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Showing papers in "Optical Engineering in 2009"


Journal ArticleDOI
TL;DR: This paper addresses a high dynamic range scanning technique that can measure this type of object by taking advantage of one merit of a phase-shifting algorithm: pixel-by-pixel phase retrieval.
Abstract: Measuring objects with a high variation range of surface reflectivity is challenging for any optical method: This paper addresses a high dynamic range scanning technique that can measure this type of object. It takes advantage of one merit of a phase-shifting algorithm: pixel-by-pixel phase retrieval. For each measurement, a sequence of fringe images with different exposures are taken: the brightest ones have good fringe quality in the darkest areas while the darkest ones have good fringe quality in the brightest areas. They are arranged from brighter to darker (i.e., from higher exposure to lower exposure). The final fringe images, used for phase retrieval, are produced pixel-by-pixel by choosing the brightest but unsaturated corresponding pixel from one exposure. A phase-shifting algorithm is employed to compute the phase, which can be further converted to coordinates. Our experiments demonstrate that the proposed technique can successfully measure objects with high dynamic range of surface reflectivity variation.

152 citations


Journal ArticleDOI
TL;DR: In this paper, the availability of free space optics (FSO) systems in dependence on weather conditions and on FSO link parameters, such as transmitted optical power, beam divergence, receiver sensitivity or link path distance, is discussed.
Abstract: The availability of free space optics (FSO) systems in dependence on weather conditions and on FSO link parameters, such as transmitted optical power, beam divergence, receiver sensitivity or link path distance, is discussed. A number of phenomena in the atmosphere, such as absorption, scattering, and turbulence, can affect beam attenuation, but in the case of wavelengths typical of FSO systems operation, only scattering and turbulence are appropriate to be taken into consideration. We model the power loss caused by turbulence by using the Rytov scintillation theory. Attenuation due to scattering, which can be expressed as a function of the link distance, wavelength, and meteorological visibility, is calculated from visibility data collected at several airports in Europe. Statistical evaluation of the attenuation caused by scattering and the power link margin calculated from FSO link parameters are used for calculating the link availability.

125 citations


Journal ArticleDOI
TL;DR: A series of experimental results are presented to confirm the validity of the theoretical model, demonstrating recovery of super- Nyquist frequencies for the first time and how the model can be used to optimize CCD design for lensless DH capture.
Abstract: We examine some fundamental theoretical limits on the abil- ity of practical digital holography DH systems to resolve detail in an image. Unlike conventional diffraction-limited imaging systems, where a projected image of the limiting aperture is used to define the system performance, there are at least three major effects that determine the performance of a DH system: i The spacing between adjacent pixels on the CCD, ii an averaging effect introduced by the finite size of these pixels, and iii the finite extent of the camera face itself. Using a theo- retical model, we define a single expression that accounts for all these physical effects. With this model, we explore several different DH record- ing techniques: off-axis and inline, considering both the dc terms, as well as the real and twin images that are features of the holographic record- ing process. Our analysis shows that the imaging operation is shift vari- ant and we demonstrate this using a simple example. We examine how our theoretical model can be used to optimize CCD design for lensless DH capture. We present a series of experimental results to confirm the validity of our theoretical model, demonstrating recovery of super- Nyquist frequencies for the first time. © 2009 Society of Photo-Optical Instrumen-

113 citations


Journal ArticleDOI
TL;DR: A formal investigation of the measurement principle of time-of-flight 3-D cameras using correlation of amplitude-modulated continuous-wave signals and shows that the computed range follows an offset normal distribution.
Abstract: We offer a formal investigation of the measurement principle of time-of-flight 3-D cameras using correlation of amplitude-modulated continuous-wave signals. These sensors can provide both depth maps and IR intensity pictures simultaneously and in real time. We examine the theory of the data acquisition in detail. The variance of the range measurements is derived in a concise way and we show that the computed range follows an offset normal distribution. The impact of quantization of that distribution is discussed. All theoretically investigated errors like the behavior of the variance, depth bias, saturation and quantization effects are supported by experimental results.

109 citations


Journal ArticleDOI
Song Zhang1
TL;DR: A framework to reduce the unwrapping errors of the measurement system using a digital multiple-wavelength phase- shifting algorithm and significantly alleviated the measurement errors caused by the phase noise.
Abstract: We address a framework to reduce the unwrapping errors of the measurement system using a digital multiple-wavelength phase- shifting algorithm. In particular, the following framework is proposed: 1 smooth the raw phase by smoothing the sine and cosine images of the phase computation of the inverse tangent function; 2 locate and re- move the incorrectly unwrapped points by the monotonicity condition of the phase map; 3 obtain the unwrapped phase map for the shortest wavelength without smoothing; 4 detect holes and fill them to preserve as much useful information as possible. Experiments demonstrated that the proposed framework significantly alleviated the measurement errors caused by the phase noise. © 2009 Society of Photo-Optical Instrumentation

98 citations


PatentDOI
TL;DR: In this article, a system for simultaneous real-time 3D geometry and color texture acquisition is presented, which includes a system processor for generating at least three phase shifted black and white fringe patterns with a phase shift of 2 π/3, a light projector adapted to project the fringe patterns onto an object, the projector being electrically connected with the system processor, and a color camera for capturing the fringe images.
Abstract: A system for simultaneous real-time three-dimensional geometry and color texture acquisition. The system includes a system processor for generating at least three phase shifted black and white fringe patterns with a phase shift of 2 π/3, a light projector adapted to project the fringe patterns onto an object, the projector being electrically connected with the system processor, and a color camera for capturing the fringe patterns to generate at least three raw fringe images. The fringe images are used to calculate a black and white texture image which is further converted to a color image by employing a demosaicing algorithm. The fringe images are also used to calculate a wrapped phase map that is further processed to generate a continuous unwrapped phase map by employing a phase unwrapping algorithm and the unwrapped phase map is converted to co-ordinates using calibrated system parameters for point-by-point three-dimensional shape measurement.

88 citations


Journal ArticleDOI
TL;DR: In this article, a Weibull statistical analysis of the UDRI data was performed to evaluate the cumulative failure probability and the failure probability density of polished and superpolished fused SiO2 windows as a function of biaxial tensile stress, for stressed areas ranging from 0.3 to 100 cm2.
Abstract: The development of high-energy lasers has focused attention on the requirement to assess the mechanical strength of optical components made of fused silica or fused quartz (SiO2). The strength of this material is known to be highly dependent on the stressed area and the surface finish, but has not yet been properly characterized in the published literature. Recently, Detrio and collaborators at the University of Dayton Research Institute (UDRI) performed extensive ring-on-ring flexural strength measurements on fused SiO2 specimens ranging in size from 1 to 9 in. in diameter and of widely differing surface qualities. We report on a Weibull statistical analysis of the UDRI data-an analysis based on the procedure outlined in Proc. SPIE 4375, 241 (2001). We demonstrate that (1) a two-parameter Weibull model, including the area-scaling principle, applies; (2) the shape parameter (m10) is essentially independent of the stressed area as well as the surface finish; and (3) the characteristic strength (1-cm2 uniformly stressed area) obeys a linear law, C (in megapascals) 160−2.83× (in parts per million per steradian), where characterizes the surface/subsurface "damage" of an appropriate set of test specimens. In this light, we evaluate the cumulative failure probability and the failure probability density of polished and superpolished fused SiO2 windows as a function of the biaxial tensile stress, for stressed areas ranging from 0.3 to 100 cm2.

73 citations


Journal ArticleDOI
TL;DR: A robust, miniaturized, diode-pumped high energy neodymium doped yttrium aluminium garnet (Nd:YAG) laser with passive Q-switch generating 25 mJ at 3 ns has been demonstrated at repetition rates of up to 150 Hz as mentioned in this paper.
Abstract: A robust, miniaturized, diode-pumped high-energy neodymium doped yttrium aluminium garnet (Nd:YAG) laser with passive Q-switch generating 25 mJ at 3 ns has been demonstrated at repetition rates of up to 150 Hz The device is designed for ignition of fuel air mixtures in internal combustion engines The pump diodes and Peltier cooling are integrated in the laser head, giving a compact design with a small number of optical components for easy assembly The laser was successfully operated as an optical spark plug on a test engine at high temperature and vibration levels

71 citations


Journal ArticleDOI
TL;DR: In this paper, the authors proposed a new system of the dark-bright solitons conversion using a micro-and nanoring resonators incorporating an optical add/drop filter, where the add-drop filter can be used to convert the dark soliton to a bright soliton.
Abstract: We propose a new system of the dark-bright solitons conversion using a micro- and nanoring resonators incorporating an optical add/drop filter, where the add/drop filter can be used to convert the dark soliton to a bright soliton. The key advantage of the system is that the detection of the dark soliton pulse is normally difficult due to the low level of input power. First, a dark soliton pulse is input into a microring resonator and then propagated into smaller micro- and nanoring resonators, respectively. Second, the add/drop filter is applied (connected) into the ring system, where the bright and dark solitons are obtained via the drop and through (or throughput) ports of the add/drop filter, respectively. The results obtained have shown that the detected soliton power can be controlled by the input soliton power and the ring resonator coupling coefficient, which is enough power to use in the transmission link. Thus, significant conversion-amplified signals can be achieved.

64 citations


Journal ArticleDOI
TL;DR: A new dynamic range compression technique for infrared (IR) imaging systems that enhances details visibility and allows the control and adjustment of the image appearance by setting a number of tunable parameters is proposed.
Abstract: We propose a new dynamic range compression technique for infrared (IR) imaging systems that enhances details visibility and allows the control and adjustment of the image appearance by setting a number of tunable parameters. This technique adopts a bilateral filter to extract a details component and a coarse component. The two components are processed independently and then recombined to obtain the output-enhanced image that fits the display dynamic range. The contribution made is threefold. We propose a new technique for the visualization of high dynamic range (HDR) images that is specifically tailored to IR images. We show the effectiveness of the method by analyzing experimental IR images that represent typical area surveillance and object recognition applications. Last, we quantitatively assess the performance of the proposed technique, comparing the quality of the enhanced image with that obtained through two well-established visualization methods.

61 citations


Journal ArticleDOI
TL;DR: Simulation results show that this scheme provides better reconstruction results than existing compressive sensing video acquisition schemes, such as 2-D or 3-D wavelet methods and the minimum total-variance (TV) method.
Abstract: We present a compressive sensing video acquisition scheme that relies on the sparsity properties of video in the spatial domain. In this scheme, the video sequence is represented by a reference frame, followed by the difference of measurement results between each pair of neighboring frames. The video signal is reconstructed by first reconstructing the frame differences using 1 minimization algorithm, then adding them sequentially to the reference frame. Simulation results on both simulated and real video sequences show that when the spatial changes between neighboring frames are small, this scheme provides better reconstruction results than existing compressive sensing video acquisition schemes, such as 2-D or 3-D wavelet methods and the minimum total-variance (TV) method. This scheme is suitable for compressive sensing acquisition of video sequences with relatively small spatial changes. A method that estimates the amount of spatial change based on the statistical properties of measurement results is also presented.

Journal ArticleDOI
TL;DR: This work proposes specific variants of normalized convolution and me- dian filtering, both adaptive and nonadaptive, to the denoising of the range images of time-of-flight range sensors with on-chip continuous-wave correlation of radio frequency-modulated signals.
Abstract: Time-of-flight range sensors with on-chip continuous-wave correlation of radio frequency-modulated signals are increasingly popu- lar. They simultaneously deliver depth maps and intensity images with noise and systematic errors that are unique for this particular kind of data. Based on recent theoretical findings on the dominating noise pro- cesses, we propose specific variants of normalized convolution and me- dian filtering, both adaptive and nonadaptive, to the denoising of the range images. We examine the proposed filters on real-world depth maps with varying reflectivity, structure, overexposure, and illumination. The best results are obtained by adaptive filters that locally adjust the level of smoothing using the estimated modulation amplitude as a mea-

Journal ArticleDOI
TL;DR: Based on the analysis of the geometrical meaning of the shift-invariant LPP algorithm, two algorithms to minimize the locality and maximize the globality under an orthogonal projection matrix are proposed.
Abstract: Locality preserving projections (LPP) is a recently developed linear-feature extraction algorithm that has been frequently used in the task of face recognition and other applications. However, LPP does not satisfy the shift-invariance property, which should be satisfied by a linear-feature extraction algorithm. In this paper, we analyze the reason and derive the shift-invariant LPP algorithm. Based on the analysis of the geometrical meaning of the shift-invariant LPP algorithm, we propose two algorithms to minimize the locality and maximize the globality under an orthogonal projection matrix. Experimental results on face recognition are presented to demonstrate the effectiveness of the proposed algorithms.

Journal ArticleDOI
TL;DR: The proposed method overcomes this limitation by using a laser multiple-line triangulation technique, where each of several measuring modules uses a unique laser wavelength to prevent unwanted overlapping between adjacent light patterns.
Abstract: Optical three-dimensional shape measurement of live objects is becoming an important developing and research tool because of its nonintrusive nature and high measuring speed. The current methods are reaching truly high speed in one view configuration, but in the case of the entire object shape measurement, they are limited due to mutual interference between multiple measuring modules. The proposed method overcomes this limitation by using a laser multiple-line triangulation technique, where each of several measuring modules uses a unique laser wavelength. The measuring modules are positioned so that the entire surface of the foot is digitized. This prevents unwanted overlapping between adjacent light patterns. The calibration procedure for each measuring module and for the entire system is based on measurements of the surface of a reference object. The system parameters are determined using an iterative optimization algorithm. The precision of the system is better than ±0.3 mm. The system is capable of measuring objects in motion. The results of the shape of a foot rising on its toes are given as an example.

Journal ArticleDOI
TL;DR: In this paper, a long-wave infrared division of amplitude imaging Stokes polarimeter is presented, which utilizes a wire-grid beamsplitter with imaging systems positioned at each output to analyze two orthogonal linear polarization states simultaneously.
Abstract: A long-wave infrared division of amplitude imaging Stokes polarimeter is presented. For the first time, to our knowledge, application of microbolometer focal plane array (FPA) technology to polarimetry is demonstrated. The sensor utilizes a wire-grid beamsplitter with imaging systems positioned at each output to analyze two orthogonal linear polarization states simultaneously. Combined with a form birefringent wave plate, the system is capable of snapshot imaging polarimetry in any one Stokes parameter (S1, S2, or S3). Radiometric and polarimetric calibration procedures for the instrument are provided, and the reduction matrices from the calibration are compared to rigorous coupled wave analysis and ray-tracing simulations. Image registration techniques for the sensor are discussed, and data from the instrument are presented, demonstrating the ability to measure intensity variations corresponding to polarized emission in natural environments. As such, emission polarimetry can be exploited at significantly reduced cost, sensor size, and power consumption over instruments based on more expensive mercury-cadmium telluride FPAs.

Journal ArticleDOI
TL;DR: In this paper, QR bar code and image processing techniques are used to construct a nested steganography scheme that can conceal lossless and lossy secret data into a cover image simultaneously and is robust to JPEG attacks.
Abstract: In this paper, QR bar code and image processing techniques are used to construct a nested steganography scheme. There are two types of secret data lossless and lossy embedded into a cover image. The lossless data is text that is first encoded by the QR barcode; its data does not have any distortion when comparing with the extracted data and original data. The lossy data is a kind of image; the face image is suitable for our case. Because the extracted text is lossless, the error correction rate of QR encoding must be carefully designed. We found a 25% error correction rate is suitable for our goal. In image embedding, because it can sustain minor perceptible distortion, we thus adopted the lower nibble byte discard of the face image to reduce the secret data. When the image is extracted, we use a median filter to filter out the noise and obtain a smoother image quality. After simulation, it is evident that our scheme is robust to JPEG attacks. Compared to other steganogra- phy schemes, our proposed method has three advantages: i the nested scheme is an enhanced security system never previously developed; ii our scheme can conceal lossless and lossy secret data into a cover image simultaneously; and iii the QR barcode used as secret data can widely extend this method's application fields. © 2009 Society of Photo-Optical

Journal ArticleDOI
TL;DR: In this paper, a technique to tune and calibrate bendable X-ray optics for submicron focusing is described, where the focusing is divided between two elliptically cylindrical reflecting elements, a Kirkpatrick-Baez pair.
Abstract: We describe a technique to optimally tune and calibrate bendable X-ray optics for submicron focusing. The focusing is divided between two elliptically cylindrical reflecting elements, a Kirkpatrick-Baez pair. Each optic is shaped by applying unequal bending couples to each end of a flat mirror. The developed technique allows optimal tuning of these systems using surface slope data obtained with a slope-measuring instrument, the long trace profiler. Because of the near linearity of the problem, the minimal set of data necessary for the tuning of each bender consists of only three slope traces measured before and after a single adjustment of each bending couple. The data are analyzed with software realizing a method of regression analysis with experimentally found characteristic functions of the benders. The resulting approximation to the functional dependence of the desired shape provides nearly final settings. Moreover, the characteristic functions of the benders found in the course of tuning can be used for retuning to a new desired shape without removal from the beamline and remeasuring. We perform a ray trace using profiler data for the finally tuned optics, predicting the performance to be expected during use of the optics on the beamline.

Journal ArticleDOI
TL;DR: Based on the Monte-Carlo ray-tracing method, numerical simulation results demonstrate that the light output efficiencies of these novel lenses reach as high as 98% and are 17% higher than that of traditional total internal reflection (TIR) MR16 lens as discussed by the authors.
Abstract: Light-emitting diode (LED) MR16 lamps, regarded as one typical general lighting product of LEDs, are being widely used in many applications. Light efficiency into a main beam and uniformity are two key issues for high quality illumination of LED MR16 lamps. In this study, a practical and precise nonimaging optical design method is presented, and two novel 90- and 120-deg free-form lenses for high illumination quality LED MR16 lamps are designed according to this method. Based on the Monte-Carlo ray-tracing method, numerical simulation results demonstrate that the light output efficiencies of these novel lenses reach as high as 98% and are 17% higher than that of traditional total internal reflection (TIR) MR16 lens. Moreover, more than 89% of light exiting from the surfaces of these novel lenses irradiate within the desired receive target, while only 60% irradiate for traditional TIR lens. The uniformities of illuminance distribution across the target of these novel MR16 lamps also are much higher. In addition, these novel lenses are both quite compact and no more than 1/5 of that of the TIR lens. Therefore, these LED MR16 lamps integrated by novel lenses provide an effective solution to high quality illumination.

Journal ArticleDOI
TL;DR: The experimental results conducted on billet surface images obtained from actual steel production lines show that the proposed algorithm is effective for defect detection of scale-covered steel billet surfaces.
Abstract: Vision-based inspection systems have been widely investigated for the detection and classification of defects in various industrial product. We present a new defect detection algorithm for scale-covered steel billet surfaces. Because of the availability of various kinds of steel, presence of scales, and manufacturing conditions, the features of billet surface images are not uniform. In particular, scales severely change the properties of defect-free surfaces. Moreover, the various kinds of possible defects make their detection difficult. In order to resolve these problems and to improve the detection performance, two methods are proposed. First, undecimated wavelet transform and vertical projection profile are presented. Second, a method for detecting the variations in the block features along the vertical direction is proposed. The former method can effectively detect vertical line defects, and the latter can efficiently detect the remaining defects, except the vertical line defects. The experimental results conducted on billet surface images obtained from actual steel production lines show that the proposed algorithm is effective for defect detection of scale-covered steel billet surfaces.

Journal ArticleDOI
TL;DR: In this paper, a three-wavelength interferometric technique is used with a phase-shifting phase evaluation procedure, which gives wrapped phase at any pixel corresponding to these wavelengths.
Abstract: Interferometric surface profilers using a single wavelength offer excellent vertical resolution, but have an ambiguity-free range of less than half a wavelength. Multiple-wavelength or white light interference techniques are used to overcome the problem. We discuss a three-wavelength interferometric technique used with a phase-shifting phase evaluation procedure. The phase evaluation at the three wavelengths gives wrapped phase at any pixel corresponding to these wavelengths. We use the fact that the variation of phase with wavenumber for a given profile height is linear to determine the absolute value of the profile height. The height is then used to ascertain the fringe order. The fringe order, along with the wrapped phase, gives the profile height with a resolution given by the phase-shifting technique. Experimental results for large step height measurement on etched silicon samples are presented.

Journal ArticleDOI
TL;DR: A method of conducting phase-modulated all-optical logic gates is proposed that will exploit the advantages of phase modulation not only in processing but also in encoding as well decoding also.
Abstract: It is well established that optical devices and components are more advantageous than their electronic counterparts because of inherent parallelism in optics. Basically electronics are found to be very unsuitable in high speed (above gigahertz) data processing systems whereas tremendous operational speed (in the range of terahertz) can be achieved with the help of optics. The parallelism of optics and the properties of low loss transmission make optics a powerful technology for digital computing and processing and in long-range communications. Again it is well established that logic gates are the basic building blocks of any computing or data processing system. Therefore, any optical data processor needs suitable optically run logic gates. A method of conducting phase-modulated all-optical logic gates is proposed. Here we will exploit the advantages of phase modulation not only in processing but also in encoding as well decoding also.

Journal ArticleDOI
TL;DR: An effective algorithm for colorizing a grayscale image using a reference color image, an RGB to color transform (=luminance, =chrominance), and a block-based vector quantization of luminance mapping (VQLM) technique is developed.
Abstract: We develop an effective algorithm for colorizing a grayscale image In our approach, a reference color image, an RGB to color transform (=luminance, =chrominance), and a block-based vector quantization of luminance mapping (VQLM) technique are used to automatically colorize the grayscale image The VQLM technique compares the grayscale image with the luminance of the color reference image to obtain the information of the planes of the grayscale image After the chrominance is padded, the inverse color transform, to RGB, colorizes the grayscale scene is colorized Meanwhile, we create a mean of VQLM (MVQLM) method to improve the quality of the colorized grayscale image Experimental results show the MVQLM method is better than the VQLM method Also, we investigate colorizing the grayscale image working in the and YIQ spaces The simulation results also reveal that working in the space is slightly better than working in the YIQ space Compared to other colorizing schemes, our proposed method has two advantages: 1 the codebook and MVQLM techniques colorize the grayscale images for any size image that can be evenly divided by 2 automatically; and 2 the MVQLM method obtains a smoother colorizing effect and improved quality compared to the VQLM method

Journal ArticleDOI
TL;DR: In this article, the authors examined the possibility of constructing deformable mirrors for adaptive optics with a large number of degrees of freedom from silicon wafers with bimorph piezoelectric actuation.
Abstract: This paper examines the possibility of constructing deformable mirrors for adaptive optics with a large number of degrees of freedom from silicon wafers with bimorph piezoelectric actuation. The mirror may be used on its own, or as a segment of a larger mirror. The typical size of one segment is 100 to 200 mm; the production process relies on silicon wafers and thick film piezoelectric material deposition technology; it is able to lead to an actuation pitch of the order of 5 mm, and the manufacturing costs appear to grow only slowly with the number of degrees of freedom in the adaptive optics.

Journal ArticleDOI
TL;DR: Experimental results show that the acceleration feedback proposed here can effectively enhance the bandwidth of the closed-loop system and its trajectory tracking and pointing performance.
Abstract: In the control system of a CCD-based tracking loop for a fast steering mirror (FSM), the most effective method often employed to improve pointing performance is to increase high gain of the control system for a high bandwidth, which, however, usually suffers a great deal from a low CCD sampling rate and the mechanics of the FSM. Moreover, the amount of time delay engendered by sampling and data processing can significantly reduce the performance of a closed-loop system. Therefore, a tentative approach to the implementation of a CCD-based tracking control system with acceleration feedback is proposed. In theory, the position open loop is made of double integrators with a high bandwidth of the acceleration feedback loop; in fact, however, the acceleration open loop of the FSM response includes a quadratic differential, and it is very difficult to compensate a quadratic differential with an integral algorithm. To solve this problem, a novel acceleration closed system such as a bandpass filter is proposed. The position is reconstructed into a simple first-order filter instead of a third-order control system. In addition experimental results show that the acceleration feedback proposed here can effectively enhance the bandwidth of the closed-loop system and its trajectory tracking and pointing performance. (C) 2009 Society of Photo-Optical Instrumentation Engineers. [DOI: 10.1117/1.3065500]

Journal ArticleDOI
TL;DR: The powder-in-tube technique is versatile and can be used to fabricate fibers with different dimensions and core/cladding materials as discussed by the authors, and has been used to construct silicon optical fibers with cladding diameters in the range of 40 to 240 µm and core diameters of 10 to 100 µm.
Abstract: 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 40 to 240 µm, core diameters in the range of 10 to 100 µm, and an approximate overall length of 7 cm have been fabricated. The powder-in-tube technique is versatile and can be utilized to fabricate fibers with different dimensions and core/cladding materials.

Journal ArticleDOI
TL;DR: In this article, a performance metric Δ is described that can be used to determine the parameters of a partially coherent beam for near-optimal performance of a free-space optical link.
Abstract: A performance metric Δ is described that can be used to determine the parameters of a partially coherent beam for near-optimal performance of a free-space optical link. The metric is defined as the mean received irradiance minus the standard deviation of the irradiance, and maximizing Δ balances the effects of beam spread and scintillation. An analytic form of Δ is developed for a Gaussian Schell-model beam, where the optimization parameter is the transverse coherence length. Comparisons of the metric performance are made with the more conventional probability-of-fade metric. The metric Δ is applied to determine the characteristics of the optimized coherence length as a function of a variety of link parameters and scenarios. In general, the optimized coherence length tends to decrease with increasing turbulence strength and propagation distance but increases with wavelength, although the behavior of specific scenarios can vary.

Journal ArticleDOI
TL;DR: This work proposes a method to estimate the projector parameters according to the camera image reprojection error, which does not require us to know the statistical characteristics of the projector image point and makes full use of the background knowledge of the camera images noise.
Abstract: The traditional projector calibration always assumes that the reprojection errors on the projector image are independent and identically distributed and utilize the same method as the camera calibration. Actually, even if the measured points on the camera image are independent and identically distributed Gaussian variables, it is impossible to obtain the statistical characteristics of the reprojection errors on the projector image, because the relation between the original measurement error and the reprojection error is nonlinear. We propose a method to estimate the projector parameters according to the camera image reprojection error. It does not require us to know the statistical characteristics of the projector image point and makes full use of the background knowledge of the camera image noise, because our cost function does not concern the reprojection error on the projector image as is the case in the traditional method. The simulations and experiments affirm that this method has higher precision, even if the real noise is not normal.

Journal ArticleDOI
TL;DR: This research shows three novelties compared to previous works, including the first approach to combine the finger vein and finger geometry information at the same time, and shows that recognition accuracy is significantly enhanced using the proposed method.
Abstract: 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.

Journal ArticleDOI
TL;DR: PVr is a newly proposed robust amplitude parameter that combines the PV of a 36-term Zernike fit and the root mean square of the residual that provides automatic filtering, is insensitive to system resolution, and relates directly to imaging performance via the Marechal criterion.
Abstract: Peak-to-valley departure (PV) is entrenched in optics design and manufacture as a characterization of an optical figure; modern interferometers commonly use 1k×1k detectors, the output of which may not be well represented by two points. PVr is a newly proposed robust amplitude parameter that combines the PV of a 36-term Zernike fit and the root mean square of the residual. This provides automatic filtering, is insensitive to system resolution, and relates directly to imaging performance via the Marechal criterion. Use of PVr in place of PV is recommended.

Journal ArticleDOI
TL;DR: This work introduces a novel fake-fingerprint detection method that uses multiple static features extracted from one image to determine the aliveness of fingerprints and concludes that the proposed method is a simple yet promising fake- Fingerprint inspection technique in practice.
Abstract: Recently, fake fingerprints have become a serious concern for the use of fingerprint recognition systems. We introduce a novel fake-fingerprint detection method that uses multiple static features. With regard to the usability of the method for field applications, we employ static features extracted from one image to determine the aliveness of fingerprints. We consider the power spectrum, histogram, directional contrast, ridge thickness, and ridge signal of each fingerprint image as representative static features. Each feature is analyzed with respect to the physiological and statistical distinctiveness of live and fake fingerprints. These features form a feature vector set and are fused at the feature level through a support vector machine classifier. For performance evaluation and comparison, a total of 7200 live images and 9000 fake images were collected using four sensors (three optical and one capacitive). Experimental results showed that proposed method achieved approximately 1.6% equal-error rate with optical-based sensors. In the case of the capacitive sensor, there was no test error when only one image was used for a decision. Based on these results, we conclude that the proposed method is a simple yet promising fake-fingerprint inspection technique in practice.