In-Line Fiber Michelson Interferometer for Enhancing the Q Factor of Cone-Shaped Inwall Capillary Coupled Resonators

An in-line fiber Michelson interferometer in a cone-shaped inwall capillary with the whispering gallery mode microsphere resonator integrated inside is demonstrated for enhancing the Q factor, which is fabricated on the etched capillary by the femtosecond laser micromachining to decrease the coupling paths. The modulated symmetric WGM resonances and asymmetric Fano resonances induced by the Michelson interferometer are observed in the reflection spectra, with a slope of 91.87 dB/nm and Q factor as 3.85 × 10
⁴
achieved. Numerical simulations with the transfer matrix method also validate the resonator spectra modulated by the Michelson interference. This method shows a perspective potential for the enhancement of the Q factor by tailoring interacting paths through the femtosecond laser micromachining.