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PHOSFOS (Photonic Skins For Optical Sensing) is a research and technology development project co-funded by the European Commission.
| | This article needs additional or more specific categories .(February 2021) |
PHOSFOS (Photonic Skins For Optical Sensing) is a research and technology development project co-funded by the European Commission.
The PHOSFOS project [1] is developing flexible and stretchable foils or skins that integrate optical sensing elements with optical and electrical devices, such as onboard signal processing and wireless communications, as seen in Figure 1. These flexible skins can be wrapped around, embedded in, and anchored to irregularly shaped or moving objects and allow quasi-distributed sensing of mechanical quantities such as deformation, pressure, stress, and strain. [2] This approach offers advantages over conventional sensing systems, such as increased portability and measurement range.
The sensing technology is based around sensing elements called Fiber Bragg Gratings (FBGs) that are fabricated in standard single core silica fibers, highly birefringent Microstructured fibers (MSF) and Plastic optical fibers (POF). The silica MSFs are designed to exhibit almost zero temperature sensitivity to cope with the traditional temperature cross-sensitivity issues of conventional fiber sensors. These specialty fibers are being modeled, designed, and fabricated within the programme. FBGs implemented in plastic optical fiber are also being studied because plastic fibers can be stretched up to 300% before breaking, permitting use under conditions that would result in catastrophic failure of other types of strain sensors.
Once optimized, the sensors are embedded into a flexible skin and interfaced with peripheral optoelectronics and electronics (see Figure 2).
The photonic skins developed by PHOSFOS have potential application in real-time remote monitoring of behavior and integrity of various structures such as in civil engineering (buildings, dams, bridges, roads, tunnels and mines), in aerospace (aircraft wings, helicopter blades), and in energy production (windmill blades). Applications in healthcare are also being investigated.
A summary of the key developments can be found on the PhoSFOS EU webpage and includes the demonstration of a fully flexible opto-electronic foil. [3]
Figure 3 shows the scattering of HeNe laser light from noise gratings recorded in PMMA using a 325 nm HeCd laser.
One of the early results from the project was in developing a repeatable method for joining polymer fiber to standard silica fiber — a major development that enabled using POF Bragg gratings in applications outside an optics lab. One of the first uses for these sensors was in monitoring strain in tapestries [4] shown in Figure 4. [5] In this case conventional electrical strain sensors and silica fiber sensors were shown to be strengthening the tapestries in areas where they were fixed. Because polymer fibre devices are much more flexible they did not distort the textiles as much, permitting more accurate measurement of strain.
Temperature and humidity sensing using a combined silica / POF fiber sensor has been demonstrated. [6] Combined strain, temperature and bend sensing has also been shown. [7] Using a fiber Bragg grating in an eccentric core polymer has been shown to yield a high sensitivity to bend. [8]
Other recent progress includes the demonstration of birefringent photonic crystal fibers with zero polarimetric sensitivity to temperature, [9] [10] and a successful demonstration of transversal load sensing with fibre Bragg gratings in microstructured optic fibers. [11]
The key areas where significant progress has been made are listed below: [12]
The 2nd "Benefits for Industry" Meeting of the EU FP7 Project PHOSFOS will take place on Sunday 22 May 2011 in Munich (Germany).
The meeting is co-located with the Industry Meets Academia Workshop organized by SPIE SPIE as part of the Optical Metrology Conference. It will be followed by the World of Photonics Congress and the Laser World of Photonics Trade Fair in Munich, in the week from 23 to 26 May 2011.
This Meeting is the second in its kind gathering all companies that have expressed their possible interest in the technology developed by the EU FP7 project PHOSFOS.
18 companies/institutes have registered for the Industrial User Club of PHOSFOS, new members are welcome.
A photonic crystal is an optical nanostructure in which the refractive index changes periodically. This affects the propagation of light in the same way that the structure of natural crystals gives rise to X-ray diffraction and that the atomic lattices of semiconductors affect their conductivity of electrons. Photonic crystals occur in nature in the form of structural coloration and animal reflectors, and, as artificially produced, promise to be useful in a range of applications.
Photonic-crystal fiber (PCF) is a class of optical fiber based on the properties of photonic crystals. It was first explored in 1996 at University of Bath, UK. Because of its ability to confine light in hollow cores or with confinement characteristics not possible in conventional optical fiber, PCF is now finding applications in fiber-optic communications, fiber lasers, nonlinear devices, high-power transmission, highly sensitive gas sensors, and other areas. More specific categories of PCF include photonic-bandgap fiber, holey fiber, hole-assisted fiber, and Bragg fiber. Photonic crystal fibers may be considered a subgroup of a more general class of microstructured optical fibers, where light is guided by structural modifications, and not only by refractive index differences. Hollow-core fibers (HCFs) are a related type of optical fiber which bears some resemblance to holey optical fiber.
A fiber Bragg grating (FBG) is a type of distributed Bragg reflector constructed in a short segment of optical fiber that reflects particular wavelengths of light and transmits all others. This is achieved by creating a periodic variation in the refractive index of the fiber core, which generates a wavelength-specific dielectric mirror. Hence a fiber Bragg grating can be used as an inline optical filter to block certain wavelengths, can be used for sensing applications, or it can be used as wavelength-specific reflector.
Sir David Neil Payne is a British professor of photonics who is director of the Optoelectronics Research Centre at the University of Southampton. He has made several contributions in areas of optical fibre communications over the last fifty years and his work has affected telecommunications and laser technology. Payne’s work spans diverse areas of photonics, from telecommunications and optical sensors to nanophotonics and optical materials, including the introduction of the first optical fibre drawing tower in a university.
A distributed Bragg reflector (DBR) is a reflector used in waveguides, such as optical fibers. It is a structure formed from multiple layers of alternating materials with different refractive index, or by periodic variation of some characteristic of a dielectric waveguide, resulting in periodic variation in the effective refractive index in the guide. Each layer boundary causes a partial reflection and refraction of an optical wave. For waves whose vacuum wavelength is close to four times the optical thickness of the layers, the interaction between these beams generates constructive interference, and the layers act as a high-quality reflector. The range of wavelengths that are reflected is called the photonic stopband. Within this range of wavelengths, light is "forbidden" to propagate in the structure.
Plastic optical fiber (POF) or polymer optical fiber is an optical fiber that is made out of polymer. Similar to glass optical fiber, POF transmits light through the core of the fiber. Its chief advantage over the glass product, other aspect being equal, is its robustness under bending and stretching.
An optical fiber, or optical fibre, is a flexible glass or plastic fiber that can transmit light from one end to the other. Such fibers find wide usage in fiber-optic communications, where they permit transmission over longer distances and at higher bandwidths than electrical cables. Fibers are used instead of metal wires because signals travel along them with less loss and are immune to electromagnetic interference. Fibers are also used for illumination and imaging, and are often wrapped in bundles so they may be used to carry light into, or images out of confined spaces, as in the case of a fiberscope. Specially designed fibers are also used for a variety of other applications, such as fiber optic sensors and fiber lasers.
Philip St. John Russell, FRS, is Emeritus Director of the Max Planck Institute for the Science of Light in Erlangen, Germany. His area of research covers "photonics and new materials", in particular the examination of new optical materials, especially of photonic crystal fibres, and more generally the field of nano- and micro-structured photonic materials.
A photonic integrated circuit (PIC) or integrated optical circuit is a microchip containing two or more photonic components that form a functioning circuit. This technology detects, generates, transports, and processes light. Photonic integrated circuits use photons as opposed to electrons that are used by electronic integrated circuits. The major difference between the two is that a photonic integrated circuit provides functions for information signals imposed on optical wavelengths typically in the visible spectrum or near-infrared (850–1650 nm).
Distributed temperature sensing systems (DTS) are optoelectronic devices which measure temperatures by means of optical fibres functioning as linear sensors. Temperatures are recorded along the optical sensor cable, thus not at points, but as a continuous profile. A high accuracy of temperature determination is achieved over great distances. Typically the DTS systems can locate the temperature to a spatial resolution of 1 m with accuracy to within ±1 °C at a resolution of 0.01 °C. Measurement distances of greater than 30 km can be monitored and some specialised systems can provide even tighter spatial resolutions. Thermal changes along the optical fibre cause a local variation in the refractive index, which in turn leads to the inelastic scattering of the light propagating through it. Heat is held in the form of molecular or lattice vibrations in the material. Molecular vibrations at high frequencies (10 THz) are responsible for Raman scattering. Low frequency vibrations (10–30 GHz) cause Brillouin scattering. Energy is exchanged between the light travelling through the fibre and the material itself and cause a frequency shift in the incident light. This frequency shift can then be used to measure temperature changes along the fibre.
A fiber-optic sensor is a sensor that uses optical fiber either as the sensing element, or as a means of relaying signals from a remote sensor to the electronics that process the signals. Fibers have many uses in remote sensing. Depending on the application, fiber may be used because of its small size, or because no electrical power is needed at the remote location, or because many sensors can be multiplexed along the length of a fiber by using light wavelength shift for each sensor, or by sensing the time delay as light passes along the fiber through each sensor. Time delay can be determined using a device such as an optical time-domain reflectometer and wavelength shift can be calculated using an instrument implementing optical frequency domain reflectometry.
A subwavelength-diameter optical fibre is an optical fibre whose diameter is less than the wavelength of the light being propagated through it. An SDF usually consists of long thick parts at both ends, transition regions (tapers) where the fibre diameter gradually decreases down to the subwavelength value, and a subwavelength-diameter waist, which is the main acting part. Due to such a strong geometrical confinement, the guided electromagnetic field in an SDF is restricted to a single mode called fundamental. In usual optical fibres, light both excites and feels shear and longitudinal bulk elastic waves, giving rise to forward-guided acoustic wave Brillouin scattering and backward-stimulated Brillouin scattering. In a subwavelength-diameter optical fibre, the situation changes dramatically.
Hard-clad silica (HCS) or polymer-clad fiber (PCF) is an optical fiber with a core of silica glass and an optical cladding made of special plastic. In contrast to all-silica fiber, the core and cladding can be separated from each other.
Kenneth O. Hill is a Mexican Canadian physicist who specializes in the field of photonics. In the late 1970s, he discovered the phenomena of photosensitivity in optical fiber and has worked extensively in its applications. He first demonstrated Fiber Bragg gratings and their applications in optical communication and optical sensor systems. Further areas of his discovery and innovation include the phase mask technique for grating fabrication, fiber grating dispersion compensators, and wavelength selective fiber filters, multiplexers and demultiplexers. This field of research has led to the ability to create high speed fiber optic networks as well as many other communication applications that have revolutionized the telecommunications industry.
Structural coloration in animals, and a few plants, is the production of colour by microscopically structured surfaces fine enough to interfere with visible light instead of pigments, although some structural coloration occurs in combination with pigments. For example, peacock tail feathers are pigmented brown, but their microscopic structure makes them also reflect blue, turquoise, and green light, and they are often iridescent.
Electronic skin refers to flexible, stretchable and self-healing electronics that are able to mimic functionalities of human or animal skin. The broad class of materials often contain sensing abilities that are intended to reproduce the capabilities of human skin to respond to environmental factors such as changes in heat and pressure.
Soft robotics is a subfield of robotics that concerns the design, control, and fabrication of robots composed of compliant materials, instead of rigid links. In contrast to rigid-bodied robots built from metals, ceramics and hard plastics, the compliance of soft robots can improve their safety when working in close contact with humans.
Jonathan C. Knight, is a British physicist. He is the Pro Vice-Chancellor (Research) for the University of Bath where he has been Professor in the Department of Physics since 2000, and served as head of department. From 2005 to 2008, he was founding Director of the university's Centre for Photonics and Photonic Materials.
An addressed fiber Bragg structure (AFBS) is a fiber Bragg grating, the optical frequency response of which includes two narrowband components with the frequency spacing between them being in the radio frequency (RF) range. The frequency spacing is unique for every AFBS in the interrogation circuit and does not change when the AFBS is subjected to strain or temperature variation. An addressed fiber Bragg structure can perform triple function in fiber-optic sensor systems: a sensor, a shaper of double-frequency probing radiation, and a multiplexor. The key feature of AFBS is that it enables the definition of its central wavelength without scanning its spectral response, as opposed to conventional fiber Bragg gratings (FBG), which are probed using optoelectronic interrogators. An interrogation circuit of AFBS is significantly simplified in comparison with conventional interrogators and consists of a broadband optical source, an optical filter with a predefined linear inclined frequency response, and a photodetector. The AFBS interrogation principle intrinsically allows to include several AFBSs with the same central wavelength and different address frequencies into a single measurement system.
Photonic crystal sensors use photonic crystals: nanostructures composed of periodic arrangements of dielectric materials that interact with light depending on their particular structure, reflecting lights of specific wavelengths at specific angles. Any change in the periodicity or refractive index of the structure can give rise to a change in the reflected color, or the color perceived by the observer or a spectrometer. That simple principle makes them useful colorimetric intuitive sensors for different applications including, but not limited to, environmental analysis, temperature sensing, magnetic sensing, biosensing, diagnostics, food quality control, security, and mechanical sensing. Many animals in nature such as fish or beetles employ responsive photonic crystals for camouflage, signaling or to bait their prey. The variety of materials utilizable in such structures ranging from inorganic, organic as well as plasmonic metal nanoparticles makes these structures highly customizable and versatile. In the case of inorganic materials, variation of the refractive index is the most commonly exploited effect in sensing, while periodicity change is more commonly exhibited in polymer-based sensors. Besides their small size, current developments in manufacturing technologies have made them easy and cheap to fabricate on a larger scale, making them mass-producible and practical.