neurons used in the convolutional layers by orders of magnitude. This last feature unlocks new possibilities, where neuron count and processing speed can be interchanged so as to meet the constraints of different applications.

Strain induced polarization chaos in a solitary VCSEL

Physical curiosity at the beginning, optical chaos is now attracting increasing interest in various technological areas such as detection and ranging or secure communications, to name but a few. However, the complexity of optical chaos generators still significantly hinders their development. In this context, the generation of chaotic polarization fluctuations in a single laser diode has proven to be a significant step forward, despite being observed solely for quantum-dot vertical-cavity surface-emitting lasers (VCSELs). Here, we demonstrate experimentally that a similar polarization dynamics can be consistently obtained in quantum-well VCSELs. Indeed, by introducing anisotropic strain in the laser cavity, we successfully triggered the desired chaotic dynamics. The simplicity of the proposed approach, based on low-cost and easily available components including off-the-shelf VCSELs, paves the way to the wide spread use of solitary VCSELs for chaos-based applications.

1060-nm 28-Gb/s <inline-formula> <tex-math notation="LaTeX">$\times 4$ </tex-math></inline-formula>-Channel Modules Operated Over the Case Temperature Range

To reduce the power consumption of 4-channel 28-Gb/s miniature optical modules, a 4-channel double intra-cavity 1060-nm InGaAs/GaAs quantum-well vertical-cavity surface-emitting laser (VCSEL) array with 5-μm-wide apertures, a high differential gain, and a low temperature-insensitive differential resistance in conjunction with a specially optimized thermo-electric cooler heat sink for a reduced thermal resistance are used. Most important is the excellent resistance compatibility between the VCSEL and a low-power SiGe BiCMOS driver IC. Consequently, a 4-channel 28-Gb/s NRZ PRBS 2 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">31</sup> - 1 link operation at a bit error rate of 10-12 for an operational case temperature ranging from 25 °C to 70 °C was achieved at an unprecedentedly low VCSEL bias current of only 4 mA.

The effect of electron blocking layer on the performance of MQW oxide-confined intracavity-contacted InGaN-based vertical cavity surface emitting lasers

The effects of inserting AlGaN electron blocking layer (EBL) in the GaN-based vertical cavity surface emitting laser (VCSEL) structures on the LD performance has been investigated by Integrated System Engineering Technical Computer Aided Design (ISE TCAD) program software. The simulation results indicated that the performance characteristics of GaN-based quantum-well VCSEL were improved when the AlGaN EBL has been added. The effect of Al mole fraction (x) of the AlxGa1−xN EBL on the GaN-based VCSEL performance ranging from x=0.15 to x=0.25 was also studied. At x=0.15 to x=0.17, the threshold current was reduced. This reduction in the threshold current is due to the increase in the carrier confinement which is achieved by accumulated much more carrier close to the active region caused by the added AlxGa1−xN EBL. Above the x=0.17, the threshold current was increased which is attributed to the saturation of the carriers inside the active region that leads to increase in the leakage current. It also was due to that the EBL obstacle the hole flowing in the active region in the x>0.17. GaN-based VCSEL had the optimum performance with Al0.17Ga0.83N EBL; therefore, the effect of Al0.17Ga0.83N EBL thickness on the GaN-based quantum well VCSEL performance has also been investigated. According to the simulation results, the GaN-based VCSEL had the optimum performance when the EBL thickness was 25nm.

Polarization axis fluctuations in a single mode VCSEL laser at 780nm

We present a transmission method to determine the polarization axis fluctuations for VCSEL (Vertical Cavity Surface Emitting Laser). The research is focused mainly on commercial lasers operatingat 780 nm, designed forlaser spectroscopy. The angle fluctuation of the laser linear axis polarization iselaborated to be less than 150 mrad. Measurement errors of this method are studied and calculated. The measurement uncertainty is ?1,4 mrad andthis is equivalent to ? 5? of arc.Changes of the linear polarization axis depending on the laser current and temperaturearepresented. Full Text: PDF References T. Ohtoshi et al., "Dependence of optical gain on crystal orientation in surface?emitting lasers with strained quantum wells", Appl. Phys. Lett.63, 1886 (1994). CrossRef K. Tateno et al., "Growth of vertical-cavity surface-emitting laser structures on GaAs (311)B substrates by metalorganic chemical vapor deposition", Appl. Phys. Lett.70, 3395 (1997). CrossRef O. Tadanaga et al., "An 850-nm InAlGaAs strained quantum-well vertical-cavity surface-emitting laser grown on GaAs (311)B substrate with high-polarization stability", IEEE Photon. Tech. Lett.12, 942 (2000) CrossRef K. Choquette, R. Leibenguth, "Control of vertical-cavity laser polarization with anisotropic transverse cavity geometries", IEEE Photon. Tech. Lett. 6, 40 (1994) CrossRef B. Weigl et al., "High-performance oxide-confined GaAs VCSELs", IEEE J. Sel. Top.Quantum Electron. 3, 409 (1997) CrossRef P. Dowd et al., "Complete polarisation control of GaAs gain-guided top-surface emitting vertical cavity lasers", Electron. Lett. 33, 1315 (1997) CrossRef M. Grabherr et al., "Volume production of polarization controlled single-mode VCSELs", Proc. SPIE,6908, 690803 (2008) CrossRef R. Roy et al., "First-Passage-Time Distributions under the Influence of Quantum Fluctuations in a Laser", Phys. Rev. Lett.45, 1486 (1980) CrossRef J. Martin-Regalado et al., "Polarization switching in vertical-cavity surface emitting lasers observed at constant active region temperature", Appl. Phys. Lett. 70, 3350 (1997) CrossRef M. B. Willemsen et al., "Polarization Switching of a Vertical-Cavity Semiconductor Laser as a Kramers Hopping Problem", Phys. Rev. Lett. 82, 4815 (1999) CrossRef M. B. Willemsen et al., "Anatomy of a Polarization Switch of a Vertical-Cavity Semiconductor Laser", Phys. Rev. Lett. 84, 4337 (2000) CrossRef T. Mukaihara et al., "Excess intensity noise originated from polarization fluctuation in vertical-cavity surface-emitting lasers", IEEE Photon. Technol. Lett. 7, 1113 (1995) CrossRef

Polarization axis fluctuations in a single mode VCSEL laser at 780nm

We present a transmission method to determine the polarization axis fluctuations for VCSEL (Vertical Cavity Surface Emitting Laser). The research is focused mainly on commercial lasers operatingat 780 nm, designed forlaser spectroscopy. The angle fluctuation of the laser linear axis polarization iselaborated to be less than 150 mrad. Measurement errors of this method are studied and calculated. The measurement uncertainty is ?1,4 mrad andthis is equivalent to ? 5? of arc.Changes of the linear polarization axis depending on the laser current and temperaturearepresented. Full Text: PDF References T. Ohtoshi et al., "Dependence of optical gain on crystal orientation in surface?emitting lasers with strained quantum wells", Appl. Phys. Lett.63, 1886 (1994). CrossRef K. Tateno et al., "Growth of vertical-cavity surface-emitting laser structures on GaAs (311)B substrates by metalorganic chemical vapor deposition", Appl. Phys. Lett.70, 3395 (1997). CrossRef O. Tadanaga et al., "An 850-nm InAlGaAs strained quantum-well vertical-cavity surface-emitting laser grown on GaAs (311)B substrate with high-polarization stability", IEEE Photon. Tech. Lett.12, 942 (2000) CrossRef K. Choquette, R. Leibenguth, "Control of vertical-cavity laser polarization with anisotropic transverse cavity geometries", IEEE Photon. Tech. Lett. 6, 40 (1994) CrossRef B. Weigl et al., "High-performance oxide-confined GaAs VCSELs", IEEE J. Sel. Top.Quantum Electron. 3, 409 (1997) CrossRef P. Dowd et al., "Complete polarisation control of GaAs gain-guided top-surface emitting vertical cavity lasers", Electron. Lett. 33, 1315 (1997) CrossRef M. Grabherr et al., "Volume production of polarization controlled single-mode VCSELs", Proc. SPIE,6908, 690803 (2008) CrossRef R. Roy et al., "First-Passage-Time Distributions under the Influence of Quantum Fluctuations in a Laser", Phys. Rev. Lett.45, 1486 (1980) CrossRef J. Martín-Regalado et al., "Polarization switching in vertical-cavity surface emitting lasers observed at constant active region temperature", Appl. Phys. Lett. 70, 3350 (1997) CrossRef M. B. Willemsen et al., "Polarization Switching of a Vertical-Cavity Semiconductor Laser as a Kramers Hopping Problem", Phys. Rev. Lett. 82, 4815 (1999) CrossRef M. B. Willemsen et al., "Anatomy of a Polarization Switch of a Vertical-Cavity Semiconductor Laser", Phys. Rev. Lett. 84, 4337 (2000) CrossRef T. Mukaihara et al., "Excess intensity noise originated from polarization fluctuation in vertical-cavity surface-emitting lasers", IEEE Photon. Technol. Lett. 7, 1113 (1995) CrossRef

Optimization of GaInNAs quantum-well vertical-cavity surface-emitting laser emitting at 2.33 μm

In the present paper, a comprehensive computer simulation is used to determine optimal structure of the InP-based GaInNAs quantum-well (QW) active region and to investigate a possibility of reaching room-temperature (RT) continuous-wave (CW) single-fundamental-mode 2.33-μm operation of vertical-cavity surface-emitting laser (VCSEL) with such an active region. From among various considered InP-based active regions, the one with the Ga0.15In0.85N0.015As0.985/Al0.138Ga0.332In0.530As QW, i.e. with barriers lattice matched to InP, seems to be optimal for the 2.33-μm VCSEL performance. Its QW material is chosen for the required long-wavelength emission whereas its barrier is expected to ensure promising laser performance at room and higher temperatures. The latter is mostly connected with the QW conduction band offset equal in the above active region to as much as 413 meV, which is much larger than those of its possible lattice matched to InP competitors, e.g. 276 meV for the Ga0.47In0.53As barrier and 346 meV for the Ga0.327In0.673As0.71P0.29 one. Our simulation reveals that from among various considered structures, a VCSEL with a 4-μm-diameter tunnel junction and two 6-nm Ga0.15In0.85N0.015As0.985/Al0.138Ga0.332In0.530As QWs exhibits the lowest calculated threshold current of 0.88 mA. Its promising RT CW performance suggests that it may represent a very interesting alternative to GaSb-based VCSELs.

A low-threshold and high-power oxide-confined 850-nm AlInGaAs strained quantum-well vertical-cavity surface-emitting laser

A low-threshold and high-power oxide-confined 850-nm AlInGaAs strained quantum-well (QW) vertical-cavity surface-emitting laser (VCSEL) based on an intra-cavity contacted structure is fabricated. A threshold current of 1.5 mA for a 22 μm oxide aperture device is achieved, which corresponds to a threshold current density of 0.395 kA/cm2. The peak output optical power reaches 17.5 mW at an injection current of 30 mA at room temperature under pulsed operation. While under continuous-wave (CW) operation, the maximum power attains 10.5 mW. Such a device demonstrates a high characteristic temperature of 327 K within a temperature range from −12 °C to 96 °C and good reliability under a lifetime test. There is almost no decrease of the optical power when the device operates at a current of 5 mA at room temperature under the CW injection current.

Microwave determination of electron-hole recombination dynamics from spontaneous to stimulated emission in a quantum-well microcavity laser

By studying the optical microwave frequency response of a microcavity quantum-well vertical cavity surface-emitting laser (VCSEL) in the transition, over a low (a spread-out) mode density, from spontaneous to coherent operation, we resolve the dynamics (spontaneous to stimulated) of electron-hole recombination and reveal the existence of “fast” spontaneous recombination (τBspon&amp;lt;159 ps) in a carrier population generally characterized by a large average lifetime of ∼1 ns (Δn/τav=Δn1/τfast+(Δn−Δn1)/τslow,τfast&amp;lt;τslow). The measured average spontaneous lifetime is not a constant but is altered by the device size, geometry, and boundary conditions (e. g., cavity and current input-output boundary conditions).

Microwave characterization of Purcell enhancement in a microcavity laser

A sensitive microwave method is described to study the optical frequency response of a microcavity laser, demonstrating that a quantum-well vertical cavity surface-emitting laser (∼3 μm aperture, ITH=180 μA) can exhibit almost single mode operation (nearly threshold free), and an electron-hole spontaneous lifetime Purcell enhancement of 2.08 times. The microwavemeasurement method employing electrical-to-optical conversion, and distinct separation of electrical input and optical output, is more revealing than photoluminescence decay experiments (and the inconvenient overlap of optical input and output).

Experimental Study of the Lasing Modes of 1.3-&lt;formula formulatype="inline"&gt;&lt;tex Notation="TeX"&gt;$\mu$&lt;/tex&gt;&lt;/formula&gt;m Highly Strained InGaAs&amp;#x2013;GaAs Quantum-Well Oxide-Confined VCSELs

We present an experimental study of the main modes involved in the emission properties of InGaAs-GaAs quantum-well oxide-confined long wavelength vertical-cavity surface-emitting lasers. Lasing properties are dominated by the so-called "oxide modes" and by aperture modes, respectively, for small and large driving currents. We present complementary investigations of the laser emission including far-field angular distribution and spectroscopic near-field optical microscopy to a better understanding of the nature of the "oxide modes".

Analysis of anticipated performance of 650-nm GaInP/AlGaInP quantum-well GaAs-based VCSELs at elevated temperatures

AbstractThe possibility of application of the 650-nm oxide-confined GaInP/AlGaInP quantum-well vertical-cavity surface-emitting diode lasers (VCSELs) at elevated temperatures as sources of the carrier 650-nm wave in the fibre optical communication using POFs has been investigated with the aid of the comprehensive self-consistent model. An increase in the VCSEL threshold current at higher temperatures has been found to be mostly associated with both the carrier leakage from the valley of the Ga0.43In0.57P quantum-well material to the X-valley of the (Al0.67Ga0.33)0.52In0.48P barriers and the band-to-band absorption within the Ga0.52In0.48P layer of the band-gap comparable with the energy of emitted radiation. Nevertheless, the AlGaInP VCSELs exhibit encouraging thermal behaviour with the characteristic temperature T0 equal to as much as 134 K for the active-region temperatures up to 357 K. For the 5-μm devices, the maximal achievable output has been determined to decrease from a quite high value of 1.0 mW for 293 K to 0.6 mW for 320 K and to still high 0.33 mW for 340 K. However, an efficient operation of the above VCSEL at elevated temperatures requires still some structure modifications leading to a reduction of both the above effects, the electron leakage from the valley and the band-to-band absorption within GaInP layers.

Threshold analysis of highly detuned long-wavelength GaAs-based GaInNAsSb/GaNAsQWVCSELs

Comprehensive 3D optical–electrical–thermal-gain self-consistent simulation of physical processes taking place inside a laser volume of the GaAs-based GaInNAsSb/GaNAs quantum-well (QW) vertical-cavity surface-emitting diode laser (VCSEL) is carried out to examine a possibility to reach the long-wavelength room-temperature (RT) continuous-wave (CW) laser operation in highly detuned devices. The RT CW 1.422-μm lasing emission has been found to be reached practically without troubles. However, to reach the 1.5-μm laser wavelength, it is necessary to increase the QW active region temperature by about 100 K, which may be done by a proper increase in the RT CW operation current.

Self-consistent model of 650 nm GaInP/AlGaInP quantum-well vertical-cavity surface-emitting diode lasers

A comprehensive fully self-consistent model of oxide-confined GaAs-based vertical-cavity surface-emitting diode lasers (VCSELs) with GaInP/AlGaInP quantum-well active regions to simulate their room-temperature (RT) continuous-wave (CW) operation is presented. The model takes into consideration all observed or expected special features of GaInP/AlGaInP VCSELs. A complete set of model parameters is given. The model enables a deeper understanding of a VCSEL operation with full complexity of many inter-related physical phenomena taking place within its volume. It may also be used to design and optimize the above VCSEL structures for their numerous applications, in particular as sources of the 650 nm carrier wave in communication systems using plastic optical fibres. With the aid of this model, anticipated VCSEL RT CW performance characteristics may be determined.

GaInNAsSb/GaNAs quantum-well VCSELs: Modeling and physical analysis in the 1.50−1.55 μm wavelength range

Physical analysis of the long-wavelength room-temperature (RT) continuous-wave (cw) emission within the 1.50−1.55 μm range from the GaAs-based GaInNAsSb/GaNAs quantum-well (QW) vertical-cavity surface-emitting diode lasers (VCSELs) is carried out. To this end, a comprehensive three-dimensional optical-electrical-thermal-gain self-consistent simulation of physical processes taking place inside a laser volume is applied. While the 1.50-μm emission has been found to be reached practically without trouble, the 1.55-μm emission needs additional optimizations. For the optimal QW structure, the 1.55-μm emission in highly detuned VCSELs requires RT cw threshold currents more than 18 times higher than those of the 1.50-μm one. Some threshold reduction may be achieved by adding the second quantum well. The 3λ-cavity design has been proved to be optimized for the 1.50-μm emission ensuring stable fundamental-mode operation even at elevated temperatures whereas the 1.5λ-cavity is optimal for the 1.55-μm emission for which threshold reduction is more important. For the 1.50-μm emission, some structure optimizations have been proposed. The GaInNAsSb/GaNAs structure offers promising prospects to manufacture VCSELs emitting 1.55-μm radiation, but some technology and construction improvements are still necessary.

Structure Optimisation of a Possible 1.5-μm GaAs-based Vertical-cavity Surface-emitting Laser Diode with the GaInNAsSb/GaNAs Quantum-well Active Region

Structure optimisation of the GaAs-based GaInNAsSb/GaNAs quantum-well (QW) vertical-cavity surface-emitting diode lasers (VCSELs) has been carried out using the comprehensive three-dimensional self-consistent physical model of their room-temperature (RT) continuous-wave (CW) threshold operation. The model has been applied to investigate a possibility to use these devices as carrier-wave lasing sources in the third-generation optical-fibre communication. In this simulation, all physical (optical, electrical, thermal and gain) phenomena crucial for a laser operation including all important interactions between them are taken into consideration. As expected, the 1.5λ-cavity VCSEL has been found to demonstrate the lowest RT CW threshold. However, for many VCSEL applications, the analogous VCSEL equipped with a longer 3λ-cavity should be recommended because it exhibits only slightly higher threshold but manifest much better mode selectivity – the desired single-fundamental-mode operation has been preserved in these devices up to at least 380 K. The Auger recombination has been found to be decidedly the main reason of the threshold current increase at higher temperatures. A proper initial red detuning of the resonator wavelength with respect to the gain spectrum may drastically decrease CW lasing thresholds, especially at higher temperatures.

Low-Threshold and High-Power Oxide-Confined 850 nm AlInGaAsStrained Quantum-Well Vertical-Cavity Surface-Emitting Lasers Based onIntra-Cavity Contacted Structure

The low-threshold and high-power oxide-confined 850 nm AlInGaAs strainedquantum-well (QW) vertical-cavity surface-emitting lasers (VCSELs) basedon the intra-cavity contacted structure are fabricated. The thresholdcurrent of 0.1 mA for a 10-μm oxide-aperture device is obtainedwith the threshold current density of 0.127 kA/cm2. For a 22-μmoxide-aperture device, the peak optical output power reaches to14.6 mW at the current injection of 25 mA under the room temperatureand pulsed operation with a threshold current of 2 mA, whichcorresponds to the threshold current density of 0.526 kA/cm2. Thelasing wavelength is 855.4 nm. The full wave at half maximum is2.2 nm. The analysis of the characteristics and the fabrication ofVCSELs are also described.

Continuous wave optically pumped lead-salt mid-infrared quantum-well vertical-cavity surface-emitting lasers

Continuous wave optically pumped mid-infrared lead-salt quantum-well vertical-cavity surface-emitting lasers with an eleven-period PbSe/PbSrSe quantum-well active region are demonstrated. The cw emissions are observed up to 230 K at the emission wavelengths around 4.03 μm. The lowest threshold pump density of 2.6 kW/cm2 appears at 190 K, 65 °C lower than that of the pulsed measurements. This indicates the temperature difference between the active region and the heat sink of the episide-up mounted on-wafer testing under cw pumping.

Strain-dependence of the gain saturations in InGaAsP/InP quantum-well gain media

Numerical analyses of polarization-dependent optical gain saturations are given for quantum-well (QW) lasers in the presence of strain in the well regions in order to investigate the strain dependence of polarization-bistable operations. Gain saturation coefficients are obtained from nonlinear susceptibilities calculated in the perturbative analyses of density matrices. Band dispersions and dipole matrix elements, which are put into the density matrices, are calculated by diagonalizing Luttinger's Hamiltonian, including valence band mixing. The strain induces a change in band dispersions and wavefunctions, leading to strain-dependent saturation coefficients. The self-saturation coefficients and the cross-saturation coefficients (with orthogonal optical polarizations) pertinent to InGaAsP/InP QW vertical-cavity surface-emitting lasers are calculated. We find that the relative magnitudes of self- and cross-saturation coefficients are strongly dependent on the strain; in the presence of compressive strain, the cross-saturation coefficients are larger than the self-saturation in the wide range of the linear gain spectra, especially in the vicinity of the gain peak, indicating that the compressively strained structure is more favorable for the polarization-bistable operations.

High-speed modulation of 850-nm intracavity contacted shallow implant-apertured vertical-cavity surface-emitting lasers

GaAs-AlGaAs quantum-well (850 nn) vertical-cavity surface-emitting lasers, with lateral current injection and shallow implanted apertures, show small signal modulation bandwidths of at least 11 GHz and large signal data rates of at least 10 Gb/s. The devices achieved a maximum output power of 2.1 mW, with a threshold current and voltage of 1 mA and 1.71 V, respectively. The shallow implantation step provides photolithographically precise aperture formation (using O/sup +/ ions), for efficient lateral current injection into the quantum-well active region of the laser, from intracavity contacts. The device aperture was 7 μm in diameter, and the opening in the annular top contact was 13 μm in diameter. The optical spectrum showed several transverse modes.