Coupler to connect a solid core fiber with a hollow core fiber

A coupler comprising:

• a single mode fiber (SMF) portion;
• a hollow core fiber (HCF) portion;
• a graded index fiber (GRIN) portion having a GRIN proximal end and a GRIN distal end, wherein the GRIN proximal end touches the SMF portion;
• and
• a secondary fiber portion having a secondary fiber proximal end and a secondary fiber distal end, wherein the secondary fiber proximal end is attached to the GRIN distal end by fusion splicing or by using an adhesive, and wherein the secondary fiber distal end is engineered to reduce back-reflection.