Applied Mechanics and Materials Vols. 130-134

Abstract: A classical joint transform correlator (JTC) usually yields large correlation sidelobes as well as a large correlation peak width, strong zero-order peak, and low diffraction efficiency, which make the detection ability of JTC lower. To overcome these difficulties, firstly, a joint power spectrum (JPS) subtraction technique in Fourier plane was proposed, where reference image power spectrum and object image power spectrum are subtracted from the JPS before inverse Fourier-transform operation, it is obvious that the modified JPS removes the zero-order term. Secondly, a fringe-adjusted filter (FAF) was presented to suppress sidelobes and noises. The modified JPS is multiplied by a FAF before the inverse Fourier-transform operation to obtain the cross-correlation peak. Computer simulations demonstrated the improved method can obviously remove zero-order diffraction and effectively suppress the sidelobes and noises compared with classic JTC, and then improve the detection ability for JTC. Experimental results presented the sharp correlation peak and also confirmed the method effectiveness.

Abstract: The point diffraction interferometer (PDI), which generates the nearly ideal spherical wavefront with the pinhole method, is realized the absolute interferometric measurement without the use of reference surface. But it is hard to detect the diameter of the pinhole and hard for use of phase shifting interferometers in PDI. However the advanced fiber point diffraction interferometer (FPDI) not only replaces the pinhole with the fiber, but also makes it possible to implement phase shifting and maintain advantage of traditional PDI. In this paper, the different methods of measuring surface are proposed according to different experimental conditions and different targets (such as concave spherical surface, convex spherical surface, flat surface) with the fiber point diffraction interferometer built in the laboratory. Base on these experiments, there are several key factors in the measurement process such as measurement configuration, laser source, polarization beamsplitter, optical fiber. And these factors, affecting the experiment accuracy, were analyzed seriously.

Abstract: This paper give a new design of three level phase delay control polarization controller, which is the key components for state of polarization (SOP) control in the area of coherent optical communication and polarization mode dispersion compensation. Piezoelectric ceramic are used in three of the phase delay unit to realize phase delay control. The polarization controller can achieve infinite control, convert arbitrary input state of polarization to arbitrary expected output state of polarization under low control voltage.

Abstract: We introduce an all-fiber sensor capable of simultaneous measurement of temperature and refractive index (RI). The sensor system consists of a single mode fiber Bragg grating (FBG) and a single-mode-multimode-single-mode (SMS) structure which serves as a Mach-Zehnder interferometer (MZI), and the multimode fiber (MMF) is etched by hydrofluoric acid solution. The experimental results demonstrate that the temperature sensitivities of FBG and MZI are 0.016nm/°C and 0.093nm/°C, respectively, and the RI sensitivity of MZI achieves 226.25nm/RIU. The interesting properties of the sensor include compact size, high sensitivity and good operation linearity.

Abstract: A switchable fiber laser based on Mach-Zehnder interferometer (MZI) and photonic crystal fiber (PCF) is demonstrated. A section of PCF in the fiber laser is used to induce four-wave mixings (FWM) effect and MZI acts as a comb filter. Experimental results show that stable single-wavelength, dual-wavelength and triple-wavelength operations can be obtained with the adjustment of the polarization controller. The power of two peaks of the dual-wavelength laser is almost the same under room temperature with an output power fluctuation less than 0.6dB. The advantages of the proposed fiber laser include quite stable wavelength and narrow linewidth owing to the contributions of FWM in the PCF.

Abstract: Here based on the combination of Comsol and the transmission matrix of Matlab, the spectrums of etched micro-structured gratings are simulated and two different modes of etched micro-structured fiber gratings are made in experiment. Etched micro-structured fiber grating is formed by using hydrofluoric acid (HF)-based wet chemical etching or femtosecond laser etching. This can reduce the clad layer along a standard grating partly or entirely and change the transmission feature of the grating. As a result, the thinner cladding layer changes the core propagation features and thus induces a phase delay on the guided mode, leading to the formation of a defect state inside the original grating band-gap in agreement with the phase shift grating theory. The defect state is mainly influenced by three parameters: the length and depth of the perturbation and the surrounding refractive index (SRI).

Abstract: Considering the traditional LED road illumination drive power supply existence some shortcomings,such as the illuminance can not be adjustable, output current constant poor accuracy and so on. Therefore this paper design a high-precision intelligent PWM optically controlled LED road illumination drive power supply,which use the fuzzy control algorithm can automatically adjust power output drive current according to ambient light, and achieve LED optically controlled, then improve power efficiency and save energy.The experimental results show that the design has very good characteristics of LED road illumination intelligent optical ly controled, high-precision output constant current, strong adaptability, stable and reliable performance.

Abstract: A new-type controllable slow light system based on a multi-stage delay Stimulated Brilliouin Scattering (SBS) structure is proposed. In this experiment, a shorter fiber (600 meters) is used to raise the Brillouin thresholds, and the pump power is also increased, therefore the unsaturated gain and the single-stage delay effect are enhanced. Moreover, the two fiber segments of slow light delay are cascaded by two circulators in the configuration, which can increase the delay time and the utilization rate of stokes signal during the experiment, the signal light which the power is-15dBm has acquired 51.299dB gain and the delay time is 55.333ns. Compared with the single-stage delay, the delay time has been increased.

Abstract: This paper presents a rotate speed sensor using fiber Bragg grating (FBG) as sensitive component and constant strength cantilever structure as elastomer. The sensor is applied in large rotating experimental platform testing changes of impeller rotate speed through the vibration of the sensor's elastomer. The center reflection wavelength of FBG enters fiber grating demodulation device sm130, where light signal is demodulated. Experimental results demonstrate that the sensor can test the rotate speed of rotating machine repeatedly and sensitively. In addition, the sensor's easy theory and portable structure lay the foundation for further study on shaft torsional vibration detection of rotating machinery.

Abstract: It is a difficult task to binarize image under uneven illumination, and this problem is always met in the image recognition system, such as two-dimensional barcode scanning terminal. In this paper, an efficient approach is proposed to binarize image which can tolerant uneven illumination and different light intensity. The method initializes thresholds with local average gray level and adjusts thresholds by calculating light density ratio. Due to characteristic of our approach, it can even obtain a sound result by limiting number of iterations which will seriously reduce computations and space cost. According to experiments, we can find that our method can achieve a good performance and meet the real-time requirement and quality demand for barcode scanning terminal.