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We present a stable and switchable dual-wavelength erbium-doped fiber laser. In the ring cavity, an inverse-Gaussian apodized fiber Bragg grating serves as an ultranarrow dual-wavelength passband filter, a semiconductor optical amplifier biased in the low-gain regime reduces the gain competition of the two wavelengths, and a feedback fiber loop acts as a mode filter to guarantee a stable single-longitudinalmode operation. Two lasing lines with a wavelength separation of approximately 0.1 nm are obtained experimentally. A microwave signal at 12.51 GHz is demonstrated by beating the dual wavelengths at a photodetector. [c] 2010 Optical Society of America OCIS codes: 060.2330, 060.3510, 060.3735.

This paper deals with a computer simulation and an experimental realization of an optical setup for automatic quality control of microlens arrays. The method is based on a 4f coherent light correlator setup with an amplitude filter placed in the Fourier plane. The output intensity signal is proportional to the first derivative of the distortion of the input wavefront. An analysis can be carried out with the use of the Zernike polynomial expansion method. It must be carried out separately for each lens, but it allows for a more precise, quantitative assessment of their quality. What is important is that the analysis is computer-based and performed on the basis of the initial single optical measurement. OCIS codes: 070.4550, 070.6110, 120.5050, 120.6650.

Wafer identifications (wafer ID) can be used to identify wafers from each other so that wafer processing can be traced easily. Wafer ID recognition is one of the problems of optical character recognition. The process to recognize wafer IDs is similar to that used in recognizing car license-plate characters. However, due to some unique characteristics, such as the irregular space between two characters and the unsuccessive strokes of wafer ID, it will not get a good result to recognize wafer ID by directly utilizing the approaches used in car license-plate character recognition. Wafer ID scratches are engraved by a laser scribe almost along the following four fixed directions: horizontal, vertical, plus 45[degrees], and minus 45[degrees] orientations. The closer to the center line of a wafer ID scratch, the higher the gray level will be. These and other characteristics increase the difficulty to recognize the wafer ID. In this paper a wafer ID recognition scheme based on an asterisk-shape filter and a high--low score comparison method is proposed to cope with the serious influence of uneven luminance and make recognition more efficiently. Our proposed approach consists of some processing stages. Especially in the final recognition stage, a template-matching method combined with stroke analysis is used as a recognizing scheme. This is because wafer IDs are composed of Semiconductor Equipment and Materials International (SEMI) standard Arabic numbers and English alphabets, and thus the template ID images are easy to obtain. Furthermore, compared with the approach that requires prior training, such as a support vector machine, which often needs a large amount of training image samples, no prior training is required for our approach. The testing results show that our proposed scheme can efficiently and correctly segment out and recognize the wafer ID with high performance. OCIS codes: 100.0100, 100.3008, 100.5010.

Accurate automated alignment of laser beams in the National Ignition Facility (NIF) is essential for achieving extreme temperature and pressure required for inertial confinement fusion. The alignment achieved by the integrated control systems relies on algorithms processing video images to determine the position of the laser beam images in real time. Alignment images that exhibit wide variations in beam quality require a matched-filter algorithm for position detection. One challenge in designing a matched-filter-based algorithm is to construct a filter template that is resilient to variations in imaging conditions while guaranteeing accurate position determination. A second challenge is to process images for thousands of templates in under a second, as may be required in future high-energy laser systems. This paper describes the development of a new analytical template that captures key recurring features present in the beam image to accurately estimate the beam position under good image quality conditions. Depending on the features present in a particular beam, the analytical template allows us to create a highly tailored template containing only those selected features. The second objective is achieved by exploiting the parallelism inherent in the algorithm to accelerate processing using parallel hardware that provides significant performance improvement over conventional processors. In particular, a Xilinx Virtex II Pro field programmable gate array (FPGA) hardware implementation processing 32 templates provided a speed increase of about 253 times over an optimized software implementation running on a 2.2 GHz AMD Opteron core. OCIS codes: 070.5010, 100.3008, 100.4999, 150.5758, 220.1140, 140.3538.

We present a technique to measure velocity, acceleration, and higher order derivatives of motion using periodic and nonperiodic spatial filters. The technique can be applied using a single detector or an array of detectors. In one configuration, the velocity distribution of an object such as a fluid can be measured by imaging the object onto an array of detectors. In another configuration, multiple projections of an object are used to reconstruct a cross-sectional velocity distribution using a tomography algorithm. The advantages and disadvantages of our technique applied to uniform and spatially varying motions are described. OCIS codes: 120.7250, 170.3340, 280.7250, 280.0280.

The authors have proposed and experimentally demonstrated all-optical logic gates using a single SOA and delay interference filtering that enable simultaneous logic functions of OR and NOR at 40 Gbits/s. The proposed scheme, which utilizes the combinative filtering profile of a delay interferometer and an optical bandpass filter, has great merits for use in generating logic outputs with high quality in terms of pulse shape, extinction ratio, and eye diagram. Reconfiguration between the two gates is achieved by adjusting the tunable filter and the delay interferometer. OCIS codes: 060.2330, 200.4660.

We develop a unified algorithm for performing blind deconvolution of a noisy degraded image. By incorporating a low-pass filter into the asymmetric multiplieative iterative algorithm and extending it to multiframe blind deconvolution, this algorithm accomplishes the blind deconvolution and noise removal concurrently. We report numerical experiments of applying the algorithm to the restoration of short-exposure atmosphere turbulence degraded images. These experiments evidently demonstrate that the unified algorithm has both good blind deconvolution performance and high-resolution image restoration. OCIS codes: 100.3020, 100.1455, 100.1830, 100.2000.

Multivariate calibration models are constructed through the use of Gaussian basis functions to extract relevant information from single-beam spectral data. These basis functions are related by analogy to optical filters and offer a pathway to the direct implementation of the calibration model in the spectrometer hardware. The basis functions are determined by use of a numerical optimization procedure employing genetic algorithms. This calibration methodology is demonstrated through the development of quantitative models in near-infrared spectroscopy. Calibrations are developed for the determination of physiological levels of glucose in two synthetic biological matrixes, and the resulting models are tested by application to external prediction data collected as much as 4 months outside the time frame of the calibration data used to compute the models. The calibrations developed with the Gaussian basis functions are compared to conventional calibration models computed with partial least-squares (PLS) regression. For both data sets, the models based on the Gaussian functions are observed to outperform the PLS models, particularly with respect to calibration stability over time.

We discuss the theoretical and experimental investigation of acousto-optic dispersive tunable filters, based on quasi-collinear geometry of light-sound interaction in a tellurium dioxide single crystal. The geometry uses the effect of strong acoustic anisotropy in the paratellurite as well as peculiarities of acoustic wave reflections at the free boundary of the crystal. A mathematical concept for determination of optical, electrical, and constructional parameters of the filters is developed. Different experimental acousto-optic filters intended for femtosecond pulse shaping are designed and tested. Preliminary experiments are performed in a subpetawatt optical parametric chirped pulse amplification laser system. The experimental data conform completely with the predicted data. OCIS codes: 230.1040, 140.7090, 190.4970.

We demonstrate a simple and straightforward method of producing Bessel beams using a 4-f spatial filtering system that requires no specialized optical components. The experiment employs the established technique of diffraction from a thin ring source, but the ring source is produced by the high-pass filtering of a uniformly illuminated circular aperture, yielding Bessel beams with a central spot radius of less than 35 [micro]m which persist over a distance of 160 mm. The experiment unifies diffraction theory, Fourier optics, and the properties of Bessel beams in a manner appropriate for an advanced undergraduate laboratory.

We present results of the design and testing of a modified optical Solc notch filter for use in the deep ultraviolet (DUV, 190-300nm) spectral range. The filter was designed to block a specific wavelength in this region. In addition, a sequence of blocked wavelengths occurs at wavelengths both shorter and longer than the specified wavelength. For Raman applications utilizing tunable lasers, the provision of multiple blocked wavelengths by a single filter may be especially useful. The filter design presented here produces extinction ratios >240 with transmission minima ~1 nm full width at half-maximum. Specific results are shown for the Raman spectra of Teflon excited at 248.4nm. OCIS codes: 230.0230, 230.7408, 230.5440, 230.1150, 300.6450, 300.6540.

We propose three amplitude filters for visualization of phase objects. They interact with the spectra of pure-phase objects in the frequency plane and are based on tangent and error functions as well as antisymmetric combination of square roots. The error function is a normalized form of the Gaussian function. The antisymmetric square-root filter is composed of two square-root filters to widen its spatial frequency spectral range. Their advantage over other known amplitude frequency-domain filters, such as linear or square-root graded ones, is that they allow high-contrast visualization of objects with large variations of phase gradients. OCIS codes: 070.0070, 070.1170, 070.6110, 120.0120, 120.5050.

We propose a novel approach to designing an optical filter with a flat-top and ultranarrow transmission band by using a sampled fiber Bragg grating (SFBG) having multiple equivalent phase shifts (EPSs). In the proposed approach, multiple EPSs are fabricated by adjusting several sampling periods of the SFBG. The obtained multiple EPSs are then arranged properly to get a flat-top transmission band in the narrow--1st reflection band of the SFBG, leading to the generation of a flat and ultranarrow transmission band. Filters with two or five EPSs are designed by simulation and experiment, with low ripples and ultranarrow l dB bandwidths observed in transmission bands. OCIS codes: 050.2770, 120.2440, 060.2340, 050.5080.

We propose three types of narrowband optical filters based on a Fox-Smith resonator. We demonstrate that by choosing the appropriate combination of coating materials on each prism facet, one can design either a high reflectance or a high transmittance optical filter, suitable for low bit rate optical communication applications with International Telecommunication Union-Telecommunication Standardization Sector (ITU-T) standards. We also show the possibility of designing an optical filter having a desirable finite reflectance/transmittance ratio with simultaneous peaks at ITU-T standard wavelengths. Such filters could be suitable for wavelength tuning applications. OCIS codes: 060.4510, 130.7408, 230.1480, 230.5480, 230.7408, 310.1210.

The problem of imaging through turbulent media has been studied frequently in connection with astronomical imaging and airborne radars. Therefore most image restoration methods encountered in the literature assume a stationary object, e.g., a star or a piece of land. In this paper the problem of interferometric measurements of slowly moving or deforming objects in the presence of air disturbances and vibrations is discussed. Measurement noise is reduced by postprocessing the data with a digital noise suppression filter that uses a reference noise signal measured on a small stationary plate inserted in the field of view. The method has proven successful in reducing noise in the vicinity of the reference point where the size of the usable area depends on the degree of spatial correlation in the noise, which in turn depends on the spatial scales present in the air turbulence. Vibrations among the optical components in the setup tend to produce noise that is highly correlated across the field of view and is thus efficiently reduced by the filter. OCIS codes: 090.2880, 010.7060, 110.0115.

The article presents a comparative study of the power density and efficiency of thermophotovoltaic energy conversion that is achieved by using a photo-crystal emitter and a 2-D metal-grid filter. Photonic crystals are shown to be extremely advantageous, as they exhibit high emission and an extremely narrow emission linewidth.

Solar occultation in the infrared, part of the Spectoscopy for Investigation of Characteristics of the Atmosphere of Venus (SPICAV) instrument onboard Venus Express, combines an echelle grating spectrometer with an acousto-optic tunable filter (AOTF). It performs solar occultation measurements in the IR region at high spectral resolution. The wavelength range probed allows a detailed chemical inventory of Venus's atmosphere above the cloud layer, highlighting the vertical distribution of gases. A general description of the instrument and its in-flight performance is given. Different calibrations and data corrections are investigated, in particular the dark current and thermal background, the nonlinearity and pixel-to-pixel variability of the detector, the sensitivity of the instrument, the AOTF properties, and the spectral calibration and resolution. OCIS codes: 050.1950, 120.0280, 120.6200, 230.1040, 300.6340, 010.1280.

Metal-dielectric multiple-band high-reflection coatings are designed as induced filters and fabricated by reactive deposition. [Ta.sub.2][O.sub.5] and Si[O.sub.2] are used as high- and low-refractive-index layers, and Cr and Al are used as bonding and reflective layers, respectively, for constructing the filters. The metal-dielectric coatings are deposited on a light-shaping flexible plastic substrate for use as a screen with high-contrast enhancement performance. This screen was suitable for miniprojectors with red, green, and blue LEDs as light sources. Mechanical properties such as stress, hardness, and adhesive strength of these multilayer films are investigated also. OCIS codes: 310.1620, 310.1860.

The cooled infrared filters and dichroic beam splitters manufactured for the Mid-Infrared Instrument are key optical components for the selection and isolation of wavelengths in the study of astrophysical properties of stars, galaxies, and other planetary objects. We describe the spectral design and manufacture of the precision cooled filter coatings for the spectrometer (7 K) and imager (9 K). Details of the design methods used to achieve the spectral requirements, selection of thin film materials, deposition technique, and testing are presented together with the optical layout of the instrument. OCIS codes: 120.2440, 350.1270, 350.2460, 310.3840, 310.1860, 310.6860.

The optical path difference (OPD) and amplitude of a sinusoidal wavelength scanning (SWS) are controlled with a double feedback control system in an interferometer, so that a ruler marking every wavelength and a ruler with scales smaller than a wavelength are generated. These two rulers enable us to measure an OPD longer than a wavelength. A liquid-crystal Fabry-Perot interferometer (LC-FPI) is adopted as a wavelength-scanning device, and double sinusoidal phase modulation is incorporated in the SWS interferometer. Because of a high resolution of the LC-FPI, the upper limit of the measurement range can be extended to 280 [micro]m by the use of the phase lock where the amplitude of the SWS is doubled in the feedback control. The ruler marking every wavelength is generated between 80 [micro]m and 280 [micro]m, and distances are measured with a high accuracy of the order of a nanometer in real time. OCIS codes: 120.3180, 120.3930, 120.5050, 120.5060, 230.3720.

A procedure for deconvolution of multiple images of the same object with space-variant point-spread functions (PSFs) is presented. It is based on expressing deconvolution with inverse filtering as convolution with kernels corresponding to inverse PSFs. Sets of basis functions are made from these inverse PSFs, given at discrete sample points, through Karhunen--Loeve (K-L) decomposition. The entire field of view can then be convolved with the K-L kernels. Coadding the results using continuous maps of expansion weights, interpolated for every pixel between the sample points, results in an image that is deconvolved with smoothly varying PSFs that match the discrete measurements. A demonstration data set is used to show how the transition between the grid points improves deconvolutions compared to piecewise deconvolution and mosaicking by avoiding the blending of discontinuities at the interfaces between adjacent subfields.

In this paper, a sequential color light emitting diode (LED) backlight driving system for liquid crystal display (LCD) panels is proposed. Due to improvement on luminous efficacy, long life and wide color gamut, LED has gradually substituted for cold cathode fluorescent lamp as backlight. The proposed driving system adopts sequential color scanning scheme to improve light utilization efficiency by removing color filter. To meet display performance requirement that chromaticity variation [DELTA]uv needs to be limited below 0.002, this paper also proposes a family of output current ripple free topologies to control the average driving current precisely, which in turn can reduce chromaticity variation. In addition, an LED bypass circuit is proposed to prevent LED arrays from open-circuit, and a driving voltage resetter is introduced to eliminate current spikes, improving backlight reliability and availability significantly. A forward-type output current ripple free converter has been built to sequentially drive color LED arrays, from which experimental measurements have verified the discussed performance and feasibility of the proposed system. Index Terms--Light emitting diode (LED), liquid crystal display (LCD), ripple free, sequential color display.

This study reports the validity of the modified Shanks' conjecture on the planar least squares inverse (PLSI) method of stabilizing two-dimensional (2-D) recursive digital filters. A theoretical procedure proposed based on the Lagrange multiplier method of mathematical optimization. The results indicate that the modified Shanks' conjecture reported by Jury was valid for special classes of 2-D polynomials. Key words: PLSI, autocorrelation, filter stability, Lagrange multiplier, INTRODUCTION Two-dimensional (2-D) recursive digital filters find many applications, such as biomedical electronics, image processing, seismic record processing, etc. For a given response characteristic, recursive filters have less hardware requirements [...]

A four-dimensional (4-D) dual-fan filter bank (4-D-DFFB) is proposed and designed to extract objects over a range of depths in a light field model of a scene by cascading two appropriately designed fan filter banks. The results have shown how a light field might be selectively filtered for a range of depths by forming a 4-D frequency passband that has surrounded the intersection of two 4-D fans.

We propose to use a differential operator for representing the influence of phase-only filters on the defocused modulation transfer function of the clear pupil aperture. We present a phase-only filter that implements optically Taylor's theorem in phase space. We show numerical simulations of the modulation transfer functions and the images that can be obtained by using the proposed filter. OCIS codes: 110.4100, 110.4850, 070.6110, 050.1950, 100.5090, 110.6880.

Gradient index coatings and optical filters are a challenge for fabrication. In a round-robin experiment, basically the same hybrid antireflection coating for the visible spectral region, combining homogeneous refractive index layers of pure materials and linear gradient refractive index layers of material mixtures, has been deposited. The experiment involved three different deposition techniques: electron-beam evaporation, ion-beam sputtering, and radio frequency magnetron sputtering. The material combinations used by these techniques were [Nb.sub.2][O.sub.5]Si[O.sub.2], Ti[O.sub.2]/Si[O.sub.2], and [Ta.sub.2][O.sub.5]Si[O.sub.2], respectively. The spectral performances of samples coated on one side and on both sides have been compared to the corresponding theoretical spectra of the designed profile. Also, the reproducibility of results for each process is verified. Finally, it is shown that ion-beam sputtering gave the best results in terms of deviation from the theoretical performance and reproducibility. OCIS codes: 310.1210, 310.1620, 310.1860.

Variable narrowband transmission filters are useful for the development of compact spectrometers. For this purpose the filter should be directly coupled to the detector and the wavelength of the transmission peak should move in one surface direction over a length of a few millimeters. To obtain both a wide measurement spectrum and high accuracy, the ratio of extreme operating wavelengths is required to be greater than 2:1 and the width of the transmission band narrower than 10 nm. A metal-dielectric variable transmission filter, with an operating range of 400-1000 nm, is proposed. The method for obtaining variable transmission filters, with dimensions of a few millimeters, is described. OCIS codes: 310.1620, 230.4170, 240.0310, 120.2440, 120.6200.

We report the development of a technique for adaptive selection of polarization ellipse tilt and ellipticity angles such that the target separation from clutter is maximized. From the radar scattering matrix [S] and its complex components, in phase and quadrature phase, the elements of the Mueller matrix are obtained. Then, by means of polarization synthesis, the radar cross section of the radar scatters are obtained at different transmitting and receiving polarization states. By designing a maximum average correlation height filter, we derive a target versus clutter distance measure as a function of four transmit and receive polarization state angles. The results of applying this method on real synthetic aperture radar imagery indicate a set of four transmit and receive angles that lead to maximum target versus clutter discrimination. These optimum angles are different for different targets. Hence, by adaptive control of the state of polarization of polarimetric radar, one can noticeably improve the discrimination of targets from clutter. OCIS codes: 100.2000, 280.5600, 290.3200, 110.0110.

A wide variety of bioluminescent luciferase proteins are available for use in transcriptional or biochemical reporter assays. However, spectral overlap normally prevents them from being monitored simultaneously. To address this problem, a Java plug-in for ImageJ was written to de-convolute bioluminescent images composed of signals from multiple luciferases. The methodology was validated by testing the program with both simulated and real luciferase images. Bioluminescent images were acquired using a CCD camera equipped with optical filters, and the images were deconvoluted using the ImageJ plug-in. HeLa cells were transfected with either click beetle red luciferase (CBR), click beetle green luciferase (CBG99), or Renilla luciferase (Rluc), and mixed lysates were imaged in varying proportions in a 96-well plate to biochemically validate the methodology. After spectral deconvolution, the predicted, pure luciferase signals could be recovered with maximal cross-talk errors of [+ or -] 1.5%. In addition, live cells expressing CBR, CBG99, and Rluc were simultaneously imaged and deconvoluted in 96-well plates to demonstrate the feasibility of applying this methodology to high-throughput applications. Finally, multicolor transcriptional and posttranslational modification reporters were simultaneously imaged and shown to deconvolute normalized I[kappa]B kinase activity in longitudinal assays. Thus, our software provided a rapid, simple, and accurate method for simultaneously measuring multiple bioluminescent reporters in living cells.

Photonic signal processing offers the prospect of realizing extremely high multigigahertz sampling frequencies, overcoming inherent electronic limitations. This stems from the intrinsic excellent delay properties of optical delay lines. These processors provide new capabilities for realizing high time-bandwidth operation and high-resolution performance. In-fiber signal processors are inherently compatible with fiber-optic microwave systems and can provide connectivity with built-in signal conditioning. Fundamental principles of photonic signal processing, including sampling, tuning, and noise, are discussed. Structures that can extend the performance of photonic signal processors are presented, including methods for improving the filter shape characteristics of interference mitigation filters, techniques to increase the stop-band attenuation of bandpass filters, and methods to achieve large free spectral range. Several photonic signal processors, including high-resolution microwave filters, widely tunable filters, arbitrary waveform generators, and fast signal correlators, are discussed. Techniques to solve the fundamental noise problem in photonic signal processors are described, and coherence-free structures for few-tap notch filters are discussed. Finally, a new concept for realizing multiple-tap coherence-free processor filters, based on a new frequency-shifting technique, is presented. The structure not only eliminates the phase-induced intensity noise limitation, but can also generate a large number of taps to enable the achievement of processors with high performance and high resolution. Index Terms--Microwave photonics, optical delay lines, optical filters, photonic signal processing.

A noniterative method of retrieving the two-dimensional phase of a wave field from two intensity measurements is proposed. In the measurements, one records two far-field intensities of the wave field modulated and unmodulated with an exponential filter. The phase retrieval method is based on the solution of the simultaneous equations with unknown coefficients of the two-dimensional discrete Fourier transform for the phase. Then there is no need for the information about the wave field, which is used in iterative phase-retrieval methods. The usefulness of this method is shown in computer-simulated examples of the reconstruction of two-dimensional complex amplitude objects. OCIS codes: 100.0100, 100.5070.

The accuracy and flexibility of the technique proposed by Davis et al. [Appl. Opt. 35, 2488 (1996)] for the encoding of the amplitude and the phase of a filter onto a single liquid-crystal spatial light modulator operating in a phase-only regime has been exploited to implement several filter designs in a convergent optical correlator. We have selected some filters, that given their mathematical structure showing some degree of rotational invariance, or having a parameter to regulate their behavior, require a more precise encoding. We present correlation results of outstanding quality for various rotationally invariant filter designs that have never been previously implemented with a real-time optical correlator. OCIS codes: 100.5760, 100.5010, 100.4550, 230.6120.