Guofu Chen

Polarization patterns hide and display using photoinduced anisotropy of photochromic fulgide

Photoinduced anisotropy of a photochromic pyrrylfulgide/PMMA film was investigated by using two linearly polarized beams. Excitation by linearly polarized light induces into the film an optical axis that has the same polarization as the excitation beam. This causes a change of the transmittance and of the polarization state of the detection beam. With a microscope a matrix of 4x4 light spots with different polarizations were recorded in the pyrrylfulgide/PMMA film. If readout with non-polarized light, the matrix of light spots show no information pattern. However, when readout with differently polarized lights, different patterns can be displayed. The experiment demonstrates that pyrrylfulgide/PMMA films can be used to hide two differently polarized patterns, which may be applied in camouflage technology.

Polarization holographic high-density optical data storage in bacteriorhodopsin film

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 images 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.

Phase matching analysis of noncollinear optical parametric process in nonlinear anisotropic crystals

Phase matching for noncollinear optical parametric generation is investigated. All the possible phase matching configurations and existence conditions for general noncollinear three-wave mixing interactions are derived for propagation within the crystal principal planes. Numerical expressions for the critical phase matching angles are presented wherever possible. Finally, as an application of these expressions, several numerical calculations of the phase matching angles for general noncollinear phase matched optical parametric amplification in the nonlinear-optical crystals such as beta -BaB2O4, LiB3O5 and KTiOPO4 are completed. and the results are graphically presented

Optical image processing using the photoinduced anisotropy of pyrrylfulgide

A synthesized photochromic compound-pyrrylfulgide--is prepared as a thin film doped in a polymethylmethacrylate (PMMA) matrix. Under irradiation by UV light, the film converts from the bleached state into a colored state that has a maximum absorption at 635 nm and is thermally stable at room temperature. When the colored state is irradiated by a linearly polarized 650 nm laser, the film returns to the bleached state; photoinduced anisotropy is produced during this process. Application of optical image processing methods using the photoinduced anisotropy of the pyrrylfulgide/PMMA film is described. Examples in non-Fourier optical image processing, such as contrast reversal and image subtraction and summation, as well as in Fourier optical image processing, such as low-pass filtering and edge enhancement, are presented.

Optical Properties and Applications of Photochromic Fulgides

ABSTRACT The optical properties and potential applications of four kinds of fulgide and fulgimide were studied. A parallel optical storage apparatus was set up, which could reach the area density of 4.8 × 107 bits/cm2 on the fulgide/PMMA film. Fourier transform orthogonal circular polarization holographic data storage was performed with high signal-to-noise-ratio reconstruction image, which obtained the storage density of 2 × 108 bits/cm2 for single hologram. Two-photon induced micro-patterns were recorded on the fulgimide/PMMA film with 800 nm, 100 fs, 1 KHz, 50 mW femtosecond laser. Dual-wavelength (650 nm and 488 nm) optical images storage were tested on a two-color mixing fulgides/PMMA film.

Kinetic spectra of light-adaptation dark-adaptation and M-intermediate of BR-D96N

BR-D96N is a kind of genetically site-specific mutants of bacteriorhodopsin (BR) with obvious photochromic effect. Compared to the wild type BR, the lifetime of M state of BR-D96N is prolonged to several minutes so that the photochromic kinetics and the intermediates formation can be studied by the conventional spectra analysis. In the experiment, the absorption spectra of the sample at different time after light illumination are measured with spectrophotometer. By fitting and analyzing the variation of the spectra, we suppose that there are three main states in the photochromic process, i.e., B state (light-adapted state), M state and D state (dark-adapted state). The absorption spectra of the B state, M state and D state are extracted from the experimental data based on this three-state model and the spectra at various time are fitted with the least-square method. So, the variations of population percentages of the M state, B state and D state are obtained and the M state and B state lifetimes are estimated. In another way, from the measurement of the absorption dynamics at 407 and 568 nm, the M state and B state lifetimes are also obtained by two exponential data fitting, which give coincident results with those of the spectra analysis.

Experimental study of optical storage characteristics of photochromic material: pyrrylfulgide

Optical data storage is a frontier in the information science. Currently, there are mainly two kinds of storage materials, i.e., thermal-optic and photonic materials. The storage methods are divided into serial and parallel modes. In the market, the mature technique is CD-RW, which uses the thermal-optic material and serial method. The storage density of the CD-RW is restricted by the size of material particles, the conduction of heat, etc. Besides, the recording speed is seriously limited by the process of heating. Photonic materials and parallel method will be the trend in the optical data storage. Because it is based on the photon reaction on the molecule scale, the storage density and speed will be greatly increased. In this paper, a new kind of organic photochromic material -- pyrrylfulgide was studied. A parallel optical data storage system was established. Using the pyrrylfulgide/PMMA film as a recording medium, micro-images and binary digital information could be recorded, readout and erased in this parallel system. The recorded information on the film can be kept for at least 8 months in dark at room temperature. So far, the storage density is 3 x 107 bit/cm2.

Photoinduced anisotropy in pyrrlfulgide and its application in optical image processing and polarization holography

Photoinduced anisotropic properties of pyrrylfulgide are studied. From measurement of the photoinduced spectrum of dichroism, the birefringence spectrum is evaluated by Kramers-Kronig relations. At optimal exposure of 13 ~ 20J/cm2 a maximum photoinduced dichroism (Dperpendicular - Dparallel) of about 0.1 and a maximum photoinduced birefringence (nperpendicular - nparallel) of about 8×10-4 are achieved. We exploit this photoinduced anisotropy and use a pyrrylfulgide/PMMA film to demonstrate optical image processing such as contrast reversal, image subtraction and summation, low-pass filtering and edge-enhancement. From the spectra of dichroism and birefringence the spectrum of the diffraction efficiency for polarization holography is calculated. We demonstrate that diffracted images with high signal-to-noise-ratio (SNR) can be obtained by holographic recording with orthogonal polarization.

Photochromic kinetic spectra and intermediates of BR-D96N

BR-D96N is a kind of genetically site-specific mutant of bacteriorhodopsin (BR) with obvious photochromic effect. Compared to the wild type BR, the lifetime of M state of BR-D96N is prolonged to several minutes so that the photochromic kinetics and the intermediates formation can be studied by the conventional spectra analysis. In the experiment, the absorption spectra of the sample at different time after light illumination are measured with spectrophotometer. By fitting and analyzing the variation of the spectra, we suppose there are three main states in the photochromic process, i.e. B state (light-adapted state), M state and D state (dark-adapted state). The absorption spectra of the B state, M state and D state are extracted from the experimental data based on this three-state model and the spectra at various time are fitted with the least square method. So, the variations of population percentages of the M state, B state and D state are obtained and the M state and B state lifetimes are estimated. In another way, from measuring the absorption dynamics at 407 nm and 568 nm, the M state and B state lifetimes are also obtained by two exponential data fitting, which give coincident results with those of the spectra analysis.

Experimental investigation of parallel optical data storage using pyrrylfulgide photochromic material

The optical storage characteristics of a new kind of organic photochromic material—pyrrylfulgide were experimentally investigated in the established parallel optical data storage system. Using the pyrrylfulgide/PMMA film as a photon-mode recording medium, micro-images and encoded binary digital data were recorded, readout and erased in this parallel system. The storage density currently reaches 3xl07bit/cm2. The recorded information on the film can be kept for years in darkness at room temperature.