Optics: measuring and testing – By particle light scattering – With photocell detection
Patent
1995-05-05
1998-01-20
Font, Frank G.
Optics: measuring and testing
By particle light scattering
With photocell detection
G01B 902
Patent
active
057106290
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The present invention relates to an interferometric measuring device comprising two waveguides arranged in a rigid block and achieved according to an integrated optics technology to constitute two distinct optic transmission channels for mutually coherent input signals, means to make these signals interfere and means for analyzing the interference fringes obtained.
To perform interferometric measurements of the optic path variations due to the variations of a variable physical parameter, and to determine the direction in which these variations take place, it is necessary, with known apparatuses, to have available two identical pieces of equipment each enabling interference fringes of signals coming from two distinct optic channels to be obtained, but one of which is in addition equipped with a phase shifter, such as for example a quarter-wave plate.
Document EP-A-286,528, for example, uses two dephased reference beams each interfering with a part of a measurement beam so as to form two interference signals whose variations in time are representative of a mobile movement and of the direction of this movement. In document WO-A-9,011,484, analog signals are obtained from comparison to a reference signal of two measurement signals corresponding to two different polarization directions.
The fact of having to use two pieces of equipment may induce errors in the measurements and naturally complicates the handling operations.
In particular, when the experimental setup is made with discrete components in conventional optics, a complex alignment and tuning procedure has to be implemented.
SUMMARY OF THE INVENTION
The object of the invention is to overcome these drawbacks by achieving a precise, reliable interferometric measuring device of simple and economical construction, and considerably easier to use than known devices.
For this purpose, the device according to the invention is characterized in that it comprises a beam broadening device interposed on each optic channel so as to generate spread flat beams, the broadening devices of the two channels being identical and disposed in such a way that the spread flat beams have substantially flat wavefronts forming between them a preset angle presenting an axis of symmetry, said wave fronts creating a spatial interference pattern in an interference zone, the analysis means comprising detection means disposed in the interference zone perpendicularly to said axis of symmetry.
The angle is preferably about one degree.
According to a particularly advantageous embodiment, the beam broadening devices comprise at least one planar lens achieved according to an integrated optics technology into said rigid block.
According to an alternative embodiment, the beam broadening devices may comprise tapers.
According to a preferred embodiment, the means for analyzing the fringes may comprise a detection device comprising at least one extended detector having a length corresponding substantially to a half-fringe of the interference pattern.
BRIEF DESCRIPTION OF THE DRAWINGS
Other advantages and features will become more clearly apparent from the following description of an illustrative embodiment of the invention, given as a non-restrictive example only and represented in the accompanying drawings, in which:
FIG. 1 represents a schematic view illustrating the operating principle of the device according to the invention.
FIG. 2 represents an advantageous embodiment of the device of the invention .
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
FIG. 1 is a schematic view which illustrates the principle of the interferometric measuring device according to the invention. Two optical guides 10 and 20 convey mutually coherent input signals. On each of these guides which determine two optic channels, there is placed a beam broadening device 11 and 21, respectively, that function is to extend the spatial profile of each optic channel. Upstream from the broadening devices, the wavefronts 10', 20' are called "confined", and downstream the wavefronts 10", 20
REFERENCES:
patent: 4850693 (1989-07-01), Deason et al.
patent: 4865453 (1989-09-01), Gidon et al.
patent: 5141319 (1992-08-01), Kajimura et al.
IEE Proceedings, vol. 147, Pt. J, No. 6, Dec. 1990. Stevenage, Herts., GB pp. 347-356. M.N. Armenise et al. "Design and simulation of an on-board lithium niobate integrated optical preprocessor".
Benech Pierre
Duport-Schanen Isabelle
Kevorkian Antoine
Font Frank G.
Merlino Amanda
Schneider Electric S.A.
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