Optical waveguides – Polarization without modulation
Reexamination Certificate
1999-06-28
2001-04-03
Kim, Robert (Department: 2877)
Optical waveguides
Polarization without modulation
C385S012000
Reexamination Certificate
active
06212305
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to fiberoptic devices and, more particularly, to optical isolators useful in allowing the transmission of light signals in one direction along an optical fiber and blocking the transmission of light signals in the opposite direction.
In present day optical fiber technology, it is often very useful for light signals to move only in one direction along an optical fiber. For example, semiconductor lasers are typically used to generate and to relay light signals on optical fibers. These lasers are particularly susceptible to light signal reflections, which can cause a laser to become unstable and noisy. Optical isolators are used to block these reflected signals from reaching the laser. Ideally, an optical isolator transmits all of the light signals in the forward direction and blocks all of the signals in the reverse direction.
Of course, optical isolators do not attain ideal performance levels and improvements are constantly sought. Furthermore, lowered manufacturing costs are desirable to encourage the spread of optical fiber networks with their inherently large bandwidths. With an optical isolator generally required for each laser generating signals on an optical fiber, it is beneficial that the cost of the optical isolators be lowered as much as possible. Finally, for ease of installation, reliability and low material costs, a small size for optical isolators are desirable also.
The present invention substantially meets those goals by offering a miniaturized optical isolator having a high performance. The optical isolator is capable of being manufactured at lowered costs.
SUMMARY OF THE INVENTION
The present invention provides for an optical isolator having a sleeve with a longitudinal channel, a pair of optical fibers in the longitudinal channel, a first, second and third birefringent crystals, a GRIN lens, a Faraday rotator and a mirror element. Each of the optical fibers in the longitudinal channel has an end facet. The first birefringent crystal covers the end facet of one of the pair of optical fibers, and the second and third birefringent crystals cover the end facet of the other of the pair of optical fibers. The GRIN lens has first and second end faces with the first end face proximate the first, second and third birefringent crystals. The Faraday rotator is located between the mirror element and the second end face of the GRIN lens. The end facets of the pair of optical fibers, the first, second and third birefringent crystals, the GRIN lens, the Faraday rotator, and the mirror element are arranged and oriented with respect to each other so that light in one direction from a first optical fiber of the pair passes through, and back from, the first, second and third birefringent crystals, the GRIN lens, the Faraday rotator and the mirror element into a second optical fiber of the pair. On the other hand, light in a reverse direction from the second optical fiber passes through, and back from, the first, second and third birefringent crystals, the GRIN lens, the Faraday rotator and the mirror element, but not into the first optical fiber so that an optical isolation function is achieved.
Multiple optical isolators may be obtained with multiple pairs of optical fibers fixed in the channel of the ferrule. The end facets of the pairs of optical fibers, the first, second and third birefringent crystals, the GRIN lens, the Faraday rotator, and the mirror element are arranged and oriented with respect to each other so that light in one direction from a first optical fiber of each pair passes through, and back from, the first, second and third birefringent crystals, the GRIN lens, the Faraday rotator and the mirror element into a second optical fiber of the pair. On the other hand, light in a reverse direction from the second optical fiber of each pair passes through, and back from, the first, second and third birefringent crystals, the GRIN lens, the Faraday rotator and the mirror element, but not into the corresponding first optical fiber of the pair so that an optical isolation function is achieved with each pair of optical fibers.
REFERENCES:
patent: 5033830 (1991-07-01), Jameson
patent: 5208876 (1993-05-01), Pan
patent: 5768005 (1998-06-01), Cheng et al.
patent: 5796889 (1998-08-01), Xu et al.
E-Tek Dynamics, Inc.
Kim Robert
Townsend and Townsend / and Crew LLP
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