Characteristics Of Semiconductor Lasers Research Articles

Noise Characteristics of semiconductor Laser with Phase- Conjugate Feedback

Noise spectra of semiconductor laser subject to a phase-conjugate feedback were investigated theoretically. Time-delayed rate equations with feedback were solved and characteristic equations for relative intensity noise and frequency noise spectra were derived. Numerical results indicate that the relaxation resonance peak was moved to a new frequency region determined by the amount of feedback, This is a technological importance for the improvement of modulation bandwidth, Noise level was affected by the feedback parameters, mainly; the response time and the feedback rate.

Analyses of numerical and experimental results for optical signal generation using heterodyne scheme

In this paper, we have proposed a heterodyne technique to generate an optical millimeter-wave signal for ultra-wideband communication. First, we have investigated the characteristics of semiconductor lasers locked to another semiconductor under the RF modulation having many sidebands. The RF-modulated master laser is represented by a series of Bessel functions. This model is then inserted into Lang's rate equations. By numerically solving the resulting rate equations, we have determined the locked laser output characteristics as well as the RF spectrum of the beat signals. The result is that the unselected sidebands can produce undesired beat signals whose power may be comparable to that of the desired beat signal. Furthermore, their strength is affected by the injected ML light power. With reduced ML light, undesired beat signals and the injection-locking bandwidth can be suppressed. Second, we have experimented a new technique for generating millimeter-wave signals from a semiconductor laser. A 32 GHz signal is generated using a multisection semiconductor laser operated under a continuous wave by injecting optical pulses at a repetition rate equal to the fourth subharmonic (8 GHz). The generated millimeter-wave signal exhibits a large subharmonic suppression ratio, a large frequency detuning range, low levels of phase-noise and a large locking range. These simulation results are confirmed by experimental results. The high-frequency signal can be used in the field of ultra-wideband communication employing local multipoint distribution system (LMDS), wireless local loop (WLL) and mobile broadband system (MBS).

Effect of internal optical loss on threshold characteristics of semiconductor lasers with a quantum-confined active region

We develop a general approach to including the internal optical loss in the description of semiconductor lasers with a quantum-confined active region. We assume that the internal absorption loss coefficient is linear in the free-carrier density in the optical confinement layer and is characterized by two parameters, the constant component and the net cross section for all absorption loss processes. We show that, in any structure where the free-carrier density does not pin in the presence of light generation, the free-carrier-density dependence of internal loss gives rise to the existence of a second lasing threshold above the conventional threshold. Above the second threshold, the light-current characteristic is two-valued up to a maximum current at which the lasing is quenched. We show that the presence of internal loss narrows considerably the region of tolerable structure parameters in which the lasing is attainable; for example, the minimum cavity length is significantly increased. Our approach is quite general but the numerical examples presented are specific for quantum dot (QD) lasers. Our calculations suggest that the internal loss is likely to be a major limiting factor to lasing in short-cavity QD structures.

Carrier lifetime variation and its effects on the chaotic behaviors in semiconductor laser

Modeling theoretically the chaotic behaviors of semiconductor lasers, the carrier lifetime is usually treated as a constant (in this paper, it is called as the constant carrier lifetime assumption (CCLA)). In this paper, after considering the actually recombination mechanism of the carriers in the semiconductor, the variation of the carrier lifetime with the time has been obtained, and the chaotic characteristics of semiconductor laser with optical feedback have been investigated numerically. The obtained results have been compared with those obtained with CCLA, and the obvious differences can be observed.

Quantitative prediction of semiconductor laser characteristics based on low intensity photoluminescence measurements

A general scheme for the determination of vital operating characteristics of semiconductor lasers from low intensity photoluminescence spectra is outlined and demonstrated. We describe a comprehensive model that allows us to determine properties of the running device like gain spectra, peak gain wavelengths, bandwidths or differential gains, as well as inhomogeneous broadening and actual carrier densities of PL-signals. This information can then be used to compute characteristics like the temperature dependence of the gain, threshold densities, optical field distributions or near-field and far-field outputs.

Steady State Characteristics of Semiconductor Lasers affected by Gain Compression

Steady state traveling wave rate equations, including the gain compression factor, have been solved, and a set of implicit analytical solutions to the equations has been deduced. With the solutions, static characteristics of diodes related to the gain compression factor have been studied. It is realized that the average carrier density of an above threshold biased diode increases with the pump current. This provides the possibility of extracting the gain compression factor of semiconductor lasers through measuring carrier density dependent static characteristics, for example the spontaneous emission etc.

Degradation of modulation and noise characteristics of semiconductor lasers after propagation in optical fiber due to a phase shift induced by stimulated Brillouin scattering

Here we demonstrate theoretically that stimulated Brillouin scattering (SBS) can induce a phase shift of the optical carrier relative to its sidebands due to the waveguiding effect of the optical fiber on the acoustic wave. This causes conversion of frequency modulation to intensity modulation, which results in an increase in the relative intensity noise and degradation of the modulation response of directly modulated lasers after propagation in an optical fiber, in agreement with our experimental observations. Suppression of SBS can be achieved at low frequencies and high modulation powers due to the laser adiabatic chirp.

Relative intensity noise for laser diodes with arbitrary amounts of optical feedback

A unified study of the noise characteristics of semiconductor lasers with optical feedback and short external cavity length is presented. A new set of nonlinear rate equations that can describe a laser diode with any amount of optical feedback is proposed. The relative intensity noise (RIN) is calculated by using a numerical solution of these equations. This paper concentrates mainly on the moderate and strong feedback regimes. The spectral phenomena observed during the transition from the weak feedback to the coherence collapse regime and then to the strong feedback regime are studied and explained. The effect of the variation of some of the laser diode parameters on the RIN characteristics is also investigated.

Learning Semiconductor Laser Characteristics Using Virtual Analogue Simulation

This article describes a simple method for simulating typical characteristics of semiconductor lasers based on the rate equations of the device. The method being implemented in PSpice may be used to demonstrate the light-current characteristics, charge number clamping, modulation response, transient and nonlinear behaviour of semiconductor laser diodes.

Effects of carrier transport on the L-I characteristics of QW lasers in the presence of spatial hole burning

In this paper, we study the effects of carrier transport and carrier capture on the linearity of the light-current characteristics of a semiconductor laser using an analytically solvable model. We include various physical processes within the model and study how they affect laser linearity. The technique used shows how to integrate the photon and electron transport within a single model, and the conclusions reveal some interesting aspects of semiconductor laser characteristics.

Influence of injection-current noise on the spectral characteristics of semiconductor lasers

The spectral characteristics of a semiconductor laser are altered by injecting additional noise current into its current-drive port. A continuously varying spectral linewidth from about 5 MHz to above 100 MHz is achieved experimentally in this semiconductor laser. The conditions under which the line shape changes from a standard Lorentzian shape to a Gaussian shape as functions of laser power and noise current are investigated and compared with an existing theoretical treatment.

半導体レーザの微小な非直線特性の測定

半導体レーザの微小な非直線特性の測定

A contribution based on circuit modelling to study the effect of nonlinear gain on high-frequency characteristics of semiconductor lasers

The high-frequency characteristics of semiconductor lasers are described using an equivalent circuit model. The paper investigates the small-signal intensity modulation (IM) and frequency modulation (FM) when the parabolic gain approximation is used and when lateral diffusion of carriers in the active region of the laser is taken into account via a one-dimensional diffusion equation. We have performed the small-signal analysis to give a more transparent description of the influence of parabolic gain approximation on the modulation response. The inclusion of parabolic gain approximation and the gain compression characteristics of the active region in the expression derived for IM, FM and the chirp-to-modulated power ratio allows the present model to reflect the influence of the laser structure on the modulation performances.

Intensity noise and linewidth characteristics of laser diodes with phase conjugate optical feedback

The intensity noise and linewidth characteristics of semiconductor lasers with phase conjugate optical feedback are investigated numerically. The results are compared to those from conventional mirror optical feedback. The dynamics of semiconductor lasers with phase conjugate optical feedback are also considered. The relevance to phase conjugate optical feedback of the feedback regimes used to describe conventional mirror optical feedback is discussed.

Injection locking characteristics of semiconductor lasers in double phase conjugate mirror geometry

Phase locking of two semiconductor lasers is demonstrated by injection of the feedback from a double phase conjugate mirror. The stability or quality of the locking is characterised from fringe visibility measurements. Phase conjugate injection into the central mode exhibits an asymmetric stable locking region which extends to greater detunings and asymmetry with increased feedback. High quality locking is also demonstrated by phase conjugate injection into sidemodes up to nine longitudinal mode spacings from the target mode.

Effects of optical feedback on the light-current characteristics of semiconductor lasers

Theoretical and experimental investigations of the continuous wave (CW) output-power current characteristics of semiconductor lasers with optical feedback are reported. An analytical expression is presented which accounts for the external reflection in the form of an effective facet reflectivity. The coherence properties of the compound cavity laser field are incorporated by the correlation function of the optical field. An experimental setup was established to adjust and to control for different feedback levels. The normalized threshold current variation, due to feedback shows a dependence on the laser structure. This results from different confinement factors of the various waveguide structures. Up to reflection levels well within the coherence collapse regime the change of the slope of the light versus current curve is higher than calculated from incoherent feedback.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Effect of phase-conjugate feedback on the noise characteristics of semiconductor lasers.

This paper considers the effect of phase-conjugate feedback (PCF) on the noise characteristics of semiconductor lasers. By using the single-mode, rate-equation formalism, it is shown that semiconductor lasers can achieve a steady state as long as the amount of PCF is below a critical value. For an ideal phase-conjugate mirror, the average value of the steady-state phase of the semiconductor laser is found to be locked to a fixed value, determined by the linewidth-enhancement factor of the laser. The noise characteristics in the presence of PCF are studied by adding the Langevin-noise terms representing the effect of spontaneous emission to the rate equations and solving them approximately. Both the intensity noise and the frequency noise are reduced at low frequencies (below 100 MHz). In particular, the frequency noise nearly vanishes at zero frequency because of the phase-locked nature of the steady-state solution. The spectral line shape does not remain Lorentzian in the presence of PCF. The satellite peaks occurring at the relaxation-oscillation frequency are considerably enhanced because of a reduction in the damping rate of such oscillations.

Semiconductor lasers and fiber lasers for fiber-optic telecommunications

Abstract Be performance characteristics of semiconductor lasers for fiber telecommunication systems will be reviewed. Modulation speed, intensity noise, singlefrequency line width, and tunability are addressed. In addition, recent results concerning the same characteristics in single-frequency, tunable, fiber lasers are reviewed and compared with the semiconductor laser.

Threshold and Modulation Characteristics of Photon-Recycled Semiconductor Lasers

Threshold current characteristics of semiconductor lasers with photon recycling are theoretically investigated. By introducing rate equations modeling the reabsorption of spontaneous emission, the effect of photon recycling has been elucidated. The possibility of threshold reduction by a factor of more than three is suggested for a realizable closed cavity. In addition, modulation characteristics are also discussed.

Some experiments on semiconductor laser characteristics

The use of an off-axis holograpic optical element (HOE) as a powerful spectrograph to observe the buildup of laser oscillation as excitation is increased through the threshold value is described. The spectrum in the focal plane may be sensed by a charge-coupled device with output displayed on an oscilloscope screen. The lessons that can be learned from this experiment are discussed.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>