Fiber optic ferrule and interface for coupling hollow-core and solid-core optical fibers
A fiber coupling assembly for interfacing solid core and a hollow core optical fibers includes first and second fiber optic ferrules each having a bore between proximal and distal end faces thereof. At least one ferrule end face is non-perpendicular to longitudinal axes of the ferrules. A bore of one ferrule contains a hollow core optical fiber, and a bore of the other optic ferrule contains a solid core optical fiber with a mode field diameter (MFD) transition region, to bridge a MFD mismatch between the fibers. An air gap may be provided between at least portions of ferrules at an inter-ferrule region. A fiber optic ferrule includes a bore that is non-parallel with a longitudinal axis of the ferrule, and at least one end face that is non-perpendicular to the longitudinal axis, with an optical fiber in the bore optionally including a MFD transition region.
1. A fiber optic coupling assembly comprising:
a first fiber optic ferrule comprising a first body structure having a first longitudinal axis, a first proximal end face, and a first distal end face, the first body structure defining a first bore extending from the first proximal end face to the first distal end face; and
a second fiber optic ferrule comprising a first body structure having a second longitudinal axis, a second proximal end face, and a second distal end face, the second body structure defining a second bore extending from the second proximal end face to the second distal end face;
wherein:
the second longitudinal axis is coaxial with the first longitudinal axis;
at least a portion of the first proximal end face is non-parallel to the second proximal end face;
a first portion of the first proximal end face is in contact with a first portion of the second proximal end face, and an air gap is provided between a second portion of the first proximal end face and a second portion of the second proximal end face;
at least one of the first proximal end face or the second proximal end face is non-perpendicular to each of the first longitudinal axis and the second longitudinal axis;
the first bore contains a solid core optical fiber having a first mode field diameter at the first proximal end face, having a second mode field diameter at the first distal end face, and having a mode field diameter transition region arranged between the first proximal end face and the first distal end face, the mode field diameter transition region providing a mode field diameter that transitions from the first mode field diameter to the second mode field diameter; and
the second bore contains a hollow core optical fiber.
2. The fiber optic coupling assembly of claim 1 , further comprising an antireflection coating at the first proximal end face.
3. The fiber optic coupling assembly of claim 1 , wherein the first mode field diameter exceeds the second mode field diameter by at least 10 μm.
4. The fiber optic coupling assembly of claim 1 , wherein the first body structure has a generally cylindrical shape, and the second body structure has a generally cylindrical shape.
5. The fiber optic coupling assembly of claim 1 , wherein the first body structure comprises a frustoconical portion proximate to the first proximal end face, and the second body structure comprises a frustoconical portion proximate to the second proximal end face.
6. The fiber optic coupling assembly of claim 1 , wherein one of the first bore or the second bore is non-parallel with the first and second longitudinal axes, while the other of the first bore or the second bore is parallel with the first and second longitudinal axes.
7. The fiber optic coupling assembly of claim 6 , wherein for the one of the first bore or the second bore that is non-parallel with the first and second longitudinal axes and the second longitudinal axis, an angular mismatch between the bore and the first and second longitudinal axes is in a range of 1.0 degrees to 1.5 degrees.
8. The fiber optic coupling assembly of claim 6 , wherein a center of the first bore is coincident with the first longitudinal axis at the first proximal end face, and a center of the second bore is coincident with the second longitudinal axis at the second proximal end face.
9. The fiber optic coupling assembly of claim 1 , wherein a proximal end of the hollow core optical fiber is non-parallel with the second proximal end face, an inset region is provided between the second end face and the proximal end of the hollow core optical fiber, and an air gap is provided between a portion of the proximal end of the hollow core optical fiber and portion of a proximal end of the solid core optical fiber.
10. The fiber optic coupling assembly of claim 1 , wherein:
the first fiber optic ferrule comprises a plurality of first bores extending from the first proximal end face to the first distal end face;
the second fiber optic ferrule comprises a plurality of second bores extending from the second proximal end face to the second distal end face;
each first bore of the plurality of first bores contains a solid core optical fiber having a first mode field diameter at the first proximal end face, having a second mode field diameter at the first distal end face, and having a mode field diameter transition region arranged between the first proximal end face and the first distal end face, the mode field diameter transition region providing a mode field diameter that transitions from the first mode field diameter to the second mode field diameter; and
each second bore of the plurality of second bores contains a hollow core optical fiber.
11. The fiber optic coupling assembly of claim 1 , comprising a first connector that comprises the first fiber optic ferrule, and comprising a second connector that comprises the second fiber optic ferrule.
12. The fiber optic coupling assembly of claim 1 , wherein the first proximal end face is angularly offset away from the second proximal end face by to an angle in a range of from 3.35° to 4.7°.