Laser with coupled optical waveguides

Details Laser with coupled optical waveguides Laser with coupled optical waveguides

1992-04-28

1994-05-10

Epps, Georgia Y.

Coherent light generators

Particular resonant cavity

Plural cavities

372 50, 372 23, 372 71, 372 70, 385 3, H01S 3082

Patent

active

053115406

DESCRIPTION:

BRIEF SUMMARY
BACKGROUND OF THE INVENTION

The invention relates to coherent optical sources, particularly solid state lasers.
Lasers operating on the principle of a structure with multiple parallel optical waveguides coupled laterally with each other (multiple optical waveguide structure) have already been devised.
In these structures, if the optical waveguides are placed side by side, very close to each other, there is a mutual coupling of the optical wave travelling in one guide with the optical wave of neighbouring guides. It is therefore possible by making use of the mutual coupling between guides, i.e. in practice by correctly choosing the distances between neighbouring guides, to obtain at the output optical waves that are coherent, with a distribution of electric field, and therefore of light energy, which is not the simple superposition of the electric fields produced in each guide but which is a composition corresponding to a mode of propagation characteristic of the multiple guide structure.
Consequently, whereas uncoupled juxtaposed guides would lead to a distribution of light energy distributed uniformly between the outputs of the different guides, mutual optical coupling can lead to a non-uniform energy distribution, possibly concentrated at the centre, for example with a shape that is approximately Gaussian. Such a structure is thus very worthwhile since it enables the energy from a spatially distributed output to be concentrated.
Unfortunately, experiment shows that practical realization is very difficult. In effect, it is very difficult to control the dimensions and homogeneity of optical waveguides, and nobody has actually succeeded in making a laser operate in this way, with a beam really possessing an overall natural mode produced from the individual modes of the different guides. A correct concentration of energy is therefore not obtained.
An attempt has been made to achieve this, for example with semiconductor lasers, in which the emission of light is stimulated by the injection of currents into the junctions. However, it is realised that the injection of current alters the refractive indices in the guides. These changes in index modify the phases of the optical waves. There is a failure to obtain in the different guides a distribution of phases which would combine to give a beam intensity distributed spatially in the desired manner.


SUMMARY OF THE INVENTION

The invention proposes a method of producing a laser operating on the principle of multiple optical waveguide structures and having an intensity distribution of desired output.
According to the invention, a laser is proposed comprising a plurality of juxtaposed parallel optical waveguides having a mutual lateral optical coupling between them, with means for individually controlling the refractive index in the different guides or between the different guides. Through this individual local control of the indices, it is possible to control the relative phases of the optical wave in the different guides and hence the overall distribution of light intensity at the output of the coupled structure.
The preferred embodiment is as follows: the optical waveguides are made from an electro-optical material and provision is made for control electrodes placed in the vicinity of the guides in order to achieve individual control of the refractive index in the guides, and for means of applying individual potentials to these electrodes so as to adjust the relative phases of the wave in the different guides. This adjustment of phase is carried out through the intermediary of an adjustment of the effective refractive index in a guide; the index of the guide depends on the potential applied to an electrode placed near this guide because the guide is made of an electro-optical material.
In this embodiment, the optical waveguides form an integral part of the resonant cavity producing the laser effect. Plane mirrors or other means of reflection are placed at the ends of the guides in order to form this cavity.
It is possible in this way to produce a solid laser in

REFERENCES:
patent: 3725809 (1973-04-01), Ulrich et al.
patent: 4714312 (1987-12-01), Thaniyavarn
patent: 4763975 (1988-08-01), Scifres et al.
patent: 4878724 (1989-11-01), Thaniyavarn
patent: 5121400 (1992-06-01), Verdiell et al.
SPIE, vol. 1131, Optical Space Communication, Paris, Apr. 24-26, 1989, E. Lallier et al.: "Towards a laser diode pumped Nd:LiNbO3 waveguide laser", pp. 247-251.

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