Investigation of polarization effects of microresonators

Abstract

This final year report documents the simulations and experiments of investigating

polarization effects of microresonator. Microresonator is made by microfiber/nanofiber,

It includes a waveguide to channel light in a closed ring shape loop. This project mainly

studied the polarization effects at the resonator’s coupling region in order to analyze the

resonance phenomenon precisely.

Two types of resonators, ring resonator and loop resonator were researched in this

project. Simulations using Rsoft FULLWAVE were carried out as the first step of the

investigation. It was found that the polarization properties of the twist resonators were

mainly varied with the length of coupler. For twist resonator with coupling length 20µm

to 35µm, self coupling transmission spectra overlapped with a minor shift of critical

coupling wavelength. When the coupling length was around 150µm to 160µm, self

coupling transmission spectra were clearly separated with splitting at the peak of the

curve. For loop resonators, it showed well separated self coupling transmission spectrum

without peak splitting. It was also noticed that the cross coupling transmission spectra

for both loop and twist resonator were polarization insensitive.

During the practical experiments, hand-made twist resonator was tested to support the

simulation results. By carefully adjusting the resonator shape, slight self coupling

transmission spectrum peak splitting was inspected for twist resonator with coupling

length 160µm. This result coincided with simulation outcome. For resonator with 70µm

coupling length, obvious resonance was inspected and it was noticed that critical

coupling wavelength shifted for different polarization status. The phenomena observed

during the experiment proved that the polarization properties of a microresonator were

closely related to the coupler length.