A freeform collimating lens is designed to project light rays emitted from an LED light source to a far target plane. Generally, the projection distance is assumed to be more than 100 m, and the light beam to have negligible divergence. The lens consists of a total internal reflection (TIR) side surface, a spherical surface in the rear, a vertical plane surface in the outer part of the front, and a freeform refractive surface in the central part of the front. Light rays emitted from the LED source with large spread angles hit the TIR surface and are redirected parallel to the light axis, and those having small spread angles will be collimated by the freeform refractive surface, which is designed with a simple approximation method, and then travel parallel to the light axis. Computer simulation results show that an optical efficiency of 81.5% is achieved under a view angle of ±5 deg and for a 1 mm×1 mm LED source.

Wavefront coding can be used to extend the depth of field of incoherent imaging systems and is a powerful system-level technique. In order to assess the performance of a wavefront-coded imaging system, defocused optical transfer function (OTF) is the metric frequently used. Unfortunately, to the best of our knowledge, among all types of phase masks, it is usually difficult to obtain the analytical OTF except the cubic one. Although numerical computation seems good enough for performance evaluation, the approximate analytical OTF is still indispensable because it can reflect the relationship between mask parameters and system frequency response in a clearer way. Thus, a method is proposed to derive the approximate analytical OTF for two-dimensional rectangularly separable phase masks. The analytical results are well consistent with the direct numerical computations, but the proposed method can be accepted only from engineering point of view and needs rigorous proof in future.

We present a theoretical analysis and a comparison to experimental results on self-mixing interference. From the theoretical analysis and experiment, the error of the velocity measurement, which is caused by a speckle pattern, has been investigated and optimization of the laser diode velocity system by selecting suitable experiment parameters and proper signal processing methods has been reported. The actual measurement error is <3.1% over a wide velocity range (5.2-479 mm/s).

The effect of various parameters that limit the performance of fiber lasers are calculated for yttrium aluminum garnet (YAG) as the fiber core. The optimum core diameter, the optimum fiber length, and the corresponding output power capability are determined for a variety of optical and structural parameters of YAG, based on available data in the literature to date. It is shown that a conservative limit for YAG fiber laser is 6 kW per fiber in multimode operation, compared to 1.8 kW for a silica-based fiber laser. Furthermore, it is shown that if stimulated brillouin scattering gain, a key limiting parameter, is <10−12 m/W in YAG, as a recent publication suggests, the maximum output power is 30 kW per fiber without a significant increase in fiber core diameter. Similar gains are predicted for single-mode operation, although with much lower output power limits. A parametric study shows the relative merits of improving on various optical parameters.

Switchable multiwavelength fiber laser outputs with a wide tuning range are experimentally observed in an ultralong cavity. Because of the long spooled single-mode fiber and filter effect of the cavity, multiwavelength lasers with the spacing of ~14.5 nm are obtained. The proposed fiber laser has the capacity of simultaneously emitting the three wavelengths. By means of adjusting the polarization controllers, the arbitrary single- and dual-wavelength operations are achieved in our laser.

According to the magneto-optic coupling characteristics of magneto-optic fiber Bragg gratings (MFBGs), we present a nonmagnetic equivalent model of a uniformly magnetized MFBG to analyze the optical polarization states output from the MFBG for incident linearly polarized light. The Faraday rotation of transmitted light is enhanced at the edges of a grating bandgap, and then can be applied to the measurement of a magnetic field by employing the wavelength speeding method. The use of apodized MFBGs helps to simultaneously achieve a good linear magnetic field response and extremely small fluctuation of transmittivity. For a typical paramagnetic terbium-doped and apodized MFBG, the temperature coefficient of the Faraday rotation is calculated to be −2.5×10−4 m/K.

A simple modal interferometer is proposed, to be produced by splicing a section of a novel ring-core photonic crystal fiber (RPCF) and two segments of single-mode fibers. Owing to the effects of the collapsed region, the ring modes in the RPCF can be effectively activated. This is the first demonstration of an interferometer based on the interference between ring modes, as opposed to previously reported interferometer based on the interference of core modes or cladding modes. The effects of the length of RPCF and the wavelength on the temperature and strain characteristics of the interferometer are investigated. The strain sensitivity increases with RPCF length and with wavelength. Based on the interferometer, a strain sensor with low temperature sensitivity is proposed, which has strain sensitivity of 1.777 pm/(µm/m).

We present a new design of a surveillance system via a vehicular ad hoc network (VANET) integrated by a 3-G or 4-G cellular wireless network. We propose dense wavelength division multiplexing wavelength enhancement for increasing the channel capacity and signal security. Increase in the number of channels can be obtained by increasing the wavelength density. Signal security is introduced by a specific wavelength filter controlled by the central operator. Optical communication wavelength enhancement is reviewed. The advantage of this proposed system is that it can easily be implemented and incorporated into the existing communication link in either a cellular or ad hoc wireless system, where signal security and hence privacy can be provided.

We propose a real, highly nonlinear, As₂Se₃-based chalcogenide photonic crystal fiber in which a supercontinuum (SC) spanning more than 2 octaves is generated at =2.8 µm in the femtosecond regime. The designed PCF is characterized for ultrabroadband mid-infrared SC generation in only few millimetres of fiber length. A full modal analysis of the optical properties of the fiber is presented in terms of the effective area, the nonlinearity coefficient, and the chromatic dispersion. A second-order Sellmeier approximation is proposed to estimate the variation of the refractive index of the As₂Se₃ material as a function of wavelength. The numerical study shows that a SC spanning from 1.9 to 4 µm can be generated in the chalcogenide PCF with an air-hole diameter of 1.26 µm and a pitch of 1.77 µm. We examine the interplay of the nonlinear effects that lead to the construction of the SC as a function of the input power and the fiber length. We find that the dynamics behind the SC generation is mainly ruled by the effects of self phase modulation and stimulated Raman scattering. The intrinsic properties of the chalcogenide glasses and the microstructure provide enhanced optical properties and offer numerous applications in the infrared field.

We integrate transmitting and receiving parallel optical subassemblies (POSAs) that are suitable for high-speed and parallel optical modules between optical components by using a simple and high-accuracy alignment technique. Characteristics of the proposed POSAs include a low coupling loss of 0.75 dB, a wide bandwidth for 10 Gbits/s transmission per channel, and low optical and electrical crosstalk of less than 30 dB. As a result, a data transmission rate of 10 Gbits/s×12 channels is well demonstrated with clean eye diagrams.

The optical network on-chip is a popular option due to its low latency and high bandwidth with significantly lower power dissipation. A butterfly-fat-tree based optical network on-chip (BONoC) is designed with new optical router architecture. A hybrid signaling scheme is designed with the control information transferred and processed in the electronic domain. An energy efficient routing is proposed by considering the power consumption of the microresonators and signaling progress. Evaluation of the new optical butterfly-fat-tree NoC is made in three aspects-energy, latency, and throughput. The comparison of power consumption with its electronic counterpart shows that 64-core ONoC can save about 78.6% energy when compared to an electronic one of the same size. Finally, we simulate butterfly-fat-tree ONoC, and show the end-to-end delay and throughput with different traffic loads and various packet sizes.

In the performance evaluation of phase-shifting interferometers for figure metrology, the height response, or height transfer function, is rarely taken into consideration, because in most applications smooth surfaces are measured and only the lowest spatial frequencies are of interest. For measurements with low uncertainty it is important to understand the height response as a function of the spatial-frequency content of a surface under test, in particular when it contains form-error components with frequencies at the high end of an interferometer's spatial-frequency passband. A mirror with a patterned area of 140-mm diameter, consisting of several subpatterns with varying spatial frequency, was used to evaluate the spectral response. Our goal was to develop a method for efficient mapping of the spectral response over the circular field of view of a phase-shifting interferometer. A new way of representing the dependence of the spectral response on the field of view of an interferometer is described.

An automatic method for the positioning of the test surface in a non-null interferometer is presented. A major task in the interferometric testing of surfaces is to avoid the introduction of surface aberrations due to an incorrect placement of the test object in the interferometer cavity. In the case of plane and spherical surfaces, adjustment errors can usually be distinguished from surface figure errors and therefore removed, but in the case of aspherical surfaces this task becomes nontrivial. In this work, the effect on the measured phase due to lateral and axial displacements of the aspherical surface is calculated, and an adjustment method for the positioning of the surface at a predefined measurement location presented. Experimental results showing the feasibility of the proposed procedure are shown.

Computer-generated holography is a computationally intensive process particularly well suited to the architecture of graphics processing units (GPUs). This work investigates the performance improvements achievable through utilization of a GPU for optimization of holograms via simulated annealing. Two examples are given; accelerated training of an optical correlator to accept or reject inputs over sets of varying sizes, followed by an investigation into optimization of a hologram to produce a desired complex distribution in a portion of the far field with varying resolutions. Specifically, results comparing a Quad-core 3.0-GHz CPU and an nVidia GTX260 GPU are presented, demonstrating performance improvements of up to 2400%. This work offers details on what steps have been taken to optimize the algorithm for both the CPU and GPU platforms, and may be of interest to those looking to utilize GPU hardware for scientific computation.

We present a novel numerical modeling of ultrasonic Lamb and Rayleigh wave propagation and scattering by through-thickness defects like holes and slots in homogeneous plates, and its experimental verification in both near and far field by a self-developed pulsed TV holography system. In contrast to rigorous vectorial formulation of elasticity theory, our model is based on the 2-D scalar wave equation over the plate surface, with specific boundary conditions in the defects and plate edges. The experimental data include complex amplitude maps of the out-of-plane displacements of the plate surface, obtained by a two-step spatiotemporal Fourier transform method. We find a fair match between the numerical and experimental results, which allows for quantitative characterization of the defects.

A secure holographic system is proposed, based on the principle of two-wave encryption in the Fresnel domain under convergent random illumination. The convergent random wavefront, instead of the commonly used plane wavefront, improves the security of a holographic encryption system, providing better protection from unauthorized users. Our system has two new encryption parameters (the convergence distance and randomized lens phase function) in addition to the propagation distance and random phase masks in the reference arm. Validity and feasibility of the proposed method are verified with numerical simulation and experimental results.

We present a novel approach to adaptive and progressive image transmission, based on the decomposition of an image into compositions and superpositions of monovariate functions. The monovariate functions are iteratively constructed and transmitted, one after the other, to progressively reconstruct the original image: the progressive transmission is performed directly in the 1D space of the monovariate functions and independently of any statistical properties of the image. Each monovariate function contains only a fraction of the pixels of the image. Each new transmitted monovariate function adds data to the previously transmitted monovariate functions. After each transmission step, by using the updated monovariate functions the image is reconstructed with an increased resolution. Finally, once all the monovariate functions have been transmitted, the original image is reconstructed exactly. This approach is characterized by its flexibility and robustness to packet loss: any numbers of intermediate transmissions and reconstructions are possible, and in case of packet loss, the global appearance of the transmitted image is preserved. Moreover, the intermediate images can be reconstructed at any resolution, and for any number of intermediate reconstructions, the original image will be exactly reconstructed. Finally, the quantity of data to be transmitted only depends on the image size and is independent of the number of intermediate reconstructions. Our main contributions are the modification of the decomposition scheme defined by the Kolmogorov superposition theorem to enable multiresolution image reconstructions and its application for progressive image transmission, using successively increasing resolutions. We illustrate this approach on several images and evaluate the reconstruction quality, decomposition flexibility, and error resilience during transmission.

Over the years, numerous methods have been proposed separately for restoring images corrupted by either impulse noise or Gaussian noise. Nevertheless, because of the distinct nature of both types of degradation processes, not much work has been developed to effectively remove mixed noise from images, a problem that is commonly found in practice. To alleviate this problem, we propose a two-stage approach based on impulse detectors and detail-preserving regularization. We employ the detectors to identify impulse noise, and then restore them and smooth the remaining Gaussian noise simultaneously based on regularization framework. A novel error norm that can adaptively mimick traditional l1 and l2 norms is used in the regularization process. This adaptivity enables our approach to be universally capable of removing various degrees of impulse noise and mixed noise, while preserving fine image details well. Extensive experiments have been conducted to test the proposed approach and shown its improvements over the algorithms existing in the literature.

We present a novel unsupervised learning algorithm for discovering objects and their location in videos from moving cameras. The videos can switch between different shots, and contain cluttered background, occlusion, camera motion, and multiple independently moving objects. We exploit both appearance consistency and spatial configuration consistency of local patches across frames for object recognition and localization. The contributions of this paper are twofold. First, we propose a combined approach for simultaneous spatial context and temporal context generation. Local video patches are extracted and described using the generated spatial-temporal context words. Second, a dynamic topic model, based on the representation of a bag of spatial-temporal context words, is introduced to learn object category models in video sequences. The proposed model can categorize and localize multiple objects in a single video. Objects leaving or entering the scene at multiple times can also be handled efficiently in the dynamic framework. Experimental results on the CamVid data set and the VISAT™ data set demonstrate the effectiveness and robustness of the proposed method.

An image feature extraction method based on the two-dimensional (2-D) mel cepstrum is introduced. The concept of one-dimensional mel cepstrum, which is widely used in speech recognition, is extended to 2-D in this article. The feature matrix resulting from the 2-D mel-cepstral analysis are applied to the support-vector-machine classifier with multi-class support to test the performance of the mel-cepstrum feature matrix. The AR, ORL, and Yale face databases are used in experimental studies, which indicate that recognition rates obtained by the 2-D mel-cepstrum method are superior to the recognition rates obtained using 2-D principal-component analysis and ordinary image-matrix-based face recognition. Experimental results show that 2-D mel-cepstral analysis can also be used in other image feature extraction problems.

Watermark embedding processes usually result in some degradation of the digital multimedia contents. Hence, they are not suitable for valuable and sensitive digital multimedia contents. Therefore, schemes combining signature with digital watermarking-like techniques have been proposed. Based on the general model for these combined schemes, a new scheme for image copyright protection by utilizing the pinned field of the protected image is proposed in this paper. The pinned field explores the texture information of the images and can be used to enhance the watermark robustness. Experimental results show that the proposed scheme works well under different signal-processing and geometric transformation attacks. On the other hand, in comparison with related schemes in the literature, our proposed scheme also has better performance. Furthermore, the proposed scheme is robust to both JPEG lossy compression and additive Gaussian noise.

This paper proposes a high-definition video watermarking method robust against compound geometrical attacks by camcorder capture as well as common video processing such as frame-rate conversion and transcoding. Unlike traditional watermarking systems using the original reference pattern, the proposed method exploits the reference pattern estimated from the watermarked video. Since the reference pattern and watermark pattern are embedded in the same spatial position of each frame, the two patterns estimated from the embedded video are always in spatial sync. Thus, the watermark information can be simply detected without an additional synchronizing step, even if geometrical distortions happen to the marked video. Also, the problem of misestimation of the reference pattern caused by temporal video clipping is solved using the proposed two-pass detector. Extensive experiments prove that the proposed method is robust against various temporal and spatial distortions.

Dusk and dawn are usually the most beautiful moments of the day, and are almost always too short for busy people nowadays to witness their coming. In this work, an efficient strategy for simulating a dusk scene of an outdoor scene image taken at other times before the sunset is presented. The strategy is a hybrid approach combining the piece-wise multiple regression (PMR) of data, discrete cosine transformation (DCT), and a look-up table algorithm. The process begins using a series of color-block images taken in the afternoon of a day. The best fitting functions of PMR for these color block images exist on separate planes (red, green, and blue) in the DCT domain individually. The reference databases of the DCT coefficients varying with respect to time are then established according to the best fitting functions of PMR. Finally, the dusk scene of an outdoor scene taken in the afternoon is synthesized by querying the reference database. The experiment results show that the presented algorithm can precisely simulate the desired dusk scene from a scene image taken in the afternoon.

We present a novel algorithm to remove motion blur from a single blurred image. To estimate the unknown motion blur kernel as accurately as possible, we propose an adaptive algorithm using anisotropic regularization. The proposed algorithm preserves the point spread function (PSF) path while keeping the properties of the motion PSF when solving for the blur kernel. Adaptive anisotropic regularization and refinement of the blur kernels are incorporated into an iterative process to improve the precision of the blur kernel. Maximum likelihood (ML) estimation deblurring based on edge-preserving regularization is derived to reduce artifacts while avoiding oversmoothing of the details. By using the estimated blur kernel and the proposed ML estimation deblurring, the motion blur can be removed effectively. The experimental results for real motion blurred images show that the proposed algorithm can removes motion blur effectively for a variety of real scenes.

We propose an approach for textured image segmentation based on amplitude-modulation frequency-modulation models. An image is modeled as a set of 2-D nonstationary sinusoids with spatially varying amplitudes and spatially varying frequency vectors. First, the demodulation procedure for the models furnishes a high-dimensional output at each pixel. Then, features including texture contrast, scale, and brightness are elaborately selected based on the high-dimensional output and the image itself. Next, a normalization and weighting scheme for feature combination is presented. Finally, simple K-means clustering is utilized for segmentation. The main characteristic of this work provides a feature vector that strengthens useful information and has fewer dimensionalities simultaneously. The proposed approach is compared with the dominant component analysis (DCA)+K-means algorithm and the DCA+ weighted curve evolution algorithm on three different datasets. The experimental results demonstrate that the proposed approach outperforms the others.

Under the assumption that no dynamic prior is given, the main obstacle to practical human-motion tracking is the high number of dimensions associated with a 3-D articulated full-body model. We present a method for 3-D human-motion tracking when the training data are unavailable in advance and no motion pattern prior is assumed. Based on the framework of the annealed particle filter, the proposed algorithm incrementally learns the eigenspace as a compact representation of motion patterns and efficiently adapts to pose changes. The model updates using the principal-component analysis, and introduces a forgetting factor to avoid overfitting. In addition, the likelihood measure is modeled by minimizing a cost function on the 3-D Markov random field (MRF), which integrates the information from visual hull and shape priors. A dynamic graph cut is performed to speed up the minimization process. As a result, the proposed approach is capable of obtaining the pose in parallel with the voxel data. Experimental results suggest that our method performs online tracking robustly and generates reconstructions beyond the shape from silhouette method from sparse camera views.

A microdisplay system based on an optical fiber driven by a 2-D piezoelectric actuator is presented. An optical fiber is extended from the free end of a 2-D piezoelectric actuator (free length 4.3 mm). A field programmable gate array (FPGA) drives the actuator using a triangular waveform to deflect the optical fiber in orthogonal directions. The FPGA also controls a LED light source, and the light is coupled into a chemically tapered single-mode fiber (SMF-28, core diameter 10 µm). At a preset pairing of near-resonance frequencies (horizontal 22 Hz, vertical 5070 Hz), the deflected optical fiber in combination with controlled light produces an output image with an approximate dimension of 0.1×0.1 mm², and a potential resolution of 400 lines per scan. This work details the design and fabrication of the microdisplay system. The mechanical and optical design for the microresonating scanner is discussed. In addition, the mechanical and optical performance and the resulting output of the 2-D scanner is presented.