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US 7,064,889 B2Granted
Double-clad fiber lasers and amplifiers having long-period fiber gratings
AssigneeThe Board of Trustees of the Leland Stanford Junior University
InventorsMichel J. F. Digonnet, Vinayak Dangui
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Abstract
Long-period fiber gratings are placed in a predetermined pattern along a double-clad optical fiber having an outer cladding, an inner cladding and a core. The core is doped with an optically active material such as, for example, a rare earth ion or other laser ion. The long-period fiber gratings couple light between a mode of the inner cladding and a mode of the core. As a consequence of increased coupling into the core resulting from the use of long-period fiber gratings, the length of double-clad optical fiber needed to transfer light between the inner cladding and the core is reduced.
Claims43
A double-clad optical fiber comprising:
- a core doped with an optically active dopant, the core having a core refractive index;
- an inner cladding surrounding the core, the inner cladding having an inner cladding refractive index, the core refractive index being greater than the inner cladding refractive index, and the core supporting at least one core mode;
- an outer cladding surrounding the inner cladding, the outer cladding having an outer cladding refractive index, the inner cladding refractive index being greater than the outer cladding refractive index, and the inner cladding supporting at least one cladding mode;
- and
- at least one long-period fiber grating formed in the fiber by a substrate applied against the fiber to perturb the refractive index of at least one of the core and the inner cladding, the long-period fiber grating coupling light from the at least one cladding mode to the at least one core mode.
2 more elements
A double-clad optical fiber comprising:
- an optically active core having a core refractive index;
- an inner cladding surrounding the core, the inner cladding having an inner cladding refractive index, the core refractive index being greater than the inner cladding refractive index, and the core supporting at least one core optical mode;
- an outer cladding surrounding the inner cladding, the outer cladding having an outer cladding refractive index, the inner cladding refractive index being greater than the outer cladding refractive index, and the inner cladding supporting at least one cladding optical mode;
- and
- a plurality of long-period optical gratings formed in the fiber to couple light from the at least one cladding mode to the at least one core mode, at least one of the long-period optical gratings formed by at least one substrate applied against the fiber to perturb the refractive index of at least one of the core and the inner cladding.
2 more elements
A double-clad optical fiber comprising:
- an optically active core having a core refractive index;
- an inner cladding surrounding the core, the inner cladding having an inner cladding refractive index, the core refractive index being greater than the inner cladding refractive index, and the core supporting at least one core optical mode;
- an outer cladding surrounding the inner cladding, the outer cladding having an outer cladding refractive index, the inner cladding refractive index being greater than the outer cladding refractive index, and the inner cladding supporting at least one cladding optical mode;
- and
- a plurality of long-period optical gratings formed in the fiber to couple light from the at least one cladding mode to the at least one core mode, the long-period optical gratings longitudinally positioned at different locations spaced apart by selected distances along a length of the optical fiber, wherein the selected distances between adjacent long-period optical gratings vary along said length of the fiber.
2 more elements
A double-clad optical fiber comprising:
- an optically active core having a core refractive index;
- an inner cladding surrounding the core, the inner cladding having an inner cladding refractive index, the core refractive index being greater than the inner cladding refractive index, and the core supporting at least one core optical mode;
- an outer cladding surrounding the inner cladding, the outer cladding having an outer cladding refractive index, the inner cladding refractive index being greater than the outer cladding refractive index, and the inner cladding supporting at least one cladding optical mode;
- and
- a plurality of long-period optical gratings formed in the fiber to couple light from the at least one cladding mode to the at least one core mode, wherein at least two of the long-period optical gratings are laterally disposed with respect to each other.
2 more elements
A double-clad optical fiber comprising:
- an optically active core having a core refractive index;
- an inner cladding surrounding the core, the inner cladding having an inner cladding refractive index, the core refractive index being greater than the inner cladding refractive index, and the core supporting at least one core optical mode;
- an outer cladding surrounding the inner cladding, the outer cladding having an outer cladding refractive index, the inner cladding refractive index being greater than the outer cladding refractive index, and the inner cladding supporting at least one cladding optical mode;
- and
- a plurality of long-period optical gratings formed in the fiber to couple light from the at least one cladding mode to the at least one core mode, wherein at least a first long-period optical grating has a first optical period and at least a second long-period optical grating has a second optical period, wherein the first optical period differs from the second optical period.
2 more elements
A method of coupling light into a double-clad fiber that comprises an optically active core supporting at least one core mode, an inner cladding supporting at least one inner cladding mode, and an outer cladding, the method comprising:
- coupling light into the inner cladding to transfer optical power into an inner cladding mode;
- forming a long-period fiber grating by applying a substrate against the fiber to perturb a refractive index of at least one of the core and the inner cladding;
- and
- propagating inner cladding mode light proximate the long-period fiber grating, the long-period fiber grating causing light to be coupled from the inner cladding mode to the core mode to transfer at least a portion of the optical power from the inner cladding to the core, the long-period fiber grating having a period selected to provide phase matching between the inner cladding mode and the core mode to cause the optical power to be coupled between the inner cladding mode and the core mode.
1 more element
A method of coupling light into a double-clad fiber that comprises an optically active core supporting at least one core mode, an inner cladding supporting at least one inner cladding mode, and an outer cladding, the method comprising:
- coupling light into the inner cladding to transfer optical power into an inner cladding mode;
- forming a long-period fiber grating by applying a substrate against the fiber to perturb a refractive index of at least one of the core and the inner cladding;
- and
- propagating inner cladding mode light in the effect of long-period fiber grating, the long-period fiber grating causing light to be coupled from the inner cladding mode to the core mode to transfer at least a portion of the optical power from the inner cladding to the core, the long-period fiber grating having a period selected to provide phase matching between the inner cladding mode and the core mode to cause the optical power to be coupled between the inner cladding mode and the core mode.
1 more element
A double-clad optical fiber having a longitudinal axis therethrough, said double-clad optical fiber comprising:
- a core doped with an optically active dopant, the core having a core refractive index;
- an inner cladding surrounding the core, the inner cladding having an inner cladding refractive index that decreases with lateral distance away from said longitudinal axis, the core refractive index being greater than the inner cladding refractive index, and the core supporting at least one core mode;
- and
- an outer cladding surrounding the inner cladding, the outer cladding having an outer cladding refractive index, the inner cladding refractive index being greater than the outer cladding refractive index, and the inner cladding supporting at least one cladding mode;
- and
- at least one long-period fiber grating positioned on the fiber to couple light from the at least one cladding mode to the at least one core mode, the long-period fiber grating formed by a substrate applied against the fiber to perturb the refractive index of at least one of the core and the inner cladding.
3 more elements
A double-clad optical fiber system comprising:
- a core doped with an optically active dopant, the core having a core refractive index;
- an inner cladding surrounding the core, the inner cladding having an inner cladding refractive index, the core refractive index being greater than the inner cladding refractive index, and the core supporting at least one core mode;
- an outer cladding surrounding the inner cladding, the outer cladding having an outer cladding refractive index, the inner cladding refractive index being greater than the outer cladding refractive index, and the inner cladding supporting at least one cladding mode;
- a substrate applied against the fiber, the substrate producing variations of the refractive index of at least one of the core and the inner cladding;
- and
- at least one long-period fiber grating formed in the fiber by the variations, the long-period fiber grating coupling light from the at least one cladding mode to the at least one core mode.
3 more elements
A double-clad optical fiber comprising:
- a core doped to provide signal gain, the core having a core refractive index;
- an inner cladding surrounding the core, the inner cladding having an inner cladding refractive index, the core refractive index being greater than the inner cladding refractive index, and the core supporting at least one core mode;
- an outer cladding surrounding the inner cladding, the outer cladding having an outer cladding refractive index, the inner cladding refractive index being greater than the outer cladding refractive index, and the inner cladding supporting at least one cladding mode;
- and
- at least one long-period fiber grating formed in the fiber by a substrate applied against the fiber to perturb the refractive index of at least one of the core and the inner cladding, the long-period fiber grating coupling light from the at least one cladding mode to the at least one core mode.
2 more elements
Dependencies are inferred from the claim text.