Showing papers on "Semiconductor optical gain published in 2001"

Optoelectronics and Photonics: Principles and Practices

Abstract: (NOTE: Each chapter concludes with Questions and Problems.) 1. Wave Nature of Light. Light Waves in a Homogeneous Medium. Refractive Index. Group Velocity and Group Index. Magnetic Field, Irradiance and Poynting Vector. Snell's Law and Total Internal Reflection (TIR). Fresnel's Equations. Multiple Interference and Optical Resonators. Goos-Hanchen and Optical Tunneling. Temporal and Spatial Coherence. Diffraction Principles. 2. Dielectric Waveguides and Optical Fibers. Symmetric Planar Dielectric Slab Waveguide. Modal and Waveguide Dispersion in the Planar Waveguide. Step Index Fiber. Numerical Aperture. Dispersion in Single Mode Fibers. Bit-Rate, Dispersion, Electrical and Optical Bandwidth. The Graded Index Optical Fiber. Light Absorption and Scattering. Attenuation in Optical Fibers. Fiber Manufacture. 3. Semiconductor Science and Light Emitting Diodes. Semiconductor Concepts and Energy Bands. Direct and Indirect Bandgap Semiconductors: E-k Diagrams. pn Junction Principles. The pn Junction Band Diagram. Light Emitting Diodes. LED Materials. Heterojunction High Intensity LEDs. LED Characteristics. LEDs for Optical Fiber Communications. 4. Stimulated Emission Devices Lasers. Stimulated Emission and Photon Amplification. Stimulated Emission Rate and Einstein Coefficients. Optical Fiber Amplifiers. Gas Laser: The He-Ne Laser. The Output Spectrum of a Gas Laser. LASER Oscillation Conditions. Principle of the Laser Diode. Heterostructure Laser Diodes. Elementary Laser Diode Characteristics. Steady State Semiconductor Rate Equation. Light Emitters for Optical Fiber Communications. Single Frequency Solid State Lasers. Quantum Well Devices. Vertical Cavity Surface Emitting Lasers (VCSELs). Optical Laser Amplifiers. Holography. 5. Photodetectors. Principle of the pn Junction Photodiode. Ramo's Theorem and External Photocurrent. Absorption Coefficient and Photodiode Materials. Quantum Efficiency and Responsivity. The pin Photodiode. Avalanche Photodiode. Heterojunction Photodiodes. Phototransistors. Photoconductive Detectors and Photoconductive Gain. Noise in Photodetectors. 6. Photovoltaic Devices. Solar Energy Spectrum. Photovoltaic Device Principles. pn Junction Photovoltaic I-V Characteristics. Series Resistance and Equivalent Circuit. Temperature Effects. Solar Cells Materials, Devices and Efficiencies. 7. Polarization and Modulation of Light. Polarization. Light Propagation in an Anisotropic Medium: Birefringence. Birefringent Optical Devices. Optical Activity and Circular Birefringence. Electro-Optic Effects. Integrated Optical Modulators. Acousto-Optic Modulator. Magneto-Optic Effects. Non-Linear Optics and Second Harmonic Generation. Notation and Abbreviations. Index. CD-ROM: Optoelectronics and Photonics Contents.

Optical Frequency Synthesis Based on Mode- Locked Lasers

Abstract: The synthesis of optical frequencies from the primary cesium microwave standard has traditionally been a difficult problem due to the large disparity in frequency. Recently this field has been dramatically advanced by the introduction and use of mode-locked lasers. This application of mode-locked lasers has been particularly aided by the ability to generate mode-locked spectra that span an octave. This review article describes how mode-locked lasers are used for optical frequency synthesis and gives recent results obtained using them.

Very compact tunable solid-state laser utilizing a thin-film organic semiconductor.

Abstract: Optically pumped organic semiconductor lasers are fabricated by evaporation of a thin film of tris(8-hydroxyquinoline) aluminum Alq3 molecularly doped with a laser dye on top of a polyester substrate with an embossed grating structure. We achieve low-threshold, longitudinally monomode distributed-feedback laser operation. By varying the film thickness of the organic semiconductor film, we can tune the wavelength of the surface-emitting laser over 44 nm. The low laser threshold allows the use of a very compact all-solid-state pump laser (≈10 cm long). This concept opens up a way to obtain inexpensive lasers that are tunable over the whole visible range.

Novel 3R regenerator based on semiconductor optical amplifier delayed-interference configuration

Abstract: A novel 3R regenerator based on a single semiconductor optical amplifier in a delayed-interference configuration is presented and experimentally tested. The retiming capability of the device exceeds 6 ps at 10 Gb/s.

Experimental measurement of nonlinear polarisation rotation in semiconductor optical amplifiers

Abstract: Measurements are presented of the nonlinear polarisation rotation of light pulses passing through a semiconductor optical amplifier. It is shown that the induced phase differences between TM and TE modes can be substantial (-/spl pi//4 radians) for modest gain modulations (/spl sim/4 dB).

Optical transmitter comprising a stepwise tunable laser

Abstract: An optical fiber transmitter for emitting an information-carrying laser beam comprises an optically or electrically pumped single mode MQW (multi-quantum well) semiconductor amplifying mirror as a gain medium and a separate external reflector to form a cavity. The external cavity length defines a comb of optical modes, all or a subset of which correspond to channel wavelengths of an optical telecommunications system having plural optical channels. The semiconductor gain element has a homogeneously broadened gain region; a tuning arrangement tunes the laser from mode to mode across the gain region, thereby selecting each one of the plural optical channels. When the maximum gain bandwidth is less than mode-to-mode spacing defined by the cavity, the tuning arrangement includes a means of altering the temperature of the amplifying mirror, thereby translating the frequency of the gain peak from one mode to another. An optical modulator adds modulation to provide an information-carrying laser beam, and a coupler couples the information-carrying laser beam into an optical fiber of the optical telecommunications system. A calibration method based on detecting inter-mode optical transitions (mode hopping) is described. The parameters of the amplifying mirror and tuning arrangement can be adjusted during operation to switch quickly from one cavity mode to another in stepwise fashion.

Three-dimensional model for vectorial fields in vertical-cavity surface-emitting lasers

Abstract: The electromagnetic problem of modeling vertical-cavity surface-emitting lasers with their full three-dimensional characteristics is analyzed, including oxide confinement, mesa mirrors, metal contacts, and noncircular geometries. The model is based on the mode expansion of the electromagnetic field in the continuous basis of cylindrical TE and TM modes of the cavity medium and on coupled mode theory. The full vectorial treatment of the problem allows a correct analysis of the polarization characteristics of these lasers, which is a topic of great interest both for the device physics and for many applications. A comparison between the fully vectorial treatment and the LP scalar approximation is carried out and polarization resolved results for rectangular and elliptical structures are presented.

Self-consistent solutions to the intersubband rate equations in quantum cascade lasers: Analysis of a GaAs/AlxGa1-xAs device

Abstract: The carrier transition rates and subband populations for a GaAs/AlGaAs quantum cascade laser operating in the mid-infrared frequency range are calculated by solving the rate equations describing the electron densities in each subband self-consistently. These calculations are repeated for a range of temperatures from 20 to 300 K. The lifetime of the upper laser level found by this self-consistent method is then used to calculate the gain for this range of temperatures. At a temperature of 77 K, the gain of the laser is found to be 34 cm−1/(kA/cm−2), when only electron–longitudinal-optical phonon transitions are considered in the calculation. The calculated gain decreases to 19.6 cm−1/(kA/cm−2) when electron–electron transition rates are included, thus showing their importance in physical models of these devices. Further analysis shows that thermionic emission could be occurring in real devices.

Gain spectra of (GaIn)(NAs) laser diodes for the 1.3-μm-wavelength regime

Abstract: Optical gain spectra of (GaIn)(NAs)/GaAs quantum-well lasers operating in the 1.3-μm-emission-wavelength regime are measured and compared to those of a commercial (GaIn)(AsP)/InP structure. Good agreement of the experimental results with computed spectra of a microscopic many-body theory is obtained. Due to the contributions of a second confined subband, a spectrally broad gain region is expected for (GaIn)(NAs)/GaAs at elevated carrier densities.

Tunable controlled laser array

Abstract: A semiconductor laser capable of emitting in any one of standard communication wavelengths is of great practical value. To this end, a single semiconductor chip is fabricated on which many different distributed feedback (DFB) lasers are integrated. The device parameters of the different DFB lasers are varied such that each laser emits at a different wavelength. In addition a micro-mechanical optical element is packaged with the laser array, such that the position of the optical element controls which laser stripe is coupled to the output fiber. The micro-mechanical element or switch in various embodiments is a sliding waveguide, a movable lens, or a mirror that tilts. By selecting the particular DFB laser, controlling the temperature to fine tune the wavelength, and adjusting the position of the micro-mechanical optical element, the output wavelength is set to one of many communication wavelengths.

Maximum modal gain of a self-assembled InAs/GaAs quantum-dot laser

Abstract: Gain and threshold current of a self-assembled InAs/GaAs quantum-dot (QD) laser are simulated. A small overlap integral of the electron and hole wave functions in pyramidal QDs is shown to be a possible reason for the low single-layer modal gain, which limits lasing via the ground-state transition at short (under a millimeter) cavity lengths.

Two types of synchronization in unidirectionally coupled chaotic external-cavity semiconductor lasers.

Abstract: We study numerically two distant unidirectionally coupled single-mode semiconductor lasers subject to coherent optical feedback. We show that two fundamentally different types of chaotic synchronization can occur depending on the strengths of the coupling and of the feedback of the receiver laser.

Low confinement factors for suppressed filaments in semiconductor lasers

Abstract: Filament formation through self-focusing of light in semiconductor lasers leads to beam quality degradation, as well as lifetime and facet degradation. In this paper, we rederive an expression for the growth rate of sinusoidal perturbations, or filaments superimposed on the steady-state field in a semiconductor laser. We note that while the mode gain decreases with the confinement factor in a linear manner, the gain for filaments decreases far more rapidly. This agrees with recent observations of improved beam quality in broad-area semiconductor lasers with lowered confinement factors. Finally, we describe design rules for low-confinement-factor semiconductor lasers offering low-filamentation and greatly improved beam quality.

Optically pumped, surface-emitting semiconductor laser device and method for the manufacture thereof

Abstract: The invention is directed to an optically pumped surface-emitting semiconductor laser device having at least one radiation-generating quantum well structure and at least one pump radiation source for optically pumping the quantum well structure, whereby the pump radiation source comprises an edge-emitting semiconductor structure. The radiation-generating quantum well structure and the edge-emitting semiconductor structure are epitaxially grown on a common substrate. A very efficient and uniform optical pumping of the radiation-generating quantum well structure is advantageously possible with this monolithically produced semiconductor laser device. Methods for manufacturing inventive semiconductor laser devices are also specified.

Waveguide grating mirror for large-area semiconductor lasers

Abstract: We have fabricated and tested a waveguide grating mirror that uses anomalous reflection of light associated with excitation of waveguide modes. Sharp features are observed in the reflection spectra in both the wavelength and the angular domains. We confirm experimentally that, when the waveguide grating mirror is placed a short distance in front of a large-area semiconductor laser, it can control the emission spectrum. This demonstration opens a new approach to the design of very compact semiconductor lasers operating in the single-frequency–single-mode regime.

Synchronization of optical-feedback-induced chaos in semiconductor lasers by optical injection

Abstract: We study the synchronization of feedback-induced chaos in semiconductor lasers by the optical injection scheme that consists of a transmitter laser with external optical feedback and a receiver laser with optical injection from the transmitter laser. The stable synchronization condition and the effects of the frequency detuning between the transmitter and the receiver lasers are investigated using numerical simulation. The results show that positive and negative frequency detuning exert different influences on the synchronization. A time lag between the waveforms of the transmitter and the receiver lasers in the case of a large frequency detuning is found and its experimental significance is commented on.

All-optical hysteresis control by means of cross-phase modulation in semiconductor optical amplifiers

Abstract: We describe the principle of operation of an all-optical flip-flop based on dispersive bistability in a distributed feedback semiconductor optical amplifier. Cross-phase modulation controls the photonic bandgap and Bragg resonances of the amplifier, thereby shifting the hysteresis and switching thresholds to higher or lower powers. We give the details of a simple theoretical model that is used to simulate the set and reset operations. We also experimentally investigate the dependence on set-signal power and the response to back-to-back set signals, and we apply the theoretical model to understand these experimental results.

Semiconductor optical amplifier using laser cavity energy to amplify signal and method of fabrication thereof

Abstract: A semiconductor optical amplifier (SOA) apparatus and related methods are described The SOA comprises a signal waveguide for guiding an optical signal along a signal path, and further comprises one or more laser cavities having a gain medium lying outside the signal waveguide, the gain medium being sufficiently close to the signal waveguide such that, when the gain medium is pumped with an excitation current, the optical signal traveling down the signal waveguide is amplified by an evanescent coupling effect with the laser cavity When the gain medium is sufficiently pumped to cause lasing action in the laser cavity, gain-clamped amplification of the optical signal is achieved Additional features relating to segmented laser cavities, separate pumping of laser cavity segments, DFB/DBR gratings, current profiling to improve ASE noise performance, coupled-cavity lasers, avoidance of injection locking effects, manipulation of gain curve peaks, integration with a tunable vertical cavity coupler, integration with a photodetector, integration with an RZ signal modulator, and other described features may be used with the evanescent coupling case or with an SOA having a laser cavity gain medium that is coextensive with the gain medium of the signal waveguide

Experimental observation of synchronization and anti-synchronization of chaotic low-frequency-fluctuations in external cavity semiconductor lasers

Abstract: Experimental investigations of synchronization and anti-synchronization of optically coupled semiconductor lasers with external cavities are presented. Both lasers show chaotic low-frequency intensity fluctuations that are (anti-) synchronized due to optical coupling by light injection. For uni-directional coupling response lasers with and without external cavity are considered. In the case of bi-directional coupling synchronized fluctuations are observed even without external mirrors.

Sequence influence of nonidentical InGaAsP quantum wells on broadband characteristics of semiconductor optical amplifiers--superluminescent diodes.

Abstract: Extremely broadband emission is obtained from semiconductor optical amplifiers-superluminescent diodes with nonidentical quantum wells made of InGaAsP/InP materials. The well sequence is experimentally shown to have a significant influence on the emission spectra. With the three In(0.67) Ga(0.33) As(0.72) P(0.28) quantum wells near the n -cladding layer and the two In(0.53) Ga(0.47) As quantum wells near the p -cladding layer, all bounded by In(0.86) Ga(0.14) As(0.3)P(0.7) barriers, the emission spectrum could cover from less than 1.3 to nearly 1.55 microm, and the FWHM could be near 300 nm.

Dynamics of periodically forced semiconductor laser with optical feedback.

Abstract: Recently it was proposed that semiconductor lasers with optical feedback present a regime where they behave as noise driven excitable units. In this work we report on an experimental study in which we periodically force one of these lasers and we compare the results with the solutions of a simple model. The comparison is based on a topological analysis of experimental and theoretical solutions.

Gain dynamics in traveling-wave semiconductor optical amplifiers

Abstract: A theoretical analysis of the optical properties of multiquantum well semiconductor optical amplifiers (MQW-SOA) have been performed in the time-dependent regime. We describe the interaction between pulse propagation and gain compression within a pump-probe excitation in polarization insensitive MQW-SOA. We use a phenomenological model based on rate equations (describing the carrier dynamics in the different heterolayers along the growth axis for both bulk and MQW structures), coupled with the description of picosecond optical pulse propagation within a semiconductor slab (along the active waveguide axis), to describe the way gain dynamics determine the optical response of the SOA. Our model agrees well with available experimental data and also reveals the conditions for the validity of previous simpler approaches.

Gain saturation and the linewidth enhancement factor in semiconductor lasers

Abstract: There is an asymmetry in the optical spectrum of the semiconductor laser under weak current modulation. It arises because the linewidth enhancement factor that describes the proportionality between the real and imaginary parts of the optical susceptibility due to the differential gain is not appropriate for the gain saturation. This asymmetry can be used to determine the proportionality for the gain saturation term, and to measure the value of the linewidth enhancement factor, a parameter that has been difficult to accurately measure. Data for an oxide-confined vertical-cavity surface-emitting laser is presented that shows a gain saturation term with a different, but nonnegligible, proportionality.

Control of nonlinear dynamics of a semiconductor laser with filtered optical feedback

Abstract: How to control the highly complex dynamics that occur in a diode laser with delayed optical feedback is addressed A numerical study shows that through an external optical frequency filter one can have external control over several dynamical attractors

Format conversion of optical data using four-wave mixing in semiconductor optical amplifiers

Abstract: We present an analysis of the effect of four-wave mixing (FWM) on the pulse propagation in the active region of semiconductor optical amplifiers (SOAs). Our model, based on a rate equation approach, successfully predicts operation of optical data sampling using FWM interaction between a signal bitstream and an optical clock. Such a process can be used for format conversion of optical pulses from nonreturn-to-zero to return-to-zero bitstreams.

Optical transmitter including a linear semiconductor optical amplifier

Abstract: An improved optical transmitter comprises a vertically lasing semiconductor optical amplifier (VLSOA) coupled to an external modulator and/or a laser source. The VLSOA, external modulator and laser source are discrete devices or alternatively integrated onto a common substrate. The integrated optical transmitter may be fabricated using a number of different methods, including based on selective area epitaxy, impurity induced disordering, etch and fill and silicon optical bench.

Optical gain-bandwidth product of vertical cavity laser amplifiers

Abstract: Trade-off between amplifier gain and optical bandwidth is investigated in the case of novel long-wavelength vertical-cavity semiconductor optical amplifiers. In agreement with measurements, simple formulas for the gain-bandwidth product are presented. Mirror optimisation promises gain-bandwidth products in the THz range.

Semiconductor laser devices, and semiconductor laser modules and optical communication systems using the same

Abstract: A semiconductor laser device and module for use in a dense wavelength division multiplexed optical communications system are shown. The laser device preferably has cavity lengths greater than 1000 μm, and compressive strain multi-quantum well active layer, and front-facet reflectivity of less than about 4%. Higher optical outputs and longer cavity lengths are achieved. Preferred modules use these laser diodes with external wavelength-selective reflectors that have narrow bandwidths of 3 nm or less, and which include a plurality of longitudinal mode subpeaks within the bandwidth. Relationships between reflectivity value of the front facet and the peak reflectivity of the wavelength-selective reflector for long cavity length laser device are also disclosed, with the relationships providing higher output power along with a stabilized output spectrum.

Characterization of a high-power tapered semiconductor amplifier system

Abstract: We have characterized a semiconductor amplifier laser system which provides up to 200 mW output after a single-mode optical fiber at 780 nm wavelength. The system is based on a tapered semiconductor gain element, which amplifies the output of a narrow-linewidth diode laser. Gain and saturation are discussed as a function of operating temperature and injection current. The spectral properties of the amplifier are investigated with a grating spectrometer. Amplified spontaneous emission (ASE) causes a spectral background with a width of 4 nm FWHM. The ASE background was suppressed to below our detection limit by a proper choice of operating current and temperature and by sending the light through a single-mode optical fiber. The final ASE spectral density was less than 0.1 nW/MHz, i.e. less than 0.2% of the optical power. Related to an optical transition linewidth of Γ/2π=6 MHz for rubidium, this gives a background suppression of better than -82 dB. An indication of the beam quality is provided by the fiber coupling efficiency of up to 59%. The application of the amplifier system as a laser source for atom-optical experiments is discussed.