Role of lateral Core-Offset in the sensitivity enhancement of single Mode-No core-Single mode fiber cascaded structure

Abstract

In this study, an extensive examination of the influence of core-offset on different sensitivities of a single-mode-no-core-single-mode (SNS) fiber sensor probe in a variety of external disturbances, including refractive index changes, strain, and temperature, has been presented and thoroughly investigated. To achieve this, a consistent sensing length of 5 cm no-core fiber (NCF) was utilized between two single-mode fibers (SMFs) with different offset values, facilitated by the built-in options of a fusion splicer. The theoretical and experimental principles of sensitivity are discussed in detail. Key aspects such as spectral analysis and fast Fourier transform of the disclosed transmission spectrum underwent meticulous scrutiny. The outcome of the experiment indicates that the SNS fiber sensor exhibits an increasing sensitivity to refractive index (RI) over the 1.333–1.398 range when the offset value increases, with a maximum of 201.221 nm/RIU sensitivity. On the other hand, the RI sensitivity decreases with increasing offset value in the range of 1.402–1.441; the highest sensitivity attained is 656.641 nm/RIU. The strain sensitivity shows a decreasing trend with increasing offset, with the maximum sensitivity reaching −1.59 pm/µε in a wide range of 0 to 2000 µε. For temperature sensing, the sensitivity remains unaffected with a core offset; consistently, the achieved sensitivity is approximately 11.51 pm/°C over a broad range of temperature of 30 °C to 120 °C Compared with RI, it is found that the reliance of core-offset on strain sensitivity is very low whereas on temperature sensing almost insensitive, provided that the sensing length and diameter remain constant. These results provide insightful direction for the creation of extremely sensitive sensors for a variety of applications.