Whispering Gallery Mode (WGM) sensors provide high sensitivity, high resolution, small footprint, and resistance to electromagnetic interference, making them a great option for displacement sensing. An efficient method of coupling light into and out of WGM resonators is through the use of tapered tapers, but their instability can be a limitation in practical applications. Conventional packaging methods for WGM resonators use UV-curable polymers with low refractive indices to improve robustness, but their rigidity can make them less suitable for displacement sensing. Additionally, their high cost, potential toxicity and the interference from ambient moisture pose a critical issue. In this study, we demonstrate an alternative method of packaging WGM devices using non-toxic polydimethylsiloxane (PDMS). The Q-factor of 107 is achieved at the 780 nm band. The PDMS packaging technique not only improves the robustness and compactness of the WGM device, but also enhances humidity resistance significantly. By take advantages of the unique flexibility of PDMS, we demonstrate displacement detection with a high sensitivity of ~0.1 pm/μm and a detection limit of 600 nm.
Optical Whispering Gallery Mode (WGM) microresonators have shown great promise in sensing applications. Various efforts have been made to package WGM sensors in order to enhance their robustness for field applications. Previously, polydimethylsiloxane (PDMS) and other low index polymers have been employed for packaging of WGM sensors. However, the long curing time of PDMS and the rigidity of polymers pose other difficulties, thereby limiting their performance. Hydrogels, with shorter polymerization time and increased flexibility, transparency and biocompatibility, offer a great alternative to current packaging materials. The flexibility and optical transparency of hydrogels, in conjunction with the capability to functionalize them for specific applications, provide superior functionality and improved stability of WGM sensors. Herein we propose the use of laponite nanoclay and N, N, dimethylacrylamide (DMAA) based hydrogel for the packaging of WGM sensors. Microbubble resonators were used for the demonstration of hydrogel-based packaging. The hydrogel was synthesized by mixing DMAA in exfoliated nanoclay suspension at different concentrations with sodium persulfate as an initiator and Tetramethylethylenediamine (TEMED) as an accelerator. The microbubble resonators were packaged on 3D-printed chips and were characterized through their transmission spectra.
Whispering Gallery Mode (WGM) microresonators are a class of optical sensors with the ability to trap and confine light under optical resonance conditions. Typically, this resonance is excited inside a WGM resonator using expensive and bulky tunable diode lasers, which can be a limiting factor in low-resource settings and in developing economies. In the manuscript, we describe a method of “reverse tuning” to modify the resonance conditions, paving the way for lower cost WGM excitation and ultimately lower cost sensing. We demonstrate three different methods of reverse tuning the WGM using temperature, pressure, and refractive index in a microbubble resonator (MBR), a subclass of WGM sensors that is particularly well-suited for reverse tuning using the three aforementioned methods. By reducing the cost of the MBR platform through reverse tuning, we can make these ultra-sensitive devices more practical and accessible in low-resource settings.
A pH sensor can help understand chemical conditions of solutions, such as precise cell culture medium monitoring in real time. High-quality whispering-gallery-mode (WGM) microresonators have been utilized for surface sensing and are mainly based on the tracking of refractive index changes occurring within a wavelength range from their wall surface. This high sensitivity, reaching up to 10-5 RIU (~2.5 nm/RIU and measured at a femtometer resolution) leads to a broad range of applications, especially for biosensing purposes through the monitoring of molecular binding events. Here, we study the deposition of thin layers of poly(vinyl alcohol)/poly(acrylic acid) (PVA/PAA) hydrogels inside a whispering gallery mode (WGM) microbubble resonator (MBR), fabricated inline with a silica capillary. The generation of such layers is achieved by withdrawing a liquid solution of 25% PVA/PAA in pure water into the MBR and locally heating the microbubble region, resulting in hydrogel formation only in the cavity. The capillary is then rinsed and tested with varying pH solutions. The swelling ability of these gels is directly proportional to the pH of samples brought into contact with the cavity, leading to physical modifications of the WGM coupling properties. We show the preliminary results obtained for the polymerization and characterization of these gels in microbubbles and present the related signal shifts observed for several pH values. We also discuss the gel kinetics over time and investigate practical uses such as reversible and tunable detection of small pH changes.
KEYWORDS: Temperature metrology, Sensors, Resonators, Optical sensing, Databases, Biological and chemical sensing, Signal detection, Sensing systems, Calibration
Precise temperature measurement is highly desirable in many scientific, engineering, and industrial areas. Optical sensors based on Whispering-Gallery-Mode (WGM) microresonators offer the advantages of high sensitivity, high resolution, and small footprint. However, conventional sensing methods rely on tracking the changes in a single-mode, which limits the dynamic range of the measurement. We demonstrate an optical WGM barcode technique involving simultaneous monitoring of the patterns of multiple modes that can provide a direct temperature readout from the spectrum. This work lays the foundation for developing a high-resolution temperature sensor with superior sensitivity over a broad dynamic range.
Whispering Gallery Mode (WGM) microresonators are a powerful class of optical devices with the ability to confine light within a small volume. These devices offer the advantages of high sensitivity, diversities in their geometries to meet the needs of different applications, and ease of integration with conventional electronic systems. Among various kinds of WGM resonators, microbubble resonators are a unique type of WGM device in which the optical and fluidic components are combined. We have developed a packaged silica microbubble resonator device for biosensing applications. HF etching is used to control the wall thickness and approach to the quasi-droplet regime in the packaged devices.
Optical Whispering Gallery Mode (WGM) microresonators have become a powerful tool in fundamental physics as well as significant applications. Optical sensors based on WGM resonators have shown ultra-high sensitivity levels for various analytes. Among various kinds of WGM resonators, microbubble resonators (MBRs) are especially appealing as sensors, since the optical and fluidic elements are combined into a single component. We have developed a simple, rapid, and reliable packaging technique for silica microbubble resonators using 3-D printed packaged chips. The packaged MBR offer Q-factors at high as 106 with stability to environmental fluxes such as temperature. As an initial application, we demonstrate internal pressure sensing with our packaged MBR devices. The integration of both optical and fluidic components shows potential in a wide variety of field-based and point-of-care applications.
Whispering gallery mode devices have emerged as a powerful class of optical devices in which light-matter interactions are significantly enhanced within micron-scale structures, making them an ideal platform for both fundamental science and applications such as advanced sensors, low-threshold lasers and nonlinear optics, just to name a few. Typically, fibers tapers or prisms are used as optical couplers for the resonators. We demonstrate angle-polished fibers as an alternative option to efficiently couple light to a high-quality whispering-gallery resonator. Angle-polished fibers offer the advantage of rapid fabrication, increased mechanical stability versus fiber tapers, and the ability to tune the excitation angle of light. We demonstrate the use of angle-polished fibers for coupling light out of a whispering-gallery device as well as a rapid, low-cost method for fabricating the couplers.
Whispering Gallery Mode (WGM) microresonators are a powerful class of optical devices in which light is confined within a small volume. These devices offer the advantages of high sensitivity, affordable cost of fabrication, and ease of integration with conventional electronic systems. In particular, microbubble resonators are a unique type of WGM devices in which the optical and fluidic elements are combined into a single component. We have developed a packaged, silica microbubble resonator device for field applications using 3-D printed substrates. These devices offer Qfactors at high as 106.
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