Optimized butt coupling between single mode fiber and hollow-core photonic crystal fiber

• Butt coupling of hollow core photonic crystal fiber with single mode fiber.
• Gap between HC-PCF and SMF is provided.
• Theoretically, Fresnel diffracted MFD matches with receiving fiber core diameter.
• Optimum gap is theoretically calculated and experimentally verified.

In this paper, the optimum gap for maximum light coupling between Single Mode Fiber (SMF) & Hollow Core Photonic Crystal Fiber (HC-PCF) is theoretically computed and experimentally demonstrated. The Gaussian beam profile emanating from transmitting fiber undergoes Fresnel diffraction in the air up to some distance till its diffracted Mode Field Diameter (MFD) matches with the core diameter of receiving fiber. Theoretically computed such distance provides an optimum gap for maximum light coupling between these two fibers. The optimum gap is numerically computed as 7.618 μm and 12.598 μm for SMF to HC-PCF and HC-PCF to SMF light transmission configurations respectively and is verified experimentally. This optimized gap is useful for HC-PCF based devices to be joined to SMF as a transmission medium.