Low-power Control Signals Research Articles

All optical Q-switched laser based spiking neuron

This paper studies theoretically the use of a Q-switch laser with side light injection as a spiking all-optical neuron for photonic spiking neural networks (PSNN). Ordinary differential equations for the multi-section laser are presented, including terms for the side light injection for gain quenching and saturable absorption. The behaviour of the laser mimics that of a spiking neuron with ultrafast pico-second scale response and low power control signals.

Light Propagation in Confined Nematic Liquid Crystals and Device Applications

Liquid crystals are interesting linear and nonlinear optical materials used to make a wide variety of devices beyond flat panel displays. Liquid crystalline materials can be used either as core or as cladding of switchable/reconfigurable waveguides with either an electrical or an optical control or both. In this paper, materials and main device structures of liquid crystals confined in different waveguide geometries are presented using different substrate materials, such as silicon, soda lime or borosilicate glass and polydimethylsiloxane. Modelling of the behaviour of liquid crystal nanometric molecular reorientation and related refractive index distribution under both low-frequency electric and intense optical fields is reported considering optical anisotropy of liquid crystals. A few examples of integrated optic devices based on waveguides using liquid crystalline materials as core for optical switching and filtering are reviewed. Reported results indicate that low-power control signals represent a significant feature of photonic devices based on light propagation in liquid crystals, with performance, which are competitive with analogous integrated optic devices based on other materials for optical communications and optical sensing systems.

Heart rate control during treadmill exercise using input-sensitivity shaping for disturbance rejection of very-low-frequency heart rate variability

Abstract Background Automatic and accurate control of heart rate (HR) during treadmill exercise is important for prescription and implementation of training protocols. The principal design issue for feedback control of HR is to achieve disturbance rejection of very-low-frequency heart rate variability (VLF-HRV) with a level of control signal activity (treadmill speed) which is sufficiently smooth and acceptable to the runner. This work aimed to develop a new method for feedback control of heart rate during treadmill exercise based on shaping of the input sensitivity function, and to empirically evaluate quantitative performance outcomes in an experimental study. Methods Thirty healthy male subjects participated. 20 subjects were included in a preceding study to determine an approximate, average nominal model of heart rate dynamics, and 10 were not. The design method guarantees that the input sensitivity function gain monotonically decreases with frequency, is therefore devoid of peaking, and has a pre-specified value at a chosen critical frequency, thus avoiding unwanted amplification of HRV disturbances in the very-low-frequency band. Controllers were designed using the existing approximate nominal plant model which was not specific to any of the subjects tested. Results Accurate, stable and robust overall performance was observed for all 30 subjects, with a mean RMS tracking error of 2.96 beats/min and a smooth, low-power control signal. There were no significant differences in tracking accuracy or control signal power between the 10 subjects who were not in the preceding identification study and a matched subgroup of subjects who were (respectively: mean RMSE 2.69 vs. 3.28 beats/min, p = 0.24; mean control signal power 15.62 vs. 16.31 × 10 −4 m 2 /s 2 , p = 0.37). Substantial and significant reductions over time in RMS tracking error and average control signal power were observed. Conclusions The input-sensitivity-shaping method provides a direct way to address the principal design challenge for HR control, namely disturbance rejection in relation to VLF-HRV, and delivered robust and accurate tracking with a smooth, low-power control signal. Issues of parametric and structural plant uncertainty are secondary because a simple approximate plant model, not specific to any of the subjects tested, was sufficient to achieve accurate, stable and robust heart rate control performance.

Hysteresis Modeling of Smart Structure MR Devices using Describing Functions

Magnetorheological (MR) devices have been quite promising for semiactive control, thanks to their capability of adjusting structural parameters, under a low-power control signal, to effectively withstand severe dynamic loadings including seismic events. MR devices, using visco-elastic and ferromagnetic materials, are subject to hysteresis, which may degrade the performance of smart structures. Therefore, this multivalued nonlinearity needs to be properly modeled and characterized for control and health monitoring. As engineering structures operate as low-pass filter in normal conditions, it is suitable to use the classical describing function (DF) method for modeling and analysis of the hysteretic behaviors in MR device-based smart structures. Data obtained from characterizing tests are recorded in look-up tables to obtain the DFs for these devices, using a curve-fitting technique. The proposed DFs are then useful in structural frequency analysis. Experimental results are reported for a steel beam with MR pin joints subject to quake-induced vibrations provided by a shake table.

All-Optical Reversible Logic Gates with Optically Controlled Bacteriorhodopsin Protein-Coated Microresonators

We present designs of all-optical reversible gates, namely, Feynman, Toffoli, Peres, and Feynman double gates, with optically controlled microresonators. To demonstrate the applicability, a bacteriorhodopsin protein-coated silica microcavity in contact between two tapered single-mode fibers has been used as an all-optical switch. Low-power control signals (<200 μW) at 532 nm and at 405 nm control the conformational states of the protein to switch a near infrared signal laser beam at 1310 or 1550 nm. This configuration has been used as a template to design four-port tunable resonant coupler logic gates. The proposed designs are general and can be implemented in both fiber-optic and integrated-optic formats and with any other coated photosensitive material. Advantages of directed logic, high Q-factor, tunability, compactness, low-power control signals, high fan-out, and flexibility of cascading switches in 2D/3D architectures to form circuits make the designs promising for practical applications.

Design of All-Optical Reconfigurable Logic Unit With Bacteriorhodopsin Protein Coated Microcavity Switches

We present a theoretical design of an all-optical reconfigurable logic unit based on optically controlled microcavity switches, for realization of all-optical computing circuits. It can execute different logic and arithmetic operations such as half and full adder or subtractor, by only changing the control inputs on the same circuit. Theoretical designs considering bacteriorhodopsin (BR) protein coated microcavities in tree architecture have been presented. The combined advantages of high Q-factor, tunability, compactness, switching of near-IR signals at telecom wavelengths (1310/1550 nm) with low-power control signals, and flexibility of cascading switches to form circuits, makes the designs promising for practical applications. They combine the ultrahigh sensitivity of both BR and microresonators to define a novel paradigm of all-optical computing based on hybrid nanobiophotonic integration.

Novel proposal for all-optical Fredkin logic gate with bacteriorhodopsin-coated microcavity and its applications

We present a design of the conservative, reversible, and universal all-optical Fredkin logic gate based on a single bacteriorhodopsin (BR)-protein-coated silica microcavity. The switching of a near-IR laser beam at 1310 or 1550 nm by photoactivating a silica microsphere coated with BR monolayers with a low power control signal at 532 nm, in contact between two tapered single-mode fibers, is used as a template for a four-port tunable resonant coupler Fredkin gate. The proposed gate has also been used to design low-power all-optical AND, OR, NOT, XOR, and X-NOR gates and full-adder and demultiplexer/multiplexer circuits. The advantages of high Q-factor, tunability, compactness, low-power control signals, high fan-out, and flexibility of cascading switches in 2-D to 3-D architectures to form circuits, makes the designs promising for practical applications. The proposed design provides a new paradigm for hybrid nanobiophotonic integration for all-optical computing.

All-optical switching with bacteriorhodopsin protein coated microcavities and its application to low power computing circuits

We show all-optical switching of an input infrared laser beam at 1310 nm by controlling the photoinduced retinal isomerization to tune the resonances in a silica microsphere coated with three bacteriorhodopsin (BR) protein monolayers. The all-optical tunable resonant coupler re-routes the infrared beam between two tapered fibers in 50 μs using a low power (<200 μW) green (532 nm) and blue (405 nm) pump beams. The basic switching configuration has been used to design all-optical computing circuits, namely, half and full adder/subtractor, de-multiplexer, multiplexer, and an arithmetic unit. The design requires 2n−1 switches to realize n bit computation. The designs combine the exceptional sensitivities of BR and high-Q microcavities and the versatile tree architecture for realizing low power circuits and networks (approximately mW power budget). The combined advantages of high Q-factor, tunability, compactness, and low power control signals, with the flexibility of cascading switches to form circuits, and reversibility and reconfigurability to realize arithmetic and logic functions, makes the designs promising for practical applications. The designs are general and can be implemented (i) in both fiber-optic and integrated optic formats, (ii) with any other coated photosensitive material, or (iii) any externally controlled microresonator switch.

A compact single layer injection-locked linear scanning array

A compact, single layer, CPW-fed, patch scanning array architecture using injection locking at 9.83 GHz is presented. The patch antennas are printed on the front side of the substrate while the electronics are situated at the back side leading to a simple and compact design. The unit element for the array is a self oscillating active patch antenna with a GaAs FET centered behind the patch for tight packing. The feedback for the oscillator is provided through electromagnetic coupling using a twin-slot arrangement behind the patch. A low power control signal is injected through parasitic coupling at the CPW side of the circuit. Phase shifting of the elements is achieved by electronically adjusting the gate voltage of the GaAs FETs. A scan range of -12/spl deg/- +9.5/spl deg/ is obtained for a four element prototype array.

Frequency Converter Technology for Aircraft Power Systems

This paper presents an overview of frequency converter technology in qualitative terms, with the objective of conveying insight into the rationale for selecting particular power circuit arrangements. The tradeoffs involved in the design process are discussed, especially with regard to factors affecting size and performance. At present, the practical choice for an aircraft converter is between a cycloconverter and a rectifier-dc link-inverter. HE introduction of high-power semiconductor devices has enabled the development of efficient static power conversion equipment that can perform the frequency trans- formation required to match a variable-speed generator to constant-frequency load in an aircraft power system. Over the past 20 years, considerable effort has been expended in the in- vestigation of different circuit approaches, reduction of size, and refinement of controls to achieve the desired perform- ance. Present variable-speed, constant-frequency (VSCF) sys- tems can deliver power of a quality equal to or better than that available from a conventional constant-speed drive system. The most important controlled semiconductor device for high-power applications is the thyristor. When the anode is positive with respect to the cathode, a low-power control signal applied to the gate electrode will trigger the device from a blocking to a conducting state. However, gate control cannot turn the current off (except in specially designed devices); the circuit in which the thyristor operates must in some way extinguish the current and then apply reverse voltage for a short time before forward voltage can be reapplied. This external process is known as commutation, and is conveniently classified as either natural commutation or forced commutation. When the power source is ac, natural commutation for thyristor devices can be obtained if the circuit is constrained to operate within the limits of the cyclic voltage reversals. With dc sources, at least some of the devices must be force commutated. Since forced commutation requires additional circuit components, it is obviously preferable to employ a naturally commutated converter, provided that it can satisfy the per- formance objectives. When forced commutation is necessary, additional commutation components can be avoided if power transistors can be used, since they can be forced off by removing or reversing their base current. However, tran- sistors are limited in their power rating so that converters employing transistors are similarly restricted. Phase-Controlled Converters