# All-Optical Tuning Based on Magnetic Fluid-Filled Microcapillary Resonators Inserted with Half-Cone Fiber

## TL;DR

This paper presents a small, sensitive, and low-cost optical sensor using magnetic fluid-filled microcapillary resonators for sensing applications.

## Contribution

The novel contribution is an all-optical tuning system using magnetic fluid in microcapillary resonators for high sensitivity and repeatability.

## Key findings

- The larger resonator showed a sensitivity of 0.0347 nm/mW when pump light power increases.
- The smaller resonator demonstrated higher sensitivity of 0.1018 nm/mW when pump light power increases.

## Abstract

In this study, we designed and experimentally demonstrated an all–optical tuning system based on the absorption effect of magnetic nanoparticles on a pump light. The all-optical tuning process induces a temperature change in the microcavity–taper coupling system, resulting in a shift in the WGM resonance spectrum. The core of the sensor involved in this study is a microcapillary resonator with a microfluidic channel, in which a magnetic fluid is filled within the channel of the microcapillary resonator. We tested the sensing sensitivity of microcapillary resonators with two sizes. The experimental results indicate that for the larger microcapillary resonator, the sensitivity is 0.0347 nm/mW when the pump light power increases, and 0.0331 nm/mW when the pump light power decreases. For the smaller microcapillary resonator, the sensitivity significantly increases, with 0.1018 nm/mW and 0.1029 nm/mW as the power increases and decreases, respectively. The demonstrated optofluidic device has the advantages of small size, good repeatability, high sensitivity, and low price, and thus shows great potential for sensing applications.