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 10−9 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.

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 141-fs (over 100 Hz to 1 MHz) 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 −112 dBc/Hz at 10 kHz away from carrier, and the side modes are perfectly suppressed.

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 investigate three-flat calibration methods based on rotational symmetry and mirror symmetry for absolute interferometric flatness measurements of circular flats in the presence of deformations caused by the support mechanism for the flats, which are a significant problem for large, heavy flats. We show that the mirror-symmetric component of the mounting-induced deformation can be determined by comparing flat test solutions based on mirror symmetry and on rotational symmetry, when the flats have identical deformations. We also describe a novel solution to the three-flat problem for three flats with identical mounting-induced deformations. In the new three-flat solution, the flat deformation is calculated along with the wavefront flatness errors for the three flats. Formulas for the uncertainty of three-flat test solutions are derived.

A method using two prisms for measurement of small dynamic angles is proposed in which the measurement is based on a simple tangent equation and a phase-modulating interferometer with a laser diode to measure dynamic optical path differences with higher accuracy. Owing to the simple tangent equation, the symmetry requirement on the two prisms in the optical configuration is eliminated, and easy measurement of the separations between two parallel beams with a position-sensitive detector is achieved. Small-dynamic-angle measurements are experimentally demonstrated with high accuracy.

We discuss several illumination effects in gemstones and present maps to evaluate them. The matrices and tilt views of these maps permit one to find the stones that perform best in terms of illumination properties. By using the concepts of the main cutter's line, and the anti-cutter's line, the problem of finding the best stones is reduced by one dimension in the cutter's space. For the first time it is clearly shown why the Tolkowsky cut, and other cuts adjacent to it along the main cutter's line, is one of the best round brilliant cuts. The maps we introduce are a valuable educational tool, provide a basis for gemstone grading, and are useful in the jewelry industry to assess gemstone performance.

One of the more challenging applications of optical metrology is real-time dimensional control and surface inspection in industrial applications, where strong requirements of cost, speed of operation, ease of setup and applicability in adverse environments greatly limit the number of applicable technologies. The design and uses of an optic profilometer, based on conoscopic holography, have been reported previously, but there are still some drawbacks that should be addressed. One of the most important is signal processing, which is a relatively expensive process and limits the acquisition rate at no more than 70 profiles per s. We present a new approach to the signal processing problem, deriving that the phase information contained in one fringe pattern, which corresponds to one profile, can be considered as a combination of multiple one-dimensional (1-D) patterns that carry the same information but for a phase difference in the carrier wave, making it possible to apply efficient phase-shifting interferometry (PSI) techniques and resulting in a reduction of more than two orders of magnitude in computational needs.

We present an innovative method for quantitative and/or qualitative flow visualization by fringe projection through a test section with nonuniform refractive index distribution induced by convective heat transfer. Fringes are generated by a diffractive optical element (DOE). Information about the temperature gradient, encoded in the deformed fringe pattern, is demodulated by Fourier transform algorithms. The main advantages of the proposed procedure are flexibility in suiting to different heat transfer phenomena; full digital and automated data processing to provide both qualitative visualizations and quantitative maps of the temperature gradient field; full-field visualization; and low cost compared to interferometric equipment. The main disadvantages are reduced investigation area with low-cost TV cameras; sensitivity (i.e., smallest detectable temperature gradient); and lower accuracy than that of conventional interferometric and Schlieren techniques.

The illuminance responsivity dependencies on spectral power distributions (SPDs) of different types of light sources are studied. In this work we used three types of calibrated photometers, one of which was home-made and two were commercial photometers. A monochromator-based facility was used to scan SPDs of light sources. The dependencies of spectral mismatch correction factors F(St,Ss) and the illuminance responsivities of photometers versus the SPDs of tungsten-filament incandescent, fluorescent, high-pressure sodium, and metal-halide light sources and white/colored light-emitting diodes are presented throughout this work.

We describe the geometric optic design and analysis of the optimal retroreflection corner-cube sheets with the effective retroreflective area ratio of 100%. The maximum condition of the effective retroreflective area of elementary retroreflection corner-cube is investigated, and as a result, the analytic design formulas of optimal retroreflection corner-cube structure are derived. We propose a novel packing method for the elementary retroreflection corner-cube to construct optimal retroreflection corner-cube sheets with the effective retroreflective area ratio of 100%.

Research into novel technologies for active and adaptive optics is essential to ensure the required performance for the demanding science goals set for next-generation astronomical observatories. Both in space and on the ground, the potential gain from ultralightweight and thermally stable deformable optics is high. Surface quality, form, and a high level of stability during operation are important criteria for such mirrors. In 2006 we reported our initial results of the design and manufacture of a prototype carbon fiber reinforced polymer (CFRP) deformable mirror, including a description of the mirror's assembly with a stiff backing structure and actuator array, and an extensive characterization of the system. Here we discuss results of dynamical testing and influence function measurements as well as details of the methodology. Influence function shapes showed reasonable agreement with the finite element analysis predictions, confirming the suitability of the finite element method as a design aid for precision optical systems. While problems remain with this technology, our results highlight some important issues and provide useful guidelines for further research.

We have developed a new type of dual-wavelength transversely excited atmospheric pressure (TEA) CO2 laser that possesses space overlap and time synchronization. Our experiments have proven that the time interval of two output pulses with different frequencies can be adjusted from 1000 ns to 200 ns. In this way, the requirement of dual-wavelength excitation in a material can be achieved for isotope separation purposes. This TEA CO2 laser contains a grating-plate cavity formed by one germanium plate and two gratings, where the two gratings partially overlap in the space. The gratings, which are placed in tandem, are mutually beneficial via the germanium plate and establish double-frequency oscillation. The dual-wavelength laser is exported from the germanium plate. It is a changing of the effective area of two gratings that enables us to adjust the space overlap of the two output pulses. By simultaneously adjusting the quantity of misalignment in the gratings angle to vary the spectral line geometry loss, which can be used to reduce the time interval of the two output pulses, a time synchronization can be achieved.

Dead spaces are generated in the fast-axis direction of the laser diode stack (LDS) because of the construction of the LDS. A new method of using a plane-parallel plate array to eliminate dead spaces between the bars of the LDS is presented. The design method of the plane-parallel plate is also investigated, and the beam parameter product is used to evaluate the quality of the beams. As an example, the plane-parallel plate array for an LDS consisting of four bars is designed and simulated. The simulation results show that the dead spaces are eliminated, the spots size is compressed from 6.5 mm×10 mm to 3.5 mm×10mm, and the energy loss is about 2%.

A Raman lidar system for detection of hydrogen gas has been developed. The lidar system consists of a pulsed Nd:YAG laser of wavelength 355 nm and a Newtonian telescope of aperture 212 mm. The system can detect hydrogen gas by either rotational or vibrational Raman backscatter up to a distance of 30 m in outdoor, daylight conditions. Furthermore, the system can perform two-dimensional mapping of the hydrogen gas distribution by spatial scanning of the laser beam within the telescope field of view.

A laser flying marking system with a galvanometer scanner could be widely used as a workhorse because the moving speed of product on the workline would not be affected while being marked. A laser flying marking system, with high-speed galvanometer scanners, was set up. Two kinds of marking effects, vector style and matrix style, were realized in the system. Different motion-tracing methods, including a closed-loop feedback tracing mode and an open-loop computing tracing mode, were studied and utilized in the control software. Experimental results show that the system using the closed-loop feedback motion-tracing method has more adaptability for variable-speed applications.

A single-mode waveguide is fabricated using ion exchange in a molten bath of KNO3 salt. The mode effective index is measured using a mode-lines (M-lines) experiment. The waveguide is then etched, and the M-lines experiment is performed again. The two measurements are sufficient for refractive index profile (RIP) reconstruction, which is assumed to be Gaussian. The reconstructed profile is checked using a numerical technique and is then compared to the inverse technique, showing the inverse technique limitations.

We report on the design, fabrication, and optical characteristics of arrayed waveguide grating (AWG) devices on silicon-on-insulator (SOI) platforms to act as multiplexers in a hybridly integrated wavelength division multiplexing (WDM) transmitter for telecommunications and datacom applications. In order to achieve efficient coupling to laser diodes, SOI layers with 4-µm-thick Si were used to form rib waveguides. The AWG devices comprised eight channels with a channel spacing of 200 GHz around a center wavelength at 1550 nm. AWG integration with variable optical attenuators is demonstrated to add channel equalization ability.

Optical wireless communication systems usually adopt on-off keying (OOK), binary pulse position modulation (BPPM), and binary phase-shift keying (BPSK). In this work, the scheme of systems based on a turbo code of OOK, BPPM, and BPSK is proposed, and the three different iterated maximum a posteriori (MAP) algorithms of turbo code are deduced. To use the turbo code based on different modulated formats over optical wireless channels we deduce the formula of an atmospheric channel signal-to-noise ratio versus the atmospheric visibility. Simulations show that the turbo code based on BPSK is well suited for optical wireless communication systems.

An equivalent refractive mathematic model is presented according to the geometrical structure of twin-hole poling optical fibers. The characteristics of losses and polarizations of the fibers are theoretically analyzed. The theoretical analysis and experimental results indicate that when the metal electrode is close to the fiber core, the loss of y-polarization mode is far lower than that of x-polarization mode, and the electrode-manufacturing method of inserting metal wires has better loss performance than that of injecting melting alloys. (The former is less than 0.04 dB/cm, and the latter is 2.5 dB/cm.) The experimental measurements agree well with the theoretical predictions.

A two-wavelength wavelength-division-multiplexing (WDM) externally modulated transport system employing photonic crystal fiber (PCF) as a dispersion compensation device to compensate the fiber dispersion and to reduce the cross-phase modulation (XPM)–induced cross talk is proposed and demonstrated. In comparison with a two-wavelength WDM externally modulated transport system without a dispersion compensation device or with a conventional dispersion compensating fiber (DCF) as a dispersion compensation device, good performances of composite second-order (CSO) and composite triple beat (CTB) were obtained accompanied by acceptable carrier-to-noise ratio (CNR) in our proposed system.

The coupling characteristics of newly proposed photonic-crystal-fiber couplers are rigorously analyzed using a 3-D finite-difference vector beam propagation method. The coupling length and efficiency of the couplers are investigated as a function of their geometrical parameters at different wavelengths. Size variability of the central hole is considered as a means of improving the coupling between the two cores. A determination of the guiding properties of the couplers, such as the propagation constants and the effective indices, is performed using a mode solver based on the plane-wave method. We show that it is possible to design very short photonic-crystal-fiber couplers with submillimeter coupling lengths. Nonuniformities are deliberately introduced in the coupler pattern to decrease the coupling length in comparison with the ideal structures. This study confirms that the designed coupler can act as an efficient ultrasmall-wavelength splitter or polarization-preserving directional coupler for wavelength division multiplexing systems.

The effect of an imperfect antireflection (AR) coating on a birefringent interleaver (an important optical communication component) and on an optical communications system containing such a birefringent interleaver is investigated. We demonstrate how the imperfect AR coating on the rhomb surfaces affects the birefringent interleaver's intensity spectrum and generates undesirable chromatic dispersion (CD) ripples for an interleaver that should be dispersion-free by design. Our results show that a rhomb with a close-to-perfect AR surface coating (T=99.8%) can still generate a ±30-ps/nm CD ripple, causing a nonnegligible power penalty in an optical communications system. We also demonstrate a simple and practical approach to reduce the CD ripple caused by the imperfect AR coating.

This paper proposes a radio-on-fiber (RoF) radio-space transmission system. We consider the orthogonal frequency- and space-division multiple access system, in which the orthogonal frequency-division multiple access (OFDMA) and space-division multiple access (SDMA) are combined. In this system, two frequency-channel scheduling schemes are also proposed for OFDMA, and two grouping methods are proposed for SDMA. The performance of the proposed systems is analyzed by computational simulations. It is shown that the random grouping method does not degrade the performance compared with a more complicated grouping method. In the proposed frequency-channel scheduling schemes, the control station estimates all users' signal-to-noise ratios (SNRs), and these schemes allow the system to assign subcarriers to different users according to their channel conditions so that each user can transmit on subcarriers where it has high SNR. Simulation results show that users can avoid frequency-selective fading and achieve higher bit-error-rate performance.

A theoretical method to analyze four-layer large flattened mode (LFM) fibers is presented. The influence of the second cladding on the properties of four-layer LFM fiber, including the fundamental and higher-order modal fields, effective area, bending loss, and dispersion, are studied by comparison. At the same time, the reasons for the different characteristics are considered. The obtained results indicate that the effective area of the four-layer LFM fiber is about 1.6 times larger than that of the conventional standard step-index fiber and the fibers have better bend-induced filtering ability than three-layer LFM fibers.

We report the theoretical investigation of the coupling optics involving a laser diode and an elliptic-core single-mode step index fiber with a hyperbolic microlens on the tip of the fiber in the presence of possible transverse and angular mismatches. By employing Gaussian field distributions for both the source and the fiber, and also the prescribed ABCD matrix for refraction by a hyperbolic interface, we formulate analytical expressions for the concerned coupling efficiencies and evaluate them using few computations. The elliptic-core single-mode fiber has already emerged as a candidate in a polarization-conserving fiber optic sensor, in coherent fiber optical communication, etc. Therefore, our analysis, which to our knowledge is this first theoretical investigation in this context, will be extremely useful for the design of optimum launch optics involving an elliptic-core single-mode fiber. In addition, this analysis will be useful in the case of any inherent noncircularity that may arise due to fabrication problems in the circular core fiber.

We address the problem of routing dynamic connections with differentiated reliability (DiR) requirements in wavelength-division multiplexing (WDM) mesh networks when spare capacity sharing is allowed. The problem is called routing with DiR (ROWD). In order to meet the reliability requirement of each connection request, not only an active path (AP) but also a backup path (BP) or a set of backup segments (BSs) should be derived. We propose two novel heuristics, single-protection-segment-based heuristic (SPBH) and auxiliary-graph-based heuristic (AGBH), for problem ROWD. While SPBH computes a single BS to protect the AP, AGBH computes as many BSs as necessary to protect the AP. Numerical results from extensive simulations demonstrate the good performance of the two algorithms.

We present a new simultaneous differential phase-shift keying (DPSK) payload and subcarrier-multiplexed (SCM) label generation technique using a single dual-electrode Mach-Zehnder modulator (DE-MZM). We conduct simulations to verify the feasibility of the new SCM labeling scheme and examine the mutual interference between the DPSK payload and the SCM label. By selecting the subcarrier at half of the payload bit-rate frequency, we can significantly suppress the SCM label induced-power penalty to the DPSK payload. Moreover, we apply the SCM label generated by the proposed labeling technique to chromatic dispersion monitoring for DPSK systems. Simulation results show that by detecting radio frequency power of both the clock tone and the SCM label, the monitoring range is greatly improved.

We describe a heterodyne interferometry system based on a complementary metal-oxide semiconductor digital signal processor (CMOS-DSP) camera that is utilized for full-field optical phase measurement using a carrier-based phase retrieval algorithm, with no need for electro-mechanical scanning. Camera characterization test results support the adoption of a single-pixel approach to perform quasi-instantaneous differential phase measurements, which are immune to mechanical vibrations and thermal drifts. We developed an optical configuration based on a Mach-Zehnder heterodyne interferometer to perform a static test on a mirror surface. The profiles of the mirror surface set at two angular positions, the relative displacements in the range of nanometers, and the corresponding tilt angle were determined.

A full-color electroholographic 3-D display system employing LEDs is presented, and a virtual image reconstruction technique for it is studied. It is shown that the image blur observed in the reconstruction is suppressed to a lower level than in reconstruction employing a metal halide lamp. In addition, direct, independent drives on LEDs through RGB waves make the adjustment of white balance easier, and a wide viewing angle can be attained. Full-color, high-contrast 3-D images are obtained.

A common difficulty in displaying a Fresnel hologram in real time the required calculation of huge amounts of information. We propose a novel digital hologram generation method for real-time holographic display. It depends on compensation of the phase-added stereogram, and can generate high-quality holograms rapidly. We describe a generation algorithm for the phase-added stereogram, using the fast Fourier transform (FFT) for fast calculation, and the compensated phase-added stereogram to get a reconstructed image as clear as the Fresnel hologram. Moreover, we present a method to define the optimum size of segmentation to get a clear reconstruction image and to achieve fast computation using the FFT. We have built a demonstration system to implement the proposed method. The system consists of a server, a client, and an optical holographic display system for real-time holographic display. The server generates 3-D information and transmits it on Ethernet. The client receives the information and generates a digital hologram using the compensated phase-added stereogram. Finally, the generated hologram is displayed on the optical holographic display system in real time. We have achieved display of digital holograms at 15 frames/s with 1000 object points.

Starting with the recently introduced phase correlation function of a general-type beam, the angle-of-arrival fluctuations are derived and evaluated in atmospheric turbulence for lowest-order Gaussian, cos-Gaussian, cosh-Gaussian, annular, and flat-topped beams. Our motivation is to examine the improvement in the performance of optical atmospheric links when such beams are employed. For these beams, the dependence of the angle-of-arrival fluctuations on the propagation length, displacement and focusing parameters, source size, inner and outer scales of turbulence, and receiver radius is investigated. It is found that in the majority of the cases examined, the angle-of-arrival fluctuations remain small and hence are not expected to adversely affect the operation of free-space atmospheric links. It is observed that amongst the beams considered, the cos-Gaussian beam offers the least amount of angle-of-arrival fluctuations, while the worst behavior is exhibited by the cosh-Gaussian beam. This situation is reversed, however, if focused beams are used.

The ability to detect relative changes in backscatter polarization from a scanning high-pulse-energy lidar system at 1.54-µm wavelength is demonstrated. The new capability was tested during the dissemination of various biological aerosol simulants and other particulate emissions at the U.S. Army's Dugway Proving Ground. Results demonstrate that the lidar is sensitive to different types of aerosols, and departures from the atmospheric background depolarization ratio are consistent with the limited amount of information available on the degree of particle sphericity. We conclude that the polarization-sensitive coatings of the beam-steering unit mirrors are presently the largest source of error and that this error is minimized when scanning with a near-zero elevation angle. This is an encouraging result for aerosol source surveillance applications, where the depolarization information may be useful in determining the aerosol generation mechanism or provide an additional scalar variable for use in delineating the plume from the background.

We describe the development, experimentation, collected data, and results of research designed to gain an understanding of the temporal and spatial image collection guidelines for tracking humans. More specifically, we seek a quantitative understanding of the relationship between human observer performance and the spatial and temporal resolutions. We measure performance as a function of the number of video frames per second, the imager spatial resolution, and the ability of the observer to accurately determine the destination of a moving human target. Our research is restricted to data and imagery collected from typical modern, low- to mid-altitude, persistent surveillance platforms using a wide field of view. The ability of the human observer to track a human target unaided was determined by the observer's completion of carefully designed perception experiments. In these experiments, the observers were presented with simulated imagery from the U.S. Army Night Vision and Electronic Sensor Directorate's EOSim urban terrain simulator. The details of the simulated targets and backgrounds, and the design of the experiments as well as their associated results, are included in this treatment.

An essential role of model-based vision deals with the problem of solving for the values of all viewpoint and model parameters to be computed for the dimensions of an object for a three-dimensional (3-D) model. We propose a new method using only three vanishing points for recovering the dimensions of an object, its position, and the focal length of the camera from a single image of weak perspective projection. Our aim is to compute the dimension vector v of a model represented by the unit vector of objects from the image. The optimization of the dimension vector v for the object can be thus solved by the standard nonlinear optimization techniques with a multistart method that generates multiple starting points for the optimizer by sampling the parameter space uniformly. Experimental results demonstrate the dimension vector v of the proposed method for the 3-D model and show that the performance of the proposed method is better than the conventional. We also address that the actual dimensions of object from the image agree well with the simulated results from the single image of weak perspective projection.

The H.264/AVC video coding standard uses seven variable block sizes ranging from 16×16 to 4×4 in interframe coding. The motion estimation (ME) with seven modes needs very high computational complexity. To reduce the complexity of the ME module in H.264/AVC, the conventional partial distortion searching (PDS) algorithm, from a top-to-bottom sequential line-matching scan, is employed for fast full search (FFS) on the test software JM (called JM-FFS). We propose a two-stage sorting-based PDS (TS-PDS) algorithm for a fast lossless ME module in H.264/AVC by using the characteristics of pattern similarity matching errors. Two significant features of the image block pattern, bit-plane and absolute difference of means (ADM), are used to determine the calculation order in the TS-PDS. Moreover, a two-stage sorting-based normalized PDS (TS-NPDS) for a fast lossy ME module is also implemented in the same way. The TS-PDS can find the same motion vectors as the JM-FFS, and the TS-NPDS can obtain relatively accurate motion vectors with a large reduced computational load. Simulation results show that the average of the computational reduction ratio from the TS-PDS is 14.5% over the JM-FFS without any loss of peak signal-to-noise ratio of luminance (PSNRY) performance, and the TS-NPDS is 39.6% over the JM-FFS with the PSNRY performance very close to the JM-FFS.

We propose a two-stage method for removing impulse noise in images. In the first stage, we use a novel noise detector, called the augmentation-of-ordered-difference detector, to identify pixels that are likely to be corrupted by impulse noise. This detector achieves accurate impulse-noise detection by augmenting the difference between the center pixel's intensity value and its neighbors' intensity values in a local window. In the second stage, noise pixels are restored using an iterative and adaptive median-based filter. This filter is adaptive according to the number of noise pixels in the filtering window. Thus, noise-free pixels are unaltered, and noise pixels are filtered by the adaptive filter. Simulation results indicate that the proposed method is better than other impulse-noise reduction filters in suppressing impulse noise and preserving image details.

We propose a robust method to extract silhouettes of foreground objects from color-video sequences. To cope with various changes in the background, we model the background as a Laplace distribution and update it with a selective running average and static pixel observation. All pixels in the input video image are classified into four initial regions using background subtraction with multiple thresholds. Shadow regions are eliminated using color components, and the final foreground silhouette is extracted by smoothing the boundaries of the foreground and eliminating errors inside and outside of the regions. Experimental results show that the proposed algorithm works very well in various background and foreground situations.

A visual secret sharing (VSS) scheme is a secret image sharing scheme that divides a secret pixel into several subpixels (the number of subpixels is called the pixel expansion). The secret image encrypted by the VSS technique can be visually revealed without additional computations. However, the contrast of recovered image is poor and thus the VSS framework is always a research issue and does not have practical applications. We introduce a new framework that prioritizes the pixels with different pixel expansions to enhance the image contrast for practical use. Also, by integrating the optical character recognition with the proposed VSS scheme we show a new visual authentication scheme.

This paper proposes a multiresolution method for video object segmentation in the compression domain. We first calculate global motion parameters using only background macroblocks with tiny residual dc coefficients of the P frame, and then get true motion vectors projected to the immediate adjoined I frame. The basic layer image is obtained with only dc coefficients of the I frame. The enhancement texture characteristics are provided by the ac coefficients for partial decoding. The true object motion vectors and the basic layer image are fed into a morphological motion filter to get the lowest-resolution regions of moving objects, called the layer4 region of interest (L4-ROI). Only some of the ac coefficients in L4-ROI are decoded to obtain a higher-resolution image, called layer3, that mainly consists of blocks of the moving object. The moving object of interest in the highest resolution is obtained from a morphological motion filter with L2-ROI and the true object motion vectors. The number of ac coefficients determines the resulting resolution. Experiments show that the new algorithm can extract multiresolution moving objects efficiently.