This PDF file contains the editorial “Editorial: Chinese Optical Society” for OE Vol. 32 Issue 03

Tilt corrector based on a spring-type magnetostrictive actuator (STMA) was investigated for wavefront tilt correction. The STMA is a very efficient type of macroactuator for application in large ground- and space-based adaptive optics. By means of the STMA it is possible to deliver, in a real-time scale (1 to 10 ms), precision displacements in a range up to 100 μm with a 0.1-μm positioning accuracy. On the basis of experimentally investigated static and dynamic characteristics of STMAs the real-time two-coordinate mirror positioning system for precise optical engineering was developed and investigated. A dynamic range of corrected tilts up to 8 arc mm with a frequency range up to 50 Hz delivered by the developed tilt corrector allowed compensation for natural thermoconvectionally induced tilts with accuracy of 0.1 arc sec.

We describe a diode laser frequency control scheme that dynamically locks the laser to an absorption resonance line while simultaneously allowing the quantitative measure of absorption strengths as weak as a few parts in 10⁶. The method exploits a novel modulation scheme, and is capable of locking the laser to both stable and transient species in an electrically noisy environment such as that found in plasma etching reactors. We present an experimental demonstration using a lead salt diode laser operating near an rt plasma etching diode reactor and in an industrial-type triode reactor.

A resonant cavity electro-optic phase modulator has been designed and implemented to operate at a data rate of 10 Mbps. The modulator consists of an electro-optic crystal located in a highly resonant cavity. The cavity is electro-optically switched on and off resonance, and the phase dispersion nearthe cavity resonance provides the output phase modulation. The performance of the modulator was measured by first heterodyne-detecting the signal to an intermediate frequency and then measuring the spectral characteristics using an rf spectrum analyzer. The measured phase shift is shown to be in good agreement with the theoretical predictions. Further theoretical analysis shows that the design of the modulator can be scaled to operate at 100 Mbps.

A simple expression for determining the time response limitations of Fabry-Pérot etalons as a function of the cavity finesse and cavity length is developed. This expression is confirmed by simulations ofthe interactions of short pulses with etalons, as calculated by frequency analysis, and shows that Fabry-Pérot devices can be used with picosecond or shorter pulses, as long as adequate consideration is given to the etalon bandwidth (as determined by the finesse and effective cavity length). For Gires-Tournois etalons, there are stronger limitations on the maximum finesse and effective cavity length because the device operates only on the phase components of the pulse and can cause more severe distortions than the Fabry-Pérot, in which the primary source of pulse distortion is reflection of the edge frequencies of the pulse.

unique optical associative memory architecture is presented that combines the optical processing environment of a Fabry-Pérot confocal resonator with the dynamic storage and recall properties of volume holograms. The confocal resonator reduces the size and complexity of previous associative memory architectures by folding a large number of discrete optical components into an integrated, compact optical processing environment. Experimental results demonstrate the system is capable of recalling a complete object from memory when presented with partial information about the object. A Fourier optics model of the system's operation shows it implements a spatially continuous version of a discrete, binary Hopfield neural network associative memory.

The cross coupling of the polarization modes of polarization-maintaining fibers is measured in a temperature control chamber. The temperature dependence of the extinction ratio is analyzed in terms of a steady temperature gradient and a fluctuating component that are experimentally controlled. The consistency of the experimental results with the theoretical analysis in this study can be used to limit the applications of fibers to specific desirable designs. Temperature range for the required accuracy is also addressed.

The application of symmetrical directional couplers or two-mode interference devices to be used as filters in spread spectrum fiber optic communication systems is described. It is shown that such devices act as their own matched filters. This allows their use as encoders and decoders of ultrashort pulses, even in the case of high-bandwidth input signals.

An integrating-cavity sensor for temperature measurement of the steel sheet in a continuous annealing furnace is described. The sensor includes a fiber optic cable for transmission of the infrared radiation from the sensor head within the furnace to the double-wavelength detection unit located outside the furnace. The sensor head includes a reflecting conical cavity positioned above the steel sheet to increase, and thus stabilize, the effective infrared emissivity of the sheet surface as well as to reduce spurious reflections from other sources within the furnace. The fiber optic cable is both decentered and tilted with respect to the cavity axis to minimize straight-reflection losses through the fiber cable gate. Preliminary results after in-furnace installation are described.

A procedure to mathematically model and design embedded interferometric optical sensors to measure more than one load is given for the case of an axisymmetric member. This design can avoid the ill-conditioning problems of the transfer functions found in other multiparameter sensors, and the coefficients of the transfer functions are defined analytically rather than experimentally. The sensor with two active fibers, generalizing acoustical sensors, measures external radial pressure and external axial stress. The device sensitivity, which differs from optimizing the optical response of a single embedded fiber, is defined, and methods are obtained to optimize this sensitivity by adding a coating layer to each embedded fiber. The relative effect of strains that are transverse and parallel to the fiber is predicted. The effect on strain response of varying coating material properties is modeled. Strain concentrations created by the presence of the fiber are computed, and the separation required between fibers in the sensor is determined. Approximate models based on the small diameter of the fiber and its coating compared to that of the body overlook these strain concentrations. The design of an embedded fiber optic load sensor depends both on the mechanical properties of the body in which it is embedded and the loads to be monitored.

This paper treats some of the general requirements of optoelectronic instrumentation systems for fiber optic chemical sensors and points out how nonimaging optical elements can be used to meet those requirements. Passive fiber optic chemical sensors, specifically remote spectroscopic absorbance, fluorescence, and Raman systems are discussed. The operation of nonimaging optics (NIOs) is explained, as are applications of these optical elements in fiber illumination, sample light collection, and filtering subsystems. Optical signal detection methodologies are also presented. The above topics are treated in an introductory or "tutorial" fashion.

The holo-diagram is a diagram originally designed as a tool for teaching the making and evaluation of holograms. It was soon found to include much more general uses than first expected. During the 20 years since its introduction this diagram has been applied to explain many different fields, such as holography, interferometry, diffraction, Fermat's principle, light-in-flight recordings, three-dimensional measurements with ultrashort light pulses, and the special theory of relativity.

novel tunable wave division multiuse (WDM) device has been formed on a microscope slide substrate. On the surface of the substrate is a K-ion-exchanged directional coupler with zero separation. On the top of the interaction region a Ti-film heater is placed. The operational behavior of the device is controlled by thermo-optical effect, and thus by the current through the Ti-film heater. Operational wavelengths designed for the device are 0.85 and 0.6328 μm. The measured results show that the device has predicted characteristics and thatthe design is reasonable.

Interest in the liquid crystal television (LCTV) kinoform has been reported recently by several investigators. The technique requires a modulation depth of about 2π, which most of the commercially available LCTVs cannot attain. We discuss an experimental study of generating an LCTV kinoform in which the the modulation depth is limited by π. The major drawbacks of the ir phase variation are that, compared with 2π variation, it reduces the diffraction efficiency as well as the space bandwidth product to a degree of about one-fourth. Verification of these findings is reported.

Microcreep deformations in pure copper specimens are studied by a new moiré method. In this method, a fine micrograting prepared by electron beam lithography is used as a model grating, and a scanning exposure ofthe primary electron beam in a scanning electron microscope (SEM) as a master grating. The scanning exposure of the electron beam on the specimen with the model grating produces moiré fringes of bright and dark lines formed in response to the different amounts of the emitted secondary electrons for each primary electron. This new method makes it possible to obtain a clear and fine moiré fringe without an image-processing system and to observe the moiré fringe pattern and the SEM image at the same time. By this method, the inhomogeneous microcreep deformations such as grain boundary sliding, coarse slip, and localized strain are measured with high accuracy. It is confirmed that the creep strain is nonuniform even in the same grain and the strain distribution is caused mainly by the grain boundary sliding.

The effects of object-to-image vibration are studied with the purpose to quantitatively define the maximum acceptable vibration level as a function of resolution, linewidth control, exposure and focus toterances, proximity condition, and illumination coherence. The exposure-defocus trees and windows of optically projected images are used to derive the vibration tolerance as well as the optimum exposure as a function of vibration amplitude. Normalized variables for resolution, focus, and exposure are used so that the results are universally applicable for any given diffraction-limited lens system. Time histograms are used instead of the frequency spectrum to unambiguously define a given vibration environment. The results are plotted in depth of focus as a function of the vibration amplitude. Resolution ranges from 0.48 to 1.2 λ/NA with the aperture ratio σ = 0.4, 0.6, and 0.8. The optimum exposure for maximum depth of focus is similarly plotted.

The design for a rotationally symmetric four-mirror optical system with reduction magnification 5 x for deep UV (λ = 248 nm of a KrF excimer laser) submicrometer lithography is developed. Initially by using the paraxial quantities, numerical solutions are found for the system, which is free from the four off-axial third-order aberrations-coma, astigmatism, field curvature, and distortion. Aspherization is carried out to the spherical mirror surfaces to reduce the axial and residual off-axial higher order aberrations. The numerical aperture of the final system is as large as 0.38, which gives a Rayleigh resolution of 0.4 μm and hence is useful in submicrometer lithographic applications.

The plasma reflectivity edge in the infrared reflectivity spectrum measured on a narrow-gap semiconductor HgCdTe has been found to be very sensitive to the variation of carrier concentration under certain circumstance, based on which a new way of infrared modulation is studied, where the estimated modulation gain in power is impressively high. Thus, infrared radiation in far- and mid-infrared can be effectively modulated by electromagnetic waves with shorter wavelengths, and hence a less sensitive room-temperature infrared detector could be as sensitive as the existing cooled infrared detectors. The suggested new optoelectronic device, which can be termed an optical transistor, working with light beams instead of electronic currents, is quite promising for fiber communication and infrared detection as well as for investigating the relaxation processes of excess carriers in semiconductors. The detectivity for the plasma-edge detector, which is a detector equipped with an optical transistor, is calculated.

Front surface metal mirrors need protection of the inherently fragile metal film deposited on a glass substrate. Conventional evaporated dielectric thin-film overcoats provide limited protection because of their less than dense packing. These films usually have a columnar structure with voids between the columns. The voids give access to the underlying metal film for humidity and corrosive gases or liquids. Some progress in developing better coatings was made in the early 1980s with ion-assisted deposition. Front surface aluminum mirrors with dielectric thin films deposited by reactive low-voltage ion plating have a still higher survival time, by a factor of up to 3 under comparable test conditions. The transmission of our best samples increased to only 10% when immersed in 0.2 M NaOH for 20 h. By comparison, an unprotected aluminum film dissolves in less than 5 mm. Electron beam evaporated dielectric coatings provide protection for about 1 .5 to 2 h in the same test solution. The reason for the significant improvement brought about by reactive low-voltage ion plating deposition, and its advantage for large-scale production is discussed.

Mechanisms have been investigated for increasing the abundance of atomic oxygen in the process environment during reactive low-voltage ion plating, a plasma-assisted evaporation process. Feeding several percent of nitrogen into the coating chamber led to enhanced oxidation and consequential reduction of residual optical absorption of ion-plated oxide films of tantala.

We compare computer simulation results of optical correlator performance using synthetic discriminantfunction filters encoded in binary phase versus ternary phase and amplitude for distortion-tolerant pattern recognition. We examine two different ternary filter formulations designed to enhance discrimination and SNR. The simulated situation is for very similar in-class and out-of-class images, which makes discrimination between the two sets difficult. The ultimate performance criterion of interest is the probability of correct identification in the presence of image noise, which we address as a function ofthe range of distortion tolerance offered by the filters. We find that the ternary filters offer improved system performance and greater possible distortion range in comparison to the binary filters, and in particular that the ternary filters with a region of support designed to enhance SNR have the best performance for the image sets studied here. Knowledge of the out-of-class images allows the filter designer to create filters that maximize the probability of correct identification. We present numerical examples of this performance figure for two sets of training images.

It is proposed that the primary standards of length and time have now reached a sufficient level of maturity that they may be removed from the standards laboratories and used directly for measurement calibration with minimal recourse to the use of intermediate secondary standards. In particular, if a measurement can be configured to give a time-related output such as decay time, time of flight (TOF), frequency, or phase shift, then direct traceability to the primary atomic clock standard can be realized through use of the LORAN C or global position satellite systems. Twelve illustrative examples are considered covering a wide range of optical and spectroscopic measurements. This approach is then extended to mass, the remaining primary standard that is not currently photon based. An optical definition of mass is realizable in terms of length and time through the angular momentum properties of the photon measured using the torsion balance. The constant 2π/h gives the circularly polarized photon flux required to produce a torque of 1 N . m from which mass may be derived in terms of the mechanical moment of inertia. The need to distinguish the sign as well as the magnitude ofthe photon angular momentum then suggests that the unit of time should also have a sign. This sign distinguishes the roles of left and right circularly polarized light for matter and antimatter.

The self-pumped phase conjugation in strontium barium niobate (SBN) crystal is demonstrated by causing the laser beam to enter into the crystal from negative c face. Comparison is made between the experimental results and those obtained by the conventional configuration. The analysis and discussion are also presented.

Optical absorption measurements were used to study the optical properties of semi-insulating polycrystalline silicon (SIPOS) with different levels of oxygen dopings and a variety of annealing conditions. The optical properties of SIPOS were found to be closely related to the SIPOS microstructure. The absorption coefficient in SIPOS films with a high oxygen content displays a blue shift. From the absorption edge measurements, it has been observed that more band-tail states were introduced forthe higher oxygen contentsamples. During the heat-annealing processes, changes occur in the absorption spectra of SIPOS: the absorption coefficient of SIPOS displays a blue shift, whereas after high-temperature (T > 900°C) treatments, the absorption coefficient of SIPOS shows a red shift. These features of the optical properties of SIPOS are interpreted as the contribution of the distribution of Si-O bonds in the films and the recrystallization of SIPOS during low-temperature and high-temperature annealing processes, respectively.

The measurement requirements of fifth-place refractometers based on the critical angle condition are analyzed. It is shown that the reference prism geometry limits the working interval of these instruments and that polarized light can be used to improve sensitivity.

A method is presented for the remote sounding of the mixing ratio of carbon dioxide in the atmosphere from a satellite, including the inversion method and preliminary calculation results. The results indicate that the measurement accuracy of the mixing ratio of carbon dioxide in 0.25 ppm, calculated according to volume, in ground field of view of 1127 x 1162 km² for an instrument such as the HIRS-2 on the U.S. National Oceanographic and Atmospheric Administration meteorological satellite.

A study is made of p-type HgCdTe surface passivation with ZnS. Measurements of capacitance-voltage characteristics for metal insulator semiconductor (MIS) devices show that the interface electrical properties strongly depend on the surface preparation. Under some appropriate surface pretreatment, the fixed interface charge density can be lowered to near -1 x 10¹¹ cm^-2, and the slow trap density can be less than 1 x 10¹¹ cm^-2, but the interface trap density is still as high as 10¹² cm^-2 eV^-1. Experimental results are discussed.

A variable time-delay system for broadband phased array receiving and other transversal filtering applications is presented. The approach uses a segmented mirror device (SMD) and a linear fiber array to realize a quantized variable delay line. The use of the SMD allows for extremely high packing density withoutthe large losses usually associated with switched fiber schemes. The system presented is compatible with a SMD-based true time-delay transmitter that has been developed. Experimental results are presented.

We have improved the stability and temporal response of the laser speckle strain gauge that detects strain from speckle displacement caused by surface deformation. In the gauge, a narrow laser beam is incident on a diffuse surface, and speckle patterns appearing in the light scattered through the symmetrical angles are detected by a pair of linear image sensors. Speckle displacement is derived by a real-time correlator as the peak of the cross correlation between the current frame and a reference frame of the sensor driven at 1000 frames per second. The reference frame is fixed until the correlation peak becomes lower than a threshold. Using a pair of image sensors, followed by the correlators, and a laser of output power of a few tens of milliwatts, we could measure dynamic strain of polymer films at the frequency between a fraction of hertz and 100 Hz. The resolution of the gauge, which only depends on geometry of the optical system and the sensor pitch, is a few tens of microstrains. The upper limit of the measurement can be extended arbitrarily because small incremental strain is integrated.

Transmission images of highly scattering objects can be produced by recording and discriminating between the times of flight of transmitted photons. High spatial resolution requires a detector with high temporal resolution, and a streak camera has proven to be particularly effective. However, since the aperture of a streak camera is necessarily a narrow slit, the camera must consecutively sample different regions of the object in order to generate a two-dimensional image. A method is described that involves sampling a series of lines across an object. The benefits and limitations of this method are discussed, and the results of an experiment are presented that illustrate the inherent spatial resolution. Our conclusion is that the line scan method is more efficient than a point scan method in terms of light collection and probably need not result in a substantial decrease in spatial resolution.

A new method of data processing is presented for a time-resolved optical computer tomography (CT) imaging of a strongly scattering and weakly absorbing medium, similar to a living body. A fundamental experiment and a numerical calculation of time-resolved spectroscopy are conducted to validate the proposed temporally extrapolated absorbance concept. A numerical simulation shows a possibility of a new method of time-resolved optical CT imaging. A reference cylinder is filled with a uniformly scattering medium, and an object cylinder has a weakly absorbing portion in addition to the uniform scattering in the reference cylinder. The extrapolated values of the difference in the absorbance to the shortest time of flight reduce to the line integrals of the difference in the absorption coefficient along the incident beam lines. By this process, the information of the weak absorption is extracted from the signals subject to the strong scattering, and the extrapolated values provide a set of projection data for a conventional filtered back projection of the CT reconstruction algorithm. The reconstructed image reproduces the difference in the absorption coefficient between the object and the reference with a reasonable accuracy and spatial resolution. This type of image describing the absorption change is useful to noninvasive diagnostics of the oxygen metabolism inside bodies.

This PDF file contains the editorial “Book Rvw: Optical Computing, an Introduction," by Mohammad A. Karim and Abdul A.S. Awwal for OE Vol. 32 Issue 03

This PDF file contains the editorial “Book Rvw: Contemporary Nonlinear Optics," by Govind P. Agrawal and Robert W. Boyd for OE Vol. 32 Issue 03