Dynamics of optically switched bistable diode laser amplifiers

Measurements of the switch-off time of an optically switched Fabry-Perot InGaAsP/InP laser amplifier indicate that the device can turn off in less than the spontaneous carrier lifetime. The switching dynamics of the amplifier are numerically modeled using the van der Pol equation with optical injection and the rate equation for the carrier density. The simulations show that the device switches off faster as its injection current is increased toward the threshold level. A qualitative analytical analysis is presented which shows that this fast switch off is due to the very large cavity finesse of the amplifier when biased near its lasing threshold.     

Measurement of Auger recombination in silicon by laser excitation

A new experimental arrangement for the study of Auger recombination in silicon is described and analyzed. A relatively weakly absorbed YAG:Nd laser beam was used for excitation. The decay of the carrier concentration after the injection pulse was studied by measuring the recombination radiation in a direction perpendicular to the laser beam. At some distance from the injection surface the influence of surface recombination and diffusion is then negligible. It has previously been shown that in this geometry the carrier concentration distribution after the laser excitation is accurately described by an analytical expression which accounts for attentuation of the laser beam by both interband and free carrier absorption. Thus the local carrier concentration in the sample can be computed to a high degree of accuracy, which is essential in the determination of the Auger recombination coefficient from decay measurements. Furthermore, this experimental geometry eliminates the problems with laser stray light. Assumptions regarding the influence of surface recombination and diffusion are not necessary in the interpretation of the experiments. The method is usable for silicon in the temperature interval 150–400 K. Preliminary measurements of the Auger coefficient at room temperature are reported.     

WDM-PON system based on the laser light injected reflective semiconductor optical amplifier

This paper proposes a WDM-PON system which uses the laser light injected reflective semiconductor optical amplifier (R-SOA) as the optical transmitter. In the system, optical carrier of laser lights is supplied from the central office (CO) to the R-SOA both in CO and in the subscriber's side. The optical carrier consists of a pair of the perpendicularly polarized laser lights to avoid the polarization dependence of R-SOA. The optical carrier can be shared by several WDM-PON systems to save the cost. We measured the transmission performance of R-SOA which modulates the polarization mixed injection laser at 1.25 Gbps. It is shown that the combined effect of Rayleigh backscattering and the intensity noise induced by the feedback of optical signals into the R-SOA increases the required level of optical injection power into the R-SOA.     

Noise of strongly-multimode laser diodes used in interferometricsystems

A unified model of the phase and partition noise of a multimode semiconductor injection laser is presented in the context of the assumption that all modes radiate the same average optical power. Noise is shown to be associated with two processes: phase fluctuations common to all modes, arising from carrier fluctuations, and partition and phase fluctuations describable in terms of a random walk of the optical field state on the surface of an abstract sphere. Both processes are driven by spontaneous emission. The model is solved analytically; results for the intensity noise level to be expected at the output of an unbalanced interferometer illuminated by a multimode diode laser are derived. These predictions are confirmed experimentally using a laser with nine modes at full width half maximum     

Power scaling in quantum-well laser amplifiers

The effects of increasing excitation on the performance of quantum-well semiconductor laser amplifiers were investigated. Amplified spontaneous emission (ASE) and gain roll over at high injected carrier densities are two limitations to the power scaling of these devices. A Rigrod analysis was used to study the effects of these limitations on the gain, ratio of signal to ASE power, and efficiency for different values of injection current, facet reflectivity, and input laser intensity. Comparisons are made with an equivalent amplifier operating with a bulk semiconductor gain medium. This analysis suggests that quantum-well semiconductor amplifier performance improves with a double-pass configuration     

Fiber-optic sensor using an injection-locked local laser

An interferometric fiber-optic sensor using a local laser is proposed. An Er-doped-fiber ring-laser is injection locked to a signal carrier using a fiber coupler, and the extracted carrier is directly homodyned with the signal light at the output of the coupler. With a feedback loop suppressing the local laser instability, demodulation linearity over two decades and minimum detection in the 10^-3 rad range are attained. The Er-doped fiber ring laser constructed for this work has a linewidth of less than 1.4 kHz. Acceptable signal frequency ranges and the linearity and sensitivity of the proposed sensor are examined. Also discussed is the applicability of this configuration to simple, long-spanned sensors     

Spatio-temporal dynamics of gain-guided semiconductor laser arrays

A continuous model based on the coupled field-matter Maxwell-Bloch equations for a two-level homogeneously broadened single mode laser is developed. The model includes a Langevin formulation to model thermal and spontaneous emission noises and accounts for carrier diffusion, optical field diffraction and current spreading. Our model is flexible enough to simulate any gain-guided longitudinally uniform laser geometry and is applied to both a single-stripe and a four-stripe gain-guided semiconductor lasers where the influence of the injection current, the interstripe distance and carrier diffusion is discussed within the context of the laser dynamics. We show that an array operating with quasi-independent stripes may be achieved at low pumps and larger interstripe distances. However, as injection current is increased or the interstripe distance is decreased, the device passes through a variety of dynamical instabilities which can be analyzed in the context of lateral cavity modes. Moreover, we also show that the array dynamics is strongly influenced by carrier diffusion which may also lead to different thresholds for each element of the array     

Planar stripe with waist and/or notch (SWAN) injection laser

This paper describes a novel planar stripe-geometry injection laser (referred as SWAN laser) showing a single transverse and longitudinal mode operation made by a simple fabrication method. This stripe-geometry is composed of a main stripe section with the width of around 10 μm and mode control section with the nominal width near to carrier diffusion length, less than 5 μm, a shape of which looks like waist(s) and/or notch(es) along the stripe. A "kink", which often appears in the relation between a light output and a current in conventional planar injection lasers, is not observed at the power level of more than 20 mw/ facet. The laser has advantage of controlling modulation dynamics by the shape of waist(s) and/or notch(es) along the stripe that enables control of the lateral carrier diffusion profile in the vicinity of an active layer and the amount of spontaneous emission into laser mode.     

Fabry-Perot semiconductor laser injection locking

Injection locking of a semiconductor laser is studied using a Fabry-Perot (FP) model. For low injection powers the FP model gives the same results as the rate equation model. At higher injection powers, the FP laser has an unlimited injection locking bandwidth; however, regions of the bandwidth are dynamically unstable. The influence of the linewidth enhancement factor on injection locking and its stability are also studied using the FP model. Finite values of the linewidth enhancement factor lead to increased locking bandwidth, asymmetry in the locking range and a saddle-node bifurcation in the injection locked solutions, of which only lower carrier density arm has linearly stable solutions.     

Injection locking of a 1.3 ?m laser diode to an LiNdP4O12 laser yields narrow linewidth emission

A multi-longitudinal-mode InGaAsP laser diode was injection-locked to a low-power LiNdP4O12 laser operating at 1.319 ?m. A net gain of 24 dB was measured with ?28 dBm of injection power. The beat spectrum between the acousto-optically frequency-shifted LiNdP4O12 laser output and the laser diode output displays a 40 dB carrier to pedestal ratio (in 300 kHz bandwidth) under these conditions.     

Nonequilibrium model for semiconductor laser modulation response

Presents a laser model for describing the effects of nonequilibrium carrier distributions. The approach is based on the coupled Maxwell-semiconductor-Bloch equations, with carrier-carrier and carrier-phonon collisions treated in the relaxation rate approximation. Using examples involving relaxation oscillation, current modulation, and optical injection, we demonstrate how the model can be used to study the influences of spectral hole burning, dynamic carrier population bottleneck, and plasma heating on semiconductor laser modulation response     

Two-dimensional numerical simulator for multielectrode distributedfeedback laser diodes

A two-dimensional program for the analysis of multielectrode distributed feedback (DFB) laser diodes under nonuniform carrier injection conditions has been developed. The program self-consistently solves the carrier transport together with optical equations. In addition, the present simulation system offers a user-friendly graphic interface during input and output stages. The effectiveness of the program has been demonstrated through a three-section DFB LD. The improvement of the spatial hole burning effect under nonuniform carrier injection has been elucidated by directly monitoring the carrier and/or current density distribution and indirectly evaluating the cavity loss     

Planar stripe with waist/notch (swan) injection laser

This letter describes a novel planar stripe-geometry injection laser (termed the Swan laser), showing a single transverse and longitudinal mode operation, made by a simple fabrication method. This stripe geometry is composed of a main stripe section with a width of ?10 ?m and a mode-control section with a nominal width near the carrier diffusion length less than 5 ?m; the shape looks like a waist/notch along the stripe. The kink of the light output does not appear at a power level of more than 20 mW/facet.     

High output power tunable twin-guide laser diodes with improved lateral current injection structure

Tunable twin-guide laser diodes with improved lateral current injection structure and high output power are reported. By optimising the doping profile of the n-InP layer laterally surrounding the buried stripe, inherent leakage currents are effectively minimised. Thereby, the carrier injection efficiency of the laser diode is significantly increased and high output powers of up to 24 and 3.3 mW are obtained at operation temperatures of 20 and 80/spl deg/C, respectively.     

Capture of charge carriers and output power of a quantum well laser

The effect of noninstantaneous carrier capture by a nanoscale active region on the power characteristics of a semiconductor laser is studied. A laser structure based on a single quantum well is considered. It is shown that delayed carrier capture by the quantum well results in a decrease in the internal differential quantum efficiency and sublinearity of the light-current characteristic of the laser. The main parameter of the developed theoretical model is the velocity of carrier capture from the bulk (waveguide) region to the two-dimensional region (quantum well). The effect of the capture velocity on the dependence of the following laser characteristics on the pump current density is studied: the output optical power, internal quantum efficiency of stimulated emission, current of stimulated recombination in the quantum well, current of spontaneous recombination in the optical confinement layer, and carrier concentration in the optical confinement layer. A decrease in the carrier capture velocity results in a larger sublinearity of the light-current characteristic, which results from an increase in the injection current fraction expended to parasitic spontaneous recombination in the optical confinement layer and, hence, a decrease in the injection current fraction expended to stimulated recombination in the quantum well. A comparison of calculated and experimental light-current characteristics for a structure considered as an example shows that good agreement between them (up to a very high injection current density of 45 kA/cm²) is attained at a capture velocity of 2 × 10⁶ cm/s. The results of this study can be used to optimize quantum well lasers for generating high optical powers.     

A dual-color injection laser based on intra- and inter-band carriertransitions in semiconductor quantum wells or quantum dots

A new type of semiconductor injection laser capable of simultaneously generating radiation in the mid-infrared (MIR) (λ~10 μm) and near-infrared (NIR) (λ~0.9 μm) spectral regions is proposed. The MIR emission is a result of intersubband (intraband) electron transitions within a three-level conduction band in a quantum well or a quantum dot. The NIR emission, on the other hand, is due to conventional interband recombination of injected electrons and holes into the conduction and valence bands, respectively. The conditions for population inversion in the intersubband emission process are determined by an appropriately engineered energy structure for a three-level system in the conduction band of a quantum well or dot structure: for the quantum-well-based system, the structure has an asymmetric funnel shape to provide long electron-phonon lifetime at the third (top) energy level. Under high carrier injection, NIR interband emission depopulates the conduction ground level of the quantum well, thereby stabilizing the electron concentration at this level-a necessary condition fur the operation of the MIR laser. This paper discusses the calculation of the population inversion conditions, the requisite gain, and threshold current for MIR laser operation. We also present a preliminary design of the laser structure with a composite waveguide that accommodates both mid- and NIR stimulated emission     

Polarization optical bistability induced by TM mode injection to aDFB laser with complex coupled coefficient

A novel method is proposed to produce an optical bistability by using a dynamically stable complex coupled DFB (CC-DFB) laser with TM mode injection. In this paper polarization optical bistabilities are analyzed in detail using coupled mode equations and rate equations for the CC-DFB lasers considering the longitudinal hole burning and carrier dependent complex coupling coefficients. Several parameters reflecting the physical features of a complex coupled DFB laser are discussed. It is shown that for a CC-DFB laser the polarization bistability induced by the TM mode injection is much stronger for the antiphase of complex coupling than that for the in-phase. In addition, the influences of initial coupling condition for gain grating structure on the optical bistability are also investigated considering both cases of the antiphase and in-phase     

Amplified spontaneous emission and carrier pinning in laser diodes

Theoretical and experimental results for the temperature dependence of amplified spontaneous emission (ASE) in laser diodes (LDs) and light-emitting diodes (LEDs) are presented. The theoretical model takes into account conduction band nonparabolicity and band-gap renormalization. The gain spectrum is calculated from the theoretical spontaneous emission spectrum, and both compare very well with experimental data. From a fit to the observed temperature dependence of ASE for an LED and the gain spectrum for an LD with a structure identical to that of the LED except for mirror reflectivity, it is possible to establish carrier density as a function of injection current for both devices. It is shown that photons fluctuating into cavity modes give rise to substantial subthreshold carrier pinning in laser diodes. These fluctuations extract an extra current from the device and play an increasingly important role with increasing temperature     

Nearly degenerate four-wave mixing in laser diodes subject tostrong probe injection power

Nearly degenerate four-wave mixing (FWM) in above-threshold laser diodes with symmetric or asymmetric facet reflectivities, subject to strong probe injection power, is investigated theoretically, taking into account the effects of pump depletion, carrier diffusion, gain saturation, gain compression, total power dependence of the gain and coupling coefficients as well as the longitudinal dependence of the nonlinear interaction. It is shown that the reflectivity efficiencies of probe and conjugate waves demonstrate significantly different behaviors for strong probe injection power, compared to small probe injection power, and a greater than 3 dB enhancement of reflectivity efficiencies can be achieved in an asymmetric laser diode, compared to a symmetric laser     

Picosecond injection laser: a new technique for ultrafastQ-switching

A modification of a method for self-Q-switching in a laser with an isotypic saturable absorber is suggested and implemented in a multisegmented injection laser. The method consists of the transportation of most parts of the excited absorber population to the amplifier. The carrier transport time must be less than the spontaneous recombination time in the absorber. In a three-section AlGaAs/GaAs double-heterostructure laser with modified Q-switching, optical pulses of 5 ps in duration with a repetition rate as high as 18.5 GHz and peak power above 10 W have been obtained. The latter value is the largest ever reported for a picosecond injection laser. Unique temporal and spectral features exhibited by these lasers have been observed, including the stepped variation of pulse repetition frequency, its dependence on the pump current, large emission spectral width (on the order of kT), spectral chaos and bistability