Search

Optical films containing the genetic variant bacteriorhodopsin BR-D96N were experimentally studied in view of their properties as media for holographic storage. Different polarization recording schemes were tested and compared. The influence of the polarization states of the recording and readout waves on the retrieved diffractive image's intensity and its signal-to-noise ratio were analyzed. The experimental results showed that, compared with the other tested polarization relations during holographic recording, the discrimination between the polarization states of diffracted and scattered light is optimized with orthogonal circular polarization of the recording beams, and thus a high signal-to-noise ratio and a high diffraction efficiency are obtained. Using a He-Ne laser (633 nm, 3 mW) for recording and readout, a spatial light modulator as a data input element, and a 2D-CCD sensor for data capture in a Fourier transform holographic setup, a storage density of 2 x 10(8) bits/cm2 was obtained on a 60 x 42 microm2 area in the BR-D96N film. The readout of encoded binary data was possible with a zero-error rate at the tested storage density.

In polymeric films of bacteriorhodopsin (BR) a photoconversion product, which was named the F620 state, was observed on excitation of the film with 532 nm nanosecond laser pulses. This photoproduct shows a strong nonlinear absorption. Such BR films can be used for write-once-read-many (WORM) optical data storage. We demonstrate that a photoproduct similar or even identical to that obtained with nanosecond pulses is generated on excitation with 532 nm femtosecond pulses. This photoproduct also shows strong anisotropic absorption, which facilitates polarization storage of data. The product is thermally stable and is irretrievable to the initial B state either by photochemical reaction or through a thermal pathway. The experimental results indicate that the product is formed by a two-photon absorption process. Optical WORM storage is demonstrated by use of two polarization states, but more polarization states may be used. The combination of polarization data multiplexing and extremely short recording time in the femtosecond range enables very high data volumes to be stored within a very short time.

Holographic gratings recorded in photochromic media often do not obtain the maximally achievable diffraction efficiency because of diminishing the fringe contrast caused, e.g., by a photochemically active readout beam or unequal intensities of object and reference waves. For nonreversible materials this problem causes a decrease in diffraction efficiency that is proportional to the signal-to-noise ratio (SNR). However, in nonlinear materials such as photochromic media, for which saturation effects need to be considered, an out-of-proportion decrease in the SNR results. It is shown that an overshooting peak during hologram growth, which then decays to a lower permanent level of diffraction, is an indicator for such a situation. Even a weak readout beam may cause such effects, which significantly affect the hologram kinetics. The observed overshooting diffraction efficiency may even be misinterpreted to be dependent on material properties. Experimental and theoretical proof that with low levels of auxiliary light this type of problem can be eliminated completely is presented. Throughout this research bacteriorhodopsin films were used, but the results are valid for photochromic media in general.

Incoherent optical processing with films made from the biological photochrome bacteriorhodopsin (BR) is accomplished by use of the photoinducible anisotropy of polymeric BR films. BR has two spectrally well separated states, B and M, both of which show a high degree of optical anisotropy. Whereas with green and blue light the BR molecule can be switched between the two states, the accompanying changes in the refractive index may be nondestructively read out by wavelengths in the red, e.g., at 676nm. As the sensitivity of CCD arrays is quite high for such wavelengths, even low-power light sources are sufficient for detection. We describe a BR-based XOR computing module for incoherent optical data processing.

First experimental results from a direct-view display made from bacteriorhodopsin (BR) are presented. A dielectric mirror in direct contact with the photoactive BR layer forms the core of the BR display. The dielectric layer both decreases the light intensity necessary for writing and protects the observer from transmitted laser light. By illuminating the BR display with a suitably filtered light source from the rear we achieve the result that the information appears to the observer with an intensity contrast of more than 70:1, accompanied by a significant color shift. The combination of both enhances the visibility of and the ability to discern the information significantly. On the BR display the information appears in yellow on a dark purple-red background.

A self-pumped, phase-conjugating mirror (diameter 17 mm) is described that contains the bacteriorhodopsin variant D96N as the photoactive material. Resonant reflectivities up to 30% were obtained with an intensity of 25 mW/cm(2) at 647 nm. Rise times of less than 1 ms were observed with an intensity of 500 mW/cm(2) at 532 nm. Wave-front restoration with spatial light modulators as the dynamic input device was demonstrated, and the dependence of the reflectivity on the intensity and polarization was analyzed. The reflectivity shows no significant decrease with increasing angle between the pump and signal beams as a result of the high resolution of the bacteriorhodopsin films.

An adaptive correlator system is presented that uses a bacteriorhodopsin film as the active holographic material. Because M-type holography with bacteriorhodopsin films is used, the TV frame rate is met at fairly low intensities. No limitations arising from the heterodyne operation of the dual-axis joint-Fourier-transform correlator were observed. The system's capability to monitor autonomously the speed of an object moving randomly in the whole viewing field of a video camera is demonstrated.

A dual-axis joint-Fourier-transform correlator is described with two liquid-crystal television screens as input devices and a bacteriorhodopsin film as the active holographic material in the Fourier plane. The experimental data presented demonstrate that this system is capable of processing two independent video signals in real time with a signal-to-noise ratio of 45 dB.

The biological photochrome bacteriorhodopsin (BR) is contained within the purple membrane (PM) of Halobacterium halobium. Artificial derivatives with improved optical properties can be generated by genetic methods and isolated from mutated halobacterial strains. The use of PM films that contain wild-type BR and BR variants as real-time recording media for various holographic applications has been reported previously, and the advantages of BR variants have been demonstrated. The high reversibility (>> 10(5) record/erase cycles), the fast time scale of its photoconversions (femtoseconds to milliseconds), and the large photochromic shift ( approximately 160 nm) occurring during its photocycle make it a promising material for real-time applications. A dual-axis joint-Fourier-transform (DA-JFT) correlator is used to demonstrate the applicability of PM films in holographic pattern recognition. One major advantage of PM films in this application is their high spatial resolution of more than 5000 lines/mm. Severe restrictions on the overall performance of the DA-JFT correlator system are caused by scattered light and result in a low signal-to-noise ratio. Since PM patches typically have a diameter in the range of the visible wavelengthsthat are used for hologram recording, light scattering is an intrinsic problem of PM films. The polarization recording properties of PM films are employed to overcome this problem. More than 20-fold improvement of the signal-to-noise ratio in the DA-JFT correlator output is obtained.