Fiber optic ferrule and interface for coupling hollow-core and solid-core optical fibers

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.