Highly sensitive optofluidic refractive index sensor based on a seven-liquid-core Teflon-cladding fiber

We propose and theoretically demonstrate a highly sensitive optofluidic refractive index (RI) sensor based on a spectral filter formed by a segment of liquid-filled seven-hole Teflon-cladding fiber sandwiched by two standard single mode fibers (SMFs). When liquid flows through the air hole channels of the seven-hole Teflon-cladding fiber, it forms a seven-liquid-core fiber (SLCF) and the lightwaves are well guided by the liquid cores owing to total inner reflection. When the input SMF is aligned to the central core of the SLCF, the light excited in the central core will couple to outer cores periodically along the length of the SCLF. At the detection port, the output SMF is also aligned to the central core of the SLCF. Since the coupling coefficient depends on wavelength, the coupling efficiency is also wavelength dependent, leading to a filter spectrum for a given length of the SLCF. The spectral response of the filter to the change in RI of the liquid cores is numerically simulated based on the coupled-mode theory through finite-element method. The dependence of the RI sensitivity on the diameter and pitch of air holes of the SLCF are studied, respectively. Finally, a very high sensitivity of 25,300 nm/RIU for RI around 1.333 is achieved.