Patrick Meyrueis

Fringe pattern analysis with a parametric method for measurement of absolute distance by a frequency-modulated continuous optical wave technique

Interferometry associated with an external cavity laser of long coherence length and broad wavelength tuning range shows promising features for use in measurement of absolute distance. As far as we know, the processing of the interferometric signals has until now been performed by Fourier analysis or fringe counting. Here we report on the use of an autoregressive model to determine fringe pattern frequencies. This concept was applied to an interferometric device fed by a continuously tunable external-cavity laser diode operating at a central wavelength near 1.5 microm. A standard uncertainty of 4 x 10(-5) without averaging at a distance of 4.7 m was obtained.

Thermoplastic film camera for holographic recording of extended objects in industrial applications

Optimization of a thermoplastic film recording camera and its performance for holography of extended objects are reported. Special corona geometry and accurate control of development heat by constant current heating and high-resolution measurement of the development temperature enable easy recording of reproducible, large aperture holograms. Experimental results for transfer characteristics, diffraction efficiency characteristics, and spatial frequency response are given.

New holistic handwritten word recognition and its application to french legal amount

This paper presents a holistic recognition of handwritten word based on prototype recognition. Its main objective is to arrive at a reduced number of candidates corresponding to a given prototype class and to determine from them the handwritten class to be recognized. The proposed work involves only an accurate extraction and representation of three zones namely; lower, upper and central zones from the off-line cursive word to obtain a descriptor which provides a coarse characterization of word shape. The recognition system is based primarily on the sequential combination of Hopfield model and MLP based classifier for prototype recognition yielding the handwritten recognition. The handwritten words representing the 27 amount classes are clustered in 16 prototypes or models. These prototypes are used as fundamental memories by the Hopfield network that is subsequently fed to MLP for classification. Experimental results carried out on real images of isolated wholly lower case legal amount bank checks written in mixed cursive and discrete style are presented showing an achievement of 86.5 and 80.75 % rate for prototype and handwritten word recognition respectively. They confirm that the proposed approach shows promising performance results and can be successfully used in processing of poor quality bank checks.

Hopfield-multilayer-perceptron serial combination for accurate degraded printed character recognition

Degraded printed character recognition is a hard and ever-present problem in optical character recognition. Previous work has explored serial combination of multilayer perceptron (MLP) and autoassociators networks for printed character recognition. The MLP is used as a first step classifier for its discrimination capability and is not very well suited for rejection. On the other hand, the autoassociator used as a second step classifier is more appropriate when a very small error and rejection are required. Unfortunately, this better behavior with respect to rejection is either paid in terms of rejection error or in terms of computational complexity, particularly when the number of classes is high. In this paper, we propose a serial combination of the Hopfield and MLP networks in order to achieve accurate recognition of degraded printed characters. We introduce a relative distance and use it as a quality measurement of the degraded character, which makes the Hopfield-based classifier very powerful and very well-suited for rejection. This relative distance is compared to a rejection threshold in order to accept or reject the incoming degraded character by the Hopfield model used as a first classifier. Due to its discrimination capability, the MLP network is used as a second classifier to avoid rejection error and to diminish computational complexity. The proposed method is devoted to solving the problem of recognition of single font characters collected from poor quality bank checks. We report experimental results from a comparison of three neural architectures: the Hopfield network, the MLP-based classifier, and the proposed combined architecture. The proposed method is also compared to five other recognition systems. It is shown that the proposed architecture exhibits the best performance, with no significant increase in the computational burden. In this paper, we propose also a bank check processing procedure for account check number (ACN) detection, localization, and character retrieval...

Application of Laser Engineering to Industrial Measurement of Commercialized Diamonds

The development of a system for pricing diamonds, whose price differs greatly for gems of equal weight, must be matched by the development of the techniques of quality control. Until the present time, most of the control relied on human perception. The interaction of laser light, in controlled conditions, with the gem gives enough data to quantify all the commercialized gems.

CSM-autossociators combination for degraded machine printed character recognition

This paper presents an OCR method that combines the complementary similarity measure (CSM) method with a set of autossociators for degraded character recognition. In the serial combination, the first classifier must achieve lower errors and be very well suited for rejection, whereas the second classifier must allow only low errors and rejects. We introduce a rejection criterion mode used as a quality measurement of the degraded character which makes the CSM-based classifier very powerful and very well suited for rejection. We report experimental results for a comparison of three methods: the CSM method, the autoassociator-based classifier and the proposed combined architecture. Experimental results show an achievement of 99.59% of recognition rate on poor quality bank check characters, which confirm that the proposed approach can be successfully used for effective degraded printed character recognition.

Study of the influence of processing baths on the modulation profile of volume holographic gratings

Over the last 20 years, dichromated gelatin has been considered to be the best holographic recording material. However, the non-reproducibility of results in relation to light sensitivity, for a large number of experimental factors, restricted the use of this material. In this work, we consider the refractive index modulation profile and its stability. We propose a mixed method using Kogelniks coupled wave theory (an approximate theory) and an alternative theory of diffraction in modulated media (an exact theory). The aim of this contribution is to use this mixed method in order to study the evolution of the modulation profile in correlation with the modification of the chemical environment during the final stage of processing. In our study we compare the effect of different kinds of final processing baths on the refractive index modulation profile. In order to characterize our holograms we have developed an experimental set-up for diffractive elements analysis. The experimental results are compared with the theoretical ones. For the numerical study we have carried out a complete set of numerical computations by using our own programs. These programs are based on a complete and exact solution of the Maxwell equations.

Brillouin backscattering in fiber optic gyroscope

This paper treats the Brillouin backscattering in a single mode optical fiber and its implications on the Brillouin Ring Laser Gyroscope (BRLG). The BRLG consists of a fiber ring cavity in which stimulated Brillouin scattering is induced and provides two resonant counterpropagating backscattered waves. If this cavity is rotating around its axis, the backscattered waves get different resonant frequencies because of the Sagnac effect. The frequency difference is proportional to the rotation rate (Omega) by inducing a frequency offset between the counterpropagating waves. Some reported Brillouin spectra exhibit several peaks, which means that one pump wave provides at least two backscattered waves with distinguishable frequencies. In order to understand this multi-backscattering and to take advantage of it for the BRLG, we present results of a simulation of the Brillouin backscattering in a single mode optical fiber.

Un nouveau matériau pour le multiplexage holographique sur réseau de fibres optiques

AnalyseLe multiplexage en fréquence par réseau de diffraction permet de réaliser des multiplexeurs pour la transmission sur fibres optiques. Les possibilités de l’holographie ont été validées pour la réalisation de réseaux de ce type. Les matériaux halogéniques cependant limitaient l’efficacité de diffraction et les possibilités de séparation angulaire. Le matériau que nous avons mis au point, dénommé optrigelac, est une gélatine dopée au bichromate d’ammonium. Il permet d’atteindre des efficacités de diffraction proche de la limite théorique de 100 % avec un bruit faible, une sélectivité angulaire et fréquentielle ajustables. Les auteurs décrivent dans cet article les procédés de fabrication, de couchage, de sensibilisation et de développement. Les relations de cause à effet sont explicitées permettant la définition d’une méthodologie de travail fonction des performances finales du réseau désiré.AbstractFrequency multiplexing, using gratings, in optical fiber systems is now well known. The potentials of holography have already been validated for this kind of application. However, the silver halide photosensitive materials limited the diffraction efficiency and also the achievable angular discrimination. The material we have developed, called optrigelac, is a gelatin doped with ammonium dichromate. This material allows high diffraction efficiencies, up to the theoretical limit of 100 %, with low noise and adjustable angular and wavelength selectivity. The coating, sensitizing and development procedures, and a model relating the final hologram properties to a practical working procedure are described.

Principles Of A Switching Extensive Fiber Optic Network

In this paper we discuss a method to achieve expansion of a fiber optic bus on the base of a distributed star configuration. Also, we demonstrate the fundamentals of a fiber optic network with commutation properties that handles high traffic and a large number of subscribers.