This PDF file contains the editorial “Editorial” for OE Vol. 40 Issue 06

Optical interference coatings are used in filter-based T-format fluorimeters to make beamsplitters, bandpasses, and bandblocking filters that separate excitation and emission signals. Commercially available filters usually perform well in these applications, but better performance may be possible if the system of optical filters is tailored to the specific analysis. We provide a general method for designing optical filters for the optical train of a specific fluorescence sensor system simultaneously using two light-emitting diode (LED) excitation sources (blue and green) and two different fluorescent indicators. We approach the problem of designing the optics of the system by first constructing a hypothetical target spectrum for each filter using the optical spectrum of the excitation source, and the excitation and emission spectra of the fluorescence sensors. Structural designs for Nb2O5/SiO2 multilayer interference filters are then synthesized. An iterative evaluation procedure is then used to improve the performance of the system for minimal leakage of the excitation sources onto our detector array. We also provide experimental results for the construction of these filters using reactive magnetron sputtering.

We propose a practical method for the expeditious determination of the performance of imaging CCD and CMOS camera systems. special attention is paid to the operation of these devices in varying illumination conditions, which is typical to many surveillance and consumer electronics applications. One emerging application utilizing imaging sensors in variable illumination conditions is the third generation mobile phone, which will deliver wirelessly pictures, graphics, and video. In our method, determination of the system performance is based on the imaging of a calibrated gray scale test chart as a function of illuminance. At each level of illumination the system response is characterized by a signal to random noise figure. The signal is calculated as the difference of the system response to the lightest and darkest areas of the gray scale. The random noise is measured as the standard deviation of the gray values in a difference of two successive images of the test pattern. The proposed method is applied in three exemplary cases: 1. comparison of inexpensive CCD and CMOS cameras, 2. analysis of the effect of wireless image transmission, and 3. comparison of the effects of automatic and manual gain controls.

A new approach to the problem of impulsive-noise reduction for color images is introduced. The major advantage of the technique is that it filters out the noise component while adapting itself to the local image structures. In this way the algorithm is able to eliminate strong impulsive noise while preserving edges and fine image details. As the algorithm is a fuzzy modification of the commonly used vector median operator, it is very fast and easy to implement. Our results show that the proposed method outperforms all standard algorithms for the reduction of impulsive noise in color images.

A noncontacting and noninterferometric depth discrimination technique, which is based on differential confocal microscopy, was used to measure the inverse piezoelectric extension of a piezoelectric ceramic lead zirconate titanate actuator. The response characteristics of the actuator with respect to the applied voltage, including displacement, linearity, and hysteresis, were obtained with nanometer measurement accuracy. Errors of the measurement have been analyzed.

We describe a new design of a detachable bulk-optic sensor for electric current detection. The sensor consists of two separate parts: an L-shaped arm cut to the critical angle and a straight arm to complement the L-shaped arm to form a right-angled triangular structure. With this design, the light beam needs to undergo only one total internal reflection along the optical path, making it more forgiving than the conventional design in terms of fabrication tolerance. An experimental sensor has been tested for its sensitivity to applied currents as well as to stray magnetic fields.

Microlenses, microlens arrays, and diffraction gratings can be made by irradiating a polyethylene substrate with a CO2 laser. These elements are meant to work with mid-infrared light (10.6-?m wavelength). The influence of some fabrication process variables in the final parameters of the elements is analyzed. Their quality was characterized by the direct measurement of their surface profiles. The ability of microlenses to focus mid-infrared light and to form infrared images is shown, and an introductory study of the gratings is given.

The aim of this work is an advancement of digital holographic interferometry by using a digital micromirror device (DMD) for real-time display of interferometric fringes. The theory describing the formation of the diffracted image produced by a coherently illuminated DMD is presented. Digital holograms of simple structures are calculated assuming plane and spherical reference waves, respectively. These synthetic holograms are used to control the micromirrors of the DMD, which now acts as a reflective hologram. Experimental holographic reconstructions of synthetic holograms prove the feasibility of DMDs in principle for this aim. Further experimental results show the reconstructed interferogram of fields recorded by digital holography and superposed numerically. This opens a new range of applications in digital holographic interferometry.

The enhancement of laterally emitting thin film electroluminescent (LETFEL) device outcoupling efficiency has been achieved via the introduction of a novel outcoupling mechanism, the surface emitting edge emitter. This method incorporates plasma enhanced chemically vapor deposited (PECVD) SiO2 microstructures underlying the device thin films at the device apertures, which consequently bend the LETFEL structure at these locations. Additional etching of the bent thin films provides shaped edges at both sides of the aperture, which outcouple the internally generated light as conventional edge emitters. Comparison of the conventional nonetched and surface emitting edge emitter light outputs demonstrates an improvement in the outcoupling efficiency by a factor of 4 at 620 V. Additionally, a Gaussian angular distribution with a FWHM ~40 deg has been measured from each edge, being the Gaussian maximum coincident with the microstructure wall side angle. In this research, 45 deg wall sided microstructures have been utilized, however, perpendicular microstructures are proposed to further enhance the coupling efficiency for the two main LETFEL applications, head mounted displays, and electrophotographic printing. The fabrication route that successfully defines the surface emitting edge emitter mechanism is presented for the first time; this incorporates ion milling as the sputter etch technique to shape the device aperture.

We investigate some practical problems and propose their solutions for the display of fractal images. The original sizes and coordinates of fractal images are usually different, and they can be measured only from the decoded results. This is a drawback, since the decoded fractal image may not be shown with adequate size and may not locate in a desired position. In this paper, we propose a hierarchical fixed-pointseeking method that can directly determine the original size and the coordinates of a fractal image from its iterated function system (IFS) code. With a modification of the translation parameters in the IFS code, we can resize and relocate the decoded image. On the other hand, we discuss the quantization effects due to the finite word length in the hardware implementation. Finally, a method for determining the iteration number in the random iteration algorithm is also proposed. In computer simulation, we demonstrate some examples to verify the proposed solutions.

This paper presents a new block-based motion estimation algorithm that employs motion-vector prediction to locate an initial search point, which is called a search center, and an outward spiral search pattern with motion-vector refinement, to speed up the motion estimation process. It is found that the proposed algorithm is only slightly slower than cross search, but has a peak signal-to-noise ratio (PSNR) very close to that of full search (FS). Our research shows the motion vector of a target block can be predicted from the motion vectors of its neighboring blocks. The predicted motion vector can be used to locate a search center in the search window. This approach has two distinct merits. First, as the search center is closer to the optimum motion vector, the possibility of finding it is substantially higher. Second, it takes many less search points to achieve this. Results show that the proposed algorithm can achieve 99.7% to 100% of the average PSNR of Fs, while it only requires 1.40% to 4.07% of the computation time of FS. When compared with six other fast motion estimation algorithms, it offers the best tradeoff between two objective measures: average PSNR and search time.

There are two kinds of video image sequence distortions caused by vibration of the camera. The first is the vibration of the line- of-sight, causing location changes of the scene in successive frames. The second distortion is the blur of each frame of the sequence due to frame motion during its exposure. The relative effects of these two types of degradations on the ability of observers to recognize targets are investigated. This study is useful for evaluating the amount of effort required to compensate each effect. We found that the threshold contrast needed to recognize a target in a vibrating video sequence under certain conditions is more affected by the motion blur of each frame than the oscillation of the line-of-sight. For digital sequence restoration methods, this study determines the required precision of the deblurring and registration processes. It shows that the deblurring process should not be neglected, as it often is.

A new class of nonlinear filters using rank-order operations over spatially connected neighborhoods and fast algorithms for the design of these filters are presented. Many rank-order processing techniques may be implemented by using filters such as noise suppression, enhancing, and restoring images. The performance of the proposed filters for suppression impulsive noise, additive noise, and mixed additive and impulsive noise in test images is compared to conventional rank-order algorithms. The comparisons are made using a mean square error, a mean absolute error, and a subjective human visual error criteria.

Measurement of differences in optical path length in monochromatic light with any interferometric method is insensitive to errors that are whole numbers of waves. If measurements are performed in several wavelengths, this ambiguity can be resolved. We present a general algorithm for finding the correct distance post facto, given multiple measurements in different wavelengths. Applied to piston measurements of a segmented mirror, the capture range of a wavefront sensor can be extended from ± half a wave to several waves. The extended capture range can be calculated and depends on the selection of wavelengths used for measurements and the expected accuracy of the method used.

The next generation digital versatile disk (DVD) using blue lasers will have a capacity of 13 to 15 Gbytes. Compared with current DVD, the wavelength will be shorter and the numerical aperture (NA) will be higher. But with the increase of NA and decrease of wave length, the depth of focus (DOF) decrease rapidly, which makes it hard for the servo-system to track. We propose an optimized three-portion phaseshifting apodizer to increase the depth of focus and at the same time minimize the spot size, which makes the DOF of next generation DVD comparable to current DVD. The simulation result shows that an optical system with this apodizer also has a good defocus characteristic.

We propose a novel method to measure the astigmatism of laser diodes that is based solely on power measurements and does not require the use of any imaging system. Experimental realization of this method resulted in a sensitive measuring technique. Using it, a linear dependence of astigmatism change on drive current is demonstrated for commercial index-guided laser structures. The proposed method is believed to be highly adaptable to any experimental environment. Its advantages over currently employed methods are discussed.

We demonstrate the utility of laser-illuminated imaging for high-resolution clandestine nighttime surveillance from a simulated airborne platform at standoff ranges in excess of 20 km. In order to reduce the necessary per-pulse laser energy required for illumination at such long ranges, and to mitigate atmospheric turbulence effects on image resolution, we have investigated a unique multiframe postprocessing technique. It is shown that in the presence of atmospheric turbulence and coherent speckle effects, this approach can produce superior results to conventional scene flood illumination.

We tackle the complex problem of taper heating inside an optical fiber tip used in scanning near-field optical microscopes. The technique is based on the usual ray tracing. Its interest is in the modeling, taking into account not only the power input distribution but any shape of tapers. The thermal-optical behavior of a shell-shaped taper is compared with that of a pure conical taper. Sharp power concentration peaks inside nonlinear taper profiles have been demonstrated, in contrast with the smooth power distribution inside cone shapes. The results present heat zones that are in agreement with our thermal model.

We present an optical design of a near-IR (at FeI15648.5 Å) birefringent filter system that is used to form a magnetograph to obtain chromatic images of the sun and measure the solar magnetic field at the Big Bear Solar Observatory (BBSO). This magnetograph consists of an interference prefilter, a polarization analyzer, a wavelength-tunable birefringent filter, and a Fabry-Perot Etalon. This system is expected to achieve a clean narrow pass band of 1/8 Å. It can also be tuned across the spectral line to obtain line profiles of 2-D fields of view. During the design of the tunable near-IR birefringent filter and the testing of its components, we found that the value of the birefringent index ?(ne?no) of calcite at a spectral range near 15648.5 Å is different from the value quoted in the literature. Because the birefringent index is important for the design of optical components, the birefringent index of calcite and its thermal coefficient were measured. Test results of the four pairs of calcite plates used in the birefringent filter are presented.

The optical properties of a cyclic olefin copolymer, Topas™, made by Celanese AG, are presented. This class of materials is attractive on account of their high use temperature, excellent optical transmission, low birefringence, and low moisture uptake. These materials are compared with other commonly used thermoplastics, namely, polycarbonate and polymethyl methacrylate. Finally, Topas™ is compared with a number of other optical polymers being studied for optical waveguiding applications. It is found that at 830 nm Topas™ has low losses (less than 0.5 dB/cm), so that it may be useful for datacom applications. At the telecommunication wavelength of 1550 nm the losses are in the range of 0.7 dB/cm.

The irradiance in the exit pupil of a typical optical data storage system (i.e., the detector pattern) consists of fringes formed by the interference of fields reflected from the optical disk. The reflected fields are decomposed using Babinet's principle into desired and undesired components. The behavior of the fringes depends on the interaction of the focused light spot with the features on the optical disk and media parameters, such as mark and land reflectivities, groove depth, and mark pattern. The behavior of the desired and of the undesired fringes are determined for both write-bright media (bright data marks written on a dark background) and write-dark media (dark marks written on a bright background). Both a theoretical development and a scalar diffraction simulation tool are used in the analysis.

We describe the design and performance of modular jack type mini-MT connectors that employ a compact 2-fiber ferrule in a newly designed housing and adaptor. The basic mechanism for coupling the housings is similar to that of a conventional electric modular jack type connector. Our connectors have a locking mechanism to prevent accidental disconnection and a high packaging density of 2 fibers/cm2. Fabricated connectors for single-mode 2-fiber ribbons exhibit a low insertion loss of 0.18 dB and a high return loss of more than 40 dB using a flat endface ferrule with protruding fiber finish. In addition, they have an insertion loss of 0.20 dB and a return loss of 60 dB when an angled endface ferrule is used. We have confirmed that these connectors are highly effective for use in the duplex connection of advanced optical networks.

There are several methods to measure the optical fiber dispersion and dispersion slope. They are, generally, divided into time and frequency domain methods. The modulation phase shift technique (MPS) is a frequency domain method providing the highest accuracy. Time domain methods have lagged behind their frequency domain counterparts. Recently, a paper by Tong et al., used the spatial-temporal analogy to improve the time domain measurement past the previous simple minded pulse broadening measurement over the known length of the fiber. In spite of marked improvement, the time domain measurement still remains inferior to MPS. We show that by using a pair of short optical pulses instead of a single pulse, one can alleviate some of the previous shortcomings of time domain methods. The new method achieves excellent agreement with the frequency domain technique.

This paper describes the dual-layer scalable optical interconnection network being developed at Tianjin University. The top layer of the network is a multiwavelength bidirectional optical bus, which has large bandwidth and low latency. The bus is made up of passive components. No wavelength-tunable devices are used. As a result, the bus has a low communication latency that is mainly determined by the optical fiber length. The sublayer of the network is a single-wavelength ring, which has low communication latency and high scalability. In each ring, a wavelength routing node is designed for data transmission between the ring and the optical bus. Each node computer is connected to the ring through an optical network interface card. The communication latency inside the ring is decreased by using synchronous pipelining transmission.

Coherent homodyne crosstalk in optical systems is examined. A general approach is introduced to theoretically model the crosstalk of single and multiple interferers in DFB and FP laser systems with a finite modulation extinction ratio, with PIN and APD receivers, in external modulation systems. The theoretical results of this model are verified experimentally and are compared with other theoretical models. In addition, the trade off between modulation extinction ratio and crosstalk tolerance is investigated and optimized. The general mathematical model is implemented in a computer simulator program, creating an inclusive and pragmatic engineering tool. This computer simulator dramatically improves the design of next generation crossconnects, switched and routers.

A method with high precision for measurement of optical retardation angles of wave plates is presented, based on laser birefringent longitudinal-mode-splitting technology. When a wave plate is placed in the laser cavity, a laser longitudinal mode will be split into two modes because of the birefringence of the wave plate. The optical retardation angle of the wave plate is proportional to the ratio of the frequency difference between the two modes to the laser longitudinal-mode interval. The retardation angle can be determined by measuring these two frequencies. The method uses a compact setup and attains high resolution and accuracy. The error is less than 8 arcmin. The paper discusses a crystal quarter-wave plate at 632.8-nm wavelength as an example, but the method is suited for other laser wavelengths and wave plates.

We describe the operating principle of a silicon optoelectronic modulator based on the plasma dispersion effect used in conjunction with a distributed Bragg reflector, which converts the phase shift, induced by the free carriers injected by a P-i-N diode, into variations of its reflectivity. The device is integrated in a low-loss silicon-on-insulator waveguide. Two different approaches in the driving schemes are proposed. Moreover, we show how it is possible to reach a theoretical l0o% modulation depth by exploiting in a concurrent way both the variations of the refractive index and the increased optical absorption. An exhaustive description of the optical structure and its guiding properties, together with the analysis of the electrical behavior of the modulator, is given. Finally, a comparison with other interferometric structures is analyzed, and it is shown how this kind of modulator exhibits satisfactory characteristics in terms of dissipated power and reduced occupation of area on a chip.

When light travels through a diffusing medium, the incident radiation is scattered and a part of it is reemitted. The reflected proportion is defined as the reflectance and provides the quantification of color sensations. Many authors have tried to derive reflectance values by various means. This bibliographical synthesis reviews the main theories on the subject, comparing them and especially their assumptions and derivations. First, the widely used theory of Kubelka and Munk?which has been proved to be a particular case of Schuster's formula?is described, according to its terms, limits, improvements, and applications. Next, the well-known electromagnetic approach by Mie is presented, along with methods derived from radiative transfer theory, multilayer methods (the "pile of plates'' due to Stokes), multiflux methods (developed by Mudgett and Richards or Völz for instance), and the corpuscular treatment proposed by Silvy. Finally, new methods are listed that allow the calculation of reflectance values, such as Monte Carlo simulations, expert systems, or neural networks. A chronological organization chart is also given to place each work or advance relative to the others.

This paper presents a dynamic simulation loop that gives tracking results for a two-color concentric annular ring (CAR) reticle seeker. Our simulation tool includes a target flare model and a proportional navigation guidance loop. The CAR reticle system's performance and the flare effects are analyzed in various scenarios. When a flare is present in the field of view, the simulation results show that the reticle seeker cannot maintain precise target tracking. We propose a two-color countercountermeasure using the least-mean-square method to cope with a presence of infrared (IR) flares. The proposed method makes use of simultaneous processing of the modulation output in two IR wavelength bands. One is the midwave IR (a primary input signal), and the other is the shortwave IR (a reference input signal). Simulation results have shown that our adaptive algorithm can achieve effective cancellation of flare signals with high intensity.

Thermal effects are investigated using laser interferometric and infrared thermometric techniques in diode-end-pumped solid state lasers operating under lasing and nonlasing states. The laser interferometry provides high resolution to determine the optical path difference (OPD) induced by thermal effects of the crystal. The infrared thermometer measuring the temperature distribution at the end pump face is proposed to evaluate the thermal lensing power induced by the index part. It is found that the temperature variations across the crystal face under nonlasing operation increase 20 to 27% compared with lasing conditions in Nd:YVO4 crystals. Thermal lensing power under the actual lasing condition is measured to be 0.2 m-1 to 2.1 m-1 with the pump power ranging from 1 to 8.3 W; the index part takes the proportion of about 59% in the total thermal lensing effect for end-pumped Nd:YVO4 lasers.

All main international metrological organizations are proposing a parameter called uncertainty as a measure of the accuracy of measurements. A mathematical model that enables the calculation of uncertainty of temperature measurement with thermal cameras is presented. The standard uncertainty or the expanded uncertainty of temperature measurement of the tested object can be calculated when the bounds within which the real object effective emissivity er, the real effective background temperature Tba(r), and the real effective atmospheric transmittance Ta(r) are located and can be estimated; and when the intrinsic uncertainty of the thermal camera and the relative spectral sensitivity of the thermal camera are known.

Optical components such as mirrors or windows consisting of a substrate and a coating made up of thin films created at elevated temperatures exhibit substantial residual stresses induced by growth strains and/or thermoelastic strains that develop during the cool-down phase. A comprehensive description of these stresses must include not only the normal stresses in the film layers and the substrate but also the interfacial shearing stresses, which may cause delamination to occur. We take advantage of recent progress in describing elastic interactions in multilayered laminates for obtaining conceptually correct formulas for the residual stresses and the substrate’s curvature of thin-film coated optics. Available analytical solutions for the normal stresses of elastically isotropic structures make no assumptions regarding layer thicknesses, but disregard the potential impact of edge effects. For circular structures such as coated optics, we show that recent work by Suhir now allows us to describe the distribution of both normal and interfacial stresses as long as the thin-film conditions are satisfied. The task of evaluating the deflection turns out to be fairly straightforward, leading to the conclusion that edge effects do not alter the bow of large compliant structures. The case of diamond-coated ZnS windows illustrates how thermal expansion mismatches can give rise to compressive film stresses of gigapascal intensity, which cause substrate deformations that are unacceptable in terms of the optical performance. Since the deflection of a multilayercoated substrate reflects the sum of the contributions (positive or negative) induced by each film, the deflection can be minimized by properly designing the film stack. For a diamond-coated ZnS window, this means that a suitable buffer must be in tension; in principle, a buffer made of calcium lanthanum sulfide, about 350 mm thick, can mitigate the bending force exerted by a 50 ?m thick diamond film and suppress the shear at the substrate/coating interface, thus enhancing the adhesion

Because light is scattered and absorbed by seawater, the images obtained underwater are always blurry after transmitted through a certain distance. The point spread function (PSF) and modulation transfer function (MTF) are important properties of seawater to predict underwater light propagation and underwater image quality. We describe the laboratory facilities to measure the PSF and MTF of water body by the image transmission method and the restoration methods of underwater blurred images. The measured results are given and compared with the theories. The blurred images of a bar target transmitted through different water paths are restored with the measured MTF using a Wiener filter.

The present work describes the measurement of small out-ofplane vibrations in quasi real time using a photorefractive crystal as a medium for recording speckle patterns. Vibrating circular fringes are generated by interference between the reconstructed speckles recorded for a stationary object beam, and vibrating speckles transmitted through a BaTiO3 crystal after introducing a small out-of-plane shift in the diffuser position. Vibration amplitudes, of the order of the wavelength of light, have been measured by counting of fringes evolving from, and sinking into the center of the circular fringe pattern at the observation plane. The vibration frequency is measured by the number of times the change takes place in the fringes from evolution to sinking mode per unit time. Object vibration in an arbitrary direction is also analyzed and found to produce similar results.

Silicon nitride (Si3N4) passivation was attempted on x-cut LiNbO3 10-Gb/s optical integrated modulators. Although silicon nitride films are commonly used to chemically protect semiconductor device surfaces,1 to our knowledge, applicability of the film to rf optoelectronic devices such as high-speed LiNbO3 modulators has not been reported. The purpose of our investigation is to confirm that the silicon nitride passivation films do not degrade the electro-optic (EO) characteristics and bias-drift performance of LiNbO3 modulators.

Commercially available tympanic thermometers are used in many clinical settings and are intended to determine the core temperature of the body.1,2