Bias and Geometrical Effects on Optically Controlled MESFETs

A detailed characterization of the optical response of illuminated MESFETs due to several operating and geometrical conditions is presented. The characterization targets important optical performance factors including terminal photocurrent peak value and discharge time. A figure-of-merit is defined to quantify the overall response to these effects. The simulation results should be very useful in device operation and optimization

Bias and Geometrical Effects on Optically Controlled MESFETs

A detailed characterization of the optical response of illuminated MESFETs due to several operating and geometrical conditions is presented. The characterization targets important optical performance factors including terminal photocurrent peak value and discharge time. A figure-of-merit is defined to quantify the overall response to these effects. The simulation results should be very useful in device operation and optimization

Plasmonic Nanostructured Cellular Automata

In this work, we have investigated the scattering plasmonic resonance characteristics of silver nanospheres with a geometrical distribution that is modelled by Cellular Automata using time-domain numerical analysis. Cellular Automata are discrete mathematical structures that model different natural phenomena. Two binary one-dimensional Cellular Automata rules are considered to model the nanostructure, namely rule 30 and rule 33. The analysis produces three-dimensional scattering profiles of the entire plasmonic nanostructure. For the Cellular Automaton rule 33, the introduction of more Cellular Automata generations resulted only in slight red and blue shifts in the plasmonic modes with respect to the first generation. On the other hand, while rule 30 introduced significant red shifts in the resonance peaks at early generations, at later generations however, a peculiar effect is witnessed in the scattering profile as new peaks emerge as a feature of the overall Cellular Automata structure rather than the sum of the smaller parts that compose it. We strongly believe that these features that emerge as a result adopting the different 256 Cellular Automata rules as configuration models of nanostructures in different applications and systems might possess a great potential in enhancing their capability, sensitivity, efficiency, and power utilization

Acute presentation of a heterotopic pregnancy following spontaneous conception: a case report

Spontaneous heterotopic pregnancy is a rare clinical condition in which intrauterine and extra uterine pregnancies occur at the same time. It can be a life threatening condition and can be easily missed with the diagnosis being overlooked. We present the case of a 40 year old patient who was treated for a heterotopic pregnancy. She had a transvaginal ultrasound because of a previous ectopic pregnancy and an intrauterine gestational sac was seen with false reassurances. The patient presented acutely with a ruptured tubal pregnancy and this was managed laparoscopically. The ectopic pregnancy was not suspected at her initial presentation. A high index of suspicion is needed in women with risk factors for an ectopic pregnancy and in low risk women who have free fluid with or without an adnexal mass with an intrauterine gestation

Effects of Electrode Spacing on the Response of Optically Controlled MESFETs

In microwave GaAs MESFETs, carrier transport is a strong function of carrier energy. When illuminated, the carrier energy and carrier distribution inside the device are substantially affected by the incident optical energy. To account for these effects an accurate model based on the energy formulation of the transport equation coupled with optical energy conversion equations is used [1-2]. This model is used to investigate the optimum design of optically controlled MESFET structures considering the trade -off between the degradation in electric characteristics and the improvement in photoelectric conversion efficiency. Time domain simulations show the significant effect of electrode spacing, specifically, the drain-gate separation

Effects of Electrode Spacing on the Response of Optically Controlled MESFETs

In microwave GaAs MESFETs, carrier transport is a strong function of carrier energy. When illuminated, the carrier energy and carrier distribution inside the device are substantially affected by the incident optical energy. To account for these effects an accurate model based on the energy formulation of the transport equation coupled with optical energy conversion equations is used [1-2]. This model is used to investigate the optimum design of optically controlled MESFET structures considering the trade -off between the degradation in electric characteristics and the improvement in photoelectric conversion efficiency. Time domain simulations show the significant effect of electrode spacing, specifically, the drain-gate separation

A Higher-order Accurate FDTD Solution to Scalar SHG Problems

A higher-order accurate FDTD simulation algorithm for the solution of the phase-dependent SHG problem is presented. This algorithm approximates the spatial derivatives in the propagation direction using 4th order FD schemes. It has been shown that this scheme guarantees the convergence of the solution using significantly less computation time and less memory requirement as compared to 2nd order scheme

Microwave Performance of Optically Controlled MESFETs

This paper presents the characterization of illuminated high-frequency active devices using a time -domain physical simulation model. The model is based on Boltztnann’s Transport Equation (BTE), which accurately accounts for carrier transport in microwave and millimeter wave devices with sub-micrometer gate lengths. Illumination effects are accommodated in the model to represent camer density changes inside the illuminated device. The simulation results are compared to available experimental records for a typical MESFET for validation purposes. The calculated y-parameters of the device show the profound effect of illumination on the microwave characteristics. These findmgs make the model an important tool for the design of active devices under illumination control

Full-wave Solution of the Second Harmonic Generation Problem Using a Nonlinear FDTD Algorithm

A vectorial time-domain simulator of integrated optical structures containing second order nonlinearities is presented. The simulation algorithm is based on the direct solution of nonlinear Maxwell's equations representing the propagating fields and is solved using the FDTD method. Because the proposed algorithm accounts for the full optical coefficient tensor, the inaccuracies associated with the scalar and paraxial approximations are avoided. It should find application in a wide range of device structures and in the analysis of short-pulse propagation in second order nonlinear devices