Narrow Results

Erythrosine B based poly (methacrylate) films with varying even number of methylene spacers have been prepared by the free radical polymerization method. All optical switching and beam deflection effects of polymer films have been investigated by using Nd:YAG laser (532 nm) as a pump beam and a He–Ne laser (632.8 nm) as a probe beam. The nonlinear refractive indices of polymer films are determined using the Z-scan technique. The optical switching and beam deflection effects are due to the change of the refractive index of polymer under the pump beam. The experimental results show that erythrosine B based poly (methacrylate) films have potential application in optical switching.

We investigate the transmission properties and its photoinduced change in a one-dimensional photonic crystal slab. This periodic waveguide consist of quartz grating substrate and a thin polymer film containing a photosensitive protein bacteriorhodopsin. We propose a scheme to achieve light-controlled optical switching using the photoinduced refractive index change of bacteriorhodopsin.

We investigate the detailed transition of the dark to antidark soliton-like states in a system of finite deep nonlinear Bragg grating equipped with a movable metallic mirror and illuminated by a continuous laser source. As reported previously, the transition can be induced mechanically by moving the mirror as well as optically by changing the light source intensity.

A numerical study on the hysteretic responses of deep nonlinear Bragg grating systems with symmetric three-layer unit cells has been carried out on the basis of a generalized coupled mode theory modified to accommodate deeper nonlinear refractive index modulation. The results show that the in-gap bistability offers the most favorable features in terms of switching width and threshold for optical switching application. Calculated variations of these operational features with respect to the layer thickness, operating wavelength and nonlinear index contrast provide useful guidance for the design of grating systems intended for specific optical switching applications.

We discuss the transmission properties of non-linear phase-shifted grating. Using a direct integration method, we show that phase-shift in linear sinusoidal grating introduces a very narrow resonance in the band gap with very high amplification factor. Using frequency in the vicinity of this resonance, we show that the threshold of switching can be reduced significantly. Based on the direct integration method, it is shown that Coupled-Mode Theory may produce inaccurate results for the case of both linear and non-linear grating structure with and without phase-shift.

The ability of optical axis gratings (OAGs) to fully transfer the energy of an unpolarized incident light beam into the ±1st diffraction orders is explored below for development of a polarization-independent optical system with nonlinear transmission. Diffractive properties of OAGs based on azo dye doped liquid crystals (azo LCs) are efficiently controlled with low power radiation. Switching from diffractive to transmissive states of the OAG takes place within 50 ms at 60 W/cm² power density level, while the diffractive state is restored within ~ 1 s in the absence of radiation. High contrast optical switching is demonstrated with violet as well as green laser beams. A photoswitchable OAG is paired with a light-insensitive OAG in diffraction compensation configuration to obtain an optical system switchable from high to low transmission state. The thinness of OAGs required for high contrast switching ensures high overall transmission of the system. Given also the spectrally and angularly broadband nature of OAG diffraction and the capability of azo LC material systems to respond both to cw as well as short laser pulses makes the optical system under discussion very promising for optical switching applications. Presentation of these results is preceded by an "opinionated" review of prior developments and demystifying of the fabrication technique of high efficiency large area OAGs.

We use an optical parametric amplifier to obtain and demonstrate a fast and flexible pump–probe system with minimal conversion needed. The readily aligned laser may be used to quickly test samples with broadband pump–probing as well as femtosecond time-resolved spectroscopy. As a proof of concept, we produce results on optical modulation in vanadium dioxide thin films similar to that previously obtained by other groups.

In this work, we studied the optical bistability of Fiber Bragg Grating (FBG) under nonlinear regime, considering three increasing and decreasing profiles of nonlinearity: linear, quadratic and exponential. We varied the nonlinearity range in each profile, and obtained different curves of bistability and reflectivity. We analyzed the powers $P_{up\uparrow }$ and $P_{down\downarrow }$, as well as the width of the photonic band gap (${\mathrm{\Delta }}_{\uparrow \downarrow })$ of each device under different nonlinearity profiles, and we observed the changes in reflectivity of the FBG. The power intensities $P_{up\uparrow }$ and $P_{down\downarrow }$ obtained for the bistability of decreasing profiles were lower than those obtained for the increasing profiles, and the values of ${\mathrm{\Delta }}_{\uparrow \downarrow }$ were also lower in decreasing profiles, which is useful for optical switching applications.

We demonstrate a novel rotary micromirror for fiber-optic switching. A very simple fabrication process which uses SOI wafer and DRIE technology has been employed to micromachine this electrotastically actuated vertical mirror. Based on this one-mask process, 2N-switch-architecture crossconnects with all the components, inlcuding optic fiber couplers electrostatic comb drives and reflective vertical mirrors, has been integrally fabricated on a monolithic silicon substrate.

We describe the properties of a 1D anisotropic periodic structure, designed to have a band edge with fourth order degeneracy, called a degenerate band edge (DBE). A giant field resonance at the transmission peak frequency closest to this band edge has been verified by rigorous numerical calculation and is supported by experimental evidence. Simulations are presented of the consequences of a χ³ nonlinear index change at a DBE resonant frequency which can provide all-optical switching and transmission self-limiting.