Optics: measuring and testing – By light interference – Rotation rate
Reexamination Certificate
1999-05-10
2001-06-05
Turner, Samuel A. (Department: 2877)
Optics: measuring and testing
By light interference
Rotation rate
C356S462000
Reexamination Certificate
active
06243167
ABSTRACT:
The invention concerns a multimode optical fiber gyroscope, single or multi-axial, with improved resolution and stability.
The improvement essentially relates to diagonal stability and the scaling factor.
Ring-shaped gyroscopes with multimode optical fibers are known in the art. However, the prior art solutions do not present practical solutions for industry, nor do they achieve the objectives of the present invention or respond to industrial needs.
These prior art solutions depend upon the SAGNAC effect and often upon the physical principle of reciprocity, according to which an extrinsic disturbance produces the same phase effects on both counter-rotating waves propagating within a ring guide. These considerations make it necessary for the system's inlet/outlet device to be equipped with a reciprocal dual coupling, which increases manufacturing costs and has a negative effect on output.
Furthermore, prior art devices often resort to particular methods of modulation and detection which are difficult to implement and impose very strict manufacturing limitations.
The essential advantage of the present invention consists in the use of a source, an optical fiber, and a detection circuit in an economical device, easily adapted to industry
To achieve these objectives, the components which are selected must meet two essential criteria.
The first requirement is to obtain maximum dispersion between two adjacent modes, no matter what modes are being considered. This condition is fulfilled by making the appropriate selection first, of the source characteristics, that is, its spectral width and central wave length, and second, the parameters influencing the fiber's dispersion characteristics such as length, numerical aperture, index profile, and other opto-geometric characteristics of the fiber.
The preferred version of the invention has a source with a broad spectrum associated with a highly dispersive fiber.
The second criterion concerns the symmetry of modal distributions in both propagation directions.
The principal goal of the present invention is to furnish an output value proportionate to the speed known as rotation speed, that is, angular displacement, which is independent of the principal diverse fluctuations of the gyroscope components.
According to one variation, the invention furnishes data about the independent rotation speed of the various principal fluctuations in the gyroscope components. Until now, variations in the source wave length have remained difficult to quantify.
From that point, in a broad range of operating temperatures, it is no longer necessary to take multiple precautions to minimize variations in the source wave length.
Other advantages of the invention are enumerated below:
The use of multimode fiber with a large core diameter and large numerical aperture allows the use of a strongly divergent light source without affecting energy output at injection. A simple, inexpensive, light-emitting diode accomplishes this. The same holds true for other connection operations.
It is no longer necessary for the design of the gyroscope to incorporate two reciprocal input/output couplers. A single X coupler can be used, which decreases manufacturing costs and improves the power output of the sensor.
Since the light signal within the fiber is completely depolarized, it is no longer necessary, as with monomode fiber gyroscopes, to use polarizers, polarization controls, or depolarizing systems. In addition, the sensor becomes completely immune to magnetic fields (Faraday effect) and electrical fields (Kerr effect). It is no longer necessary to use expensive materials to block these effects. This reduces the number of components substantially and simplifies assembly.
The system's stability depends upon the optical properties of its components. This results from the possibility of assimilating the gyroscope with a large number of independent, elementary gyroscopes. Thus, it is no longer necessary to reset the gyroscope to zero before each use, and systems can be stored and put to immediate use as necessary.
The ability to manufacture a small size gyroscope is an important advantage in certain applications requiring mini-gyroscopes.
The signals chosen, that is, 0
th
, 1
st
and 2
nd
order harmonics in the mathematical formulas adopted, result in gyroscopes with a scaling factor which is independent of the principal fluctuations characterizing gyroscopes of this type.
REFERENCES:
patent: 4634282 (1987-01-01), Shaw et al.
patent: 4828389 (1989-05-01), Gubbins et al.
patent: 5048961 (1991-09-01), Okamoto
patent: 2680570 (1993-02-01), None
patent: 2725784 (1996-04-01), None
patent: 83/01683 (1983-05-01), None
Davis & Bujold P.L.L.C.
Talltec Technologies Holdings S.A.
Turner Samuel A.
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