Optical Microfiber Coupler Decorated by Erbium–Ytterbium Co-Doped Silica Film for Photothermal Optical Modulation and Multifunctional Sensing

Currently, there are few reports of optic fiber devices that combine efficient photothermal optical modulation and multifunctional sensing in one device. We reported an optical microfiber coupler (OMC) decorated by erbium-ytterbium co-doped silica film with significant photothermal effect, which can be used in the field of optical modulation and multifunctional sensing. It is experimentally verified that a 980-nm laser driven by the current of 500 mA enables the temperature of the decorated OMC waist region up to <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$82.5~^{\circ }$ </tex-math></inline-formula> C, and it reveals extreme layer stability, remarkable adsorption properties, and excellent thermo-desorption effects of the device. The OMC encapsulated with polydimethylsiloxane (PDMS) has a temperature sensitivity of up to 1106.88 pm/°C in the temperature range of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$28~^{\circ }$ </tex-math></inline-formula> C–<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$48~^{\circ }$ </tex-math></inline-formula> C. And achieved a maximum air-flow sensitivity of 529.39 nm<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\cdot $ </tex-math></inline-formula> s/m within the speed range of 0–18.2 m/s using hot-wire-based method. The device is placed in a <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$20~^{\circ }$ </tex-math></inline-formula> C water tank to achieve a modulation sensitivity of 24.47 pm/mA with a maximum modulation depth of 16.7 dB, effectively addressing both the response delay and high-temperature hazard caused by thermal accumulation. The device’s compact structure, low cost, high sensitivity, and multifunctional applications make it a promising application in the field of multifunctional integration.