Optical: systems and elements – Optical modulator – Light wave temporal modulation
Patent
1995-08-09
1997-04-29
Hellner, Mark
Optical: systems and elements
Optical modulator
Light wave temporal modulation
359290, H01S 300
Patent
active
056254849
DESCRIPTION:
BRIEF SUMMARY
The invention refers to an optical modulator allowing to modulate a coherent light beam by an optical signal.
BACKGROUND OF THE INVENTION
It is known that an optical signal can be modulated by an electrical signal, for example a Pockels cell, or by a mechanical signal, such as a diaphragm or a pivoting mirror. Since light has an increasing importance in telecommunications and in data processing, methods are required by which an optical signal can be modulated by another optical signal. However, the results obtained by photo-refractive crystals on laboratory scale must still to be confirmed in practice.
The invention aims to propose an optical modulator, the modulating signal of which is also optical. According to the invention, this aim is achieved by an optical modulator such as defined in the main claim.
Preferred features of an embodiment of this modulator are defined in the secondary claims.
The invention will now be described more in detail by means of three figures.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 shows in perspective the disposition of the elements constituting the modulator according to the invention.
FIG. 2 shows two substrates of an optical cavity used in the detector shown in FIG. 1.
FIG. 3 shows schematically how the three-dimensional interferometric lattices are recorded on the substrates of the optical cavity.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The modulator according to FIG. 1 comprises a laser generator 1 which emits a coherent light beam 2 of a very reduced transversal dimension towards an optical cavity 3. The nature of this optical cavity will be described later on in more detail by means of FIG. 2. The side of this cavity which is opposed to that which is hit by the beam 2 is susceptible to be illuminated by a modulation source 4, which might be constituted by a source of white light or a coherent light source.
As can be seen in FIG. 2, the optical cavity 2 comprises two holographic plates 8 and 9, each constituted by a glass substrate which carries on one surface a photographic emulsion, on which a three-dimensional interferometric lattice has previously been recorded, such as a so-called holographic lens. The two recordings are identical. The emulsions are, for one of the plates 8, disposed on the surface regarding the other plate 9, whereas for this plate 9, the emulsion is disposed on the side opposite to the first plate 8. The two plates have a thickness of about 1 to 4 mm and a rectangular or square outer shape, the length of one side thereof being between 10 and 40 cm. In FIG. 2, the two plates have been shown at a mutual distance, in order to show more clearly the disposition of the emulsions, but in reality, the plates are applied against one another, leaving only very little air between the two substrates. This small quantity of air defines together with the plates the real optical cavity.
FIG. 3 shows schematically how the holographic lenses are recorded on a substrate 15 carrying a photo-emulsion. A laser 11 sends a coherent beam, possibly via a mirror 12, on a beam separator 13 constituted by a semi-reflecting mirror. One of the beams is directly pointed via a spatial filter 14 onto the substrate 15, whereas the other one is reflected by a second mirror 12' towards a second spatial filter 14' in order to reach the substrate 15 according to a different angle of incidence. The spherical waves of the diverging beams 16 and 16' create in cooperation the three-dimensional lattice in the emulsion on the substrate 15 which has then to be developed and fixed. The two plates 8 and 9 of FIG. 2 are prepared in the same way and are then assembled for constituting the optical cavity 3 of FIG. 1.
When the beam 2 is sent onto the optical cavity, a micro-lattice of interference fringes is locally created on the air layer present between the two plates, these fringes being displayed by reflection of the laser light 1 of the cavity 3 on a display screen 7. By then applying a modulating signal from the source 4 onto the rear side of said cavity 3, either in the shape o
REFERENCES:
patent: 4497544 (1985-02-01), Mitchell et al.
European Economic Community (CEE)
Hellner Mark
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