Ultrahigh-sensitivity temperature fiber sensor based on multimode interference

Abstract

The proposed sensing device relies on the self-imaging effect that occurs in a pure silica multimode fiber (coreless MMF) section of a single-mode-multimode-single-mode (SMS)-based fiber structure. The influence of the coreless-MMF diameter on the external refractive index (RI) variation permitted the sensing head with the lowest MMF diameter (i.e., 55 μm) to exhibit the maximum sensitivity (2800 nm/RIU). This approach also implied an ultrahigh sensitivity of this fiber device to temperature variations in the liquid RI of 1.43: a maximum sensitivity of -1880 pm/°C was indeed attained. Therefore, the results produced were over 100-fold those of the typical value of approximately 13 pm/°C achieved in air using a similar device. Numerical analysis of an evanescent wave absorption sensor was performed, in order to extend the range of liquids with a detectable RI to above 1.43. The suggested model is an SMS fiber device where a polymer coating, with an RI as low as 1.3, is deposited over the coreless MMF; numerical results are presented pertaining to several polymer thicknesses in terms of external RI variation.

Recent Developments in Fiber Optics Humidity Sensors

“…The single mode-multimode-single mode (SMS) fiber structure has found many applications owing to its unique spectral characteristics [70]. The physical principle of this interferometer is that light transmitted through the fundamental mode of the SMF is coupled to several modes into the MMF section and re-coupled to the fundamental mode of the SMF at the end of the MMF segment [70].…”

“…The physical principle of this interferometer is that light transmitted through the fundamental mode of the SMF is coupled to several modes into the MMF section and re-coupled to the fundamental mode of the SMF at the end of the MMF segment [70]. A SMS optical fiber coated with PVA provides a sensitivity of 90 pm/%RH [71], whereas by combining SMS optical structure, the tapering method, and a coating consisting of SiO 2 nanoparticles, the OFHS developed in [72] and shown in Figure 11 offers a sensitivity of 584.2 pm/%RH.…”

Curvature and Temperature Discrimination Using Multimode Interference Fiber Optic Structures—A Proof of Concept

“…Previous studies have shown that the first self-image (and multiples) exhibits minimum losses and therefore maximum amplitudes of the spectral signals may be achieved [3]- [9].…”

“…MMI fiber devices have been developed mainly for fiber laser applications [5] or sensing elements like strain [6], temperature [7], curvature [8], refractive index [9] and simultaneous measurement of strain and temperature [10], [11]. Recently, a curvature SMS sensor with residual sensitivity to temperature and strain was also proposed [12].…”

Multimode-interference-structure optical-fiber temperature sensor with high sensitivity

“…The MMI optical signal is highly sensitive to the refractive-index (RI) change of the medium surrounding the MMF; hence, it has been used in some RI sensor applications [3,4,5,6]. The influence of the coreless MMF diameter on the external RI variation of a liquid has been examined, and ultra-high sensitivity of the device to the variation in temperature in a high-RI liquid has been attained [7].…”