ABSTRACT
Fiber-optic sensors are an indispensable element of modern sensing technologies by virtue of their low cost, excellent electromagnetic immunity, and remote sensing capability. Optical Vernier effect is widely used to enhance sensitivity of fiber-optic sensors but requires bulky and complex cascaded interferometers. Here we propose and experimentally demonstrate an ultracompact (â¼2 mm by â¼2 mm) Vernier-effect-improved sensor by only using a single microfiber-knot resonator. With the Vernier effect achieved by controlling the optical beating with the spectral ripple of a super light emitting diode (SLED), we show â¼20x sensitivity enhancement for quantitative temperature monitoring. Our sensor creates a new practical method to realize Vernier effect in fiber-optic sensors and beyond.
ABSTRACT
In this work, the dynamics of hydrogen bonds (as well as the hydrogen-bonded wire) in excited-state tautomerization of 7-hydroxyquinoline·(NH3)3 (7HQ·(NH3)3) cluster has been investigated by using time-dependent density functional theory (TDDFT). It shows that upon an excitation, the hydrogen bond between -OH group in 7-hydroxyquinoline (7HQ) and NH3 moiety would extremely strengthened in S1 state, which could effectively facilitate the releasing of the proton from the phenolic group of 7HQ moiety to the hydrogen-bonded wire and the forming an Eigen-like cationic wire (NH3···NH4(+)···NH3) in the cluster. To fulfill the different optimal angles of NH4(+) in the wire, a wagging motion of hydrogen-bonded wire would occur in excited state. Moreover, the wagging motion of the hydrogen-bonded wire would effectively promote excited-state proton transfer reaction. As the results, an excited-state multiple proton transfer (ESMPT) mechanism containing two concerted and asymmetrical processes has been proposed for the proton transfer dynamics of 7HQ·(NH3)3 cluster.
