According to Wikipedia (so it must be true), the phrase “A picture is worth a thousand words” is attributed to an article by Fred R. Barnard in the trade journal Printers’ Ink in 1921. He went on to say later that he attributed it to a Chinese proverb so people would take it seriously.

The microwave phase shifter using 25-GHz dense wavelength division multiplexing (DWDM) channel spacing tuning on the silicon-on-insulator microring resonator (MRR), which was utilizing the multimode interference as the coupling function to achieve wavelength independence, is proposed and demonstrated. With a quality factor of 1199 for the MRR, there was 25-deg phase tuning for every 25-GHz DWDM channel spacing at 5-GHz microwave frequency. The total tunability from the microwave phase shifter could achieve 350 deg using 22 DWDM channels with 25-GHz spacing.

The leakage losses of a bent equiangular spiral photonic crystal fiber (ES-PCF) have been analyzed in this paper by employing a full-vectorial finite element method. The analysis shows that the confinement and bending losses of ES-PCF are several orders of magnitude less than that of the conventional hexagonal lattice PCF (H-PCF) with similar dimensions. Also, the bending loss increases less rapidly in ES-PCF than in H-PCF for similar bending radii. It has also been found that no mode degeneration between fundamental core mode and first cladding mode occurs in ES-PCF. The reason of higher field confinement in ES-PCF than its hexagonal counterpart is also discussed.

We experimentally demonstrate transmission of cable television (CATV) radio frequency signals over a pointed indoor optical wireless link. The length of the optical link was 15 m. Collimators used at both the transmitter and the receiver sides required good alignment before sufficient optical power could be received. The system was placed at a height of 2 m, which is more than average human height, so human movements throughout the room did not obstruct the link. The optical wireless propagation path was almost lossless. The originality in this experimental demonstration is the transmission of full range of CATV signals compared to other works in this area. This experiment of radio over free-space optics showed that point-to-point indoor optical wireless links can be utilized as an alternative means for transmission of multimedia data.

A plane-parallel plate of a specific thickness placed in front of the collecting lens in a confocal microscope (CM) is used to produce multiple-transmitted-light interference to sharpen the Airy main lobe so that the lateral resolution in the x-direction can be further improved. Numerical experiments show that the lateral full-width at half maximum in the x -direction has been narrowed down to 50 nm, and the lateral resolution has been improved by 80% in comparison with a conventional CM when thickness d =5  mm , reflectivity R=0.7 , and NA=0.65 .

This special section of Optical Engineering on speckle metrology has been published as a follow-up to the conference “Speckle 2012: V International Conference on Speckle Metrology,” which was held in Vigo, Spain, from 10–12 September 2012.

Digital shearography has demonstrated great potential in direct strain measurement and, thus, has become an industrial tool for nondestructive testing (NDT), especially for NDT of delaminations and detection of impact damage in composite materials such as carbon fiber reinforced plastics and honeycomb structures. The increasing demand for high measurement sensitivity has led to the need for real-time monitoring of a digital shearographic phase map. Phase maps can be generated by applying a temporal, or spatial, phase shift technique. The temporal phase shift technique is simpler and more reliable for industry applications and, thus, has widely been utilized in practical shearographic inspection systems. This paper presents a review of the temporal phase shift digital shearography method with different algorithms and the possibility for real-time monitoring of phase maps for NDT. Quantitative and real-time monitoring of full-field strain information, using different algorithms, is presented. The potentials and limitations for each algorithm are discussed and demonstrated through examples of shearographic testing.

We present the development of a speckle interferometer based on a CO[sub] 2 laser and using a thermal infrared camera based on an uncooled microbolometer array. It is intended to be used for monitoring deformations as well as detecting flaws in aeronautical composites, with a smaller sensitivity to displacement compared to an equivalent system using visible (VIS) lasers. Moreover the long wavelength allows working with such interferometers outside the laboratory. A mobile system has been developed on the basis of previous laboratory developments. Then it is validated in a variety of industrial nondestructive testing applications in field working conditions.

Speckle can be modeled by analyzing the statistics of an image of a phase object such as a rough surface. The image can be calculated using the coherent transfer function of the imaging system and the angular spectrum representation. This approach gives a three-dimensional image, and includes the effects of high numerical aperture and the finite depth of the structure. In addition to Gaussian correlation, different correlation coefficients can be assumed, including fractal distributions, such as exponential correlation.

A portable device to essentially measure residual stress fields outside an optical bench is presented. This system combines the hole-drilling technique with digital speckle pattern interferometry. A novel feature of this device is its high degree of compaction since only one base supports simultaneously the measurement module and the hole-drilling device. A new version of the American society for testing and materials standard E837 for the measurement of residual stresses has been improved including a computation method for nonuniform residual stresses. According to this standard, a hole with a maximum depth of 1.0 mm should be introduced into the material to assess the stress distribution along the hole’s depth. The discretization of the stress distribution is performed in 20 equal steps of 0.05 mm, getting the deformations generated for stress relief in every drilling step. A description of the compact device showing the solution for a fast and easy interchanging process between modules is also presented. The proposed system was compared with a traditional method using strain gages, and a good agreement was shown between stress distributions measured with both methods. Finally, the portable device was used to evaluate the residual stress distribution in a sample with a rod welded by friction hydro pillar processing.

The inspection of optically rough surfaces searching for defects or other macroscopic features, or with the aim of characterizing roughness, are tasks well suited to optical techniques. We present the concept, the architecture, the mathematical modeling, the calibration, and some results of a device with episcopic coaxial illumination, specifically developed for surface inspections, which simultaneously renders both a coherent image and the energy spectrum of the complex reflection coefficient of a portion of the surface, precisely delimited by the illuminating laser spot. This concept is based on the well-known, single-lens, coherent image processing setup with beamsplitters added to insert the illuminating beam and to allow simultaneous access to the Fourier transform plane and to the image plane. Information about the resolved macroscopic features and the nonresolved surface microstructure (through the corresponding speckle signature) is obtained in both planes which enables different surface analysis strategies. The speckle sizes in the spectrum, and in the image, can be controlled by selecting the size of the illuminated area of the object and the lens aperture, respectively. Some envisaged applications are the detection and characterization of defects or macroscopic structures in rough surfaces, identification of authentication marks, evaluation of roughness parameters, and of speckle statistics.

Before a machine learning system can be deployed, it typically needs to undergo a training phase, which enables it to acquire the necessary structures and information to solve similar problems. The performance of a machine learning system is commonly assessed by measuring how well the system is able to solve problems, which are generally similar but not identical to those used as examples during the training phase. We investigate applying machine learning to a key step of interferogram analysis, namely the identification of phase discontinuities. Identifying phase discontinuities correctly can be an especially challenging task due to the inherently noisy nature of speckle interferograms. Traditionally, automated edge detection operators are employed for this task, often producing inferior results as compared to those produced manually by an expert human operator. We present a machine learning approach to the phase discontinuity identification problem, discuss its potential and merits, and examine the challenges encountered during the training phase. We describe novel measures for quantifying the learning attainment levels of the system and describe how these measures can be used to guide the training phase in a methodical and intuitive manner.

I discuss dynamic properties of multispectral speckle in the context of digital holographic interferometry and image correlation. I outline the correlation of speckles in free space, in an imaging system, and, in the case of interferometric detection, caused by reflection off an inclined diffuse surface. It is shown that interferometric phase gradients and speckle movements are closely related where in fact the phase gradients are the generator of speckle movements in a defocused plane. The theory is exemplified by three typical situations encountered in image-plane digital holographic interferometry.

A two-step electronic speckle pattern interferometry (ESPI) method with blind phase shift of a reference wave, in which the phase shift extraction is fulfilled by using both a correlation and a discrete Fourier transform (DFT) approaches, is presented here. In the correlation approach, the blind phase shift is calculated via the correlation coefficient between two similar speckle interferograms (SI) differing only by the reference wave phase shift. The DFT approach is based on the blind phase shift extraction from frequency components of SI Fourier spectra. Comparative analysis of these approaches has testified to their high performance. Moreover, it is shown that the correlation approach is more preferable for blind phase shift extraction from SIs with a rough surface than from interferograms with a smooth surface; hence, it is more convenient for ESPI than for phase-shifting interferometry. In addition, this approach provides a lesser level of systematic error of extracted phase shift in comparison with the DFT. The correlation approach was used for experimental definition of Poisson’s ratio for duralumin constructional material by the two-step ESPI method.

The growing interest in the applications of digital holography interferometry has led to an increasing demand for reliable phase unwrapping techniques. In digital holography, the phase carries three-dimensional surface information about the object. However, phase mapping is ambiguous as the extracted phase is returned in a form that suffers from 2π phase jumps. Furthermore, the presence of noise in the measured data, in which many singular points (SP) are found, often makes general phase unwrapping algorithms fail to produce accurate unwrapped results. Therefore, it is necessary to use a powerful phase unwrapping method to recover the desired smooth phase surface. For this reason, we developed a phase unwrapping algorithm that is applicable to digital hologram maps. The developed algorithm solves the singularity problem caused by SPs as a result of compensating its effect by using rotational and direct compensators. We show a difference in performance between our developed phase unwrapping algorithm and other well known phase unwrapping methods for digital holographic data. In addition, the methods to extract phase information of the object from hologram maps are also investigated. Results show that the developed algorithm gives satisfactory unwrapped results with low computational time cost.

Pulsed TV-holography (PTVH) can be used for obtaining two-dimensional maps of instantaneous out-of-plane displacements in plates. In particular, our group has demonstrated that scattering patterns generated by the interaction of elastic waves with defects can be measured with PTVH and employed for the characterization of damage in nondestructive inspection of plate structures. Recently, we have succeeded in obtaining a quantitative description of experimental scattering patterns of quasi-Rayleigh (qR) waves produced by holes in harmonic regime using a finite element method (FEM) combined with a two-dimensional scalar wave equation, avoiding the standard and more complex vector approaches based on the rigorous linear elasticity theory. This scheme has been extended here for characterizing equivalent scattering phenomena in transient regime. Simulated scattering patterns, obtained with the scalar FEM, and the corresponding experimental patterns associated to the interaction of qR waves with holes, measured with our specifically developed PTVH system, have been compared. Results have shown that, except for the evaluation of the backscattering coefficient, a reasonable agreement between theory and experiment is obtained in both amplitude and phase, which confirms the feasibility and potential of the proposed scalar approximation for the characterization of experimental transient scattering patterns measured with our PTVH technique.

A new method to measure shape by analyzing the speckle movements in images generated by numerical propagation from dual-wavelength holograms is presented. The relationship of the speckle movements at different focal distances is formulated, and it is shown how this carries information about the surface position as well as the local slope of the object. It is experimentally verified that dual-wavelength holography and numerically generated speckle images can be used together with digital speckle correlation to retrieve the object shape. From a measurement on a cylindrical test object, the method is demonstrated to have a random error in the order of a few micrometers.

It is well known that displacement components estimated using digital image correlation are affected by a systematic error due to the polynomial interpolation required by the numerical algorithm. The magnitude of bias depends on the characteristics of the speckle pattern (i.e., the frequency content of the image), on the fractional part of displacements and on the type of polynomial used for intensity interpolation. In literature, B-Spline polynomials are pointed out as being able to introduce the smaller errors, whereas bilinear and cubic interpolants generally give the worst results. However, the small bias of B-Spline polynomials is partially counterbalanced by a somewhat larger execution time. We will try to improve the accuracy of lower order polynomials by a posteriori correcting their results so as to obtain a faster and more accurate analysis.

The idea of remote laboratories is reviewed, and the potential of the approach on selected examples with special focus on the field of optical metrology is illustrated. The concept of remote metrology is extended beyond the simple exchange of data between distant laboratories and the remote access to experimental facilities embedded in modern educational concepts. We describe an architecture that provides the opportunity to communicate with and eventually control the physical setup of a remote metrology system. We show that such a concept can be implemented within cloud-computing environments, and may extend their current performance by the access to experimental facilities.

In recent years, flat-panel display (FPD) technology has undergone great development, and now FPDs appear in many devices. A significant element in FPD manufacturing is the display front surface. Manufacturers sell FPDs with different types of front surfaces, which can be matte (also called anti-glare) or glossy screens. Users who prefer glossy screens consider these displays to show more vivid colors compared with matte-screen displays. However, on the glossy screens, external light sources may cause unpleasant reflections that can be reduced by a matte treatment in the front surface. In this work, we present a method to characterize FPD screens using laser-speckle patterns. We characterize three FPDs: a Samsung XL2370 LCD monitor of 23 in. with matte screen, a Toshiba Satellite A100 LCD laptop of 15.4 in. with glossy screen, and a Grammata Papyre 6.1 electronic book reader of 6 in. with ePaper screen (E-ink technology). The results show great differences in speckle-contrast values for the three screens characterized and, therefore, this work shows the feasibility of this method for characterizing and comparing FPDs that have different types of front surfaces.

Acoustically induced vibrations of the tympanic membrane (TM) play a primary role in the hearing process, in that these motions are the initial mechanical response of the ear to airborne sound. Characterization of the shape and three-dimensional (3-D) displacement patterns of the TM is a crucial step to a better understanding of the complicated mechanics of sound reception by the ear. Sound-induced 3-D displacements of the TM are estimated from shape and one-dimensional displacements measured in cadaveric chinchillas using a lensless dual-wavelength digital holography system (DWDHS). The DWDHS consists of laser delivery, optical head, and computing platform subsystems. Shape measurements are performed in double-exposure mode with the use of two wavelengths of a tunable laser, while nanometer-scale displacements are measured along a single sensitivity direction with a constant wavelength. Taking into consideration the geometrical and dimensional constrains imposed by the anatomy of the TM, we combine principles of thin-shell theory together with displacement measurements along a single sensitivity vector and TM surface shape to extract the three principal components of displacement in the full-field-of-view. We test, validate, and identify limitations of this approach via the application of finite element method to artificial geometries.

Surface roughness of technical surfaces is an important parameter in, for example, quality control. Speckle interferometry (SI) is a powerful tool for acquiring information about a surface under test. Recent investigations concentrated on deriving analytical functions to describe the dependency of surface roughness on SI, assuming normally distributed surface roughness. The common approach is to use the correlation of the standard deviation of height distribution σ and single speckle-related parameters like fringe visibility V or spectral speckle correlation C to estimate surface roughness. Furthermore, roughness cannot be described clearly using only one parameter (e.g., Ra ), which makes it often necessary to estimate more roughness parameters. A new approach in roughness measurement using SI is presented. A multivariate data analysis for generating a regression model is employed, which may include many speckle-related parameters on one hand and offers the possibility to acquire different roughness parameters on the other hand. Finally, the regression models created for four exemplary roughness parameters Rq , R3z , Rp , and Mr1 are discussed and the accuracy in the prediction of these parameters is indicated.

Digital speckle pattern interferometry (DSPI) has been applied to analyze surface corrosion processes in a metallic sample immersed in a 0.1 M Cu(NO ₃ ) ₂ solution. The corrosion process induces changes in the surface and in the solution refractive index. A detailed analysis of the DSPI measurements has been performed to obtain a two-dimensional visualization of the surface changes and an evaluation of the refractive index changes of the solution. The possibilities of DSPI for measuring surface changes in these conditions have been analyzed.

High dynamic range (HDR) imaging has been the focus of interest for scientific, technical, and artistic communities in recent years. Progress in capture and display technologies, combined with increasing availability of processing power in both professional and consumer devices, as well as the continuing drive for more photorealistic and higher quality image and video content, have attracted further attention to HDR imaging. One can argue that HDR imaging could lead to the next revolution in image and video representation, similar to past transitions from grayscale to color, standard definition to high definition, and 2-D to 3-D. This special section is composed of seven original contributions aimed at providing readers with some of the latest developments and emerging technologies in the HDR image- and video-processing chain, either at component level, underlying fundamentals, or end-to-end and system issues.

The high thermal sensitivity of modern infrared (IR) cameras allows us to distinguish objects with small temperature variations. In comparison with the dynamics of standard displays, the sensed IR images have a high dynamic range (HDR). In this context, suitable techniques to display HDR images are required in order to improve the visibility of the details without introducing distortions. In the recent literature of IR image processing, a common framework to perform HDR image visualization relies on DR reduction (DRR) with a cascaded processing for local contrast adjustment (CA). In this work, a novel method, named cluster-based DRR and contrast adjustment (CDCA) is introduced for the visualization of IR images. The CDCA method is composed of two cascaded steps: (1) DRR clustering-based approach and (2) a CA module specifically designed to account for IR image features. The effectiveness of the introduced technique is analyzed using IR images of surveillance scenarios collected in different operating conditions. The results are compared with those given by other IR-HDR visualization methods and show the benefits of the proposed CDCA in terms of details enhancement, robustness against the horizon effect and presence of hot objects.

Super resolution is a signal processing method that utilizes information from multiple degraded images of the same scene in order to reconstruct an image with enhanced spatial resolution. The method is typically employed on similarly exposed pixel valued images, but it can be extended to differently exposed images with a high combined dynamic range. We propose a novel formulation of the joint super-resolution, high dynamic range image reconstruction problem, using an image domain in which the residual function of the inverse problem relates to the perception of the human visual system. Simulated results are presented, including a comparison with a conventional method, demonstrating that the proposed approach avoids some severe reconstruction artifacts.

Because the real world scenes have a high dynamic range which exceeds the range of the imaging devices, the captured images sometimes contain under-exposed and saturated regions. In this paper, we propose a simple but effective method to achieve high dynamic range (HDR) rendering results from three multiexposure images comprising under-, normal-, and over-exposure. First, we generate the weight function, for the fusion of multiexposure images, according to the brightness. Then, we employ the bilateral filter-based retouching to enhance image details, especially in the dark regions. Experimental results demonstrate that the proposed method produces clear details in images and achieves natural HDR rendering results on mobile imaging devices.

The goal of this paper is to simulate the functionality of a digital camera system. The simulations cover the conversion from light to numerical signal, color processing, and rendering. A spectral image processing algorithm is used to simulate the radiometric properties of a digital camera. In the algorithm, we take into consideration the spectral image and the transmittances of the light source, lenses, filters, and the quantum efficiency of a complementary metal-oxide semiconductor (CMOS) image sensor. The optical part is characterized by a multiple convolution between the different point spread functions optical components such as the Cooke triplet, the aperture, the light fall off, and the optical part of the CMOS sensor. The electrical part consists of the Bayer sampling, interpolation, dynamic range, and analog to digital conversion. The reconstruction of the noisy blurred image is performed by blending different light exposed images in order to reduce the noise. Then, the image is filtered, deconvoluted, and sharpened to eliminate the noise and blur. Next, we have the color processing and rendering blocks interpolation, white balancing, color correction, conversion from XYZ color space to LAB color space, and, then, into the RGB color space, the color saturation and contrast.

High-dynamic range (HDR) imaging is expected, together with ultrahigh definition and high-frame rate video, to become a technology that may change photo, TV, and film industries. Many cameras and displays capable of capturing and rendering both HDR images and video are already available in the market. The popularity and full-public adoption of HDR content is, however, hindered by the lack of standards in evaluation of quality, file formats, and compression, as well as large legacy base of low-dynamic range (LDR) displays that are unable to render HDR. To facilitate the wide spread of HDR usage, the backward compatibility of HDR with commonly used legacy technologies for storage, rendering, and compression of video and images are necessary. Although many tone-mapping algorithms are developed for generating viewable LDR content from HDR, there is no consensus of which algorithm to use and under which conditions. We, via a series of subjective evaluations, demonstrate the dependency of the perceptual quality of the tone-mapped LDR images on the context: environmental factors, display parameters, and image content itself. Based on the results of subjective tests, it proposes to extend JPEG file format, the most popular image format, in a backward compatible manner to deal with HDR images also. An architecture to achieve such backward compatibility with JPEG is proposed. A simple implementation of lossy compression demonstrates the efficiency of the proposed architecture compared with the state-of-the-art HDR image compression.

Multiexposure image fusion algorithms are used for enhancing the perceptual quality of an image captured by sensors of limited dynamic range. This is achieved by rendering a single scene based on multiple images captured at different exposure times. Similarly, multifocus image fusion is used when the limited depth of focus on a selected focus setting of a camera results in parts of an image being out of focus. The solution adopted is to fuse together a number of multifocus images to create an image that is focused throughout. A single algorithm that can perform both multifocus and multiexposure image fusion is proposed. This algorithm is a new approach in which a set of unregistered multiexposure/focus images is first registered before being fused to compensate for the possible presence of camera shake. The registration of images is done via identifying matching key-points in constituent images using scale invariant feature transforms. The random sample consensus algorithm is used to identify inliers of SIFT key-points removing outliers that can cause errors in the registration process. Finally, the coherent point drift algorithm is used to register the images, preparing them to be fused in the subsequent fusion stage. For the fusion of images, a new approach based on an improved version of a wavelet-based contourlet transform is used. The experimental results and the detailed analysis presented prove that the proposed algorithm is capable of producing high-dynamic range (HDR) or multifocus images by registering and fusing a set of multiexposure or multifocus images taken in the presence of camera shake. Further, comparison of the performance of the proposed algorithm with a number of state-of-the art algorithms and commercial software packages is provided. In particular, our literature review has revealed that this is one of the first attempts where the compensation of camera shake, a very likely practical problem that can result in HDR image capture using handheld devices, has been addressed as a part of a multifocus and multiexposure image enhancement system.

We study the issue of quality assessment in tone mapping-based high-dynamic-range (HDR) image compression. In this, there are two stages at which a decision should be made regarding perceptual visual quality: (a) for finding the optimal parameters of the dynamic range reduction function so that the visual quality is maximized, and (b) visual quality judgment of the decompressed image. We first investigate two objective optimization criteria, namely mean squared error and structural similarity index measure, toward optimization of a tone mapping model-based HDR image compression method. We then conduct a comprehensive subjective study to evaluate the visual quality of the compressed HDR images. Therefore, we consider both objective and subjective aspects for HDR image compression. To our knowledge, no systematic and comprehensive studies exist in the current literature which shed light on the issue of quality assessment in HDR compression. So this study brings in new knowledge and perspective for the relatively less investigated topic of HDR compression from the view point of perceptual quality. We further evaluate the prediction performances of four objective methods on the 140 compressed HDR images that have been subjectively rated.

The fusion of imaging lidar information and digital imagery results in 2.5-dimensional surfaces covered with texture information, called texel images. These data sets, when taken from different viewpoints, can be combined to create three-dimensional (3-D) images of buildings, vehicles, or other objects. This paper presents a procedure for calibration, error correction, and fusing of flash lidar and digital camera information from a single sensor configuration to create accurate texel images. A brief description of a prototype sensor is given, along with a calibration technique used with the sensor, which is applicable to other flash lidar/digital image sensor systems. The method combines systematic error correction of the flash lidar data, correction for lens distortion of the digital camera and flash lidar images, and fusion of the lidar to the camera data in a single process. The result is a texel image acquired directly from the sensor. Examples of the resulting images, with improvements from the proposed algorithm, are presented. Results with the prototype sensor show very good match between 3-D points and the digital image (<2.8 image pixels), with a 3-D object measurement error of <0.5% , compared to a noncalibrated error of ∼3% .

Biometrics is a method of identifying individuals by their physiological or behavioral characteristics. Among other biometric identifiers, iris recognition has been widely used for various applications that require a high level of security. When a conventional iris recognition camera is used, the size and position of the iris region in a captured image vary according to the X , Y positions of a user’s eye and the Z distance between a user and the camera. Therefore, the searching area of the iris detection algorithm is increased, which can inevitably decrease both the detection speed and accuracy. To solve these problems, we propose a new method of iris localization that uses wide field of view (WFOV) and narrow field of view (NFOV) cameras. Our study is new as compared to previous studies in the following four ways. First, the device used in our research acquires three images, one each of the face and both irises, using one WFOV and two NFOV cameras simultaneously. The relation between the WFOV and NFOV cameras is determined by simple geometric transformation without complex calibration. Second, the Z distance (between a user’s eye and the iris camera) is estimated based on the iris size in the WFOV image and anthropometric data of the size of the human iris. Third, the accuracy of the geometric transformation between the WFOV and NFOV cameras is enhanced by using multiple matrices of the transformation according to the Z distance. Fourth, the searching region for iris localization in the NFOV image is significantly reduced based on the detected iris region in the WFOV image and the matrix of geometric transformation corresponding to the estimated Z distance. Experimental results showed that the performance of the proposed iris localization method is better than that of conventional methods in terms of accuracy and processing time.

A real-time means for three-dimensional (3-D) fingerprint acquisition is presented. The system is configured with only one camera and some white light-emitting diode lamps. The reconstruction is performed based on the principle of photometric stereo. In the algorithm, a two-layer Hanrahan–Krueger model is proposed to represent the finger surface reflectance property instead of the traditional Lambert model. By the proposed lighting direction calibration and the nonuniform lighting correction methods, surface normal at each image point can be accurately estimated by solving a nonlinear optimization problem. Finally, a linear normal transformation is implemented for the enhancement of 3-D models. The experiments are implemented with real finger and palm prints, and the results are also compared with traditional means to show its feasibility and improvement in the reconstruction accuracy.

A time-of-flight (ToF) depth camera can capture a depth map of the scene by measuring the phase delay between the emitted and reflected infrared (IR) light signals. In addition, an intensity map that represents the magnitude of the reflected light can be obtained by the ToF camera. If we consider the light source of the ToF camera as a flash, the intensity map can be deemed as an IR flashed image. Building on ideas from flash/no-flash photography and dark flash photography, we devise a color image enhancement framework that exploits information from the intensity and depth maps. To this end, ToF-related distortions of the intensity and depth maps are first reduced. We then restore fine details of color images captured under weak illumination by combining mutually beneficial information from the visible and IR band signals. In addition, we show that the depth map can be used to produce depth-adaptive effects such as depth-adaptive smoothing at the resultant color image.

Newton’s rings fringe pattern is often encountered in optical measurement. The digital processing of the fringe pattern is widely used to enable automatic analysis and improve the accuracy and flexibility. Before digital processing, sampling and quantization are necessary, which introduce quantization errors in the fringe pattern. Quantization errors are always analyzed and suppressed in the Fourier transform (FT) domain. But Newton’s rings fringe pattern is demonstrated to be a two-dimensional chirp signal, and the traditional methods based on the FT domain are not efficient when suppressing quantization errors in such signals with large bandwidth as chirp signals. This paper proposes a method for suppressing quantization errors in the fractional Fourier transform (FRFT) domain, for chirp signals occupies little bandwidth in the FRFT domain. This method has better effect on reduction of quantization errors in the fringe pattern than traditional methods. As an example, a standard Newton’s rings fringe pattern is analyzed in the FRFT domain and then 8.5 dB of improvement in signal-to-quantization-noise ratio and about 1.4 bits of increase in accuracy are obtained compared to the case of the FT domain. Consequently, the image quality of Newton’s rings fringe pattern is improved, which is beneficial to optical metrology.

To reduce transmission loss and improve spatial resolution, a diffractive-refractive lens with an aperture diameter of 120 mm has been designed, fabricated, and demonstrated for the submillimeter focal plane imaging system. We analyze the lens’ characteristics, such as focal length, depth of focus, beams spot size, spatial resolution, and field of view, theoretically and experimentally. It is the first time this is used as a focusing lens in the submillimeter wave imaging system. The results show that the lens’ characteristics are identical with theoretical analysis.

The viewing zone of a contact-type multiview three-dimensional imaging system are divided into nine viewing regions by assuming that at least n−2 pixel cells can be viewed at each of the regions, where n is the total number of pixel cells in horizontal direction of a display panel. Each of these regions consists of m ² subregions, where m is the number of pixels in the horizontal of a pixel cell. The image viewed at each of the subregions reveals a disparity of 1 pixel distance with that viewed at its adjacent subregion. Hence, each subregion is defined as a basic image cell that can provide the disparity of a pixel distance with its immediate neighbors. The width of the cell is independent of the focal length of the viewing zone forming optics but highly sensitive to the pixel size. It can be smaller than viewers’ pupil sizes by decreasing the pixel size.

An improved fringe-adjusted joint transform correlation (FJTC) technique is proposed, which employs a new real-valued filter, called the logarithmic fringe-adjusted filter. The Fourier-plane image subtraction technique is applied to the joint power spectrum before applying the inverse Fourier transform to generate better correlation output. The proposed technique yields better correlation output compared to alternate optical pattern recognition techniques when the target is embedded in noise-corrupted input scenes. Test results are presented to verify the performance of the proposed technique.

This paper proposes a new phase shifting method: wave-plate phase shifting method. By different combinations of a quarter-wave-plate, a half-wave-plate, and an analyzer, phase delays are introduced in the interference light path in order to achieve the phase shifting digital holography. Theoretical analysis, numerical simulation, and experiments are conducted to verify the validity of this method. The numerical simulation shows that the result of the wave-plate phase shifting method is consistent with that of the traditional four-step phase shifting method. The experimental results successfully reconstruct the object light intensity in the image plane. Based on the wave-plate phase shifting method, a pixelated wave-plate array structure is designed to achieve real-time phase shifting digital holography. The wave-plate array phase shifting method not only can reconstruct object image of high quality, but also can be used in dynamic phase measurement. Therefore, pixelated wave-plate array structure and wave-plate array phase shifting method could be widely used in practical applications.

Infrared sensors, such as indium antimonide (InSb) detectors, are generally required to be cooled to 77 K in operation. High fracture probability under thermal shock, especially in large InSb infrared focal plane arrays (IRFPAs), limits their applicability. It is necessary to establish a realistic three-dimensional (3-D) structural model of large-format InSb IRFPAs. However, few data are available on 3-D high-fidelity structural modeling and simulation of large IRFPAs due to their complicated structure and huge meshing numbers. A simple equivalent modeling method had been used in our early works, which could reduce meshing numbers, but did not consider the complicated structure, and also brought a new problem that the equivalent outer region of the model was not consistent with the actual IRFPAs. To solve the problems, an improved equivalent modeling method is proposed, where a small-format array is first split into two parts and then employed to equivalently replace the real large-format array. A 3-D high-fidelity structural model of large-format hybrid InSb IRFPAs is developed; here, a 32×32 array is adopted to replace the real 128×128 array. The results show that the simulated stress and strain distribution characteristics of InSb chip are well in agreement with the fracture photograph of actual 128×128 InSb IRFPAs in testing, verifying the validity and feasibility of the 3-D structural model of large-format IRFPAs. All these are beneficial to further explore fracture mechanisms and improve the reliability of large-format hybrid InSb IRFPAs.

Distributed video codec (DVC) has been developed to construct a simple encoder that utilizes information theory for distributed sources in the circumstance of mobile multimedia communication. In the DVC codec, an efficient algorithm to generate side information (SI) is one of the most important techniques to improve the coding performance. We propose a scheme to increase the quality of SI frame, where the proposed scheme consists of three steps. In the first step, SI frame is constructed by motion estimation and motion compensation in the DVC decoder. Then, in the second step, the blocks in the temporary SI frame are classified into reliable or unreliable ones. The unreliable blocks are updated by block boundary matching algorithm in the third step. Simulation results show that the proposed algorithm outperforms the conventional methods significantly. In addition, the proposed scheme can be combined with the conventional schemes generating SI frame to increase the coding performance of the DVC codec.

This paper addresses the problem of tracking and recognizing faces via incremental local sparse representation. First a robust face tracking algorithm is proposed via employing local sparse appearance and covariance pooling method. In the following face recognition stage, with the employment of a novel template update strategy, which combines incremental subspace learning, our recognition algorithm adapts the template to appearance changes and reduces the influence of occlusion and illumination variation. This leads to a robust video-based face tracking and recognition with desirable performance. In the experiments, we test the quality of face recognition in real-world noisy videos on YouTube database, which includes 47 celebrities. Our proposed method produces a high face recognition rate at 95% of all videos. The proposed face tracking and recognition algorithms are also tested on a set of noisy videos under heavy occlusion and illumination variation. The tracking results on challenging benchmark videos demonstrate that the proposed tracking algorithm performs favorably against several state-of-the-art methods. In the case of the challenging dataset in which faces undergo occlusion and illumination variation, and tracking and recognition experiments under significant pose variation on the University of California, San Diego (Honda/UCSD) database, our proposed method also consistently demonstrates a high recognition rate.

We propose an integral imaging in which the micro-lens array (MLA) in the pickup process called MLA 1 and the micro-lens array in the display process called MLA 2 have different specifications. The elemental image array called EIA 1 is captured through MLA 1 in the pickup process. We deduce a pixel mapping algorithm including virtual display and virtual pickup processes to generate the elemental image array called EIA 2 which is picked up by MLA 2. The three-dimensional images reconstructed by EIA 2 and MLA 2 do not suffer any image scaling and distortions. The experimental results demonstrate the correctness of our theoretical analysis.

A new method based on four photoelastic modulators (PEMs) and a charged couple device (CCD) camera, to rapidly image the samples’ entire Mueller matrix, is proposed and optimized. The full imaging of Mueller matrix elements using time-gated technique synchronized with the four PEMs’ modulation is demonstrated. Evolutionary algorithm is employed to choose the 16 time points, from which the Mueller matrix elements can be recovered with minimized sensitivity to noise. The suitability of several configurations of four PEMs with different frequencies and optical axes for the proposed imaging method is discussed through numerical examples. The ability to perform Mueller matrix imaging in the millisecond range with improved SNR in the absence of mechanically moving parts should prove advantageous in polarimetric characterization of biological tissues.

Two-dimensional cross-phase grating (CPG), diffracting the incident wave into (+1,+1 ), (+1,−1 ), (−1,−1 ), and (−1,+1 ) orders diffraction light, is used as a wavefront shearing element in cross-phase grating lateral shearing interferometer. However, the manufacture errors always exist, and they produce unwanted diffraction orders in the process of CPG manufacture. The appearance of the unwanted orders will increase the background noise of the interferogram and may affect the accuracy of the interferogram analysis. So, it is necessary to analyze the influences of manufacture errors and to determine the manufacture tolerances to remove the effect. A method based on Fourier transform analysis is presented to characterize manufacture tolerances of CPG. In this method, first, the normalized intensity distribution produced by CPG with manufacture errors in the far field is obtained. In addition, relative intensity of other unwanted orders to (+1,−1 ) order diffraction light of the four replicas is calculated, respectively. According to the relative intensity, the influences due to different types of manufacture errors can be evaluated, and the manufacture tolerances can also be determined. Using the proposed method, the manufacture tolerances of CPG at 632.8 nm are determined. Experimental evaluation of the proposed method using the manufactured CPG at 632.8 nm is also carried out.

Fourier transform white-light interferometry possesses high resolution and wide dynamic range for the absolute measurement of fiber optic interferometric sensors. However, the white-light optical spectrum distributed along wavelength is a chirp signal because the phase of the optical spectrum has a nonlinear relationship with the scanning wavelength. The chirped spectrum is considered as a constant period signal when it is Fourier transformed. The chirp in the period would bring errors into the phase shift and reduce the measurement resolution. A nonlinear wavelength sampling algorithm is proposed in this paper. The chirp characteristics of the white-light optical spectrum are considered, and the nonlinear wavelength sampling intervals vary with the wavelength. By using the nonlinear wavelength sampling algorithm, the errors in the phase shift can be reduced effectively, whereas the chirp characteristics of the signals can be retained entirely for filtering and extracting the chirped optical spectrum signals from the composite signal. The experimental results show that the standard deviation decreases from 0.016 to 0.005 μm by using the nonlinear wavelength sampling, when a fiber optic extrinsic Fabry-Perot interferometric sensor with a cavity length of 1512.2 μm is interrogated.

An optical system formed by four point-diffraction interferometers is used for measuring the temperature distribution of a candle flame. It is assumed that the phase can be expressed in terms of the Radon transform, and it is processed with a tomographic iterative algorithm to obtain the temperatures. The interferograms show the asymmetry of the candle flame, justifying the use of a tomographic iterative algorithm instead of the Abel inversion. The resulting temperature distribution verifies the usefulness of the proposed method.

In manufacturing, automotive, and aerospace industries, there is a need for accurately measuring the geometric parameters of surface defects to give an approximate prediction of the remaining life of the part. For this purpose, we describe a multipose measurement system with a combined laser-and-camera sensor to measure surface defects on rotary metal parts accurately. By using the combined sensor and multipose measuring method, the system can accurately measure the defects of the whole surface with time-saving and the dimensions of the defects can be obtained. We mainly focus on system calibration and defect extraction. First, to eliminate strong correlations among all the parameters, kinematic calibration and camera position calibration are accomplished by using a designed compound calibration artifact. Second, a new defect extraction method based on contourlet transform integrating with active contour model is proposed for precisely and rapidly locating defects. Experimental tests were conducted to verify the capability of the developed system in achieving accurate measurement of surface defects on rotary metal parts. The system can measure defects down to ∼6  μm in height/depth and ∼50  μm in lateral dimension.

An architecture based on the Faraday effect to minimize the crosstalk effect in optical current sensors (OCSs) is proposed. It was demonstrated that the magnetic field integral along a discrete loop can meet Ampere’s law under certain conditions, and the mathematical model of zero-sum points was given. Based on it, a zero-sum OCS (ZOCS) was proposed, which consists of several OCSs forming a symmetrical discrete loop. Ideally, the currents that flow outside the ZOCS do not contribute to the measurement of the currents inside it. The experimental results showed that the magnetic crosstalk-induced errors of ZOCS were less than 0.2%, and the influence of external current was reduced one order compared with conventional OCSs.

The performance of a structured light system (SLS) highly depends on its calibration especially in applications such as surface metrology and product quality control where high accuracy is required. Motivated by building a real-time highly accurate flatness measurement system, we propose a plane-based residual error compensation algorithm for improving the calibration accuracy of SLSs. Following the highly accurate procedure of geometric calibration using circular control points, the proposed algorithm enforces the planar constraint on the three-dimensional reconstruction of the circular control points, which are projected on a perfect plane, to further reduce the residual calibration error. Our method compensates for the largest proportion of the residual error, in most cases being the model error of the lens distortion in the system. Experimental results show that the compensation elevates the calibration accuracy to a higher level—the planarity error is reduced by 70% and this accuracy is comparable to a well-reputed industrial mechanical measuring machine.

Formation of ettringite and gypsum from sulfate attack together with carbonation and chloride ingress have been considered as the most serious deterioration mechanisms of concrete structures. Although electrical resistance sensors and fiber optic chemical sensors could be used to monitor the latter two mechanisms on site, currently there is no system for monitoring the deterioration mechanisms of sulfate attack. In this paper, a preliminary study was carried out to investigate the feasibility of monitoring sulfate attack with optical fiber excitation Raman spectroscopy through characterizing the ettringite and gypsum formed in deteriorated cementitious materials under an optical fiber excitation + objective collection configuration. Bench-mounted Raman spectroscopy analysis was also conducted to validate the spectrum obtained from the fiber-objective configuration. The results showed that the expected Raman bands of ettringite and gypsum in the sulfate-attacked cement paste can be clearly identified by the optical fiber excitation Raman spectrometer and are in good agreement with those identified from bench-mounted Raman spectrometer. Therefore, based on these preliminary results, it is considered that there is a good potential for developing an optical fiber-based Raman system to monitor the deterioration mechanisms of concrete subjected to sulfate attack in the future.

The AZ31B magnesium alloy 3.3-mm-thick sheets optimal welding condition was investigated. A three-dimensional, semistationary finite element thermal model was developed. It allowed the estimation of energy parameters like the absorbed power and the melting and welding efficiencies. The numerical model was calibrated comparing weld bead morphological parameters obtained from experiments and numerical model. The desirability function approach was used for the optimization of multiple responses both in terms of energy parameters and mechanical properties. The optimal condition was represented by the lower heat input given to the joint.

In order to calibrate the primary mirror of the Southern African large telescope, a high-accuracy numerical model of the existing mirror support truss and its actual, current behavior is required. In this investigation, structural optimization techniques are used to tune a numerical model so that it accurately matches the measured output of a structure under a given load or combination of loads. A methodology for obtaining an accurate numerical model of such a structure by first investigating the behavior of the different strut types before attempting to model the structure as a whole is presented. This method yielded vast improvements in the numerical accuracy of a smaller, simpler laboratory structure’s numerical model.

Hollow rooftop mirrors, also known as dihedral retroreflectors, can simultaneously preserve polarization, minimize chromatic dispersion, and allow beams to be stacked inside an interferometer. Two hollow rooftop mirrors were fabricated and characterized using a Fizeau interferometer and an inexpensive home-built jig instead of a master cube. The mass was 3.3 g for a clear aperture surface area of 110  mm ² with maximum retroreflected beam deviation of 12 arc s. With a hollow rooftop mirror mounted on a piezoelectric transducer in one arm of a Mach-Zehnder interferometer, a displacement stability of ±0.8  nm rms was achieved using active feedback. The rooftop mirrors’ suitability for Fourier transform spectroscopy was demonstrated.

We describe a simple bilayer photoresist that is particularly well suited for laser lithography at an exposure wavelength of 405 nm on glass substrates, which are often used for the fabrication of binary diffractive optics and computer-generated holograms. The resist consists of a poly-dimethyl glutarimide (PMGI) bottom layer that is used as an antireflection coating between a glass substrate and a positive or negative photoresist. The optical properties of the PMGI layer at 405 nm result in excellent suppression of reflections into the photoresist and good process latitude.

We propose and demonstrate a new wireless visible light communication (VLC) technology using optical beamforming to improve signal-to-noise ratio (SNR) and transmission distance. Optical beamforming is a technology that can focus light-emitting diode (LED) light on a desired target device. Our experimental results show that SNR can be improved by 12 dB and transmission distance can be almost doubled by using optical beamforming. We can also control the modulation depth of the optical beamforming if we want to use the LED light as illumination at the same time. We also propose an algorithm to direct the beam to the target device automatically.

The generation of femtosecond optical vortex beam based on direct wave-front modulation with phase-only liquid crystal spatial light modulator is demonstrated. The spatial and temporal properties of the generated femtosecond vortices are investigated in detail. The experimental results show remarkable agreement with the results of the theoretical analysis and simulations, and indicate that the method we utilized can efficiently generate femtosecond optical vortex beam of arbitrary topological charge. The temporal and spectral properties of the femtosecond pulsed beam are hardly affected by the phase dislocation imposed on the wave-front.

Cascaded optical parametric oscillations generating a tunable terahertz (THz) wave are analyzed to solve the problem of low quantum conversion efficiency in a THz-wave parametric oscillator. The forward and backward optical parametric processes are theoretically analyzed based on periodically poled lithium niobate (PPLN) as an example. Tuning characteristics of the THz wave that relate to the parameters of the pump wavelength, the grating period of PPLN, and the working temperature are numerically simulated. The gain and absorption characteristics of the generating THz wave are deduced in the situation of quasiphase-matching configuration at different working temperatures.

Low-loss hollow waveguides with a multiple dielectric layer are designed and fabricated for use in cavity ring-down spectroscopy (CRDS). Calculations of the waveguide design revealed that hollow waveguides for infrared CRDS system need to have transmission loss of 0.1  dB/m or less. We fabricated rectangular hollow waveguides with multiple dielectric layers to obtain low-loss properties. The waveguides are composed of four glass strips each with a dielectric multilayer deposited on the surface in advance. Experimental results show that the waveguides with double dielectric layers have lower losses at a target wavelength in the infrared than those with a single dielectric layer. The measured transmission loss of a 10-cm long waveguide deposited with a multilayer of Si/Al₂O₃ /Ag for the transverse magnetic wave and Al₂O₃ /Ag for the transverse electric wave was 0.24 dB at a target wavelength of 5.2 μm. The loss of the waveguide will be reduced when only the lowest-order mode is excited in the waveguide.

We demonstrate a saturable absorber (SA) based on cladding-filled graphene in a specially designed and manufactured photonic crystal fiber (PCF) for the first time. The saturation absorption property is achieved through the evanescent coupling between the guided light and the cladding-filled graphene layers. To boost the mutual interaction, the PCF is designed to contain five large air holes in the cladding and small-core region. Employing this graphene-PCF SA device, we construct an erbium-doped all-fiber laser oscillator and achieve mode-locked operation. This device can pave the way for high power and all-fiber applications of photonics with graphene with some unique advantages, such as single-mode operation, nonlinearity enhancement, high-power tolerance, environmental robustness, all-fiber configuration, and easy fabrication.

We report on the use of semiconductor optical amplifier (SOA) gain compression for achieving intensity noise reduction in light from an incoherent broadband source, running at high data rate of 10  Gb/s in a narrow spectrum-sliced high-intensity channel of 20 GHz (∼0.16  nm ) bandwidth, in order to improve quality of performance in future spectrum-sliced systems. Data have been collected on the performance of a single SOA as noise reducer at various input powers and biases. Improvements of ∼20  dB in the relative intensity noise, together with commensurate improvements in both signal-to-noise ratio and quality factor, have been achieved at a nominal 0 dBm of power inserted into the SOA at 0.15 A bias. The overall results obtained herein give designers a knowledge of the best SOA operating conditions required, particularly in terms of bias and input power, in order to achieve a desired intensity noise reduction, and thus an overall system performance improvement, while still obtaining some signal gain from the SOA as well.

We demonstrated a passively Q-switched Nd:YAG laser operating at 1.319 μm using a transmission-type single-wall carbon nanotube (SWCNT) as the saturable absorber. This is the first report on using SWCNT as a Q-switcher for 1.319 μm Nd:YAG laser in a side-pumped configuration. A maximum output power of 780 mW was obtained with 1.15-μs pulse duration and 42.7-kHz repetition rate.

A new beam-shaping technique is proposed to improve the beam quality of a high-power diode laser area light source. It consists of two staggered prism arrays and a reflector array, which can cut the slow axis beam twice and rearrange the divided beams in fast axis to make the beam quality of both axes approximately equal. Furthermore, the beam transformation and compression can be carried out simultaneously, and the assembly error of this technique induced by the machining accuracy of prism’s dimensions also can be greatly decreased. By this technique, a fiber-coupled system for one three-bar laser diode stack is designed and characterized. The experimental results demonstrate that the laser beams could be transformed into the required distribution with ∼93.4% reshaped efficiency and coupled into a 400  μm/0.22  NA fiber, which are consistent with the theory.

The 2,7-bis(4-pyridyl)fluorene (BPF) was synthesized via a Suzuki coupling reaction. The optical spectra properties of BPF and BPF-deoxyribonucleic acid (DNA)-cetyltrimethyl ammonium (CTMA) thin films composed of BPF, DNA, and CTMA were characterized by the measurements of UV/Vis absorption spectra and fluorescence spectra. The amplified spontaneous emission (ASE) of the BPF-DNA-CTMA films was researched experimentally by pumping of a pulse laser with a wavelength of 355 nm. The results show that the absorption peak and the fluorescence peak of BPF are located at 327 and 380 nm, respectively. The emission peak of BPF corresponds to the vibronic transitions from an excited state of S ₁ level to the ground state of S ₀ level. The ASE peak of the BPF-DNA-CTMA film is located at 384 nm, and the threshold of ASE excited energy density is 3.12  mJ⋅cm ⁻² .

All-optical wavelength conversion using cross-phase modulation in a high nonlinear fiber is demonstrated. The output extinction ratio and bit error rate dependence of the probe wavelength, probe power, input signal power, and fiber length are investigated. A 10-Gbit/s measurement has been performed and a 1.2-dB power penalty at 10 ⁻⁹bit error rate level is obtained.

An interrogation system for the time-division multiplexed sensor array based on 1310-nm band ultra-weak fiber Bragg gratings (FBGs) was proposed in this study. Power spectral density was introduced to budget the optical power and evaluate the interrogation capability of the proposed system. The proposed system consists of one tunable laser and two semiconductor optical amplifiers, where the former scans the wavelength, and the latter modulates the light and separates the reflected pulses from different FBGs through delayed switching. Up to 1000 serial FBGs, with a peak reflectivity of −40 to −45  dB and a spatial resolution of 5 m along an optical fiber, were interrogated to demonstrate the feasibility of the interrogation system.

High-index contrast slab and slot optical waveguides have a high index variation both along the lateral and vertical interfaces and are usually analyzed numerically, requiring large computer memory and time. In this article, their analysis is done semianalytically using an effective-index based matrix method. This method, which is computationally very fast, was earlier used successfully for low-index profile waveguide structures only and is now suitably modified for use in high-index contrast structures. The electric field profile of the waveguide structures is plotted and the effective refractive index at different wavelengths is calculated. The results are compared with results obtained from numerical techniques like finite element method, finite-difference time-domain, and beam propagation method and they match very well. The dependence of their different optical characteristics with the waveguide parameters is also studied. These studies will help in obtaining improved sensitivity of slot waveguides for sensing applications.

An innovative method based on dynamic particle swarm optimization (DPSO) algorithm is presented to demodulate the strain profile along a fiber Bragg grating (FBG) from its reflection spectrum, which is calculated by using the modified transfer matrix method. To improve the optimization performances of algorithm itself, the inertia weight of the DPSO algorithm is adjusted dynamically according to the distance between the individual particle and the global optimal particle in the current population. Then the numerical simulation and experimental verification of the reconstruction of nonuniform strain profiles are comprehensively carried out. Both the simulation examples and experimental results verify the feasibility and validity of the present method.

A simple fiber optic vibration sensor is designed and demonstrated using fiber optic fused 2×2 coupler that utilized the principle of reflected light intensity modulation. In order to avoid source signal power fluctuations and fiber bending losses, the rational output (RO) technique is adopted. A calibrated 1-mm linear and high sensitivity of 0.36  a.u./mm (2.1  mV/μm ) region of the displacement characteristic curve is considered for vibration measurement. The experimental results show that the sensor is capable of measuring the frequency up to 3500 Hz with ∼0.03−μm resolution of vibration amplitude over a dynamic range of 0 to 1 mm. The signal-to-noise ratio of the RO is also improved with respect to the sensing signal. In comparison with dual-fiber and bifurcated-bundle fiber, the designed sensor consists only of a single slope that makes the sensor alignment simple by eliminating the dark region and front slope. Simplicity in design, noncontact measurement, high degree of sensitivity, and economical, along with advantages of fiber optic sensors, are the attractive attributes of the designed sensor that lend support to real-time monitoring and embedded applications.

We propose and demonstrate a fast-response liquid crystal (LC) variable optical retarder or attenuator with several transmission levels. The fast-response LC optical device consists of dual π -cells. The device is designed so that the transition between any two states is controlled by the application of an increased voltage level rather than by applying a lower level. This design offers transition times in the range of tens of microseconds between any transmission states. A limitation of the device is that the time between transitions cannot be arbitrarily short and is typically milliseconds.

This article [Opt. Eng.. 52, (6 ), 061304 (2013)] was originally published online on 7 January 2013 with an error in the numerator of Eq. (13) that propagated into Eqs. (14), (15), and (17). The corrected Eq. (13) and subsequent equations are given here: