Bistable Hysteresis Loop Research Articles

Peculiar behavior of the magneto-impedance in Fe-based amorphous wires under torsion

The inductive ( ωL) and resistive ( R) components of the impedance of an amorphous wire (Fe 77.5Si 7.5B 15) subjected to torsional stresses are measured. For a critical value of the AC driving current L abruptly increases due to irreversible magnetization processes in the circumferential configuration. Suitable combinations of the AC driving current amplitude and frequency give rise to a peak in the resistive variations and a minimum in the inductance. The inductance shows a bistable asymmetric hysteresis loop ( L vs. H). The torsional stress increases the coercivity of the longitudinal hysteresis loop of the wire but favors the reaching of the saturation magnetization at lower fields.

Giant magnetoimpedance of glass-covered amorphous microwires of Co–Mn–Si–B and Co–Si–B

A study of magnetic hysteresis and giant magnetoimpedance (GMI) in amorphous glass-covered Co–Si–B and Co–Mn–Si–B wires is presented. The wires, about 10 μm in diameter, were obtained by a glass-coated melt spinning technique. Samples with positive magnetostriction (MS) have a rectangular bistable hysteresis loop. A smooth hysteresis loop is observed for wires with nearly zero MS. When the MS is negative, almost no hysteresis is observed. The GMI was measured in the frequency range between 20 Hz and 30 MHz. The shapes of the impedance versus field curves are qualitatively similar to each other for both positive and zero MS samples. The impedance is maximum at zero field, and decreases sharply in the range of 10–20 Oe. For the negative MS wires, when the driving current is small, the impedance is maximum at a finite external field. The position of the maximum approaches zero with increasing current. The contributions of the moment rotation and domain wall motion in the three cases are discussed.

Theoretical analysis of polarization bistability in vertical cavity surface emitting semiconductor lasers

The polarization bistability of vertical cavity surface emitting lasers under external optical injection is analyzed theoretically. It is found that on the condition where the optical gain is blue-shifted relative to the cavity mode, the bistable characteristics of VCSEL's can be improved significantly: (1) low optical power of the external injection light is required, (2) the influence of self-heating effects is minimized, and (3) wide bistable hysteresis loop width can be maintained. Furthermore, it is also shown that the reflectivity of Bragg reflectors should also be optimized to improve the performance of VCSEL's as bistable switches.

Infrared Absorptive and Dispersive Optical Bistabilities of Semiconductor Superlattice Etalons

We have derived Maxwell-Bloch equations of a two-subband model suitable for studying intersubband-transition induced optical-nonlinearities of semiconductor superlattices (SLs). Analytical expressions and numerical illustrations for absorptive and dispersive optical bistabilities (OBs) of SL etalons are given. Both OBs can be realized in infrared region with high frequency selectivity, and their bistable domains and hysteresis loops are much larger than those of a two-level system. The dispersive OB is preferable due to its lower value of the input power.

Intersubband optical nonlinearity and bistable behavior of semiconductor superlattices

The optical nonlinearity and bistability (OB) induced by intersubband transitions (ISBTs) in semiconductor superlattices are studied by means of the Kronig–Penney model and the density-matrix method. The OB state equation in a Fabry–Perot configuration is derived. It is shown that the ISBT-induced OB can be realized over a wide frequency range, and its bistable domain and hysteresis loop are much larger than those of a two-level system. Numerical illustration of the OB behavior in a GaAs/AlxGa1−xAs superlattice is also given.

A Novel Nonlinear Device Based on a Reflective Fiber Optic LP01↔LP02 Mode Converter: Dispersion Bistability

A novel nonlinear device for optical bistability based on a reflective fiber grating through the mode coupling between the LP 01 and counter propagating LP 02 modes (i. e., the reflective LP 01 ↔ LP 02 mode converter) is proposed and investigated. Both the transmissive and reflective properties of this nonlinear device are analysed, which show that the output-versus-input relation exhibits the optical bistability. The dispersion effect of optical bistability, i. e. the bistability in respect to the input wavelength, is also investigated. Our results show that when the input wavelength shifts to the shorter wavelength compared with the Bragg wavelength of DFB structure, the threshold of the switching power for the optical bistability can be reduced. When the input wavelength shifts to the longer wavelength, the bistable hysteresis loop is widened and the bistability is strengthened but this is at the expense of increasing the threshold of switching power on. In addition, we also demonstrate that both the threshold powers of switching on and off for a nonlinearly reflective LP 01 ↔ LP 02 mode converter are much lower than those of a conventional nonlinear fiber Bragg grating reflector.

Optical bistability via a phase fluctuation effect of the control field

The steady-state behavior in a unidirectional cavity has been analyzed by taking into account the effect of phase fluctuation in the control field based on a Λ-type atomic model. It is shown that even if both fields are in resonance with the corresponding atomic transitions, optical bistability can still be realized due to a phase fluctuation in the control field. Furthermore, the bistable hysteresis loop becomes wider as the linewidth increases.

Dynamic behavior of reflection optical bistability in a nonlinear fiber ring resonator

We present an analysis of the dynamic behavior of a nonlinear fiber ring resonator when an optical pulse with an arbitrary shape envelope is incident into it through a fiber directional coupler. The transient analysis is based on the extension of a well-known multiple-beam interference method to non-linear transmission problems. The steady-state analyses reported so far predict that the ring resonator exhibits reflection optical bistability in the input-output characteristics under appropriate conditions. But, our transient analysis shows that a nearly periodical oscillation of the transmitted power always takes place at a suitable initial detuning when the resonator has no loss or a small loss. It seems that the present instability is caused by the repetition of accumulation and release of the power in the ring resonator. We can obtain a bistable hysteresis loop by introducing a loss to the directional coupler. The dynamic behavior of bistability in a nonlinear fiber ring resonator with coupler loss is then investigated. It is found that a remarkable undershoot and overshoot occur in the switch-off curve and switch-on curve, respectively.

Multiple bistability in an optical fibre double-ring resonator by using degenerate two-wave mixing

A theoretical study is presented of multiple bistability in a single-mode optical fibre double-ring resonator using an all-fibre scheme involving degenerate two-wave mixing. Two successive bistable hysteresis loops (one is a normal type and another an inverting type) are formed in the input-output transmission curve. The dependence of the multiple bistability on major parameters of the fibres and the couplers is investigated.

Bistability of the pump beam in one-coupler and two-coupler optical fiber ring resonators by using degenerate two-wave mixing

Bistability in the pump beam of one-coupler and two-coupler single-mode optical fiber ring resonators by using two different all-fiber schemes of degenerate two-wave mixing is demonstrated theoretically. The bistable behavior of the pump beam (or the input beam) can be controlled by changing the intensity of either the pump beam or the input beam. Depending on the scheme of the degenerate two-wave mixing and the controlling beam, the bistable hysteresis loop of the pump beam may be a normal type or an inverting type. The dependence of the bistability on some major parameters of the fibers and the couplers is investigated.

Observation of Optical Bistability Hysteresis Loop with Surface Waves in Doped Polymer Film

Optical bistability hysteresis loop has been observed experimentally with a setup using prism excitation of surface wave in a doped polymer thin film. A simple model has been developed to analyze its operation. The observed bistability hysteresis loop can be explained in terms of surface plasmon excitation and laser induced refractive index variations.

Observation of Optical Bistability Hysteresis Loop with Surface Waves in Doped Polymer Film

Optical bistability hysteresis loop has been observed experimentally with a setup using prism excitation of surface wave in a doped polymer thin film. A simple model has been developed to analyze its operation. The observed bistability hysteresis loop can be explained in terms of surface plasmon excitation and laser induced refractive index variations.

Tension annealing cold-drawn amorphous CoFeSiB wires

Amorphous magnetostrictive Co-Fe-Si-B wires exhibiting square and bistable hysteresis loops have been obtained by tension annealing treatments of the wires cold-drawn to lower than 0.05 mm in diameter from the as-quenched state (0.125 mm in diameter). Bistable switching characteristics were observed even in a 1-cm length of the annealed wire. The switching field is variable from 0.3 to 2.3 Oe with annealing condition, and fluctuation of the individual value is very small. It seems to be useful not only for a small pulse generator element, but also for classifying or identifying objects. Wires with asymmetric hysteresis loops have also been realized using this method.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Bistable magnetization reversal in 50 µm diameter annealed cold-drawn amorphous wires

Amorphous magnetostrictive 50 μm diameter Fe <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">77.5</inf> Si <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">7.5</inf> B <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">15</inf> wires exhibiting square and bistable hysteresis loops have been obtained by field-tension annealing and flash annealing treatments of cold-drawn as-quenched wires. Highest switching field, 1.3 Oe, and domain drive field, 0.5 Oe, for annealing temperature 330 C , time 30 min, axial tension 150 Kg/mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> and axial field 200 Oe are an order of magnitude improvement over the as-quenched (AQ) state. Corresponding induced peak voltage is 0.5 mV/turn with exciting sinusoidal field 2 Oe and 60 Hz. Shorter pulse generation elements (≈ 2 cm) than for AQ wires (≈ 6 cm) were realized with 0.5 mV/turn peak voltage. Maximum squareness ratio is close to unity, twice that of AQ (125 μm) wires.

Theory of absorptive bistability

A model for a resonatorless absorptive optical bistability in laser-excited semiconductors is presented. The intensity-dependent absorption coefficient is calculated microscopically taking into account band-gap renormalization and band filling due to formation of an electron-hole plasma. The spatial and temporal variations of the carrier density and the light intensity in the crystal are calculated from solutions of their coupled transport equations. An intrinsically bistable propagation mechanism for a density kink is found, which gives rise to additional structures in the bistable hysteresis loop. The influence of different carrier diffusion coefficients on the results is calculated.