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US 4,556,293 AGranted
Broadband unpolarized light source
AssigneeThe United States of America as represented by the Secretary of the Navy
InventorsWilliam K. Burns, Robert P. Moeller
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Abstract
Broadband, unpolarized light is produced by coupling a birefringent optical fiber to a light emitting device, such as a superluminescent diode, which is capable of emitting broadband, partially polarized light. The optical fiber is made sufficiently long to provide an optical differential path length between its birefringent axes which is longer than the coherence length of the light emitting device.
Claims6
An unpolarized light source comprising:
- means for generating a broadband beam of light having a predominant plane of polarization;
- and
- means for depolarizing said light beam comprising a highly birefringent optical fiber having birefringence axes with different group velocities corresponding to each axis, and one of its ends coupled to said light generating means with each of said birefringance axes orientated approximately 45 degrees away from said predominant plane of polarization of said light generating means, and having a physical length long enough to produce an optical differential path length between said birefringance axes which is longer than the coherence length of said broadband beam of light in said fiber.
An unpolarized light source comprising:
- a superluminescent diode capable of generating broadband light which has a predominant plane of polarization;
- and
- a highly birefringent optical fiber approximately 1 meter or more in length, having a set of birefringence axes with different group velocities corresponding to each axis, said velocities having a group delay line difference greater than or equal to 0.1 nsec/km, said birefringent optical fiber being butt-coupled to said superluminescent diode with said birefringence axes each orientated at an angle of approximately 45 degrees away from said predominant plane of polarization.
A method for depolarizing light comprising:
- generating a beam of broadband light having a predominant plane of polarization;
- and
- coupling said beam of light into a highly birefringent optical fiber haing birefringence axes with different group velocities corresponding to each axis, said axes orientated at an angle of approximately 45 degrees to said predominant plane of polarization;
- and
- passing said beam of light through said optical fiber until an optical differential path length between said birefringence axes exceeds the coherence length of said broadband beam of light in said fiber.
2 more elements
Dependencies are inferred from the claim text.