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Proceedings Paper

Photonic applications of bacteriorhodopsin
Author(s): Devulapalli V. G. L. N. Rao; Francisco J. Aranda; Joby Joseph; Joseph A. Akkara
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Paper Abstract

The photochromic protein bR is receiving much attention as an interesting alternative to conventional inorganic semiconductor based materials for a variety of applications in optical recording and information processing. Recent advances in genetic engineering techniques for tailoring molecular properties without degrading of its inherent mechanical and thermal stability make it an outstanding photonic material. Some of the photonic applications already demonstrated by our group are reviewed. We exploit the parallel processing of optics and the real-time nature of bR films for the implementation of several photonic applications. We reported a convenient method to obtain all-optical light modulation in bacteriorhodopsin films using a degenerate four-wave mixing geometry. Chemically stabilized films of bacteriorhodopsin in a polymer matrix for which the life time of the excited M state is tens of seconds are used to demonstrate all-optical light intensity modulation. Small intensities of order mW/cm2 are used in the modulation experiments. The fast photochemical transition from M to B permits reasonably fast modulation speeds independent of the slow thermal M to B relaxation time. The experimental system can also be viewed as an all-optical switch, that uses molecular states in a bacteriorhodopsin thin film, where a low power blue pulse turns on a signal red beam. All-optical logic gates are implemented with wild- type and chemically stabilized films of bacteriorhodopsin using a two-color backward degenerate four- wave mixing geometry. The sensitivity of each bR film is markedly different due to the large differences in the saturation intensity. Red light is used to form a grating due to the B to M transition and blue light is used to form a grating due to the fast photochemical transition from M to B. Each of the two wavelengths in the experimental system acts as an input to the all-optical gate and the phase conjugate signal beam bears the output of the gate. To establish the origin of the nonlinearity we studied the intensity dependence of the self-focusing and self-defocusing properties of wild-type bR in water solution using the Z-scan technique with low power cw lasers at two wavelengths on either side of the absorption band. Our measurements indicate that the sign of the nonlinearity depends on the wavelength and the magnitude depends on the fluence of the incident laser beam. The observed self-defocusing and focusing is not due to the intrinsic electronic nonlinearity. The observations can be explained in terms of the Kramers-Kronig dispersion relation that relates the real and imaginary parts of the complex index of refraction to the absorption spectrum.We developed an optical pattern recognition system using Optical Fourier Transform with bR films. The photoinduced dichroism and its dependence on light intensity allows one to use the bR film as a real-time self-adaptive spatial filter at the FT plane. We also demonstrate flow disturbance visualization and beam shaping.

Paper Details

Date Published: 2 January 1998
PDF: 10 pages
Proc. SPIE 3211, International Conference on Fiber Optics and Photonics: Selected Papers from Photonics India '96, (2 January 1998); doi: 10.1117/12.345549
Show Author Affiliations
Devulapalli V. G. L. N. Rao, Univ. of Massachusetts/Boston (United States)
Francisco J. Aranda, Univ. of Massachusetts/Boston (United States)
Joby Joseph, Univ. of Massachusetts/Boston (United States)
Joseph A. Akkara, U.S. Army Natick Research, Development & Engineering Ctr. (United States)

Published in SPIE Proceedings Vol. 3211:
International Conference on Fiber Optics and Photonics: Selected Papers from Photonics India '96

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