Effects In Semiconductor Lasers Research Articles

Delay induced high order locking effects in semiconductor lasers.

Multiple time scales appear in many nonlinear dynamical systems. Semiconductor lasers, in particular, provide a fertile testing ground for multiple time scale dynamics. For solitary semiconductor lasers, the two fundamental time scales are the cavity repetition rate and the relaxation oscillation frequency which is a characteristic of the field-matter interaction in the cavity. Typically, these two time scales are of very different orders, and mutual resonances do not occur. Optical feedback endows the system with a third time scale: the external cavity repetition rate. This is typically much longer than the device cavity repetition rate and suggests the possibility of resonances with the relaxation oscillations. We show that for lasers with highly damped relaxation oscillations, such resonances can be obtained and lead to spontaneous mode-locking. Two different laser types--a quantum dot based device and a quantum well based device-are analysed experimentally yielding qualitatively identical dynamics. A rate equation model is also employed showing an excellent agreement with the experimental results.

Band-gap shrinkage calculations and analytic model for strained bulk InGaAsP

Band-gap shrinkage is an important effect in semiconductor lasers and optical amplifiers. In the former it leads to an increase in the lasing wavelength and in the latter an increase in the gain peak wavelength as the bias current is increased. The most common model used for carrier-density dependent band-gap shrinkage is a cube root dependency on carrier density, which is strictly only true for high carrier densities and low temperatures. This simple model, involves a material constant which is treated as a fitting parameter. Strained InGaAsP material is commonly used to fabricate polarization insensitive semiconductor optical amplifiers (SOAs). Most mathematical models for SOAs use the cube root bandgap shrinkage model. However, because SOAs are often operated over a wide range of drive currents and input optical powers leading to large variations in carrier density along the amplifier length, for improved model accuracy it is preferable to use band-gap shrinkage calculated from knowledge of the material bandstructure. In this letter the carrier density dependent band-gap shrinkage for strained InGaAsP is calculated by using detailed non-parabolic conduction and valence band models. The shrinkage dependency on temperature and both tensile and compressive strain is investigated and compared to the cube root model, for which it shows significant deviation. A simple power model, showing an almost square-root dependency, is derived for carrier densities in the range usually encountered in InGaAsP laser diodes and SOAs.

Internal and External Optical Feedback Effect in Fiber Linear Lasers

In this paper, models of internal and external optical feedback effect in fiber linear lasers have been presented. The effects of optical feedback could be equivalent to the variation of laser cavity loss, and the output expressions of two models are deduced. According to the simulation results, the optical feedback system in fiber linear lasers has the same phase sensitivity as the traditional self-mixing effect in semiconductor lasers. The experimental results show a good agreement with the simulated results. Comparing the output of internal structure with that of external structure, we can conclude that the internal optical feedback system can get higher output gain and stripe depth, which reveals that the internal feedback structure has better sensing characteristics

The study of internal cavity optical feedback effect in fiber linear lasers

In this paper, an internal cavity optical feedback system is presented based on the structure of fiber linear lasers. As the effects of optical feedback could be equivalent to the variation of laser cavity loss, we deduced the output variation equation of the optical feedback system. The output characteristics obtained by simulation and experiment observation are similar to the characteristics of self-mixing interference effect in semiconductor lasers. The similarity indicates the former system presented in this paper can be used in active sensing applications, such as displacement, reflectivity, and distance measurement.

Peak Count Correction Methods for a Distance Sensor Using Self-coupling Effect of Semiconductor Laser

In this paper peak count correction methods for a self-coupling distance sensor with a Vertical-Cavity Surface-Emitting Laser (VCSEL) are reported on. The distance to the target in these distance sensors is usually calculated by determining the frequency of power fluctuations that are produced by the self-coupling effect. In this study it is proposed that the peak count correction method using statistical feature with little computational effort than Fast Fourier Transform (FFT) and higher accuracy than traditional peak count methods. The counting error is reduced to less than 1/100 with the peak count correction methods under adverse condition.

Nonlinear-optical effects in semiconductor lasers based on InGaAs/GaAs/AlGaAs quantum-confinement heterostructures

Generation of a difference-frequency wave by two electromagnetic waves propagating in a heterolaser is analyzed theoretically. Calculations are carried out for InGaAs/GaAs/AlGaAs heterostructures of design optimized to attain maximum lasing power. It is shown that phase matching between the primary waves and the difference-frequency wave may persist over a distance of ∼1 mm, comparable to the cavity length (2–3 mm), and the conversion coefficient can be as large as several percent.

Dynamics of Multisection Semiconductor Lasers

We consider a mathematical model (the so-called traveling-wave system) which describes longitudinal dynamical effects in semiconductor lasers. This model consists of a linear hyperbolic system of PDEs, which is nonlinearly coupled with a slow subsystem of ODEs. We prove that a corresponding initial-boundary value problem is well posed and that it generates a smooth infinite-dimensional dynamical system. Exploiting the particular slow-fast structure, we derive conditions under which there exists a low-dimensional attracting invariant manifold. The flow on this invariant manifold is described by a system of ODEs. Mode approximations of that system are studied by means of bifurcation theory and numerical tools.

Semiconductor lasers with an inversely biased active region for generation of millimeter wave modulated signals

A semiconductor laser structure is proposed to introduce field effects in its active region. It has five layers of p-n-i-p-n with four electrical contacts to the doped layers, where the current injection into an inversely biased active region is based on the operation of two complementary bipolar transistors with their base-collector junction common. The inverse bias is useful to incorporate carrier transfer phenomena like Gunn effect in semiconductor lasers. Our analysis on the proposed lasers shows that its lasing operation is possible while applying a high electric field more than 106 V/m in the carrier transfer domain.

Mathematical Modelling of Electrical-Optical Effects in Semiconductor Laser Operation

A mathematical model describing the coupling of electrical and optical effects in semiconductor lasers is introduced. Through a multiple-scale asymptotic expansion, the governing equations in the active region are reduced to one parabolic and four first-order hyperbolic partial differential equations. By making further assumptions, partially and fully lumped models for the active region are deduced, which complement (and provide a more systematic derivation of) previous well-established lumped models.

半導体レーザの自己結合効果を用いた自己補正型距離計

半導体レーザの自己結合効果を用いた自己補正型距離計

Mathematical modeling of thermal runaway in semiconductor laser operation

A mathematical model describing the coupling of electrical, optical and thermal effects in semiconductor lasers is introduced. Through a systematic asymptotic expansion, the governing system of differential equations is reduced to a single second-order boundary value problem. This highly nonlinear equation describes the time-independent maximum temperature in the boundary layer adjacent to the mirror facet. The solution of the problem is a multi-valued function of current. The graph of the maximum steady-state temperature as a function of current gives a fold-shaped response curve, which indicates that no bounded steady state exists beyond a critical value of current. For certain device parameters and initial conditions, thermal runaway occurs. A mechanism for the sudden mode of semiconductor laser failure is described in terms of thermal runaway.

Mathematical modelling of thermal hot-spots in semiconductor laser operation

A new mathematical model describing the coupling of electrical, optical and thermal effects in semiconductor lasers is introduced. The underlying (perfect) isothermal system has a transcritical bifurcation as the current varies. The steady-state light intensity is found to exhibit exponential growth as the wave traverses the laser and the steady-state electron concentration satisfies an integral equation, the solution of which specifies the threshold current. The (imperfect) isothermal and thermal problems also have this behaviour at leading order. In the thermal problem, an asymptotic analysis results in the decoupling of the various time-scales and length-scales leading to considerable simplification. Composite asymptotic expansions are constructed on each time-scale and compared with numerical results. These analytical solutions provide valuable insight and predict the role played by the various physical processes. In particular, the temperature rise of the active region is found to exhibit localized hot-spots at both mirrors, in contrast to the temperature rise of the surround where no such hot-spots are observed.

Role of a high gain of the medium in superradiance generation and in observation of coherent effects in semiconductor lasers

A theoretical model of superradiant pulse generation in semiconductor laser structures is developed. It is shown that a high optical gain of the medium can overcome phase relaxation and results in a built-up superradiant state (macroscopic dipole) in an assembly of electron—hole pairs on a time scale much longer than the characteristic polarisation relaxation time T2. A criterion of the superradiance generation is the condition αcmT2>1, where α is the gain coefficient and cm is the speed of light in the medium. The theoretical model describes both qualitatively and quantitatively the author's own experimental results.

The single-mode rate equations for semiconductor lasers with thermal effects

A mathematical model describing the coupling of electrical, optical and thermal effects in semiconductor lasers is introduced. Numerical and asymptotic solutions are derived, including expressions for key physical quantities such as the initial time delay, the frequency of spike oscillation and the temperature rise, together with its influence on the photon density, the electron concentration and the threshold current. The consequences of thermal effects in reducing efficiency are thus quantified.

Effect of semiconductor laser clipping impulsive noise in hybrid fiber-CDMA cellular radio networks

Effect of semiconductor laser clipping impulsive noise in hybrid fiber-CDMA cellular radio networks

The multi-mode rate equations for semiconductor lasers with thermal effects

A simple mathematical model describing coupled electrical, optical and thermal effects in semiconductor lasers is introduced. The bifurcation structure of the underlying (perfect) isothermal equations is examined to acquire insight into the nature of the steady states. An infinite set of steady states is obtained at one of these bifurcation points. In the (imperfect) isothermal and thermal problems, an asymptotic analysis provides expressions for the parameter regions which characterise the stable steady states of single-mode operation. The reason that semiconductor lasers usually operate with a single dominant mode is that this corresponds to the only stable steady state. Parameter regions in which two modes share dominance are also identified.

半導体レーザの光音響効果を利用した欠陥検出と光音響信号の伝搬特性

半導体レーザの光音響効果を利用した欠陥検出と光音響信号の伝搬特性

Mathematical modelling of thermal effects in semiconductor laser operation

A time-dependent mathematical model describing coupled electrical, optical and thermal effects in semiconductor lasers is introduced. A numerical scheme devised to solve the model is presented. The results of a simulation are exhibited for a particular laser design.

Performance of a 16-QAM channel in a hybrid AM-VSB/QAM fiber-optic transmission system based on a subcarrier-multiplexing (SCM) technique

The performance of a hybrid multichannel optical-fiber system for the transmission of analog (AM) and digital (QAM) channels by a subcarrier-multiplexing (SCM) technique is presented. The experimental results are compared with a theoretical model recently proposed that takes into account the clipping effect in semiconductor lasers, which gives rise to an impulsive noise affecting system performance. © 1997 John Wiley & Sons, Inc. Microwave Opt Technol Lett 15: 39–43, 1997.

Effects of carrier heating on laser dynamics-a Monte Carlo study

The static and dynamic properties of semiconductor quantum-well (QW) lasers have traditionally been analyzed by using rate equations that couple cold carriers to photons in the lasing cavity. This assumption of cold carriers, however, has often been disputed because it does not account for heating due to carrier relaxation, hot phonon effects, and spectral hole burning. All these processes affect laser performance significantly by modifying the gain because gain depends on carrier temperature as well as spectral broadening. In this paper, we study the carrier dynamics of QW lasers using a Monte Carlo method and conclude that hot carrier effects in semiconductor lasers are important and need to be considered for the analysis and design of semiconductor lasers.