A New Technique to Sense Humidity Based on Optical Heterodyne detection (original) (raw)

Recent Developments in Fiber Optics Humidity Sensors

Sensors, 2017

A wide range of applications such as health, human comfort, agriculture, food processing and storage, and electronic manufacturing, among others, require fast and accurate measurement of humidity. Sensors based on optical fibers present several advantages over electronic sensors and great research efforts have been made in recent years in this field. The present paper reports the current trends of optical fiber humidity sensors. The evolution of optical structures developed towards humidity sensing, as well as the novel materials used for this purpose, will be analyzed. Well-known optical structures, such as long-period fiber gratings or fiber Bragg gratings, are still being studied towards an enhancement of their sensitivity. Sensors based on lossy mode resonances constitute a platform that combines high sensitivity with low complexity, both in terms of their fabrication process and the equipment required. Novel structures, such as resonators, are being studied in order to improve the resolution of humidity sensors. Moreover, recent research on polymer optical fibers suggests that the sensitivity of this kind of sensor has not yet reached its limit. Therefore, there is still room for improvement in terms of sensitivity and resolution.

Polyvinyl alcohol–coated hybrid fiber grating for relative humidity sensing

Journal of Biomedical Optics, 2011

A relative humidity (RH) sensor based on a hybrid fiber grating coated with polyvinyl alcohol is proposed and demonstrated experimentally. The hybrid fiber grating is formed by superimposing a normal fiber Bragg grating (FBG) and a tilted-FBG around the same position of a single-mode fiber so that it can work in the reflection mode. Optical power of the reflected signal changes with the refractive index of the moisture sensitive polyvinyl alcohol, and humidity measurement can be realized. Experimental results show that the measurement range is 30 to 95% with the maximum sensitivity of 0.737 nW/% RH. The average response time is ∼2 s and the measurement is nearly insensitive to temperature. Compared with the wavelength detection method used in normal FBG-based relative humidity sensors, the intensity demodulation method in this report is simpler and more cost-efficient.

Design System of Optical Heterodyne Detection Based on Temperature Sensor

IOP Conference Series: Materials Science and Engineering, 2019

Optical Heterodyne Detection (OHD) technique is based on two separate sources with optical interference between them. The optical signal from a specific light source is compared with a separate reference signal from another source. The Fiber Bragg grating (FBG) reflect a specific wavelength λ B and transmit the other wavelengths within the laser source spectral. This is achieved by changing the refractive index generated by periodic variation of optical fiber core, which reflect a specific wavelength, so FBG can be used to withhold a certain wavelength and allow other wavelengths to transmit. In this paper, a new method of an OHD has been designed using Optisystem software. Optical fiber as a temperature sensor element with single source and two FBGs have used in this system. the first FBG used as a tunable source and the other has used as a sensing element. The two optical signals have been combined utilizing a photodetector. It has a linear response to the light energy, while havi...

Optical Fiber Relative Humidity Sensor Based on a FBG with a Di-Ureasil Coating

Sensors, 2012

In this work we proposed a relative humidity (RH) sensor based on a Bragg grating written in an optical fiber, associated with a coating of organo-silica hybrid material prepared by the sol-gel method. The organo-silica-based coating has a strong adhesion to the optical fiber and its expansion is reversibly affected by the change in the RH values (15.0-95.0%) of the surrounding environment, allowing an increased sensitivity (22.2 pm/%RH) and durability due to the presence of a siliceous-based inorganic component. The developed sensor was tested in a real structure health monitoring essay, in which the RH inside two concrete blocks with different porosity values was measured over 1 year. The results demonstrated the potential of the proposed optical sensor in the monitoring of civil engineering structures.

Humidity sensor based on a long-period fiber grating coated with a hydrophobic thin film

SPIE Proceedings, 2010

In this work it is proposed a novel fiber optic humidity sensor based on a functionally coated long-period fiber grating (LPG). The coating is composed of tetraorthosilicate matrix functionalized with perfluorooctyltriethoxysilane and its fabrication was performed by the sol-gel technique using a dip coating process using the LPG as substrate. The fabricated sensor was tested in a programmable temperature and climatic chamber. Relative humidity (RH) was varied in range from 20%RH to 80%RH at room temperature. The results showed a smooth exponential-like wavelength shift of the LPG attenuation band. ACKNOWLEDGEMENTS ACKNOWLEDGEMENTS ACKNOWLEDGEMENTS This work was funded in part by the Spanish Ministry of Education and Science-FEDER Research Grant TEC2009-09210 CONCLUSIONS CONCLUSIONS CONCLUSIONS We propose a new HR sensor based on a coated LPG. The hydrophobic sensitive overlay was fabricated using the sol-gel technology. The sensitive overlays have been successfully placed onto the LPG with a strong hydrophobic behavior.

Performance Analysis of Humidity Tapered Optical Fiber Sensor

Research Square (Research Square), 2022

Among different interferometric fiber optic sensors a Relative Humidity sensor based on a singlemode-no-core-singlemode tapered fiber structure is proposed. The mathematical model of the interferometer structure is developed, simulated and validated as a refractive index sensor. Different materials for coating the No-core fiber section are analyzed for better Relative Humidity sensitivity. Agarose, Porous Silica and SiO2 nanoparticles were selected as coating materials for Pure Silica and d-PMMA fibers. The d-PMMA fiber with Agarose coating presents the highest average sensitivity of 533.46pm/RH% in the 0-60% RH range, when the tapered section has zero length. Furthermore, variations in the dimensions of the structure are explored showing that we can tune the sensitivity according to the tapered length and radius. An extension of the tapered section up to 4000µm gives an improvement of 227% in the average sensitivity. Moreover, a reduction of the tapered radius from 15µm to 1.5µm gives an rise in the sensitivity of 295%.

Influence of Humidity on Fiber Bragg Grating Sensors

Advances in Materials Science and Engineering, 2014

We demonstrate the influence of the relative humidity (RH) on the wavelength of fiber Bragg grating sensors (FBGS), performing tests with five FBGS at different humidity and temperature conditions. These tests were performed in a climate chamber whose RH changes according to a scheduled profile from 30% to 90%, in steps of 10%. These profiles were repeated for a wide range of temperatures from10∘Cto70∘C, in steps of10∘C. Two different types of instrumentation methods have been tested, spot welding and epoxy bonding, in two different materials, steel and carbon fiber reinforced polymer (CFRP). We discuss the results for each type of sensor and instrumentation method by analyzing the linearity of the Bragg wavelength with RH and temperature.

Toward a New Generation of Photonic Humidity Sensors

Sensors, 2014

This review offers new perspectives on the subject and highlights an area in need of further research. It includes an analysis of current scientific literature mainly covering the last decade and examines the trends in the development of electronic, acoustic and optical-fiber humidity sensors over this period. The major findings indicate that a new generation of sensor technology based on optical fibers is emerging. The current trends suggest that electronic humidity sensors could soon be replaced by sensors that are based on photonic structures. Recent scientific advances are expected to allow dedicated systems to avoid the relatively high price of interrogation modules that is currently a major disadvantage of fiber-based sensors.