Showing papers on "Semiconductor optical gain published in 2017"

Toward continuous-wave operation of organic semiconductor lasers.

Abstract: The demonstration of continuous-wave lasing from organic semiconductor films is highly desirable for practical applications in the areas of spectroscopy, data communication, and sensing, but it still remains a challenging objective. We report low-threshold surface-emitting organic distributed feedback lasers operating in the quasi-continuous-wave regime at 80 MHz as well as under long-pulse photoexcitation of 30 ms. This outstanding performance was achieved using an organic semiconductor thin film with high optical gain, high photoluminescence quantum yield, and no triplet absorption losses at the lasing wavelength combined with a mixed-order distributed feedback grating to achieve a low lasing threshold. A simple encapsulation technique greatly reduced the laser-induced thermal degradation and suppressed the ablation of the gain medium otherwise taking place under intense continuous-wave photoexcitation. Overall, this study provides evidence that the development of a continuous-wave organic semiconductor laser technology is possible via the engineering of the gain medium and the device architecture.

Towards zero-threshold optical gain using charged semiconductor quantum dots.

Abstract: Colloidal semiconductor quantum dots are attractive materials for the realization of solution-processable lasers. However, their applications as optical-gain media are complicated by a non-unity degeneracy of band-edge states, because of which multiexcitons are required to achieve the lasing regime. This increases the lasing thresholds and leads to very short optical gain lifetimes limited by nonradiative Auger recombination. Here, we show that these problems can be at least partially resolved by employing not neutral but negatively charged quantum dots. By applying photodoping to specially engineered quantum dots with impeded Auger decay, we demonstrate a considerable reduction of the optical gain threshold due to suppression of ground-state absorption by pre-existing carriers. Moreover, by injecting approximately one electron per dot on average, we achieve a more than twofold reduction in the amplified spontaneous emission threshold, bringing it to the sub-single-exciton level. These measurements indicate the feasibility of ‘zero-threshold’ gain achievable by completely blocking the band-edge state with two electrons. Blocking band-edge absorption of compositionally graded quantum dots with suppressed Auger recombination by pre-existing electrons allows for demonstrating near-zero-threshold optical gain and amplified spontaneous emission at sub-single-exciton pump levels.

Optics, light and lasers : the practical approach to modern aspects of photonics and laser physics

Abstract: Preface 1 Light rays 11 Light rays in human experience 12 Ray optics 13 Reflection 14 Refraction 15 Fermat's principle: the optical path length 16 Prisms 17 Light rays in wave guides 18 Lenses and curved mirrors 19 Matrix optics 110 Ray optics and particle optics Problems for chapter 1 2 Wave optics 21 Electromagnetic radiation fields 22 Wave types 23 Gaussian beams 24 Polarization 25 Diffraction Problems for chapter 2 3 Light propagation in matter 31 Dielectric interfaces 32 Complex refractive index 33 Optical wave guides and fibres 34 Functional types and applications of optical fibres 35 Photonic materials 36 Light pulses in dispersive materials 37 Anisotropic optical materials 38 Optical modulators Problems for chapter 3 4 Optical images 41 The human eye 42 Magnifying glass and eyepiece 43 Microscopes 44 Telescopes 45 Lenses: designs and aberrations Problems for chapter 4 5 Coherence and interferometry 51 Young's double slit 52 Coherence and correlation 53 The double-slit experiment 54 Michelson interferometer: longitudinal coherence 55 Fabry-Perot interferometer 56 Optical cavities 57 Thin optical films 58 Holography 59 Laser speckle (laser granulation) Problems for chapter 5 6 Light and matter 61 Classical radiation interaction 62 Two-level atoms 63 Stimulated and spontaneous radiation processes 64 Inversion and amplification Problems for chapter 6 7 The laser 71 The classic system: the He-Ne laser 72 Mode selection in the He-Ne laser 73 Spectral properties of the He-Ne laser 74 Applications of the He-Ne laser 75 Other gas lasers 76 Molecular gas lasers 77 The workhorses: solid-state lasers 78 Selected solid-state lasers 79 Tunable lasers with vibronic states 710 Tunable ring lasers Problems for chapter 7 8 Laser dynamics 81 Basic laser theory 82 Laser rate equations 83 Threshold-less lasers and micro-lasers 84 Laser noise 85 Pulsed lasers Problems for chapter 8 9 Semiconductor lasers 91 Semiconductors 92 Optical properties of semiconductors 93 The heterostructure laser 94 Dynamic properties of semiconductor lasers 95 Laser diodes, diode lasers, laser systems 96 High-power laser diodes Problems for chapter 9 10 Sensors for light 101 Characteristics of optical detectors 102 Fluctuating opto-electronic quantities 103 Photon noise and detectivity limits 104 Thermal detectors 105 Quantum sensors I: photomultiplier tubes 106 Quantum sensors II: semiconductor sensors 107 Position and image sensors Problems for chapter 10 11 Laser spectroscopy 111 Laser-induced fluorescence (LIF) 112 Absorption and dispersion 113 The width of spectral lines 114 Doppler-free spectroscopy 115 Transient phenomena 116 Light forces Problems for chapter 11 12 Photons - an introduction to quantum optics 121 Does light exhibit quantum character? 122 Quantization of the electromagnetic field 123 Spontaneous emission 124 Weak coupling and strong coupling 125 Resonance fluorescence 126 Light fields in quantum optics 127 Two-photon optics 128 Entangled photons Problems for chapter 12 13 Nonlinear optics I: optical mixing processes 131 Charged anharmonic oscillators 132 Second-order nonlinear susceptibility 133 Wave propagation in nonlinear media 134 Frequency doubling 135 Sum and difference frequency 136 Optical parametric oscillators Problems for chapter 13 14 Nonlinear optics II: four-wave mixing 141 Frequency tripling in gases 142 Nonlinear refraction coefficient (optical Kerr effect) 143 Self-phase modulation Problems for chapter 14 Appendix A Mathematics for optics A1 Spectral analysis of fluctuating measurable quantities A2 Poynting theorem B Supplements in quantum mechanics B1 Temporal evolution of a two-state system B2 Density-matrix formalism B3 Density of states Bibliography Index

Semiconductor optical amplifiers at 2.0‐µm wavelength on silicon

Abstract: A semiconductor optical amplifier at 2.0-µm wavelength is reported. This device is heterogeneously integrated by directly bonding an InP-based active region to a silicon substrate. It is therefore compatible with low-cost and high-volume fabrication infrastructures, and can be efficiently coupled to other active and passive devices in a photonic integrated circuit. On-chip gain larger than 13 dB is demonstrated at 20 °C, with a 3-dB bandwidth of ∼75 nm centered at 2.01 µm. No saturation of the gain is observed for an on-chip input power up to 0 dBm, and on-chip gain is observed for temperatures up to at least 50 °C. This technology paves the way to chip-level applications for optical communication, industrial or medical monitoring, and non-linear optics.

Reconfigurable Radar Waveform Generation Based on an Optically Injected Semiconductor Laser

Abstract: We propose and experimentally demonstrate an approach to generating reconfigurable radar waveforms based on an optically injected semiconductor laser. In the proposed system, the semiconductor laser is operated at period-one oscillation state, in which an optical output signal containing a microwave modulation on the intensity is generated. After photo detection, a frequency-tunable microwave signal is obtained with its instantaneous frequency determined by the optical injection strength and/or the detuning frequency between the master and slave lasers. Since the dynamical behavior of a semiconductor laser evolves at a subnanosecond time scale, by properly designing a control signal to manipulate the optical injection strength, reconfigurable microwave waveforms with desired parameters can be generated for radar and other applications. In particular, the generation of continuous-wave or pulsed, linearly chirped, and frequency-hopping microwave waveforms with reconfigurable parameters are experimentally demonstrated. In addition, a high-resolution distance measurement experiment is performed to verify the feasibility of applying the proposed microwave waveform generator to radar applications.

Carrier-envelope offset frequency stabilization of a gigahertz semiconductor disk laser

Abstract: Optical frequency combs based on ultrafast lasers have enabled numerous scientific breakthroughs. However, their use for commercial applications is limited by the complexity and cost of femtosecond laser technology. Ultrafast semiconductor lasers might change this issue as they can be mass produced in a cost-efficient way while providing large spectral coverage from a single technology. However, it has not been proven to date if ultrafast semiconductor lasers are suitable for stabilization of their carrier-envelope offset (CEO) frequency. Here we present what we believe to be the first CEO frequency stabilization of an ultrafast semiconductor disk laser (SDL). The optically pumped SDL is passively modelocked by a semiconductor saturable absorber mirror. It operates at a repetition rate of 1.8 GHz and a center wavelength of 1034 nm. The 273 fs pulses of the oscillator are amplified to an average power level of 6 W and temporally compressed down to 120 fs. A coherent octave-spanning supercontinuum spectrum is generated in a photonic crystal fiber. The CEO frequency is detected in a standard f–to–2f interferometer and phase locked to an external reference by feedback applied to the current of the SDL pump diode. This proof-of-principle demonstrates that ultrafast SDLs are suitable for CEO stabilization and constitutes a key step for further developments of this comb technology expected in the coming years.

Tunable X-Band Optoelectronic Oscillators Based on External-Cavity Semiconductor Lasers

Abstract: Laser diodes with optical feedback can exhibit periodic intensity oscillations at or near the relaxation-oscillation frequency. We demonstrate optoelectronic oscillators based on external-cavity semiconductor lasers in a periodic dynamical regime tunable over the entire $X$ -band. Moreover, unlike standard optoelectronic oscillators, we need not employ the time-dependent optical intensity incident on a photodiode to generate the microwave signal, but rather have the option of generating the electrical microwave signal directly as a voltage $V(t)$ at the laser-diode injection terminals under constant current operation; no photodiode need be involved, thus circumventing optical-to-electrical conversion. We achieve a timing jitter of $\lesssim 10$ ps and a quality factor of $\gtrsim 2\times 10^{5}$ across the entire $X$ -band, that ranges from 6.79 to 11.48 GHz. Tuning is achieved by varying the injection current $J$ .

Multipulse dynamics of a passively mode-locked semiconductor laser with delayed optical feedback.

Abstract: Passively mode-locked semiconductor lasers are compact, inexpensive sources of short light pulses of high repetition rates. In this work, we investigate the dynamics and bifurcations arising in such a device under the influence of time delayed optical feedback. This laser system is modelled by a system of delay differential equations, which includes delay terms associated with the laser cavity and feedback loop. We make use of specialised path continuation software for delay differential equations to analyse the regime of short feedback delays. Specifically, we consider how the dynamics and bifurcations depend on the pump current of the laser, the feedback strength, and the feedback delay time. We show that an important role is played by resonances between the mode-locking frequencies and the feedback delay time. We find feedback-induced harmonic mode locking and show that a mismatch between the fundamental frequency of the laser and that of the feedback cavity can lead to multi-pulse or quasiperiodic dynamics. The quasiperiodic dynamics exhibit a slow modulation, on the time scale of the gain recovery rate, which results from a beating with the frequency introduced in the associated torus bifurcations and leads to gain competition between multiple pulse trains within the laser cavity. Our results also have implications for the case of large feedback delay times, where a complete bifurcation analysis is not practical. Namely, for increasing delay, there is an ever-increasing degree of multistability between mode-locked solutions due to the frequency pulling effect.

Monolithic Semiconductor Lasers with Dynamically Tunable Linear-to-Circular Polarization

Abstract: The ability to control the polarization state of emission from semiconductor lasers is essential for many applications in spectroscopy, imaging, and communications, inter alia, with monolithic integration approaches being extremely beneficial. Although manipulating the output polarization of radiation from a laser can be achieved through a number of approaches, obtaining continuous dynamic control, e.g., from linear to circular, remains extremely challenging. In this paper, we demonstrate that the polarization of terahertz (THz) frequency radiation can be continuously tuned electronically from linear to circular polarization by monolithically integrating in-plane metasurfaces with two phase-locked semiconductor-based THz quantum cascade lasers. Moreover, the metasurfaces—metal antenna arrays in this case—also act as efficient beam collimators, yielding a collimated beam divergence of ∼10° × 10°. Our results, however, have broad applicability to a wide range of semiconductor lasers operating from the visib...

Measurement of the emission spectrum of a semiconductor laser using laser-feedback interferometry

Abstract: The effects of optical feedback (OF) in lasers have been observed since the early days of laser development. While OF can result in undesirable and unpredictable operation in laser systems, it can also cause measurable perturbations to the operating parameters, which can be harnessed for metrological purposes. In this work we exploit this ‘self-mixing’ effect to infer the emission spectrum of a semiconductor laser using a laser-feedback interferometer, in which the terminal voltage of the laser is used to coherently sample the reinjected field. We demonstrate this approach using a terahertz frequency quantum cascade laser operating in both single- and multiple-longitudinal mode regimes, and are able to resolve spectral features not reliably resolved using traditional Fourier transform spectroscopy. We also investigate quantitatively the frequency perturbation of individual laser modes under OF, and find excellent agreement with predictions of the excess phase equation central to the theory of lasers under OF.

Non-equilibrium ultrashort pulse generation strategies in VECSELs

Abstract: Vertical external cavity surface emitting lasers are ideal testbeds for studying nonlinear many-body systems driven far from equilibrium. The classical laser gain picture fails, however, when a high peak intensity optical pulse of duration shorter than the intrinsic carrier scattering time interacts with electrons in the conduction and holes in the valence band, and the non-equilibrium carrier distributions cannot recover during the presence of the exciting pulse. We present the optimization of ultrashort mode-locked pulses in a vertical external cavity surface emitting laser cavity with a saturable absorber mirror by modelling non-equilibrium quantum dynamics of the electron-hole excitations in the semiconductor quantum-well gain and absorber medium via the semiconductor Bloch equations and treating the field propagation at the level of Maxwell’s wave equation. We introduce a systematic design that predicts the generation of stable mode-locked pulses of duration less than twenty femtoseconds. This factor of five improvement is of interest for mode-locking and ultrafast semiconductor dynamics applications.

Simultaneous Generation of Microwave, Millimeter-Wave, and Terahertz Photonic Signal Based on Two-Color Semiconductor Laser Subject to Single-Beam Optical Injection

Abstract: In this paper, dual-mode semiconductor laser is presented and demonstrated experimentally based on multimode Fabry–Perot laser diode with a built-in cavity. The spacing of both emission modes can be tuned by adjusting the bias current and operating temperature of active region. The generated dual-mode resonance can give rise to terahertz (THz) photonic signal with more than 300 GHz frequency. Under an external injection mode launched into the two-color semiconductor laser condition, it is possible to simultaneously generate photonic signals with various frequencies, ranging from less than 10 GHz to several THz, by selecting a proper resonance mode as the reference mode of injection beam. In this study, photonic signal including microwave (MW), millimeter-wave (mm-wave), and THz wave whose frequency range is from a few gigahertz to more than 0.5 THz are given, and the corresponding optical spectrum and electrical spectrum for low-frequency MW signal as well as simulated electrical spectrum for high-frequency mm-wave and THz wave signal are presented and discussed in detail.

Subterahertz Nanosecond Switches Driven by Second-Long Laser Pulses

Abstract: Subterahertz semiconductor waveguide switches designed for nanosecond pulse regimes have been studied at much longer pulse durations up to 1 s. The problems of heat dissipation in such switches are discussed. Substituting the microwave Joule heating dissipation mechanism with similarly distributed laser heating in the semiconductor, we can estimate the maximum commutated microwave power, which the switch can operate safely. Operation of a nanosecond-performance switch driven by a 1-s laser pulse, which produced a 1-s microwave pulse at the output, has been demonstrated experimentally. The new typical relaxation time associated with the size of the heat dissipation area in the semiconductor plate has been measured. The process of semiconductor blowout under 20-W laser emission has been recorded and discussed. The minimum commutation time under the maximum waveguide transmittable power has been obtained.

Interactions and collisions of topological solitons in a semiconductor laser with optical injection and feedback

Abstract: We present experimental and numerical results about dynamical interactions of topological solitons in a semiconductor laser with coherent injection and feedback. We show different kind of interactions such as repulsion, annihilation, or formation of soliton bound states, depending on laser parameters. Collisions between single structures and bound states conserve momentum and charge.

Performance Evaluation of Integrated Semiconductor Ring Laser Gyroscope

Abstract: We present a mathematical analysis and comparison of the performance of integrated on-chip semiconductor ring laser gyroscope (SRLG) fabricated using GaAs/AlGaAs and InP/InGaAsP technologies. The performance parameters of the gyro are modeled in terms of fundamental material, waveguide, and resonator parameters. In addition to this, influence of phenomena specific to semiconductor lasers such as nonlinear coupling, spatial hole burning, gain grating formation, and carrier induced index change on the gyro performance is also included. The analysis helps in identifying critical parameters, which must be optimized to improve the gyro performance.Best achievable performance of integrated SRLG is calculated, and design modifications are suggested to enhance it for high-performance military applications.

Effect of Bias Current on Complexity and Time Delay Signature of Chaos in Semiconductor Laser With Time-Delayed Optical Feedback

Abstract: The effect of bias current on the complexity and time-delay signature of chaotic signals in semiconductor lasers with polarization preserved optical feedback has been studied experimentally and theoretically. The peak value of the autocorrelation coefficient and the normalized permutation entropy at the feedback round trip time are used to quantify the time delay signature and complexity, respectively. The results show that the time-delay signature is approximately in an inverse relationship with the complexity of chaos when the semiconductor laser is subject to low or strong optical feedback. However, the inverse relationship disappears when the laser operates at higher bias currents with intermediate feedback strength. The simulation results are qualitatively agreed with the experimental results.

Resonance-free optical response of a vertical cavity transistor laser

Abstract: Optical resonance in a semiconductor laser is a major limitation in high speed data communications, resulting in bit error rate degradation and requiring additional power consuming error-correction circuits to counter these effects. In this work, we report the microwave bandwidth measurement of a vertical cavity transistor laser with an oxide-confined aperture of 4.7 × 5.4 μm2 and demonstrate a 3 dB bandwidth of 11 GHz resonance-free optical response via base-current or collector-voltage modulation. The emission spectra exhibit single-mode operation around 970 nm with a narrow linewidth of Δλ ∼ 0.23 A (cavity Q of 42 216). The resonance-free optical response is explained by the absence of carrier “accumulating” due to the fast base electron-hole recombination lifetimes and a gradient in the minority carrier charge in the transistor active mode.

Quantum-Dot Semiconductor Optical Amplifier: Performance and Application for Optical Logic Gates

Abstract: We proposed a novel structure of ultrafast all optical Feynman logic gate based on the cross-phase modulation that is principle nonlinear effect in a quantum dot semiconductor optical amplifier assisted with a Mach-Zehnder interferometer at the wavelength of 1.55 µm. To realize ultrafast mechanism, an active layer with a thickness of 1.7-µm, and the confinement factor of 0.75 and 0.7 respectively for both TE0 and TM0 modes, are provided. By solving the rate equations, a gain difference up to 0.1 dB has been obtained. The proposed structure has the potential application in advanced optical devices such as optical memristors.

Dynamic phase response and amplitude-phase coupling of self-assembled semiconductor quantum dots

Abstract: The optical excitation of semiconductor gain media introduces both gain and refractive index changes, commonly referred to as amplitude-phase coupling. Quantum-confined structures with an energetically well separated carrier reservoir usually exhibit a decreased amplitude-phase coupling compared to bulk materials. However, its magnitude and definition is still controversially discussed. We investigate the fundamental processes influencing the amplitude-phase coupling in semiconductor quantum-dot media using a coupled-carrier rate-equation model. We are able to analyze the dependence on the electronic structure and suggest routes towards an optimization of the dynamic phase response of the gain material.

Coupled-waveguides for dispersion compensation in semiconductor lasers

Abstract: The generation of optical frequency combs via direct electrical pumping of semiconductor lasers is an attractive alternative to the well-established mode-locked laser sources in terms of compactness, robustness and integrability. However, the high chromatic dispersion of bulk semiconductor materials can prevent the generation of frequency combs or lead to undesired pulse lengthening. In this letter, we present a novel dual waveguide for intracavity dispersion compensation in semiconductor lasers. We apply the concept to a short mid-infrared wavelength quantum cascade laser operating in the first atmospheric window (\lambda $ \approx$ 4.6 \mu m). As a result, stable comb operation on the full dynamical range is achieved in this device. Unlike previously proposed schemes, the dual waveguide approach can be applied to various types of semiconductor lasers and material systems. In particular, it could enable efficient group velocity dispersion compensation at near-infrared wavelengths where semiconductor materials exhibit a large value of that parameter.

The optically pumped semiconductor membrane external-cavity surface-emitting laser (MECSEL): a concept based on a diamond-sandwiched active region

Abstract: Semiconductor disk lasers with all their advantages1 became an important stand-alone class of solid-state lasers during the last years. However, these systems suffer from heat incorporation into the active region caused by the excess energy of the pump photons. To overcome this limitation we realized the semiconductor membrane external-cavity surface-emitting laser as a diamond heat spreader sandwiched active region design. A detailed process description towards the MECSEL2 approach is given as well as fundamental performance values. Furthermore, parasitic lateral lasing effects are discovered and investigated. Nevertheless, the MECSEL approach indicates enormous potential to revolutionize the semiconductor based disk lasers regarding available output powers at room temperature and material combinations.

Nonlinear optical properties of asymmetric n-type double δ -doped GaAs quantum well under intense laser field

Abstract: The effect of non-resonant intense laser field on the intersubband-related optical absorption coefficient and refractive index change in the asymmetric n-type double δ-doped GaAs quantum well is theoretically investigated. The confined energy levels and corresponding wave functions of this structure are calculated by solving the Schrodinger equation in the laser-dressed confinement potential within the framework of effective mass approximation. The optical responses are reported as a function of the δ-doped impurities density and the applied non-resonant intense laser field. Additionally, the calculated results also reveal that the non-resonant intense laser field can be used as a way to control the electronic and optical properties of the low dimensional semiconductor nano-structures.

The effects of a geometrical size, external electric fields and impurity on the optical gain of a quantum dot laser with a semi-parabolic spherical well potential

Abstract: In this paper, a G a A s / A l x G a 1 − x A s quantum dot laser with a semi-parabolic spherical well potential is assumed. By using Runge-Kutta method the eigenenergies and the eigenstates of valence and conduct bands are obtained. The effects of geometrical sizes, external electric fields and hydrogen impurity on the different electronic transitions of the optical gain are studied. The results show that the optical gain peak increases and red-shifts, by increasing the width of well or barrier, while more increasing of the width causes blue-shift and decreases it. The hydrogen impurity decreases the optical gain peak and blue-shifts it. Also, the increasing of the external electric fields cause to increase the peak of the optical gain, and (blue) red shift it. Finally, the optical gain for 1s–1s and 2s–1s transitions is prominent, while it is so weak for other transitions.

Extended Modal Gain Measurement in DFB Laser Diodes

Abstract: A practical method is proposed for complete gain measurement in distributed feedback (DFB) laser diodes. It is non-destructive and does not require any reference device. It includes the whole range of continuous gain values, from its minimum to threshold, passing through the transparency condition. The method requires a single absolute gain measurement for calibration. An example is reported for a DFB preserving Fabry–Perot multi-modes in the sub-threshold regime.

Theoretical analysis of a method for extracting the phase of a phase-amplitude modulated signal generated by a direct-modulated optical injection-locked semiconductor laser

Abstract: The phase modulation (PM) and amplitude modulation (AM) of optical signals can be achieved using a direct-modulated (DM) optical injection-locked (OIL) semiconductor laser. We propose and theoretically analyze a simple method to extract the phase component of a PM signal produced by a DM-OIL semiconductor laser. The pure AM component of the combined PM–AM signal can be isolated by square-law detection in a photodetector and can then be used to compensate for the PM–AM signal based on an optical homodyne method. Using the AM compensation technique, we successfully developed a simple and cost-effective phase extraction method applicable to the PM–AM optical signal of a DM-OIL semiconductor laser.

High peak power cavity dumping semiconductor lasers.

Abstract: We report on the development of a nanosecond pulsed kW-class optically pumped InGaAs semiconductor laser emitting around 1020 nm, which is suitable for applications such as incoherent laser radar, nonlinear optics, and materials processing. Using an intracavity Pockels cell to cavity-dump VECSELs, we are able to access large pulse energies by storing energy in the optical cavity rather than in the gain medium. We demonstrate peak powers >1 kW and 3 μJ pulses, show the pulse length is equivalent to the photon round-trip time, and show that the wavelength can be tuned within the gain bandwidth of the semiconductor gain.