Modal Interference Techniques for Strain Detection in Few-mode Optical Fibers

Interference between the modes of an optical fiber results in specific intensity patterns which can be modulated as a function of disturbances in the optical fiber system. These modulation effects are a direct result of the difference in propagation constants of the constituent modes. In this presentation it is shown how the modulated intensity patterns created by the interference of specific mode groups in few-mode optical fibers (V \u3c 5.0) can be used to detect strain. A detailed discussion of the modal phenomena responsible for the observed strain induced pattern modulation is given and it is shown that strain detection sensitivities on the order of 10-9 can be expected. Data taken during the evaluation of an actual experimental strain detection system based on the developed theory is also presented

Review: \u27Theory of Dielectric Optical Waveguides,\u27 2nd edition, by Dietrich Marcuse

I suppose I ought to say up front that while preparing this review I often found myself feeling very much like a student evaluating his teacher. After all, it was, in part, the first edition of Dietrich Marcuse\u27s Theory of Dielectric Optical Waveguides (among a handful of other similar texts) from which I first studied the principles of optical waveguide theory under the demanding, yet patient and graceful guidance of Dr. Ahmad Safaai-Jazi. Thus with the utmost respect for a teacher whom I have never met, I shall try to faithfully share my thoughts and feelings regarding the second edition of the Theory of Dielectric Optical Waveguides

Investigation of Real-Time Optical Scanning Holography

Real-time holographic recording using an optical heterodyne scanning technique was proposed by Poon in 1985. The first part of this dissertation provides a detailed theoretical treatment of the technique, based on a Gaussian beam analysis. Topics to be addressed include the derivations of the optical transfer function (OTF) and impulse response of the scanning holographic recording system, reconstructed image resolution and magnification, methods of carrier frequency hologram generation and experimental verification of the recording technique based on careful measurements of a hologram corresponding to a simple transmissive slit. Furthermore, computer simulations are presented pertaining to the incoherent nature of the scanning holographic process and it is shown that this new technique can be used to reduce the effects of bias buildup common in conventional incoherent holographic methods. The reconstruction of holograms generated by the heterodyne scanning technique is then considered in the second part of the dissertation. The primary concentration is on real-time reconstruction using an electron beam addressed spatial light modulator (EBSLM). For comparison, experimental coherent reconstruction methods are presented as well. Additional topics to be addressed are the spatial frequency limitations of the EBSLM and the derivation of the overall incoherent point spread function (PSF) for the holographic imaging (recording/reconstruction) system. Based upon the derived overall PSF, the reconstructed real image of a simple slit object is formulated, compared to, and shown to be consistent with experimental observations

The Physics of Fire by Friction

In what follows I will attempt to produce a rigorous, macroscopic, time averaged model of the process of creating fire by friction – up to the point of initial ember formation. I will employ reasonable, practical approximations with the goal of developing mathematical results that are experimentally verifiable. Although force, velocity, pressure and the like are actually vector quantities, due to the symmetry of the problem I will perform a scalar analysis only. Also, to simplify the analysis I will assume that the assortment of variables we will encounter are independent. Mostly this assumption is valid, though on occasion I will point out where the assumption is, or may be weak. I will also occasionally point out where further research and analysis may be of interest to pursue. There are, of course, a variety of methods for creating fire by friction. This article will focus exclusively on fire drills with solid rotating spindles. The initial analysis will focus on the bow drill, though near the end I’ll describe some modifications that will make the models I’ll develop appropriate for the pump drill as well. I have made no attempt to model the fire thong, fire saw, fire plow or any other method of fire by friction

Review: \u27Optical Fiber Communications\u27 (2nd edition), by Gerd Keiser

If first impressions are worth anything (and they usually are), I would have to admit that my first impression of the second edition of Gerd Keiser\u27s now popular text Optical Fiber Communications was quite good. My compliments are hereby extended to the publisher for choosing a rather handsome cover and dust jacket. It stands in strong contrast to the text\u27s first edition, which still ranks as probably the ugliest book I own, with color choices ranging from dull cream and baby blue to pale pink! I am now happy to say that this older version has been discretely·retired to the lower reaches of my furthest office bookshelf, down near my few remaining college texts on psychology and chemistry and a long-forgotten copy of David Singmaster\u27s classic Notes on Rubik\u27s Magic Cube

Review: \u27Integrated Optics: Design and Modeling,\u27 by Reinhard Marz

My overall impression is that Integrated Optics: Design and Modeling will make a fine addition to almost anyone\u27s collection of books on integrated optics. It will, however, serve its readers better as a reference book than as a text from which to first learn the basic concepts of integrated optics. I say this because the book is written at a fairly sophisticated technical level, though the author often moves rather quickly to the bottom line without providing material much beyond what is first necessary to introduce a problem or concept, and then a statement of the results and/or implications. It seems that the reader is assumed to have the necessary background in mathematics, quantum mechanics, and waveguide electromagnetics to fill in the blanks. An uninitiated reader will likely find this book both disappointing and frustrating. Nevertheless, Integrated Optics contains lots of useful and interesting information for the skilled engineer interested in designing and/or modeling integrated waveguide devices and structures

Interferometric and Holographic Imaging of Surface-Breaking Cracks

Two advanced nondestructive evaluation systems are developed for imaging surface-breaking cracks in aerospace materials. The systems use scanning heterodyne interferometry and frequency-translated holography principles to image ultrasonic displacement fields on material surfaces with high resolution and sensitivity. Surface-breaking cracks are detected and characterized by visualizing near-field ultrasonic scattering processes, which in turn results in local intensification of ultrasonic displacement fields in the immediate vicinity of a crack. The local intensification permits cracks to be easily distinguished from background levels, and creates unique displacement field images that follow the contours and morphology of the cracks with microscopic precision. The interferometric and holographic imaging approaches each provide noncontact and near optical-diffraction-limited measurement capabilities that are essential for probing ultrasonic displacement fields in the immediate vicinity of cracks. Several representative crack-imaging results are provided, along with detailed descriptions of both experimental techniques, and the capabilities and limitations of each method. The resulting systems provide simple yet very powerful tools for evaluating surface-breaking cracks in detail

Index-matched Boundary Techniques for the Elimination of Acoustical Resonances

We extend the principle of optical index of refraction to apply the concept of acoustical index for transverse acoustical wave propagation in strings. The relationship between acoustical index and mass density of the acoustic material is developed. With this theoretical link established, classic index-matching techniques are explored at acoustical boundaries. Proper selection of boundary interface segments leads to the elimination of resonant vibrationalmodes that occur in rigidly supported strings, while maintaining the nonresonant vibration response

Sensitivity Comparison of Ladar Receivers Designed to Detect Glint Targets

We present four receiver designs for a ladar system, based on an optical parametric amplifier, that is designed to collect returns from glint targets. After coupling the return energy into periodically poled lithium niobate, the target backscatter is detected with either an infrared camera or a CCD array. Assuming reasonable detector and system characteristics, the sensitivity of each design is then evaluated by setting the receiver SNR detection threshold equal to one and using the minimum transmitted energy as the figure of merit. Through numerical analysis, we show that an upconversion receiver followed by a visible CCD array offers the best trade-off between sensitivity and practical design for airborne ladar applications

Wide Angle Achromatic Prism Beam Steering for Infrared Countermeasures Applications

The design and analysis of achromatic doublet prisms for use in laser beam steering is presented. The geometric relationships describing the maximum steering angle are given, as are discussions of first- and second-order dispersion reduction. Infrared (IR) material alternatives and optimum IR material characteristics for wide-angle achromatic prism beam steering are also investigated. Sixteen materials in 120 different combinations have been examined to date. For midwave IR applications it is shown that the minimum dispersion currently achievable across the full 2 to 5 μm spectrum is 1.7816 mrad at an average maximum steering angle of 45 deg. This is accomplished using LiF/ZnS doublet prisms. Several issues related to the azimuth and elevation angles into which light is steered as a function of prism rotation angles are also presented