Simultaneous measurement of refractive index and temperature or temperature and axial strain based on an inline Mach-Zehnder interferometer with TCF-TF-TCF structure

Simultaneous measurement of axial strain and temperature based on a twin-core single-hole fiber with the optical Vernier effect

An ultrasensitive optical fiber sensor based on the optical Vernier effect is proposed for the simultaneous measurement of axial strain and temperature. The sensor structure comprises two cascaded Mach-Zehnder interferometers (MZIs) with different free space ranges. The single MZI is built up by fusion splicing a segment of ∼3 mm twin-core single-hole fiber (TCSHF) between two pieces of ∼5 mm none core fibers (NCF). When acting separately, each MZI can respond linearly to the axial strain change with a sensitivity of ∼ 0.6 pm/µε and temperature with a sensitivity of ∼34 pm/°C. When the two MZIs are cascaded in series, the sensitivities are amplified about 30 times because of the optical Vernier effect. Experimental results demonstrate that the cascaded structure exhibits a high axial strain sensitivity of ∼ 17 pm/µε in the range of 0 to 2000 µε and temperature sensitivity of ∼1.16 nm/°C in the range of 30 to 70 °C. Moreover, the cascaded structure can simultaneously measure the axial strain and temperature change in the acceptable error ranges.

Highly sensitive temperature and strain sensor based on an antiresonant hollow core fiber probe with the Vernier effect

A highly sensitive temperature and strain sensor based on an antiresonant hollow core fiber (ARHCF) probe with the Vernier effect is proposed and experimentally demonstrated. The ARHCF probe is used as a reference interferometer by sandwiching an ARHCF, which is insensitive to temperature, strain, and refractive index, between a single-mode fiber (SMF) and a polarization-maintaining fiber (PMF). The polarization mode interferometer (PMI), fabricated by splicing a section of PMF with a fiber polarizer at a 45-degree angle, works as a sensing interferometer. The Vernier effect is introduced by connecting the reference interferometer and the PMI in parallel. The experimental results show that by introducing the Vernier effect, the temperature sensitivity is improved from -1.68 to -15.7nm/^∘C and the strain sensitivity is improved from 5.09 to 47.65 pm/µε. The magnification is consistent with the theoretical results. The reference segment of the proposed sensor is not affected by ambient factors, which provides a new strategy and idea for the development of multiparameter sensors based on the Vernier effect.

Highly Modulated In-Fiber Mach-Zehnder Interferometer Based on an Ultracompact Leaky-Guided Liquid Core

We proposed a novel sensor based on an ultracompact leaky-guided liquid core fiber Mach-Zehnder interferometer (LLCFMZI) for high modulation of an interference spectrum. The sensor structure is based on a micro-sized hollow-core fiber (HCF) splicing a tilt end face single-mode fiber (SMF) to create a miniature oblique gap for the effective access of different liquids. The liquid core with a relatively lower refractive index (RI) than the cladding can achieve a leaky-mode optical waveguide (LMOW) mechanism, and its volume is only approximately 7.85 pL. In addition, the utilized micro-length HCF can reduce the energy loss of core in the LMOW to obtain an acceptable extinction ratio (>30 dB) with high temperature (T) sensitivity in the interference spectra. Experimental results show that the interference spectra can be highly modulated within the wide measurement range of 1250-1650 nm with a steadily linear response for thermal effect. The measured temperature sensitivities (T-sensitivities) of various liquids of DI water, ethanol, and Cargille-liquid (n_D = 1.305) are 0.8869, 4.4754, and 4.8229 nm/°C, and the corresponding measured thermal optics coefficient (TOC) are -4.16 × 10^-5, -2.11 × 10^-4, and -3.6 × 10^-4 °C^-1, respectively. Measurement results demonstrate that the used liquids with a higher TOC can obtain better T-sensitivity modulation. The highest experimental sensitivity of the liquid-core filled with Cargille-liquid (n_D = 1.40) is up to +13.87 nm/°C with a corresponding TOC of -4.07 × 10^-4 °C^-1. Furthermore, the experimental and theoretical values are in good agreement according to FSR the measuring scheme that investigates the effectiveness of the proposed LLCFMZI.

Simultaneous temperature and refractive index sensor based on an L-like Michelson interferometer

We experimentally demonstrate, to the best of our knowledge, temperature and refractive index (RI) sensing with a novel L-like Michelson interferometer (MI). Two MIs are designed based on single-mode fiber (SMF) and multimode fiber (MMF), respectively, fabricated via an oxyhydrogen flame and a rotatable platform. By comparative experiments on the size and bent degree of the sensor, the corresponding parameters of the sensor with excellent performance are determined for measurement experiments. The RI sensitivity of the SMF L-like MI reaches -131.0nm/RIU, and the highest temperature sensitivity is 94.17 pm/°C. The highest RI of the MMF L-like MI is 176.5 nm/RIU, and the temperature sensitivity is 104.2 pm/°C. The L-like MI has advantages of low cost and easy fabrication, and is a promising temperature and RI sensor in a wide range of measurements.

High-sensitivity transverse-load and high-temperature sensor based on the cascaded Vernier effect

In this paper, we demonstrate a novel, to the best of our knowledge, transverse-load and high-temperature sensor based on the cascaded Vernier effect. Two Fabry-Perot interferometers fabricated by a piece of hollow-core fiber (HCF) and a piece of polarization-maintaining photonic crystal fiber (PM-PCF) are connected by a long part of single-mode fiber with a length of 1 m, and play the roles of transverse-load sensor and high-temperature sensor, respectively. The sensitivity of not only the transverse load but also that of temperature can be enhanced by the Vernier effect. The sensitivity of the transverse load is raised by 7.7 times to 5.84 nm/N, and the temperature sensitivities increased by 5.5 and 5.9 times to -0.0689nm/^∘C and -0.1038nm/^∘C within the temperature range of 50-400°C to 400-900°C. Moreover, both the HCF cavity and PM-PCF cavity can be split and combined flexibly. Hence, such a sensor could have great potential in sensing applications.

Ultra-sensitive optical fiber sensor based on intermodal interference and temperature calibration for trace detection of copper (II) ions

An ultrahigh sensitive optical fiber sensor for trace detection of Cu²⁺ concentration in aqueous solution with temperature calibration has been developed in this article. Based on the intermodal interference, the sensor is coated with a hydrogel sensing membrane with specific binding to Cu²⁺ on the no-core fiber/single mode fiber/no-core fiber structure by using our new spray coating method. The imidazole group in the sensing film combines with Cu²⁺ to produce chelation, which changes the refractive index of the sensing film. The Cu²⁺ at trace concentration can be detected by monitoring the displacement of the interference trough. The experimental limit of detection of 3.0×10^-12 mol/L can be achieved with the spectral resolution of 0.02 nm. The sensor has also long-term stability of the concentration measurement with the average standard deviation of 1.610×10^-12 mol/L over 2 hours observation time and can be compensated the influence of ambient temperature on concentration detection by conducting the temperature calibration. In addition, the sensor has the advantages of strong specificity, simple fabrication and low cost.