Shutian Liu

Double image encryption by using iterative random binary encoding in gyrator domains

We propose a double image encryption by using random binary encoding and gyrator transform. Two secret images are first regarded as the real part and imaginary part of complex function. Chaotic map is used for obtaining random binary matrix. The real part and imaginary part of complex function are exchanged under the control of random binary data. An iterative structure composed of the random binary encoding method is designed and employed for enhancing the security of encryption algorithm. The parameters in chaotic map and gyrator transform serve as the keys of this encryption scheme. Some numerical simulations have been made, to demonstrate the performance this algorithm.

Optical image encryption with multistage and multichannel fractional Fourier-domain filtering.

We present a novel image-encryption algorithm that employs multichannel and multistage fractional Fourier-domain filtering architecture. We perform the encryption and decryption by randomly filtering the spatial frequency of the image and then recombining the information from the algorithm in a multistage fractional Fourier domain with pure random-intensity-encoded masks and their complements in a multichannel scheme. The algorithm can be implemented iteratively in an electro-optical setup. Numerical simulations have verified the validity of the algorithm.

Optical image encryption based on multifractional Fourier transforms

We propose a new image encryption algorithm based on a generalized fractional Fourier transform, to which we refer as a multifractional Fourier transform. We encrypt the input image simply by performing the multifractional Fourier transform with two keys. Numerical simulation results are given to verify the algorithm, and an optical implementation setup is also suggested.

Optical image encryption by cascaded fractional Fourier transforms with random phase filtering

We propose a novel architecture of optical image encryption that uses cascaded multi-stages of fractional Fourier transforms with a random phase mask at each stage. Without increasing the complexity of the optical hardware, such algorithm can result in a more secure image encryption with the addition of the extra degrees of freedom provided by the fractional Fourier transforms, i.e. the fractional orders. Numerical simulations have verified its validity.

Random fractional Fourier transform

We propose a novel random fractional Fourier transform by randomizing the transform kernel function of the conventional fractional Fourier transform. The random fractional Fourier transform inherits the excellent mathematical properties from the fractional Fourier transform and can be easily implemented in optics. As a primary application the random fractional Fourier transform can be directly used in optical image encryption and decryption. The double phase encoding image encryption schemes can thus be modeled with cascaded random fractional Fourier transformers.

Generation of hollow Gaussian beams by spatial filtering

We demonstrate that hollow Gaussian beams can be obtained from Fourier transform of the differentials of a Gaussian beam, and thus they can be generated by spatial filtering in the Fourier domain with spatial filters that consist of binomial combinations of even-order Hermite polynomials. A typical 4f optical system and a Michelson interferometer type system are proposed to implement the proposed scheme. Numerical results have proved the validity and effectiveness of this method. Furthermore, other polynomial Gaussian beams can also be generated by using this scheme. This approach is simple and may find significant applications in generating the dark hollow beams for nanophotonic technology.

Asymmetric cryptosystem using random binary phase modulation based on mixture retrieval type of Yang–Gu algorithm

We propose an asymmetric optical image encryption scheme that uses an amplitude and phase mixture retrieval of the Yang-Gu algorithm. The encryption process is realized by employing a cascaded Yang-Gu algorithm together with two random phase masks that serve as the public encryption keys. The two private keys are generated in the encryption process and are randomly distributed binary matrices to be used for performing one-way binary phase modulations. Without the private keys, illegal users cannot retrieve the secret image. Numerical simulations are carried out to demonstrate the validity and security of the proposed scheme.

Image encryption by encoding with a nonuniform optical beam in gyrator transform domains

Based on an optical gyrator transform system, an image encryption algorithm is designed and studied. An original secret image is regarded as the output intensity of the second gyrator transform. A coherent nonuniform optical beam is converted into the input of the first gyrator transform. A Gerchberg-Saxton phase retrieval algorithm is employed for obtaining the compensation phases in the first gyrator transform pair. The compensation phases are regarded as the encrypted image and key in this algorithm. The parameters of the laser beam and gyrator transform can serve as the additional key of encryption method. The decryption process of this encryption algorithm can be achieved with an optical system. Numerical simulations are performed to test the validity and capability of the encryption algorithm.

A theoretical and experimental study on optical limiting in platinum nanoparticles

Optical limiting performance of PVP-stabilized platinum nanoparticles in methanol is investigated with 8 ns pulses at 532 nm. The experimental results show that the platinum nanoparticles possess strong optical limiting effect. We propose a theoretical model based on Mie extinction theory to describe nonlinear optical limiting (OL) behavior of metal nanoparticles. The theoretical analysis and experimental results show that the main mechanism for OL of platinum nanoparticles can be attributed to interband transition of platinum during the excitation of nanosecond pulses.

Optical nonlinearities and optical limiting properties in gold nanoparticles protected by ligands

Abstract Optical nonlinearities of gold nanoparticles protected by ligands have been investigated by Z-scan technique. Absorptive and refractive optical limiting (OL) effects have been measured with 8 ns duration laser pulses at 532 nm. Significant differences have been found experimentally for these two nanoparticles that differ only by their ligands. Such differences indicate that nonlinear optical responses in two nanocomposites are strongly influenced by the surface plasmon resonance of gold nanoparticles and also the nature of ligands. Both of these two nanocomposites show stronger refractive optical limiting effects than C 60 in toluene.