Synthetic Aperture Radar (SAR) images are inherently affected by multiplicative speckle noise, which is due to the coherent nature of the scattering phenomenon. Speckle noise of SAR affects image quality and image interpretation seriously. To alleviate deleterious effects of speckle, various ways have been devised to suppress it. An ideal algorithm should smooth the speckle without blurring edges and fine details. But most classical algorithms cannot satisfy these two demands very well. Due to the property of SAR images speckles is multiplicative noise, it difficult to estimate the variance of the high-frequency subband coefficients. Most classical approaches such as wavelet thresholding or shrinkage scheme of Donoho and Johnstone are not suitable for SAR images speckle noise removal. In this paper, a novel approach to SAR image speckle reduction is presented, which is based on second generation bandelets and a kernel-based possibilistic C-means clustering algorithm (BKPCM).
In fiber Bragg grating (FBG) sensors, detecting the Bragg wavelength accurately could be difficult due to a low signal-to-noise ratio (SNR) in the FBG spectrum. Two common sources of noise are the general random noise from the broadband sources and the interferometric noise caused by the residual reflections in the sensor system. Conventional filtering techniques could be quite effective in removing random Gaussian-white noise, but not so for the interferometric noise, which is very structured. On the other hand, parameter estimation techniques such as nonlinear least squares can be used to identify the parameters in the interferometric noise and remove it accordingly. However, since the parameter estimation problem is nonlinear, the larger the number of parameters, the higher the chance that the algorithm will get trapped into a local minimum and fail to identify the correct parameters. In this paper, it is proposed to combine the nonlinear least squares method with a Kalman smoother. Hence, the number of parameters to be estimated by the nonlinear least squares algorithm will be greatly reduced. To do this, a continuous-time linear time-varying state-space model is derived for the FBG spectrum and then the model is discretized so that the Kalman smoother can be applied. An interesting point to note is that this model is linear
time-varying instead of nonlinear, thus not requiring an extended
Kalman filter. Computer simulations are provided in the paper to
demonstrate the effectiveness of the proposed method, followed by
applications to real experimental data. Improvements in the
accuracy of Bragg wavelength detection are observed.
A novel FSR tunable Fabry-Perot Filter scheme with a superimposed fiber Bragg grating has been proposed. And a cantilever beam-based tuning setup has been demonstrated to obtain large linear chirp to a superimposed uniform fiber Bragg grating without central wavelength shift. Finally, as an example, an FPF with a continuously tunable FSR of 0.1-0.5nm is obtained.
Resilient Packet Ring (RPR) is a more promising solution to the bottleneck of metropolitan-area networks (MANs). The ring network architecture and associated protocol has been standardized by the IEEE 802.17 working group in 2004. To achieve high bandwidth utilization, optimum spatial reuse and fairness simultaneously, a policy of fair bandwidth assignment must be implemented in current RPR network. The existing fairness mechanisms suffer from severe oscillations under certain conditions, such as unbalanced traffic scenario and noticeable time delay. With our proposed fairness algorithm, the system performance of the three-node unbalanced traffic scenario, where the traffic loads are fixed, can be sustained by simply adjusting the compensating factor with respect to the time delay. In this paper, the time delay is constant, we investigate how this compensating factor should be adjusted with respect to the degree of unbalance. Furthermore, we study a four-node scenario, each node-to-node pair has different time-delay as well as unbalance degree. The simulation results show that the system performance remains excellent with the guidelines summarized.
The photonic crystal fiber (PCF) and the PCF based structure are playing more and more important role in the optical communication and optical sensors fields. Fabrication technique is the key for realizing the design of PCF. In this paper the fabrication process of PCF is described, which includes stacking, jacketing, collapsing, stretching and drawing on a conventional drawing tower. To maintain the uniform air hole structure, positive micro-pressure has been introduced in the drawing processing. The multi-pole method is used to analyze the PCF structure with one hexagonal array of air cylinder photonics crystal fibers. The theoretical and experimental results show that the PCF fabricated under this way has good performance and coincidence indicator. Several PCF based structures have been studied and developed. It is predicted that the PCF based structures have some funny characteristics, which could find important application in the fiber-optic communication and sensing systems.
Pumping source is the key technology of fiber Raman amplifiers (FRA) which are important for ultra long haul and high bit rate dense wavelength division multiplexing (DWDM) systems. In this paper the research work of the project, "Fiber Raman Laser and Amplifier pumped by Nd<sup>3+</sup>:YVO<sub>4</sub> Solid State Laser", supported by the National High-tech Program (863-program) of China is introduced, in which a novel 14xx nm pump module with fine characteristics of high efficiency, simplicity, compactness and low cost is researched and developed. A compact 1342 nm Nd<sup>3+</sup>:YVO<sub>4</sub> diode pumped solid state laser (DPSSL) module is developed with the total laser power of 655mW and the slope efficiency of 42.6% pumped by a 2W 808nm laser diode (LD). A special C-lens fiber collimator is designed to couple the 1342nm laser beam into a piece of single mode fiber (SMF) and the coupling efficiency of 80% is reached. The specific 14xx nm output laser is generated from a single stage Raman resonator which includes a pair of fiber Bragg gratings and a piece of Germanic-silicate or Phospho-silicate fiber pumped by such DPSSL module. The slope efficiency for conversion from 1342 to 14xx nm radiation is 75% and the laser power is more than 300mW each. Finally, Raman gain experiments are carried out with 100km SMF. 100 nm bandwidth with 10dB on-off Raman gain and 1.1dB gain flatness is achieved by pumped at 1425, 1438, 1455 and 1490nm.