A humidity and temperature optical fiber sensor based on a long-period grating (LPG), which can provide simultaneous response to both magnitudes, is proposed and demonstrated via experiments. Previously, the LPG was fully coated with humidity sensitive nanostructured polymeric thin films by the Layer-by-Layer (LbL) nano assembly technique. Hence the surrounding refractive index was changed, so provoking wavelength shifts of the attenuation bands of the transmission spectrum. This fully coated LPG was exposed to relative humidity (RH) and temperature tests, varying from 20% to 80% RH and from 25 to 85 °C, respectively. Then, half of the LPG coating was chemically removed and this results in the splitting of the main attenuation band into two different contributions. When this semi-coated LPG was also exposed to RH and temperature tests, the new two attenuation bands presented different behaviors for humidity and temperature. This novel dual-wavelength based sensing method enables the simultaneous measurement of RH and temperature using only one LPG.

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Simultaneous measurement of humidity and temperature based on a partially coated optical fiber long period grating

Needs for sensor miniaturization, versatile sensing solutions, and improved measurements’ performances in difficult operating environments have recently driven considerable research in optical fiber sensor for multiparameter measurements. Multiparameter sensors not only enable new sensors’ functionalities, but can also improve achievable measurement performances for some frequently measured parameters considerably. This study provides a review of work in the field of miniature fiber-optic sensors that allows independent and simultaneous measurements of two or more different physical or chemical parameters. Sensor designs and corresponding signal processing schemes are reviewed and compared.

https://www.spiedigitallibrary.org/journals/optical-engineering/volume-58/issue-7/072009/Multiparameter-fiber-optic-sensors-a-review/10.1117/1.OE.58.7.072009.pdf

Multiparameter fiber-optic sensors: a review

Water level sensing: State of the art review and performance evaluation of a low-cost measurement system

A Mach-Zehnder interferometer (MZI) based fiberoptic refractive index (RI) sensor is constructed by uniformly tapering standard single mode fiber (SMF) for RI measurement. A custom flame-based tapering machine is used to fabricate microfiber MZI sensors directly from SMFs. The fabricated MZI device does not require any splicing of fibers and shows excellent RI sensitivity. The sensor with a cladding diameter of 35.5 µm and length of 20 mm exhibits RI sensitivity of 415 nm/RIU for RI range of 1.332 to 1.384, 1103 nm/RIU for RI range of 1.384 to 1.4204 and 4234 nm/RIU for RI range of 1.4204 to 1.4408, respectively. The sensor reveals a temperature sensitivity of 0.0097 nm/°C, which is relatively low in comparison to its ultra-high RI sensitivity. The proposed inexpensive and highly sensitive optical fiber RI sensors have numerous applications in chemical and biochemical sensing fields.

https://www.mdpi.com/1424-8220/19/7/1652/pdf

Tapered Fiber-Optic Mach-Zehnder Interferometer for Ultra-High Sensitivity Measurement of Refractive Index.

In this letter, a temperature sensor based on a fiber ring laser with a reflective Sagnac loop is proposed. The reflective Sagnac loop inserted into the fiber ring laser through a downlead optical fiber is used as the filter and sensing head to supply high temperature sensitivity. As the temperature varies, the transmission spectrum of Sagnac loop changes, leading to the shift of emission wavelength of a fiber ring laser. We obtain a temperature sensor system with a high temperature sensitivity of 1.739 nm/°C, a narrow 3-dB bandwidth less than 0.05 nm, and a high signal-to-noise ratio $\sim 50$ dB. Moreover, it is convenient to achieve the remote sensing by changing the length of the downlead optical fiber.

Temperature Sensor Based on Fiber Ring Laser With Sagnac Loop

Simultaneous measurement of temperature and refractive index based on a Mach–Zehnder interferometer cascaded with a fiber Bragg grating

A fiber laser sensor for liquid level and temperature based on two taper structures and fiber Bragg grating

High temperature fiber sensor based on spherical-shape structures with high sensitivity

An all-fiber sensor based on a cascaded optical fiber device is proposed and demonstrated, and its sensor head is composed of a core-offset Mach-Zehnder interferometer (MZI) and a long-period fiber grating (LPFG). In the experiment, two dips shaped by the intermodulation between the interference fringe of MZI and the resonant wavelength of LPFG are monitored. Experimental results show that temperature sensitivities of two dips are 0.060 7 nm/°C and 0.056 3 pm/°C, and the refractive index (RI) sensitivities are −18.025 nm/RIU and −55.06 nm/RIU, respectively. The simultaneous measurement of the temperature and external RI is demonstrated based on the sensitive matrix. Its low fabrication cost, simple configuration and high sensitivity make this sensor have potential applications in chemical and biological sensing.

Simultaneous measurement of temperature and refractive index based on a core-offset Mach-Zehnder interferometer cascaded with a long-period fiber grating

An all-fiber sensor for simultaneous measurement of temperature and microdisplacement is presented and demonstrated. The sensor head is fabricated by a peanut structure Mach–Zehnder interferometer (MZI) cascaded with a fiber Bragg grating (FBG). Experimental results show that the temperature sensitivities of the MZI (dip1) and the FBG ( dip FBG ) are 0.0909 and 0.0121  nm/°C , respectively. The microdisplacement sensitivities are −0.0233 and 0.0122  nm/ μ m , respectively. The simultaneous measurement of the temperature and microdisplacement is demonstrated based on the sensitive matrix. With the advantages of low cost and easy fabrication, this sensor has potential applications in security, construction, and energy.

Shuo Yuan

Papers

Simultaneous measurement of temperature and refractive index based on a Mach–Zehnder interferometer cascaded with a fiber Bragg grating

A fiber laser sensor for liquid level and temperature based on two taper structures and fiber Bragg grating

High temperature fiber sensor based on spherical-shape structures with high sensitivity

Simultaneous measurement of temperature and refractive index based on a core-offset Mach-Zehnder interferometer cascaded with a long-period fiber grating

Simultaneous measurement of temperature and microdisplacement based on a Mach–Zehnder interferometer cascaded with a fiber Bragg grating