Bifilar optical fiber stowage for fiber-optic gyroscope

A method of constructing a fiber-optic gyroscope includes optically coupling first and second optical fibers to an optical path of an interferometer having an outer surface, coupling at least a portion of the first and second fibers to the outer surface, and optically coupling the first and second fibers to an optical path of an integrated optics chip (IOC).

BACKGROUND OF THE INVENTION

Fiber optic gyroscopes (FOGs) have become widely used technologies in many systems to sense the rotation and angular orientation of various objects, such as aerospace vehicles. FOGs work by directing light in opposite directions around a closed optical path enclosing an area whose normal is along an axis of rotation. If the device is rotated about the axis of rotation, the optical path length for the light traveling in one direction will be reduced, while the optical path length for the light traveling in the opposite direction will be increased. The change in path length causes a phase shift between the two light waves that is proportional to the rate of rotation.

Referring toFIG. 1, a typical FOG10includes a light source15, a rate detector20, a coupler25, an integrated optics chip (IOC)30, and an interferometer, such as a sensing coil35. As shown inFIG. 1, a red fiber service lead40and blue fiber service lead45of the IOC30is spliced50,55to the red fiber service lead60and blue fiber service lead65of the fiber coil interferometer35. Each of these service leads are often approximately two meters in length to allow optical splicing needed in the build process. Since these fiber service leads for splicing are functionally part of the interferometer35, the manner in which the service leads are stowed is a key gyroscope performance parameter.

In conventional FOG builds, these lead fibers are stowed in a thread-like winding pattern in a holding compartment having independent thermal characteristics from the interferometer35. Specifically, in such an approach, waves counter-propagating through the coil35may “see” different environment effects at different points in time. High-performance polarization maintaining gyroscopes must have Lorentz reciprocity between the counter-propagating waves. Lorentz reciprocity requires light propagating in a medium to have identical effects independent of the direction of light propagation. Environmental effects can easily degrade Lorentz reciprocity and gyroscope performance. As such, these conventional approaches typically have degraded Lorentz reciprocity caused by environmental effects.

SUMMARY OF THE INVENTION

In an embodiment, a method of constructing a fiber-optic gyroscope includes optically coupling first and second optical fibers to an optical path of an interferometer having an outer surface, coupling at least a portion of the first and second fibers to the outer surface, and optically coupling the first and second fibers to an optical path of an integrated optics chip (IOC).

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

An embodiment provides for a service-lead stowage location on the outer layer of an interferometric fiber coil, thereby providing improved performance as compared to a separate compartment storage.

An embodiment of a bifilar service-lead routing method provides improved performance under time-varying thermal gradients and reduces the Shupe effect of these service leads.

An embodiment provides bifilar fiber routing method that ensures service leads are confined to a single outer layer of a coil and not additional layers, which would be subject to more stress over temperature changes.

An embodiment provides a reduction of the number of points where optical fiber crosses over itself, as well as twists in the fiber, thereby improving gyroscope bias stability.

By routing the fibers in such a bifilar-pair fashion, points equal and opposite in the sensing loop are physically adjacent to each other and see the same effects over varying environments.

Referring now toFIG. 2, illustrated is a front view of the outer surface of an interferometer200along which are routed, according to an embodiment, a red service lead fiber210(illustrated inFIG. 2as a solid fiber element) and a blue service lead fiber220(illustrated inFIG. 2as a cross-hatched fiber element) connecting an optical path of the interferometer200to the optical path of an IOC (not shown).

In an embodiment of the invention, a first portion of the red fiber210directly coupled to the optical path of the interferometer200is seen emerging from the center of the interferometer and is oriented along a left-to-right path along the outer surface. Similarly, a first portion of the blue fiber220directly coupled to the optical path of the interferometer200is seen emerging from the center of the interferometer and is oriented along a right-to-left path along the outer surface. As such, a second portion of the red fiber210and a second portion of the blue fiber220converge toward one another so as to form a “Y”-junction230.

Subsequently, beginning at a region240of the outer surface, multiple turns of respective third portions of the red fiber210and blue fiber220are wrapped around the outer surface a predetermined integer number of times to form a winding250. As best seen inFIG. 4, the winding is formed so as to form only a single layer along the outer surface of the interferometer200in a direction normal to a center axis400of the interferometer. Additionally, it should be noted that, in forming the winding250, the red and blue fibers210,220do not cross or otherwise overlap each other.

After forming the winding250, a fourth portion of the red fiber210and a fourth portion of the blue fiber220are routed up and away from the winding and in the opposite direction so as to form a “U-turn” configuration260, or perhaps an even more rounded, “lasso” type configuration (not shown). In an embodiment, if there is a disparity in length between the red and blue fibers210,220, the distance between the red and blue fibers may be increased at the “U” portion of the configuration260to accommodate the longer fiber.

After forming the U-turn configuration260, as best illustrated inFIG. 3, the red and blue fibers210,220are oriented in a substantially sinusoidal, or serpentine, configuration300along the outer surface, also in the direction opposite of the direction in which the winding250was formed. The red and blue fibers210,220may then be subsequently coupled to the optical path of the IOC.

In an embodiment, the red and blue fibers210,220are coupled to the outer surface of the interferometer200in a manner that reduces or eliminates light cross-coupling.

It should be further noted that the only time the red and blue fibers210,220cross each other or otherwise overlap is at the points of transition from the winding250to the “U-turn” configuration260as illustrated in the example ofFIG. 2.