Auger effect on the output power of InGaAsP DH lasers

A model has been developed for CW operation of InGaAsP Double-heterostructure (DH) lasers considering Auger recombination as the major source of nonradiative recombination inside the active region. The model uses a two dimensional temperature distribution solution inside of the active layer of stripe geometry InGaAsP DH lasers to get better average value for the active region temperature. Then, utilizing Haug\u27s model of threshold current density for lasing, together with Asada and Suematsu\u27s model for the external differential quantum efficiency, the light output power P[subscript]L as a function of the injection current I is obtained;The developed model allows us to make a theoretical study of P[subscript]L versus I characteristics of a laser under CW (continuous wave) operation. The effect of changes in the heat sink temperature T[subscript]H, in the doping concentration level of the active layer, and in the dimensions of the passive layer as well as the active layer upon the optical output power are investigated in detail. It is shown that quantities like P[subscript]Lm (the maximum value of P[subscript]L), I[subscript]m (the value of injection current at which P[subscript]L takes its maximum value), [delta] I (the range of injection current over which CW operation is possible), and [delta] T[subscript]H (the range of heat sink temperature over which CW operation is possible) vary significantly with the heat sink temperature T[subscript]H, the doping level of the active layer (p[subscript]0 for the p-type and n[subscript]0 for the n-type doping), and the dimensions of the active and passive layers. For instance, P[subscript]Lm and [delta] I decrease as T[subscript]H increases, while P[subscript]Lm, [delta] I, [delta] T[subscript]H, and I[subscript]m tend to increase for some doping levels. Thus, the results suggest that proper doping of active layer of laser is desirable;The result of our theoretical study shows that there is a strong evidence that Auger process plays a major role in influencing the P[subscript]L versuv I characteristics of an InGaAsP DH Laser under CW operation because this process could contribute significantly to the internal heating of the device, thereby leading to acute temperature sensitivity of the laser output;The model developed in the present study should also provide an intuitive and rapid way of finding such laser parameters as the threshold current I[subscript]th for lasing and the quantum efficiency [eta][subscript]d for pulsed as well as CW operation of an InGaAsP DH laser. This should be useful to future designers of semiconductor DH lasers

Sagnac interferometric switch utilizing Faraday rotation

In this paper, a novel fiber-based, magneto-optic switch based on a Sagnac interferometer is presented. Experimental results at 1550 nm are reported and device performance such as extinction ratio for both single-mode and multi-mode fiber is presented. The performance is modeled using an analytical model which includes reflections at magneto-optic interfaces. The paper examines ways to improve the extinction ratio and the performance of the Sagnac configuration

Methods of high current magnetic field generator for transcranial magnetic stimulation application

This paper describes the design procedures and underlying concepts of a novel High Current Magnetic Field Generator (HCMFG) with adjustable pulse width for transcranial magnetic stimulation applications. This is achieved by utilizing two different switching devices, the MOSFET and insulated gate bipolar transistor (IGBT). Results indicate that currents as high as ± 1200 A can be generated with inputs of +/-20 V. Special attention to tradeoffs between field generators utilizing IGBT circuits (HCMFG1) and MOSFET circuits (HCMFG2) was considered. The theory of operation, design, experimental results, and electronic setup are presented and analyzed

Optimization of Magnetooptic Device by Low Switching Field Domains

This paper expounds on the optimization of magnetooptic devices using preferential domains that switch at low field strengths. In particular, an all-optical switch for transparent networks based on theMach-Zehnder interferometer configuration is examined in detail. The switch utilizes bismuth-substituted iron garnets with a specific composition of (Bi1.1Tb1.9)(Fe4.25Ga0.75)O12 as Faraday rotators. It is proposed that switch figures of merit can be improved by preferentially choosing domains which align with applied fields at field strengths much lower than required by the bulk material. Measurement of magnetic domain orientation in the material and Faraday rotation within domains is reported. The domain behavior in low magnetic fields is also investigated to achieve a switch with lower switching times and higher extinction ratios

Interferometric Detection of Pinned Interactions in Bismuth-Substituted Iron Garnet

The utilization of a bismuth-substituted iron garnet as a magnetooptic Faraday rotator (MOFR) has been reported for all-optical networking purposes as well as for other applications. Our measurements and observations demonstrate that the MOFR saturates once a significantly large magnetic field (\u3e225 G) is applied. After the applied magnetic field enters the saturation region, the material\u27s magnetic domains can become pinned at intermediate levels of magnetization. Pinning in this form has not been reported nor well studied for this application. In this paper, a method to detect and describe anomalous pinning in terms of Faraday rotation is presented. Measurements on the changes in the state of polarization that a pinned material produces are examined. This paper will also present practical methods for unpinning the MOFR material, which are traditionally considered to be challenging

Synthetic Aperture Focusing Technique Using the Envelope Function for Ultrasonic Imaging

In traditional ultrasonic imaging systems, a transducer is scanned across the surface of a specimen at constant intervals. Synthetic aperture focusing techniques (SAFT) have been utilized extensively to process the RF data in order to enhance the signal-to-noise ratio of the image [1]. However, the implementation of the algorithm using sampled RF data has the disadvantage of requiring large memory and high-speed devices. These requirements can be reduced by using the envelope of the RF signal which involves processing the baseband signal. The envelope detection can be easily implemented as part of the receiver circuit

Philosophical and Educational Perspectives on Engineering and Technological Literacy, II

Unknown to each other two groups of engineers and engineering educators began to consider aspects of philosophy and engineering. One held a workshop of engineers and philosophers- “Engineering meets Philosophy” at Delft University and the other held a special session at the annual Frontiers in Education Conference on engineering education and philosophy. Since then the former has held a biannual workshop that have resulted in two impressive publications. The other continued its discussions through FIE and ASEE conferences. There are now regular sessions on philosophy and engineering education at the annual FIE conferences.https://lib.dr.iastate.edu/ece_books/1001/thumbnail.jp

Finite Element Modeling of Binary Acoustic Fresnel Lenses

Binary acoustic Fresnel lenses (BAFLs) have recently emerged as possible replacements for spherical lenses for applications in acoustic microscopy. BAFLs are surface relief structures that are relatively easy to manufacture compared to conventional spherical lenses. While the latter requires careful grinding and polishing, the former can be easily fabricated to sub-micron dimension accuracy using existing VLSI etching technology. The term binary arises from the fact that each masking step during the lens production creates two phase levels. Therefore, a total of 2 n phase levels are created in n masking etching steps. A special case is when n = 1 (2 phase levels), which corresponds to the conventional Fresnel lens (zone plate)

Transcranial Magnetic Stimulation: Design of a Stimulator and a Focused Coil for the Application of Small Animals

Transcranial magnetic stimulation (TMS) is a non-invasive, safe, effective, and food and drug administration approved treatment for major depressive disorder. TMS relies on time-varying magnetic fields to induce an electric field in the brain, resulting in depolarization or hyperpolarization of the neurons. Recently, there has been extensive research to improve the magnetic coil design, effectiveness of TMS treatment, and improvement in the computer modeling of human brains, yet little development is reported on the TMS pulse generators and coil design for small animals. TMS pulse generators, or stimulators, are the circuits which provides pulse current to drive the inductive coils (TMS coils), used to generate time-varying magnetic fields. Commercial TMS stimulators are expensive and have limitations of using standard and non-customizable coils. These stimulators do not support small inductive loads, which require high-current capabilities. Furthermore, the commercial animal coil stimulates the entire body of a mouse, as they are designed for large animals. In this paper, the authors present the design of a small sized TMS stimulator and a focused coil for the application on small animals such as mice. The proposed TMS stimulator will have the potential of handling small inductive loads enabling stimulation of specific regions within the mouse brain

Detection and estimation of magnetization induced resonances in unilateral nuclear magnetic resonance (NMR) sensors

In this work a systematic identification of factors contributing to signal ringing in unilateral nuclear magnetic resonance (NMR) sensors is conducted. Resonant peaks that originate due to multiple factors such as NMR, electrical, magneto-acoustic, core material response, eddy currents and other factors were observed. The peaks caused by the measurement system or electrical resonances and induced magnet vibrations are further analyzed. They appear in every measurement and are considered as interference to signals received from the magnetic core. Forming a distinction between different peaks is essential in identifying the primary contribution to the captured resonant signal. The measurements for the magnetic core indicate that the magnetization induced resonant peaks of the core have relatively higher amplitudes and shorter decay times at low frequencies