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.     

Optical bistability in BaTiO3

In this paper experimental results concerning the optical bistability of a ferroelectric monocrystal of BaTiO₃ are presented. Two laser beams were used to interact with the monocrystal which resulted in the bistability of the intensity of the transmitted wave. This was achieved without the application of any optical resonator. The feedback was provided by the electronic system through a mechanism typical to all photorefractive materials.     

Optical bistability in BaTiO3

In this paper experimental results concerning the optical bistability of a ferroelectric monocrystal of BaTiO₃ are presented. Two laser beams were used to interact with the monocrystal which resulted in the bistability of the intensity of the transmitted wave. This was achieved without the application of any optical resonator. The feedback was provided by the electronic system through a mechanism typical to all photorefractive materials.     

光折变聚合物材料的研究进展

与无机光折变晶体相比,光折变聚合物材料具有非线性光学系数大,响应时间快,成本低廉,制备灵活等优点,成为近代研究的热点。综述了光折变聚合物材料的发展状况,并分析了当前工作所面临的问题及发展前景。     

Field enhancement and large optical nonlinearity in Ag nanocomposite polymer film

We report a simple in situ synthesis for Ag nanocomposite polymer film. The extinction spectrum and the distribution of the local field intensities for Ag nanoparticles are performed by means of the dipole discrete approximation. The local field intensity is enhanced over 20 times to that of the incident light at the peak wavelength of the extinction spectrum. Nonlinear optical measurements, performed by using the Z-scan techniques, are presented afterwards. Giant enhancement of nonlinear optical responses is found for Ag/PMMA film compared with pure PMMA (polymethyl methacrylate) film. The nonlinear refractive index γ of the Ag/PMMA film is measured to be 3.708 × 10^?2 cm² GW^?1. The enhanced optical properties are due to the surface plasmon resonance of Ag nanoparticles. These results are in agreement with the previous field calculations. Analyzed with respect to Stegeman figures of merit, Ag/PMMA nonlinear polymer film shows promise for practical use in ultrafast optical devices.     

Electrical bistabilities and memory mechanisms of organic bistable devices fabricated utilizing SnO2 nanoparticles embedded in a poly(methyl methacrylate) layer

Organic bistable devices fabircated utilizing SnO2 nanoparticles embedded in a poly(methyl methacrylate) (PMMA) polymer layer were formed by using a spin coating method. Transmission electon microscopy images and photoluminescence spectra showed that synethized SnO2 nanoparticles were randomly distributed in the dibutyl ehter solution. Current-voltage (I-V) measurements on the Al/SnO2 nanoparticles embedded in PMMA layer/ITO devices at 300 K showed current bistability due to the existence of SnO2 nanoparticles. Current-time (I-t) results showed the memory retention characteristic of the device. Carrier transport mechanisms of the device are described on the basis of the I-V experimental results and electronic structures.     

Image cross-connector using a photorefractive polymer

We propose an image cross-connector using an organic photorefractive polymer. With this device, it is possible to perform a reconfigurable connection between multiple input–output image ports by setting the incident angle of individual control beams to minute levels. The use of a polymer can reduce the thickness of the index grating to be induced inside the medium, which can also reduce the distortion of the output image and bring about high precise image connection without an additional optical system. We conduct an experiment with a hole-transport polymer PATPD to verify the operations of an image cross-connector, in which different images from a vertical array of input images would be connected separately to two output ports by two control beams that were injected at different angles.     

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.     

Low-switching power (<45 mW) optical bistability based on optical nonlinearity of ytterbium-doped fiber with a fiber Bragg grating pair

We propose a new optical bistable device (OBD), which is constructed by connecting two symmetrical fiber Bragg gratings with a ytterbium-doped fiber to form a nonlinear Fabry–Perot cavity. The principle of this new OBD is described using the transfer-matrix method, and the two groups of transmitted and reflected optical bistability loops under different parameters are investigated symmetrically. Compared with single fiber Bragg grating switching, whose switching power is greater than 2?kW, this new device has evident merits in reducing the switching power to less than 45?mW.     

Photorefractive Polymers and Composites

Materials demonstrating a photorefractive effect are principal candidates for numerous applications, including high-density optical data storage, optical image processing, phase conjugated mirrors and lasers, dynamic holography, optical computing, pattern recognition, etc. Considerable progress has been made in the research on photorefractive polymers and composite materials in the last few years. These materials have many advantages over inorganic photorefractive crystals, including large optical nonlinearities, low dielectric constants, low cost and ease of fabrication. A large number of materials, including those exhibiting an extremely large photorefractive effect, have been developed. In addition, a number of interesting phenomena particular to polymeric photorefractive materials have been reported and corresponding mechanisms have been proposed to account for these phenomena. Possible applications of these materials have been explored with the demonstration of a volume holographic storage device based on photorefractive polymers. This paper reviews the latest developments of the young and exciting field of polymeric photorefractive materials.     

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.     

Microfabricated polymer analysis chip for optical detection

A coupling between multimode polymer waveguides and microfluidic channels on a polymethylmethacrylate (PMMA) capillary electrophoresis (CE)-chip for optical analytical applications has been successfully realised. This technology allows the integration of polymer optical waveguides together with hermetically sealed fluidic channels. The microchannels and waveguides are made in PMMA by the approved hot-embossing technology. The technology developed for the fabrication of polymer waveguides on the microfluidic chip offers the possibility of great flexibility in the choice of core materials, design and alignment of the polymer waveguides. The integration of polymer waveguides on an analysis chip enables highly spatially resolved optical detection without the large and expensive conventionally used apparatus. The optical properties of the analytical system developed are verified by transmission and propagation loss measurements. The results of measurements prove the suitability of the presented device for optical applications between 440 and 800 nm. This was shown with absorbance measurements of the dye Sulfanilazochromotrop (SPADNS) within 50 microm fluidic channels.     

Photoinduced changes in refractive index of nanostructured shungite-containing polyimide systems

Photoinduced changes in the refractive index of a conjugate polyimide (PI) matrix sensitized by shungite carbon nanoparticles have been studied for the first time. The results are compared to the data of previous investigations of the photorefractive properties of PI matrices doped with fullerenes, carbon nanotubes, and quantum dots. The nonlinear refractive index of the proposed material has been determined using the dynamic holography techniques. The position of conjugate polymer materials of this type among the other nonlinear optical systems is considered.     

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.     

非线性光学聚合物薄膜DCDHF-2-V/PMMA的特性

将新型有机非线性光学分子DCDHF-2-V按一定比例掺入聚甲基丙烯酸甲酯(PMMA)中,采用旋涂方法制备聚合物薄膜。为了得到宏观二阶非线性光学特性,在90℃对薄膜进行电晕极化,形成各向异性。对极化前后的薄膜进行紫外/可见光吸收频谱分析和原子力显微镜分析。采用RHF方法在6-31G基组上对DCDHF-2-V/PMMA薄膜体系中的DCDHF-2-V分子和PMMA进行闭壳层Hartree-Fock理论计算,得到它们的一阶超极化率β分别为60.278755×10-30esu和10.902267×10-34esu。     

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.     

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.     

Optically induced three-dimensional nonlinear photonic lattices in LiNbO3:Fe crystal

We fabricate three-dimensional nonlinear photonic lattices in self-defocusing iron-doped lithium niobate photorefractive crystal for the first time by an improved Michelson interferometer device. The experimental setup is simple and inexpensive. The period of the induced photonic lattices can be dominated easily. We analyze the three-dimensional nonlinear photonic lattices by plane wave guiding and far field diffraction pattern imaging. The induced nonlinear photonic lattices can exist stably for a long time in the photorefractive crystal.     

Optical bistability in metal-insulator-metal plasmonic waveguide with nanodisk resonator containing Kerr nonlinear medium

We numerically investigate the optical bistability effect in the metal-insulator-metal waveguide with a nanodisk resonator containing a Kerr nonlinear medium. It is found that the increase of the refractive index, which is induced by enhancing the incident intensity, can cause a redshift for the resonance wavelength. The local resonant field excited in the nanodisk cavity can significantly increase the Kerr nonlinear effect. In addition, an obvious bistability loop is observed in the proposed structure. This nonlinear structure can find important applications for all-optical switching in highly integrated optical circuits.     

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.