Efficient All-optical Switching Research Articles

Optical bistability via dual electromagnetically induced transparency in a coupled quantum-well nanostructure

We investigate optical bistability (OB) behavior in an asymmetric three-coupled quantum well structure inside a unidirectional ring cavity. By controlling the assisting coherent driven field and the frequency detunings of the two control laser fields, we find that the appearance and disappearance of OB can easily be controlled by adjusting the positions of the dual electromagnetically induced transparency windows. Analysis in the dressed-state picture is also given. Our scheme may be used for building more efficient all-optical switches and logic-gate devices for optical computing and quantum information processing.

Highly efficient all-optical switching of magnetization in GdFeCo microstructures by interference-enhanced absorption of light

Employing magnetization-sensitive microscopy techniques, we address the light-induced magnetization dynamics of patterned samples of rare-earth transition metal alloys. We experimentally find that smaller structures require a lower energy density to undergo all-optical switching of the magnetization. With the aid of simulations we explain this reduction in terms of enhanced light absorption by interference of the light within the structure. This results in a decrease of about 60% in the energy densities required for all-optical switching compared with those in continuous thin films of the same alloy. Moreover, we envisage that an energy lower than 10 fJ should be sufficient to switch a 20 × 20 nm 2 structure.

Nonlinear Plasmonic Cloaks to Realize Giant All-Optical Scattering Switching

Here we extend the reach of Fano resonant coupling by combining this concept with cloaking and plasmonic resonances in a single nonlinear nanoparticle, in order to realize giant all-optical scattering nanoswitches controlled by moderate pumping intensities. We show that a core-shell nonlinear plasmonic particle may be designed to abruptly switch from being completely cloaked to being strongly resonant, with up to a 40 dB cross-sectional difference. Self-tunable optical cloaks and resonant scatterers are envisioned for use as efficient all-optical switches and nanomemories.

Optical bistability and multistability via dual electromagnetically induced transparency windows

We investigate the optical bistability and multistability behaviors in a four-level Λ-type system using a microwave field driving a hyperfine transition between two lower states inside a unidirectional ring cavity. By controlling the microwave field and the frequency detunings of the three fields, we find that the appearance and disappearance of OB (or OM) can easily be controlled by adjusting the positions of the dual-EIT windows. Our scheme may be used for building more efficient all-optical switches and logic-gate devices for optical computing and quantum information processing.

ANALYSIS OF THE OPTICAL MULTISTABILITY BEHAVIOR IN A FOUR-LEVEL ATOMIC SYSTEM WITH AN ASSISTING MICROWAVE-DRIVEN FIELD

We show the steady-state optical multistability (OM) behavior in a four-level atomic system inside a unidirectional ring cavity. We find that the intensity and the detunings of the fields can affect the optical multistability behavior dramatically, which can be used to control the transition from OM to OB or vice versa without the need to resort to the effect of spontaneously generated coherence (SGC). The effect of the atomic cooperation parameter on OM is also studied. Our scheme may be used for building more efficient all-optical switches and logic-gate devices for optical computing and quantum information processing.

Efficient All-Optical Switching Using Slow Light within a Hollow Fiber

We demonstrate a fiber-optical switch that is activated at tiny energies corresponding to a few hundred optical photons per pulse. This is achieved by simultaneously confining both photons and a small laser-cooled ensemble of atoms inside the microscopic hollow core of a single-mode photonic-crystal fiber and using quantum optical techniques for generating slow light propagation and large nonlinear interaction between light beams.

Control of the switch between optical multistability and bistability in three-level V-type atoms

We theoretically investigated a hybrid absorptive–dispersive optical bistability and multistability behaviour in a three-level V-type system using a microwave field driving a hyperfine transition between two upper excited states inside a unidirectional ring cavity. We find that the intensity and the frequency detuning of the coupling field as well as the intensity of the microwave field can affect the OM behaviour dramatically, which can be used to control the transition from OM to OB or vice versa without need to resort the effect of the quantum interference. The effects of the phase, the quantum interference and the atomic cooperation parameter on the OM are also studied. Our scheme may be used for building more efficient all-optical switches and logic-gate devices for optical computing and quantum information processing.

Nano-Dispersed Organic Liquid and Liquid Crystals for All-Time-Scales Optical Switching and Tunable Negative-and Zero- Index Materials

We present an overview of recent results obtained in nano-dispersed nonlinear neat organic liquids and liquid crystals. Experimental observations confirm the enhancement of nonlinear absorption in gold nano-spheres doped neat nonlinear liquids and extension of the bandwidth of efficient all-optical switching operation for visible-near infrared lasers in time scales ranging from sub-picoseconds through nanoseconds and microseconds and longer. Similar nano-particulate doped liquid crystal films also exhibit efficient all-optical switching capabilities for microseconds – cw lasers. Meta-materials fabricated with core-shell nano-spheres dispersed nematic liquid crystals show effective refractive indices that are tunable from negative through zero to positive values.

Efficient all-optical dual-channel switches, logic gates, half-adder, and half-subtracter in a one-dimensional photonic heterostructure

We have proposed a kind of one-dimensional photonic heterostructure for efficient all-optical dual-channel switches, logic gates, half-adder, and half-subtracter, based on the combined usage of two high-quality and one low-quality resonant modes with their electric fields strongly enhanced in the same defect regions. By exciting the low-quality modes with a low-intensity pump beam, one can efficiently shift the spectral positions of two high-quality modes and thus simultaneously control the propagation of signals at two frequency channels. For an AlGaAs/SiO2 heterostructure with two GaAs defect regions, the peak pump intensity can be lower than 6.2mW/mm2. When the frequency of the signal light is properly set relative to the two high-quality modes, its propagation can be logically controlled by pump beams with low intensity on the order of 10mW/mm2. Moreover, the frequency interval between the two high-quality modes and that between the high- and low-quality modes are adjustable in a wide range.

Optical bistability in a three-level semiconductor quantum-well system

Optical bistable behavior in a unidirectional ring cavity (or a Fabry–Perot cavity) containing a semiconductor quantum well, described as a three-level ladder-type system with similar transition energies, has been studied. The system interacts with a strong driving field which is in two-photon resonance with the intersubband transition and thus simultaneously drives all three levels into phase-locked quantum coherence. The threshold for switching to upper branch of the bistable curve is found to be reduced due to the presence of quantum interference. Such system can be used for making efficient and fast all-optical switching devices.

Stable propagation and all-optical switching in planar waveguide–antiwaveguide periodic structures

A planar periodic nonlinear structure composed of alternating waveguiding (WG) and antiwaveguiding (AWG) sections is considered. Detailed simulations demonstrate that fairly long stable propagation of a beam in this structure is achieved when the lengths of the AWG and WG sections are equal, i.e., both ∼25 wavelengths. Another interesting result is that the stable-propagation length is much larger in both a uniform AWG and in the alternate structure if the input has a Gaussian transverse profile rather than a specially prepared shape that corresponds to the eigenmode of the (anti)waveguide. It is demonstrated that an efficient all-optical switching scheme, controlled by a weak hot spot, which is created by a laser beam shone normally to the structure and focused off axis near the end of any AWG section, can readily be realized in the alternate waveguide.

On the mechanism of non-linear optical attenuation at 1.3–1.5 μm in arsenic sulfide and tellurium oxide glasses

The mechanism of optical non-resonant non-linear refraction and absorption/attenuation in glasses at 1.3–1.5 μm is of interest for efficient all-optical switching in optical fibre telecommunications. We discuss the mechanism of non-resonant non-linear attenuation (loss) at 1.3–1.5 μm in glasses with the largest linear refractive indices, such as As 2S 3- and TeO 2-based glasses. These glasses are transparent and possess the largest non-resonant non-linear refraction at 1.3–1.5 μm to date (up to 10 −14 cm 2/ W ), allow single-mode fiberization and therefore are suitable for all-optical fibre switching. We show that with a single beam Z-scan technique we identify the contribution of small-angle non-linear scattering to the total non-linear attenuation at 1.3–1.5 μm. We show that small-angle non-linear scattering does contribute to the non-linear attenuation at such irradiances at which non-linear absorption is not present yet.

All-optical switching based on cascading of second-order nonlinearities in a periodically poled titanium-diffused lithium niobate waveguide

We report efficient all-optical switching by using a periodically poled titanium-diffused lithium niobate (Ti:PPLN) waveguide. The periodically domain inversion of the Ti:PPLN waveguide is achieved by electric field poling. The switching is driven by the second-order nonlinear effect of the cascading of phase-matched sum-frequency-generation and difference-frequency-generation processes. It is found that about 12% of the signal is switched by a 20-W gate power.

Nonlinear phase shift and all-optical switching in quasi-phase-matched quadratic media

Recently it was shown that in quasi-phase-matched quadratic media the average intensities are subject to an induced Kerr effect. We analytically study the influence of this induced cubic nonlinearity on the amplitude and phase modulation of the fundamental wave and predict efficient all-optical switching.

All-optical switching via second harmonic generation in a nonlinearly asymmetric directional coupler

Taking advantage of the nonlinear phase-shift obtainable via up- and down-conversion of a beam to and from its second- harmonic, an efficient all-optical switch can be realized adopting the standard directional coupler configuration with strong nonlinear asymmetry. Using coupled-mode theory we numerically demonstrate power switching in a half-beat length coupler with remarkable functional characteristics in a wide range of parameters.

Ultrafast all-optical switching in semiconductor nonlinear directional couplers at half the band gap

Efficient ultrafast all-optical switching in nonlinear directional couplers made of AlGaAs and AlGaAs/GaAs quantum wells near half the band gap is reported. The switching is limited by multiphoton absorption which is dominated by three-photon absorption in this spectral range. The three-photon absorption in the quantum well nonlinear directional coupler is stronger than that of bulk AlGaAs. Autocorrelations of the output pulses in the bar and cross states confirm pulse breakup through nonlinear coupling, and illustrate the effects of multiphoton absorption. All sets of experimental data are fitted well by a theoretical model.