Optics: measuring and testing – For optical fiber or waveguide inspection
Reexamination Certificate
1999-04-16
2001-02-13
Font, Frank G. (Department: 2877)
Optics: measuring and testing
For optical fiber or waveguide inspection
C385S014000
Reexamination Certificate
active
06188472
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates generally to optical systems, and relates more particularly to a system and method for direct measurement of alignment error in a fiber coupler.
2. Description of the Background Art
Implementing techniques for efficient coupling between optical elements is a significant consideration of designers, manufacturers, and users of optical systems. Many modern optical systems use light beams, usually laser-generated, to carry various types of information. These light beams may travel through free space or through optical elements such as optical fibers. In optical systems, a light beam may alternate between travelling in free space and travelling in a fiber. This free-space-to-fiber coupling often occurs in the context of an optical switch.
Free-space-to-fiber coupling should be efficient to avoid unnecessary losses in light. Coupling efficiency is especially important in optical systems where light beams are sent through a fiber and then reflected back. If the free-space-to-fiber coupling is not efficient, then the amount of light reflected back through the fiber might be insufficient for its intended purpose.
For efficient coupling, a light beam travelling through free space must contact a fiber so that the amount of light transmitted through the fiber is maximized. The most efficient coupling between a free space beam and a fiber occurs when the light beam is centrally positioned on the core of the fiber (on the fiber center). This central positioning results in the maximum amount of light being transmitted through the fiber.
However, once positioned on the fiber center, the light beam may not remain in place. If the optical system suffers a shock or vibration, the physical components of the optical system may shift, causing the light beam to be offset from the fiber center.
Other factors may also cause the light beam to be offset from the fiber center. For example, thermal expansion of a fiber may cause it to shift, reducing the coupling efficiency between the light beam and the fiber. This type of offset poses a different problem from offset due to movements of the physical components of the optical system. A system and method for efficient coupling must be able to correct offsets due to vibration, thermal expansion, and any other cause. Therefore, an improved system and method are needed for direct measurement of alignment error in a fiber coupler.
SUMMARY OF THE INVENTION
In accordance with the present invention, a system and method are disclosed for direct measurement of alignment error in a fiber coupler. The preferred embodiment of the present invention is implemented in the context of an optical switch. In the optical switch, a light beam couples with a selected optical fiber in a fiber bundle. Efficient coupling occurs when the light beam is positioned on the center of the selected fiber.
In one embodiment of the present invention, an optical switch utilizes a beam deflection mirror. The optical switch first performs a coarse-adjustment of the beam deflection mirror to direct an incident light beam to a particular fiber terminator, after which the optical switch performs fine-adjustment steps. In the fine-adjustment steps, an incident light beam is sent through the beam deflection mirror, which may be in a position of geometric error with respect to a beam focusing lens and the axial center of a fiber terminator. If so, then the beam focusing lens impinges the incident beam upon the fiber terminator at a location that is an error distance away from the axial center. The beam travels down the fiber to a magneto-optical head, where the incident beam reflects from a magneto-optical storage media to become a return beam. The return beam then travels down the fiber and exits the fiber at the axial center of the fiber terminator.
The centered return beam departs the axial center of the fiber terminator. Because the return beam departs the axial center at a different location than the incident beam impinged upon the fiber terminator, the return beam traverses the beam focusing lens along a different path than the incident beam path. This return beam, traveling along a different path, is therefore deflected by the beam deflection mirror along a different path than the incident beam path. This different path causes a beam splitter to send a portion of the return beam to an off-center location on a quadrant detector. Anode currents in the quadrant detector carry a direct measurement of the alignment error in the optical switch.
Once the alignment error is measured, then this measured alignment error, coded on the anode currents of the quadrant detector, may be used to drive a servo-control circuit to finely-adjust the beam deflection mirror.
REFERENCES:
patent: 4637683 (1987-01-01), Asawa
patent: 6023338 (2000-02-01), Bareket
Belser Karl A.
Gage Edward C.
Gerber Ronald E.
Hurst, Jr. Jerry E.
Flehr Hohbach Test Albritton & Herbert LLP
Font Frank G.
Iolon, Inc.
Nguyen Tu T.
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