Optical waveguides – Polarization without modulation
Reexamination Certificate
1999-06-22
2003-03-25
Ullah, Akm E. (Department: 2874)
Optical waveguides
Polarization without modulation
C385S012000, C385S123000
Reexamination Certificate
active
06539134
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This application relates to optical devices that transform light between linearly and elliptically polarized states.
2. Description of Related Art
Devices that transform linearly polarized light to circularly polarized light and the reverse are known in the literature. To make such optical devices, one may use one birefringent fiber with two beams of light of equal frequency and amplitude (or, equivalently, one beam that is the vector sum of these two beams). If the two beams are propagated perpendicular to an optic axis, circularly polarized light may result. Alternatively, linearly polarized light may be transformed to circularly polarized light by using one beam and two fibers.
In practice, constructing a single-beam transformer of linearly to circularly polarized light involves first starting with a length of transforming fiber greater than a predetermined length, and performing several iterations of cutting and measuring polarization until the polarization is deemed to be circular to within some specification. Needless to say, this is a tedious and lengthy procedure requiring lots of guesswork.
SUMMARY OF THE INVENTION
A transformer of polarized light comprising a birefringent fiber which is twisted through an angle into a corkscrew shape at an appropriate distance from an end of the fiber is presented herein; the angle and distance are so chosen that linearly polarized light entering the other end of the fiber exits the fiber elliptically polarized. In various embodiments, the angle is approximately &pgr;/4 radians, or an odd multiple thereof, and the distance is approximately one quarter of a beatlength, or an odd multiple thereof. The transformer of polarized light may include an optical fiber twisted about a central axis running therethrough wherein the fiber is characterized by the absence of spliced sections.
A method of fabricating a transformer of polarized light comprising twisting a birefringent fiber through an angle to produce a corkscrew shape is also presented; twisting a birefringent fiber may include twisting the fiber through an angle of approximately &pgr;/4 radians, or an odd multiple thereof, and twisting the fiber at a distance of approximately one quarter of a beatlength, or an odd multiple thereof, from an end of the fiber.
A method of fabricating a transformer of polarized light is also presented which may include heating a birefringent fiber, having a core and a cladding, so as to cause the core to diffuse into the cladding, and thereby changing the state of polarization of light that may exit the fiber. The method may further include previously twisting the fiber through an angle to produce a corkscrew shape. (In one embodiment, this angle is &pgr;/4 radians.) Twisting the fiber includes twisting the fiber at a distance of approximately one quarter of a beatlength from an end of the fiber.
Also presented is a method of transforming substantially linearly polarized light into substantially circularly polarized light including twisting a birefringent fiber through an angle of &pgr;/4 radians to produce a corkscrew shape at a distance of approximately one quarter of a beatlength from an end of the fiber; shining substantially linearly polarized light through the other end of the fiber; and fine tuning the polarization of the light exiting the fiber by heating the fiber so as to cause the core to diffuse into the cladding, until the light is substantially circularly polarized. The twist in the fiber can be accomplished by heating the fiber before, during, or after the twisting.
The invention further includes a transformer of polarized light comprising a birefringent fiber. The fiber has a first end through which the polarized light enters and a second end through which light exits. The fiber is also twisted through an angle into a corkscrew shape at an appropriate distance from the second end, the angle and distance so chosen that polarized light entering the first end exits the second end randomly polarized. The appropriate length may be greater than a decoherence length.
Also presented is a method of transforming substantially polarized light into substantially randomly polarized light including twisting a birefringent fiber, having a first end through which the substantially polarized light enters and a second end through which the substantially randomized light exits, through an angle of &pgr;/4 radians to produce a corkscrew shape at a distance of at least one decoherence length from the second end of the fiber; and shining substantially polarized light through the first end of the fiber to allow substantially randomly polarized light to exit the second end.
Also presented is a method of transforming substantially linearly polarized light into substantially circularly polarized light comprising twisting a birefringent fiber, having two ends, about its central axis through an angle approximately equal to an odd multiple of &pgr;/4 radians, at a distance of slightly more than odd multiple of one quarter of a beatlength from a first end of the fiber, shining substantially linearly polarized light through a second end of the fiber, and fine turning the polarization of the light exiting the first end of the fiber by heating the fiber between the twist and the first end, so as to cause the core to diffuse into the cladding, until the exiting light is substantially circularly polarized. The odd multiple of one quarter of a beatlength may be 1. The odd multiple of &pgr;/4 radians may be 1. The birefringent fiber may be twisted while being heated near the location of the twist or after having been heated near the location of the twist.
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patent:
Doan Jennifer
Foley & Hoag LLP
KVH Industries, Inc.
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