Tunable All-optical Switch Research Articles

Tunable Nonlinear Optical Bistability Based on the Fabry–Perot Cavity Composed of Dirac Semimetal and Two Symmetric Photonic Crystals

In this paper, we study the nonlinear optical bistability (OB) in a symmetrical multilayer structure. This multilayer structure is constructed by embedding a nonlinear three-dimensional Dirac semimetal (3D DSM) into a Fabry–Perot cavity composed of one-dimensional photonic crystals. The OB phenomenon stems from the third order nonlinear conductivity of 3D DSM. The local field of resonance mode could enhance the nonlinearity and reduce the thresholds of OB. This structure achieves the tunability of OB due to the fact that the transmittance could be modulated by the Fermi energy. It is found that the OB threshold and threshold width could be remarkably reduced by increasing the Fermi energy of the 3D DSM. Besides, we also found that the OB curve depends heavily on the angle of incidence of the incident light, the structural parameters of the Fabry–Perot cavity, and the position of the 3D DSM inside the cavity. After parameter optimization, we obtained OB with a threshold of 106 V/m. We believe this simple multilayer structure could provide a reference idea for realizing low-threshold and tunable all-optical switching devices.

Controlling optical bistability, multistability and all-optical switching through multi-photon excitation process

We present a theoretical study on optical bistability (OB), optical multistability (OM) and tunable all-optical switching in a four-level cascade type atomic system. The density matrix formalism is used to find out the response of the probe laser field. We explore OB and OM under unidirectional optical ring cavity configuration. A comparison between the effects of electromagnetically induced transparency and electromagnetically induced absorption windows on OB is presented. The threshold of OB and the hysteresis width can be tuned effectively by adjusting the applied coherent fields. A transition from OB to OM and vice-versa can be easily achieved by tuning the field parameters and the atomic cooperation parameter. Dynamic control of the probe laser propagating through the medium has been investigated. We also demonstrate conversion of a continuous wave input probe field into output switched pulse. The ON/OFF time of the switched probe pulse can also be controlled by tuning the field parameters.

The role of tunable nonlinear dark resonances on vacuum Rabi splitting and optical bistability in an atom-cavity system

The phenomenon of “dark resonances” is a well-known concept in quantum optics and laser spectroscopy. As a general rule, interactions involving in such a “dark state” lead to multiple quantum superposition states that interact coherently and are undesirable. In this paper, two types nonlinear interaction in an atomic cavity, namely the nested and cascaded interactions, are theoretically analyzed how the dark resonances form the dark state peak to modulate the vacuum Rabi splitting (VRS) and optical bistability (OB) behavior. In both the zero- and high order modes, there are four VRS peaks generated in the nested interaction and three in the cascade interaction. Dark resonance can modulate not only the peak number of VRS, but also the OB thresholds. It is found that dark state can determine the asymmetric OB distribution of nested type and symmetric OB distribution of cascade type. Besides that, the distinctive OB thresholds in two kinds of interaction also be studied. The observations not only conceptually extend the conventional “dark resonances” phenomenon, but also opens the door for a variety of new applications in tunable all-optical switch and quantum communication.

Quantum optical response of a hybrid optomechanical device embedded with a qubit

We theoretically investigate the optical response in a hybrid quantum optomechanical system consisting of two optically coupled micro-cavities in which a two-level system (qubit) is coupled with a mechanical membrane. The qubit can either be a defect which interacts with the mechanical oscillator via the linear Jaynes–Cummings interaction or a superconducting charge qubit coupled with the mechanical mode via non-linear interaction. We find that coherent perfect transmission (CPT), coherent perfect synthesis (CPS) and optomechanically induced absorption (OMIA) can be generated by suitably adjusting the system parameters. We find that the qubit and its interaction with the mechanical oscillator emerges as a new handle to control these quantum optical properties. The presence of the qubit results in four points where CPT and CPS can be realized compared to the pure optomechanical case (i.e. in the absence of a qubit) where only three points are attained. This shows that the presence of the qubit gives us more flexibility in choosing the appropriate parameter regime where CPT and CPS can be attained and controlled. We also find that OMIA shows three distinct peaks both in the linear and non-linear cases. In the absence of the qubit, OMIA is converted to optomechanically induced transmission (OMIT). An increase in the qubit decay rate also shows a transition from OMIA to OMIT. Our study reveals that the optical response of the non-linear case is relatively rapid and more sensitive compared to the linear case to changes in the system parameters. This demonstrates the potential use of this hybrid system in designing a tunable all-optical switch and photon router, both of which form important elements of a quantum information network.

A tunable silicon-on-insulator valley Hall photonic crystal at telecommunication wavelengths

Silicon-on-insulator (SOI) combined with topological photonics provides on-chip integrated photonic devices CMOS-compatibility and backscattering-suppression. Here we propose a tunable SOI-based valley Hall topological insulator with two nonequivalent air holes to break inversion symmetry. Due to free-carrier excitation, the real and imaginary parts of the refractive index are modified to cause a blue-shift of bandgap and a reduction of transmittance, respectively. Based on this mechanism, we design a tunable all-optical switch with the merits of high transmittance contrast (about 23) and polarization-resolved characteristics simultaneously. Our proposed approach has potential in broadband tunable integrated photonic devices at telecommunication wavelengths.

Tunable interaction-free all-optical switching in a five-level atom-cavity system

A scheme is proposed for tunable all-optical switching based on the double-dark states in a five-level atom-cavity system. In the scheme, the output signal light of the reflection and the transmission channels can be switched on or off by manipulating the control field. When the control light is coupled to the atom-cavity system, the input signal light is reflected by the cavity. Thus, there is no direct coupling between the control light and the signal light. Furthermore, the position of the double-dark states can be changed by adjusting the coherent field, and, thus, the switching in our scheme is tunable. By presenting the numerical calculations of the switching efficiency, we show that this type of the interaction-free all-optical switching can be realized with high switching efficiency.

应用反向准位相匹配的基于多纳米谐振腔的双向可调全光开关

应用反向准位相匹配的基于多纳米谐振腔的双向可调全光开关

应用反向准位相匹配的基于多纳米谐振腔的双向可调全光开关

Based on the second-order nonlinearity, we present a bidirectional tunable all-optical switch at C-band by introducing backward quasi-phase-matching technique in Mg-doped periodically poled lithium niobate (MgO:PPLN) waveguide with a nano-structure called multiple resonators. Two injecting forward lights and one backward propagating light interact with difference frequency generations. The transmission of forward signal and backward idler light can be modulated simultaneously with the variation of control light power based on the basic phase shift structure of a single resonator. In this scheme, all the results come from our simulation. The speed of this bidirectional optical switch can reach to femtosecond if a femtosecond laser is used as the control light.

Bidirectionally tunable all-optical switch based on multiple nano-structured resonators using backward quasi-phase-matching

Bidirectionally tunable all-optical switch based on multiple nano-structured resonators using backward quasi-phase-matching

All-Optical Switching in Pharaonis Phoborhodopsin Protein Molecules

Low-power all-optical switching with pharaonis phoborhodopsin (ppR) protein is demonstrated based on nonlinear excited-state absorption at different wavelengths. A modulating pulsed 532-nm laser beam is shown to switch the transmission of a continuous-wave signal light beam at: 1) 390 nm; 2) 500 nm; 3) 560 nm; and 4) 600 nm, respectively. Simulations based on the rate equation approach considering all seven states in the ppR photocycle are in good agreement with experimental results. It is shown that the switching characteristics at 560 and 600 nm, respectively, can exhibit negative to positive switching. The switching characteristics at 500 nm can be inverted by increasing the signal beam intensity. The profile of switched signal beam is also sensitive to the modulating pulse frequency and signal beam intensity and wavelength. The switching characteristics are also shown to be sensitive to the lifetimes of ppR(M) and ppR(O) intermediates. The results show the applicability of ppR as a low-power wavelength tunable all-optical switch.

Low threshold and tunable all-optical switch using two-photon absorption in array of nonlinear ring resonators coupled to MZI

In this paper a novel structure based on Mach–Zehnder Interferometer (MZI) and an array of nonlinear ring resonators for all-optical switching including very low threshold, fast and all-optically tunable is presented. In this proposal, an array including N ring resonators is coupled to one arm of MZI to introduce the required nonlinear phase shift to switching. Also, two-photon absorption phenomenon is used and will be proposed as another alternative for manipulation of optical switching properties. The proposed idea needs small chip area (∝1/Ntraditional cases) for implementation. We show that the switching threshold intensity can be decreased with increase of N, decrease of the coupling coefficient and increase of the two-photon absorption coefficient. In this structure with traditional optical fibers with the low nonlinear index of refractions (10-18m2/W) and using an array including 15 ring resonators with 6mm diameter for each rings only 3mW for the switching threshold power is required. Also, using erbium-doped fiber for implementation of the rings with the high nonlinear index of refractions (10-15m2/W) and five ring resonators including 0.3mm diameter, the switching threshold power can be reduced to μW level. If the nonzero two-photon absorption coefficient is considered, the switching threshold will be very smaller than the above-mentioned values. We show that with changing the optical amplifier gain the switching threshold can be tuned. So, the proposal can be used as a functional block for the integrated optical switch with very small and tunable threshold.

Tunable all-optical switching in periodic structures with liquid-crystal defects

We suggest that tunable orientational nonlinearity of nematic liquid crystals can be employed for all-optical switching in periodic photonic structures with liquid-crystal defects. We consider a one-dimensional periodic structure of Si layers with a local defect created by infiltrating a liquid crystal into a pore, and demonstrate, by solving numerically a system of coupled nonlinear equations for the nematic director and the propagating electric field, that the light-induced Freedericksz transition can lead to a sharp switching and diode operation in the photonic devices.