Open-Cavity Fabry-Perot Interferometer Based on Etched Side-Hole Fiber for Microfluidic Sensing

Abstract

An open-cavity fiber-optic Fabry-Perot interferometer (FPI) is designed and demonstrated, with a particular consideration for microfluidic refractive index (RI) sensing. The FPI is composed of an etched side-hole fiber (SHF) sandwiched between two single-mode-fibers. Chemical etching method is used to open up the cavity in the SHF. Experimental results show that an optimal RI sensitivity of more than 1250 nm/RI can be achieved with an open-cavity length of 38 µm for the microfluidic RI range from 1.3400 to 1.3470. In addition, the temperature sensitivity can reach an ultralow level of 1.1 pm/°C. The ease of fabrication, capability for in situ measurement, and excellent performance results suggest that the proposed FPI is highly promising as an inline refractometer for temperature-insensitive label-free microfluidic detection and sensing.

Optical Fiber Fabry–Pérot Microfluidic Sensor Based on Capillary Fiber and Side Illumination Method

“…As the most basic property, the RI changes with the concentration of solutes in the solution. Common systems exhibit this behavior, such as saline or aqueous ethanol solution [ 7 , 8 ], etc. Furthermore, the state of biological systems can be inferred from the refractive indices of liquid components, such as glucose dissolved in plasma, which are important for the treatment of diabetes [ 9 , 10 ].…”

“…With the invention of various new optical fibers and the upgrading of optical fiber processing technology, the optical fiber sensors have been deeply studied by an increasing number of scholars, and various optical fiber sensors with new structures or new sensing mechanism have sprung up [ 7 , 8 , 9 , 10 , 11 , 12 , 13 , 14 , 15 , 16 , 17 , 18 , 19 , 20 , 21 , 22 , 23 , 24 , 25 , 26 ]. Due to the superior advantages of small size, high sensitivity, simultaneous measurement of multiple parameters, optical fiber refractive index (RI) sensors have attracted a great deal of attention for physical, chemical and biomedical sensing [ 1 , 2 , 3 , 4 ].…”

“…The interference fringe of FPI can be used to obtain the optical length of the cavity in linear proportion to the RI of the medium in the cavity. At present, the technologies for fabricating open-cavity FPI microstructures mainly include femtosecond laser etching technology [ 14 , 15 , 16 , 17 , 18 ], special fiber fusion technology [ 19 , 20 ] and selective etching technology [ 8 ]. Femtosecond laser beam etching technology forms a microstructure by opening side holes on the fiber [ 26 , 27 ].…”

“…The construction of a fiber drawing tower often leads to high cost and customized fiber fusing processes lead to the bad fabrication consistency. In addition, the selective etching technology uses hydrofluoric acid (HF) solution to chemically etch the optical fiber to form the microstructure [ 8 , 28 , 29 ]. However, the randomness of hydrofluoric acid (HF) etching often leads to instability of the FPI microstructure, which limits the practical application of FPI based microfluidic sensors.…”

“…In this paper, a simple hybrid Fabry–Pérot (HFP) microfluidic sensor formed by the capillary fiber (CF) and side illumination method is proposed. Since fabricating without expensive laser machining [ 14 , 15 , 16 , 17 , 18 ], customized fiber fusion or cutting process [ 8 , 19 , 20 , 28 , 29 ], the proposed sensor offers a good performance of reproduction, low-cost and easy fabrication. Taking advantage of the silica cavity formed by the solid silica wall of CF, which is only sensitive to the surrounding temperature, the RI measurement results can be compensated by the common cross-sensitivity matrix method.…”