Search Results (6)

A sensitivity-enhanced temperature sensor based on a Mach–Zehnder interferometer (MZI) coated by polydimethylsiloxane (PDMS) film is proposed and investigated. The MZI with a compact size of 2.28 mm is fabricated by embedding a tapered single-mode fiber (SMF) between two multimode fibers (MMFs). Since PDMS has a higher thermo-optical coefficient than silica, the proposed sensor has better temperature sensing performance than the case without PDMS coating, which is demonstrated by simulation and experiment. The experimental results show that the sensitivity of the proposed sensor is as high as −1.06 nm/°C in the range from −5 °C to 45 °C. Full article

Dissolved gases in the aquatic environment are critical to understanding the population of aquatic organisms and the ocean. Currently, laser absorption techniques based on membrane separation technology have made great strides in dissolved gas detection. However, the prolonged water–gas separation time of permeable membranes remains a key obstacle to the efficiency of dissolved gas analysis. To mitigate these limitations, we demonstrated direct measurement of dissolved gas using the evanescent-wave absorption spectroscopy of a tapered silica micro-fiber. It enhanced the analysis efficiency of dissolved gases without water–gas separation or sample preparation. The feasibility of this sensor for direct measurement of dissolved gases was verified by taking the detection of dissolved ammonia as an example. With a sensing length of 5 mm and a consumption of ~50 µL, this sensor achieves a system response time of ~11 min and a minimum detection limit (MDL) of 0.015%. Possible strategies are discussed for further performance improvement in in-situ applications requiring fast and highly sensitive dissolved gas sensing. Full article

A fiber-optic refractometer for various liquids with refractive indices in the range from 1.33 to 1.43 has been manufactured and tested. The sensor is based on a thin silicon oxynitride (Si₃N_4-xO_x) film coated thinned optic fiber section (taper) obtained in a multimode all-silica optical fiber by chemical etching of the reflective cladding. The film was deposited on the cylindrical surface of the thinned fiber by the surface plasma chemical vapor deposition method (SPCVD). Lossy mode resonance (LMR) was observed in the transmission spectrum of the coated taper at a wavelength dependent on the refractive index of the liquid in which the taper was immersed. We tested the obtained sensors in distilled water, isopropyl alcohol, dimethylformamide, and their aqueous solutions. It was found that with the help of the SPCVD, one can obtain a set of sensors in a single deposition run with the dispersion of sensitivity and spectral position of LMR no more than 5%. Maximum sensitivity of the manufactured sensors to surrounding media refractive index (SMRI) variation exceeds 1090 nm/RIU, which is the highest value recorded to date for a sensor with a non-oxide coating. Full article

Optical trapping of sub−micrometer particles in three dimensions has been attracting increasing attention in a wide variety of fields such as physics, chemistry, and biologics. Optical fibers that allow stable trapping of such particles are not readily available but beneficial in system integration and miniaturization. Here, we present a readily accessible batch fabrication method, namely fiber pulling assisted tubeless chemical etching, to obtain sharp tapered optical fibers from regular telecommunication single−mode fibers. We demonstrated the applications of such fiber tapers in two non−plasmonic optical trapping systems, namely single− and dual−fiber−taper−based trapping systems. We realized single particle trapping, multiple particle trapping, optical binding, and optical guiding with sub−micrometer silica particles. Particularly, using the dual fiber system, we observed the three−dimensional optical trapping of swarm sub−micrometer particles, which is more challenging to realize than trapping a single particle. Because of the capability of sub−micrometer particle trapping and the accessible batch fabrication method, the fiber taper−based trapping systems are highly potential tools that can find many applications in biology and physics. Full article

Micro-optical resonators have been introduced as sensors in many applications for a wide number of variable types of stimuli due to their very high resolution, high sensitivity, and high-quality factor. In this paper, a novel micro-optical sensor was designed and tested as a concentration meter for chemical composition of a solution. The micro-optical resonator used is based on whispering gallery mode (WGM). This phenomenon appears when a tapered, single-mode laser carrying micro-optical fiber is evanescently coupled with a polymeric or silica micro-optical resonator. The presented sensor shows the change in concentration by experiencing a change in its morphology due to the varied viscosity of its environment. The variation of concentrations or fluid contents results in a change between the radii of the micro-optical resonator. With varied chemical composition and concentration in the tested sample varied infinitesimally small morphological changes are detected. The change in the resonators shape is read as a WGM shift in the resonance transmission spectrum, which is interpreted using a technique called cross-correlation, which compares the output across time to display the shift, which is later translated into distinct concentration levels. The proposed, exceptionally low-cost sensors were able to detect change at very high resolutions allowing better sensitivity along with wider range of variation. Experimental work for detection of ranges of concentrations of variable type of contaminants is presented. Full article

Long-period fiber gratings (LPGs) are well known for their sensitivity to external influences, which make them interesting for a large number of sensing applications. For these applications, fibers with a high numerical aperture (i.e., fibers with highly germanium (Ge)-doped fused silica fiber cores) are more attractive since they are intrinsically photosensitive, as well as less sensitive to bend- and microbend-induced light attenuations. In this work, we introduce a novel method to inscribe LPGs into highly Ge-doped, single-mode fibers. By tapering the optical fiber, and thus, tailoring the effective indices of the core and cladding modes, for the first time, an LPG was inscribed into such fibers using the amplitude mask technique and a KrF excimer laser. Based on this novel method, sensitive LPG-based fiber optic sensors only a few millimeters in length can be incorporated in bend-insensitive fibers for use in various monitoring applications. Moreover, by applying the described inscription method, the LPG spectrum can be influenced and tailored according to the specific demands of a particular application. Full article