Whispering gallery mode temperature sensor of liquid microresonastor

Abstract

We propose and demonstrate a whispering gallery mode (WGM) resonance-based temperature sensor, where the microresonator is made of a DCM (2-[2-[4-(dimethylamino)phenyl] ethenyl]-6-methyl-4H-pyran-4-ylidene)-doped oil droplet (a liquid material) immersed in the water solution. The oil droplet is trapped, controlled, and located by a dual-fiber optical tweezers, which prevents the deformation of the liquid droplet. We excite the fluorescence and lasing in the oil droplet and measure the shifts of the resonance wavelength at different temperatures. The results show that the resonance wavelength redshifts when the temperature increases. The testing sensitivity is 0.377 nm/°C in the temperature range 25°C-45°C. The results of the photobleaching testing of the dye indicate that measured errors can be reduced by reducing the measured time. As far as we know, this is the first time a WGM temperature sensor with a liquid state microcavity has been proposed. Compared with the solid microresonator, the utilization of the liquid microresonator improves the thermal sensitivity and provides the possibility of sensing in liquid samples or integrating into the chemical analyzers and microfluidic systems.

Microlasers Enabled by Soft‐Matter Technology

“…Lasing modes exhibited a linear blue‐shift with the increase of temperature. The sensitivity was determined to be about 1.5 nm °C −1 , about four times better than the previous work . Very recently, Yang's group reported the use of an optical WGM microcavity in a wireless sensor for thermal sensing and aerial mapping .…”

“…For example, Sun's group demonstrated strain‐induced bidirectional tuning of the WGM resonances, enabling the possibility of bend sensing applications. Liu et al performed temperature sensing using dyed‐doped oil droplet immersed in aqueous solution . The temperature induced wavelength shifts giving bywhere α = Δ n /Δ T is the thermos‐optical coefficient and β = Δ R /( R Δ T ) is the thermal expansion coefficient, R is the radius of the microsphere resonator; n is the refractive index of the resonator; T is the ambient temperature.…”

Tuning of Polarization-Dependent Whispering Gallery Modes in Grapefruit Microstructured Optical Fibers Infiltrated With Negative Dielectric Anisotropy Liquid Crystals

“…Tuning of WGMs in microresonators have been an interesting research topic since the pioneering studies on WGM devices in the 1990s. As reported in previous studies, tunable WGM microresonators could be achieved by altering microresonator size [11,12], controlling environmental temperature [13,14], changing solution concentration or simply replacing one fluid infiltrated in the microresonator with another [4]. Although large WGM resonance wavelength shift could be achieved, it would be difficult to precisely control the microresonator size and environmental temperature.…”

Optothermal dynamics in whispering-gallery microresonators

“…Specifically, a high thermal sensing sensitivity of −1.17 nm/K has been realized in a silk fibroin microtoroid, which is attributed to the large thermal expansion effect. 127 An alternative experimental design for temperature sensing is the use of microdroplets, which can be made of a variety of materials, such as dye-doped cholesteric liquids, liquid crystals, 128 oils, 129 etc. The advantage of microdroplet-based thermal sensor is the ease of integration with conventional microfluidics, as well as diverse choices of materials with relatively high thermal refraction coefficients.…”