Surface plasmon-assisted fluorescence and imaging from Rhodamine 6G dye molecules in polymethyl methacrylate (PMMA) thin films deposited on gold-coated corrugated gratings of various periodicities fabricated by laser interference lithography were investigated. The fluorescence enhancement depends significantly on the periodicity of the corrugated gratings for the green light excitation centered at 548 nm with maximum enhancements at 500 and 1000 nm grating periods. A dielectric PMMA spacer layer placed between the fluorophore layer and the metal surface resulted in a further three-fold enhancement of fluorescence. The period dependent enhancement is caused by the efficient coupling of the excitation radiation to the gold gratings due to the resonant excitation of propagating surface plasmons, which assist the excitation of the fluorophores. Fluorescence imaging shows that the emitted signal is stronger from the top of the corrugated grating surface rather than from that of the valleys. It was ascertained, through surface plasmon resonant dispersion measurements and electromagnetic computations, that enhanced absorption of excitation light through propagating plasmon resonances is the prime contributor to the enhanced fluorescence.
Logic gates are the fundamental building blocks in any digital data-processing circuit. We propose a new method to implement a NAND logic operation controlled from a long distance. To realize it we consider two types of Gaussian pulses: the control beam and the signal beam. The signal beam propagates first through an electro-optic modulator and then through a nonlinear waveguide, whereas the control beam propagates directly through the optical fiber. Controlling the applied voltage of the electro-optic modulator, we can change the phase relation between the pulses. Hence a NAND switching operation can be realized at a very long distance in the optical fiber.
Transfer of light energy from one fiber to another due to a direct coupling mechanism can be used in various applications in all-optical data communication. We report an analytical approach for finding the exact amount of coupled light from one waveguide to other, if the nonlinearity of the guiding media is considered in this coupling. The significant difference of this coupling phenomenon (effected by the nonlinearity of the waveguide) with the conventional coupling mechanism obtained as coupled optical output is also discussed.
An optical soliton pulse can be effectively used as an information-carrying signal in a nonlinear optical fiber medium. We propose an analytical model for phase-sensitive switching by the use of two mutually orthogonal polarized Gaussian pulses. To realize it we consider a Gaussian pulse first propagating through an electro-optic modulator. The orthogonal components of the pulse are introduced into the optical fiber. By controlling the applied voltage across the modulator we can change the phase relation between the components. By this method, switching at a very long distance can be implemented in the optical fiber.
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