All-optical image switch based on bacteriorhodopsin film

While two waves are coupled in bacteriorhodopsin (bR) film, a beam of incident light carrying the image is transferred to two diffraction beams whose intensities can increase from zero to a maximum and then decrease to a stable value with the increase of the writing time. Based on the relation among the polarization states of image in a recording beam and diffraction beams, we have proposed and demonstrated the all-optical image transfer switch which depends on the effective time and has the function that within the effective time, a polarization state image is automatically transferred to two images whose polarization states are perpendicular, and the transfer stops automatically beyond the effective time. A time-dependent all-optical image switch with muti-outputs is implemented.     

All-optical display using photoinduced anisotropy in a bacteriorhodopsin film

Photoinduced anisotropy in a bacteriorhodopsin film using the pump-probe method was investigated. A diode-pumped second-harmonic YAG laser was used as the pump beam, and three wavelengths, at lambda = 442, 532, 655 nm, from different lasers were used as probe beams. Without the pump beam, the probe light cannot transmit the analyzer to the detector. However, because of photoinduced anisotropy, a portion of the probe light is detected when the pump beam is present. Based on this property, we demonstrate a full-color all-optical display.     

Time-dependent all-optical logic-gates with bacteriorhodopsin film

In this paper, we proposed time-dependent AND, NOT and operation based on the relation between input and output intensities of the first-order diffraction beams in degenerate multi-wave coupling. When two coherent green beams are coupled in bacteriorhodopsin (bR) film with a small angle, the intensities of the diffraction beams decrease along with writing time. Based on the phenomenon that the diffraction beams decay along with writing time and the relation between the intensities of input and output beams, we demonstrated the time-dependent optical AND, NOT and operations.     

基于细菌视紫红质膜的全光逻辑门

基于在细菌视紫红质膜中的自衍射，我们提出了全光非、异或、半加器及同或门逻辑操作。利用衍射光与记录光偏振状态之间的关系，我们演示了非门和同或门逻辑操作。 通过衍射光，记录光和读出光之间的偏振状态的关系，我们实现了异或逻辑操作和具有三个输入端的半加器逻辑操作。所用方法简单实用。     

The study of the nonlinear absorption in the nonlinear-imaging technique with phase object

The nonlinear absorption can produce a nonlinear image very similar with the one created by the nonlinear refraction when using the nonlinear-imaging technique with phase object to measure the third-order nonlinearity of materials, but the principles of them are different. The formation of the nonlinear absorption image is explained, and the condition that the highest sensitivity of the nonlinear absorption measurement can be reached is deduced. For the materials with both nonlinear absorption and refraction, we find a proper phase shift of the phase object where the effect of the nonlinear refraction to the measured signal can be eliminated. The nonlinear absorption and refraction are numerically simulated when the phase shift of phase object to be π/2 that is normally used. The qualitative tendency of the signal variation is presented.     

All-optical switch and limiter based on nonlinear polarization in Mach-Zehnder interferometer coupled with a polarization-maintaining fiber-ring resonator

A novel all-optical switch based on nonlinear polarization mechanism using polarization-maintaining fiber ring with a polarization rotator is proposed. Optical switching with low threshold of mW order and optical limiting with broader limiting range, less fluctuation, higher damage threshold and response speed are demonstrated numerically. The deterioration of switching and the improvement of limiting originating from losses are also studied. Considering the tradeoff between switching power and bandwidth, the way to increase bandwidth is discussed.     

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.     

Holographic simultaneous readout polarization multiplexing based on photoinduced anisotropy in bacteriorhodopsin

Bacteriorhodopsin (bR) is a reversible photochromic protein that can be used as a holographic medium. The dichroic absorption of the bR molecule is polarization dependent, thereby allowing for the recording of polarization holograms. The properties of polarization holograms can be used to multiplex two independent images in a single bR film. A new technique and associated polarization-multiplexing scheme are demonstrated that allow for simultaneous readout of two orthogonally polarized images while achieving a high normalized diffraction efficiency for each of the individual images.     

Image watermarking based on an iterative phase retrieval algorithm and sine-cosine modulation in the discrete-cosine-transform domain

A novel digital image watermarking system based on an iterative phase retrieval algorithm and sine-cosine modulation in the discrete-cosine-transform (DCT) domain is proposed. The original hidden image is first encrypted into two phase masks. Then the cosine and sine functions of one of the phase masks are introduced as a watermark to be embedded into an enlarged host image in the DCT domain. By extracting the watermark of the enlarged superposed image and decryption we can retrieve the hidden image. The feasibility of this method and its robustness against some attacks, such as occlusion, noise attacks, quantization have been verified by computer simulations. This approach can avoid the cross-talk noise due to direct information superposition and enhance the imperceptibility of hidden data.     

A half-blind color image hiding and encryption method in fractional Fourier domains

We have proposed a new technique for digital image encryption and hiding based on fractional Fourier transforms with double random phases. An original hidden image is encrypted two times and the keys are increased to strengthen information protection. Color image hiding and encryption with wavelength multiplexing is proposed by embedding and encryption in R, G and B three channels. The robustness against occlusion attacks and noise attacks are analyzed. And computer simulations are presented with the corresponding results.     

Color image encoding in dual fractional Fourier-wavelet domain with random phases

A new cryptology in dual fractional Fourier-wavelet domain is proposed in this paper, which is calculated by discrete fractional Fourier transform and wavelet decomposition. Different random phases are used in different wavelet subbands in encryption. A new color image encoding method is also presented with basic color decomposition and encryption respectively. All the keys, including random phases and fractional orders in R, G and B three channels, should be correctly used in decryption, otherwise people cannot obtain the totally correct information. Some numerical simulations are presented to demonstrate the possibility of the method. It would have widely potential applications in digital color image processing and protection.     

All-optical dual-direction half-subtracter based on sum-frequency generation

We report a simple method to realize all-optical dual-direction half-subtracter at 40 Gb/s based on sum-frequency generation (SFG) using only one periodically poled lithium niobate (PPLN) waveguide. The SFG process generates the Borrow outputs and the combination of the outputs from PPLN after SFG results in the Difference. The operation performance of the proposed scheme is simulated, including eye diagrams, Q-factor, extinction ratio, and tunability. For different input optical powers, the length of the PPLN waveguide is optimized.     

All-optical neural-net-like image processing with photosensitive nonlinear nematic film

Received June 30, 2003 We demonstrate that some neural-net image-processing operations can be realized in an all-optical manner by use of the natural diffraction property of light in conjunction with the photosensitivity and optical nonlinearities of a transparent thin film. An example of image edge enhancement is illustrated with photosensitive supranonlinear nematic liquid-crystal films.     

Modelling the vertical grating-waveguide coupler for the description of its nonlinear symmetry-breaking dynamics

We propose a new scheme to observe the symmetry-breaking dynamics of two counter-propagating beams in a Kerr-type nonlinear waveguide coupler. Using a grating to couple light at normal incidence upon the waveguide allows for a single-beam geometry. The ability of the grating to couple light symmetrically is demonstrated on the basis of a linear coupled-mode approach especially adapted to vertical coupling. The nonlinear symmetry-breaking dynamics is studied analytically.     

Control of the switch between optical multistability and bistability in three-level V-type atoms

We theoretically investigated a hybrid absorptive-dispersive optical bistability and multistability behaviour in a three-level V-type system using a microwave field driving a hyperfine transition between two upper excited states inside a unidirectional ring cavity. We find that the intensity and the frequency detuning of the coupling field as well as the intensity of the microwave field can affect the OM behaviour dramatically, which can be used to control the transition from OM to OB or vice versa without need to resort the effect of the quantum interference. The effects of the phase, the quantum interference and the atomic cooperation parameter on the OM are also studied. Our scheme may be used for building more efficient all-optical switches and logic-gate devices for optical computing and quantum information processing.     

Two orthogonally polarized optical beams in a family of Kerr-law nonlinear shifted parabolic graded-index rod lenses

The field, the propagation and the imaging characteristics of two Gaussian optical beams with orthogonal polarization passing through a family of Kerr-law nonlinear shifted parabolic graded-index rod lenses are investigated. The coupled differential equations of the dimensionless beam-width parameters of two Gaussian optical beams are derived by using a variational approach and then solved. It is concluded that there are two regimes of propagation and that the power, the incident waist radius and the position of one beam have large effects on the field, the propagation and the imaging characteristics of the other beam.     

Optical vortices in self-focusing Kerr nonlinear media

In this work we numerically compare the interaction of optical vortices (OVs) in self-defocusing and self-focusing Kerr nonlinear media. We find that the basic scenarios (attraction/repulsion, translation/rotation vs. background) in the interaction of two and three vortices with equal and alternative topological charges (TCs) are the same in both media. However, the vortex dynamics under self-focusing conditions is influenced by the reshaping of the surrounding part of the background. Square structure of OVs with alternating TCs is found to be stable with respect to the vortex positions in self-focusing media. This elementary cell is successfully generalized in a large square array of OVs with alternative TCs which brings ordering in the multiple filamentation of the background beam in self-focusing conditions.     

Passive harmonic mode-locking in a fiber laser with nonlinear polarization rotation

On basis of numerical simulation and analytical treatment, we investigate the multiple pulse passive mode-locking of a fiber laser with nonlinear loss due to the nonlinear polarization rotation technique. Various additional mechanisms resulting in the ordering of ultrashort pulses inside the laser resonator and in the realization of harmonic passive mode-locking are analyzed. Among which are the active harmonic modulation of the intracavity loss or of the refractive index, the passive modulation of the index due to the inertial properties of intracavity elements, and the amplification modulation due to the depletion and the relaxation of the gain. The velocity of pulses relative to each other is determined, it results in attractive or repulsive pulse-pulse interaction, and allows to evaluate the conditions of ordering of the pulses inside the cavity.     

Degenerate four-wave mixing based on excited-state absorption in azo-dye-doped polymer films

Degenerate Four-Wave Mixing (DFWM) based on excited-state absorption in azo-dye doped polymer films is firstly reported. Under a pre-exciting argon laser at 514.5 nm, DFWM is performed using a 632.8 nm HeNe laser which is absorbed only slightly when the molecules are in the ground state. The dynamic behavior of the DFWM signal due to excited-state absorption is also treated theoretically.     

Characterization of the KNSBN: Cu crystal with two-wave coupling at visible and infrared wavelengths

We have optically characterized the newly-developed photorefractive crystal KNSBN: Cu by two-wave coupling at visible and near-infrared wavelengths. The effective electrooptic coefficients(k _g)r ₁₃ and(k _g)r ₃₃, the effective charge carrier densityN _eff, the dark conductivity _d, the product of mobility and electron-trap recombination time _R, the formation and decay rate of index grating and the absorption coefficient of the crystal were determined from visible to near-infrared wavelengths. Their wavelength dependences were also studied. It is interesting to notice that the KNSBN: Cu crystal has a very largeN _eff and large gain coefficient for ordinary ray (o-ray) in the visible region, and the photorefractive properties of the crystal are very different in the visible and near-infrared spectral regions.