Reconfigurable microresonators induced in side-coupled optical fibers

TL;DR

This paper demonstrates the creation of reconfigurable high-Q microresonators in side-coupled optical fibers through controlled coupling near cutoff wavelengths, enabling tunable optical properties for various photonics applications.

Contribution

It introduces a novel method to induce and mechanically reconfigure microresonators in optical fibers by exploiting coupling effects near cutoff wavelengths.

Findings

High Q-factor microresonators achieved in bent optical fibers.

Microresonator dimensions can be mechanically tuned from millimeters to 100 microns.

Free spectral range varies from picometers to hundreds of picometers.

Abstract

We experimentally demonstrate that side-coupling of coplanar bent optical fibers can induce a high Q-factor whispering gallery mode (WGM) optical microresonator. To explain the effect, we consider WGMs with wavelengths close to the cutoff wavelengths (CWs) of these fibers which slowly propagate along the fiber axes. In the vicinity of the touching region, WGMs of adjacent fibers are coupled to each other, and CWs experience sub-nanoscale axial variation proportional to the coupling strength. We show that in certain cases the CW variation leads to full localization of the WGMs and the creation of an optical microresonator. By varying the characteristic curvature fiber radius from the centimeter order to millimeter order, we demonstrate fully mechanically reconfigurable high Q-factor optical microresonators with dimensions varying from the millimeter order to 100-micron order and free spectral range varying from a picometer to hundreds of picometers. The new microresonators may find applications in cavity QED, microresonator optomechanics, frequency comb generation with tunable repetition rate, tunable lasing, and tunable processing and delay of optical pulses.