All-optical Switching Schemes Research Articles

Optical fibers with a frequency-dependent Kerr nonlinearity: Theory and applications

This review provides a detailed discussion of both the mathematical treatment and the impact of a frequency-dependent Kerr nonlinearity on the propagation of short pulses in optical fibers. We revisit the theoretical framework required to deal with the frequency dependence of the nonlinear response without incurring any physical inconsistencies, such as the non-conservation of the photon number. Then, we point out the role of the zero-nonlinearity wavelength, its interplay with the zero-dispersion wavelength, and their influence on evolution of optical pulses in optical fibers, specifically by looking at soliton propagation and the ensuing generation of Cherenkov radiation. Finally, by means of a space–time analogy involving the collision of a weak control pulse and an intense soliton, we describe an all-optical switching scheme in the presence of a zero-nonlinearity wavelength within a photon-conserving framework.

High-efficiency all-optical switching based on broadband coherent perfect absorption in an atom-cavity system

We propose an ultrahigh-efficiency and broadband all-optical switching scheme based on coherent perfect absorption (CPA) in linear and nonlinear excitation regimes in a cavity quantum electrodynamics (CQED) system. Two separate atomic transitions are excited simultaneously by two signal fields coupled from two ends of an optical cavity under the collective strong coupling condition. Three polariton eigenstates are produced which can be tuned freely by varying system parameters. The output field intensities of multiple channels are zero when the CPA criterion is satisfied. However, destructive quantum interference can be induced by a free-space weak control laser when it is tuned to be resonant to the polariton state. As a consequence, the CQED system acts as a coherent perfect light absorber/transmitter as the control field is turned on/off the polariton resonances. In particular, the proposed scheme may be used to realize broadband multi-throw all-optical switching in the nonlinear excitation regime. The proposed scheme is useful for constructing all-optical routing, all-optical communication networks and various all-optical logic elements.

GaN film optical nonlinearity: wavelength dependent refractive index for All-Optical switching application

Gallium Nitride (GaN) is fast becoming a potential replacement for silicon in complex electronic and photonics circuitries and systems. At higher optical intensity, optical effects such as non-linear effects would become non-trivial. To this end, we investigated nonlinear optical properties of metal–organic chemical vapor deposited GaN. Specifically, continuous-wave laser Z-scan techniques were employed to obtain nonlinear refractive index, n2, of a 1-µm thin layer on a c-plane sapphire substrate. FESEM, PL, XRD and EDS analysis confirmed the good quality growth of GaN thin film. We detected a reversal of polarity of the n2 value at 637 nm and 405 nm of CW laser excitation and femtosecond laser pulse at 808 nm. This is substantiated by theoretical calculation of GaN’s n2 showing sign switchover at wavelength shorter than 420 nm. This presents a new all-optical switching scheme based on the switchover of wavelength dependent n2. These findings point to opportunities for GaN-based integrated photonics for nonlinear and quantum photonics applications.

Laser-Induced Hole Coherence and Spatial Self-Phase Modulation in the Anisotropic 3D Weyl Semimetal TaAs.

Laser-induced electron coherence is a fascinating topic in manipulating quantum materials. Recently, it has been shown that laser-induced electron coherence in 2D materials can produce a third-order nonlinear optical response spatial self-phase modulation (SSPM), which has been used to develop a novel all-optical switching scheme. However, such investigations have mainly focused on electron coherence, whereas laser-induced hole coherence is rarely explored. Here, the observation of the optical Kerr effect in 3D Weyl semimetal TaAs flakes is reported. The nonlinear susceptibility (χ(3) ) is obtained, which exhibits a surprisingly high value (with = 9.9×10-9 e.s.u. or 1.4×10-16 m2 V-2 at 532nm). This cannot be explained by the conventional electron mobility, but can be well understood by the unique high anisotropic hole mobility of TaAs. The wind-chime model and χ(3) carrier mobility correlation adequately explain the results, suggesting the crucial role of laser-induced nonlocal ac hole coherence. These observations extend the understanding of SSPM from 2D to 3D quantum materials with anisotropic carrier mobility and from electron coherence to hole coherence.

Temporal reflection and refraction in the presence of a zero-nonlinearity wavelength.

We put forth a theoretical model allowing for the analysis of short-pulse interactions at time boundaries in waveguides with arbitrary frequency-dependent nonlinear profiles, in particular those exhibiting a zero-nonlinearity wavelength. Moreover, this is performed within a photon-conserving framework, thus circumventing use of the nonlinear Schrödinger equation in such scenarios, as it may lead to unphysical outcomes. Results indicate that the waveguide zero-nonlinearity wavelength has a great influence on said interactions, specifically by defining spectral bands where either signal total reflection or signal transmission can occur. We believe these findings to be of relevance in the area of all-optical switching schemes based on the interaction of short pulses in nonlinear media.

Interaction-free bidirectional multi-channel all-optical switching in a multi-level coupling atom-cavity system.

We propose a scheme of interaction-free bidirectional multi-channel all-optical switching in a multi-level coupling system consisting of four-level atoms confined in a cavity and coupled by a free-space control laser. A signal laser field is coupled into the cavity and excites two separate transitions of atoms simultaneously under the collective strong coupling condition. The transmission and reflection of signal fields form bidirectional output channels. A free-space control laser induces destructive quantum interference in the multi-level excitation of an atom-cavity system, which can be used to switch on/off the output signal lights of transmission/reflection channels. There is no direct coupling of control light and signal light through the cavity-confined atoms because the output of signal light is nearly totally suppressed to the opposite direction when control light is present. The proposed all-optical switching scheme can be realized with high switching efficiency, broad bandwidth, and weak light intensity. It may be useful for future devices of optical routing, optical communications, and various quantum logic elements.

Numerical study of all-optical switching of ferromagnetic thin film using temporally controlled optothermal and optomagnetic pulses

All-optical switching (AOS) allows the ultrafast control of magnetization states in a thin film and has the potential to increase the magnetic data recording speed by a few orders of magnitudes. The mechanism of AOS in ferrimagnetic materials has been successfully explained by using the magnetic circular dichroism and the angular momentum transfer between sublattices, but the mechanism for the observed AOS in the ferromagnetic materials is still under debate. One hypothesis explains the AOS in the ferromagnetic film by hypothesizing the existence of a prolonged magnetic field excited by the inverse Faraday effect. Theoretical calculation suggests that the switching result is sensitive to the magnetic field during the cooling down process, particularly across the Curie temperature. However, the optomagnetic excitation originates from the same pulse and decays faster than the optothermal response, which typically makes the induced magnetic field fade away before the material reaches the Curie temperature. Here, we numerically study a dual-pulse AOS scheme that temporally and spatially decouples the ultrafast optothermal and optomagnetic responses and allows the timing control of the induced magnetic field to facilitate the AOS. This dual-pulse scheme may guide to experimentally confirm the hypothesis of the prolonged magnetic field for the ferromagnetic AOS process.

Spin-optical solitons in liquid crystals

A theoretical and numerical investigation shows the formation of spin-orbit optical solitons in nematic liquid crystals as a consequence of a nonlinear modulation of the optic axis and the resulting geometric phase in the birefringent medium. The unusual self-trapping mechanism may allow for new all-optical waveguiding and switching schemes.

Quantum Optical Switching Based on Local Single-excitation Resonance

We note that the all-optical switching schemes are based on electromagnetically induced transparency. In this paper, we will study the optical switching based on another mechanism, i.e., local single-excitation resonance. The average-photon-number distribution in the steady state is studied in a system of two linearly coupled cavities, where one of cavity includs a two-level atom inside, and the cavity without the atom is driven by a classical light field. We find that the steady-state average-photon-number distribution of the two cavities can be controlled, which means that our scheme can be used as a quantum optical switching. Our finding may has potential application in quantum information and quantum computation.

Thermal-motion-induced optical switching with standing-wave coupled atom-cavity system

We report an experimental scheme of three-channel all-optical switching based on the conversion between single and double dark states in an atom-ring-cavity system driven by a coherent standing-wave coupling field. By turning on and off the counter-propagating part of the coupling field, the switching for the probe field at three different frequencies is simultaneously achieved. We give a theoretical interpretation to the experimental results via the intracavity susceptibility for thermal atoms at different velocities. The switching performance is experimentally analyzed by introducing an additional coherent pumping light.

Design and performance analysis of all-optical cascaded adder using SOA-based MZI

With the performance enhancements in all-optical signal processing and switching schemes in terms of data rate and processing speed, various devices enabled with all-optical operation are becoming primary requirements for current and future telecommunications and data networks. All-optical logic gates represent the best solution to realize both combinational as well as sequential devices in the optical domain, representing the basic building blocks for optical computing circuits. We propose herein an all-optical cascaded adder whose elementary blocks are a half-adder and full-adder, designed using semiconductor optical amplifier (SOA)-based Mach–Zehnder interferometer (MZI) gate configurations. They have high thermal stability and require low power. The nonlinear effects in the SOA device are used to implement different logic operations. The proposed cascaded adder was simulated in OptiSystem. The optical signal-to-noise ratio, bit error rate (BER), and Q-factor values were evaluated for different data rates. The design showed good performance up to 60 Gbps. The proposed design could find application in implementation of multistage arithmetic logic units.

Nonlinear refractive index induced collision and propagation of nematicons

Nematic liquid crystals (NLCs) have proved to be excellent materials for nonlinear optics and its applications because of their large nonresonant nonlinearity and their extended spectral transparency. We demonstrate the exemplary collision scenario of both optical solitons and nematicons induced by the nonlinear refractive index in nematic liquid crystals. We invoke Hirota's bilinearization method for two coupled partial differential equations governing the dynamics of self-focusing of a laser light in a nematic liquid crystal system. We believe that this type of collision of optical solitons and nematicons reveals the many possibilities of all-optical switching schemes for spatial demultiplexing, network reconfiguration and logic gates.

Transverse optical instability patterns in semiconductor microcavities: Polariton scattering and low-intensity all-optical switching

We present a detailed theoretical study of transverse exciton-polariton patterns in semiconductor quantum-well microcavities. These patterns are initiated by directional instabilities in the uniform pump-generated polariton field and are measured as optical patterns in a transverse plane in the far field. Based on a microscopic many-particle theory, we investigate the spatio-temporal dynamics of the formation, selection, and optical control of these patterns. An emphasis is placed on a previously proposed low-intensity, all-optical switching scheme designed to exploit these instability-driven patterns. Simulations and detailed analyses of simplified and more physically transparent models are used. Two aspects are studied in detail. First we study the dependencies of the stability behaviors of various patterns, as well as transition time scales, on parameters relevant to the switching action(the degree of built-in azimuthal anisotropy in the system and the switching beam intensity). It is found that if the parameters are varied, the pattern system undergoes abrupt transitions at threshold parameter values which are accompanied by multiple-stability and hysteresis behaviors. Moreover, during a real-time switching action, the transient dynamics of the system may depend significantly on the proximity of unstable patterns. The second aspect is a classification and detailed analysis of the polariton scattering processes contributing to the pattern dynamics, giving us an understanding of the selection and control of patterns as results of these processes' intricate interplay. The crucial role played by the relative phases of the polariton field in determining the gains or losses of polariton densities in various momentum modes is highlighted, and interpretation of the actions of the various processes in terms of concepts commonly used in classical pattern-forming systems is given.

Enhanced all-optical switching with double slow light pulses

We experimentally demonstrate an all-optical switching (AOS) scheme based on double slow light (DSL) pulses, in which one pulse is switched by another due to the cross-Kerr nonlinearity. The interaction time is prolonged by optically dense atomic media and matched group velocities. The interaction strength is maintained at a high level by keeping both fields at their electromagnetically-induced-transparency resonances to minimize the linear loss. In the AOS without the DSL scheme, the group velocity mismatch sets an upper limit on the switching efficiency of two photons per atomic cross section as discussed by Harris and Hau [Phys. Rev. Lett. 82, 4611 (1999)]. Compared to that limit, we have obtained an enhanced switching efficiency by a factor of 3 with our DSL scheme. The nonlinear efficiency can be further improved by increasing the optical depth of the medium. Our work advances low-light-level nonlinear optics and provides essential ingredients for quantum many-body physics using strongly interacting photons.

Compact all-optical switch for WDM networks based on Raman effect in silicon nanowavegide

We propose an all-optical switching scheme based on Raman gain in a silicon nanowaveguide suitable for multichannel optical communication. Raman gain is used for amplification of a control pulse with a higher wavelength, which depletes the tuned channel signal. Separation between control and signal pulses should be equal to the Raman shift in silicon. By employing a 3 mm channel nanowaveguide, we demonstrate a channel attenuation of about 12 dB, while the suppression ratios for the first and second neighboring channels are about 1.6 dB and 1 dB, respectively. This scheme can be used as an all-optical switch in dense wavelength division multiplexing networks. Moreover, we demonstrate that the depleted channel can be retrieved by a control pulse with lower wavelength in which the pulse amplifies the channel in contrast to the prior situation.

Phase-controlled all-optical switching based on coherent population oscillation in a two-level system

We theoretically propose a scheme of phase-controlled all-optical switching due to the effect of degenerate four-wave mixing (FWM) and coherent population oscillation (CPO) in a two-level system driven by a strong coupling field and two weak symmetrically detuned fields. The results show that the phase of the FWM field can be utilized to switch between constructive and destructive interference, which can lead to the transmission or attenuation of the probe field and thus switch the field on or off. We also find the intensity of the coupling field and the propagation distance have great influence on the performance of the switching. In our scheme, due to the quick response in semiconductor systems, a fast all-optical switching can be realized at low light level.

All-optical discrete vortex switch

We introduce discrete vortex solitons and vortex breathers in circular arrays of nonlinear waveguides. The simplest vortex breather in a four-waveguide coupler is a nonlinear dynamic state changing its topological charge between $+1$ and $\ensuremath{-}1$ periodically during propagation. We find the stability domain for this solution and suggest an all-optical vortex switching scheme.

Performance of field-enhanced optical switching in fiber Bragg gratings

We compare the performance of two well-known all-optical switching schemes based on fiber Bragg gratings: a uniform grating and a grating with a π phase shift. We express their performance in terms of linear measures: the intensity enhancement inside the grating, which lowers the nonlinear threshold, and the relative resonance bandwidth, which determines the device’s response time. We show that in both grating types, the product of the enhancement and the relative bandwidth is proportional to the refractive index contrast, and that it is superior for a phase-shifted grating. We also evaluate the sensitivity of the devices to loss. We confirm results of our analysis by simulating nonlinear coupled-mode equations. More generally, our results indicate the advantage of structures with a high refractive- index contrast for all-optical switching.

All-optical regeneration based on a nonlinear long period grating

We theoretically investigate a nonlinear all-optical switching scheme based on a long period grating written in a highly nonlinear chalcogenide fiber. We investigate the impact of two-photon absorption on the device and show that the influence of a modest amount of two photon absorption is actually beneficial to device performance as quantified by the power transfer function and improvement of the Q-factor of an incident signal.

All-optical switch based on the local nonlinear Mach-Zehnder interferometer

We proposed a new all-optical switch by using the phase modulation of spatial solitons. The proposed structure is composed of the nonlinear Mach-Zehnder interferometer (MZI) with the straight control waveguide, the uniform nonlinear medium and the nonlinear output waveguides. The local nonlinear MZI functions like a phase shifter. The light-induced index changes in the local nonlinear MZI make the output signal beam routing in the uniform nonlinear medium. The all-optical switching scheme employs angular deflection of spatial solitons controlled by phase modulation created in the local nonlinear MZI. By properly launching the control power and increasing the length of the uniform nonlinear medium, this device can be generalized to a 1xN all-optical switch. It would be a potential key component in the applications of ultra-high-speed optical communications and optical data processing system.