An optical key distribution method based on aero-optical effect of boundary layer flow is proposed. The technique exploits the underlying dynamics of the turbulence boundary layer to generate secret key for both communication parties. Corresponding computer simulation and experiments are carried out. The bit error rate of key distribution is 0.05% and 0.22% in the simulation and the experiment, respectively. Further test also shows that the proposed key generation technique is valid to work with optical encryption technique.
Fuzzy control iterative algorithm for beam uniformity enhancement of gas laser through boundary layer flow is presented. The iterative process of the proposed algorithm is controlled by the fuzzy control theory. In each loop, the MSE and the TUI value are evaluated to fuzzily determine which one is relatively greater, leading to different approaches in the iteration. Computer simulation results proved the effectiveness of the proposed method. Gerchberg- Saxton algorithm, profile smoothing algorithm and fuzzy control iterative algorithm are applied to the diffractive optical element design for the correction of laser beam distorted by a Blausius boundary layer. Fuzzy control iterative algorithm leads to better result than Gerchberg-Saxton algorithm and profile smoothing algorithm. Both mean square error and top ununiformity index of the result obtained by fuzzy control iterative algorithm are rather low.
A new fully distributed optical fiber sensing and location technology based on the Mach-Zehnder interferometers is
studied. In this security system, a new climbing point locating algorithm based on short-time average zero-crossing rate
is presented. By calculating the zero-crossing rates of the multiple grouped data separately, it not only utilizes the
advantages of the frequency analysis method to determine the most effective data group more accurately, but also meets
the requirement of the real-time monitoring system. Supplemented with short-term energy calculation group signal, the
most effective data group can be quickly picked out. Finally, the accurate location of the climbing point can be
effectively achieved through the cross-correlation localization algorithm. The experimental results show that the
proposed algorithm can realize the accurate location of the climbing point and meanwhile the outside interference noise
of the non-climbing behavior can be effectively filtered out.
A novel optical security technique for safeguarding user passwords based on an optical fractal synthesizer is proposed. A validating experiment has been carried out. In the proposed technique, a user password is protected by being converted to a fractal image. When a user sets up a new password, the password is transformed into a fractal pattern, and the fractal pattern is stored in authority. If the user is online-validated, his or her password is converted to a fractal pattern again to compare with the previous stored fractal pattern. The converting process is called the fractal encoding procedure, which consists of two steps. First, the password is nonlinearly transformed to get the parameters for the optical fractal synthesizer. Then the optical fractal synthesizer is operated to generate the output fractal image. The experimental result proves the validity of our method. The proposed technique bridges the gap between digital security systems and optical security systems and has many advantages, such as high security level, convenience, flexibility, hyper extensibility, etc. This provides an interesting optical security technique for the protection of digital passwords.
An optic-electronic hybrid certificate validation technique based on Fresnel encoding is proposed. A confirming experiment has been carried out. This technique consists of two processes: encoding and decoding. During the encoding process, an original image is encoded by a computer into an encoded image, which is subsequently printed on a certificate. During the decoding process, the encoded image is extracted from the certificate and decoded optically. The experimental result proves the validity and reveals some advantages of our method. Compared with some previous works, more useful original information can be encoded in our method. The security level of our method is also enhanced by importing the Fresnel diffraction range z as another key. This paper also explores practical application of this technique.
In this paper, we propose a new encoding method to make a binary amplitude-based phase-only-encoded barcode in a
security system based on the conventional random phase encoding technique. In this method, the values of the phase
distribution in the system are quantified with a high phase level, and afterwards the result is encoded into a binary matrix
based on the rule of decimal-binary conversion. The binary matrix is arranged specially and printed as the 2-D anti-counterfeit
label which can be printed by standard halftoning technology and read by optical scanning device. It is
obvious that the higher phase level could be chosen to obtain the better reconstruction image in the improved method
and the fabrication is also very convenient. In additions, computer simulations and optical scanning experiments are
illustrated in detail. The tolerance to data loss of the encoded barcode is also studied particularly. The results show that
the presented encoding method has advantage of robustness and high security, and very convenient to be popularized in
The robustness and security of random phase encoding technique are analyzed. We study the tolerance to data loss of the decrypting key for binary text and a grayscale image. To enhance the security, an improved phase coding scheme based on the chaos theory is proposed. The proposed optical setups for image decryption are depicted. The analyses show that the improved scheme can effectively improved the security.
In the processing diagnosis of the inertia confinement fusion (ICF), the ring coded aperture imaging technique is applied in order to gain high space and time resolutions simultaneously. The key of acquiring high spatial resolution is how to obtain a point spread function of an imaging system. The common method is the firsthand projection method which is an approximate one. The x-ray diffraction effect is neglected in the method, so the resolution of reconstructed image is decreased. We have derived the point spread function (PSF) of the ring coded aperture from scalar diffraction theory. And the Wiener filter is fabricated on the basis of the PSF. In National Key Laboratory of Laser Fusion, at China Academy of Engineering Physics, the imaging experiment on the diagnosis of ICF is completed using the ring coded aperture plate with inner diameter d1 = 250μm and outer diameter d2 = 260μm .The obtained coded image is processed by the Wiener filter which diffractive effect is considered. The processed results have shown that resolution and modulation contrast of acquired image are evidently better than the results obtained by the firsthand projection method.
In the latest 20 years, x-ray imaging technology has developed fast in order to meet the need of x-ray photo-etching, spatial exploration technology, high-energy physics, procedure diagnosis of inertial confinement fusion (ICF) et al. Since refractive index of materials in the x-ray region is lower than 1, and x-ray is strongly absorbed by materials, it is very difficult to image objects in the x-ray region. Conventional imaging methods are hardly suitable to x-ray range. In general, grazing reflective imaging and coding aperture imaging methods have been adopted more and more. In this paper, according to user’s requirement, we have designed a non-coaxial grazing KBA microscope. The microscope consists of two sets of perpendicular spherical mirrors, each set includes two parallel mirrors. Taking it as an example, we have compiled an optical computing program for the non-coaxial grazing imaging systems so as to analyze and evaluate aberrations of KBA microscope. Thus it can help us to get an optimal comprehension of KBA x-ray imaging system. In the same time, the analytical results provide reliable foundation for evaluating imaging quality of KBA microscope.
An improved chaotic algorithm for image encryption on the basis of conventional chaotic encryption algorithm is proposed. Two keys are presented in our technique. One is called private key, which is fixed and protected in the system. The other is named assistant key, which is public and transferred with the encrypted image together. For different original image, different assistant key should be chosen so that one could get different encrypted key. The updated encryption algorithm not only can resist a known-plaintext attack, but also offers an effective solution for key management. The analyses and the computer simulations show that the security is improved greatly, and can be easily realized with hardware.
The light deflector is one of the key components in laser scanning and imaging system, such as rotating holographic gratings, galvanometric mirrors, acoustooptical scanners and rotating polygonal scanners, etc. Of these scanning elements the most commonly used scanner is rotating polygonal scanner. This paper will first briefly discuss the operating principle of rotating polygon and two different polygon scanning configurations: a post-objective scanning scheme and a so-called pre-objective scanning scheme using flat-field scan lens (f-theta scan lens). The emphases will be put on the analysis of the relationship between scanning error and some important error factors of polygon used in the pre-objective scanning scheme. A set of formulae are developed to calculate the tolerance of polygonal reflecting surface, divided angle, the degree of malalignment between reflect surface and the axis of rotation and rotating speed error etc. It provides a reliable foundation for the constitution of the tolerance polygon and rotating speed.