A double-image encryption method is reported using chaotic maps, nonlinear non-DC joint transform correlator (JTC), and fractional Fourier transform (FrFT). The double images are converted into the amplitude and phase of a synthesized function through the application of chaotic pixel scrambling. The synthesized function bonded with a chaotic random phase mask (CRPM) and another different CRPM serve as the input signal of the JTC architecture in the fractional Fourier domain to obtain a real-valued encrypted image. The nonlinear and non-DC operation is also done to improve the security and decrypted image quality. The parameters in joint FrFT correlator and chaotic map serve as the encrypted keys. Numerical simulations have been done to demonstrate the feasibility and validity of this algorithm.
A parallel common path phase-shifting interferometer is presented using a digital reflective grating realized by a digital micromirror device (DMD). The interferometer based on a modified Michelson architecture is constructed by a beamsplitter, a pinhole mirror, a digital reflective Ronchi grating and two lenses with same focal length to build a 4f optical system. In the interferometer, the pinhole mirror is used to low-filter the input-beam to act as reference beam, and the grating is used to introduce phase shift among +1, 0, and −1 diffraction orders of the input-beam to act as object beam. Then the specimen phase can be reconstructed from the three phase-shifted interferograms recorded in one shot using a normalize algorithm. The theoretical analysis and experiments are carried out to demonstrate the feasibility and accuracy of the proposed method.
A reflective off-axis point-diffraction interferometer based on Michelson architecture is built to measure static and dynamic quantitative phase in a single shot. The interferometer is constructed by a beam-splitter, a pinhole mirror, a reflective mirror and two lenses to build a 4f optical system. The pinhole mirror is used as a low-pass spatial filter to generate reference wave. By tilting the reflective mirror, a small angle is created between the object beam and the reference beam to enable an off-axis interferogram. To reconstruct an interferogram with a few fringes, Kreis Fourier method is used to recovery the specimen phase. Using a plano-convex cylinder lens and an evaporative alcohol drop as the specimens, experiments are run to verify the effectiveness and robustness with this interferometer. Experimental results show that this interferometer has not only simple setup and good anti-interference performance, but also good real-time ability, which makes it suitable for dynamic phase measurement.
A curvature radius (CR) measurement method using a parallel two-step spatial carrier phase-shifting common-path interferometer is presented. This interferometer is built on a 4f optical system with two windows in the input plane and a ronchi grating outside the fourier plane. A test lens is placed in front of one of the two windows. The phase of the test lens is retrieved from the two phase shifted interferograms recorded using this interferometer and then the profile can be obtained. The CR of the test lens is thus directly derived from the profile according to their geometrical relations. The theoretical model and experimental setup are established to illustrate this method and the measurement processes. Experiments are constructed to verify the effectiveness of the CR measurement using this interferometer. The results prove that this interferometer is an effective approach for the CR measurement with inherent simplicity, high robustness and accuracy.
A method using two-windows common-path interferometry with phase grating is presented to measure the curvature
radius (CR). This interferometry is built using a 4f optical system with binary phase grating implemented by spatial light
modulator (SLM) as spatial filter. The input plane is formed by two windows, which are used for the measured lens and
reference beam, respectively. In the output plane, an interferogram can be achieved by a proper choice of the windows’
spacing with respect to the grating period. The phase of the lens can be retrieved from the shift phase of composite
interferograms achieved by lateral movements of the grating. The curvature radius of the lens is thus directly derived
from the phase function. A theoretical model is also established using Fourier transform theory and phase retrieval
algorithm to describe the measured process using phase-shifting interferometry. Analyzed results indicate that the
method is an effective approach for the radius measurement with inherent simplicity, high robustness and flexibility.
Fiber-optic sensors are widely used and researched in-depth. Interferometric fiber optic sensor is an
important category of fiber optic sensor because of its high sensitivity. However, polarization-induced fading
phenomena always appear in the output of sensors which constructed of low-birefringence single mode fibers.
In this paper, we firstly give the structure of a fiber-optic sensor based on M-Z fiber optic interferometer. And
we use polarization optics to study the light state in this sensor. Taking the polarization state of input light in
fiber-optic interferometer is random we calculate the Jones vector of the output light. To study the polarization
fading phenomena we calculate the intensity of output light. We caculate the degree of polarization fading by
computer software. The result shows that sensing signal will completely vanish. Thus we can't get steady
sensing signal and we must use depolarization fading technology. We give a simple structure of a polarizationinsensitive
optical fiber sensor. Two Faraday rotator mirrors (FRM) are added into Michelson optical fiber
interferometer to improve the visibility. We also use polarization optics to study the output light of this
structrue. Theoretical analysis and experimental study indicates that this convenient method can improve
visibility to 1. The feature of the method is convenient, accuracy and practical. And it can apply to various kinds
of complex construction.
The detection abilities of PGC scheme dealing with the single frequency signal are investigated, based on which, the
frequency domain of the signal is analyzed. Based on the Bessel function theoretic, the mathematical model has been
established to analyze the performance of interferometric fiber-optic sensor under the PGC demodulation scheme. The
spectrums of interferometer output signals are analyzed when the input signal is single frequency signal and multifrequency
signal. Simulation results show that the dynamic domain upper limit of fiber-optic sensor when it operates with the multi-frequency signal must be much smaller than that it operates the single frequency signal.
An intensity modulated optical fiber accelerometer is designed. It can be applied in the real-time measurement of dynamic vibration acceleration. The theoretical analysis shows that the relation between the light intensity and displacement can be indicated by the same expression just with the difference in coefficient, though models of the fiber-optic intensity distribution at launching fiber end are different, such as Gaussian distribution, uniform distribution and those midst the upper two. Because of the simpleness of the expression, by means of specific linearization processing for the modulating function, a real-time and undistorted acceleration signal can be obtained.
A particular compensation is adopted to avoid the effect due to the static drift of the original distance between the launching fiber end and the reflective surface.
A novel scheme of a fringe count interferometric accelerometer is proposed. In view of practicability, the sensor must be made up of only fiber. Two 3dB directional couplers and singlemode fibers are used in this scheme to compose an imbalance Mach-Zehnder interferometer.
Phase modulation is achieved by modulating LD frequency to scan the interference fringes. With special technique, only one PIN is needed to count and identify the moving direction of the interference fringes. The signal can be transmitted more than several kilometers in a pair of fibers.
The two arms of the interferometer work at push-pull mode, which is favorable for temperature compensation. The resolution is significantly improved by fringe sub-division. A real-time dynamic vibration signal can be measured without distortion by this system.