This PDF file contains the editorial “The Optics Evangelist” for OE Vol. 40 Issue 05

We propose and demonstrate, for the first time, an externally modulated NTSC AM-VSB erbium-doped fiber amplifier repeated system in the 1550-nm region, which uses a chirped fiber grating as well as a large effective area fiber as the dispersion compensation devices. In comparison with the conventional externally modulated fiber optical CATV system, excellent performances of carrier-to-noise ratio ?50 dB, composite second order ?78 dB, and composite triple beat ?68 dB were obtained for the full channel band after a 100-km fiber span transmission.

Optical fibers are being used more and more as chemical sensors or biosensors. Some of these devices are based on thin film plasmon excitation in which a metal coating is evaporated onto the core or end of an etched optical fiber. A new sensor configuration is presented for detecting liquid adsorbates with different indices of refraction. Instead of exciting surface plasmon waves on a thin film, localized surface plasma waves are excited on metal islands. The fiber is coated with three very thin layers of gold. Each layer is annealed before the next layer is evaporated onto it. This is done to avoid any light leakage, a problem discovered in a prior version with only one gold coating. Different sets of fibers were tested and sensitive and reproducible results for liquids with refraction indices varying from 1.563 to 1.683 were obtained.

A new generation of filters are presented that are ideal for blocking visible light while passing near-infrared radiation. These filters are based on the novel use of selenium-based chalcogenide glasses with a low softening point on the one hand, and thermoplastic polymers on the other hand. A technology was developed that allows "sandwich" structures to be obtained, which include thin layers of polymers and chalcogenide glasses. The technology permits the cutoff edge of filters to be controlled with high accuracy. This can be done either by varying components of the "sandwich" or by varying the thickness of the chalcogenide glass layer.

This paper presents a data extraction and identification method for paper-based Chinese road maps. First, the extraction of the map title box and the legend index table is accomplished by a rule with trained parameter values. Then they are identified by distinguishing the characters from the legends using Bayes’s theorem. Second, the graylevel histogram of the large components is constructed and smoothed, and then the road images are filtered out using the multilevel thresholding technique. The extracted roads are further vectorized into line segments to save storage. The gaps between line segments are filled by a postprocessing procedure. Third, the characters and the legends are segmented by combining the small-component image and the difference image between the large-component image and the road images. The extracted legends are recognized by the proposed probabilistic template matching method. The performance of the proposed system is evaluated on 20 test maps, and the experimental results show that the proposed system is effective.

Spectral matching factors for starlight and full moon illumination conditions, GaAs and multialkali photocathodes, and some commonly encountered objects are computed and compared. For the S251 photocathode, these factors for combinations of dark green paint, green vegetation, and rough concrete are 0.27, 0.13, and 0.23 in clear starlight conditions and 0.55, 0.28, and 0.49 in full moon conditions, respectively. For the S252 photocathode, the former are 0.57, 0.48, and 0.56 and the latter are 0.72, 0.68, and 0.72. Finally, for the GaAs photocathode, they are 0.58, 0.65, and 0.61 and 0.45, 0.69, and 0.52, respectively. These values can be used for realistic estimates of the field performance and to optimize the design of night vision systems.

The performance of an IR detector in an area array is studied by numerically solving the 2-D diffusion equation for thermal and photogenerated carriers. The zero-bias resistance area product R0A, quantum efficiency ?, and the noise equivalent temperature difference NETD for diodes of different size and junction depth are calculated for long wavelength infrared (LWIR) HgCdTe n+-on-p diffusion-limited diodes in the backside illuminated configuration. The 2-D calculations incorporate thermally generated- and photocarriers that originate under the junction (the ‘‘normal’’ current), as well as those that originate from around the junction (the lateral current). The calculation of the diffusion currents— both optical and thermally generated carriers—is made using a trapezoidal grid, which better fits the symmetry of diodes in an area array. The present results are compared with previous calculations in which a uniform grid was used. The results of R0A and ? calculated by the uniform and trapezoidal grids differ significantly, especially for diodes with deep junctions or diodes that are small compared to the center-to-center distance between diodes. Both the uniform and trapezoidal grid calculations have been compared with spot scan measurements and Semicad simulation in a stripe diode array in the literature.

Phase-step heights of a kinoform grating are determined from its diffraction efficiencies. The diffraction orders of the measured kinoform grating are compared with theoretical ones of the pure phase- stepped grating, and then, by a minimization procedure, the set of heights of the phase steps is found.

The demand for fiber Bragg gratings (FBG) for use in optical transmission devices has grown exponentially in the telecommunication industry. A stable temperature compensation mechanism is essential to the successful use of FBG-based devices. In this paper, a tubular temperature-compensating package with a tunable component is described. Such a mechanism serves for posttuning the fixture in order to obtain a designed central wavelength. With the aid of the developed experimental procedure, this compact and easily manufactured package can achieve a temperature coefficient of 8.3X10-4 nm/°C in the temperature range from ?40 to 80°C. The same package can also be used for multi-FBG applications.

This paper presents a new fractal coding scheme to find a suboptimal transformation by performing an iterative encoding process. The optimal transformation can be defined as the transformation generating the closest attractor to an original image. Unfortunately, it is impossible in practice to find the optimal transformation, due to the heavy computational burden. In this paper, however, by means of some new theorems related with contractive transformations and attractors, it is shown that for some specific cases the optimal or suboptimal transformations can be obtained. The proposed method obtains a suboptimal transformation by performing iterative processes as is done in decoding. Thus, it requires more computation than the conventional method, but it improves the image quality. For a simple case where the optimal transformation can actually be found, the proposed method is experimentally evaluated against both the optimal method and the conventional method. For a general case where the optimal transformation is unavailable due to heavy computational complexity, the proposed method is also evaluated in comparison with the conventional method.

Fresnel-type lenses and mirrors are designed and their performance is simulated. These lenses and mirrors employ random spac- ings between elements to minimize intense higher order diffraction terms while maintaining good overall light concentration.

The intensity-hue-saturation (IHS) and Brovey transforms are two widespread image fusion methods in the remote sensing community. However, both are sensitive to the characteristics of the analyzed area. Restated, they often face color distortion problems with fused images. This work investigates models representing the color space in images. Schemes governing saturation change during fusion are also evaluated to derive the correct saturation values for each pixel in a fused image. In addition, algorithms that compensate distorted saturation values for distinct image fusion methods are derived and discussed. Methods to extend current image fusion methods to any arbitrary order are also outlined. Finally, an illustrative example of a fused SPOT image demonstrates the color distortion problem while an IKONOS image is adopted to evaluate various contemporary image fusion methods.

Subband coding is a well-established technique. Coding algorithms, however, rarely try to exploit residual similarities between subbands in order to get both coding gain and improvement in visual appearance. In this work we propose a simple postprocessing technique for edge enhancement and ringing-artifact reduction in subband-coded images. The proposed technique employs morphological filtering for preliminary image simplification and uses a novel dual-window nonlinear operator for subsequent edge enhancement. Visual appearance and numerical results confirm the validity of the approach. A simple coding scheme, designed to test the efficiency of the approach, gives good results.

Oil spillage in a body of water has been of great environmental concern. We present in this paper an automatic oil-spill detection system, which employs thin-film and wavefront-splitting interference techniques to determine the existence of surface oil or oil drops in water. Two independent automatic decision-making systems have been built to provide a reliable means of oil-spill detection. Initially a LabVIEWTM computer code and a charge-coupled-device camera were employed to discern and monitor the interference fringes generated from oil slicks. The LabVIEW imaging system was then replaced by a compact and low-cost imaging circuit that functions reliably in a buoy with relatively low power consumption.

The effects of a general small inclination between the two grating planes on the moire fringes in Talbot interferometry under illumination with a plane wave are studied. The inclination is generated by rotating the beamsplitter grating through two small angles around the two perpendicular axes in the grating plane, making an arbitrary angle with the line direction of the grating. Some simple judgement and adjustment methods for the inclination are presented. The results obtained by theoretical analysis have been verified by experiments.

We present computer simulations of interferometric imaging with the Very Large Telescope Interferometer (VLTI) of the European Southern Observatory and the Astronomical Multibeam Recombiner (AMBER) phase-closure instrument. These simulations include both the astrophysical modeling of a stellar object by radiative-transfer calculations and the simulation of light propagation from the object to the detector (through atmosphere, telescopes, and the AMBER instrument), simulation of photon noise and detector readout noise, and finally data processing of the interferograms. The results show the dependence of the visibility error bars on the following observational parameters: different seeing during the observation of object and reference star (Fried parameters r0object and r0,ref ranging between 0.9 and 1.2 m), different residual tip-tilt error (?tt,object and ?tt,ref ranging between 0.1% and 20% of the Airy-disk diameter), and object brightness (Kobject= 0.7 to 10.2 mag, Kref= 0.7 mag). As an example, we focus on stars in late stages of stellar evolution and study one of the key objects of that kind, the dusty supergiant IRC+10420, which is rapidly evolving on human time scales. We show computer simulations of VLT interferometry (visibility and phase- closure measurements) of IRC+10420 with two and three auxiliary telescopes (in AMBER wide-field mode, i.e., without fiber optic spatial filters) and discuss whether the visibility accuracy is sufficient to distinguish between different theoretical model predictions.

A new real-time calibration algorithm for phase shifting based on the fast Fourier transform (FFT) is presented. The purpose of this algorithm is to determine the phase shift between two fringe images rapidly and accurately. in it, the background distributions of two current fringe images are removed by recording additional fringe data with arbitrary phase shifts S. Thus, the phase shift between these two fringe patterns can be obtained correctly by the FFT method. With the help of an adaptive bandpass filter and a new modulation function defined in this paper, the accuracy of the phase-shift determination is further improved. By this method, we can simultaneously control the phase shift of the projection grating. The accuracy and the automation of the PMP system are enhanced greatly.

We describe the fundamental principle of operation of a vectorial shearing interferometer, featuring variable shear and tilt. They may be implemented along an arbitrary direction, in our experimental setup, by controlling the relative angle between a pair of wedge prisms. We show the simulated interferometric patterns of primary aberrations. We compare them with those exhibited by spherical and aspherical optical elements obtained experimentally. The number and orientation of fringes is controllable with the shear direction and its magnitude. The vectorial shearing interferometer is shown to be effective in testing optical elements and in aligning optical systems.

The minimum number of samples that must be taken from a sinusoidal signal affected by white Gaussian noise, in order to find its frequency with a predetermined maximum error, is derived. This analysis is of interest in evaluating the performance of velocity-measurement systems based on the Doppler effect. Specifically, in laser Doppler anemometry (LDA) it is usual to receive bursts with a poor signal-to-noise ratio, yet high accuracy is required for the measurement. In recent years special attention has been paid to the problem of monitoring the temporal evolution of turbulent flows. In this kind of situation averaging or filtering the data sequences cannot be allowed: in a rapidly changing environment each one of the measurements should rather be performed within a maximum permissible error and the bursts strongly affected by noise removed. The method for velocity extraction that will be considered here is the spectral analysis through the squared discrete Fourier transform, or periodogram, of the received bursts. This paper has two parts. In the first an approximate expression for the error committed in LDA is derived and discussed. In the second a mathematical formalism for the exact calculation of the error as a function of the signal-to-noise ratio is obtained, and some universal curves for the expected error are provided. The results presented here appear to represent a fundamental limitation on the accuracy of LDA measurements, yet, to our knowledge, they have not been reported in the literature so far.

A new dye Trans-4-[p-(N,N-diethylamino) styryl]-N- methylpyridinium iodide (abbreviated as DEASMPI) has been synthesized. The two-photon absorption (TPA), TPA-induced frequency up- conversion emission, and two-photon pumped (TPP) frequency up- converted lasing properties of this new dye have also been experimentally studied. This new dye has a moderate TPA cross section of ?2 = 6.9x 10-48 cm4.s/photon at 1064-nm, but exhibits a high lasing efficiency. The net conversion efficiency from the absorbed 1064-nm pump pulse energy to the 628-nm up-converted lasing energy is 3.2% at the pump energy level of 3 mJ.

Microcracking of wood caused by drying was investigated by detecting the intensity variations of a speckle pattern induced by a focused laser beam scattered from the surface. Two trials were carried out to test the usefulness of this method. The trials were used to compare the severity of different drying treatments and to follow the development of cracking during drying. The data gathered from these experiments revealed clear correlation between the amount of cracking on a wood surface and severity of the drying treatment. Furthermore, an increase in the amount of cracks was observed as drying proceeds.

A new method of three-dimensional shape measurement, called digital speckle temporal sequence correlation, is presented. Random digital speckle is projected on the reference plane, which is moved N times in equal depthwise steps. At each step, speckle image is captured by a CCD camera and saved in a computer as the reference-plane set R(t ). Replacing the reference plane with the object, the modulated speckle image O was also captured. The cross correlation between any subimage O(x ,y) in O and the serial subimages R(x ,y ;t ) located at the same position in R(t ) is approximately quadratic. The position of the main peak of the correlation curve is the height of the object point. In order to measure speckle-sets complicated objects, two new methods, called multiple reference-speckle-sets and multiple correlation-peak optimization, are also presented. Experiment proves them very effective. Our method surpasses the limitations of the horizontal correlation in previous methods and is a true temporal sequence correlation method. It is simple in principle and offers higher measurement precision without complicated phase-unwrapping and calibration processes, and can be used to measure discontinuous and spatially isolated shapes.

The application of beatwave Fabry-Perot interferometers (BFPIs) to nonlinearity error calibration is limited by the short tuning range of the slave He-Ne laser. In this paper, a 633-nm tunable externalcavity diode laser (ECL) is proposed as the slave laser of a BFPI. The ECL consists of an antireflection-coated quantum-well laser diode, a collimating lens, and a diffraction grating in Littrow configuration. In addition, an intracavity glass plate is adopted to provide cavity fine tuning, which makes the ECL more convenient, as it is easier to align the light in the cavity. At an optical length of 45 mm, a coarse-tuning range of 4 nm around 633 nm is obtained by rotating the grating. It is also demonstrated that this ECL can operate in a single-mode regime and can be continuously tuned over a frequency range of 1.8 GHz by tilting the intracavity glass plate.

Lens arrays are common in many standard lighting products. We present some instructive models to predict lens-array performance and demonstrate the effects of lens arrays with various tilings. In some cases the beam intensity can be approximated by the convolution of the source intensity with the lens-array intensity response (e.g., lens intensity using collimated illumination). In more complex cases, the beam intensity can be approximated by the superposition of the source intensity convolved with each lenslet's intensity response. We demonstrate this effect using Monte Carlo ray-trace simulations for both uniform- intensity sources and nonuniform-intensity sources such as a lamp in a parabolic reflector.

Micro-optical systems based on refractive microlenses are investigated. These systems are integrated on a chemical chip. They focus an excitation beam into the detection volume (microliter or even submicroliter scale) and collect the emitted light from fluorescent molecules. The fluorescence must be carefully separated by spatial and spectral filtering from the excitation. This paper presents the ray tracing simulation, fabrication, and measurement of three illumination systems. The measurements show that an adroit placement and combination of microfabricated lenses and stops can increase the separation between the excitation light and the fluorescence light. Moreover we present the successful detection of a 20 nM Cy5™ (Amersham Life Science Ltd.) solution in a 100-?m-wide and 50-?m-deep microchannel (excitation volume ?250 pL) using one of these illumination systems. The microchemical chip with the micro-optical system has a thickness of less than 2 mm.

A new moiré interferometer for determining 3-D displacement field of a slightly strained body is proposed. In this interferometer, the specimen grating not only diffracts the incoming beam into several beams but also rediffracts the diffracted beams, each of them is reflected from a mirror back to the path of the incoming beam. The rediffracted beams are then directed to a camera to generate three interference patterns, which are sufficient to determine the 3-D displacement field. The governing equations corresponding to these interference patterns are derived, and the advantages of using this interferometer are described. Some experiments were carried out to verify the governing equations and advantages.

Angular microvibrations of platform jitter on a three-axis attitude-stabilized satellite are measured in space using an onboard laser communication terminal. Stable optical tracking control allows the measurement of relative angular variations from the reference line of sight of the optical link. The tracking accuracy in this measurement is less than 1 ?rad rms. The angular variation and the drift rate on the satellite are measured at a sampling rate of 500 Hz, and these data are downlinked to a ground station via a satellite-to-ground optical communication link. The power spectral density of the satellite microvibration is calculated by a Fourier transform analysis. The frequency spectrum of the gimbal mirror's angular variation is also obtained when the coarse tracking control is operational. The rms value agrees with the residual coarse tracking error estimated before launch of the satellite. These results will be useful for the future design of a tracking control loop for optical communication systems.

An optical profilometer based on the principle of differential interference has been developed. Using a common-light-path interference scheme, the instrument is insensitive to vibration, air turbulence, and temperature variation. Experimental results demonstrate that the vertical resolution and the repeatability of the instrument are both better than 1 nm in an ordinary environment.

Normally, the dynamic range of a Shack-Hartmann sensor is limited by the foci leaving their respective subapertures, thus a definite attachment of the foci to their subapertures is difficult. By using an array of spatial light modulators in front of the microlenses of the sensor to switch on and off the subapertures, a definite assignment of the spots to their subapertures is possible. We present a coding algorithm that needs only log2N+1 frames to assign N spots unequivocal to their subapertures.

When only certain filter pixels in a spatial light modulator (SLM) are allowed to transmit light, those "on" pixels constitute the region of support (ROS) for the filter. At the frequencies where noise power overwhelms signal power, or where the available values of the filter are not well aligned with the ideal spectral filter, the filter can actually work against the intent of the metric, and zero transmittance is preferable to what the SLM can do. In contrast to prior theories, which applied to only unit-magnitude filters, we present algorithms for optimizing and studying ROS for an arbitrary SLM. We also present laboratory demonstrations of improvement in signal-to-noise ratio when a blocking mask is inserted into an optical correlator. A mask has detailed functional dependence on the signal, the noise power spectral density, the selected metric, and the realizable filter values. Broadly useful rules are given for designing a mask. Conjecture is offered that it could be beneficial to build a permanent ROS into SLMs.

We propose a new method to increase the resolution of an optical system by modifying part of the spatial-frequency spectrum, viz., displacing the lower-frequency light to a high-frequency band, which makes the central maximum in the diffraction pattern narrower and increases the depth of focus. Simulation results show that this kind of apodizer (the term apodization was originally used to describe ways to reduce the sidelobes of the PSF, but in this paper, we use it in a wider sense) is superior to the phase-shifting ones.

Pt-, Pd-, and Zr-doped SnO2 thin films and dopant-free VOx films were fabricated by planar magnetron sputtering. Tests for sensitivity to SO2 for all samples were conducted at 180°C, and the sensitivities were investigated exsitu with photometric and ellipsometric methods at room temperature. It was found that the optical sensitivities as well as the sensitive wavelength region for SnO2 films could be tuned by doping. The Pd-doped SnO2 films had good sensitivity in the visible range, and the Zr-doped in the near IR. The dominant sensitive wavelength region for VOx films fell into the visible range, and the ratio of the sensitivity in the visible to that in the near IR increased with O2/Ar in the depositing atmosphere.

A zero-tree wavelet image coding technique with resiliency to transmission errors that typically occur on noisy channels is proposed. Key tools employed consist of the bit partitioning algorithm, and the bit reorganization algorithm, which is called the error resilient entropy code (EREC). To take full advantage of the bit reorganization algorithm, the bit partitioning algorithm divides the data into separate code blocks, although the zero-tree wavelet coding algorithm is not a block-based compression method. The bit reorganization algorithm requires a very low redundancy for the sequential transmission of variable length blocks, offering a virtually guaranteed code and block synchronization. The wavelet transform and the wavelet packet transform are used. Simulation results verify the error resiliency of the proposed algorithm for image coding. The experimental data show that the proposed coders outperform the existing error resilient coders over both noise-free channels and noisy channels. In addition, it is confirmed that the proposed algorithm is more error resilient than previously reported error-resilient coders for various channel error conditions.

A nonuniform background distribution may cause a global thresholding method to fail to segment objects. One solution is using a local thresholding method that adapts to local surroundings. In this paper, we propose a novel local thresholding method for image segmentation, using multiscale threshold functions obtained by wavelet synthesis with weighted detail coefficients. In particular, the coarse-to-fine synthesis with attenuated detail coefficients produces a threshold function corresponding to a high-frequency-reduced signal. This wavelet-based local thresholding method adapts to both local size and local surroundings, and its implementation can take advantage of the fast wavelet algorithm. We applied this technique to physical contaminant detection for poultry meat inspection using x-ray imaging. Experiments showed that inclusion objects in deboned poultry could be extracted at multiple resolutions despite their irregular sizes and uneven backgrounds.