Showing papers in "IEEE Journal of Quantum Electronics in 2013"

Graphene-Si Schottky IR Detector

Abstract: This paper reports on photodetection properties of the graphene-Si schottky junction by measuring current–voltage characteristics under 1.55- $\mu{\rm m}$ excitation laser. The measurements have been done on a junction fabricated by depositing mechanically exfoliated natural graphite on top of the pre-patterned silicon substrate. The electrical Schottky barrier height is estimated to be (0.44–0.47) eV with a minimum responsivity of 2.8 mA/W corresponding to an internal quantum efficiency of 10%, which is almost an order of magnitude larger than regular Schottky junctions. A possible explanation for the large quantum efficiency related to the 2-D nature of graphene is discussed. Large quantum efficiency, room temperature IR detection, ease of fabrication along with compatibility with Si devices can open a doorway for novel graphene-based photodetectors.

Fast Random Bit Generation Using a Chaotic Laser: Approaching the Information Theoretic Limit

Abstract: We design and implement a chaotic-based system, enabling ultra-fast random bit sequence generation. The potential of this system to realize bit rates of 160 Gb/s for 8-bit digitization and 480 Gb/s for 16-bit digitization is demonstrated. In addition, we provide detailed insight into the interplay of dynamical properties, acquisition conditions, and post-processing, using simple and robust procedures. We employ the chaotic output of a semiconductor laser subjected to polarization-rotated feedback. We show that not only dynamics affect the randomness of the bits, but also the digitization conditions and postprocessing must be considered for successful random bit generation. Applying these general guidelines, extensible to other chaos-based systems, we can define the optimal conditions for random bit generation. We experimentally demonstrate the relevance of these criteria by extending the bit rate of our random bit generator by about two orders of magnitude. Finally, we discuss the information theoretic limits, showing that following our approach we reach the maximum possible generation rate.

Extremum-Seeking Control of a Mode-Locked Laser

Abstract: An adaptive controller is demonstrated that is capable of both obtaining and maintaining high-energy, single-pulse states in a mode-locked fiber laser. In particular, a multi-parameter extremum-seeking control (ESC) algorithm is used on a nonlinear polarization rotation (NPR) based laser using waveplate and polarizer angles to achieve optimal passive mode-locking despite large disturbances to the system. The physically realizable objective function introduced divides the energy output by the kurtosis of the pulse spectrum, thus balancing the total energy with the coherence of the mode-locked solution. In addition, its peaks are high-energy mode-locked states that have a safety margin near parameter regimes where mode-locking breaks down or the multipulsing instability occurs. The ESC is demonstrated by numerical simulations of a single-NPR mode-locked laser and is able to track locally maximal mode-locked states despite significant disturbances to parameters such as the fiber birefringence.

Heterodyne Random Bit Generation Using an Optically Injected Semiconductor Laser in Chaos

Abstract: Heterodyne generation of parallel random bit streams from chaotic emission of an optically injected semiconductor laser is investigated. The continuous-wave optical injection invokes chaotic dynamics in the laser. The broadband chaotic emission is detected through optical heterodyning and electrical heterodyning into different channels. The channels digitize the signals into parallel independent random bit streams. Because of efficient utilization of different portions of the chaos bandwidth, heterodyne detections enable parallel generation of random bit streams, offer high total output bit rates, and require no high-bandwidth analogue-to-digital converters. In the experiment, two optical heterodyne channels and four electrical heterodyne channels are implemented. Each channel is required to digitize only 2.5 GHz of a much broader chaos bandwidth. The sampling rate is 10 GHz with five least significant bits selected from every 8-bit sample. The total output bit rate reaches 100 Gb/s and 200 Gb/s for optical and electrical heterodyning, respectively. The standard test suite of the National Institute of Standards and Technology verifies the randomness of both individual and interleaved output bit streams.

InGaN/GaN Quantum Dot Red $(\lambda=630~{\rm nm})$ Laser

Abstract: Lasers emitting in the 600 nm wavelength range have gained attention for a number of important applications, including optical information processing, plastic fiber communication systems, optical storage, and full color (RGB) laser displays and laser projectors. Visible lasers are currently realized with GaN-based heterostructures having InGaN/GaN quantum wells as the gain media. The performance of these devices, particularly at longer wavelengths, is limited by materials inhomogeneity and effects related to a large strain-induced polarization in the quantum wells. A laser emitting in the red (λ ~ 630 nm) has not been realized. Here, we demonstrate lasers which emit at 630 nm, the longest wavelength achieved with the nitride system, by incorporating InGaN/GaN self-organized quantum dots as the gain media. Strain relaxation during dot formation results in reduced polarization fields and consequently low threshold current density, Jth=2.5 kA/cm2, small blue shift of the emission peak, very weak temperature dependenc eof Jth (T0=236 K), and linearly TE polarized output.

Theoretical Study of Metal-Insulator-Metal Tunneling Diode Figures of Merit

Abstract: The performance of metal-insulator-metal (MIM) diodes is investigated. In this paper, we derive an analytical model that uses the Transfer Matrix Method based on the Airy Functions (AF-TMM) for the tunneling transmission probability through any number of insulating layers. The fast-computing AF-TMM simulator results show a complete matching with the numerical Non-Equilibrium Green's Function and a reasonable matching with previously published experimental results. This study shows the effect of the work function difference and insulator thickness on MIM diode performance. The advantage of using two insulator layers on enhancing the diode responsivity, resistance, and nonlinearity is also investigated.

High-Gain InAs Avalanche Photodiodes

Abstract: We report two InAs avalanche photodiode structures with very low background doping in the depletion region. Uniform electric fields and thick depletion regions have been achieved. Excess noise measurements are consistent with k~0 and gain as high as 70 at room temperature is observed. The measured gain-bandwidth product is >; 300 GHz. All measurements are consistent with Monte Carlo simulations.

A Radio-Over-Fiber System With Frequency 12-Tupling Optical Millimeter-Wave Generation to Overcome Chromatic Dispersion

Abstract: A radio-over-fiber system with frequency 12-tupling optical millimeter-wave (mm-wave) generation using an integrated nested Mach-Zehnder modulator (MZM) is proposed and demonstrated by simulation. Through properly adjusting the direct current bias voltages of two sub-MZMs, the RF local oscillator (LO) voltages and phases, and the gain of base-band signal, the frequency 12-tupling optical mm-wave with data only carried by one sixth-order sideband is generated. As the signal is transmitted along the fiber, there is no periodical fading and bit walk-off effect caused by chromatic dispersion. The eye diagrams stay open even when the signal is transmitted over 60 km and the power penalty is 0.67 dB at a BER of 10-10. Furthermore, it is also proved to be valid that the BER is insensitive to the deviation of modulator extinction ratio and RF LO voltage.

Steady-State Raman Gain in Diamond as a Function of Pump Wavelength

Abstract: The variation in the Raman gain coefficient in single-crystal diamond for pump wavelengths between 355 and 1450 nm is measured. Two techniques are used: a pump-probe approach giving an absolute measurement and a stimulated Raman oscillation threshold technique giving a relative measurement. Both approaches indicate that the Raman gain coefficient is a linear function of pump wavenumber. With the pump polarized along a ; direction in the crystal, the Raman gain coefficient measured by the pump-probe technique is found to vary from 7.6 ± 0.8 for a pump wavelength of 1280 nm to 78 ± 8 cm/GW for a pump wavelength of 355 nm. With the established dependence of the Raman gain coefficient on the pump wavelength, the Raman gain coefficient can be estimated at any pump wavelength within the spectral range from 355 up to 1450 nm.

Optimization of Wavefront Distortions and Thermal-Stress Induced Birefringence in a Cryogenically-Cooled Multislab Laser Amplifier

Abstract: The optimization of the Yb:YAG gain medium and absorbing clad parameters was investigated for efficient heat removal in cryogenically-cooled multislab amplifiers operating in the kilowatt average power range (100 J/10 Hz). The 3-D distributions of temperature, stress, strain, and birefringence were calculated by a finite element analysis. Based on these data, the space-resolved optical path difference and depolarization losses were determined considering eight slabs, two laser heads, and four passes. We have found that a combination of properly designed (doping/width) index matching material and helium cryogenic cooling leads to a quasi-constant transverse temperature distribution in the pump area and a very small axial thermal gradient in the slab. It is shown that the resulting thermally induced phase aberrations, stresses, and average depolarization are rendered insignificant.

Non-Drude Behavior in Indium-Tin-Oxide Nanowhiskers and Thin Films Investigated by Transmission and Reflection THz Time-Domain Spectroscopy

Abstract: A comparative study of indium-tin-oxide (ITO) nanowhiskers (NWhs) and thin films as transparent conductors in the terahertz frequency range are conducted. We employ both transmission-type and reflection-type terahertz time-domain spectroscopies (THz-TDTS and THz-TDRS) to explore the far-infrared optical properties of these samples. Their electrical properties, such as plasma frequencies and carrier scattering times, are analyzed and found to be fitted well by the Drude-Smith model over 0.1-1.4 THz. Further, structural and crystalline properties of samples are examined by scanning electron microscopy and X-ray diffraction, respectively. Non-Drude behavior of complex conductivities in ITO NWhs is attributed to carrier scattering from grain boundaries and impurity ions. In ITO thin films, however, the observed non-Drude behavior is ascribed to scattering by impurity ions only. Considering NWhs and thin films with the same height, mobility of the former is ~ 125 cm2V-1s-1, much larger than those of the ITO thin films, ~ 27 cm2 V-1 s-1. This is attributed to the longer carrier scattering time of the NWhs. The dc conductivities ( ~ 250 Ω-1 cm-1) or real conductivities in the THz frequency region of ITO NWhs is, however, lower than those of the ITO thin films ( ~ 800 Ω-1 cm-1) but adequate for use as electrodes. Partly, this is a reflection of the much higher plasma frequencies of thin films. Significantly, the transmittance of ITO NWhs ( ≅ 60%-70%) is much higher ( ≅ 13 times) than those of ITO thin films in the THz frequency range. The underneath basic physics is that the THz radiation can easily propagate through the air-space among NWhs. The superb transmittance and adequate electrical properties of ITO NWhs suggest their potential applications as transparent conducting electrodes in THz devices.

Speckle Pattern Errors in Self-Mixing Interferometry

Abstract: We analyze the random errors occurring in interferometric measurements because of the speckle pattern regime, when the remote target is a diffusing surface. First, we review the statistical properties of speckle and discuss amplitude fading that is affecting the self-mixing interferometer (SMI) signal and methods to alleviate it. Second, we derive intra-speckle phase errors using the bivariate conditional probability, and find that the noise-equivalent-displacement for small displacement Δ is proportional to the ratio of Δ to speckle longitudinal size sl. Last, we extend the analysis to inter-speckle displacements (Δ > s1) and, after deriving speckle systematic and random errors, show that operation up to meters on a diffusing surface target is possible with a small (≈ λ) error. Results are mainly focussed on SMI, yet they have general validity for any configuration of interferometry.

Delayed Feedback Dynamics of Liénard-Type Resonant Tunneling-Photo-Detector Optoelectronic Oscillators

Abstract: We use the nonlinear dynamics approach for studying delayed feedback optoelectronic oscillators (OEOs) formed by hybrid integration of resonant tunneling diode (RTD) photo-detectors with laser diodes, in both single and dual optical fiber feedback routes. In the single loop topology, the performance of the RTD-OEO free-running self-sustained oscillator is improved in terms of phase noise, with a compromise between the delay line and the strength of the optical re-injection. In the dual-loop configuration, superior performance is achieved due to the suppression of the side modes associated with the optical cavity length, resulting in a side mode suppression ratio of up to -60 dBc of the carrier frequency. We compare experimental results with numerical simulations based on a system of delay differential equations comprising a Lienard oscillator model driven by white Gaussian noise and coupled with laser rate equations. The delayed feedback Lienard oscillator model gives considerable insight into the RTD-OEO dynamical regimes predicting its main features in both single- and dual-loop configurations.

Barrier Engineered Infrared Photodetectors Based on Type-II InAs/GaSb Strained Layer Superlattices

Abstract: We present the design, growth, fabrication, and characterization of unipolar barrier photodiodes, pBiBn, based on type-II InAs/GaSb superlattice for midwave and longwave infrared detection. Design optimization of barriers using bandgap and band-offset tailorability of InAs/GaSb/AlSb superlattice system, their advantages and evolution of heterostructure designs are discussed for both the regimes. Dark current densities of 1.6 × 10-7 and 1.42 × 10-5 A/cm2 are measured at 77 K for midwave and longwave detectors with cutoff wavelengths of 5 and 10 μm, respectively. Responsivities of 1.3 (QE = 38%) and 1.66 A/W (QE = 23.5%) are measured at 4.2 and 8.7 μm for the midwave and longwave, respectively, at 77 K. Shot noise limited peak detectivity of 8.9 × 1012 and 7.7×1011 cm-Hz1/2-W-1 are observed at -10 and -40 mV for midwave infrared and longwave infrared detectors, respectively, at 77 K.

High Peak Power, Passively Q-Switched Yb:YAG/Cr:YAG Micro-Lasers

Abstract: A high peak power (>MW), passively Q-switched Yb:YAG/Cr:YAG micro-laser end-pumped by fiber-coupled 120-W QCW LDs (Repetition rate <; 100 Hz) is developed. The convex output coupler with a curvature of -2 m successfully enlarges the fundamental mode size in the micro-laser cavity, and the output pulse energy increases to 3.6 mJ at a Cr:YAG initial transmission of 89% without optical damage. The TEM00 transverse mode and the single-frequency oscillation are confirmed. The pulse duration is 1.3 ns, and then the peak power is estimated as 2.8 MW. To our knowledge, these are the highest pulse energy and peak power ever reported in Yb:YAG/Cr:YAG micro-lasers. The Yb:YAG rod with 5 at.% Yb concentration and 4.2-mm thickness keeps more than 80% single-pass pump absorption ranging from 15°C to 45 °C in LD temperature. On the other hand, the characteristic temperatures of Yb:YAG/Cr:YAG and Nd:YAG/Cr:YAG lasers were estimated as 110 and 278 K, respectively. This means that the ratio of the increase in threshold pump energy to temperature of a Yb:YAG/Cr:YAG laser is twice or higher than that of a Nd:YAG/Cr:YAG laser due to a quasi-3-level system of Yb:YAG.

Extending the 1-D Hovel Model for Coherent and Incoherent Back Reflections in Homojunction Solar Cells

Abstract: In this paper we extend the analytical drift-diffusion model, or Hovel model, to model the electrical characteristics of solar cells incorporating a back mirror. We use a compact summation approach to derive modified optical generation functions in Homojunction solar cells, considering both coherent and incoherent reflections from the back reflector. These modified generation functions are then used to derive analytical formulae for the current-voltage characteristics of mirrored solar cells. We simulate the quantum efficiency of a simple GaAs np diode with a planar gold back reflector, and compare the results with the standard Hovel model using a generation function given by the Beer-Lambert law. Finally, we use the model to simulate the performance of a real GaAs solar cell device fabricated using an epitaxial-lift-off procedure, demonstrating excellent agreement between the simulated and measured characteristics.

Tuning and Focusing of Terahertz Radiation by DC Magnetic Field in a Laser Beating Process

Abstract: The role of an external DC magnetic held in tuning the frequency and power of terahertz (THz) radiation and obtaining focused radiation is clarified in a beating process using two spatial-triangular lasers, where a nonlinear ponderomotive force acting on the electrons provides oscillating current in longitudinal and transverse directions. The transient transverse current oscillating at the beating frequency produces THz radiations in extraordinary mode, when the beating frequency of lasers matches the upper hybrid frequency for the resonant excitation. Based on the maximum momentum transfer with the application of density ripples, this scheme is realized with high efficiency (>;0.01), where the radiation may attain >;107 V/cm held amplitude. This held can be further enhanced using higher amplitudes of density ripples and lasers fields. The consequences of any deviation from the triangular profile of lasers are also discussed by comparing the results with rounded triangular shape lasers.

Near-Infrared Organic Photodiodes

Abstract: Organic photodiodes (OPDs) are attractive as solution-processed devices for sensing applications. Industrial and medical sensors often have the requirement to operate in the near-infrared (NIR) spectrum between 650 and 900 nm and are ideally visible-blind. Due to the tailored spectral sensitivity of the organic semiconductors, OPDs are attractive as filter-free solid-state alternative. In addition, the large active areas of the OPDs potentially allow fabricating lens-free light-barrier and reflective sensors. In this paper, we discuss different approaches toward NIR sensitive OPDs with a large active area up to 1 cm2 applying polymers and small molecules as light absorbers. We demonstrate that with layer stacks optimized to the solution-processed semiconductor properties photodiodes with bulk heterojunctions with a minimum external quantum efficiency peak in the NIR and a rectification ratio of ~105 can be achieved, which match industrial sensing requirements.

Frequency-Tunable THz Source Based on Stimulated Polariton Scattering in ${\rm Mg{:}LiNbO}_{3}$

Abstract: We report a very compact, laser diode end-pumped THz laser source, which utilizes two resonators to generate frequency-tunable radiation across the range 1.53-2.82 THz via stimulated polariton scattering (SPS) in a Mg:LiNbO3 crystal. To the best of our knowledge, this THz system operates with the lowest pump power threshold (2.4 W), and highest conversion efficiency (6.45tW average output power at 1.82 THz for 5 W input diode pump power) ever reported for a THz source based on SPS.

Avalanche Double Photodiode in 40-nm Standard CMOS Technology

Abstract: This paper investigates a silicon (Si) avalanche double photodiode (ADPD) fabricated in 40-nm standard CMOS technology. Two different types of double photodiodes (DPDs) will be introduced. The first one is a P-well/deep-N-well/P-substrate(PW/DNW/P-substrate) DPD, and the second one is a P+/N-well/P-substrate (P+/NW/P-substrate) DPD. The basic structure of the proposed ADPD is formed by P+/NW and NW/P-substrate junctions in which the avalanche effect occurs at the P+/NW junction. The P+/NW/P-substrate ADPD demonstrates responsivity of 0.84 A/W and a 3-dB electrical bandwidth of 0.7 GHz at 850 nm. For 660 nm, the ADPD shows a responsivity of 0.49 A/W with an electrical bandwidth of 1.8 GHz. For 520 nm, a responsivity of 2.04 A/W and an electrical bandwidth of 1.4 GHz are achieved.

Efficient Continuous-Wave 1053-nm Nd:GYSGG Laser With Passively Q-Switched Dual-Wavelength Operation for Terahertz Generation

Abstract: Research on an efficient continuous-wave Nd:GYSGG laser at 1053 nm with excellent stability is demonstrated. The maximum output power is 4.17 W, corresponding to the conversion efficiency of 33.9% and the slope efficiency of 42.92%. Using a Cr:YAG absorber, pulsed dual-wavelength operation at 1053 and 1058.4 nm is obtained, of which the maximum single pulse energy and peak power are 172.1 μJ and 26.1 kW, respectively, when the pulse width is 6.6 ns and the repetition rate is 4.3 kHz. A polarization property is observed, owing to the anisotropy of Cr:YAG. This stably Q-switched dual-wavelength laser is a good pump source for the generation of a terahertz wave at 1.53 THz.

Simulation of High-Efficiency GaN/InGaN p-i-n Solar Cell With Suppressed Polarization and Barrier Effects

Abstract: The photovoltaic characteristics of Ga-face GaN/InGaN p-i-n solar cells are investigated numerically. The severe polarization and barrier effects induced by the GaN/InGaN hetero-interfaces are demonstrated to be detrimental for the carrier collection. The conversion efficiency could be degraded to be out of application when the degree of polarization and/or indium composition are high. To efficiently eliminate both critical issues, the solar cell structure with appropriate band engineering is introduced. In the proposed structure, the photovoltaic characteristics not only show high-grade performance but also become insensitive to the degree of polarization, even in the situation of high indium composition.

3-D Vectorial Optical Model for High-Contrast Grating Vertical-Cavity Surface-Emitting Lasers

Abstract: High-Contrast Gratings (HCG) are modeled in a rigorous way by a new mode-matching approach. They are highly attractive because they have recently proved suitable to replace distributed Bragg mirrors in Vertical-Cavity Surface-Emitting Lasers (VCSELs). Through a change of basis from plane to cylindrical waves, the generalized transmission matrix of the grating layer is obtained in a form that can be directly used within VCSEL ELectroMagnetic (VELM) code. This is the fully 3-D vectorial code developed at IEIIT-CNR (Turin, Italy) for a decade, which has proven to have the capability to reproduce the experimental details of the various structures investigated so far. The inclusion of HCG in VELM is performed on the same footing as all other geometrical details and in a way that preserves the code accuracy and numerical efficiency. A full set of modes of a large-size HCG VCSEL can be computed in a few minutes on an ordinary laptop.

512 $\,\times\,$ 512 Individually Addressable MWIR LED Arrays Based on Type-II InAs/GaSb Superlattices

Abstract: Single element 33×33 μm2 InAs/GaSb superlattice light-emitting diodes (SLEDs) operating at 77 K with peak emission at approximately 4.6 μm are demonstrated. A peak radiance of 2.2 W/cm2/sr was measured corresponding to an apparent temperature greater than 1350 K within the 3-5 μm band. A 48 μm pitch, 512 × 512 individually addressable LED array was fabricated from a nominally identical SLED wafer, hybridized with a read-in integrated circuit, and tested. The array exhibited a pixel yield greater than 95%.

Suppression of Higher-Order Lateral Modes in Broad-Area Diode Lasers by Resonant Anti-Guiding

Abstract: For a maximum fiber-coupled power, high power broad-area diode lasers must operate with a small lateral far-field divergence at high continuous wave (CW) powers. However, these structures are laterally multi-moded, with a low beam quality and wide emission angles. We present a new approach to suppress higher-order lateral modes based on an anti-guiding layer with a high refractive index inserted at the edges of the active stripe. Simulations of planar waveguides containing germanium layers reveal that strong mode-coupling effects occur. These are found to vary as a function of the thickness of the inserted layer. By embedding the germanium layer in the outer region of a ridge-waveguide, the mode coupling effects result in a reduction of the modal gain of higher-order lateral modes. The lateral far-field divergence of fabricated 90- μm stripe lasers emitting at 980 nm and containing such an anti-guiding layer is narrowed by 3° at a CW output power of 10 W.

Spectral Analysis for Velocity Measurement Through Self-Mixing Interferometry

Abstract: A novel elaboration technique for a self-mixing interferometer is presented. It enables the measurement of speed and direction for a remote target, without using heterodyne detection. The elaboration employs the signal non-linearity for recovering the speed sign directly in the frequency domain. The target speed is measured by the signal frequency, whereas the speed sign is evaluated by the phases of the signal.

${\rm Er}^{3+}$ Concentration Effects in Commercial Erbium-Doped Silica Fibers Fabricated Through the MCVD and DND Technologies

Abstract: Commercial Erbium doped silica fibers fabricated through the modified chemical vapor deposition and direct nanoparticle deposition processes where ${\rm Er}^{3+}$ concentration is varied in a wide range are characterized by means of analyses of ${\rm Er}^{3+}$ fluorescence decay kinetics and nonlinear absorption coefficient at 978-nm pumping. Through theoretical modeling of the results of the entire experiment, the values of key parameters for the concentration-related effects, i.e., homogeneous and inhomogeneous upconversion processes, are determined.

Fast Active Quenching Circuit for Reducing Avalanche Charge and Afterpulsing in InGaAs/InP Single-Photon Avalanche Diode

Abstract: We characterize three different quenching circuits for InGaAs/InP single-photon avalanche diodes (SPADs) operated in gated mode: i) a simple passive quenching circuit; ii) an active quenching circuit; and iii) a fast active quenching circuit. For each of these, we acquire the shape of the avalanche current, at different excess biases, by reconstructing the waveform of the photons emitted from the detector during an avalanche and we simultaneously measure the afterpulsing probability and the dependence of dark count rate on gate period (to estimate the maximum count rate). We prove that the avalanche charge reduction is in agreement with the reduction of afterpulsing probability, giving a four-time decrease in afterpulsing when employing the fast active quenching circuit compared to the simple passive quenching circuit.

Performance Optimization of Multiple Quantum Well Transistor Laser

Abstract: A comprehensive physical model that emphasizes carrier tunneling between quantum wells (QWs) in the base of transistor lasers (TLs) is developed. This model relies on a set of multilevel coupled rate equations solved by computationally efficient numerical methods for simulating both steady state and transient TL operations. Our approach also features the explicit dependence of the structure design on device parameters such as optical confinement factor and carrier density-dependent gain. It also accounts for operation behaviors such as bandwidth roll-off and critical base width not yet addressed in the literature. Simulation results show significant enhancement in optical bandwidth as well as threshold current reduction when multiple QWs are incorporated within the base region. It predicts the dominance of tunneling transport of carriers for barriers thinner than 13.5 nm in a system with 7-nm QWs. However, the optimum QW number depends on the structure design as well as TL biasing conditions. For this purpose, we define a performance parameter as a TL figure of merit that can be maximized by optimizing both the base and the cavity designs.

Mode Competition Induced by Optical Feedback in Two-Color Quantum Dot Lasers

Abstract: We investigate theoretically the impact of optical feedback on quantum dot two-color laser dynamics when emitting from both the excited and the ground states. Detailed analysis of the laser dynamics is provided by numerical integrations and continuation techniques, as well as by analytical methods. As the feedback strength is increased the quantum dot laser undergoes a sequence of bifurcations involving steady-states, external cavity modes, self-pulsations and chaos. Furthermore, we report on two interesting mode competition results. First, the optical feedback favors the ground state emission; hence an increase of the feedback strength will generally lead to an increase of the ground state emission output power. Second, the optical feedback can select one lasing state or induce bistable switchings between different steady-states depending on the feedback strength and the injection current.