Microfiber coupler devices

A 2×2 microfiber coupler is demonstrated by laterally fusing and tapering two optical fibers using a flame brushing technique. The coupler has an overlapping length of 40mm with a uniform waist of around 5 μm. The coupler is then used to demonstrate a microfiber knot resonator (MKR) coupler. It is obtained by forming a knot within the coupling region of a microfiber coupler with a 50:50 splitting ratio. With an MKR structure, the coupler produces a resonant response at both output ports. The free spectral range (FSR) of the output spectrum from both ports is obtained at 0.2 nm at a knot diameter of 260 μm. The resonance extinction ratio (RER) of the device varies from 2 to 6 dB while the calculated Q factor and finesse are ~25646 and 3.3 respectively at both output ports.