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

Fibre Bragg grating (FBG) pressure sensors show a great potential in replacing conventional electrical pressure sensors due to their numerous advantages. However, increasing their pressure sensitivity performance for low hydrostatic pressure measurement is still a challenge. This paper reviewed recent pressure sensitivity enhancement methods that could be divided into two groups, namely intrinsic and extrinsic. For the intrinsic enhancement method, this paper reviewed polymer FBGs, special fibre sensors, interferometric sensors, and special grating sensors. For the extrinsic enhancement method, polymer-based pressure transducers, diaphragm-based pressure transducers, and other structure-based pressure transducers were reviewed in detail.

Review of high sensitivity fibre-optic pressure sensors for low pressure sensing

An all optical fiber CTD sensor used in seawater based on an OMC is demonstrated. And the OMC is fabricated by fusing and tapering two twisted conventional communication fibers based on the improved flame-brushing method. By monitoring the sensing dips, in situ measurement of salinity, temperature, and depth (pressure) in seawater can be realized, respectively. Especially, the water depth (pressure) sensing function of the OMC is demonstrated for the first time, and the pressure sensitivity is 50 times higher than a bare fiber Bragg grating (with a wide pressure measurement range from 0 to 25 MPa). The highest sensitivities of salinity, temperature, and depth are 1596 pm/‰, 2326 pm/°C, and 169 pm/Mpa, respectively. These are high enough for the requirements of marine dynamic environmental monitoring and underwater target detection of fiber-optic hydrophone system. The all optical fiber CTD sensor demonstrated here show advantages of easy fabrication, compact structure, high sensitivity, low cost, and compatibility with the optical fiber system, which may find applications in multifunction optical sensors in ocean detections and other applications.

High Sensitivity All Optical Fiber Conductivity-Temperature-Depth (CTD) Sensing Based on an Optical Microfiber Coupler (OMC)

A cost-effective edge-filter based FBG interrogator using catastrophic fuse effect micro-cavity interferometers

A fiber bragg grating pressure sensor with temperature compensation based on diaphragm-cantilever structure

A high sensitive pressure sensor using fiber Bragg grating (FBG), integrated with thin metal diaphragm is designed and investigated both theoretically and experimentally. Under pressure the diaphragm deflection causes an axially stretched-strain along the length of the FBG. The pressure sensitivity of the sensor gained from the test results is 2.05 × 10−2 MPa−1, approximately four orders of magnitude higher than that can be measured with the bare FBG. Experimental results showed good agreement with the proposed theoretical results.

A high sensitive FBG pressure sensor using thin metal diaphragm

A fiber Bragg grating (FBG) pressure sensor with high sensitivity and resolution has been designed and demonstrated The sensor is configured by firmly fixing the FBG with a metal bellows structure The sensor works by means of measuring the Bragg wavelength shift of the FBG with respect to pressure change From the experimental results, the pressure sensitivity of the sensor is found to be 906 pm/psi, which is approximately 4000 times as that of a bare fiber Bragg grating A very good linearity of 9986% is observed between the Bragg wavelength of the FBG and applied pressure The designed sensor shows good repeatability with a negligible hysteresis error of ± 029 psi A low-cost interrogation system that includes a long period grating (LPG) and a photodiode (PD) accompanied with simple electronic circuitry is demonstrated for the FBG sensor, which enables the sensor to attain high resolution of up to 0025 psi Thermal-strain cross sensitivity of the FBG pressure sensor is compensated using a reference FBG temperature sensor The designed sensor can be used for liquid level, specific gravity, and static/dynamic low pressure measurement applications

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FBG based high sensitive pressure sensor and its low-cost interrogation system with enhanced resolution

A fiber Brag grating-based high temperature sensor together with a low cost, high speed and compact size interrogation system using a long period grating was designed, developed and tested. The designed sensor measures the temperature from room temperature to 550 °C. The sensor head was configured by encapsulating an fiber Brag grating (type-I) of Bragg resonance wavelength at 1552.88 nm in a capillary tube made of copper. Long period grating with peak transmission loss at 1550 nm was employed to convert the wavelength information from fiber Brag grating into an intensity modulated signal. Temperature related optical intensity information was again converted into its equivalent electrical signal by using a photodiode. The achieved resolution of the sensor was found to be 0.5 °C.

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Fiber Bragg grating-based high temperature sensor and its low cost interrogation system with enhanced resolution

An experimental study has been carried out for the characterization of encapsulating materials for fiber Bragg grating-based temperature sensors to prevent the formation of micro-cracks and devitrification on the fiber surface at elevated temperatures by making use of a rigid probe. The developed sensor probe was configured by encapsulating a type 1 fiber Bragg grating with an aluminum nitride tube and is used to measure temperatures from 20°C to 500°C. The adapted encapsulation technique validated the sensor to achieve linearity of 99.979%, sensitivity of 14.03 ± 0.02 pm/°C, and good repeatability; its practical use in harsh environments is predicted.

Characterization of Encapsulating Materials for Fiber Bragg Grating-Based Temperature Sensors

A fiber Bragg grating (FBG)–based high-temperature sensor accompanied by a low-cost interrogation scheme with liquid-crystal display (LCD) has been designed, developed, and tested. The sensor probe is configured by encapsulating a femtosecond laser drawn FBG with an aluminum nitride capillary tube, and is used to measure the temperature from 20°C to 650°C. The interrogation system consists of a long period fiber grating, two photodiodes, a 2-channel transimpedance amplifier, and a field-programmable gate array with an LCD. It displays the temperature directly in °C with a resolution of 1°C. The sensor output is found to be linear with coefficient of 0.999, and independent of source power fluctuations. The results showed that the sensor has good accuracy with a negligible error bar of ±1.23%.

Srimannarayana Kamineni

Papers

A high sensitive FBG pressure sensor using thin metal diaphragm

FBG based high sensitive pressure sensor and its low-cost interrogation system with enhanced resolution

Fiber Bragg grating-based high temperature sensor and its low cost interrogation system with enhanced resolution

Characterization of Encapsulating Materials for Fiber Bragg Grating-Based Temperature Sensors

High-temperature measurement using fiber Bragg grating sensor accompanied by a low-cost detection system