Switch-off Time Research Articles

Dynamics of optical matter creation and annihilation in colloidal liquids controlled by laser trapping power

We investigate the dynamics of optical matter creation and annihilation in a colloidal liquid that was employed to construct an all-optical switch. It is revealed that the switching-on process can be characterized by the Fermi-Dirac distribution function, while the switching-off process can be described by a steady state followed by a single exponential decay. The phase transition times exhibit a strong dependence on trapping power. With an increasing trapping power, while the switching-on time decreases rapidly, the switch-off time increases significantly, indicating the effects of optical binding and van der Waals force on the lifetime of the optical matter.

Investigation of Electrical Transient Behavior for Ultrasonic Transducer in on/off Cycles

This paper investigates a theoretical analysis of electrical transient responses of a bolt-clamped Langevin ultrasonic transducer (BLT) and its verifications based on simulations and experiments during on/off transient states immediately after turning on/off. The simulations are determined by a power electronic simulator originally designed for power converters and motor drives. The responses include the open-circuit voltage, the terminal current, the motional current and the mechanical power loss. A linear equivalent circuit model with the initial conditions is stated first. This model is used to derive the responses characterized by simple closed-form equations. The off transient state as specified by the initial conditions regarding switching-off time of an ac sine source for the drive of the BLT is related to cyclic behavior. The derived responses are further checked by simulations and experiments. To obtain the experiments, a test system which contains an ac power supply, a digital oscilloscope and a control switch is needed. Finally, characteristics of the responses and effects of switching-on/off times of the ac sine source on the characteristics are discussed. The characteristics comprise the dc/ac time constants and the maximum/minimum wave amplitudes for the BLT during on/off transient states.

Millisecond radiative recombination in poly(phenylene vinylene)-based light-emitting diodes from transient electroluminescence

The current and electroluminescence transient responses of standard poly(phenylene vinylene)-based light-emitting devices have been investigated. The electroluminescence time response is longer (milliseconds scale) than the current switch-off time by more than one order of magnitude, in the case of small area devices (<0.1cm2). For large area devices (∼6cm2) the electroluminescence decay time decreases from 1.45msto∼100μs with increasing bias voltage. The fast current decay limits the electroluminescence decay at higher voltages. Several approaches are discussed to interpret the observed slow decrease of electroluminescence after turning off the bias. One relies upon the Langevin-type bimolecular recombination kinetics which is governed by the minority carriers (electrons), and another focuses on the slow release of trapped electrons as possible explanations. Additionally, we show that the device current density is mainly determined by the transport of the fastest carriers (holes).

All-Optical Switching in Plant Blue Light Photoreceptor Phototropin

We theoretically analyze all-optical switching in the recently characterized LOV2 domain from Avena sativa (oat) phot1 phototropin, a blue-light plant photoreceptor, based on nonlinear intensity-induced excited-state absorption. The transmission of a cw probe laser beam at 660 nm corresponding to the peak absorption of the first excited L-state, through the LOV2 sample, is switched by a pulsed pump laser beam at 442 nm that corresponds to the maximum initial D state absorption. The switching characteristics have been analyzed using the rate equation approach, considering all the three intermediate states and transitions in the LOV2 photocycle. It is shown that for a given pump pulse intensity, there is an optimum pump pulsewidth for which the switching contrast is maximum. It is shown that the probe laser beam can be completely switched off (100% modulation) by the pump laser beam at 50 kW/cm2 for a concentration of 1 mM with sample thickness of 5.5 mm. The switching characteristics are sensitive to various parameters such as concentration, rate constant of L-state, peak pump intensity and pump pulse width. At typical values, the switch-off and switch-on time is 1.6 and 22.3 micros, respectively. The switching characteristics have also been used to design all-optical NOT and the universal NOR and NAND logic gates.

A Study on Solution of Transient Electromagnetic Response During Transmitting Current Turn-off in the ATTEM System

When the transient electromagnetic method is used for survey, a blind zone will exist because of the existence of transmitting current's switch-off time, the limitation of the receiver winding's resonance frequency, and the distortion of the early transient electromagnetic signal. This paper first analyzes the formation process of the total magnetic field during the switch-off time of transmitting current. We discuss the relation among the primary field, the secondary field and the total transient electromagnetic field and demonstrate the influence of the frequency feature and switch-off time of the receiver winding on the transient electromagnetic field. We then propose a method to remove the effect of the total transient electromagnetic field from the primary field. Using this method, we can obtain the early transient electromagnetic fields during and after the current switch-off period. Using the ATTEM system developed by the Jilin University, we conduct a fault investigation in the Yitong River area of Changchun. The field experiment results show a smaller blind zone of the transient electromagnetic method, a higher accuracy and low resolution of shallow detection. It realizes survey implementation 4 meters below the earth's surface and the clear differentiation of the lower resistance anomalies. The overall results prove the effectiveness of the proposed algorithm.

Impact of hot-carrier stress on gate-induced floating body effects and drain current transients of thin gate oxide partially depleted SOI nMOSFETs

The impact of hot-carrier (HC) stress on thin gate oxide PD SOI nMOSFETs is investigated by analyzing the front and back channel current–voltage characteristics and the switch-off drain current transients. A particular hot-carrier degradation mode, characterized by a turn-around behavior for front gate threshold voltage degradation, is analyzed for devices with different geometries, bias conditions and source/drain architecture. A significant positive back gate threshold voltage shift is also observed after long HC stress. The maximum hot-carrier degradation (HCD) is obtained for the highest front gate biases, corresponding to the conditions of maximum electron valence band injection of majority carriers into the floating body. The presence of the HCD is found to reduce both the generation and the recombination switch-off drain current transient times. Unbiased thermal annealing in the range of 200–250 °C significantly reduces the hot-carrier-induced damage affecting the back channel characteristics. Whereas front gate direct tunnel stress is not causing any significant degradation for stress biases up to about two times the power supply for this technology node and reasonably short stress times, for the highest stress conditions the drain current transients are found to be progressively faster till front gate dielectric breakdown occurs.

Transient response analysis of a Rosen-type piezoelectric transformer and its applications

This paper investigates the characteristics of voltage transient response, such as the maximum voltage, direct current (DC) time constant, alternating current (AC) time constant and oscillation frequency, and their applications for a Rosen-type piezoelectric transformer (PT). The transient response is induced immediately after an AC voltage connected to the PT is switched off. For the applications, the maximum voltage is used to elucidate how to cause an electrical shock for users of the PT under open-circuit operation. The DC time constant and the AC time constant are used to estimate the equivalent resistance of the mechanical loss and the dielectric resistance of the dielectric loss, respectively. Also, the AC time constant is used to estimate the quality factor of the PT. Additionally, the oscillation frequency is used as an antiresonant frequency of the PT. In order to verify the above characteristics and applications, both an equivalent circuit with initial conditions and a drive system with a control switch interposed between the PT and its AC voltage source are adopted to derive the transient response and measure its characteristics. Effects of the load resistance of the PT and the switching-off time of the voltage source on the transient response are measured and discussed.

P-100: Electro-Optic Response of Dual-Frequency LCD

Displays with the twist structure of the LC layer hold a leading position among the LCDs. With low frequency inversion of the dielectric anisotropy sign, the use of double frequency driving in cells filled with LC material allows both switch-on and switch-off times of the electro-optic mode to be reduced. In our paper oscillograms of electrooptic response vs. high frequency (HF) voltage are presented for such LC cells. The bounce, which is induced by the back flow in strongly deformed twist cells, gradually decreases in magnitude with increasing HF voltage. It is suggested that the HF voltage suppresses the back flow in the vicinity of the cell's substrate surface. At the HF voltage that follows the disappearance of the bounce, the short response mode arises.

Electrical Characteristics of a Piezoelectric Vibrator in Open-Circuit Transient State

The electrical characteristics of a piezoelectric vibrator in the open-circuit transient state and its applications are investigated. The characteristics include peak voltages, time constants and oscillation frequency of a voltage transient response induced at the input terminals of the vibrator. These time constants can also be adopted to estimate the dielectric and mechanical losses, the equivalent circuit constants concerning the above losses, and the quality factor of the vibrator. In doing so, an equivalent circuit of the vibrator with an oscilloscope is expressed first. Then, the equivalent circuit under the initial conditions is used to derive a voltage transient response, involving DC and AC components, and its characteristics. Moreover, an AC power control system, including a resonant inverter and a control switch, is constructed to determine the transient responses and their characteristics. The measured results indicate that the losses consumed in the vibrator and the oscilloscope strongly depend on the switching-off time during the transient state.

Finding Electrical Characteristics of a Piezoelectric Transformer through Open-Circuit Operation

In this paper we investigate the electrical transient responses of a piezoelectric transformer (PT) under open-circuit operation and its response times. The transient responses are induced on both sides of the PT immediately after the AC voltage applied to the PT is switched off. An equivalent circuit with initial conditions is expressed first. Then, the equivalent circuit is used to derive an input voltage transient response and its response times. Moreover, an AC power supply system with a control switch is used to determine the transient responses, and an oscilloscope with a smoothing-and-filtering function is used to measure the transient responses and their DC components. Furthermore, the effects of load resistance, switching-off time and operating frequency on the transient responses are measured and discussed. From the measured results, the DC component of each output voltage transient response is almost zero and the AC response time of the output transient response is greatly decreased from 11.5 ms under an output open to 3.0 ms by adopting a 1 MΩ load resistance.

Femtosecond Bragg switching in opal-a-nc-Si photonic crystals

We demonstrate ultrafast all-optical switching in a three-dimensional photonic crystal made of an opal-silicon composite. We show that the switching-on time is faster than 30 fs and determined by the pump pulse duration. The switching-off time is in the order of several picoseconds. The maximum transient change in reflectivity reaches values as high as 46% at the highest excitation power.

Fast switch-off of high voltage 4H–SiC npn bipolar junction transistor from deep saturation regime

It has been demonstrated experimentally that the switch-off time of a high-voltage power (1.8 kV, 3.8 A) 4H–SiC bipolar junction transistor in the deep-saturation mode can be decreased from 200 to 25 ns by using an appropriate switch-off base signal. In such conditions, the switch-off time in the common-emitter configuration can be shorter than the switch-on time.

Protection system for the gyrotrons at TJ-II

Two 500 kW gyrotrons are used in ECRH experiment at TJ-II device. High voltage low output capacity power supply based on fast switching high frequency technology feeds the tubes. Different energy surge components and its destructive influence on a load are analyzed to elaborate design concept of the gyrotron protection system when breakdown occurs. Calculation of energy dissipation shows the necessity of additional protection even in case the switching-off time of the power supply is about 5–10 μs. Crowbar protection is highly recommended for this case. Several TVS-31 vacuum switches connected in series are proposed for such a protection system. It allows up to 10 kA short circuit current and 80 kV (130 kV) hold-off voltage. Switching-on time is less than 1 μs, total time delay is less than 3–5 μs. The system consists of the main switch, triggering unit and arcing sensor to detect the current or current derivation excess. Results of design and HV tests are presented.

Design of high-speed diamond microswitch

In this work, microswitches based on polycrystalline diamond films are investigated. Device properties such as switch-on and switch-off times are calculated and compared to measurement results obtained from fabricated structures. Pre-stress effects, common in free-standing diamond structures, have been included in the model. The influence of various geometric parameters on the transient behaviour of the switches is calculated. Diamond is shown to improve the transient behaviour of the devices in comparison with other materials such as silicon.

A dielectric study on the relaxation and switching behaviour of liquid crystals confined within a colloidal network

The molecular ordering and dynamics of a liquid crystal (LC E7) in the presence of a three-dimensional network of submicron particles have been studied by dielectric relaxation spectroscopy. The field-dependent orientation of the LC was quantified by the director order parameter and modelled by use of a three-phase model. The influence of the colloidal network on the molecular dynamics was assessed from the dielectric spectra, e.g. from the position of relaxation peaks as well as from the strength of the two principal relaxations (α and γ). The spectra changed noticeably upon application of an increasing d.c. bias. A reduction of the threshold field was observed upon addition of colloidal particles to the LC. This was associated with a switching between two metastable states induced by anchoring on the filler particles. Modelled spectra were found to be in good agreement with the experimental data. The modelling showed that the confined LC phase is composed of two fractions, viz. an ordered and a disordered one with different molecular mobilities. Furthermore, switching experiments were conducted at various temperatures in order to evaluate the impact of the colloidal network on the (temperature-dependent) orientational behaviour of the LC molecules. For the colloid-filled LC higher conductivities were found, which gave rise to longer switch-off times.

Reasons of switch-off time decrease in superconductor switches with a buffer layer

Literature referring to superconductor optoelectronic switches report about curious phenomenon of improvement of dynamical properties as a result of introduction of a thin, low thermal conductivity buffer layer. Present paper is a trial of interpretation of this phenomenon basing on analysis of non-stationary temperature fields within the element's structure. The analysis has been made using the method of numeric modelling of thermal processes occurring within the thin-layer structure consisting of high-temperature superconductor YBa 2Cu 3O 7− x sputtered over the MgO substrate and separated with an intermediate SrTiO 3 layer. The essential reason of shortening of key's switch-off time is the fact that the buffer layer limits heat diffusion towards the substrate during switching-on time; as a result its switching-off occurs through heat abstraction towards the high thermal conductivity substrate which temperature is lower than the superconductor's switch-off temperature.

Fast switching of magnetic fields in a magneto-optic trap

Magneto-optic traps which employ current windings to generate pulsed magnetic fields require rapid switch-off times for many applications. Practical difficulties in attaining rapid switch-off of the magnetic field, including the generation of induced currents, are addressed. Several methods for minimizing the switch-off time are presented which do not require complex feedback mechanisms involving direct measurement of the magnetic field.

Chaotic self-pulsation and cross-modulation in a wavelength-selective external-cavity laser diode

Chaotic self-pulsation in a single wavelength external-cavity laser diode is observed. It is shown that the self-pulsation is caused by interdependencies between the optical output power and the compound cavity losses through the refractive index of the laser diode material. Refractive index changes result in a detuning between the externally selected wavelength and the weak internal-mode structure of the anti-reflection coated laser diode. This detuning is directly related to the compound cavity losses. On the one hand, a change in optical output power results in a change of the refractive index via the carrier density. On the other hand, it results in a change of refractive index via temperature changes. Compared to the carrier induced refractive index change, the temperature induced refractive index change is opposite in sign, a factor of /spl sim/10/sup 2/ smaller and slower. The switch-on and switch-off time of the self-pulsation is governed by the carrier life time. The repetition rate of the self-pulsation is governed by the thermal time constant and is in the megahertz region. Cross-modulation resulting from the thermal induced refractive index change is demonstrated. In a two-wavelength double external-cavity laser diode, optical power at one wavelength effects the optical power at the other wavelength. This cross-modulation is shown to be related to previous experiments on a laser neural network. A novel technique is introduced to measure the thermal impedance of a laser diode that is based on the cross-modulation.

Effect of Material Response Time on Optical Bistability in Nonlinear Distributed Feedback Gratings

The dynamic behaviors of nonlinear periodic waveguides with a finite material response time have been investigated by numerically solving both the coupled-mode equations and Debye relaxation equation. When the response time of the nonlinearity is more than the transit time through the grating, a modulational instability is sufficiently suppressed and one can obtain optical bistability. Unlike a nonlinear Fabry-Perot resonator or ring resonators, overshoot in the transmission never takes place in the case of zero detuning. However, a relaxation (or damped) oscillation always takes place in the presence of detuning. It is also found that the switch-on time depends on the material response time and the switch-off time is almost independent of it.

Prandtl-Reuss elastoplasticity: On-off switch and superposition formulae

Constitutive postulates for Prandtl-Reuss elastoplasticity are selected. Based on them, sufficient and necessary conditions for plastic irreversibility are found to be the yield condition and the straining condition. This is then analyzed and it is pointed out that Prandtl-Reuss elastoplasticity is nothing but a two-phase linear system with an on-off switch, which is operated in the pace of an intrinsic measure of plastic irreversibility. Then the temporally global concept of the switch-on time ton and the switch-off time toff and their determination and bound estimation is developed. Owing to the implicit linearity, superposition formulae for the stress response are discovered. As an example, the exact constitutive solutions for circular paths based on the superposition formulae are obtained and ton and toff are determined.