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The active mode-locking technique of quantum cascade lasers is highly affected by the bias current level and the magnitude of the modulated signal because of the spatial hole burning effect. The laser generates a stable pulse train near the threshold current and for a high modulation magnitude. We show in this paper an improvement of these conditions with an integration of a single-layer graphene which works as a saturable absorber. The light-matter interaction in the laser active region is described by the two-level Maxwell-Bloch equations and in graphene layer by the Maxwell-Ampere equation and Maxwell-Bloch equations. These system equations are solved using the Finite-Difference Time-Domain (FDTD) method which has the main advantage of not involving any approximation. The weakly coupled splitting scheme is adopted for the time discretization of Maxwell and Bloch equations. The graphene saturable absorption is modelled by a saturable conductivity in Maxwell-Ampere equation and with the dipole moment and carrier density in Maxwell-Bloch equations. For a QCL structure with a gain recovery time of 50 ps, simulation results show better stability of the mode-locking over a broad range of injection current and for smaller magnitude of the modulated signal. QCL structure with gain recovery time close to 1 ps reveals the generation of two pulses per roundtrip linked to spatial hole burning. The carrier grating strength can be reduced by changing the boundary conditions of the cavity such as with a high reflectivity mirror in front of graphene layer. [ABSTRACT FROM AUTHOR]

Plasma-enhanced atomic layer deposition is used to fabricate compact tantalum (Ta)-doped titanium oxide (TiO2) thin films as electron transport layers (ETLs) and hole blocking layers for perovskite solar cells (PSCs). The effects of Ta-doped TiO2 with different annealing temperatures on film structure and electronic properties are researched. The experimental results exhibit that the substitutional Ta-doping into TiO2 (Ta content of ~1.5%) increases the stability of crystal structure and passivates the material defects, thereby improving the film quality. The annealed Ta-doped TiO2 films have a resistivity of approximately 6.5 $\boldsymbol {\Omega } \cdot $ cm which is three orders of magnitude lower than 3.4 $\times 10^{{3}}\,\, \boldsymbol {\Omega } \cdot $ cm of intrinsic TiO2. Finally, the annealing process eliminates the defects, and therefore, improves electron transport for PSCs, leading to a clearly enhanced fill factor (FF) of 0.77 and conversion efficiency of 19.62% when compared to that of undoped TiO2 ETL devices. [ABSTRACT FROM AUTHOR]

Beating between the lasing main mode and the non-lasing side modes is one of the intensity noise sources of single longitudinal mode lasers. Its characteristics were investigated experimentally recent years. This paper presents a theoretical study of mode-beating noises in semiconductor lasers, and intends to explain the experimentally observed phenomena. The effects of coherent population oscillation (CPO) induced by mode beating on gain coefficient and on reflective index are analyzed based on Maxwell-Bloch equation and rate equations. The power ratio of the side mode over its conjugation mode generated by four wave mixing (FWM) is discussed; formulas of amplitude and frequency of mode beating intensity noise are given with relations to pump levels and mode orders. The obtained results are suitable for the edge emitting diode lasers and the external cavity lasers. The line shape of mode beating intensity noises is discussed based on CPO-induced phase noise, giving explanations of the experimentally observed phenomenon of multiple sub-peak spectra. The roles of intensity noise reduction by nonlinear optical absorber (NLA) inserted in the laser cavity are described. More factors related to the mode beating noise are discussed qualitatively, such as spectral hole burning of gain (SHB), the effect of external cavity, and higher order FWM. [ABSTRACT FROM AUTHOR]

This article describes the characterization and analysis of the effects an additional polymer layer has on a high-overtone bulk acoustic wave resonator based on Ba0.5Sr0.5TiO3 (BSTO) thin film by studying its spectral information. From both the simulation (numerical model) and experimental results of the resonator with and without coating, significant difference of both cases is evident in the spacing of the parallel resonance frequencies (SPRFs), effective coupling coefficient (keff2), and quality factor distribution of the resonator. The acoustic velocity of the coated material (SU-8) is calculated from the new periodicity introduced in the SPRF distribution. The SPRF distribution of the SU-8-coated resonator decreases overall as expected due to the additional layer introduced but sharply increases in regions defined by the thickness and acoustic velocity of the SU-8 layer. The mechanical loss of the added layer has significant effect on the parameters of the resonator. The study reveals that this method of characterization can be used to approximate the mechanical loss of materials such as polymers or polymer composites. The simulation with finite-element method agrees with the experimental result. [ABSTRACT FROM AUTHOR]

Indium–gallium–zinc-oxide (IGZO) photoelectric neuromorphic transistors with low-temperature atomic layer deposited Al2O3 gate dielectrics are fabricated. Dual-functional long-term plasticity, including long-term depression (LTD) and long-term potentiation (LTP), is emulated. The emulation of LTD is achieved by applying high-electrical pulse trains on the gate electrode. The LTP emulation is realized by applying light pulse trains on the IGZO channel layer. The operation mechanisms of the LTD and the LTP are discussed based on the electron/hole trapping in the Al2O3 gate dielectrics and the persistent photoconductivity of the IGZO channel layer. [ABSTRACT FROM AUTHOR]

We report on the simulation of passive mode locking (ML) in quantum dot (QD) two-section lasers via a multi-section delayed differential equation model. The influence of the laser structural parameters on the achieved ML regimes is investigated. We show that, consistently with experimental findings, increasing the saturable absorber (SA) to gain section length ratio from 17% to 25%, a significant pulse shortening can be achieved. A physical explanation for this behavior is obtained via a detailed study of the gain and absorption saturation dynamics leading to the self consistent ML solution, in particular the competition between spectral hole burning non-linearity and total carrier density depletion responsible for the gain saturation in the gain section, balancing the absorption bleaching in the SA, is shown to play a central role in determining the observed ML regimes. In addition, the impact of introducing a tapered gain section in QD ML lasers are investigated, the possibility to achieve high power subpicosecond pulses from such devices is theoretically demonstrated and attributed to the significantly increased gain saturation energy in the tapered gain section. [ABSTRACT FROM AUTHOR]

Wavelength bi/multistability in semiconductor ring lasers is studied both theoretically and numerically based on a multimode model with nonlinear effects arising from carrier density pulsation, carrier heating, spectral hole-burning, and four-wave mixing included. Wavelength bi/multistability is explained theoretically, and conditions required for wavelength bi/multi-stable operation are derived analytically. It shows the dependence of wavelength bi/multistability on device size and other device and material properties. Radius range within which the device is wavelength bi/multistable is calculated based on the derived expressions. Both the theory and calculations are verified by numerical simulations and supported by previously reported experimental observations on wavelength bi/multistable semiconductor ring lasers. The results indicate that semiconductor microring/microdisk lasers with radius down to 10 \mum could still support wavelength bi/multistable operation. [ABSTRACT FROM AUTHOR]

Although the tunnel mass is indispensable to predict the gate leakage current of electron devices, it has been regarded as an adjustable parameter to fit the calculated leakage current with the measured ones. This appears useful because it enables calculation of the tunnel current while ignoring some details in advanced device modeling, even though it has veiled the intuitive nature of the modeling. More concretely, the adjustable tunnel mass pushes us to ignore the related issues that should carefully be considered. In this paper, we extract the tunnel masses for electrons and holes from an individual experiment and find that they are 0.85m0, wherem0 is the rest electron mass, irrespective of the molecular compound ratio between Si3N4 and SiO2 and the film thickness. This suggests a convincing model for charge trapping in [(SiO2)1-x(Si3N4)x]1-y Siy including interfacial transition layers. It is also found that the leakage mechanism is the direct tunneling enhanced by the trapped positive charge. [ABSTRACT FROM AUTHOR]

We use a traveling-wave model for explaining the experimentally observed changes in the directionality of the emission of semiconductor ring lasers and its different behavior when current is increased or decreased. The modulation of the cavity losses imposed by the light extraction sections together with the thermal shift of the gain spectrum and spatial hole burning in the carrier density play a crucial role in the directionality of the emission and its changes with operation current. The differences as the current is increased or decreased correspond to the different role played by spatial hole burning. [ABSTRACT FROM AUTHOR]

We numerically and experimentally investigate the high-speed small-signal cross-gain modulation (XGM) characteristics of a quantum-dot (QD) semiconductor optical amplifier (SOA). From a p-doped QD SOA operating at 1.3 μm, high-speed small-signal XGM responses up to 40 GHz are measured from low to high injection currents and improve at high injection currents. In the numerical model, we set up about six hundred coupled rate equations, where the carrier dynamics of QD electron and hole states are considered separately and the enhanced hole occupation due to p-type doping is included. The high-speed small-signal XGM spectra are calculated at various modulation frequencies and pump-probe detunings. We identify how the two separate XGM mechanisms of total carrier density depletion (TCDD) at low injection current and spectral hole burning (SHB) at high injection current affect the high-speed small-signal XGM behavior. From the measured and calculated results, we show that high-speed small-signal XGM responses of QD SOAs can be improved by injecting more carriers to the QD excited states, which enhances high-speed XGM induced by SHB rather than by TCDD. [ABSTRACT FROM AUTHOR]

Wavelength and directional hysteresis due to increasing and decreasing current and temperature have been investigated. Measurements indicate that lasing direction hysterysis associated with changes in injection current can be attributed to the resulting shift in the linear gain peak which is due to the change in device temperature. Enteraction between the linear gain spectrum and the asymmetric nonlinear gain spectrum results in contrasting behavior for increasing and decreasing temperature and current. The phenomena are modeled using a nonlinear time domain model including the carrier density pulsation (CDP), carrier heating (CH) and spectral hole burning (SHB) effects. The numerically reproduced hysteresis loop is in close agreement to the experimental observation. Our work further shows that mode hops to longer wavelength non lasing modes are quicker than those to shorter wavelength lasing modes due to the lack of four wave mixing (FWM) mode coupling in the non-lasing mode. The same model can be used to study the dynamics during switching of lasing directions triggered by other means, such as optical injection. [ABSTRACT FROM AUTHOR]

Nonlinear gain in semiconductor ring lasers has been investigated theoretically based on density-matrix equations, including the effects of carrier density pulsations, carrier heating, spectral hole burning, and carrier diffusion. Expressions for non-linear susceptibilities are derived analytically and compared with previous theoretical results. It is found that carrier diffusion have strong effects on both the amplitude and beat frequency dependency of the nonlinear susceptibilities. Various nonlinear parameters are also calculated based on the expressions obtained, and are consistent with published experimental results by other groups. [ABSTRACT FROM AUTHOR]

A standing-wave model based on "cold" cavity mode expansion is proposed and presented for simulation of distributed feedback (DFB) semiconductor lasers. The model is validated against the well-established traveling-wave model in terms of the static and dynamic characteristics of typical DFB lasers. Effects such as the longitudinal variation of carrier and photon densities and nonlinear gain saturation, known as the spatial and spectral hole burning, respectively, are all included in this model. Simulation examples show that the proposed approach is computationally more efficient than the traveling-wave model. The impact of the expansion mode truncation on the accuracy and efficiency is also investigated and discussed. [ABSTRACT FROM AUTHOR]

Modal characteristics of antiresonant reflecting optical waveguide (ARROW) vertical-cavity surface-emitting lasers (VCSELs) are studied under high current injection. It is found that the influence of carrier spatial hole burning increases the radiation loss margin of ARROW at low injection current, while the thermal lensing effect significantly reduces radiation loss margin of ARROW at high injection current. Hence, the excitation of multiple-transverse modes in VCSELs is inevitable under high injection current even if the dimensions of the ARROW have been optimized to maximum radiation loss margin. Therefore, it is proposed to modify the refractive index profile of the ARROW to compensate against the influence of thermal lensing in VCSELs. It can be shown that the radiation loss margin of the modified ARROW can remain unchanged under the influence of thermal lensing if the dimensions and refractive index profile of the ARROW are properly designed. Hence, stable single-mode operation can be obtained in ARROW VCSELs at high injection current. [ABSTRACT FROM PUBLISHER]

We demonstrate an RF spectrum analyzer based on spectral-hole burning (SHB) that operates with unity probability of intercept and resolution under 100 kHz. An SHB crystal, which consists of rare-earth ions doped into a crystal host, records the power spectrum of an RF signal modulated onto an optical carrier as a series of spectral holes that persist for about 10 ms. While the crystal's homogeneous and inhomogeneous linewidths place the fundamental limits on resolution and bandwidth, respectively, the practical limits depend on the lasers used to interrogate the record stored in the crystal's absorption profile. Up to now, SHB spectrum analyzers have used chirped beams from externally modulated, stabilized lasers, which have linewidths of under 10 kHz but cannot chirp over much more than octave bandwidths, or directly modulated diode lasers, which can chirp over more than 20 GHz but have linewidths of about ! MHz. Switching to chirped fiber lasers, which have natural linewidths of under 2 kHz and chirping linewidths on the order of 10 kHz, produces a measurement with fine resolution without any laser stabilization. In addition, by chirping the fiber laser with a sufficiently fast piezo, the resulting chirp could extend over tens of gigahertz in under 10 ms, yielding both fine resolution and broad bandwidth without extraordinary stabilization schemes. [ABSTRACT FROM AUTHOR]

We describe and demonstrate a Fourier-optical beamformer that modulates RF energy from an antenna array onto a corresponding array of coherent optical beams and forms RF-frequency-scaled (or beam-squinted), far-field images through a single-lens optical Fourier transform. The squinted image is formed into a cryogenically cooled spectral hole burning (SHB) crystal, where it writes spatially-localized spectral images as holes in the crystal's spatial-spectral absorption profile. The spectral-hole images at each resolvable spectral bin (10 MHz at 4.2 K) integrate during the population lifetime ( 1 ms) for frequencies within the inhomogeneous crystal bandwidth ( 20 GHz). A chirped laser diffracts from the holes, producing a sequence of spectrally resolved RF images. The diffracted light passes through a swept-zoom lens synchronized to the chirped laser readout. This zoom lens compensates for beam squint during readout and forms the squint-free images onto a charge-coupled device (CCD), where they are coherently detected. We demonstrate experimental squinted images from a 5 element array across a 350 MHz bandwidth that are recorded into and read from a Er:Eu:YSiO SHB crystal before a digital zoom compensates for beam squint. This system can be scaled up to form images from 2-D arrays with 1000s of elements across 20 GHz bandwidths. [ABSTRACT FROM PUBLISHER]

We report generation of continuous-wave yellow laser radiation in a Nd3+-doped periodically poled lithium niobate bulk crystal. Simultaneous oscillation in pi polarization of the two infrared laser channels 4F3/2 rarr4I11/2 and 4F3/2 rarr4I13/2 of Nd3+ is achieved at 1084.4 and 1373.6 nm by end pumping with a Ti:Sapphire laser. Intracavity quasiphase-matched self-sum- frequency-mixing of both infrared laser waves in the poled crystal leads to the generation of yellow laser light at 606 nm. The yellow laser power obtained is 15.6 mW from an absorbed pump power of 314 in W. [ABSTRACT FROM PUBLISHER]

We investigate the capacity of opportunistic communication in the presence of dynamic and distributed spectral activity, i.e., when the time varying spectral holes sensed by the cognitive transmitter are correlated but not identical to those sensed by the cognitive receiver. We develop a two switch model that captures the localized spectral activity estimates at the transmitter and receiver. The information theoretic framework of communication with side information is employed to characterize the capacity of the cognitive link with both causal and non-causal side information at the transmitter and/or the receiver. These capacity results are used to determine the benefits of any feedforward and feedback information. We find that cognitive radio capacity is robust to the uncertainties arising out of distributed and dynamic spectral environments, even when the communication occurs in bursts of only 3-5 symbols. The capacity depends strongly on the correlation of the local spectral environment at the cognitive transmitter and receiver. [ABSTRACT FROM AUTHOR]

Polarization-related effects are the major source of performance fluctuations in long-haul systems. Understanding the system implications of polarization-dependent loss, polarization mode dispersion, linear and nonlinear channel crosstalk, polarization-dependent gain, and polarization hole burning is important for a successful system design and operation. In this paper, the polarization and nonlinearity-driven performance fluctuations in 10-Gb/s wavelength-division multiplexing submarine transmission systems, including repeatered and unrepeatered systems, are analyzed. The proposed phenomenological model of performance fluctuations shows good agreement with data accumulated over a long period on deployed repeatered systems. Furthermore, the case of 40-Gb/s transmission is briefly discussed [ABSTRACT FROM PUBLISHER]

The optical characteristics of antiresonant reflecting optical waveguide (ARROW) vertical-cavity semiconductor optical amplifiers (VCSOAs) are investigated theoretically. Influence of spatial hole burning (SHB) and thermal lensing on the stability of the amplified output signal is taken into consideration in the studies. A design rule, which can be used to deduce the optimized dimensions of ARROW, is developed to achieve spatially stable single-spot amplified output-signal in large-area VCSOAs. It can be shown that a high saturation power yet stable output signal can be achieved in large-area ARROW VCSOAs simultaneously. [ABSTRACT FROM PUBLISHER]

In photonic crystal (PC) microlasers with point defect cavities, effective carriers are reduced by the leakage to outside of the defect, surface recombination, spatial carrier hole burning, and Auger recombination. To estimate these effects, we calculated carrier and photon behavior by solving two-dimensional rate equations in space and time domains. The result clearly shows these effects and their dependence on cavity structure, pump area, and so on. Compared with that for the microdisk laser, higher threshold values are estimated for PC microlasers. However, a comparably low threshold density and a high efficiency are expected for the quasi-periodic PC microlaser, because the hole burning by the whispering gallery mode of this cavity suppresses the carrier leakage. [ABSTRACT FROM AUTHOR]

In order to understand and explain recently reported nonlinear behaviors in semiconductor ring lasers (SRLs) and to further design novel functional devices, a multimode model has been developed for linear and nonlinear interactions between modes in an SRL lasing unidirectionally. The model includes population pulsation, spectral hole burning, carrier healing, and four-wave mixing effects. Heterodyne detection has been used to make high-resolution measurements of the lasing spectra of an SRL in which the individual resonances associated with the coupled eigenvalues can be observed. By fitting these high-resolution spectra to the model, we have extracted a number of key parameters characterizing the coupling mechanisms in the device and the semiconductor gain medium. Using these parameters, the model generates device characteristics in very good agreement with experimental results, which validate its use for future device design and optimization. [ABSTRACT FROM AUTHOR]

We demonstrate implementation of the chirp transform algorithm with photon echoes in an Er3+ :YSO crystal at 1536 nm for application to spectral analysis of RF signals. The principle and features of the technique are presented using a simple picture in the time-frequency plane. Experimental results with low-bandwidth RF signals demonstrate 40-kHz spectral resolution and a time-bandwidth product of 500. Extension to broad-band RF signals is discussed. [ABSTRACT FROM AUTHOR]

We investigate nonlinear carrier dynamics in a multiquantum-well semiconductor optical amplifier (SOA) in the context of ultrafast all-optical logic. A rate-equation model is presented that accounts for two-photon absorption, free-carrier absorption, self- and cross phase modulation, carrier heating, spectral, spatial hole burning, and self- and cross polarization modulation. The nonlinear refractive index dynamics is investigated theoretically and experimentally. We find nonlinear phase changes larger than π radians, which recovers on a timescale in the order of 1 ps. We also investigate a nonlinear AND gate that consists of an SOA that is placed in an asymmetric Mach-Zehnder interferometer. We show that the gate can be operated using 800-fJ optical pulses with duration of 200 fs while having a contrast ratio larger than 11 dB. [ABSTRACT FROM PUBLISHER]

Previous theoretical studies of distributed feedback fiber lasers (DFB-FLs) have largely relied on numerical simulations. In this paper, analytical expressions are derived for the resonant frequency and mode shape of a single-frequency, DFB-FL structure, taking into account nonuniformities and phase errors. The analysis also accounts for spatial hole burning and "gain grating" effects under the assumption that the grating strength is large compared to the available gain. This applies, in particular, to low-gain erbium-doped DBF-FLs which are of substantial interest in sensor applications. An expression for the steady-state laser power is derived. It is also shown how the analysis can be extended to higher order modes, although this is not developed in detail. [ABSTRACT FROM AUTHOR]

Transverse-leaky-mode characteristics of antiresonant-reflecting-optical-waveguide (ARROW) vertical-cavity surface-emitting lasers (VCSELs) are studied. It is found that the suppression of high-order transverse leaky modes in ARROW VCSELs can be deteriorated by the influence of spatial hole burning and thermal lensing effects. On the other hand, a new design rule is proposed to deduce the optimum dimensions of ARROW so that the suppression of high-order transverse leaky modes can be enhanced. Furthermore, the turn-on transient response of ARROW VCSELs is investigated. It is found that the radiation loss has significant influence on the built-up time of the first-order transverse leaky mode. [ABSTRACT FROM PUBLISHER]

The impact of fiber chromatic dispersion and an isolated mode hop on the bit-error performance of an external-cavity diode laser newly designed for uncooled wavelength-division-multiplexing (WDM) applications was investigated. Bit-error-rate measurements confirmed that the power penalty resulting from optical waveform distortion after a transmission through 80 km of standard single-mode fiber (SMF) was suppressed to about 1 dB. Moreover, it was confirmed that the deterioration in the bit-error performance caused by an isolated mode hop can be disregarded. [ABSTRACT FROM PUBLISHER]

The modeling of multimode operation in vertical-cavity surface-emitting laser diodes is difficult because spatial interaction between modes makes the problem very complex. In this paper, a novel circuit model is presented for such lasers, which is based on spatially dependent rate equations, and thus spatial hole burning and carrier diffusion are taken into account. These effects are studied in direct-modulated microwave vertical-cavity surface-emitting lasers by showing linear and nonlinear simulation examples in both time and frequency domains. [ABSTRACT FROM PUBLISHER]

Theoretical two-dimensional (2-D) analysis and simulations address hole-burning effects and demonstrate that the cross-section averaged carrier density increases continuously with applied bias, rising above the lasing threshold, even as Nth(T) increases with temperature. There is no "density pinning" at the threshold value corresponding to the device temperature T, contrary to the usual one-dimensional (1-D) theory conclusion. It is conjectured that there is no bias voltage pinning at the junction and the voltage-current relation exhibits modified diode law behavior. [ABSTRACT FROM PUBLISHER]

An ultrafast two-dimensional (2-D) multimode vertical-cavity surface-emitting laser (VCSEL) simulation tool suite is introduced using eigenmode expansion of the rate equations, utilizing a novel generic representation for laterally open VCSEL cavity eigenmodes by optimized-waist paraxial modes. By avoiding the need to resolve short spatial and fast temporal scales, the code runs much faster than finite difference time domain and beam propogation method codes, retaining the 2-D description for the nonuniform carrier density and intensity profiles, multimode excitation, and axial carrier density depletion ("hole burning"). Code validation results against experimental measurements, such as steady-state NF mode structure, threshold gain versus aperture diameter, and dynamic mode switching, are presented. The code yields the correct behavior regarding aperture placement, with lower thresholds for aperture at node. Fast (<1 b/s) execution time allows detailed dynamic simulation of driven response over long input streams for the statistical extraction of bit-error rate and relative intensity noise figures of merit. [ABSTRACT FROM PUBLISHER]

Self-pulsations (SPs) in phase-controlled mode beating lasers (PhaseCOMB) are very attractive for all-optical clock recovery at ultra-high bit rates. In this paper, we apply the comprehensive simulation tool Longitudinal Dynamics in Semiconductor Lasers, developed by us, for studying the SP features of PhaseCOMB lasers, considering the effects of spontaneous emission noise, longitudinal spatial hole burning, and gain dispersion. In particular, the importance of mode control for adjusting the PhaseCOMB operating conditions is pointed out. The simulation results are confirmed by measurements on fabricated devices. [ABSTRACT FROM PUBLISHER]

A new above-threshold model of α-DFB lasers is presented. It is based on a generalized beam-propagation method and takes into account spatial hole burning and self-heating effects. Up to moderate output powers, a good agreement between simulated and measured radiative characteristics is obtained. The theoretical model was used to design an optimized laser structure with a 4-mm-long cavity, which yielded a maximum output power of 3 W with a times-diffraction-limit factor of M2≍3. [ABSTRACT FROM PUBLISHER]

The nonlinear phenomena accompanying the process of light generation in high-power tapered semiconductor lasers are studied using a combination of simulation and experiment. Optical pumping, electrical overpumping, filamentation, and spatial hole burning are shown to be the key nonlinear phenomena influencing the operation of tapered lasers at high output powers. In the particular tapered laser studied, the optical pumping effect is found to have the largest impact on the output beam quality. The simulation model used in this study employs the wide-angle finite-difference beam propagation method for the analysis of the optical propagation within the cavity. Quasi-three-dimensional (3-D) thermal and electrical models are used for the calculation of the 3-D distributions of the temperature, electrons, holes, and electrical potential. The simulation results reproduce key features and the experimental trends. [ABSTRACT FROM PUBLISHER]

This paper demonstrates simulation tools for edge-emitting multiple-quantum-well (MQW) lasers. Properties of the strained MQW active region are simulated by eight-band kp calculations. Then, a two-dimensional simulation along the transverse cross section of the device is performed based on a drift-diffusion model, which is self-consistently coupled to equations for the optical field. Furthermore, a method is described that allows for an efficient quasi-three-dimensional simulation of dynamic properties of multisection edge-emitting lasers. [ABSTRACT FROM PUBLISHER]

We present a model for quantum-well (QW) semiconductor optical amplifiers (SOAs) that considers bidirectional field propagation and the carrier densities in the barrier and QW regions. Carrier capture from the barriers into the QWs and carrier escape from the QWs to the barriers are included by means of effective capture and escape times. The model incorporates the wavelength dependence of the optical response of the active region and the effects of spectral hole burning via an analytical approximation to the susceptibility of the active material, which allows one to very effectively include the wavelength dependence of the output properties of the SOA. The model is used to analyze the experimental results obtained for a multiquantum-well SOA. The simulations results show a good agreement with the experimental data when a carrier-density dependent escape time from the QW to the barrier regions is considered. [ABSTRACT FROM PUBLISHER]

A new theoretical/numerical model of the spectral hole burning (SHB) effect in erbium-doped fiber amplifiers (EDFAs) is suggested. A new measurement technique for SHB measurement is developed. Experiments are conducted to identify the particular mechanism of SHB. A computer simulation program is developed using this approach. The shape and depth of the spectral hole are in accordance with the suggested theory. [ABSTRACT FROM PUBLISHER]

We present a detailed study of oxide-confined, vertical-cavity surface-emitting lasers (VCSELs) where the reflectivity of the top mirror has been patterned by means of a metal grid, which at the same time acts also as an electrode. Owing to their features, these kind of devices are commonly referred to as phase-coupled VCSEL arrays. The analysis is based on a joint experimental and theoretical effort: the former is devoted to a complete characterization of the emission properties, while the latter is based on a comprehensive fully vectorial model for the structure eigenmodes with the details of their complex structure. The detected characteristics make them quite attractive for various applications and the comparison of their modal properties with the model is proved to be essential for a deep understanding of these lasers. In particular, we observed and explain, for the first time, a characteristic behavior of the lasing array, which displays spatially inhomogeneous polarization characteristics with symmetry properties with respect to the array diagonals. The good matching between theory and experiment opens new perspectives for optimized device, where the typical four lobe far-field emission is converted in a narrow central lobe: two different proposals will be discussed. [ABSTRACT FROM AUTHOR]

Examines a laser model for describing the effects of nonequilibrium distribution. Basis of the approach on Maxwell-semiconductor-Boch equations; Influence of optical hole burning on the semiconductor laser modulation response; Applications of semiconductor lasers.

We have, for the first time, experimentally verified the black box model based upon the knowledge in the form of characteristic tilt functions and demonstrated accurate characterization of erbium-doped fiber amplifiers (EDFAs) in wavelength division multiplexing (WDM) system operation [ABSTRACT FROM PUBLISHER]

The spectral hole burning effects and gain dynamics of all-optical gain clamped multichannel erbium-doped fiber amplifiers (EDFAs) are modeled. The two-level laser model is used to write the propagation and rate equations of the inhomogeneous laser medium. The governing equations are an uncountable system of partial differential equations (PDEs). After some mathematical manipulations, averaging over the fiber length and introducing an approximation method, the system of PDEs is converted to a finite system of ordinary differential equations (ODEs). The gain dynamics and hole burning of an all-optical stabilized multiwavelength EDFA and the transient response of an optical fiber inverter are analyzed by the solution of the system of ODEs. Theoretical results are in good agreement with the published experimental result [ABSTRACT FROM PUBLISHER]

Analyzes the rate equation model for nonequilibrium operating conditions in a self-organized quantum dot laser. Effect of temperature on spectral hole burning and spectral narrowing of gain; Negative temperature coefficient of lasing threshold.

A three-dimensional electrical-thermal-optical numerical simulator is developed and applied to model group-III-nitride-based intracavity-contacted vertical-cavity surface-emitting lasers with InGaN multiquantum-well active region. The optical model based on the effective frequency method is combined with an electrical-thermal simulator using the control volume method. Isothermal (pulsed regime imitation) and continuous-wave modes of operation are calculated over a range of voltages, covering subthreshold spontaneous emission and lasing emission. Effects of current crowding at the active region periphery are examined, and in particular, an impact on mode profiles of spatial hole burning superimposed on nonuniform gain distribution is studied. In order to reduce the current crowding and provide more uniform gain distribution within the active region, a semitransparent p-side contact design is proposed [ABSTRACT FROM PUBLISHER]

Characteristics of a single-frequency erbium-doped fiber laser (EDFL) controlled by an external light source is investigated. The frequency control is achieved by cooperatively induced spatial hole-burning (SHB) formed by the interference between the lasing light and the external light. We evaluate the frequency stability of several cavity designs of the fiber laser and the frequency control characteristics in detail. Tunable operation as wide as 30 nm wavelength range with a good frequency stability is also demonstrated [ABSTRACT FROM PUBLISHER]

A theoretical model suitable for both static and dynamic analysis of widely tunable multisection grating assisted codirectional coupler with rear sampled grating reflector (GCSR) lasers is described in this paper. For the first time wide static tunability as well as transient behavior of such lasers are simulated. The theoretical model is based on the transfer matrix method (TMM) in combination with multimode rate equation analysis and takes into account a number of physical processes in the laser cavity such as longitudinal mode spatial hole burning, nonlinear gain compression, and refractive index changes with carrier injection. Static and dynamic characteristics simulated using the proposed approach agree with the experimental results presented in the paper [ABSTRACT FROM PUBLISHER]

We present a numerical study of the noise of conventional and gain-clamped semiconductor optical amplifiers (SOAs), using a detailed device model. The model makes use of a density-matrix gain calculation, and takes into account the forward and backward amplified spontaneous emission (ASE) spectra and the spatial carrier hole-burning. The device is longitudinally divided into M sections and a rate equation for averaged photon and carrier densities is used for each section. We demonstrate that the accuracy on the calculated noise figure strictly depends on the number of sections M. We obtain a good tradeoff between the results accuracy and the computational complexity with M=8. The model is then applied to study the noise in a distributed Bragg reflector (DBR)-type gain-clamped SOA for varying signal power, pump current, and lasing wavelength. We show that changes in the spatial carrier profile caused by the input signal significantly affect the noise figure, even when the gain is constant. A slight dependence of the noise figure on lasing wavelength is also foreseen, while the dependence on the pump current is negligible. A new method for gain-clamped SOA noise figure reduction is proposed, based on unbalanced Bragg reflectors. An improvement of noise figure (NF) as large as 2 dB is devised [ABSTRACT FROM PUBLISHER]

The ultrafast gain and index dynamics in a set of InAs-InGaAs-GaAs quantum-dot (QD) amplifiers are measured at room temperature with femtosecond resolution. The role of spectral hole-burning (SHB) and carrier heating (CH) in the recovery of gain compression is investigated in detail. An ultrafast recovery of the spectral hole within ~100 fs is measured, comparable to bulk and quantum-well amplifiers, which is contradicting a carrier relaxation bottleneck in electrically pumped QD devices. The CH dynamics in the QD is quantitatively compared with results on an InGaAsP bulk amplifier. Reduced CH for both gain and refractive index dynamics of the QD devices is found, which is a promising prerequisite for high-speed applications. This reduction is attributed to reduced free-carrier absorption-induced heating caused by the small carrier density necessary to provide amplification in these low-dimensional systems [ABSTRACT FROM PUBLISHER]

Studies theoretically and experimentally the distributed-feedback laser with a curved waveguide in the active region integrated with an electroabsorption modulator. Effects of the spatial hole burning; Features and wavelength-tuning behavior of the spectrum; Suppressive effect of the curved waveguide on the longitudinal photon density profile.

Gain-difference spectra are used to show that 980-nm band pump wavelength changes can significantly effect spectral-hole burning (SHB) in erbium-doped fiber amplifiers (EDFAs). Gain measurements made using a number of different signal and pump wavelengths help to characterize the underlying inhomogeneous spectral properties of EDFAs and a framework for modeling these effects is presented. Despite the difficulty of obtaining the needed subpopulation specific cross section spectra, this model can be used to explain seemingly anomalous changes in the gain spectra of EDFA as a result of changes in signal or pump wavelength [ABSTRACT FROM PUBLISHER]

A simple dynamic model of laser-gain clamped erbium-doped fiber amplifiers (EDFAs) using ordinary differential equations is presented. The model not only provides a fast means of calculating EDFA gain dynamics, but also shows explicitly how the laser relaxation oscillation frequency and damping constant are affected by design parameters through analytical expressions. It is shown that the dynamic power excursion caused by relaxation oscillations can be reduced by increasing the oscillation frequency. The simplified model has two limitations: first, the amplified spontaneous emission (ASE) spectrum is not fully resolved and the noise figure can not be studied; second, the effect of spectral hole burning, which also causes gain excursion, can not be modeled. The first limitation can be removed by ASE-resolved modeling, where the concept of average inversion is also utilized to save computing time [ABSTRACT FROM PUBLISHER]

Carrier diffusion and spatial hole burning can have a severe impact on vertical cavity surface emitting laser (VCSEL) performance. In particular, these phenomena can produce secondary pulses, bumps, and optical tails in the VCSEL turn-off transient which limit both the system bit rate and the bit error rate (BER). To study these effects, laser rate equation models that include both spatial and temporal dependence are often employed; however, simulations which require discretization of both space and time, while accurate, typically consume vast amounts of computational power. In this paper, we demonstrate that models based on well-accepted spatially independent rate equations can be used to simulate these effects. These models exhibit the advantages of the full spatio-temporal approach but execute much more quickly. We also integrate these models into electronic computer-aided design (CAD) tools which will enable circuit and system designers to simultaneously simulate electrical and optical performance [ABSTRACT FROM PUBLISHER]