High Sensitivity Fiber Refractive Index Sensors Based on Asymmetric Supermodes Interference in Tapered Four Core Fiber

We demonstrate high sensitivity fiber refractive index (RI) sensor based on asymmetric supermode interferences in tapered four core fiber (TFCF). To make TFCF-based RI sensors, the whitelight was launched into any one of the cores to define the excitation orientation and is called a vertex-core excitation scheme. When the four-core fiber (FCF) was gradually tapered, the four cores gathered closer and closer. Originally, the power coupling occurred between its two neighboring cores first and these three cores are grouped to produce supermodes. Subsequently, the fourth diagonal core enters the evanescent field overlapping region to excite asymmetric supermodes interferences. The output spectral responses of the two cores next to the excitation core are mutually in phase whereas the spectral responses of the diagonal core are in phase and out of phase to that of the excitation core at the shorter and longer wavelengths, respectively. Due to the lowest limitation of the available refractive index of liquids, the best sensitivity can be achieved when the tapered diameter is 10 μm and the best RI sensitivity S is 3249 nm/RIU over the indices ranging from 1.41–1.42. This is several times higher than that at other RI ranges due to the asymmetric supermodes.

Fabry-Perot Interferometer Based on Suspended Core Fiber for Detection of Gaseous Ethanol

An optical fiber tip sensor based on a Fabry–Perot interferometer is proposed for the detection of ethanol in the gas phase. The sensor is fabricated by fusion splicing one end of the suspended core fiber to a single mode fiber, whereas the other end is kept open to enable the interaction between the light propagating in the suspended core and the ethanol gas molecules. The sensor was tested with different percentages of ethanol, exhibiting a linear response between 0 and 100 wt.%, with a sensitivity of 3.9 pm/wt.%. The proposed sensor, with a length of a few hundred micrometers, can be an alternative solution for the detection of gaseous ethanol in foods or beverages, such as wines and distilled drinks.

Impact of Mode-Area Dispersion on Nonlinear Pulse Propagation in Gas-Filled Anti-Resonant Hollow-Core Fiber

We numerically investigate the effect of mode-area dispersion in a tubular-type anti-resonant hollow-core fiber by using a modified generalized nonlinear Schrödinger equation that takes into account the wavelength-dependent mode area in its nonlinear term. The pulse evolution dynamics with and without the effect of mode-area dispersion are compared and analyzed. We show that strong dispersion of the mode area in the proximity of the cladding wall thickness-induced resonances has a significant impact on the soliton pulse propagation, resulting in considerable changes in the conversion efficiencies in nonlinear frequency mixing processes. The differences become more prominent when the pump has higher energy and is nearer to a resonance. Hence, the mode-area dispersion must be accounted for when modeling such a case.