All-fiber millimeter-scale M-Z interferometer based on slow light in microknot resonator

High sensitivity interferometers are key building blocks in many areas of optical and photonic devices. In this letter, we propose and experimentally demonstrate a new scheme for improving the phase sensitivity of interferometer by using slow light in a microknot resonator (MKR). The slow-light interferometer with a footprint of 1.5 mm × 4 mm is fabricated by using microfiber with a diameter of 5.6 μm. By coupling MKR to one arm of the interferometer, the slow light is introduced to enhance the phase sensitivity of the interferometer. The experimental results show that the MKR has a Q-factor of 13520, and the time delay of slow light at resonance frequency is 28 ps. The phase sensitivity of Mach-Zehnder interferometer (MZI) with slow light is 25.54 rad/THz, which is 10.4 times that of a MZI without slow light. The proposed hybrid structure has the advantages of easy fabrication, small footprint, high sensitivity and wide slow light bandwidth, allowing for potential applications in miniaturization of spectrometer and high sensitivity sensing.