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Journal of the Optical Society of America B

Read times for bacteriorhodopsin-film optical cache memory

C H Wang, M. Bacon, Ajoy Kumar Kar, B. S. Wherrett, Robert L. Baxter

Published Sep 1, 1997• 6 citations
Publisher

Abstract

We report measurements of nonlinear-optical responses of bacteriorhodopsin (BR) films of long intermediate-state lifetimes. Nanosecond-duration pulses were used as the excite beam and cw monochromatic light was used as the probe beam in excite–probe experiments. The results reveal that, whereas the response time of the BR films is of the order of milliseconds at the probe wavelength of 633 nm used in earlier experiments, it is of the order of 100 µs at probe wavelengths of 600 nm and below. Contrast ratios and insertion losses were also measured at different probe wavelengths and probe irradiance levels; the maximum contrast ratio was found to be ∼3:1. The implications of these results for the application of BR films as optical cache memory devices are discussed.

DOI
10.1364/josab.14.002304

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We report measurements of nonlinear-optical responses of bacteriorhodopsin (BR) films of long intermediate-state lifetimes. Nanosecond-duration pulses were used as the excite beam and cw monochromatic light was used as the probe beam in excite–probe experiments. The results reveal that, whereas the response time of the BR films is of the order of milliseconds at the probe wavelength of 633 nm used in earlier experiments, it is of the order of 100 µs at probe wavelengths of 600 nm and below. Contrast ratios and insertion losses were also measured at different probe wavelengths and probe irradiance levels; the maximum contrast ratio was found to be ∼3:1. The implications of these results for the application of BR films as optical cache memory devices are discussed.
We report the optical characterisation of bacteriorhodopsin (BR) films of long intermediate-state lifetimes. The M-state lifetime is extended from 10 ms for the native BR protein to ∼20 minutes for our BR films, by chemical and physical modifications of the material. Optical cache memory characteristics of thin films are studied in excite-probe experiments in which nanosecond-duration pulses are used to excite a BR film and cw monochromatic light used to monitor the transmission dynamics. The memory read-time is found to vary significantly with the probe wavelength; it is of the order of milliseconds at 633 nm and of the order of 100 µs for probe wavelengths of 600 nm and below. The memory erase-time is ∼50 µs. Contrast ratios and insertion losses are measured at different probe wavelengths, with a maximum contrast ratio following nanosecond excitation of ∼3:1 obtained in the peak absorption region of the B-state ( ∼570 nm), at an excitation fluence of 30 mJcm-2. The implications of these results for the application of BR films as optical cache memory devices are discussed.
We report direct observations of all-optical mirrorless bistability associated with saturable absorption in three kinds of bacteriorhodopsin (BR) samples: wild-type BR in water solution and dispersed in thin films of a polymer matrix as well as water solution of the genetically engineered mutant BRD96N. The experiments are carried out with picosecond pulses at 532 nm. The values measured for the saturation intensity are explained in terms of the relaxation of the excited M state population to the B state of the BR photocycle for the three kinds of samples studied.
We observed superluminal light in aqueous solution of the protein complex bacteriorhodopsin (bR) at 647.1 nm wavelength where it exhibits reverse saturable behavior, exploiting the technique of coherent population oscillations (CPO). With a modulation frequency of 10 Hz, the signal pulse through a 1 cm path cell is ahead by 3 msec relative to the reference pulse, corresponding to a group velocity of -3.3 m/sec. Following our early work on slow light in the same sample at the saturable wavelength 568.2 nm, we now explicitly observed the narrow spectral hole in the absorption band of the stable B state and further, demonstrated a close correlation between the profile of the hole and the corresponding pulse delay for various modulation frequencies. A similar behavior is observed for superluminal light versus antihole blown in the absorption band.
In spite of a small and indirect bandgap, silicon features properties that are potentially very attractive for optical applications. The unsurpassed level of impurity control leads to suppression of nonradiative recombination paths and provides for a very long minority carrier lifetime. Up to the present, observation of an optical memory effect has not been reported for crystalline silicon (c-Si). In contrast, it has been observed in GaAs and GaN. In this study, we have used c-Si doped with erbium (Er) ions, since the trivalent Er3+ ion emits at a wavelength of 1.54 μm that is suitable for telecommunication applications. In a two-color experiment, utilizing a Nd:YAG pulse excitation as a writing beam and a free-electron laser (FEL) as a reading beam, we revealed that Si exhibits optical memory and afterglow effects at low temperatures T<50 K. Both effects are, in fact, manifestations of the properties of Si itself, conveniently revealed by the optical dopant. Detailed investigations of the FEL-induced emission at 1.54 μm show that this excitation mechanism is governed by the release of a single type of charge carrier. This implies that hole and electron capture events necessary for the Er excitation could, in principle, be separated in time. Therefore it appears possible to combine optical and electrical write/read procedures for the reported memory effect.
Slow light is demonstrated in liquid phase in an aqueous bacteriorhodopsin (bR) solution at room temperature. Group velocity as low as 3 m/s (all the way to c) is achieved by exploiting the photoisomerization property of bR for coherent population oscillations. Slow light in the liquid phase offers several advantages over solids or vapors for a variety of applications: (i) shorter lifetimes of the M state facilitate slow light at higher modulation frequencies, (ii) convection makes it possible to obtain large signal delays even at high input powers, and (iii) solution concentration is another convenient parameter to vary the signal delay over a wide range.