Hybrid Mach–Zehnder interferometer and knot resonator based on silica microfibers

We propose and demonstrate an all-fiber high Q Mach–Zehnder interferometer (MZI)-coupled microknot resonator (MZKR) structure using optical microfibers drawn from silica fibers. The experimental results show that this microfiber-based structure achieved a high Q factor of ∼ 15,000 and good interference fringes with extinction ratio of up to ∼ 15 dB. By optimizing the loop-length of the microfiber knot and the optical path-difference of the MZI, the desired MZKR with higher Q factor and better extinction ratio could be obtained. A series of integrated all-fiber optical devices could be realized based on such a MZKR structure due to its outstanding advantages of easy fabrication, great flexibility, low cost, low loss, etc.