Qi Wang Song

Electro-optic beam-steering device based on a lanthanum-modified lead zirconate titanate ceramic wafer

We demonstrate a lanthanum-modified lead zirconate titanate ceramic-based electro-optic beam-steering device that has a 3 mm × 3 mm working area. A series of resistors were made by evaporation of chromium onto the substrate to produce and control the required voltage distribution among the electrodes. A steering angle of 0.04° was obtained with an applied voltage of 700 V. Design considerations, computer simulations, and experimental results are presented.

Optical switching with photorefractive polarization holograms

A switching technique that uses the polarization sensitivity of photorefractive holograms in crystals is experimentally demonstrated. The design is capable of handling a large number of 2 x 2 switching channels with only four holograms. The concept is applicable to either synchronous or asynchronous switching and also to a variety of photorefractive materials.

Time-dependent all-optical logic gates based on two coupled waves in bacteriorhodopsin film

When two coherent green beams offset from each other by a small angle are coupled in bacteriorhodopsin film, the diffraction intensity rises from zero to a maximum, and then decreases along with the writing time. Based on the change of the diffraction intensity with the writing time, we proposed and demonstrated a time-dependent all-optical exclusive not or (XNOR) operation and a time-dependent all-optical logical inverter (NOT) operation. Based on the relation between the self-diffraction intensity and the polarization states of the input beams, the time-dependent all-optical XNOR logic gate was achieved, and based on the relation between the polarization states of the diffraction beams and that of the recording beams, the time-dependent all-optical NOT logic gate was obtained.

All-optical time-delay relay based on a bacteriorhodopsin film

Using the property of dynamic complementary suppression modulated transmission of bacteriorhodopsin film, we propose and demonstrate an all-optical time-delay relay in an incoherent light system. The relay can last for a certain amount of time after the switch function of turn off (or turn on) is activated. Furthermore, the delay time can be adjusted by changing the lifetime of the M state and the intensities of blue and yellow beams.

Photoinduced anisotropy in bacteriorhodopsin films

Photoinduced anisotropy in terms of dichroism and birefringence was investigated in a series of experiments. Measurements and comparisons were made using samples of wild type bacteriorhodopsin and its mutations 3,4-dehydro BR and 4-keto BR.

Bacteriorhodopsin optical switch

A novel bacteriorhodopsin based photonic crossbar system for broadband communications is proposed. This free-space dynamically reconfigurable N X N crossbar switch utilizes an intelligent holographic system for routing and switching by dynamically reconfigurable gratings of bacteriorhodopsin, which has high write/read photocyclicity that is greater than 106. The major advantages of the system include large interconnectivity density, transparent data redistribution, and fiber optic bandwidth capacity. In addition, the switching device resolves optical-to-electronic and electronic-to- optical conversion bottlenecks and reduces signal-to-noise degradation which is due to the conversions. This crossbar design is completely free of internal blocking which is one of the major drawbacks of guided optical crossbars. The system takes advantage of the parallelism and multidimensionality inherent in optics and can be scaled to a large capacity of N X N, while it maintains a low weight and portability which are a projected requirement for future broadband communications.

Protein-based volumetric memories

This paper will explore the use of the protein, bacteriorhodopsin, as the photoactive recording medium in an optical three-dimensional memory. Although this protein has been used previously as the photoactive medium in a number of three-dimensional architectures (e.g., holographic and two- photon), a sequential one-photon volumetric architecture employing a photochemical branching reaction characteristic of the protein is currently showing the most promise. This unique branching reaction allows for long-term data storage by the protein, and rigorously excludes unwanted photochemistry. During the past two years, two prototypes have been constructed, and the preliminary results look promising. The use of chemical modification and genetic engineering of the protein has improved data reliability by roughly five-fold, but reliability remains an issue. Some of the key problems will be discussed. In addition, the use of gray-scale and polarization multiplexing to increase the storage capacity will be examined.

Effective optical nonlinearity of KNSBN: Ce crystal and its applications to continuous-wave optical limiting

The effective optical nonlinearity n2 of a Ce-doped KNSBN crystal is measured by using the Z-scan method. The dependence of n2 on the illumination wavelength and polarization is characterized. An optical limiter for strong cw illumination is demonstrated, based on self-focusing and spatial self-phase-modulation.

Chemically enhanced bacteriorhodopsin thin-film spatial-light modulator

An optically addressed spatial light modulator that is based on the chemically enhanced bacteriorhodopsin thin film is demonstrated. The underlying principle is the light-induced shift of absorption band of the protein. The device can be chemically or genetically modified for different applications. In our preliminary experiment, a resolution of about 100 line pairs per millimeter with a linear dynamic range of above 100:1 is obtained.

The behaviours of optical novelty filter based on bacteriorhodopsin film

The quality of the novelty filter image is investigated at different intensities of the incident blue and yellow beams irradiating a bacteriorhodopsin (bR) film. The relationship between the transmitted blue beams and the incident yellow beams is established. The results show that the contrast of the novelty filter image depends on the lifetime of longest lived photochemical state (M state). These results enable one to identify the direction of a moving object and to improve the quality of the novel filter image by prolonging the lifetime of M state.