Optical bistability in vertical-cavity semiconductor optical amplifiers

We present an overview of the properties and applications of optical bistability in vertical-cavity semiconductor optical amplifiers (VCSOAs). The basic physics and analytical models of this optical nonlinearity are discussed. Experimental results obtained from a VCSOA operated in the 850 nm wavelength region are presented. Counterclockwise hysteresis loops are obtained over a range of initial phase detuning and bias currents. One hysteresis loop is observed experimentally with an input power as low as 2 muW when the device is biased at 98% of its lasing threshold. Numerical simulations based on the Fabry-Perot resonator model and rate equations we developed show good agreement with our experimental observations. In addition, a low input intensity high contrast (10:1) optical and gate and 2R regeneration are demonstrated. We believe that bistable VCSOAs can significantly advance the prospect of a dense two-dimensional array of low-switching-intensity all-optical logic and memory elements.     

Ultrafast dynamics of quantum-dot semiconductor optical amplifiers

We report on a series of experiments on the dynamical properties of quantum-dot semiconductor optical amplifiers. We show how the amplifier responds to one or several ultrafast (170 fs) pulses in rapid succession and our results demonstrate applicability and ultimate limitations to application of quantum-dot amplifiers in e.g. amplification of signals in a telecommunications system. We also review experiments on pulse propagation control and show the possibility to slow down or speed up 170 fs pulses in a quantum-dot based device.     

Influence of magnetic field on electromagnetic instabilities in semiconductor superlattices

Electromagnetic instability criteria in semiconductor superlattices (SL) in the region of a negative differential conductivity (NDC) are studied in the presence of a static transverse field. The regimes with vertical constant electric field in a "short" plate of SL and with vertical current density vector in a "long" plate are considered. The effective differential conductivity tensors for both these regimes are derived and the influence of the magnetic field on the NDC threshold and the growth increment is investigated. The frequencies of the excited waves and the dependence of the growth increment on the direction of propagation for the extraordinary waves are determined.     

Analytic theory of coherent cross-gain modulation in semiconductor travelling-wave amplifiers

Abstract

We report a simple analytic solution to the problem of cross amplitude-phase modulation in nonlinear two-wave mixing, under the approximation of constant saturating power. The results are applied to travelling-wave semiconductor laser amplifiers where the linewidth enhancement factor inevitably leads to amplitude-phase coupling and asymmetric energy transfer. Our solution is used to obtain the transmission gain of each beam, the spectral profile and the amplifier input-output characteristics. Limits are established as to the applicability of the analytic solution, by comparison with numerical solutions to the related full four-wave mixing problem.     

Nanopillar arrays on semiconductor membranes as electron emission amplifiers

A new transmission-type electron multiplier was fabricated from silicon-on-insulator (SOI) material by integrating an array of one-dimensional (1D) silicon nanopillars onto a two-dimensional (2D) silicon membrane. Primary electrons are injected into the nanopillar-membrane (NPM) system from the flat surface of the membrane, while electron emission from the nanopillars is probed by an anode. The secondary electron yield (SEY) from the nanopillars in the current device is found to be about 1.8 times that of the plain silicon membrane. This gain in electron number is slightly enhanced by the electric field applied from the anode. Further optimization of the dimensions of the NPM and an application of field emission promise an even higher gain for detector applications and allow for probing of electronic/mechanical excitations in an NPM system stimulated by incident particles or radiation.     

Operation of quantum-dot semiconductor optical amplifiers under nonuniform current injection

The influence of nonuniform current injection along the active region, on the linear operation of a quantum-dot semiconductor optical amplifier (QD-SOA) is investigated. For this purpose, we have utilized some functions to generate various nonuniform current injection profiles. These profiles have been considered in our numerical calculations, where the rate equation model is employed to construct different characteristics of the QD-SOA. We have found that the gain, as well as the crosstalk, of a QD-SOA is closely associated to the variance of the carrier density along the cavity. Simulation results show that nonuniform current injection can be used as a technique for gain enhancement as well as crosstalk suppression.     

Thermal expansion of semiconductor materials

The thermal expansion of tellurides of germanium, bismuth, and intermetallic compounds is investigated over the temperature range 293-973 K.Belarusian Agricultural Technical University, Minsk. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 66, No. 5, pp. 612–616, May 1994.     

Numerical model of wavelength conversion through cross-gain modulation in semiconductor optical amplifiers

A steady-state numerical model of wavelength conversion through cross-gain modulation in semiconductor optical amplifiers is described, which includes the spatial variations of the carrier density, gain coefficient, differential gain, and internal loss. Of particular interest is the analytic gain coefficient model, which is applied to the semiconductor optical amplifier converter problem for the first time to our knowledge. The model is used to compare performances of upconverters and downconverters for cases of long and short device lengths, and in large and small signal regimes. Comparisons with results of other studies are presented.     

理论研究垂直腔半导体光放大器脉冲放大特性

从速率方程和薄膜光学理论出发,对垂直腔半导体光放大器(Vertical Cavity Semiconductor Optical Amplifiers,简称VCSOAs)在脉冲工作情况下的动态增益进行了数值模拟.在计算中考虑了载流子和光强沿光轴方向的不均匀性,以及腔内介质折射率的不连续性对光波传输的影响.详细分析了反射模式下VCSOA在脉冲通过时载流子密度和瞬时增益的变化、输出光脉冲的畸变以及抽运光功率、分布布拉格反射镜(Distributed Bragger Reflector,简称DBR)周期数、输入脉冲能量以及脉冲宽度等参量对脉冲放大中的能量增益的影响.结果表明,能量增益随抽运光功率增大而增加;在峰值功率一定时输入脉冲宽度的增加将减小能量增益;输入脉冲能量的增加也会引起能量增益的下降,而适当减少顶部DBR的周期数可以改善这种脉冲放大的能量增益饱和特性.     

Misalignment correction for optical interconnects using vertical cavity semiconductor optical amplifiers

In board-to-board optical interconnects, the misalignment between the board and the backplane connections can cause both optical loss and interchannel cross talk. A vertical cavity semiconductor optical amplifier (VCSOA) is proposed to correct optical misalignment in an optical connector between the board and the backplane. Angular or lateral misalignment can be corrected with the designed module. The correction ability is determined by the acceptance angle of the VCSOA, which was characterized to be 9.4 degrees full angle at a 3 dB gain drop for a 30 microW optical signal at 1 GHz. The lateral misalignment correction ability is 0.16f, where f is the focal length of the mini lens to converge the input light onto the VCSOA.     

Assessment of linear semiconductor amplifiers for upgrading WDM-PONs with wavelength reuse

In this work we have assessed the capacity of a linear semiconductor optical amplifier to compensate the fiber and component losses present in a wavelength division multiplexing passive optical network (WDM-PON) evolution from fiber-to-the-building (FTTB) to fiber-to-the-home access. The evaluation measurements confirm that the presence of a semiconductor optical amplifier placed at the entry of a group of optical network units that share the same wavelength channel can raise the loss budget that the link can tolerate in the fiber, compensating for the losses of a passive splitter up to a 1:16 division rate, allowing the upgrade of existing WDM-PON FTTB structures to make the fiber reach the final user's home.     

Design and implementation of cryogenic semiconductor amplifiers as interface between RSFQ circuits

Rapid single flux quantum (RSFQ) circuits create high interest in cryogenic amplifiers as interface to commercial room temperature electronics. The requirements for the amplifiers are an extremely high bandwidth (SFQ pulses with ), high voltage gain of about 10⁴ (common RSFQ output voltage level of about ), low power consumption (cryogenic environment at 4 K) and low noise. Hybrid amplifiers, based on commercial available p-HEMT transistors, can solve the problematic high-speed interface. In this paper, we present measurement results of a hybrid four stage coplanar amplifier in combination with a RSFQ Toggle Flip-Flop (RSFQ T-FF) and a Josephson array quantizer (JA-Q).     

Thermal properties of semiconductor zinc oxide nanostructures

A combination of two methods — laser modulation and 3ω — has been used to determine the heat capacity, heat conductivity, and heat diffusivity of zinc oxide nanostructures. A significant difference between the thermal parameters of zinc oxide nanostructures grown by different technological methods has been revealed. It has been shown that the relatively low heat conductivity and heat diffusivity values of oxide zinc nanostructures are due to both the internal defects and the contact resistance between the film and its base — the substrate.     

Method of developing all-optical trinary JK, D-type, and T-type flip-flops using semiconductor optical amplifiers

To meet the demand of very fast and agile optical networks, the optical processors in a network system should have a very fast execution rate, large information handling, and large information storage capacities. Multivalued logic operations and multistate optical flip-flops are the basic building blocks for such fast running optical computing and data processing systems. In the past two decades, many methods of implementing all-optical flip-flops have been proposed. Most of these suffer from speed limitations because of the low switching response of active devices. The frequency encoding technique has been used because of its many advantages. It can preserve its identity throughout data communication irrespective of loss of light energy due to reflection, refraction, attenuation, etc. The action of polarization-rotation-based very fast switching of semiconductor optical amplifiers increases processing speed. At the same time, tristate optical flip-flops increase information handling capacity.     

Concatenation performance of optical packet switches that incorporate wavelength converters based on four-wave mixing in semiconductor optical amplifiers

Four-wave mixing (FWM) in semiconductor optical amplifiers (SOAs) has been acknowledged as a useful wavelength conversion technique especially due to its ability to convert sequences of ultra fast pulses but also simultaneously a number of wavelengths. An analysis is used to investigate the concatenation performance of optical packet switch that incorporate wavelength or waveband converters based on FWM in SOAs.     

Necking instabilities in elastic-plastic plates

A sufficient condition for necking instability in an elastic-plastic plate under biaxial tension is established. The critical stress at instability is obtained and is shown to be quite sensitive to the variation in the direction of the unit normal to the yield surface at the local stress point.