A simple fabrication technique for a silica suspended-core holey fiber design is presented that features a higher air-filling fraction than most holey fibers, making it ideal for evanescent-field-sensing applications. The holes in the fiber are defined through mechanical drilling of the preform, which is a significantly quicker and more straightforward approach to the customary stacking method. During the draw, the shape of the holes are manipulated so that the final fiber design approximates that of an air-suspended rod with three fine struts supporting the core. Modeling reveals that the modal overlap is greater than at for a core diameter of , which is significantly higher than any previously reported index-guiding structure used for sensing. A basic gas sensor is demonstrated using acetylene as the sensing medium and the results are reported.
A novel binary level set method for boundary-based image segmentation is proposed, which is extended from region-based binary level set methods. The proposed binary level set method is based on the geometric active contour framework, which is a traditional level set method applied in boundary-based image segmentation. However, being different from the geometric active contour, the proposed binary level set method replaces the traditional level set function with a binary level set function to reduce the expensive computational cost of redistancing the traditional level set function. The experiments and complexity analysis show that the proposed binary level set method is more efficient than the geometric active contour for image segmentation while giving similar results to the geometric active contour.
We propose a new system of quantum key distribution via optical wireless communication links, where the required information, especially telephone conversation, can be secured by using a quantum code/decode (CODEC) technique incorporated in the networks. The entangled photons can be encoded into the classical information and then the decoded signal can also be retrieved. The proposed system consists of quantum key generation and uplink and downlink parts that can be implemented in the mobile telephone handset and networks. Such a system and technique show the feasibility of use for a perfectly security telephone networks.
Ambient light in a scene can introduce errors into range data from most commercial three-dimensional range scanners, particularly scanners that are based on projected patterns and structured lighting. We study the effects of ambient light on a specific commercial scanner. We further present a method for characterizing the range accuracy as a function of ambient light distortions. After a brief review of related research, we first describe the capabilities of the scanner we used and define the experimental setup for our study. Then we present the results of the range characterization relative to ambient light. In these results, we note a systematic error source that appears to be an artifact due to a structured light pattern. We conclude with a discussion of this error and the physical meaning of the results overall.
We propose a new scheme of computer-generated hologram (CGH) watermarking to resist rotation and scaling. To embed the inverse log-polar mapping of a mark pattern's CGH into a cover image, the twin image of the mark pattern can be directly reconstructed by fast Fourier transformation from the log-polar mapping of the watermarked image after rotation and scaling, not requiring a registration step in the extracting procedure. In an experiment, the information position of the twin image is located in the high-frequency domain and the redundant information of the low-frequency component is properly eliminated, so the contrast of the twin image is appropriately enhanced and the basic information of the mark pattern is effectively preserved to be recognized. The experimental results show that the mark-pattern's information can be effectively reconstructed when the watermarked image is scaled by 0.5 to 2 or rotated by any angle, so this watermarking scheme is effectively verified by experiment.
A simple method is found to align multielement cylindrical lenses. The method employs only equipment found in most optical shops: a precision flat mirror and a Fizeau interferometer. A combination of narrow reflection interferograms from the lens surfaces, combined with cat-eye double-pass interferograms, is employed to align the elements.
Feature extraction is a crucial step for pattern recognition. Recently, some manifold learning algorithms have drawn much attention. Although their properties of locality preserving are fairly significant, most manifold-based algorithms have limits to solve classification problems. First, they do not have good discriminant ability. Second, they fail to remove the redundancy among the extracted features. We present a new feature extraction method, called kernel uncorrelated neighborhood discriminative embedding (KUNDE), which integrates two abilities of manifold learning and pattern classification. The purpose of KUNDE is to preserve the within-class neighboring geometry while maximizing the between-class scatter. Optimizing an objective function in a kernel feature space, nonlinear features are extracted. Moreover, by putting a simple uncorrelated constraint on the computation of the basis vectors, the extracted features via KUNDE are statistically uncorrelated and thus contain minimum redundancy. Experimental results on radar target recognition indicate the promising performance of the proposed method.
A continuous variable modulation frequency optical single sideband (OSSB) can be generated by a Sagnac interferometer and a continuous variable differential group delay (DGD) element of photonic crystal fibers (PCFs). Furthermore, the OSSB signals with different modulation frequencies can be generated simultaneously.
All-optical single-to-dual channel format converter from non-return-to-zero (NRZ) to return-to-zero (RZ) is proposed and demonstrated using cascaded sum- and difference-frequency generation in a periodically poled (PPLN) waveguide. The pump optical clock is generated from the active mode locking in a reflective semiconductor optical amplifier (RSOA)-based fiber ring laser. We successfully observe 10- and single-to-dual channel NRZ-to-RZ format conversions in the experiment.
To achieve the full complex modulated range of the cascaded twisted nematic liquid crystal spatial light modulator (TNLC-SLM), we propose and demonstrate a novel amplitude compensated technique. Optical reconstructions of complex digital holograms with higher image quality are discussed in both analytical and experimental results.
Semiconductor-based optical amplifiers (SOAs) offer solutions to a variety of amplification needs covering wavelengths ranging from of 0.6 to . Gain adjustment, through the bias current, enables automatic power control to be implemented. However, this requires knowledge of the signal strength. The amplified spontaneous emission power, particularly in high gain SOAs, can be significant with respect to the signal strength, and therefore additional components may be required to derive an accurate measure of the signal strength. This increases both the complexity and cost of implementing automatic power control (APC). We report on a method for estimating the signal strength based on measurement of the total output power and the SOA drive current. The method is extendable to other methods of optical amplification, e.g., erbium-doped fiber amplifiers.
Considering the economic and technical aspects of wavelength converters, full wavelength conversion capability will not be available throughout optical networks in the foreseeable future. This letter investigates the wavelength assignment problem in wavelength-continuous optical burst switching (OBS) networks. First, we develop a novel static approach, termed balanced static wavelength assignment (BSWA), which outperforms all other static strategies, and achieves almost the same performance as dynamic strategies with the advantage that no extra dynamic information is needed. Then, we apply BSWA to a dynamic approach to accelerate network convergence and reduce the initial burst loss. Numerical results show that our approaches make significant improvements in the burst loss probability in OBS networks.
We show through numerical simulation of 10.7-Gbits/s dense wavelength-division multiplexed (DWDM) duobinary transmission over of nonzero-dispersion-shifted fiber that uncompensated dispersion can introduce significant departures from Gaussian statistics in the receiver current.
Recent studies show that wavelet-based image fusion methods provide a high spectral quality in fused satellite images. However, images fused by most wavelet-based methods have less spatial resolution because the critical downsampling is included in the wavelet transform. We propose a useful fusion method based on contourlet and local average gradient (LAG) for multispectral and panchromatic satellite images. Contourlet represents edges and texture better than wavelet. Because edges and texture are fundamental in image representation, enhancing them is an effective means of enhancing spatial resolution. Based on LAG, the proposed fusion method reduces the spectral distortion of the fused image further. Experimental results show that the proposed fusion method is able to increase the spatial resolution and reduce the spectral distortion of the fused image at the same time.
Ultrawide-band microwave amplification in the optical domain is proposed that covers the frequency range from to with over gain. A partly carrier-suppressed optically carried microwave signal is generated and amplified by erbium-doped fiber amplifier (EDFA) in this scheme.
We present the fabrication process of straight-ridge co-doped waveguides. Thin films are synthesized on silica-on-silicon wafers by middle frequency sputtering (MFS) and microwave ECR (MW-ECR) plasma source deposition. Waveguides are developed by reactive plasma etching employing gas. Photoluminescence (PL) spectrum and gain measurements at are investigated at room temperature: a net gain of is achieved from a -long waveguide obtained by MFS, and is achieved from a MW-ECR with a pump power of .
We propose an all-optical wavelength conversion method that can preserve the polarization information of an original signal based on four-wave mixing in a semiconductor optical amplifier. Using this method, we experimentally demonstrate wavelength conversion for a 10-Gb/s polarization shift keying signal with 1.6-dB power penalty at a bit error rate. To our knowledge, it is the first experiment reported on all-optical wavelength conversion for a polarization shift keying format. The converted polarization shift keying signal is successfully transmitted over a 75-km standard single mode fiber with 1.8-dB transmission penalty.
Postdeposition chemical etching of spectral-hole filters, which were fabricated as chiral sculptured thin films with central -twist defects, decreases the cross-sectional dimensions of the helical columns that such films comprise and blueshifts the spectral holes, thereby establishing the efficacy of postdeposition chemical etching as a means to tune the optical response characteristics of sculptured thin films.
Low quality images are often corrupted by artifacts and generally need to be heavily processed to become visually pleasing. We present a modified version of unsharp masking that is able to perform image smoothing, while not only preserving but also enhancing the salient details in images. The premise supporting the work is that biological vision and image reproduction share common principles. The key idea is to process the image locally according to topographic maps obtained from a neurodynamical model of visual attention. In this way, the unsharp masking algorithm becomes local and adaptive, enhancing the edges differently according to human perception.
A phase-modulator-based optoelectronic oscillator (OEO) is utilized to implement a self-starting optical pulse and microwave signal source. This system is able to simultaneously generate a 9.8-GHz optical pulse stream with (over to ) timing jitter and 6.5-ps pulse width, along with a high spectral purity electrical signal that is locked to the repetition rate of the optical pulses. The measured phase noise is at away from carrier, and the side modes are perfectly suppressed.