In this work, we proposed a ring core fiber (RCF) based all-fiber sensor used for lateral pressure sensing. The sensor is composed of 1-mm coreless fiber (CLF) and 2.5-cm RCF. Then the CL-RC fiber structure is connected to two segments of single-mode fibers (SMFs) to form a Mach-Zehnder interferometer (MZI). One of the SMFs serves as the lead-in fiber which is linked with a broadband laser source (BBS) and the other SMF is connected to the optical spectrum analyzer (OSA) for signal recording. The transmission spectrum of the MZI structure has a large extinction ratio (ER) of up to 20 dB with the free spectral range (FSR) of 9.3 nm. After the fabrication, the MZI sensor is packaged for pressure sensing at room temperature (25 ℃). The weights with different values are applied on the fiber sensor so that the intensities of pressure can be calculated and adjusted. The lateral pressure intensity is tuned from around 1.6 MPa to 9.6 MPa. With the increase of pressure intensity, the spectra of output signals show a linear redshift. The pressure sensitivity of the proposed MZI sensor reaches 607 pm/MPa with good linearity of 0.9839. The proposed pressure sensor formed by RCF has many advantages, such as easy fabrication, low cost, small size, electromagnetic resistance and good sensitivity, which can be potentially applied to diverse fields.
An ultra-high sensitivity separated Fabry-Perot interferometers (FPIs) sensor for gas pressure measurement based on hollow core Bragg fiber (HCBF) and Vernier effect is proposed. The HCBF functions as an FPI cavity and possesses low transmission loss. The sensing unit was prepared by splicing an HCBF at the millimeter scale between the single-mode fiber (SMF) and the hollow silica tube (HST). The reference unit was fabricated by sandwiching the HCBF between two SMFs. Both FPIs with similar free spectral ranges (FSRs) were connected to the 3-dB coupler parallelly to generate the Vernier effect. Experimental results showed that the proposed sensor achieved high gas pressure sensitivity of 77.80 nm/MPa with a linearity of 0.9992. Moreover, a low-temperature crosstalk of ~0.095 kPa/℃ implies that the sensor is temperature insensitive. Compared to the traditional optical fiber gas pressure sensor, the proposed sensor features high sensitivity, stability, easy fabrication, and fast response.
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