Whispering-gallery mode silica microsensors for cryogenic to room temperature measurement

Abstract

Optical resonance shifts are measured against a wide range of temperatures from cryogenic to room temperature for silica microspheres operating at whispering-gallery modes. The sensor head microsphere is coupled to a fiber taper and placed in an insulated cell where the air temperature first cools down to below 110 K and then rises steadily and slowly. The transmission resonance spectrum of a distributed feedback laser at 1531 nm exciting the microsphere-taper system is monitored and recorded for every 1 K temperature increment. The resonance wavelength shifts against the temperature changes are analyzed. Several microspheres with size from 85 to 435 μm are tested. No significant dependence of the sensor sensitivity is seen with the sphere size. A cubic dependence of the wavelength shift versus the temperature is least-squares fitted. The measured sensitivity increases from 4.5 pm K −1 to 11 pm K −1 with increasing temperature in the test temperature range, and this behavior is consistent with the temperature dependence of the sum of thermal expansion and thermo-optic coefficients of silica material. The resolution of the sensors with the current instrument could reach 3 mK.

Simulation and optimization of multilayer-coated microsphere in temperature and refractive index sensing

“…Most importantly, we can see that the resonance shift due to the simultaneous RI changes of all the materials is the sum of the shifts by the respective RI change of air, silica, and TiO 2 , which verifies the accuracy of superposition in Eq. (5). Moreover, the resonance shifts calculated by FEM directly are in agreement with the results by Eq.…”

“…Microsphere resonators supporting optical whispering-gallery modes (WGMs) have been extensively studied over the past decade in many fields including narrow linewidth microlasers [1], nonlinear optics [2], and miniature sensors [3][4][5][6][7][8]. Due to the advantages of high quality factors (Q) and low mode volumes [9], microspheres are widely used as high sensitivity temperature and RI sensors, which usually employ the measurement of wavelength shifts of WGM resonance resulting from the change of effective refractive index and/or size of the resonator.…”

WGM microresonators: sensing, lasing and fundamental optics with microspheres

“…Lately, silica microspheres have been used to measure temperatures ranging from 110 K to room temperature in REVIEW ARTICLE 1 K steps with a resolution of 3 mK. The measured wavelength shifts indicate a sensitivity range between 4.5 pm/K and 11 pm/K [102]. Thermal-based gas sensing using microspheres was developed [103] using an alignment-free fiber-coupled polystyrene microsphere resonator.…”

Biosensing in a microelectrofluidic system using optical whispering-gallery mode spectroscopy

“…[12][13][14] On the other side, temperature variation due to absorption of laser energy during laser scanning or pumping 19 could change resonator conditions because of the thermal expansion and thermo-optic effects. 20 Ma et al 20,21 measured resonance wavelength shifts against temperature changes for different silica beads. The measured sensitivities closely match with the analytical values based on bulk material properties of silica thermal expansion and thermo-optic effect in a wide temperature range.…”

“…The measured sensitivities closely match with the analytical values based on bulk material properties of silica thermal expansion and thermo-optic effect in a wide temperature range. 21 In this paper, an optical WGM micro device is proposed to be integrated with a microelectrofluidic channel to provide a new MOEFS platform for label-free detection with high sensitivity in the universal analysis of biomolecules, proteins, DNA, or chemicals. The analyte solution flow in the microchannel is driven by an external electric potential.…”