DE69721475T2 - Pickup coil of an optical fiber gyroscope with improved temperature stability - Google Patents

Description

background the invention

This invention relates generally on fiber optic gyroscopes and in particular on fiber optic gyro sensor coils and the optical fiber with which they are wound.

Fiber optic gyroscopes feel that Rotation by measuring the phase difference of the light waves wander in opposite directions through a coil with an optical fiber is wound. Waves of light passing through propagating the spool in the direction of rotation takes a long time as light waves passing through the coil in the opposite direction run in the direction of rotation. This time difference than the phase difference measured between opposing propagating light waves, is proportional to the angular velocity of the coil.

The phase difference between the opposing propagating light waves in a fiber optic gyroscope sensor coil is not only due to the angular velocity of the coil but also through changes affects the physical properties of the coil, the through changes the environmental parameters brought about temperature is the most important. A change the temperature of the coil changed the refractive index and the physical dimensions of the optical Fiber which directly affects the time it takes so that the light wave travels through the coil.

If the rate of change in temperature is low would be enough that the Coil has essentially the same temperature in its entire volume, would they be changes the propagation times of the oppositely propagating waves essentially the same, and the measured phase difference would be in essentially independent from the rate of change the temperature. However, with rates of change the temperature encountered by the fiber optic gyroscopes the opposite propagating waves are different Temperatures at a given time and complete extinction of the Temperature effects do not occur. As a result, the phase difference shows as measured by a fiber optic gyroscope, a bias (bias), which are subtracted from the measured phase difference must to to get the phase difference associated with the rotation of the coil is.

It is possible to exactly the preload to model the coils for high-precision applications are designed, with a function of Temperature (the "modeling function") associated with thermally initiated is not related to reciprocal behavior. (See D. M. Shupe in the Thermally Induced Non-Reciprocity in the Fiber Optic Interferometer (Thermally initiated non-reciprocal behavior in the fiber optic interferometer), 19 Applied Physics 654 (1980). See also U.S. Patent 5,371 593, Sensor Coil for Low-Bias Fiber Optic Gyroscope (sensor coil for a Fiber Optic Gyroscope with Low Preload) by A. Cordova and others.) To further improve the accuracy of these gyroscopes, it is very important the temperature dependence of the coefficient to eliminate or at least significantly reduce the Define modeling function.

Furthermore, reference is made to the writing US 4,708,479 which discloses a fiber optic gyroscope with temperature compensating means which imprint on the wound fiber a coefficient of thermal expansion which is selected to be approximately equal to the value of the temperature coefficient of the refractive index of the fiber, thereby reducing the scaling factor temperature coefficient. The temperature compensation means can be in the form of an element of a coating that has been applied to the fiber.

Attention is also drawn to the scriptures US 4,724,316 which is an improved type of fiber optic sensor discloses a fiber optic waveguide component of the sensor is configured to responsive to an external parameter so that the curvature of the fiber optic waveguide is responsive on forces changed is going through change of the outer parameter be initiated, the sensed becomes. The change in curvature the fiber optic waveguide causes changes in intensity of the light passing through it, these changes display the status of the external parameter. The improvement points Coating material on which the outer part of the fiber optic Wave guide covered, wherein the coating material has a coefficient of expansion and has a thickness so that the Distortion or utilization of the fiber optic waveguide, the due to thermally induced tensions between the coating material and the fiber is caused to be substantially eliminated. There is also disclosed a support member for the curved fiber optic wave guide to support wherein the support member and the fiber optic waveguide are configured and are arranged to increase the effects of thermal stress minimize that tends to undulate the shaft from the support member separate.

Summary the invention

A fiber optic gyro sensor coil with improved temperature stability for use at temperatures between T1 and T2 is provided where T1 is less than -30 ° C and where T2 is greater than 60 ° C. The coil is wound with an optical fiber that has one or more sheaths. The one or more casings are made of material, the glass transition regions outside the temperature range from T1 to T2.

Short description of the drawings

1 shows the cross section of an optical fiber for use in the winding of the sensor coil for a fiber optic gyroscope.

2 shows the modulus of elasticity as a function of temperature for a typical silicone used as the inner cladding material of the clad optical fibers with inner and outer claddings.

3 shows the modulus of elasticity as a function of temperature for a typical acrylate used as the outer cladding material for the clad optical fibers with inner and outer claddings.

4 shows the key modeling function coefficient as a function of temperature for three different coil configurations.

description of the preferred embodiments

One reason for the strong temperature dependence of the modeling function coefficients is the large change in the physical properties of the cladding of the optical fiber in the coil with the temperature. 1 shows the cross section of a typical optical fiber 1 used to wind the fiber optic gyroscope sensor coils. The optical fiber 1 has an optical core and a lining 3 , an inner sheath 5 and an outer jacket 7 , The typical inner cladding material is a silicone and the typical outer cladding material is an acrylate. The core and liner are typically made of glass. Alternative embodiments of the invention can use single clad optical fibers. The fiber can be provided for "single mode" (low birefringence or bi-refraction) or "maintain depolarization".

Theoretical calculations say sharp changes in the modeling function coefficients for coils previously with optical Fibers are wound, the conventional Have jackets at each end of a temperature range, because of the big change of the modulus of elasticity the inner silicone sheathing material at low temperatures and because of the big one change of the module of the outer acrylic coating material at high temperatures.

The modulus of elasticity as a function of temperature for the inner silicone cladding material of a fiber with a conventional cladding is shown in FIG 2 shown. The module is almost constant for temperatures above approximately –30 ° C. The modulus of elasticity as a function of temperature for the outer acrylic cladding material with a fiber with a conventional cladding is in 3 shown. The module is almost constant for temperatures down to about -10 ° C and then drops to a very low value over the temperature range from about -10 ° C to about 60 ° C. In the 2 and 3 Module recordings shown have a linear vertical scale. If the records were to have a logarithmic scale, they would show a sharp drop in module, which can be about two orders of magnitude.

The key modeling function coefficient as a function of temperature is in for three coil configurations 4 shown.

A comparison of the module curves with the modeling function coefficient curves shows the connection between the changes in the elastic modulus for the inner and outer jackets and the changes in the key modeling function coefficient for a coil wound with an optical fiber with conventional jackets. The major change in the key modeling function coefficient at low temperatures corresponds to the rapid change in the modulus of the inner cladding material ( 2 ). The more gradual change in the key modeling function coefficient at higher temperatures corresponds to the more gradual change in the modulus of the outer cladding material ( 3 ).

The temperature range over which the modulus of a cladding material from high to high changed low value, is called the "glass transition area" designated. The median of this temperature range is called the "glass transition temperature" designated. At temperatures below the glass transition area, the cladding material is soft or "rubbery". The lower end of the glass transition area is defined to be this is the temperature at which the module is a third of the high glass state value is. The upper end of the glass transition area is defined to be this is the temperature at which the module is three times as large as the value at the low rubbery state. A sheathing material can have multiple glass transition regions to have.

Ideally, the modulus of elasticity of all sheathing materials approximately constant over the Operating temperature range of the gyroscope. Therefore, the Glass transition areas of all sheathing materials outside the operating temperature range his. For the cladding materials suitable materials that are both above as well as below the operating areas of the gyroscope glass transition areas are well known in the art.

Claims (12)

Fiber optic gyro coil for use at tem temperatures between T1 and T2, where T1 is lower than –30 ° C and T2 is higher than 60 ° C, the coil with single-mode or single-mode or with polarization-maintaining single-mode or optical single-mode fibers ( 1 ) is wrapped with one or more sheathing ( 5 . 7 ), the one or more sheathing ( 5 . 7 ) is made of materials whose entire glass transition areas are outside the temperature range from T1 to T2. The fiber optic gyro coil of claim 1, wherein T2 is greater than Is 70 ° C. The fiber optic gyro coil of claim 1, wherein T2 is greater than Is 90 ° C. The fiber optic gyro coil of claim 1, wherein T2 is greater than Is 100 ° C. The fiber optic gyro coil of claim 1, wherein T1 is less than -45 ° C. The fiber optic gyro coil of claim 1, wherein T1 is less is as - 45 ° C and T2 larger than Is 70 ° C. The fiber optic gyro coil of claim 1, wherein T1 is less as -45 ° C and T2 larger than Is 90 ° C. The fiber optic gyro coil of claim 1, wherein T1 is less is as - 45 ° C and T2 is bigger than 100 ° C. The fiber optic gyro coil of claim 1, wherein T1 is less than -55 ° C. The fiber optic gyro coil of claim 1, wherein T1 is less as -55 ° C and T2 larger than Is 70 ° C. The fiber optic gyro coil of claim 1, wherein T1 is less is as - 55 ° C and T2 is bigger than 90 ° C. The fiber optic gyro coil of claim 1, wherein T2 is less is as - 55 ° C and T2 is bigger than 100 ° C.