No abstract

We show all-optical switching of an input infrared laser beam at 1310 nm by controlling the photoinduced retinal isomerization to tune the resonances in a silica microsphere coated with three bacteriorhodopsin ͑BR͒ protein monolayers. The all-optical tunable resonant coupler reroutes the infrared beam between two tapered fibers in 50 s using a low power ͑Ͻ200 W͒ green ͑532 nm͒ and blue ͑405 nm͒ pump beams. The basic switching configuration has been used to design all-optical computing circuits, namely, half and full adder/subtractor, de-multiplexer, multiplexer, and an arithmetic unit. The design requires 2 n − 1 switches to realize n bit computation. The designs combine the exceptional sensitivities of BR and high-Q microcavities and the versatile tree architecture for realizing low power circuits and networks ͑approximately mW power budget͒. The combined advantages of high Q-factor, tunability, compactness, and low power control signals, with the flexibility of cascading switches to form circuits, and reversibility and reconfigurability to realize arithmetic and logic functions, makes the designs promising for practical applications. The designs are general and can be implemented ͑i͒ in both fiber-optic and integrated optic formats, ͑ii͒ with any other coated photosensitive material, or ͑iii͒ any externally controlled microresonator switch.

No abstract

No abstract

This work deals with the sensitization of the porous TiO 2 films of thickness about 4 lm deposited on fluorine-doped tin oxide with nanocrystalline Bi 2 S 3 for photovoltaic application. The sensitization was achieved for four different sensitization times employing chemical solution deposition with bismuth nitrate and sodium thiosulphate as precursors for Bi 3? and S 2-, respectively. The unsensitized and sensitized photoelectrodes were characterized using X-ray diffractometry, scanning electron microscopy and diffused reflectance spectroscopy. XRD patterns show the signatures of both anatase TiO 2 and orthorhombic Bi 2 S 3 in the sensitized photoanodes. However, crystallinity of Bi 2 S 3 increased with increase in sensitization time from 10 to 40 min. The temporal effect of sensitization and annealing on the photovoltaic performance of the solar cells fabricated using four different photoelectrodes was studied using the photocurrent density versus photovoltage curves. Annealing apparently improved the photovoltaic performance of photoanodes. The best performance was obtained for cell fabricated using annealed TiO 2 /Bi 2 S 3 photoanode after 30 min sensitization time showing V oc * 0.37 mV, J sc * 0.52 mA/cm 2 , FF * 68 and 0.43 %.