Zero-broadening SBS slow light propagation in an optical fiber using two broadband pump beams

A new method of tailoring stimulated Brillouin scattering (SBS) gain spectrum for slow light propagation is proposed by use of two Gaussian-shaped broadband pump beams with different powers and spectral widths. The central frequency interval between the two pump beams are carefully set to be two inherent Brillouin frequency shift, ensuring that the gain spectrum of one pump has the same central frequency with the loss spectrum of the other one. Different gain profiles are obtained and analyzed. Among them a special gain profile is found that ensures a zero-broadening of the signal pulse independent of the Brillouin gain. This is owing to the compensation between the positive gain-dependent broadening and the negative GVD (group velocity dispersion) dependent broadening. The relationship of two pump beams is also found for constructing such a gain profile. It provides us a new idea of managing the broadening of SBS-based slow pulse by artificially constructing and optimizing the profile of gain spectrum. (c) 2008 Optical Society of America

Applying Pebble-Rotating Game to enhance the robustness of DHTs.

Distributed hash tables (DHTs) are usually used in the open networking environment, where they are vulnerable to Sybil attacks. Pebble-Rotating Game (PRG) mixes the nodes of the honest and the adversarial randomly, and can resist the Sybil attack efficiently. However, the adversary may have some tricks to corrupt the rule of PRG. This paper proposes a set of mechanisms to make the rule of PRG be obliged to obey. A new joining node must ask the Certificate Authority (CA) for its signature and certificate, which records the complete process on how a node joins the network and obtains the legitimacy of the node. Then, to prevent the adversary from accumulating identifiers, any node can make use of the latest certificate to judge whether one identifier is expired with the help of the replacement property of RPG. This paper analyzes in details the number of expired certificates which are needed to store in every node, and gives asymptotic solution of this problem. The analysis and simulations show that the mean number of the certificates stored in each node are [Formula: see text], where n is the size of the network

A robust haze-removal scheme in polarimetric dehazing imaging based on automatic identification of sky region

<p> Quality enhancement of images acquired in hazy conditions is a significant research area in civil and military applications. The polarimetric dehazing methods have been exploited to dehaze hazy images and have proven to be effective in enhancing their quality. In this paper, by combining the polarimetric imaging technique and the dark channel prior technique, a robust haze-removal scheme is presented for the first time. On the one hand, the polarimetric imaging technique has advantages in recovering detailed information well, especially in dense hazy conditions; on the other hand, the dark channel prior technique provides a much more precise and convenient way to estimate the airlight radiance through extracting the sky region automatically. The experiments verify the practicability and effectiveness of the proposed dehazing scheme in quality enhancement of hazy images. Furthermore, comparison study demonstrates that the proposed scheme is superior to some sophisticated methods in terms of the visibility and contrast. We believe this scheme is beneficial in the image dehazing applications, especially for real-time applications. (C) 2016 Elsevier Ltd. All rights reserved.</p

Nondestructive scheme for measuring the attenuation coefficient of polymer optical fiber

Based on the fiber macrobending and the refractive index matching technologies, a measurement scheme is proposed to gauge the attenuation coefficient of polymer optical fibers in this Letter. It is noteworthy that, by realizing both the light injecting into and the light extracting out the fiber core via the fiber cladding, this scheme will not induce any destruction during the whole measurement. Some related experiments and the theoretical verifications are given together with the nondestructive measurement principle. The comparison between the experimental results of this scheme and that of the cut-back scheme indicates a good feasibility of our scheme. As a result, it is promised to have a potential application for achieving the on-line attenuation monitoring that has never been introduced. (c) 2013 Optical Society of Americ

Calibration Method of Liquid-Crystal Spatial Light Modulator Based on a 1-D Phase Retrieval Algorithm

Liquid-crystal spatial light modulator (LC-SLM) has been widely applied as a programmable digital device. However, the LC-SLM can only manipulate on light fields accurately under designated wavelengths since, when being uploaded a specific grayscale image onto it, the phase retardance offered by the LC-SLM is relevant to the wavelength of the incident light. This means that the calibration of LC-SLM is indispensable once the working wavelength changes. In this paper, based on a phase retrieval algorithm, a novel phase calibration method with high efficiency and accuracy is proposed for scaling LC-SLM. In the method, a 1-D phase retrieval algorithm for recovering the phase of a 1-D light field distribution is used to measure the voltage-phase characteristic curve of LC-SLM, where the gradient descent algorithm with a Root Mean Square propagation is introduced to obtain the phase. Simulations and experiments show that this method is stable and has the ability of anti-noise on some conditions and can eliminate the influence caused by crosstalk between pixels on the calibration. Compared with the traditional diffraction-based method, our method improves the calibration error up to 30&#x0025; under the same experimental conditions

Single-Fiber Based Endoscopic Imaging: Methods and Characteristics

Different from imaging an object through a multimode optical fiber (MMF) directly, it is much more challenging to use a single MMF for practical endoscopic imaging in which the light wave has been distorted twice: on the way in for the illumination and on the way out for the detection. In this paper, based on obtaining the optical transmission matrix (TM) of the MMF working in the reflective mode, we demonstrate that, via the measured optical TM, the object can be reconstructed directly from its round-trip distorted output speckle fields. Compared with other single-fiber based endoscopic imaging methods, our method doesn’t involve any scanning operation during the imaging process. Such an efficient method might have potential applications for wide-field and ultrathin fiber endoscopic imaging