Optics: measuring and testing – By dispersed light spectroscopy – Utilizing a spectrometer
Patent
1994-07-11
1996-09-10
Turner, Samuel A.
Optics: measuring and testing
By dispersed light spectroscopy
Utilizing a spectrometer
G01C 1972
Patent
active
055550886
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a Sagnac effect optical gyrometer, whose physical principle is based on a relativistic effect discovered by the physicist Sagnac in 1913.
2. Description of Related Prior Art
Optical gyrometers are well known and a description is e.g. provided on pp 91 ff of Journal of Light Wave Technology, vol. Lt. 2, No. 2, April 1984.
Details will be given of the known theory and the main evolutions of such equipments with reference to the attached FIGS. 1a and 2a.
The actual probe of a Sagnac effect optical gyrometer has a ring or turn 1 traversed by light and whose two ends have a common section 2, which respectively connects them to a light source 3 and to an interference detector 4. When the light from the source 3 is injected through the common path 2 in the ring 1, said geometrical arrangement makes it possible to bring about a division thereof into two separate light waves, whereof the first "a", passes through the ring 1 in the clockwise direction and the second "b" traverses said same ring in the counterclockwise direction, the two waves being by definition in phase because they come from the same source 3. On leaving the system, the detector 4 makes it possible to observe any interference fringes resulting from the combintion of waves a and b. By design, and in the absence of any other action, the interferences between the waves a and the waves b are perfectly constructive and correspond to a strictly zero phase shift .DELTA..rho.=0.
However, if the device rotates with an angular velocity .OMEGA. with respect to an inertial reference frame, the wave passing through the ring in the rotation direction acquires a phase lead .rho. during its passage, whereas the other acquires a phase lag -.DELTA..rho.. Thus, at the exit there is a total phase shift of 2.DELTA..rho., which modifies the interference patent read by the detector 4. As the theory of the apparatus shows that the value of the phase shift .DELTA..rho. is proportional to the vector product A.LAMBDA..OMEGA. in which A is a vector, whose magnitude is proportional to the surface of the ring and whose direction is perpendicular to the plane of said same ring and .OMEGA. is the vector of the angular rotation which it is wished to measure, it is clear that the measurement of the total phase shift .DELTA..rho. performed by the study of the modification of the said interference pattern makes it possible to obtain the value of the sought rotation .OMEGA..
Devices for measuring an absolute rotation designed on the basis of this principle have been developed, particularly since the appearance of on the one hand laser light sources and on the other optical light conducting fibers.
As the sensitivity of a Sagnac optical gyrometer is proportional to the length of the path of the light wave, the aim has naturally been to lengthen said path, which was particularly easy with optical fibers and in this way it was possible to produce gyrometers, whose detecting probe was formed from a coil of optical fibers in several turns. More recently, consideration has also been given to a construction of optical gyrometers by making use of integrated optics and for artificially increasing the length of the single turn constituted by a light microguide, use has been made of the resonant gyrometer, whereof an example is diagrammatically shown in FIG. 2a.
FIG. 2a shows the resonant ring 1 constituted by an optical microguide tangentially supplied by two light guides 5, 6, each having an entrance face 7 and an exit face 8, the light guides 5 and 6 being coupled to the resonant ring 1 with the aid of two optical couplers 9, 10. The principle of this known apparatus consists of increasing the path of the two light waves, whilst permitting the light to pass through the ring several times and examining the resulting interferences of the state of the two waves after several passages of this type. The performance characteristics of such an apparatus are consequently dependent on the number of turns which can
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Interferometric Fiber Optic Gyroscope Using a Novel 3.times.3 . . . , Minford et al., Optical Fiber Sensors, vol. 2, No. 2, Jan. 27, 1988, Washington D.C., USA, pp. 385-392.
All-Single-Mode Fiber-Optic Gyroscope with Long-Term Stability, Bergh, et al., Optics Letters, vol. 6, No. 10, Oct. 1981, pp. 502-504.
An Overview of Fiber-Optic Gyroscopes, Bergh et al., Journal of Light-Wave Technology, vol. LT-2, No. 2, Apr. 1984, pp. 91-107.
Commissariat a l''Energie Atomique
Turner Samuel A.
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