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Special Issue "Resonator Sensors 2018"

A special issue of Sensors (ISSN 1424-8220). This special issue belongs to the section "Physical Sensors".

Deadline for manuscript submissions: closed (20 December 2018)

Special Issue Editor

Guest Editor
Dr. Silvia Soria Huguet

IFAC-CNR, Institute of Applied Physics, Via Madonna del Piano10, 50019 Sesto Fiorentino (FI), Italy
Website | E-Mail
Interests: optical resonators; optical sensors; nonlinear optical techniques

Special Issue Information

Dear Colleagues,

The field of sensors based on optical resonators comprises different optical cavities and resonators, ranging from, but not limited to: Whispering gallery mode resonators, photonic crystals, and grating waveguide resonators. The field has gained an increasing interest over the last few decades and it has an extremely broad range of applications as physical (temperature, pressure, displacement and field) sensors and chemical (biological, medical, agriculture and environment) sensors.

We invite manuscripts for this forthcoming Special Issue on all aspects pertinent to optical resonator sensors. Both reviews and original research articles are welcome. Reviews should provide an up-to-date and critical overview of state-of-the-art technologies such as whispering gallery modes, photonic crystals, grating waveguide resonators or any other optical resonator-based sensing mechanism. Original research papers that describe the utilization of optical resonating platforms in sensing, or new concepts and fundamental studies with potential relevance to sensing are also of interest. If you have suggestions that you would like to discuss beforehand, please feel free to contact me. I look forward to and welcome your participation in this Special Issue.

Dr. Silvia Soria Huguet
Guest Editor

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All papers will be peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

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Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 1800 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • optical sensing
  • optical microcavities
  • resonators
  • whispering gallery mode
  • grating waveguide resonators
  • morphology dependent resonances

Published Papers (11 papers)

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Research

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Open AccessArticle Effect of Uneven Electrostatic Forces on the Dynamic Characteristics of Capacitive Hemispherical Resonator Gyroscopes
Sensors 2019, 19(6), 1291; https://doi.org/10.3390/s19061291
Received: 9 February 2019 / Revised: 8 March 2019 / Accepted: 8 March 2019 / Published: 14 March 2019
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Abstract
The hemispherical resonator gyroscope (HRG) is a typical capacitive Coriolis vibratory gyroscope whose performance is inevitably influenced by the uneven electrostatic forces caused by the uneven excitation capacitance gap between the resonator and outer base. First, the mechanism of uneven electrostatic forces due [...] Read more.
The hemispherical resonator gyroscope (HRG) is a typical capacitive Coriolis vibratory gyroscope whose performance is inevitably influenced by the uneven electrostatic forces caused by the uneven excitation capacitance gap between the resonator and outer base. First, the mechanism of uneven electrostatic forces due to the significantly uneven capacitance gap in that the non-uniformity of the electrostatic forces can cause irregular deformation of the resonator and further affect the performance and precision of the HRG, was analyzed. According to the analyzed influence mechanism, the dynamic output error model of the HRG was established. In this work, the effect of the first four harmonics of the uneven capacitance gap on the HRG was investigated. It turns out that the zero bias and output error, caused by the first harmonic that dominates mainly the amplitude of the uneven capacitance gap, increase approximately linearly with the increase of the amplitude, and periodically vary with the increase of the phase. The effect of the other three harmonics follows the same law, but their amplitudes are one order of magnitude smaller than that of the first one, thus their effects on the HRG can be neglected. The effect of uneven electrostatic forces caused by the first harmonic on the scale factor is that its nonlinearity increases approximately linearly with the increase of the harmonic amplitude, which was analyzed in depth. Considering comprehensively the zero bias, the modification rate of output error, and scale factor nonlinearity, the tolerance towards the uneven excitation capacitance gap was obtained. Full article
(This article belongs to the Special Issue Resonator Sensors 2018)
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Open AccessFeature PaperArticle Fluorescent Aptamer Immobilization on Inverse Colloidal Crystals
Sensors 2018, 18(12), 4326; https://doi.org/10.3390/s18124326
Received: 10 October 2018 / Revised: 3 December 2018 / Accepted: 4 December 2018 / Published: 7 December 2018
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Abstract
In this paper, we described a versatile two steps approach for the realization of silica inverse opals functionalized with DNA-aptamers labelled with Cy3 fluorophore. The co-assembly method was successfully employed for the realization of high quality inverse silica opal, whilst the inverse network [...] Read more.
In this paper, we described a versatile two steps approach for the realization of silica inverse opals functionalized with DNA-aptamers labelled with Cy3 fluorophore. The co-assembly method was successfully employed for the realization of high quality inverse silica opal, whilst the inverse network was functionalized via epoxy chemistry. Morphological and optical assessment revealed the presence of large ordered domains with a transmission band gap depth of 32%, after the functionalization procedure. Finite Difference Time-Domain (FDTD) simulations confirmed the high optical quality of the inverse opal realized. Photoluminescence measurements evidenced the effective immobilization of DNA-aptamer molecules labelled with Cy3 throughout the entire sample thickness. This assumption was verified by the inhibition of the fluorescence of Cy3 fluorophore tailoring the position of the photonic band gap of the inverse opal. The modification of the fluorescence could be justified by a variation in the density of states (DOS) calculated by the Plane Wave Expansion (PWE) method. Finally, the development of the aforementioned approach could be seen as proof of the concept experiment, suggesting that this type of system may act as a suitable platform for the realization of fluorescence-based bio-sensors. Full article
(This article belongs to the Special Issue Resonator Sensors 2018)
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Open AccessArticle Experimental Demonstration of Temperature Sensing with Packaged Glass Bottle Microresonators
Sensors 2018, 18(12), 4321; https://doi.org/10.3390/s18124321
Received: 27 October 2018 / Revised: 23 November 2018 / Accepted: 3 December 2018 / Published: 7 December 2018
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Abstract
Whispering gallery mode (WGM) glass bottle microresonators are potential highly sensitive structures for a variety of physical and bio-chemical sensing applications. In this paper, we experimentally demonstrate the practical use of glass bottle resonators as temperature sensors. The basic parameters, such as WGM [...] Read more.
Whispering gallery mode (WGM) glass bottle microresonators are potential highly sensitive structures for a variety of physical and bio-chemical sensing applications. In this paper, we experimentally demonstrate the practical use of glass bottle resonators as temperature sensors. The basic parameters, such as WGM resonance wavelengths, free spectral ranges, and Q factors, have been investigated by coupling light from a tapered fiber to the bottle structure. We show the spectral characteristics of the WGMs by choosing different bottle dimensions and taper diameters. For practical measurements, a robust 3D-printed package that includes the bottle resonator and the tapered fiber has been proposed. The packaged bottle has a central diameter Dc = 207 µm and a length L = 300 µm. Temperature sensing experiments were also performed. A linear response of the WGM shifts as a function of the temperature is confirmed. The fitted experimental data indicate a temperature sensitivity of 10.5 pm/K at λ ~ 1550 nm, resulting in a limit of detection of 0.06 K. These values can be compared with values reported for other WGM resonators. Additionally, bottle resonators are made with simple splicing methods and their assembly method can be easily defined due to large coupling tolerances. Full article
(This article belongs to the Special Issue Resonator Sensors 2018)
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Open AccessArticle Field Evaluation of a Portable Whispering Gallery Mode Accelerometer
Sensors 2018, 18(12), 4184; https://doi.org/10.3390/s18124184
Received: 8 October 2018 / Revised: 6 November 2018 / Accepted: 23 November 2018 / Published: 29 November 2018
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Abstract
An accelerometer utilising the optomechanical coupling between an optical whispering gallery mode (WGM) resonance and the motion of the WGM cavity itself was prototyped and field-tested on a vehicle. We describe the assembly of this portable, battery operated sensor and the field-programmable gate [...] Read more.
An accelerometer utilising the optomechanical coupling between an optical whispering gallery mode (WGM) resonance and the motion of the WGM cavity itself was prototyped and field-tested on a vehicle. We describe the assembly of this portable, battery operated sensor and the field-programmable gate array automation. Pre-trial testing using an electrodynamic shaker demonstrated linear scale-factors with <0.3% standard deviation ( ± 6 g range where g = 9.81 ms 2 ), and a strong normalised cross-correlation coefficient (NCCC) of r ICP / WGM = 0.997 when compared with an integrated circuit piezoelectric (ICP) accelerometer. A noise density of 40 μ g Hz 1 / 2 was obtained for frequencies of 2–7 kHz, increasing to 130 μ g Hz 1 / 2 at 200 Hz, and 250 μ g Hz 1 / 2 at 100 Hz. A reduction in the cross-correlation was found during the trial, r ICP / WGM = 0.36, which we attribute to thermal fluctuations, mounting differences, and the noisy vehicle environment. The deployment of this hand-fabricated sensor, shown to operate and survive during ±60 g shocks, demonstrates important steps towards the development of a chip-scale device. Full article
(This article belongs to the Special Issue Resonator Sensors 2018)
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Open AccessArticle A Tellurium Oxide Microcavity Resonator Sensor Integrated On-Chip with a Silicon Waveguide
Sensors 2018, 18(11), 4061; https://doi.org/10.3390/s18114061
Received: 28 September 2018 / Revised: 31 October 2018 / Accepted: 9 November 2018 / Published: 21 November 2018
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Abstract
We report on thermal and evanescent field sensing from a tellurium oxide optical microcavity resonator on a silicon photonics platform. The on-chip resonator structure is fabricated using silicon-photonics-compatible processing steps and consists of a silicon-on-insulator waveguide next to a circular trench that is [...] Read more.
We report on thermal and evanescent field sensing from a tellurium oxide optical microcavity resonator on a silicon photonics platform. The on-chip resonator structure is fabricated using silicon-photonics-compatible processing steps and consists of a silicon-on-insulator waveguide next to a circular trench that is coated in a tellurium oxide film. We characterize the device’s sensitivity by both changing the temperature and coating water over the chip and measuring the corresponding shift in the cavity resonance wavelength for different tellurium oxide film thicknesses. We obtain a thermal sensitivity of up to 47 pm/°C and a limit of detection of 2.2 × 10−3 RIU for a device with an evanescent field sensitivity of 10.6 nm/RIU. These results demonstrate a promising approach to integrating tellurium oxide and other novel microcavity materials into silicon microphotonic circuits for new sensing applications. Full article
(This article belongs to the Special Issue Resonator Sensors 2018)
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Open AccessArticle THz Sensing With Anomalous Extraordinary Optical Transmission Hole Arrays
Sensors 2018, 18(11), 3848; https://doi.org/10.3390/s18113848
Received: 1 October 2018 / Revised: 5 November 2018 / Accepted: 6 November 2018 / Published: 9 November 2018
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Abstract
Subwavelength hole array (HA) metasurfaces support the so-called extraordinary optical transmission (EOT) resonance that has already been exploited for sensing. In this work, we demonstrate the superior performance of a different resonant regime of HA metasurfaces called anomalous EOT, by doing a thorough [...] Read more.
Subwavelength hole array (HA) metasurfaces support the so-called extraordinary optical transmission (EOT) resonance that has already been exploited for sensing. In this work, we demonstrate the superior performance of a different resonant regime of HA metasurfaces called anomalous EOT, by doing a thorough numerical and experimental study of its ability in thin-film label-free sensing applications in the terahertz (THz) band. A comprehensive analysis using both the regular and anomalous EOT resonances is done by depositing thin layers of dielectric analyte slabs of different thicknesses on the structures in different scenarios. We carry out a detailed comparison and demonstrate that the best sensing performance is achieved when the structure operates in the anomalous EOT resonance and the analyte is deposited on the non-patterned side of the metasurface, improving by a factor between 2 and 3 the results of the EOT resonance in any of the considered scenarios. This can be explained by the comparatively narrower linewidth of the anomalous EOT resonance. The results presented expand the reach of subwavelength HAs for sensing applications by considering the anomalous EOT regime that is usually overlooked in the literature. Full article
(This article belongs to the Special Issue Resonator Sensors 2018)
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Open AccessFeature PaperArticle Mode-Splitting for Refractive Index Sensing in Fluorescent Whispering Gallery Mode Microspheres with Broken Symmetry
Sensors 2018, 18(9), 2987; https://doi.org/10.3390/s18092987
Received: 14 August 2018 / Revised: 30 August 2018 / Accepted: 31 August 2018 / Published: 7 September 2018
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Abstract
Whispering gallery mode (WGM) resonators have become increasingly diverse in terms of both architecture and applications, especially as refractometric sensors, allowing for unprecedented levels of sensitivity. However, like every refractometric sensor, a single WGM resonator cannot distinguish temperature variations from changes in the [...] Read more.
Whispering gallery mode (WGM) resonators have become increasingly diverse in terms of both architecture and applications, especially as refractometric sensors, allowing for unprecedented levels of sensitivity. However, like every refractometric sensor, a single WGM resonator cannot distinguish temperature variations from changes in the refractive index of the surrounding environment. Here, we investigate how breaking the symmetry of an otherwise perfect fluorescent microsphere, by covering half of the resonator with a high-refractive-index (RI) glue, might enable discrimination of changes in temperature from variations in the surrounding refractive index. This novel approach takes advantage of the difference of optical pathway experienced by WGMs circulating in different equatorial planes of a single microsphere resonator, which induces mode-splitting. We investigated the influence of the surrounding RI of the microsphere on mode-splitting through an evaluation of the sphere’s WGM spectrum and quality factor (Q-factor). Our results reveal that the magnitude of the mode-splitting increases as the refractive index contrast between the high-refractive-index (RI) glue and the surrounding environment increases, and that when they are equal no mode-splitting can be seen. Investigating the refractive index sensitivity of the individual sub modes resulting from the mode-splitting unveils a new methodology for RI sensing, and enables discrimination between surrounding refractive index changes and temperature changes, although it comes at the cost of an overall reduced refractive index sensitivity. Full article
(This article belongs to the Special Issue Resonator Sensors 2018)
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Open AccessArticle Displacement and Strain Measurement up to 1000 °C Using a Hollow Coaxial Cable Fabry-Perot Resonator
Sensors 2018, 18(5), 1304; https://doi.org/10.3390/s18051304
Received: 28 March 2018 / Revised: 19 April 2018 / Accepted: 19 April 2018 / Published: 24 April 2018
Cited by 2 | PDF Full-text (7270 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
We present a hollow coaxial cable Fabry-Perot resonator for displacement and strain measurement up to 1000 °C. By employing a novel homemade hollow coaxial cable made of stainless steel as a sensing platform, the high-temperature tolerance of the sensor is dramatically improved. A [...] Read more.
We present a hollow coaxial cable Fabry-Perot resonator for displacement and strain measurement up to 1000 °C. By employing a novel homemade hollow coaxial cable made of stainless steel as a sensing platform, the high-temperature tolerance of the sensor is dramatically improved. A Fabry-Perot resonator is implemented on this hollow coaxial cable by introducing two highly-reflective reflectors along the cable. Based on a nested structure design, the external displacement and strain can be directly correlated to the cavity length of the resonator. By tracking the shift of the amplitude reflection spectrum of the microwave resonator, the applied displacement and strain can be determined. The displacement measurement experiment showed that the sensor could function properly up to 1000 °C. The sensor was also employed to measure the thermal strain of a steel plate during the heating process. The stability of the novel sensor was also investigated. The developed sensing platform and sensing configurations are robust, cost-effective, easy to manufacture, and can be flexibly designed for many other measurement applications in harsh high-temperature environments. Full article
(This article belongs to the Special Issue Resonator Sensors 2018)
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Review

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Open AccessFeature PaperReview Liquid Droplet Microresonators
Sensors 2019, 19(3), 473; https://doi.org/10.3390/s19030473
Received: 21 December 2018 / Revised: 17 January 2019 / Accepted: 18 January 2019 / Published: 24 January 2019
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Abstract
We provide here an overview of passive optical micro-cavities made of droplets in the liquid phase. We focus on resonators that are naturally created and suspended under gravity thanks to interfacial forces, illustrating simple ways to excite whispering-gallery modes in various slow-evaporation liquids [...] Read more.
We provide here an overview of passive optical micro-cavities made of droplets in the liquid phase. We focus on resonators that are naturally created and suspended under gravity thanks to interfacial forces, illustrating simple ways to excite whispering-gallery modes in various slow-evaporation liquids using free-space optics. Similar to solid resonators, frequency locking of near-infrared and visible lasers to resonant modes is performed exploiting either phase-sensitive detection of the leakage cavity field or multiple interference between whispering-gallery modes in the scattered light. As opposed to conventional micro-cavity sensors, each droplet acts simultaneously as the sensor and the sample, whereby the internal light can detect dissolved compounds and particles. Optical quality factors up to 107–108 are observed in liquid-polymer droplets through photon lifetime measurements. First attempts in using single water droplets are also reported. These achievements point out their huge potential for direct spectroscopy and bio-chemical sensing in liquid environments. Finally, the first experiments of cavity optomechanics with surface acoustic waves in nanolitre droplets are presented. The possibility to perform studies of viscous-elastic properties points to a new paradigm: a droplet device as an opto-fluid-mechanics laboratory on table-top scale under controlled environmental conditions. Full article
(This article belongs to the Special Issue Resonator Sensors 2018)
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Open AccessReview Temperature Sensing Performance of Microsphere Resonators
Sensors 2018, 18(8), 2515; https://doi.org/10.3390/s18082515
Received: 21 June 2018 / Revised: 13 July 2018 / Accepted: 28 July 2018 / Published: 1 August 2018
Cited by 3 | PDF Full-text (5554 KB) | HTML Full-text | XML Full-text
Abstract
In recent years, many temperature sensing devices based on microsphere resonators have emerged, attracting an increasing research interest. For the purpose of this review article, microsphere resonators are divided according to their constituting materials, namely silicone, silica, compound glass, and liquid droplet. Temperature [...] Read more.
In recent years, many temperature sensing devices based on microsphere resonators have emerged, attracting an increasing research interest. For the purpose of this review article, microsphere resonators are divided according to their constituting materials, namely silicone, silica, compound glass, and liquid droplet. Temperature monitoring relies mainly on the thermo-optic/thermal expansion of the microspheres and on the fluorescence of the doped ions. This article presents a comprehensive review of the current state of the art of microsphere based temperature sensing and gives an indication of future directions. Full article
(This article belongs to the Special Issue Resonator Sensors 2018)
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Other

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Open AccessLetter Complex Fiber Micro-Knots
Sensors 2018, 18(4), 1273; https://doi.org/10.3390/s18041273
Received: 20 March 2018 / Revised: 12 April 2018 / Accepted: 19 April 2018 / Published: 20 April 2018
Cited by 6 | PDF Full-text (909 KB) | HTML Full-text | XML Full-text
Abstract
Fiber micro-knots are a promising and a cheap solution for advanced fiber-based sensors. We investigated complex fiber micro-knots in theory and experiment. We compared the measured spectral response and present an analytical study of simple micro-knots with double twists, twin micro-knots, figure-eight micro-knots, [...] Read more.
Fiber micro-knots are a promising and a cheap solution for advanced fiber-based sensors. We investigated complex fiber micro-knots in theory and experiment. We compared the measured spectral response and present an analytical study of simple micro-knots with double twists, twin micro-knots, figure-eight micro-knots, and tangled micro-knots. This research brings the simple fabrication process and robustness of fiber micro-knots into the world of complex resonators which may lead to novel optical devices based on fiber micro-knots. Full article
(This article belongs to the Special Issue Resonator Sensors 2018)
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