The Numerical Modeling of 3D Microfiber Couplers and Resonators

We numerically investigate the optical properties of three-dimensional (3D) microfiber/nanofiber (MNF) couplers and resonators, by using the finite-difference time domain method. It is the first time that the polarization-dependent transmission properties of 3D MNF couplers and resonators are investigated numerically. For the knot coupler, the twisted structure contributes to the inter-polarization coupling, and the envelope of intraand inter-polarization coupling coefficients, respectively, has the trend as a (cosc)
²
or (sinc)
²
function. For the loop resonator, the inter-polarization coupling coefficients are relatively small. However, the coupling coefficients for both polarization states are discriminated obviously. The high Q-factor resonance spectrum in one polarized state may be overwhelmed by that of the other. We also investigate the mechanism of resonance spectrum splitting, and find out that the inter-polarization coupling at the coupler region degenerates the resonance spectrum and gives rise to the splitting. The results provide guidance to design 3-D MNF devices, for example, high Q-factor resonators.