This PDF file contains the editorial “Editorial: The International Commission for Optics” for OE Vol. 34 Issue 10

We describe a technique for aligning the axis of an optical system with the axis of a rotating mechanical system. The optical system is focused onto a linear grating that rotates in conjunction with the mechanical system. Light reflected from the grating produces an interference pattern in the pupil of the optical system. Temporal modulation of the fringes in the interference pattern is observed as the mechanical system rotates if the optical and mechanical axes are misaligned. Experimentally we demonstrate alignment to better than 0.1 μm.

Construction and characterization of the first multimode fiber couplers in the mid-IR region (2 to 10 μm) are reported. These couplers are made of step-index As₂Se₃ chalcogenide glass fibers whose cores were brought to a contact along a certain distance. Far-field measurements using selective angular excitation indicated a typical coupling ratio of 15% (8.2 dB) from couplers made of 550-μm core diameter fibers with a 10-cm interaction length. The excess insertion loss was less than 0.2 dB. Strong mode mixing caused by the coupling mechanism is observed, resulting in a significant broadening of the radiation distribution.

Based on theoretical and experimental analyses, it is shown that the spectrum of intensity fluctuations contains a high-frequency peak in the absence of a subsidiary reference wave at nonsmall angles of speckle observation. This phenomenon, interpreted as a new type of manifestation of the Doppler effect, is usual only for the case of strongly focused coherent beam scattering. The possibilities for using the observed effect in the measurements of blood and lymph flows in narrow native capillaries are discussed. The traditional Doppler method using strongly focused Gaussian beam scattering is also considered. It is shown that the frequency position of the Doppler peak in the spectrum of intensity fluctuations is defined not only by the angle of speckle observation but also by the relation between the waist beam diameter and the average size of flow inhomogeneities. This result was experimentally verified. It is concluded that the Doppler method of blood flow measurement using strongly focused Gaussian beam diffraction should be revised.

We investigate the effects of the nonreciprocity caused by time-varying, radial thermal gradients in interferometric fiber gyroscope sensing coils. Four identical sensing coils have been wound with elliptical core and Panda polarization-maintaining fibers in straight and quadrupolar wind configurations. The induced gyro bias drift, measured as a function of the elevated temperature and time, is presented and compared with a simple heat-conduction model. Qualitative agreement is reached with suitable choices of material parameters.

We have developed an integrated microscopy system combining fast dual-excitation fluorescence photometry and digital image analysis with high spatial resolution, based mainly on standard components. With the combination of these well-established techniques in one setup it is possible to monitor intracellular calcium with both sufficiently high temporal and high spatial resolution on the same preparation for many biological applications. Our system consists of a commercially available dual-excitation photometric system, an attached intensified charge coupled device (ICCD) camera, and a frame grabber board. With this integrated setup one can easily switch between the fast photometric mode (v_ratio = 100 Hz) and the imaging mode (v_ratio = 4.l7 up to 17 Hz). We used the system to record Fura-2 calcium images (340/380 nm ratios), which were correlated with the faster spot measurements and were analyzed by means of image processing. As an example for its application we reconstructed caffeine-induced calcium transients released from the sarcoplasmic reticulum of isolated and permeabilized skeletal muscle fiber preparations. Such a combined technique will also be important for cellular studies using other fluorescence indicators. Additionally, the described system has an external trigger facility that enables combination with other cell physiological methods, e.g., electrophysiological techniques.

We develop the block-circulant structure of Gabor matrices, and establish that Gabor matrices are unitarily block-diagonalizable simultaneously. It opens a new way of implementing the discrete Gabortransforms. For the most interesting cases, if the product ab of the lattice constants divides the signal length N (in particular, in the critical-sampling cases), we prove that the Gabor operators are simultaneously unitarily equivalent to non-negative pointwise multiplication operators. This leads to fast computations of the inverse of the Gabor operator and the square root of the inverse of the Gabor operator, as well as the dual Gabor wavelet and the tight Gabor wavelet. Gabor syntheses turn out to be simple, and we can also easily predetermine the stability of Gabor reconstructions.

An analysis of the polarization properties of volume phase gratings is given. The analysis is based on the two-wave coupled-wave theory. The formulation presented here differs from the well-known theory of Kogelnik by taking into account the form birefringence of the grating. Analytical expressions for the dependencies of the Bragg angles, the grating strength, the dephasing between the readout and the diffracted wave, and the diffraction efficiency on the state of polarization are given for gratings of the transmissive and the reflective types. The cases of a cosine and a rectangular refractive index profile are discussed in detail. Finally, experimental results are given to support the theory.

We describe a holographic technique suitable to manipulate the chromaticism and brightness of the diffractive colors. This technique allows us to reproduce a wide range of color sensations as true color holographic images. Experimental results that verify our proposal are included.

Substrate guided-wave (SGW) holograms, recorded and reconstructed using light waves guided through optical substrates, are currently being incorporated into visual displays, optical integrated circuits, and nondestructive testing systems. In this paper, a coupled wave approach is used to analyze the diffraction properties of SGW holograms. The expressions obtained allow SGW holograms to be compared with conventional transmission and reflection holograms. The analysis is restricted to cases in which holograms are recorded and reconstructed using plane waves. The object beam is also assumed to be at normal incidence to the hologram. Results are presented for holograms recorded on a silver halide emulsion and illuminated using a krypton laser. The study shows that SGW holograms have higher diffraction efficiencies under the Bragg condition, higher angular selectivities, and more moderate wavelength selectivities than holograms recorded using conventional means.

Synthetic-aperture holography represents an attractive approach to the problem of three-dimensional data visualization. However, scaling the technology beyond a proof of concept requires a modification of the original architecture to allow for an increased hologram space-bandwidth product. It is demonstrated how the Fourier domain of a scanned aperture display can be segmented in small domains, each being processed by a different scanning element. The behavior of a display exhibiting such a segmentation is described, and the conditions under which images can be produced without incurring significant degradation are derived. A large-scale display based on the implementation of these concepts is demonstrated.

Adaptive hierarchical algorithms of vector quantization (VQ) for image coding are proposed. First the basic codebook is generated adaptively using adaptive VQ, then the quadruplets of codes/indices in the so-called zigzag order are coded into higher level (second and third levels) codes by creating the second- and third-level index codebooks to reduce the redundancy presented in the codes. Partially matched quadruplets are also encoded in the second and third layers using the index codebooks along with corresponding correction schemes. The third-layer encoding achieves a better compression ratio than a two-layer encoding scheme, which was shown to be optimal when partial encoding was not adopted. This three-layer coding scheme achieves better compression with no extra distortion and little extra computation. Experiments show encouraging results.

A fast vector quantization algorithm is presented that exploits the spatial redundancy between neighboring vectors of pixels in an image to improve the performance of the triangle inequality elimination ruler, and employs the integral projection technique, a dimension-reduction method, to reduce the computational complexity of calculating distortion measure. Application of dimension reduction in distortion measures may result in some degradation of objective image quality. But a significant complexity reduction of over 90% in comparison with the conventional full-search method can be achieved. The degradation of image quality is only less than 0.2 dB in peak signal-to-noise ratio (PSNR). Acceptable image quality should be obtained successfully.

To investigate an accurate, rapid, and nondestructive method for wheat classification in inspection terminals, backpropagation neural network models were developed, based on single wheat kernel near-infrared transmittance spectra. Six classes of wheat were studied. Neural network models were optimized for two-class and six-class classification. The wavelength range of the spectra was 850 to 1049 nm. For two-class models with 200 input nodes, the average classification accuracy was 97% to 100%. For the six-class model with 200 input nodes, the average accuracy was 94.7%. The classification between hard red winter (HRW) and hard red spring (HRS) was least accurate among the six classes. For rapid classification, a narrower wavelength range, 899 to 1049 nm, with an interval of 2 nm, was proposed and shown to have little loss in accuracy. The most time-consuming two-class (HRW-HRS) model could be calibrated and validated in less than 7 mm. Prediction for new data was nearly instantaneous. A backpropagation neural network model with a learning coefficient of 0.6 to 0.65 and momentum of 0.4 to 0.45, without a hidden layer, was effective for wheat classification.

A synthetic discriminant function (SDF) fringe-adjusted joint transform correlator is proposed that is able to provide a high degree of image distortion invariance and classify different objects in the input scene. The SDF reference function, which is displayed alongside the input scene, is a linear combination of the training image set. An iterative algorithm is presented and utilized to obtain the linear combination coefficients from the nonlinear equations of the fringe-adjusted joint transform correlation (JTC) system. When compared with the SDF-based classical JTC and binary JTC, the SDF fringe-adjusted JTC delivers a better capability to give localized equal correlation peak heights for the same class of objects. Furthermore, when the input scene contains the different objects from the different classes of images, the SDF fringe-adjusted JTC is shown to efficiently classify the different target objects and reject the nontarget object in the input scene, whereas the SDF-based classical JTC and binary JTC fail to achieve this.

We propose a few new algorithms of two-dimensional blind deconvolution. It is known that discretization of a continuous deconvolution problem can alleviate its ill-posedness. This philosophy can be embodied by using the aperiodic convolution model. We illustrate a few gradient algorithms of blind deconvolution using the aperiodic model and show that the main calculations can be accomplished efficiently by means of the discrete Fourier transform (DFT) technique. We present an increment Wiener filter that can further improve the solution of the frequency domain deconvolution. The increment Wiener filter has an iterative form and therefore the object domain constraints can be efficiently incorporated. We propose a multiframe combination scheme of blind deconvolution that can stabilize the solution of the iterative algorithms and suggest two useful techniques: the numerical level adjustment and the updating of the support constraints. We propose that the combination of the Wiener filter, the increment Wiener filter, and the new gradient algorithm is a reasonable choice for practical blind deconvolution applications.

We propose a method of exact measurement of flat surface profiles in a phase-conjugate Fizeau interferometer. Aberration of lenses causes an undesirable phase distribution in the interference signal of the phase-conjugate Fizeau interferometer. To eliminate this phase distribution, we shift the object in two directions orthogonal to each other and we get difference values of the surface profile of the object. Additional displacements of the object surface involved in the shifts lead to some small errors in the difference values. We estimate an exact surface profile by solving the difference equations. Characteristics of the method are made clear through computer simulations and measurements of a 40-mm-diam flat mirror.

A new experimental technique has been devised to measure residual stresses in ductile materials with a combination of laser speckle pattern interferometry and spot heating. The speckle pattern interferometer measures in-plane deformations while the heating provides for very localized stress relief. The residual stresses are determined by the amount of strain that is measured subsequent to the heating and cool-down of the region being interrogated. A simple lumped-parameter model is presented to provide a description of the method. This description is followed by presentation of the results of finite-element analyses and experimental results with uniaxial test specimens. Excellent agreement between the experiments and the computer analyses was obtained.

Testing of spherical surfaces using the Twyman-Green interferometer with a laser source suffers from the presence of spurious interference fringes and dust diffraction. By reducing the spatial coherence while maintaining the temporal coherence a tremendous improvement of the fringe quality can be obtained. To conserve sufficient contrast, the reference mirror must be positioned to suitable locations relative to the test arm of the interferometer. These conditions are described and examples are presented.

The process of laser welding of plastics is studied theoretically and experimentally. Welding of cylindrical parts made from polycarbonate and polypropylene is presented as examples. A good correspondence between theoretical and experimental results is found. Some practical aspects of laser welding of plastics are given.

The mode-matching problem of a multislab cascade laser is investigated. Optimized parameters of the multislab cascade laser resonator were derived using computer simulation. The theoretical analysis was confirmed by the experiment. High output efficiency can be achieved with properly chosen resonator parameters. The output power of the two-slab cascade laser was measured at more than 90% of the output power summation of each single-slab laser.

The strong influence of facet properties on wavelength shift and wavelength chirp is studied in uncoated and coated distributed feedback (DFB) lasers. A detailed comparison is performed between various experimental laser data (spectra, electronic and thermal wavelength tunability, relative intensity noise, linewidth) and the results of model calculations combining rate equations and the transfer matrix method. From experimental data of different lasers, a set of physical DFB laser parameters is determined. We succeeded in describing all the experimental data of different lasers by the same parameter set. By use of this set and a large signal analysis we found that the wavelength chirp and the wavelength shift resulting from electronic effects including spatial hole burning varies considerably for different end facet phases (EFPs) and facet coatings, but otherwise identical DFB laser geometry.

A novel tunable, grating external cavity, strong feedback semiconductor laser with real-time wavelength monitoring was designed, constructed, and tested. The wavelength monitoring was realized by recording the position of the second-order diffraction beam of the grating on a photodiode array. A wavelength tuning range of 16 nm from 648 to 664 nm, with a tuning resolution of better than 0.01 nm, was obtained. The verified tuning accuracy of the system was 0.1 nm, limited by the 0.1 nm accuracy of the monochromator used to calibrate the laser system.

In optical storage technology, gratings consisting of curved grooves have been formed in disks to record data and in integrated optical pickup devices to read signal. Groove parameters, such as pitch, width, and depth, can be inspected by the light diftraction method. Diffraction patterns are usually analyzed without considering the curvature of grooves. A model is developed to examine diffraction patterns of curved grooves. Theories for uncurved and curved grooves are compared. An optical inspection system is developed. Experimental results are analyzed and compared with theories.

A novel, differential focus error detection scheme for use in optical recording applications is described. The technique is based on the depth-discrimination property of confocal optical systems. A simple theoretical treatment is used to predict the form of the focus error signal, which is also investigated experimentally using a scanning optical microscope. The focus error response is found to exhibit a more than adequate lock-on range and gain, and is expected to be less sensitive to tracking feedthrough and other forms of cross-talk.

In terms of the presented mode eigenvalue equation, the mode propagation and absorption loss are analyzed for Au/InGaAsP/nP, air/Au/InGaAsP/InP, and Au/SiO₂/InGaAsP/InP single-mode metalclad multiple quantum-well optical waveguides. The effects of some guided structural parameters on the mode propagation and absorption loss are discussed, such as the periodic length, the ratio of the well thickness to the periodic length, the well number, and the thicknesses of the metal cladding and the dielectric buffer layer.

A primary cause of degraded performance in pointing and tracking systems is the jitter in the line of sight. This jitter is caused by the residual angular motion of the stabilized platform within the system. A major contributor to this residual motion is the gyroscope noise. Thus, to reduce angular jitter, lower-noise gyroscopes are selected, generally at a premium cost. Another approach is to enhance the accuracy of the gyroscopes electronically (by suppressing measurement noise) before their outputs are fed into the stabilized platform control system. Optimal filtering techniques can be used for this purpose. The goal is to estimate the platform motion so that the calculated value is closer to the actual value than the measurement is. Enhanced performance is obtained at the expense of added complexity, but in many cases this approach may prove to be more economical than resorting to more precise and costly lower-noise gyroscopes. This paper presents a novel Kalman filtering method that provides more accurate angular motion estimates than the measured values. The effectiveness of this method is evaluated through a computer simulation case study. The simulation demonstrates that the new approach yields excellent 3-D angular velocity estimates, very small mean square estimation errors, and over a 5-to-i improvement (in the mean-square sense) over angular velocity measurements obtained from three orthogonal gyroscopes. The enhanced 3-D angular velocity estimates can be fed into the platform stabilization control system rather than feeding raw gyroscope measurements, thus significantly reducing the contribution of gyroscope noise toward the overall jitter in a stabilized platform. This would permit a relaxation on gyroscope noise specifications, which could lead to substantial savings while maintaining the same error budget.

An arrangement for constructing the optical rotator or circular retarder is described. The arrangement consists of two crossed quarterwave plates with a retarder or polarization modulator as the rotating element interposed between them. Experiments to demonstrate the opticalrotator arrangement are described and the results are presented.

An in situ technique for servo control of surface height during laser scanning of semiconductor wafers is described. The scheme corrects any macroscopic height changes due to tilt and bow in the wafer and rejects local and pattern-dependent changes of height and reflectivity. The waist of the scanning beam is imaged on a slit aperture placed in front of a position-sensitive photodiode, leading to an ac signal at the scanning frequency. This ac signal then undergoes synchronous detection using a reference signal at the scanning frequency. This detection scheme leads to a reduced sensitivity to low-frequency electronic and thermal drifts. Normalization circuitry provides means for excluding the effects of reflectivity which can vary over four orders of magnitude on patterned wafers. The height signal, so obtained, is used to drive a PZT stage to a nominal height position in closed loop. On patterned wafers, an rms height accuracy of better than 0.1 μm has been achieved in 20-Hz bandwidth.

A new kind of structured-lighting surface sensor based on computer vision is presented. The sensor can be used to complete dimensional measurements in an industrial environment with the help of smart calibration processes and image algorithms. The mathematical model and calibration techniques for the sensor are described in detail. In the local calibration, termed the differential method, structured parameters and the local coordinate system of the sensor are determined. Subsequently, a global calibration process is introduced briefly. As an application, a sample vision inspection system is built for checking dimensions on the left sideframe of a body-in-white (BIW). An automotive BIW is an assembled body before insertion of door, windshield, hood, decklid, and fender.

We describe research carried out to investigate a stereoscopic line-scan system for the extraction of 3-D coordinate information from a scene of interest. Initial work involved analyzing the operating characteristics of a line-scan device for the production of 2-D images. Following this, a theoretical appraisal was undertaken of a sensor in a stereoscopic arrangement, and a mathematical model was derived for the calibration of a novel camera system. Algorithms to determine the 3-D relationship of points in the object space were developed using this model. To test the suitability of the model, a complete stereoscopic line-scan system was constructed. Experiments were conducted with the stereo camera to establish the accuracy that is achieved with such a system using the developed algorithms. The results indicate that the relative position of points in the object space could be determined to an accuracy of less than 1 mm at a range of 1.5 m.

The possibility of applying the modulation function derived from the pair model of a reflective fiber sensor to the actual sensors composed of a fiber bundle is analyzed, and the related methods are proposed. For sensors with a random fiber arrangement, a concept of average distance between all the emitting and receiving fibers is introduced, and the average fiber distance in a sensor probe with circular cross section is calculated using the numerical integration method. Problems that emerge when the distance between the probe tip and the reflecting surface is small are considered, and the methods of calculating the modulation function for these situations are proposed.

The resolution capability of imaging systems is affected by blur resulting from vibration and motion during the exposure. This blur is often more severe than electronic and optical resolution limitations inherent in the system. Such image quality degradation must be considered when dealing with the development and analysis of automatic target recognition (ATR) systems. This research analyzes the influence of image vibrations and motion on the probability of acquiring a target with an ATR system. The analysis includes accepted metrics that characterize the relationship existing between the target and its background. A high level of correlation is expected between these factors and the probability of target detection permitting efficient performance in the prediction and evaluation of any ATR system. Such correlations are considered here in the presence of sensor motion and vibration and situations are considered in which the probability of recognition is improved by the motion, despite the blur. The results of this research can be implemented in military applications as well as in developing image restoration procedures for image-blur conditions.

It is necessary for a modern spectrophotometry system to possess such properties as high measuring accuracy, fast working speed, uniform spectral response in the whole wavelength band, low consumption of power, little heat accruing while working, small size and low weight, etc. To meet all these needs, a spectrophotometry system today usually employs the so-called dual-beam channel configuration in which one sampling channel with another compensatory channel and a cold light source such as a xenon flash lamp, which usually causes an increase of the complexity in the system configurations. To further simplify the instrument configuration, we put forward a new dual-channel compensatory model called the integral compensatory model. Our experimental results show that using this new model, a spectrophotometry system cannot only be greatly simplified in its hardware but can also achieve highly accurate measurements.

The influence of the deposition rate on the microstructure and hardness of TiO₂-SiO₂ and TiO₂-MgF₂ composites and their single component films prepared by reactive ion-assisted coevaporation in the deposition rate range 0.14 to 2 nm/s are investigated using an x-ray diffractometer, a transmission electron microscope, and a microhardness tester. It is found that the hardness of the composite films and their single components increase with a decreasing deposition rate. However, the hardnesses of TiO₂-SiO₂ and TiO₂-MgF₂ composite films were generally lower than that of pure SiO₂ and MgF₂, respectively, at the same component deposition rate. This indicates that the addition of TiO₂ reduces the hardness of Si02 and MgF2 films. The ultrahigh hardness of pure MgF₂ films deposited by ion assistance at the deposition rate of 0.14 nm/s probably results from the high packing density, low lattice defects, and the small grain size (<20 nm) with the preferred orientation of [110]. Furthermore, the homogeneous dispersion of these hard nanoscale MgF₂ grains within the amorphous TiO₂ matrix causes the hardening of the composite film.

This PDF file contains the editorial “Book Rvw: Optical Fiber Amplifiers, Design and System Applications," by Anders Bjarklev for OE Vol. 34 Issue 10