Methods for manufacturing microstructured optical fibers with arbitrary core size
The present invention provides methods for manufacturing microstructured optical fibers having an arbitrary core size and shape. According to one embodiment of the invention, a method of fabricating a photonic band gap fiber includes the steps of forming an assembly of stacked elongate elements, the assembly including a first set of elongate elements, the first set of elongate elements defining and surrounding a core volume, and a second set of elongate elements surrounding the first set of elongate elements, wherein the core volume defined by the first set of elongate elements has a shape that is not essentially an integer multiple of the external shape of the elongate elements of the second set of elongate elements; including the assembly in a photonic band gap fiber preform; and drawing the photonic band gap fiber preform into the photonic band gap fiber.
1. A method of fabricating a photonic band gap fiber having a photonic band gap structure, the photonic band gap structure having a pitch and a core defect void formed therein, the method comprising the steps of:
(a) forming an assembly of stacked elongate elements, the assembly including
a first set of elongate elements, the first set of elongate elements defining and surrounding a core volume, the core volume being contiguous to an outer edge of each elongate element of the first set of elongate elements, and
a second set of elongate elements surrounding the first set of elongate elements, each elongate element of the second set of elongate elements having an external polygonal shape, each of the second set of elongate elements having a hole formed longitudinally therein,
wherein the core volume defined by the first set of elongate elements has a shape that is essentially not an integer multiple of the external shape of the elongate elements of the second set of elongate elements;
(b) including the assembly in a photonic band gap fiber preform; and
(c) drawing the photonic band gap fiber preform into the photonic band gap fiber.
2. The method of claim 1 , wherein at least one of the elongate elements of the first set of elements has a substantially different external shape than the elongate elements of the second set of elongate elements.
3. The method of claim 2 , wherein each of the elongate elements of the first set of elements has a substantially different external shape than the elongate elements of the second set of elongate elements.
4. The method of claim 1 wherein the assembly includes a core tube disposed in the core volume.
5. The method of claim 4 wherein the core tube has a substantially acircular internal shape.
6. The method of claim 1 wherein the holes of the second set of elongate elements form a periodic array having a pitch, the periodic array being interrupted by the core volume.
7. The method of claim 6 wherein the assembly includes a core tube disposed in the core volume, the core tube having an inner diameter of greater than about 1.05 times the pitch of the periodic array.
8. The method of claim 7 wherein the core volume has a width of greater than about 1.05 times the pitch of the periodic array.
9. The method of claim 1 wherein each of the first set of elongate elements has a hole formed longitudinally therein, and wherein the holes of the first set of elongate elements and of the second set of elongate elements form a periodic array having a pitch.
10. The method of claim 1 wherein the core volume has a substantially different symmetry around an axis parallel to the longitudinal direction of the assembly than does the periodic array formed by the holes of the second set of elongate elements.
11. The method of claim 1 wherein the unit cell of the periodic structure formed by the second set of elongate elements has a cross-sectional shape selected from the group consisting of hexagonal, triangular, square and rectangular.
12. The method of claim 1 wherein the core volume has an external shape selected from the group consisting of circular, elliptical, hexagonal, square, and rectangular.
13. The method of claim 1 wherein at least one elongate element of the first set of elongate elements has an external shape that is a truncated version of the external polygonal shape of the elongate elements of the second set of elongate elements.
14. The method of claim 1 wherein at least one elongate element of the first set of elongate elements is formed by removing material from an elongate element substantially identical to the elongate elements of the second set of elongate elements.
15. The method of claim 1 wherein the core defect hole of the photonic band gap fiber has a radius between about 0.95 and about 1.15 times the pitch of the photonic band gap structure.
16. The method of claim 1 wherein the core defect hole of the photonic band gap fiber has a radius between about 1.30 and about 1.55 times the pitch of the photonic band gap structure.