We present an analytical model and numerical experiments to describe optimal bistable switching involving photonic crystals nonlinear cavity. The involving photonic crystals nonlinear cavity is particularly suitable for large-scale all-optical integration. It is interesting to show that the refractive index of the system can be altered by the incident intensity when the incident frequency is tuned to the evanescent mode and the cavity contains a nonlinear Kerr medium. The response of this system to high-intensity incident waves is studied in detail. A cavity host a localized mode at 1.55 um with a Q of 4000 and a mode volume of 0.055 um3, we predict the onset of bistable reflection at incident powers of ~40 mW. The downstream reflections lead to hysteresis loops in the reflectivity that are topologically distinct from conventional Lorentzian-derived loops characteristic of isolated Fabry-Perot cavities. We provide a stability argument that reveals the unstable branches of these unique hysteresis loops, and we illustrate some of the rich bistable behaviors that can be engineered with such downstream sources, this fact may be used to obtain more flexibility in designing nonlinear devices.
We present an analytical model and numerical experiments to describe optimal bistable switching involving photonic crystals nonlinear cavity. The involving photonic crystals nonlinear cavity is particularly suitable for large-scale all-optical integration. It is interesting to show that the refractive index of the system can be altered by the incident intensity when the incident frequency is tuned to the evanescent mode and the cavity contains a nonlinear Kerr medium. The response of this system to high-intensity incident waves is studied in detail. A cavity host a localized mode at 1.55 um with a Q of 4000 and a mode volume of 0.055 um3, we predict the onset of bistable reflection at incident powers of ~40 mW. The downstream reflections lead to hysteresis loops in the reflectivity that are topologically distinct from conventional Lorentzian-derived loops characteristic of isolated Fabry-Perot cavities. We provide a stability argument that reveals the unstable branches of these unique hysteresis loops, and we illustrate some of the rich bistable behaviors that can be engineered with such downstream sources, this fact may be used to obtain more flexibility in designing nonlinear devices.
The reflectivity of a single-channel waveguide mode upon resonantly coupling to a Kerr-active nonlinear resonant cavity is calculated analytically, including the effects of two-photon absorption. The resonant reflectivity takes the form of a Fano resonance because the solution includes linear reflections from perturbations downstream of the localized cavity. Instead of using a Hamiltonian formulation of the scattering problem, an intuitive set of basis states is used to expand the Green's function of the electric field wave equation. All resulting overlap functions describing the linear coupling between guided and localized states, and the nonlinear renormalization of the material's refractive index, are in terms of well-defined physical quantities. Although derived in the context of photonic crystal-based waveguides and cavities, the treatment is valid for any low-loss waveguide-resonator geometry that satisfies specific weak coupling criteria. For a cavity consisting of Al0.18Ga0.82As, hosting a localized mode at 1.55 microm with a Q of 4000 and a mode volume of 0.055 microm(3), we predict the onset of bistable reflection at incident powers of approximately 40 mW. The downstream reflections lead to hysteresis loops in the reflectivity that are topologically distinct from conventional Lorentzian-derived loops characteristic of isolated Fabry-Perot cavities. We provide a stability argument that reveals the unstable branches of these unique hysteresis loops, and we illustrate some of the rich bistable behaviors that can be engineered with such downstream sources.
We designed and manufactured an optical bistability waveguide device based on nonlinear one-dimensional photonic crystal used CdS_xSe_(1-x) doped glass. This kind of semiconductor doped glass has large nonlinear refractive index and nonlinear fast response time. The distribution of refractive index of the nonlinear one-dimensional photonic crystal waveguide satisfies sine function. We obtained the nonlinear photonic crystal waveguide by exposure holography and etching techniques. Length of the photonic crystal waveguide is about 3 mm. The height of the peak-groove of the waveguide is 0.1 μm. According to our design, the center of bandgap of the one-dimensional photonic crystal lies at 514.5 nm while the power density of the incident light, the incident light was reflected by the photonic crystal. When the power density of the incident light increasing, the bandgap is shifting to the direc-tion of short wavelength due to the decreasing of the refractive index with the increasing of the incident power density, so more incident light is transmitted. In experiment, we used an active mode-locking pulse of Ar ion laser as the light source which wavelength is 514.5 nm, repeating frequency is 82 MHz and pulse width is 200 ps. The light beam was coupled into the device by prism with a laser average power of 1.28 W (in the case of nonlinear saturation operation, optimum coupling efficiency is about 6%). Pulse wave forms of incident light and transmitted from sample were recorded in turn by 7 904 oscilloscope. The optical bistability curve of input power density and output one is fitted by computer. We obtained the threshold power density of bistable switch to be 1.60×10~5 W/cm~2 (it is equivalent to average power of 77 mW) and both the rise and fall time are 63 ps. We used the Finite Difference Time Domain Method to obtain the characteristics of the bandgap shift with the incident power density increasing of the nonlinear photonic crystal and calculate the optical bistability curve of this device. In theory, the threshold power density of bistable switch is about 1.40×10~5 W/cm~2 and the switch time is about 50 ps. The theoretical results agree well with the experimental ones. This device is a new and feasible one for optical information process and optical computing in the future.
In the last chapter, we examined the effect of cubic nonlinearity on selfrefraction of an optical beam. We have also seen that the presence of a quadratic nonlinearity can also contribute to change in the profile of a Gaussian beam in a crystal. In this chapter we will see how the effect of nonlinearity, alongwith the proper feedback, can give rise to optical bistability and hysteresis. This is not unexpected as hysteresis and bistability are also observed in nonlinear electronic circuits with feedback, such as in the Schmitt trigger, as well as in hybrid optical devices, such as an acoustooptic device with feedback (Banerjee and Poon, 1991). In what follows, we will examine two different types of optically bistable devices based on optical nonlinearities. The first is a nonlinear ring resonator comprising a two-level gain medium as the nonlinear element. We will treat both absorptive and dispersive bistability. Absorptive bistability is the case when the incident optical frequency is close to or equal to the transition frequency of the atoms from one level to another. In this case, the absorption coefficient becomes a nonlinear function of the incident intensity. On the other hand, if the frequencies are far apart, the medium behaves like a Kerr-type material and the system exhibits what is called dispersive bistability. In this case the material can be modeled by an effective n2 or v (3), meaning that the refractive index becomes a nonlinear function of the optical intensity. The second configurationwewill examine is a linear-nonlinear interface. In this case, the interface provides the feedback due to refractive index mismatch. In fact, the reflection coefficient (as well as the transmission coefficient) is modified due to the nonlinearity, which, as we shall see later, is responsible for demonstrating optical switching and bistability.
When the output parameter of an optical device could be a multivalued function of the input parameter, this device can be working in an optical bistable status. The most typical optical bistable device is a Fabry–Perot cavity containing a nonlinear optical medium, the refractive index of which depends on the light intensity. Upon the action of an intense input optical beam, the transmitted (or reflected) intensity of this device may exhibit a nonlinear response to the incident light intensity variation and, especially under appropriate working conditions, the characteristic output/input curve may manifest a single (or multiple) hysteresis loop(s). Such type of optical bistable device can be used as an optical differential amplifier, optical switch, optical limiter, optical clipper, optical discriminator, or an optical memory element, depending on the chosen nonlinear medium and operation conditions.
We demonstrate extremely low-power all-optical bistability by using photonic crystal linear resonators based on InGaAsP quantum-wells. Since the photonic crystal cavity has a high quality-factor and a small mode-volume, the photon density in the cavity is extremely high, which makes it possible to reduce the bistable power. The measured minimum bistable threshold power was 37 muW by using a fiber coupling technique, and the estimated nonlinear refractive index (n2) was -6.84times10-14m2/W at a wavelength of 1610.8 nm which is near the resonant wavelength of quantum-well. The low-power optical bistable operations in a single photonic crystal cavity open the possibility of integrated optical devices such as an all-optical memory and switch, based on photonic crystals
We present an analytical model and numerical experiments to describe optimal bistable switching in a nonlinear photonic crystal system. It is proved that only three parameters are needed to characterize a bistable switch: the resonant frequency omega(res), the quality factor Q, and parameter kappa that measures nonlinear "feedback strength." A photonic crystal enables the device to operate in single-mode fashion, as if it were effectively one dimensional. This provides optimal control over the input and output and facilitates further large-scale optical integration.