All optical image processing and pattern recognition apparatus u

Optical: systems and elements – Optical modulator – Light wave temporal modulation

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Details

359299, 359321, 359560, 359561, 382 31, 382 42, 365119, G02F 100, G02B 2746, G06K 974, G06E 300

Patent

active

052047709

DESCRIPTION:

BRIEF SUMMARY
BACKGROUND OF THE INVENTION

1. Technical Field
The present invention relates to an optical, high-speed image processing apparatus, and more particularly to an all optical image processing and pattern recognition apparatus using stimulated photon echoes, which can process quickly a number of pieces of image information in real time.
2Background Art
High-speed real time processing of two-dimensional images has a variety of applications in which large numbers of images must be stored and analyzed. These include robotic vision, satellite remote sensing, medical image analysis, artificial intelligence and pattern recognition. Optical image processing is promising for two principal reasons: parallel processing capability and potentially ultrafast speed. Among the existing techniques for two-dimensional image processing is a stimulated photon echo technique in conjunction with optical Fourier transformation.


(1) Stimulated Photon Echo

Stimulated photon echo is achieved when optical pulses are sequentially incident into a stimulated photon echo medium, the line shape function (absorption characteristic) of which is illustrated in FIG. 2. FIG. 2 shows that a photon echo medium (a rare earth ion doped dielectric crystal) includes many atoms having a narrow homogeneous broadening .DELTA..nu..sub.H, and such atoms integrally constitute an inhomogeneous broadening .DELTA..nu..sub.IH. When optical pulses P1, P2 and P3 (see FIGS. 1 and 3), the energy of which is within the stable absorption range corresponding to the inhomogeneous broadening are incident into such a medium at time t.sub.1, t.sub.2 and t.sub.3, respectively, a photon echo Pe occurs at time t.sub.4 subsequent to the time t.sub.3 (see FIG. 3).
Time t.sub.4 which the photon echo Pe occurs, is .DELTA.t (=t.sub.2 -t.sub.1) after t.sub.3, and hence, t.sub.4 -t.sub.3 =t.sub.2 -t.sub.1. The width .DELTA..tau. of the pulses incident to the photon echo medium has the following relationship with the inhomogeneous broadening .DELTA..nu..sub.IH and the homogeneous broadening .DELTA..nu..sub.H : =1/.DELTA..nu..sub.H) after the incident of the optical pulse P1. The time T.sub.2 is the coherence-decay time of absorption transition during which the photon echo medium keeps coherency of the incident light. On the other hand, the optical pulse P3 must be incident within time T.sub.1 after the incidence of the optical pulse P2. The time T.sub.1 is the population-decay time of the absorption transition in which the photon echo medium returns to its thermal equilibrium state. Thus, the incident time of the optical pulses P1 to P3 must satisfy the relationship photon echo medium during the population-decay time T.sub.1.
In this condition, time quadrature .theta.e of the amplitude of the photon echo pulse Pe is given by the following equation when the incident pulse intensity is weak: .theta..sub.3, (3) and .epsilon..sub.i are the electric fields of respective optical pulses, and .mu. is the electric dipole moment of the ion in the photon echo medium. The intensity of the photon echo pulse Pe is proportional to the product of the incident pulses P1, P2 and P3 because the photon echo occurs in the third-order nonlinear interaction. Furthermore, it is seen that the optical echo signal the waveform of which is similar to that of the optical pulse P2 can be obtained when the optical pulses P1 and P3 are similar to the delta function having no image information. Thus, the photon echo pulse similar to the optical pulse P2 stored in the photon echo medium can be read out at time t.sub.4. The optical pulses P1, P2 and P3, and the echo pulse Pe must satisfy the phase-matching condition (momentum conservation equation) expressed by pulses. The echo pulse Pe takes place in the direction to satisfy the phase-matching condition.
Examples of media having a wide inhomogeneous broadening of the absorption transition are shown in FIG. 4 and the following Table:


TABLE ______________________________________ Population-decay time (T.sub.1) and coherence-decay time (T.sub.2) for rare earth

REFERENCES:
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patent: 3766498 (1973-10-01), Brewer et al.
patent: 4321550 (1982-03-01), Evtuhov
patent: 4479199 (1984-10-01), Friedlander et al.
patent: 4640618 (1987-02-01), Tracy et al.
patent: 4726639 (1988-02-01), Brody
patent: 4739496 (1988-04-01), Marom et al.
patent: 4750153 (1988-06-01), Owechko et al.
patent: 4767195 (1988-08-01), Pepper
patent: 4948212 (1990-08-01), Cheng et al.

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