Sensitivity improvement of a humidity sensor based on silica nanospheres on a long-period fiber grating

This work addresses a new configuration that improves the sensitivity of a humidity sensor based on a long-period fiber grating coated with a SiO(2)-nanospheres film. An intermediate higher refractive index overlay, deposited through Electrostatic Self-Assembly, is placed between the fiber cladding and the humidity sensitive film in order to increase the total effective refractive index of the coating. With this intermediate design, a three-fold improvement in the sensitivity was obtained. Wavelength shifts up to 15 nm against 5 nm were achieved in a humidity range from 20% to 80%.This work was supported in part by Fundação para a Ciência e Tecnologia (FCT) with the grant SFRH/BD/30086/200

Toward a new generation of photonic humidity sensors

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

(INVITED)Chemical sensors based on long period fiber gratings: A review

Fiber optic devices are being increasingly employed in the fields of chemical and environmental sensing due to their important features, such as high accuracy, small size, chemical inertness, remote operation and multiplexing capabilities. In this work, a thorough review about the design, fabrication and characterization of fiber optic chemical sensors based on long period grating (LPG) technology is reported. The emphasis is placed on transducer designs and features as well as the techniques to enhance the sensitivity. Subsequently, coating materials to be deposited around the grating region, providing a selective response to the target analytes are described in detail. Finally, the different applications are reviewed, mainly related to the monitoring of environmental parameters, volatile organic compounds, hazardous gases, heavy metal ions, corrosion, marine salinity and food quality. The aim of this work is to deliver a comprehensive analysis regarding the state-of-the-art solutions about LPG-based chemical sensors and to summarize the current shortcomings and upcoming research paths

Optical Fiber Sensors Based on Nanoparticle-Embedded Coatings

The use of nanoparticles (NPs) in scientific applications has attracted the attention of many researchers in the last few years. The use of NPs can help researchers to tune the physical characteristics of the sensing coating (thickness, roughness, specific area, refractive index, etc.) leading to enhanced sensors with response time or sensitivity better than traditional sensing coatings. Additionally, NPs also offer other special properties that depend on their nanometric size, and this is also a source of new sensing applications. This review focuses on the current status of research in the use of NPs within coatings in optical fiber sensing. Most used sensing principles in fiber optics are briefly described and classified into several groups: absorbance-based sensors, interferometric sensors, fluorescence-based sensors, fiber grating sensors, and resonance-based sensors, among others. For each sensor group, specific examples of the utilization of NP-embedded coatings in their sensing structure are reported

Superlens-Assisted Laser Nanostructuring of Long Period Optical Fiber Gratings (LPGs) for Enhanced Refractive Index Sensing

We present an innovative method to enhance Long Period Optical Fiber Gratings (LPGs) for refractive index sensing using microsphere-assisted superlens laser nanostructuring. This technique involves self-assembling a silica microsphere monolayer on LPGs' outer surface, followed by pulsed laser irradiation to generate nanoholes (300-500 nm) forming nanohole-structured LPGs (NS-LPGs). In experiments, two nanohole densities were compared for their impact on sensing performance in sucrose and glycerin solutions. The nanostructured NS-LPGs showed improved sensitivity by 16.08% and 19.57% compared to regular LPGs, with higher nanohole density yielding greater enhancement. Importantly, the permanent nanohole structures ensure durability in harsh environments, surpassing conventional surface-coating-based LPGs. Further improvements can be achieved by refining nanostructuring density and controlling nanohole size and depth. Our work represents a notable advancement in LPG sensor engineering, prioritizing surface nanostructuring over nano-coating, promising enhanced refractive index sensing applications.Comment: 13 pages, 5 figure

Development of Novel Fiber Optic Humidity Sensors and Their Derived Applications

The main focus of this thesis is on the design and development of novel fiber optic devices for relative humidity (RH) sensing with emphasis on high sensitivity, a wide humidity range, low temperature dependence, fast response time and good stability.Novel RH sensors based on fiber bends are fabricated by coating the surface of the buffer stripped bent fiber with selected hygroscopic materials such as Polyethylene oxide or Agarose. It is shown that the Polyethylene oxide coated device has a high sensitivity in a narrow RH range while the Agarose coated fiber bend shows a linear RH sensitivity in a wide RH range. Both of these sensors demonstrate a fast response (in the order of milliseconds) to RH variations. The limitations of fiber bend based humidity sensors are also discussed in the thesis. A novel RH sensor based on a reflection type photonic crystal fiber interferometer (PCFI) is presented which does not rely on the use of any hygroscopic material. The operating principle of a PCFI sensor based on the adsorption and desorption of water vapour at the silica-air interface within the PCF capillaries is discussed. The demonstrated sensor shows a good RH sensitivity in the higher RH range. Furthermore this RH sensor is almost temperature independent and can also be used in a high temperature and high pressure environment for humidity sensing.In order to improve the sensitivity of a reflection type PCFI over a wider RH range an alternative sensor is developed by infiltrating the microholes of the PCF with the hygroscopic material Agarose. The demonstrated novel sensor has a good sensitivity, a fast response time and a compact size. The temperature dependence of the device is also investigated. A novel hybrid device based on Agarose infiltrated PCFI interacting with a fiber Bragg grating is also presented which can simultaneously measure RH and temperature.A novel RH sensor based on a transmission type photonic crystal fiber interferometer coated with Agarose is also presented and discussed. This structure is used to study the effect of Agarose coating thickness in such a sensor on the RH sensitivity. It is demonstrated that the RH sensitivity of the sensor has a significant dependence on the thickness of the coating. An experimental method is also demonstrated to select an optimum coating thickness to achieve the highest sensitivity for a given RH sensing range. The sensor with the highest demonstrated sensitivity shows a linear response in the RH ranges of 40-80 % and 80-95 % with a sensitivity of 0.57 nm/%RH and 1.43 nm/%RH respectively.Finally, a comparison of the four RH sensing devices is presented, based on their size, operating range, RH sensitivity, temperature dependence and response time, in the context of selecting suitable devices for end-user applications. Two examples of applications are presented: dew sensing and breathing monitoring. The reflection type PCFI which does not use any hygroscopic material is selected for dew sensing and the dew response of the device is presented and discussed. Finally a novel breathing sensor based on the Agarose infiltrated PCFI is developed, which due to its immunity to interference from electric and magnetic fields, is suitable for breath monitoring of patients during medical procedures such as a magnetic resonance imaging scan

Lab-on-fiber technology: a new avenue for optical nanosensors

The "lab-on-fiber" concept envisions novel and highly functionalized technological platforms completely integrated in a single optical fiber that would allow the development of advanced devices, components and sub-systems to be incorporated in modern optical systems for communication and sensing applications. The realization of integrated optical fiber devices requires that several structures and materials at nano- and micro-scale are constructed, embedded and connected all together to provide the necessary physical connections and light-matter interactions. This paper reviews the strategies, the main achievements and related devices in the lab-on-fiber roadmap discussing perspectives and challenges that lie ahead

Editorial: Nanotechnological Advances in Biosensors

A biosensor is a physicochemical or hybrid physical-chemical-biological device that detects a biological molecule, organism, or process. Because of the nature of their targets, biosensors need to be faster, smaller, more sensitive, and more specific than nearly all of their physicochemical counterparts or the traditional methods that they are designed to replace. Speed is of the essence in medical diagnosis as it permits for rapid, accurate treatment and does not allow patients to be lost to follow-up. Small size and greater sensitivity mean less-invasive sampling and detection of molecules such as neurotransmitters or hormones at biologically-relevant levels. Greater specificity allows assays to be performed in complex fluids such as blood or urine without false negative or false positive results. [...