Abstract
In this study, a new type of highly sensitive fiber-optic Fabry–Perot interferometer (FFPI) is proposed with a high sensitivity on a wide refractive index (RI) measurement range based on internal reflection mirrors of micro-cavity. The sensor head consists of a single-mode fiber (SMF) with an open micro-cavity. Since light reflections of gold thin films are not affected by the RI of different measuring mediums, the sensor is designed to improve the fringe visibility of optical interference through sputtering the gold films of various thicknesses on the inner surfaces of the micro-cavity, as a semi-transparent mirror (STM) and a total-reflection mirror (TRM). Experiments have been carried out to verify the feasibility of the sensor’s design. It is shown that the fabricated sensor has strong interference visibility exceeding 15 dB over a wide measurement range of RI, and the sensor sensitivity is higher than 1160 nm/RIU, and RI resolution is better than 1.0 × 10−6 RIU.
Highlights
The refractive index (RI) is a key parameter for characterizing of an analyte, and has been widely applied in biomolecule detection for clinical diagnosis, pharmaceutical and drug analysis, pollution control and monitoring [1,2,3]
Due to the fact that the reflection coefficients R1 and R2 are stable, the fringe visibilities of the interference spectra are around 15 dB in various RIs. These results show that the proposed fiber-optic Fabry–Perot interferometric (FFPI) sensor the RI of silica optical fiber is near 1.46, the RIs of input parameters are set as n = 1.0, n = 1.46, and can maintain a high signal intensity and a clear fringe visibility on a wide RI measurement range
We have proposed and demonstrated a new type of FFPI sensor for the RI
Summary
The refractive index (RI) is a key parameter for characterizing of an analyte, and has been widely applied in biomolecule detection for clinical diagnosis, pharmaceutical and drug analysis, pollution control and monitoring [1,2,3]. It is noted that the type of RI sensors based on an optical microfiber can provide ultrahigh sensitivity up to 18681.82 nm/RIU and better resolution with 5.35 ˆ 10 ́7 RIU [17]. These types of sensors have some downsides, such as temperature cross-sensitivity and complex structures. These kinds of sensors can only be applied to measuring mediums whose RI has to be less than that of the optical fiber, which restricts their practical applications [21]. SPR sensor systems are expensive, due to their incompatibility with the near-infrared (NIR) optical communication technology [22]
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