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Smart Sensors for Digital Agriculture
Published in Indu Bala, Kiran Ahuja, Harnessing the Internet of Things (IoT) for a Hyper-Connected Smart World, 2023
The optical sensor measures a physical quantity of light and converts it to a form that is readable by an integrated measuring device generally into an electrical signal. These can be either internal or external. External optical sensors are designed to collect and then transmit a defined light quantity, while internal sensors calibrate the directional variations in the light path. Optical sensors are capable of reading a wide variety of measurands by different optical mechanisms such as temperature, pressure, strain, velocity, displacement, vibrations, liquid level, pH value, force radiation, acoustic field, and electric field [40]. Soft water level sensing is used for assessing the water level or flow such as rain, stream, etc., with the provision of tunable time steps. For assessing soil moisture, soil density and composition in terms of its organic substances, clay, and mineral content, the reflection principle is used by these sensors [41, 42]. To be more precise, the working principle is based on the variations of wave reflections with respect to the electromagnetic spectrum. Optical fluorescence based sensors are used for measuring the plant and fruit maturation [43].
Optics Letters
Published in Qiaoliang Bao, Hui Ying Hoh, Yupeng Zhang, Graphene Photonics, Optoelectronics, and Plasmonics, 2017
Ziyu Wang, Zai-Quan Xu, Yupeng Zhang, Qiaoliang Bao
Polarization is a common property of electromagnetic waves. If the electric vectors are all along the same plane, the light is polarized; otherwise, the light is unpolarized. A polarizer is an optical filter that passes light of a specific polarization and blocks waves of other polarizations. It can convert a beam of light of unpolarized or mixed polarization into a beam with well-defined polarization, polarized light. All fiber in-line polarizer is one of the most important components in fiber-optic communication and sensor systems. The in-line devices are constructed by first polishing a short section of the lateral surface of the cladding to within the evanescent field around the fiber core, followed with cover with crystals [1,2], thin metal films [3–5], or graphene [6,7]. In a typical device, unpolarized or mix polarization light is coupled into and guided by the fiber from one end. The evanescent field of the light guided by the fiber interacts with the selective material covered on the polished parts along the fiber. The desired polarized light remains unaffected by the overlay material and is still guided by the fiber, while the light with unwanted polarization interacts with atop material and is no longer guided by the fiber. Only light with the desired polarization is coupled out in this manner.
Optical Fibers and Accessories
Published in Daniel Malacara-Hernández, Brian J. Thompson, Advanced Optical Instruments and Techniques, 2017
A polarizer is an optical device that transmits (or reflects) a state of polarization and that suppresses any transmission (or reflection) of the orthogonal state of polarization. An ideal linear polarizer is a device that transforms any input state of polarization of light to a linear output state. A linear polarizer can also be defined as a device whose eigenpolarizations (for example, the two orthogonal polarization modes in a single-mode fiber) are linear with one eigenvalue (one of the orthogonal modes) equal to zero. In optical fibers, the main method used to eliminate one of the two orthogonal modes is a loss process, in which one of the modes is coupled toward the outer medium or providing larger radiation loss for one mode than the other.
Minreview: Recent advances in the development of gaseous and dissolved oxygen sensors
Published in Instrumentation Science & Technology, 2019
Q. Wang, Jia-Ming Zhang, Shuai Li
Electrochemical oxygen sensing in oxygen detection requires larger oxygen consumption and the response time is slow. In addition, the poor security and other issues limited the applications, but the method operates in high-temperature environments. Optical oxygen sensor arecurrently the main research direction of the combination of fluorescent materials and optical fibers. Fluorescent materials offer unique fluorescence characteristics that are only sensitive to oxygen. Optical fibers provide small size, light weight, and the absence of electromagnetic interferences. Optical oxygen sensors combine the advantages of both to achieve miniaturization, online analysis with remote sensing to provide new possibilities. However, the fluorescence signal of the optical oxygen sensor based on the fluorescent material are very weak, so the collection of fluorescence is a problem that must be solved.
Real-time monitoring of railroad track tension using a fiber Bragg grating-based strain sensor
Published in Instrumentation Science & Technology, 2018
While the light is traveling inside the fiber, some portion is reflected, and the rest is transmitted due to environmental factors. It is possible to measure the magnitude of environmental factors by the analysis of this scattered light. In general, Raman, Brillouin and Rayleigh scattering are used in fiber optic sensing systems. Another method is the use of a fiber Bragg grating. Basically, a fiber optic sensor operates by modulating one or a few characteristics of the reflected light wave, such as phase, polarization and frequency, and provides an opportunity to measure environmental factors, such as strain, temperature, and pressure, from many points.[78910]
Omnidirectional cylindrical graphene-based Bragg fiber in terahertz
Published in Waves in Random and Complex Media, 2021
Optical fibers find wide usage in optical communications and are used instead of metal wires due to the less loss and the immunity to electromagnetic interference. Optical fibers also have various other applications, such as fiber optic sensors and fiber lasers [1,2]. Optical fibers that typically include a high refractive index core surrounded with a low refractive index clad keep the light using total internal reflection phenomenon and act as waveguides [3]. Recently, photonic crystal fibers (PCFs) have attracted much attention due to their ability to confine light even in low-index or hollow-cores and confinement characteristics not possible in conventional optical fibers [4–7]. Potential advantages of hollow-core fibers are lower absorption loss and higher threshold power for nonlinear effects. The PCFs were first explored in 1996 and are now finding many applications. The PCFs may classify into two main classes: PCFs with a two-dimensional transverse periodicity [8] and Bragg fibers constructed from one-dimensional periodic concentric cylindrical shells [9–11]. The idea of using Bragg reflections in cylindrical waveguides was introduced in [12], and the first Bragg fibers were produced in 2000 [13]. Recently, researchers have paid much attention to the propagation of electromagnetic waves in a cylindrical photonic crystal (CPC) structure due to advances in modern manufacturing technology and the possibility of developing photonic crystals in different geometrical structures [14,15]. As one knows, the electromagnetic waves with arbitrary propagation wave vectors ) are not separable into the transverse electric and magnetic modes in the cylindrical geometry. However, in the absence of the z-component of the propagation wave vector, it is possible to separate the electromagnetic waves into the transverse electric and transverse magnetic modes. For this reason, in most articles, the propagation of electromagnetic waves in cylindrical geometry has been studied when the propagation wave vector does not have any component along the symmetry axis of the cylindrical structure [16–19].