We experimentally demonstrate the fabrication of silicon optical fibers by using the powder-in-tube technique. The fibers are drawn from a preform utilizing a custom-made fiber drawing system. Silicon optical fibers having cladding diameters in the range of , core diameters in the range of , and an approximate overall length of have been fabricated. The powder-in-tube technique is versatile and can be utilized to fabricate fibers with different dimensions and core/cladding materials.
A compact slot waveguide polarization splitter based on the silicon (Si) material system is proposed and analyzed. The slot waveguide structure introduces significant beat-length differences for transverse electric and transverse magnetic polarizations at operation wavelength of . The special self-imaging design with limited modes and weak second-mode excitation shortens the device length to , while still delivering good performance. The polarization extinction ratio is , and the excess loss is only . The splitter also has a relaxed length tolerance of . These attributes make it an excellent candidate for polarization diversity circuits and compact electronic-photonic integrated circuits.
We propose a motion vector memory reduction scheme for the H.264 spatial scalable motion estimation. The spatial scalable prediction of H.264 scalable video coding requires a significant amount of motion vector bits from the previous layer motion prediction. This motion vector causes the Internal memory size to increase, which may result in increasing hardware cost and power consumption. To reduce the memory size of the motion vector, we propose a motion vector bit-compression scheme of the interlayer motion estimation. The proposed compression scheme uses the difference value of current motion vector and previous motion vector to get a probability for entropy coding. In addition, the proposed scheme modifies a variable length coding table of the H.264 system as a simple entropy coding table. The proposed scheme reduces the motion vector-storing bit by with less changes in hardware size.
We present an adaptive quarter-pel (Qpel) motion estimation (ME) method for H.264/AVC. Instead of applying Qpel ME to all macroblocks (MBs), the proposed method selectively performs Qpel ME in an MB level. In order to reduce the bit rate, we also propose a motion vector (MV) encoding technique that adaptively selects a different variable length coding (VLC) table according to the accuracy of the MV. Experimental results show that the proposed method can achieve about 3 average bit rate reduction.
The optical wavelength-division-multiplex filter for bidirectional optical subassembly (BOSA) is embedded to the fiber core, which results in simplicity of the BOSA module. The fiber cladding is angle polished to receive a downstream signal. The core is etched by a femtosecond laser to have a normal core facet and to transmit an upstream signal. The downstream signal, which is core mode, is coupled to the cladding mode by the long-period fiber grating and then detected by a photodiode by means of the total internal reflection effect at the angle polished cladding facet. The measured transmitted and received coupling efficiencies are 27.3 and 43.8 , respectively.
We propose a new multimodal biometric recognition based on the fusion of finger vein and finger geometry. This research shows three novelties compared to previous works. First, this is the first approach to combine the finger vein and finger geometry information at the same time. Second, the proposed method includes a new finger geometry recognition based on the sequential deviation values of finger thickness extracted from a single finger. Third, we integrate finger vein and finger geometry by a score-level fusion method based on a support vector machine. Results show that recognition accuracy is significantly enhanced using the proposed method.
We recorded a hologram in a photorefractive crystal with a two-color recording technique in transmission geometry. The holographic recording involves a light with wavelength for interference, and a light with wavelength for exciting. The short wavelength light excites more charges so that the holographic recording is affected, and the storage capacity ( -number) and the sensitivity vary accordingly. We found that the optimized intensity ratio of the interference lights and the exciting light is between 50 and 60. In the optimized conditions, the number and the sensitivity are enhanced by 43 and 35 , respectively. Because the crystal we used is a typical iron-doped crystal and the short wavelength exciting light source is inexpensive now, the proposed method is easy to be achieved in most holographic systems.
We propose a novel method to realize silicon-on-insulator (SOI)-based air slot waveguides for sensing applications. The method, based on feature size reduction using conformal thin films grown by atomic layer deposition (ALD), enables a guided slot mode in a silicon slot waveguide with a patterned slot width of more than . Feature size reduction of slot structures with ALD grown amorphous is demonstrated.
The simultaneous modulation of coherent light distributions on several closely spaced planes by one phase-only spatial light modulator is described to create 3-D light distribution. The pure phase distribution on the phase-only spatial light modulator is retrieved by a new multiplane iteration method based on the Gerchberg-Saxton iteration method, which consecutively propagates the coherent light on several parallel planes with amplitude constraints. A comparison between our proposed method and the complex distribution addition method is presented by numerical simulation. The result indicates that a sharp grayscale image is realized on each closely spaced plane by our proposed method, implying potential applications both in 3-D holographic displays and optical tweezers.
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.
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.
We use a paraxial approximating solution to calculate the point spread function of the collinear holographic storage system and show that the point spread function can be dramatically enhanced by the reference pattern with random binary phase modulation or random phase modulation.
A new motion vector coding method with optimal predictive motion vector selection is proposed. To improve compression performance, the proposed encoder selects an optimal predictive motion vector that produces minimum bits for motion vector coding. The proposed decoder estimates the optimal predictive motion vector without additional information for indicating which predictor is to be used at the encoder side. Experimental results show that compared to the H.264/AVC standard, the proposed scheme improves coding efficiency for various video sequences.
Face clustering is gaining ever-increasing attention due to its importance in optical image processing. Because traditional clustering methods do not specify the particular characters of the face image, they are not suitable for face image clustering. We propose a novel approach that employs the trace ratio criterion and specifies that the face images should be spatially smooth. The graph regularization technique is also applied to constrain that nearby images have similar cluster indicators. We alternately learn the optimal subspace and the clusters. Experimental results demonstrate that the proposed approach performs better than other learning methods for face image clustering.
Experimental results about efficient band-edge light coupling into two-dimensional planar photonic crystals by the use of a gradual interface are reported. It is shown that a chirp of both the lattice period and the hole diameter on short lengths below allows maintaining high optical transmission spectra close to the band-gap frequency where strongly dispersive phenomena can be exploited. If compared with nonoptimized structures, increased optical levels by are obtained using gradual tapering stages.
Fabrication and characterization of an integrated 3-D linear taper are reported, which is based on (111) silicon-on-insulator for efficient coupling between a single-mode fiber and planar photonic devices. The fabrication process involved wafer bonding, anisotropic etching, and dry etching. The 3-D taper measured in length. The input waveguide, in dimensions of the end facet, was compressed to dimensions of of the end facet in the output waveguide. The measured average net transmission loss was at the wavelength of .
We address the problem of unequal error protection (UEP) for SNR enhancement layer network abstraction layer (NAL) units of scalable video coding extension of H.264/AVC standard over wireless packet-erasure channel. We develop a UEP scheme by jointly selecting SNR NAL units and allocating unequal amounts of protection to selected NAL units for every group of pictures in the sequence. A simple heuristic algorithm is proposed to quickly derive the protection pattern. Experimental results demonstrate the proposed UEP scheme provides significant error resilience.
The template updating problem of Kernel-based tracking (KBT) includes two aspects: target-scale update and target-model update. The proposed algorithm can update both tracking window's scale and target model by making use of continuous adaptive distribution. The ability of KBT can be complemented within its own framework with modest computation cost. The proposed tracking algorithm tries to get a balance between the stability of KBT and adaptability of CAMSHIFT for creating a robust tracker.
Interference filters have a defect layer incorporated within a photonic crystal structure and generate a narrow transmission notch within a wide stop band. In this paper, we propose and demonstrate wavelength-tunable spatial filters by introducing diffractive optical elements in the defect layer. The spectral transmission through the device was a function of the local defect layer thickness under broadband illumination. For each wavelength, the spatial transmission followed the contours of equal defect layer optical thickness. The devices were implemented by depositing a one-dimensional photonic crystal with a centrally integrated defect layer on a silicon substrate using plasma-enhanced chemical vapor deposition. The defect layer was lithographically patterned with charge 2, 8-level vortex structures. The spectral transmission peak and linewidth was characterized by separately illuminating each zone of diffractive element using a tunable laser source and compared with model simulations. The spatial transmission through the device was imaged onto a CCD camera. Triangular wedge-shaped zones with wavelength-dependent orientations were observed. These novel devices with spectrally tunable spatial transmission have potential applications in pupil filtering, hyperspectral imaging, and engineered illumination systems.
A continuously tunable, coherence-free microwave photonic notch filter is proposed and demonstrated experimentally. This filter is based on two polarization beamsplitters with a high-birefringence linearly chirped fiber Bragg grating used as the tunable component. High stability is obtained. The polarization-maintaining structure is free from the random optical interference problem. By adjusting the operating wavelength, more than free-spectral-range tunability with notch rejection is achieved.