We realize a microdroplet-etched fiber Fabry-Perot resonator. Strong polarization discrimination is achieved due to the asymmetric fiber cross section in the cavity, which should be useful for improving the measurement precision in the refractive index (RI) sensing application. The measured RI sensitivities are ~133.8 nm/RI-unit for the x polarization and 117.1 nm/RI-unit for the y polarizations, respectively. Simultaneously, the temperature effect can be eliminated by monitoring the peak difference of the two polarizations, which have the similar temperature coefficient but different RI responses.
A high sensitivity biosensor based on graphene coated silica fiber taper interferometer is presented. Thank to the combination of graphene coating and the optical fiber taper interferometer structure, the biosensor demonstrates improved DNA concentration sensitivity of 0.4 nm/log M and good linearity, yielding the lower detection limit of 10 pM. This high sensitivity and biocompatibility enable the biosensor in precision in-situ DNA detection, even in ultra-diluted DNA solution. Based on our work, the graphene coating could convert the concentration information of target molecular to the RI variation, and further to light signals by the taper.
Phase separation process of poly (N-isopropylacrylamide) (PNIPAM) aqueous solution was investigated by tapered optical fiber technique in this work. The optical transmission spectra revealed the transition of molecular conformation and aggregation of molecular chains in the course of phase separation and identified the lower critical solution temperatures (LCST) in a simple and clear way. It was found that upon heating PNIPAM chains changed from expanded coils to collapsed globules and then aggregated. It offers a new characterization technique for studying phase separation of polymer solutions or blends, and could provide abundant information of the interaction between two different macromolecules, revealing the internal mechanism of the interaction.
In this paper, an abnormal grating evolution was recorded during microfiber Bragg grating (mFBG) inscription under 193nm excimer laser. Within 20 minutes exposing, a Type IIa FBG could be obtained with above 20dB strength in 8.5 μm microfiber. This regenerated mFBG had good survival ability against high temperature up to 800 °C. Moreover, the strain response of the regenerated grating was enlarged by the microfiber structure. Thus, highly sensitive strain sensor with considerable temperature resistance could be obtained, which had potential applications in gas/oil and aerospace territory.
We demonstrate an all-solid photonic bandgap fiber modal interferometer by concatenating two tapers separated with a middle section of the fiber. Unlike the conventional devices, our structure has a lower effective index in the core and a higher effective index in the cladding, which produce novel sensing characteristics. The measured sensing sensitivities are ~63pm/°C for temperarure and ~1.74nm/N for the axial stress, respectively.
Microfiber Bragg gratings (mFBGs) can be used as cost-effective and relatively simple-to-implement biosensors for monitoring DNA interactions in situ. The sensors are functionalized by a monolayer of poly-L-lysine (PLL) with the specific molecular recognition probe DNA sequences to bind with high specificity to a given target. By recording the wavelength seperation between the two resonant peaks of a single mFBG, the mFBG biosensor is capable of detecting the presence of specific target DNA in situ.
We demonstrate an acid-based sensor from the biofuncationalized microfiber Bragg grating. By electrostatic selfassembly layer-by-layer technique, the film consisting of sodium alginate which has hygroscopic response to the potential of hydrogen is coated on the fiber surface. Consequently, the refractive index variation of the sensing film caused by water absorption can be measured by mFBG’s higher order mode peak which can be translated into pH value information. The sensitivity of the sensor is received as high as 265pm/pH.
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