Sukhdev Roy

All-optical switching in bacteriorhodopsin based on M state dynamics and its application to photonic logic gates

Abstract All-optical switching has been theoretically analyzed in bacteriorhodopsin (bR) based on nonlinear intensity induced excited state absorption of the M state. The transmission of a cw probe laser beam at 410 nm corresponding to the peak absorption of M state through a bR film is switched by a pulsed pump laser beam at 570 nm that corresponds to the maximum initial B state absorption. The switching characteristics have been numerically simulated using the rate equation approach considering all the six intermediate states (B, K, L, M, N and O) in the bR photocycle. The switching characteristics are shown to be sensitive to various parameters such as the pump pulse width, pump intensity, life time of the M state, thickness of the film and absorption cross-section of the B-state at probe wavelength (σBp). It has been shown that the probe laser beam can be completely switched off (100% modulation) by the pump laser beam at relatively low pump powers, for σBp=0. The switching characteristics have also been used to theoretically design all-optical NOT, OR, AND and the universal NOR and NAND logic gates with two pulsed pump laser beams using the six state model.

All-optical switching with bacteriorhodopsin protein coated microcavities and its application to low power computing circuits

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 (BR) protein monolayers. The all-optical tunable resonant coupler re-routes the infrared beam between two tapered fibers in 50 μs using a low power (<200 μW) green (532 nm) and blue (405 nm) 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 2n−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 budget). The combined advantages of high Q-factor, tunability, compactness, and low power control signals, with the flexibility of cascading switches to form circuits, and r...

Fiber optic sensor for determining adulteration of petrol and diesel by kerosene

Abstract We present a simple, intrinsic intensity modulated fiber optic sensor for determining adulteration of petrol and diesel by kerosene. Experimental results for a prototype fabricated in the laboratory are presented. The sensing principle is based on modulation of intensity of light guided in the fiber due to change in the refractive index of the cladding formed by adulterated fuel and the phenomenon of evanescent wave absorption. The sensor is useful due to its simple construction, operation, safety with inflammable fuels and the possibility of making it compact and portable for on-road measurements.

All-optical switching with bacteriorhodopsin

All-optical, mirrorless switching is demonstrated with bacteriorhodopsin (bR) film using a very simple geometry. A low-power, 532 nm laser beam modulates the transmission of a cw laser beam at 635 nm, a wavelength that corresponds to peak absorption of the O-excited state in the bR photocycle. The switching contrast depends on the pulse width and average power of the modulating laser. Varying the pulse width and frequency of the modulating laser controls the phase of the switching characteristics. Simulations based on a rate equation approach consider a six-state model of the bR photocycle that successfully reproduce the experimental results.

Generalized model for all-optical light modulation in bacteriorhodopsin

We present a generalized model for the photochemical cycle of bacteriorhodopsin bR protein molecule. Rate equations have been solved for the detailed light-induced processes in bR for its nine states:

All-Optical Reversible Logic Gates with Optically Controlled Bacteriorhodopsin Protein-Coated Microresonators

(B\rightarrow K \leftrightarrow L \leftrightarrow M^I \rightarrow (M^{II}) \leftrightarrow N \leftrightarrow

All-optical biomolecular parallel logic gates with bacteriorhodopsin

O \leftrightarrow P \rightarrow Q \rightarrow B)

Femtosecond all-optical parallel logic gates based on tunable saturable to reverse saturable absorption in graphene-oxide thin films

. The complete steady-state intensity-induced population densities in various states of the molecule have been computed to obtain a general, exact, and analytical expression for the nonlinear absorption coefficient for multiple modulation pump laser beams. All-optical light modulation of different probe laser beam transmissions by intensity induced population changes due to one and two modulation laser beams has been analyzed. The proposed model has been shown to accurately model experimental results.

Novel proposal for all-optical Fredkin logic gate with bacteriorhodopsin-coated microcavity and its applications

We present designs of all-optical reversible gates, namely, Feynman, Toffoli, Peres, and Feynman double gates, with optically controlled microresonators. To demonstrate the applicability, a bacteriorhodopsin protein-coated silica microcavity in contact between two tapered single-mode fibers has been used as an all-optical switch. Low-power control signals (<200 μW) at 532 nm and at 405 nm control the conformational states of the protein to switch a near infrared signal laser beam at 1310 or 1550 nm. This configuration has been used as a template to design four-port tunable resonant coupler logic gates. The proposed designs are general and can be implemented in both fiber-optic and integrated-optic formats and with any other coated photosensitive material. Advantages of directed logic, high Q-factor, tunability, compactness, low-power control signals, high fan-out, and flexibility of cascading switches in 2D/3D architectures to form circuits make the designs promising for practical applications.