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.
A new algorithm for no-reference blurred image quality assessment is proposed. This metric is based on block-based discrete cosine transform statistics and linear prediction method. We compare the performance of the proposed method with four blur metrics on three famous databases and our work shows the best results.
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.
We present a two-step program for point-by-point flat surface measurements with a fiber point diffraction interferometer (FPDI). The point diffraction wavefront reflected by a flat mirror under test is an aberrated spherical wavefront carrying the surface information of the flat mirror. The aberrated spherical wavefront interferes with a reference point diffraction wavefront through a plate beamsplitter (BS). The aberrations of the plate BS are also measured by the FPDI method. The figure of the flat mirror can be evaluated point by point after correcting the aberrations of the plate BS. This method makes use of the nearly perfect point diffraction wavefront, thus it can assure accurate flatness measurement on the optic under test. This research extends to the field of FPDI applications, and provides a new route for the high precision measurement of flat optics.
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.
A multiple color-filter aperture (MCA) can provide a single camera with depth information and multifocusing. However, the original version of the MCA system exhibits inherent limitations such as manual, empirical tuning parameters for the color channel registration and fusion (CRF) process. Furthermore, a CRF output image still contains undesired out-of-focus blur because of the finite-sized apertures and the lateral displacement of each color-filter aperture, which results in low exposure, color mixing, deviation of color convergence, and divergence of light rays. For overcoming these problems, we present a real-time image processing solution for digital multifocusing in a MCA system.
A novel photonic technique of millimeter-wave subcarrier generation base on four-wave mixing effect in a semiconductor optical amplifier (SOA) and a dual-frequency Brillouin fiber laser configuration is proposed. In this system, two new harmonic components with six times spacing of the microwave source frequency are created when an optical signal, generated by carrier-suppressed intensity modulation, is launched into the SOA. The two residual modulation sidebands are then suppressed by stimulated Brillouin scattering process, and the leaved idlers provide an millimeter-wave subcarrier signal.
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.
In the past few years, the computer vision and pattern recognition community has witnessed the rapid growth of a new kind of feature extraction method, the manifold learning methods, which attempt to project the original data into a lower dimensional feature space by preserving the local neighborhood structure. Among them, locality preserving projection (LPP) is one of the most promising feature extraction techniques. Based on LPP, we propose a novel feature extraction method, called uncorrelated locality preserving projection (ULPP). We show that the extracted features via ULPP are statistically uncorrelated, which is desirable for many pattern analysis applications. We compare the proposed ULPP approach with LPP and principal component analysis (PCA) on the publicly available data sets, FERET and AR. Experimental results suggest that the proposed ULPP approach provides a better representation of the data and achieves much higher recognition accuracies.
The aim of the present work is to propose a brand-new algorithm based on an adaptive double threshold nonlinear anisotropic diffusion equation (DTPDE) to detect and track moving dim targets against complex cluttered background in infrared (IR) image sequences. We also illustrate the performance comparisons of the proposed algorithm DTPDE and two-dimensional least mean squares (TDLMS) on real IR image sequence data. Extensive experiment results demonstrate the proposed novel algorithm's flexibility and adaptability in detecting moving weak dim targets.
We propose a fast subpixel motion estimation algorithm for the H.264 advanced video coding (AVC) standard. The algorithm utilizes the correlation of the spatial interpolation effect on the full-pixel motion estimation best matches between different block sizes in order to reduce the computational cost of the overall motion-estimation process. Experimental results show that the proposed algorithm significantly reduces the CPU cycles in the various motion estimation schemes by up to 16 with similar rate-distortion performance when weighed up against the H.264/AVC standard.
A differential all-birefringent-fiber frequency-modulated continuous-wave Sagnac gyroscope is described. The gyroscope employs a birefringent fiber coil to construct a double unbalanced fiber optic Sagnac interferometer and uses the phase difference between the two beat signals from the fiber coil to measure the rotation velocity. The advantages of this gyroscope include doubled rotation sensitivity and less nonreciprocal phase drift.
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.
We present a perceptually-adaptive in-band preprocessing scheme for 3-D wavelet video coding. In our scheme, after the original video is decomposed by 2-D spatial wavelet transform, a preprocessor is incorporated to remove some visually insignificant wavelet coefficients (noise-like) before the motion compensated temporal filtering of each spatial subband. The preprocessing process is guided by a wavelet domain just-noticeable-distortion profile, which locally adapts to spatial wavelet transform coefficients. Experimental results show that the proposed scheme can efficiently enhance the visual quality of coded video with the same objective quality at different bitrates.