Optical fiber is a thin, flexible, adaptable, transparent fiber which is made of silica. It is a flexible transparent material consisting of core & cladding which is used for transmission of light rays based on refraction of light.
Optical fiber is the basic transmission medium for fiber-optic communication. These include the concept and classification of propagation modes along the fiber, single-mode condition, numerical aperture, mechanisms and specifications of optical attenuation and dispersion, as well as nonlinearities of optical fiber. While dispersion specifies mode-dependent or wavelength-dependent propagation speed of optical signal propagating in an optical fiber, which is both linear effects, nonlinear effects such as stimulated Raman scattering. Stimulated Brillouin scattering, and power-dependent refractive index known as Kerr effect nonlinearity may also affect wave propagation in optical fiber. Although standard optical fibers or patch cord are most often used in optical communication systems, a variety of specialty fibers have also been developed for special applications.
The optical performance of solid-core polymer-based microstructured optical fibers is the Theoretical model developed earlier is utilized for solid-core triangular air/polymer microstructured optical fibers (MPOFs). The scalar variational approach is implemented for evaluating the fundamental modal characteristics of polymer-based MOFs. Effective index for higher-order mode at terahertz (THz) regime is evaluated and the cut-off conditions are also identified. Coupling characteristics of long-period gratings (LPG) in MPOF has been examined. The sensitivity coefficient is explored for realizing efficient coupling in the evanescent field-based sensing applications.
Types of optical fiber
I. Based on the structures :
· Planar wave guide fiber- This type of fiber is made of the rectangular block containing three layers as the base, light guide, and coating. The refractive index of the base and that of the coating are lower than other layers.
· Cylindrical optical fiber- This is made up of the core, typically glass where light passes through. This core is also surrounded by a cylindrical layer of material which has a lower refractive index and is known as cladding. The refractive index difference is 0.005. The function of the jacket is to protect the core.
II. Based on the mode number:
· Single-mode fiber- Single-mode fibers, on the other hand, are better used for longer communication distances, which are appropriate for the long-distance telephone as well as multi-channel TV transmission systems. Single-mode fibers have small core diameters of 5 or 10 μm. The diameter of the cladding in the multi-mode and single-mode fibers is 125 μm.
· Multi-mode fiber- This type of fiber applies to short-distance communications such as local area network systems and video surveillance. It has a very large core diameter of 50–62.5 μm. The large diameter of the core pushes the impulse to pass along different optical routes in random mode, hence, the rays move to touch the detector at dissimilar times. It causes a temporary broadening of the signal, hindering data transmission speed and effective broadcast distance to about 200–500 m.
Hydrogel optical fibers are demonstrated for continuous glucose monitoring. A smartphone is exploited for detecting the probe's output signals. The optical technique simplifies the fabrication and readout of the fiber optic probes. The probe shows high sensitivity in the physiological glucose range. A bio compatible hydro gel fiber probe enables implantable applications. The fabricated optical fiber sensors may have applications in wearable and implantable point-of-care and intensive-care continuous monitoring systems.
The applications of the fiber optics field are still emerging (becoming apparent or prominent) and developing very fast, it is impossible to keep track of each innovation and invention. The future is not so distant when scientists and researchers will come up with more and more futuristic products and applications using optical fibers.