What is the meaning of evanescent waves?
In electromagnetics, an evanescent field, or evanescent wave, is an oscillating electric and/or magnetic field that does not propagate as an electromagnetic wave but whose energy is spatially concentrated in the vicinity of the source (oscillating charges and currents).
What is evanescent wave in optical fiber?
Evanescent wave fiber optic biosensors are a subset of fiber optic biosensors that perform the sensing function along the fiber’s cylindrical length. This phenomenon, known as the evanescent wave, extends only to a short distance from the interface, with power dropping exponentially with distance.
What is evanescent wave absorption?
Evanescent wave absorption (EWA) based fiber-optic sensors have found widespread applications ranging from environmental sensing to biosensing. A combination of bending and tapering acts as a mode converter, which results in high penetration depth of the evanescent field.
What is near-field diffraction?
In optics, the Fresnel diffraction equation for near-field diffraction is an approximation of the Kirchhoff–Fresnel diffraction that can be applied to the propagation of waves in the near field. In contrast the diffraction pattern in the far field region is given by the Fraunhofer diffraction equation.
What is near-field and far-field in optics?
An oscillating electric dipole (e.g. an antenna or an excited atom or ion) emits electromagnetic radiation. Here, the near field has an extension less than one wavelengths. The far field occurs for distances from the dipole which are much larger than the wavelength. This also applies to radiation from antennae.
What is near-field coupling?
Typically, near-field is defined as the field around the antenna up to one wavelength (λ) away (approximately up to 35 centimeters). The communications between an RFID tag and an RFID reader (via the antenna) occurs using a process known as electromagnetic coupling.
What is the meaning of near and far-field distances when dealing with placing an appropriate lens from the laser?
The near field is understood to be the region around the beam waist (focus). The far field concerns the profile far from the waist, i.e., in a distance from the focus which is large compared with the effective Rayleigh length.