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A novel all-fibre highly sensitive strain sensor based on polarization-maintaining photonic crystal fibre (PMPCF) is proposed and demonstrated experimentally. The sensing structure is formed by splicing a segment of PMPCF between two segments of thin core fibres (TCFs). Since the responses of the resonance dips induced by different order cladding modes interference with core mode are different, the strain sensitivity can be obtained by monitoring the shifts of the resonance dips. The experimental results show that the sensitivity of strain of the MZI is 4.03 pm/µϵ within the strain range from 0 µϵ to 1600 µϵ, respectively. And the temperature characteristics are also researched. This type of sensor has outstanding advantages of convenient manufacture, high-cost efficiency and insensitivity to temperature, so it has potential application prospects in physical, biological and chemical sensing. [ABSTRACT FROM AUTHOR]

• An ultrasensitive temperature sensor based on vernier effect is proposed. • The temperature-insensitive FPI is manufactured using HCPCF and is an ideal reference interferometer. • The sensing PMI is based on the UFPMF with a high birefringence coefficient, which reduces the length of the sensing fiber. • The temperature sensitivity reaches as high as 54.589 nm/℃ with the magnification factor of 47.84. • The sensitivity amplification factor can be easily adjusted by adjusting the length of the UFPMF in the sensing PMI. An ultrasensitive temperature sensor based on cascading a polarization mode interferometer (PMI) with a Fabry-Perot interferometer (FPI) is proposed and demonstrated. The sensing interferometer PMI is fabricated by splicing high-birefringence ultra-fine polarization-maintaining fiber (UFPMF) with a polarizer for temperature sensing. The FPI, made by splicing a section of hollow core photonic crystal fiber (HCPCF) between two single mode fibers (SMFs), is temperature-insensitive and is used as a reference interferometer. The free spectral ranges (FSRs) of PMI and FPI can be made close to each other by adjusting the length of the UFPMF, thus producing a vernier effect and achieving sensitivity enhancement. Experimental results show that the temperature sensitivity of the cascaded sensor is enhanced from −1.134 nm/°C for sensing PMI to 54.589 nm/°C, and its detection limit (DL) is degraded from 3.98 × 10−3 °C for sensing PMI to 5.13 × 10−3 °C, so that the appropriate sensor should be selected depending on the detection requirements in practical applications. The proposed sensor has high sensitivity, simple structure, easy manufacture, and low cost, and is suitable for application fields requiring high-sensitivity temperature measurement. [ABSTRACT FROM AUTHOR]

• A highly sensitivity temperature sensor based on Lyot filter with Vernier effect has been demonstrated. • Because the interference spectra of Fabry-Perot interferometer and the Lyot filter are both relatively uniform, it is easy to achieve the Vernier effect. • By adjusting the length of the Ultra-fine polarization maintaining fiber (UFPMF) in the Lyot filter, it is easy to achieve higher magnification based on Vernier effect. • The reference interferometer used is insensitive to temperature. • Ultra-fine polarization maintaining fiber (UFPMF) in sensing interferometers features a high birefringence (B), which effectively reduces the size of the sensor. A highly sensitive fiber-optic temperature sensor based on a Lyot filter cascaded with a Fabry-Perot interferometer (FPI) is proposed and demonstrated in this study. The FPI consists of a segment of hollow-core photonic crystal fiber (HCPCF) spliced between two single-mode fibers (SMFs), which is insensitive to temperature and strain and is an ideal reference interferometer. The Lyot filter is composed of two polarizers with an uiltra-fine polarization maintaining fiber (UFPMF) of a certain length for temperature sensing. By adjusting the length of the UFPMF, the free spectral range (FSR) of the Lyot filter is close to FPI, resulting in an optical Vernier effect and improved sensitivity. Experimental results show that with the Vernier effect, the temperature sensitivity is enhanced from −1.145 nm/℃ to −59.31 nm/℃, and the sensitivity amplification factor is about 51.8. The proposed sensor with the Vernier effect has good performance in temperature sensing and is suitable for applications fields where high sensitivity temperature measurement is required. [ABSTRACT FROM AUTHOR]

A new cascaded optical fiber temperature and strain sensor based on polarization mode interferometer (PMI) and Fabry-Perot interferometer (FPI) is proposed and demonstrated experimentally. The PMI made by fusion splicing a segment of polarization maintaining fiber (PMF) after a polarizer is used as a sensing interferometer. Integrating a FPI as a reference interferometer cascaded after the PMI to generate the Vernier effect and improve sensitivity. The FPI is made from a small segment of hollow core photonic crystal fiber (HCPCF), which is fusion spliced to PMF and multi-mode fiber (MMF) at each end to form two reflective surfaces of FPI. Based on numerical simulations, a suitable free spectral range (FSR) of the sensor is produced. Experimental results show that the temperature sensitivity can be improved from −1.095 nm/℃ to −22.753 nm/℃ and the strain sensitivity can be improved from 2.17 pm/με to 38.89 pm/με by using the Vernier effect. The measured amplification factors are about 21 and 18,respectively. The high sensitivity of PMI and FPI cascaded sensors with the Vernier effect offers a new option for simultaneous measurements in the field of temperature and strain. [ABSTRACT FROM AUTHOR]

• We proposed and experimentally demonstrated a novel high-sensitivity optical fiber temperature sensor which is composed of the Lyot filter cascading a polarization mode interferometer. • A simple method for adjusting the free spectral range based on polarization mode interferometer is proposed. • The Lyot filter is used as a reference interferometer, which provides a new strategy and method for the development of Vernier effect-based sensors. • A high sensitivity of 25.562 nm/°C for temperature is achieved in the range of 31–35 °C. • The proposed sensor has no special manufacturing process, only requiring the cleaving and fusion splicing methods. We proposed and experimentally demonstrated a novel high-sensitivity optical fiber temperature sensor (OFTS) which is composed of the Lyot filter cascading a polarization mode interferometer (PMI). The Lyot filter is fabricated by inserting a polarization-maintaining fiber (PMF) between two linear fiber polarizers at two 45-degree angles. By simply cleaving the end fiber of the PMI, the free spectral range (FSR) can be maximized to approach the FSR of the Lyot filter, which introduces the Vernier effect. Experimental results show that the cascaded sensor can provide high-temperature sensitivity of 10.666 nm/°C and 26.562 nm/°C, which are 6.71 and 12.168 times that of single PMI, respectively. The method is demonstrated to achieve a stable and controlled Vernier effect obtaining ultra-high temperature sensitivity, which agrees well with the theoretical simulation results. The proposed sensor has the advantages of high sensitivity, good stability, and easy fabrication. [ABSTRACT FROM AUTHOR]

A novel temperature and strain sensor based on fiber Sagnac interferometer (FSI) with Vernier effect is proposed and demonstrated experimentally. The FSI fabricated by fusion splicing a segment of thin polarization maintaining fiber (TPMF) with a coupler works as sensing. The Vernier effect is generated by cascading a polarization mode interferometer (PMI). The PMI is fabricated by fusion splicing a polarization maintaining fiber (PMF) with a polarizer. The suitable free spectral range (FSR) of the sensor is fabricated based on numerical simulation. The experimental results indicate that with the Vernier effect, the temperature sensitivity can be improved from −1.924 nm/°C to −32.830 nm/°C and the strain sensitivity can be improved from 25.9 pm/ μ ε to 407.32 pm/ μ ε. The measured amplification factors are about 17 and 16. The good performance of the FSI with the Vernier effect provides a new option in the temperature and strain sensing fields. • A high temperature and strain sensor based on Vernier effect is proposed. • A FSI is cascaded with a PMI to form the sensor. • The sensing FSI–PMI has a linear response in measuring range. • PMI composed of PMF is less sensitive to environmental disturbance than FSL composed of TPMF. [ABSTRACT FROM AUTHOR]

In this paper, an improved algorithm based on the reference interferometer for noise reduction is proposed. The method uses a reference interferometer to suppress the phase noise, followed by the Arctan algorithm to further reduce the intensity noise of the system. Meanwhile, it also eliminates the effects of light intensity disturbances. The results of the simulation and experiment are consistent with the theoretical analysis. Experimental results show that the noise reduction effect of the improved algorithm based on the reference interferometer is significantly improved in the 0–2 kHz frequency band. At 1 kHz, SNR is about 15 dB higher than the traditional PGC-DCM algorithm, and about 12 dB higher than the PGC-DCM algorithm based on the reference interferometer. [ABSTRACT FROM AUTHOR]

• The TCF can better excited cladding modes. Due to the small cladding diameter of UTF, a high sensitivity liquid level sensor is realized. • Simultaneous measurement of liquid level and temperature can be obtained through the demodulation matrix. • A high sensitivity of −231.67 pm/mm for liquid level is achieved in the range of 0–8 mm. And the temperature sensitivity is 77.86 pm/°C. • The proposed sensor has no special manufacturing process, only requiring the cleaving and fusion splicing methods. A compact optical fiber sensor (OFS) based on an inline Mach-Zehnder interferometer for simultaneous measurement of liquid level and the temperature is proposed and demonstrated experimentally. The proposed sensor is formed by fusion splicing a thin core fiber (TCF) with an ultra-thin fiber (UTF) with core offset, then TCF and UTF are sandwiched between two standards of single mode fibers (SMFs). The liquid level or temperature change will lead to the dips shifts in the interference spectrum, and the liquid level and temperature sensitivities can be measured independently by monitoring the resonance dips shifts. Then the simultaneous measurement of liquid level and temperature can be obtained through the demodulation matrix. Four sensors with different UTF length are fabricated based on numerical simulation. The experimental results show that the proposed sensor with a UTF length of 8 mm has the optimal liquid level and temperature sensitivities of −231.67 pm/mm and 77.86 pm/°C, respectively. The measuring liquid level and temperature ranges are 0–8 mm and 30–60 °C. The proposed sensing configuration has practical application potential in various industries due to the advantages of high sensitivity, simple fabrication and low cost. [ABSTRACT FROM AUTHOR]