Nonlinear analysis of quantum-well lasers with the effects ofcarrier transport

An improved nonlinear quantum-well (QW) laser model, which takes into account the effects of quantum capture and escape processes, is presented, based on laser rate equations and Volterra theory. This model is further expanded by proper parameter transform to include the effect of carrier diffusion in the separate confinement heterostructure region. Various QW laser distortions have been evaluated using this model and compared with the results obtained from the previous model where the transport effects are absent. The results shows that the effect of transport processes on laser dynamic nonlinearity can be significant     

Degenerate four-wave mixing measurements of high ordernonlinearities in semiconductors

Degenerate four-wave mixing experiments on ZnSe and CdTe semiconductor samples with picosecond laser pulses at wavelengths below the bandgap are described. The authors identify the dominant nonlinearities in ZnSe and CdTe. They determine these to be fast third-order nonlinearities, due to the same processes which give rise to the effects of bound-electronic refraction and two-photon absorption, while higher order effects are due to free-carrier refraction. Measurements of the absolute magnitude of the combined third order susceptibilities are described. Studies of higher order effects due to free-carrier gratings are discussed. To obtain a quantitative measurement of the carrier induced nonlinearities, an expression for the diffraction efficiency of these carrier gratings was developed, and a value for the free-carrier refractive index coefficient in ZnSe was found. By measuring the angular dependence of the grating decay, the carrier diffusion coefficient was determined as a function of carrier density     

A small-signal analysis of the modulation response of high-speedquantum-well lasers: effects of spectral hole burning, carrier heating,and carrier diffusion-capture-escape

We present a small-signal analysis of the modulation response by simultaneously considering the effects of spectral hole burning, carrier heating, and carrier diffusion capture-escape. An explicit form of the small-signal modulation response is obtained and the nonlinear gain coefficients associated with each physical process are defined. Further simplifications in our results will give analytical forms for calculating the resonant frequency and damping rate of the modulation response. One of the simplified versions of our results is shown to agree with previous investigations. The effects of the carrier dephasing time, energy relaxation time, and diffusion-capture-escape times on the high-speed performance of QW lasers are theoretically investigated     

基于电致发光成像理论的硅太阳电池缺陷检测

基于半导体电致发光（EL）的基本理论,在理想P-N结模型条件下,定量计算正向偏压时硅太阳电池EL强度与少数载流子扩散长度的对应关系;分析了电池片中缺陷和扩散长度（EL强度）的关系,指出通过硅电池EL图像检测电池缺陷的可行性。搭建实验平台,分别拍摄单晶硅和多晶硅电池的EL图像,从中成功检测出各种缺陷;编写可视化裂纹自动检...     

Nonlinear dynamics of semiconductor laser arrays: a mean fieldmodel

An analysis of the spatiotemporal dynamics of single-emitter and multiemitter index-guided semiconductor laser arrays is presented. The results are based on a propagation model that involves a pair of coupled nonlinear partial differential equations. The model describes the space-time evolution of the mutually interacting lateral field and carrier density distributions. It includes the effect of carrier diffusion and the effect of carrier-induced antiguiding. Coupling between the emitters is provided by the overlapping evanescent fields of the emitters as well as by the exchange of carriers through carrier diffusion. We show that carrier diffusion plays a significant role in the stability and the nature of bifurcations. Also we show that carrier-induced antiguiding is the principal reason of instability for singleand two-emitter arrays. We illustrate a wide variety of instabilities that demonstrate the richness of the dynamics in these devices     

Carrier Diffusion and Recombination in Photonic Crystal Nanocavity Optical Switches

Carrier dynamics in silicon photonic crystal (PhC) nanocavities are studied numerically. The results agree well with previous experimental demonstrations. It is shown that the presence of carrier diffusion makes fast switching possible, which is an advantage of nanocavity switches over other types of larger carrier based nonlinear optical switches. In particular, diffusion is effective in PhC nanocavity switches, which makes the switching recovery time even faster than that of silicon waveguide-based optical switches. In addition, calculations suggest that the thermo-optic effect can be reduced if the carriers are extracted within a few 100 ps by introducing a p-i-n structure.     

Circuit model for multiple transverse mode vertical-cavity surface-emitting lasers

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.     

Gain dispersion and saturation effects in four-wave mixing insemiconductor laser amplifiers

This paper addresses four-wave mixing (FWM) in semiconductor laser amplifiers from the point of view of a propagation problem. The gain dispersion effect, i.e., the difference of the gain factors for the pump, probe and signal waves is shown to be significant in the case of large detunings >1 THz. It is given an analytical solution of the FWM problem including gain dispersion and saturation effects. Considering the saturation behaviour, it is shown that the linear gain factors for the different waves and the nonlinear susceptibilities associated with the different nonlinear effects must be characterized by different carrier densities at transparency. A comparison of our theory with a numerical model, with previous approaches and with experimental data is given     

Nonlinear gain effects due to carrier heating and spectralholeburning in strained-quantum-well lasers

The authors present numerical results for the nonlinear gain effects due to carrier heating and spectral holeburning in 50 Å strained In_xGa_1-xAs/Al_0.3Ga_0.7 As quantum-well lasers. Calculations are performed on the basis of a 4×4 matrix system consisting of the usual Kohn-Luttinger Hamiltonian and a strain Hamiltonian for the valence band structure. In addition, the authors perform a small-signal analysis based on four dynamic equations for the photon density, carrier density, and two supplementary equations for the electron and hole energy densities to obtain information about nonlinear gain coefficients. The results indicate that the nonlinear gain is enhanced with the strain mainly due to the rapid increase of the carrier heating effect as the carrier density at the lasing threshold decreases, and that carrier heating is about five times as important compared to spectral holeburning     

Enhancement of third-order nonlinear optical susceptibilities incompressively strained quantum wells under the population inversioncondition

Third-order optical nonlinear susceptibilities χ⁽³⁾ in compressively strained and nonstrained InGaAs-InGaAsP quantum wells (QW's) under the population inversion condition are discussed. The small effective mass of compressively strained QW's increases the contribution of the carrier density pulsation effect and the carrier heating effect of χ⁽³⁾. The hole burning effect is also increased due to the decrease of the carrier-carrier scattering rate. The calculation including these effects shows an enhancement of factor 3 due to 0.8% compressive strain. The values of χ⁽³⁾ are experimentally estimated from the data of nondegenerate four-wave mixing in λ/4-shifted distributed feedback lasers. χ⁽³⁾ in 0.8% compressively strained QW's is three times larger than that in nonstrained QW's with the same linear gain     

一种花菁染料超薄膜的激光诱导瞬态光栅

采用旋涂法制备了一种五甲川花菁染料的超薄膜,利用激光诱导瞬态光栅的方法研究染料薄膜的三阶,乃至更高阶的非线性光学特性.通过理论计算得到了该样品在不同浓度下的非线性光学信号的响应时间(59～102 ps),分析表明花菁染料五甲川链上的π-π*电子跃迁是引起该染料薄膜非线性光学效应(20.5×10-13esu～30.3×10-13esu)的主要原因.研究结果表明激光诱导瞬态光栅是研究介质高阶非线性光学特性一种非常有意义的实验方法.     

Time-dependent thermal effects in current-modulated semiconductor lasers

The temporal dependence of the frequency shift in a current-modulated single-mode semiconductor laser is measured and compared with calculations based on solutions to the thermal diffusion equation. The effects of carrier density change, thermal diffusion in the semiconductor, and heat sink thermal resistance are identified.     

Electric-field enhancement and extinguishment of opticalsecond-harmonic generation in asymmetric coupled quantum wells

The second-harmonic susceptibilities of asymmetric coupled quantum wells (ACQW) and compositionally asymmetric coupled quantum wells (CACQW) under the influence of the applied electric field are investigated theoretically. Analytic forms of the second-harmonic susceptibility are derived by using the density matrix formalism. Coupled one-dimensional Schrodinger equation and Poisson's equation are solved self-consistently to find the subband eigenenergies and the envelope wavefunctions for the ACQW and CACQW structures. Dipole moment matrix elements for the ACQW and CACQW are evaluated from the resulting envelope wavefunctions and large nonlinear optical effects are predicted for these two structures. Based on the theoretical calculations, the second-harmonic susceptibilities of 50 nm/V and 35 nm/V can be achieved for the ACQW and the CACQW, respectively. This is more than two orders of magnitude enhancement as compared to that of the bulk GaAs. By a suitable choice of the composition of CACQW, a novel structure which the second-order nonlinear optical effect can be turned on or off by the applied electric field is proposed based on the results of the theoretical calculation. This phenomenon is attributed to the symmetry restoration of envelope wavefunctions of the CACQW under the quenching electric field F_off. A simple physical model to estimate the F_off has also been developed successfully     

Mode locking by cascading of second-order nonlinearities

We present a comprehensive theoretical and experimental study on a new passive mode-locking technique, called cascaded second-order nonlinearity mode locking (CSM), which exploits cascaded second-order nonlinearities to obtain large third-order susceptibilities from an intracavity second harmonic crystal. The nonlinear phase shift that originates in the nonlinear crystal is converted into a nonlinear amplitude modulation by a suitable intracavity aperture. A numerical model, based on a perturbative approach, allows the nonlinear loss modulation of resonators used for CSM to be calculated as a function of the resonator parameters and of the phase mismatch. The predictions of the model are confirmed by experiments performed on a CW Nd:YAG laser. The effects of group velocity mismatch and the limitations which it poses on the minimum achievable pulsewidth are analyzed both experimentally and theoretically     

The gain decompression effect and its applications to very fast wavelength conversions

The gain recovery in a semiconductor optical amplifier (SOA) follows a two-step process: (1) an ultrafast gain recovery process through the nonlinear gain decompression effect and (2) a slower carrier recovery process that is dominated by carrier effects like Auger recombination or carrier diffusion. We discuss and numerically demonstrate how to control this decompression gain and apply it to very fast wavelength conversions.     

Nonlinearities in p-i-n microwave photodetectors

The nonlinearities in p-i-n photodetectors have been measured and numerically modeled. Harmonic distortion measurements were made with two single-frequency offset-phased-locked Nd:YAG lasers which provide a source dynamic range greater than 130 dB and a 1 MHz-50 GHz frequency range. Carrier transport is analytically described by three coupled nonlinear differential equations, Poisson's equation and the hole and electron continuity equations. These equations are numerically solved to investigate and isolate the various nonlinear mechanisms. The numerical solution incorporates diffusion since our treatment includes carrier generation in the highly doped p-region of the device. This p-region absorption and carrier-dependent carrier velocities associated with a perturbed electric field (due to space-charge and loading effects) are shown to dominate photodetector nonlinear behavior. The numerical model was extended to predict that maximum photodetector currents of 100 mA should be possible in 20 GHz bandwidth devices before a sharp increase in nonlinear output occurs. In addition, second harmonic distortion improvements of 40-60 dB may be possible if photodetectors can be fabricated with strictly-depleted absorbing regions     

Theory of hot carrier effects on nonlinear gain in GaAs-GaAlAslasers and amplifiers

A concise and straightforward model of nonlinear grain based on the carrier heating effect in semiconductor lasers is presented. The problem is formulated using the density matrix approach and includes a priori the effect of free-carrier absorption. Coupled field-medium equations involving photon densities, carrier densities, and carrier temperatures are derived using the results of the density matrix method. The propagation of ultrashort pulses in laser amplifiers is studied and a qualitatively new model along with results on the transient gain recovery dynamics are presented. The model accounts for the wavelength dependence of the asymmetric part of the nonlinear gain observed in direct mixing experiments observed in semiconductor lasers     

Coherent current control in semiconductors: a susceptibilityperspective

We show that the all-optical generation and control of dc current in semiconductors, also known as coherent current control, can be described within the standard framework of nonlinear optics using perturbative susceptibilities. In particular, we find that such effects arise from zero frequency divergences in the susceptibilities; this identification provides a novel and convenient method to classify the various contributions in the response. However, these physical divergences are distinct from other unphysical divergences that are commonly encountered and which have led to incorrect results elsewhere in the literature. The susceptibility viewpoint offered here allows one to understand the optical response for both resonant and nonresonant excitation, exposes the relationship between second- and third-order (and higher) processes, and will provide a natural framework in which to include dissipative effects     

An experimental method for identifying nonlinear phenomenaintervening in a FWM process developed in a semiconductor opticalamplifier

The new experimental research on the four-wave mixing (FWM) phenomena described here consists in launching three optical waves (pump, probe, and test) into a semiconductor optical amplifier and measuring the test beam transmission and the conversion efficiency of the new wave generated to one side of the test beam. It allows for an excellent identification of the nonlinear phenomena involved in the FWM process. The analysis principle is based on the modulation of the gain curve for each of the three effects considered: spectral hole burning, carrier heating, and carrier density pulsation. Experimental and theoretical results are presented