Kerr nonlinearity and optical multi-stability in a four-level Y-type atomic system

The nonlinear response to applied fields of a four-level Y-type atomic system is investigated. The effect of laser intensity and quantum interference induced by spontaneous emission on optical bistability, optical multi-stability and Kerr nonlinearity is then discussed. It is found that the threshold of the optical bistability can substantially be reduced by the quantum interference. So, an enhanced Kerr nonlinearity with reduced absorption can be achieved.     

Optical bistability in metal-insulator-metal plasmonic Bragg waveguides with Kerr nonlinear defects

We numerically investigate the characteristics of the defect mode and the nonlinear effect of optical bistability in metal-insulator-metal (MIM) plasmonic Bragg grating waveguides with Kerr nonlinear defects. By means of finite-difference time-domain simulations, we find that the defect mode peak exhibits a blueshift and height-rise by enlarging the width of the defect layer, and it has a redshift and height-fall with the increase of the dielectric constant of defect layer. Obvious optical bistability is obtained in our waveguides with a length of less than 2 μm. The results show that our structure could be applied to the design of all-optical switching in highly integrated optical circuits.     

Elimination of Kerr bistability in an optical fiber ring resonator with a 3 × 3 planar fiber coupler

A special property of a type 3 optical fiber ring resonator with a 3 × 3 planar coupler in which the circulating intensity is independent of the phase change of the ring resonator can be used to eliminate unwanted Kerr bistability. At the same time the device can be used as a two-channel frequency division multiplexer or demultiplexer or a switch. Another method for the elimination of Kerr bistability is the use of two fibers whose nonlinear refractive-index coefficients have opposite signs to build the ring resonator.     

Tunable beam focusing based on optical bistability with a composite Kretschmann configuration involving a Kerr medium

A beam focuser with a composite Kretschmann configuration involving a Kerr medium is investigated theoretically. The structure employs a silver film with four slits filled with the Kerr medium. Optical bistability and beam focusing are demonstrated, and changes to the incident intensity result in optical bistability characteristics in the reflection, focused intensity, spot size, and depth of focus. The proposed structure has the potential to be applied for optical switching and nano-illumination.     

Optical bistability of surface plasmon polaritons in nonlinear Kretschmann configuration

Optical bistability based on surface plasmon polaritons in the Kretschmann configuration involving a Kerr nonlinear medium is described by analytical solutions. The conditions of forming the optical bistability with different parameters are explored. The resonant angle of surface plasmon polaritons varying with the incident light intensity also generates the phenomenon of bistability. The system could form optical bistability with the special thickness of the metal film and incident angle. This kind of system has potential application in all-optical networks.     

Optical switching and normal mode splitting in hybrid semiconductor microcavity containing quantum well and Kerr medium driven by amplitude-modulated field

ABSTRACT

We theoretically investigate optical bistability/multistability for all optical switching signature in a hybrid semiconductor microcavity system comprising a quantum well and a Kerr nonlinear substrate. The system is essentially two optically coupled microcavities with one of the microcavity being driven by an external amplitude-modulated pump laser. We show that the switching between bistable and multistable behaviour is influenced by the modulated pump laser, Kerr nonlinearity and the optical coupling between the two microcavities. We further investigate the intracavity spectrum of quantum fluctuations which exhibit the well-known normal mode splitting (NMS). The NMS behaviour is also found to be influenced by the system parameters. These results demonstrate that the present hybrid nonlinear system can be used in designing sensitive optical devices.     

Nonlinear response of a 2D photonic crystal made of Kerr effect nonlinear parallel rods of large diameter

We present the calculation of the transmission as a function of the intensity of incoming light of nonlinear parallel rods distributed in a periodic way. We have developed a new calculation combining finite elements and the multiple scattering method to take into account the distribution of the intensity inside the large rods. Indeed, in this case the energy inside the rods is no longer homogeneous when a significant Kerr effect takes place. The Kerr effect induced a broadening of the photonic band gap when the intensity increased. When a defect was inserted into the structure, an hysteresis phenomenon occurred for the resonance associated with this defect. We investigated the influence of taking into account the inhomogeneity of intensity in the rods on the bistability phenomenon. It appeared that even for a rod diameter of λ/10 the homogeneous model failed to describe correctly the bistability.     

Kerr bistability in an optical fiber ring resonator with a 3 × 3 planar fiber coupler

A theoretical study of bistability caused by the optical Kerr effect in a type 1 optical fiber ring resonator connected to a 3 × 3 planar coupler is presented. The dependence of the bistability on various parameters of the fiber and the coupler is investigated. A comparison between the bistable characteristics of this ring resonator and those of a fiber ring resonator with a 3 × 3 equilateral triangular (nonplanar) fiber coupler is made.     

Mirrorless optical bistability in a semiconductor-doped-glass plate as a result of oblique incidence

A procedure to obtain optical bistability in a third-order nonlinear film (or parallel plate) of low refractive index without any external mirrors is investigated both theoretically and experimentally. If an s-polarized light is incident obliquely at a large angle of incidence on the film, the generation of optical bistability can be expected because of the resulting increase in the reflectivity at the surfaces. Arigorous analysis of the stationary transmission characteristics of the nonlinear film is done for both positive and negative nonlinear coefficients with a plane-wave model. In the experimental demonstration, a CdS(x)Se(1-x)doped glass (Hoya Y-52) plate and a cw Ar(+) laser are used as the nonlinear material and the light source, respectively. It is shown that three operations of optical bistability, optical limiting, and differential gain can be easily obtained through adjustment of the angle of incidence as an initial detuning. The measured nonlinearity is thermal, and the magnitude and sign of the nonlinear refractive index are determined.     

Intrinsic optical bistability in doped polymer

One of the most interesting and applicable effects of nonlinear optics is optical bistability. This phenomenon is exhibited by certain resonant optical structures where it is possible to have two stable steady transmission states for the device, depending on the history of the input. Such a bistable device may be useful for optical computing elements as a result of its memory characteristics. Optical bistability behaviour is usually observed by inserting a nonlinear matter inside a Fabry–Perot interferometer. But in this study, it was shown that this can be achieved without the application of any optical resonator. Two laser beams were used to interact with the photorefractive media (doped PMMA polymer) which resulted in the bistability of the intensity of transmitted wave. Feedback was provided by a periodic grating created in the photorefractive polymer PMMA.     

Diffraction engineering Anderson localization of light in nonlinear waveguide array with Kerr and two photon absorption effects

Role of two-photon absorption (TPA) effect on light propagation in one-dimensional nonlinear waveguide array (NWA) is studied numerically with solving nonlinear Schrodinger equation. Our investigation includes unperturbed, diagonally and off-diagonally disordered NWA with inclusion of Kerr and TPA and the results are compared with each other. The simulations show that the increase of incident wave amplitude to NWA intensifies TPA and Kerr effects and these nonlinear optical effects, dramatically affect the output intensity profile and loss. Variations of intensity distribution in periodic NWA is about two and three times higher than in off-diagonal and diagonal disordered NWA, respectively. It means that localization of light in periodic NWA is more tunable than disordered lattices. These variations of intensity distribution under nonlinear optical effects enable us to propose and design a reconfigurable localization and diffraction-engineered discrete soliton.     

Controlled bistability by using array defect layers in one-dimensional nonlinear photonic crystals

Using analytical modeling and detailed numerical simulations, we investigate the input-output transmission regimes in one-dimensional (1D) nonlinear photonic crystal including array defect layers. A coupled-mode system is derived from the Maxwell equations and analyzed for the stationary-transmission regime in the new proposed structure. Using the idea about introducing defect layers into 1D nonlinear photonic crystals, a new method for creating and controlling optical bistability is proposed. The periodic optical structures with array defect layers can be used as all optical switches between lower- and higher-transmissive states, whereas it possesses one jumping from a low-transmissive state to a transparent state.     

Phase control of Kerr nonlinearity in V-type system with spontaneously generated coherence

We study phase control of linear and nonlinear optical responses in a three-level atomic system in V-configuration exhibiting spontaneously generated coherence (SGC). Because of the SGC effect, the strength of Kerr nonlinearity strongly depends upon the relative phase between the probe and control fields as well as the absorptions. By controlling the relative phase appropriately, large Kerr nonlinearity can be achieved with canceled linear and nonlinear absorptions. Combining with the phase modulation, the strict decay condition of spontaneous decay rates is not needed.     

All-optical bistable switching based on photonic crystal slab nanocavity using nonlinear Kerr effect

In this paper, we propose all-optical bistable switching based on a two-dimensional (2D) photonic crystal slab nanocavity using the nonlinear Kerr effect with improved optical properties such as on/off ratio and switching power. The nonlinear properties of different kinds of nanocavity-based L3 structures are characterized. Using the 2D finite-difference time-domain method, we present a new structure of nanocavities for all-optical switching. The device has on/off ratio greater than 15?dB and power smaller than 375?mW for input optical pulses in the range of picoseconds.     

Optical bistability and multistability in an open ladder-type atomic system

A novel scheme is proposed for controlling the optical bistability and multistability in an atomic system. In an open ladder-type three-level atomic system, it is shown that, by adjusting the ratio between atomic injections and exit rates from the cavity, the intensity threshold of optical bistability can be controlled. The effect of incoherent pumping field and spontaneously generated coherence (SGC) on optical bistability for different values of exit rates is also discussed. It is found that SGC makes the medium phase dependent, so the optical bistability and multistability threshold can be controlled via relative phase between applied fields. Moreover, it is shown that the optical bistability can be switched to optical multistability, which is favorable for the next generation of all-optical systems and quantum networks.     

Kerr Nonlinearity in 2D Graphdiyne for Passive Photonic Diodes

Graphdiyne is a new carbon allotrope comprising sp‐ and sp²‐hybridized carbon atoms arranged in a 2D layered structure. In this contribution, 2D graphdiyne is demonstrated to exhibit a strong light–matter interaction with high stability to achieve a broadband Kerr nonlinear optical response, which is useful for nonreciprocal light propagation in passive photonic diodes. Furthermore, advantage of the unique Kerr nonlinearity of 2D graphdiyne is taken and a nonreciprocal light propagation device is proposed based on the novel similarity comparison method. Graphdiyne has demonstrated a large nonlinear refractive index in the order of ≈10^?5 cm² W^?1, comparing favorably to that of graphene. Based on the strong Kerr nonlinearity of 2D graphdiyne, a nonlinear photonic diode that breaks time‐reversal symmetry is demonstrated to realize the unidirectional excitation of Kerr nonlinearity, which can be regarded as a significant demonstration of a graphdiyne‐based prototypical application in nonlinear photonics and might suggest an important step toward versatile graphdiyne‐based advanced passive photonics devices in the future.     

Optical realization of bioinspired spiking neurons in the electron trapping material thin film

A thin film of electron-trapping material (ETM), when combined with suitable optical bistability, is considered as a medium for optical implementation of bioinspired neural nets. The optical mechanism of ETM under blue light and near-infrared exposure has the inherent ability at the material level to mimic the crucial components of the stylized Hodgkin-Huxley model of biological neurons. Combining this unique property with the high-resolution capability of ETM, a dense network of bioinspired neurons can be realized in a thin film of this infrared stimulable storage phosphor. When combined with suitable optical bistability and optical interconnectivity, it has the potential of producing an artificial nonlinear excitable medium analog to cortical tissue.     

Optical Bistability and Reversed Switching Effect in a Three-photon Resonant Medium

We have developed, ab initio, a theory for the interaction of coherent laser light in three-photon resonance with two effective levels of a multilevel atom. The theory is developed to consider the optical bistability of homogeneously broadened, three-photon, resonant multilevel atoms inside a ring cavity. It is shown that optical bistable behaviour in the fundamental and the generated third harmonic can be obtained using, for example, Na atoms. The device may be useful in constructing two-channel, optical bistable switches. In certain nonlinear regimes it may be possible to obtain reversed switching between the fundamental and the third harmonic bistability.     

Ultrafast optical phase modulation with metallic nanoparticles in ion-implanted bilayer silica

The nonlinear optical response of metallic-nanoparticle-containing composites was studied with picosecond and femtosecond pulses. Two different types of nanocomposites were prepared by an ion-implantation process, one containing Au nanoparticles (NPs) and the other Ag NPs. In order to measure the optical nonlinearities, we used a picosecond self-diffraction experiment and the femtosecond time-resolved optical Kerr gate technique. In both cases, electronic polarization and saturated absorption were identified as the physical mechanisms responsible for the picosecond third-order nonlinear response for a near-resonant 532 nm excitation. In contrast, a purely electronic nonlinearity was detected at 830 nm with non-resonant 80 fs pulses. Regarding the nonlinear optical refractive behavior, the Au nanocomposite presented a self-defocusing effect, while the Ag one presented the opposite, that is, a self-focusing response. But, when evaluating the simultaneous contributions when the samples are tested as a multilayer sample (silica-Au NPs-silica-Ag NPs-silica), we were able to obtain optical phase modulation of ultra-short laser pulses, as a result of a significant optical Kerr effect present in these nanocomposites. This allowed us to implement an ultrafast all-optical phase modulator device by using a combination of two different metallic ion-implanted silica samples. This control of the optical phase is a consequence of the separate excitation of the nonlinear refracting phenomena exhibited by the separate Au and Ag nanocomposites.     

Magneto-optical switching in nonlinear all-garnet magnetophotonic crystals

Magnetic field control over the optical switching is demonstrated for a nonlinear all-garnet magnetophotonic crystal with a microcavity (MC) layer possessing both third-order Kerr nonlinearity and magnetooptical activity. A significant enhancement of the effective refractive index of the microcavity layer is observed, that results in the light-induced spectral shift of the MC mode of 2 nm. It is shown that application of the external magnetic field leads to an increase of switching contrast by a factor of two. Possible mechanisms of photorefractive effect involved in the optical switching in all-garnet magnetophotonic crystals are discussed.