Optical: systems and elements – Optical modulator – Light wave temporal modulation
Patent
1994-05-02
1997-07-29
Epps, Georgia Y.
Optical: systems and elements
Optical modulator
Light wave temporal modulation
359294, G02B 2600
Patent
active
056526725
DESCRIPTION:
BRIEF SUMMARY
The invention relates to an optical modulation device in which a visible or near-visible light wave is modulated spatially with the aid of a plurality of cells each deformable under the effect of an electrical voltage applied to their terminals. The invention relates more particularly to means for facilitating the control of such deformable cells.
In the present description, the expression "cells deformable under the effect of an electrical voltage" is intended to define cells which exhibit a variation in dimension as a function of a voltage which is applied to them, and cells made up of piezoelectric materials (that is to say exhibiting the inverse piezoelectric effect) should be considered as being in this category, as should cells made up from different materials, presented, for example, in the form of films and obeying different effects, whenever a deformation can also be noted in that case, especially by local variation in thickness, due to the application of a voltage.
Cells deformable under the effect of a voltage are used in various fields, and in particular in that of imagery through a turbulent atmosphere, especially in astronomy. In such cases, it may be necessary spatially to correct the phase of the optical wave front originating from the object which it is desired to observe, in order to reform a correct image of the latter.
It is known for this purpose to reflect the wave front by a mirror locally exhibiting differences with respect to a mean mirror plane; this is done so as to introduce local phase modifications and thus to compensate for the phase distortions introduced by passing through the turbulent atmosphere. Such a mirror is called "modulation mirror" in the remainder of the description.
The phase corrections .to be applied to the wave front are determined by a wave front sensor system, conventional in itself, such as, for example, that which is known by the name of "HARTEMAN interferometer"; this apparatus was developed in FRANCE by the l'Office National d'Etudes et Recherches Aerospatiales (O.N.E.R.A.).
FIG. 1 diagrammatically shows a conventional installation intended to correct the phase of a wave front F O with the aid of a sensor system 2 and of a modulation mirror 3 such as defined above.
The wave front F O is propagating in the direction shown by the arrow 1 towards the modulation mirror 3 and, before arriving at the latter, it is partially deflected towards the sensor system 2. The latter delivers signals S.C. in response, relating to the phase corrections to be performed. These correction signals SC are applied to a control device 4, which itself controls the modulation mirror 3.
The wave O R reflected by the modulator mirror 3 represents the corrected wave.
It is usual to use cells made of piezoelectric materials in order to modify the planarity of the reflecting surface 6 of the modulation mirror 3, as a function of the phase corrections to be applied. A conventional configuration consists, for example, in forming the reflecting surface 6 by a flexible film 7, for example of elastomer, on which a metallized layer (not represented) is arranged, intended to form the reflecting surface 6; this film is applied by a face opposite that which constitutes the reflecting surface 6, over a surface consisting of extremities forming the movable faces FM of a number n of piezoelectric cells CP1, CP2, . . . , CPn. The opposite face or extremity of each cell constitutes a fixed face FF which is mechanically integral with a plate 8. The plate 8 may be electrically conducting and thus constitute an electrode common to all the piezoelectric cells CP1 to CPn. In this case, each of the movable faces FM includes an individual electrode I for the individual control of each piezoelectric cell; an individual electrode by the use of which each cell is fixed, for example by bonding, to the flexible film 7.
In this configuration, each piezoelectric cell plays the role of a motor: for a given point of the reflecting surface 6, the distance D between this point and the plate 8 is related to the lengt
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Docket No. 154-1770-2 PCT, U.S. application No. 07/859,707, filed Nov. 8, 1991, now U.S. Pat. No. 5,535,041.
Huignard Jean-Pierre
Loiseaux Brigitte
Puech Claude
"Thomson-CSF"
Epps Georgia Y.
Robbins Thomas
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