WAn optical fiber is a flexible, transparent fiber made by drawing glass (silica) or plastic to a diameter slightly thicker than that of a human hair. Optical fibers are used most often as a means to transmit light between the two ends of the fiber and 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; in addition, fibers are immune to electromagnetic interference, a problem from which metal wires suffer. 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, some of them being fiber optic sensors and fiber lasers.
WAn 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.
WDouble-clad fiber (DCF) is a class of optical fiber with a structure consisting of three layers of optical material instead of the usual two. The inner-most layer is called the core. It is surrounded by the inner cladding, which is surrounded by the outer cladding. The three layers are made of materials with different refractive indices.
WA 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. A fiber Bragg grating can therefore be used as an inline optical filter to block certain wavelengths, or as a wavelength-specific reflector.
WHard-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.
WMulti-mode optical fiber is a type of optical fiber mostly used for communication over short distances, such as within a building or on a campus. Multi-mode links can be used for data rates up to 100 Gbit/s. Multi-mode fiber has a fairly large core diameter that enables multiple light modes to be propagated and limits the maximum length of a transmission link because of modal dispersion.
WOptical attached cable (OPAC) is a type of fibre optic cable that is installed by being attached to a host conductor along overhead power lines. The attachment system varies and can include wrapping, lashing or clipping the fibre optic cable to the host. Installation is typically performed using a specialised piece of equipment that travels along the host conductor from pole to pole or tower to tower, wrapping, clipping or lashing the fibre optic cable in place. Different manufacturers have different systems and the installation equipment, cable designs and hardware are not interchangeable.
WA cleave in an optical fiber is a deliberate, controlled break, intended to create a perfectly flat endface, perpendicular to the longitudinal axis of the fiber. The process of cleaving an optical fiber forms one of the steps in the preparation for a fiber splice operation regardless of the subsequent splice being a fusion splice or a mechanical splice; the other steps in the preparation being those of stripping and fiber alignment. A good cleave is required for a successful low loss splice of an optical fiber, often it is the case that fibers spliced by identical methods tend to have different losses, this difference can often be attributed to the quality of their initial cleaves.
WPhotonic-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.
WIn fiber optics, polarization-maintaining optical fiber is a single-mode optical fiber in which linearly polarized light, if properly launched into the fiber, maintains a linear polarization during propagation, exiting the fiber in a specific linear polarization state; there is little or no cross-coupling of optical power between the two polarization modes. Such fiber is used in special applications where preserving polarization is essential.
WIn fiber-optic communication, a single-mode optical fiber (SMF) is an optical fiber designed to carry only a single mode of light - the transverse mode. Modes are the possible solutions of the Helmholtz equation for waves, which is obtained by combining Maxwell's equations and the boundary conditions. These modes define the way the wave travels through space, i.e. how the wave is distributed in space. Waves can have the same mode but have different frequencies. This is the case in single-mode fibers, where we can have waves with different frequencies, but of the same mode, which means that they are distributed in space in the same way, and that gives us a single ray of light. Although the ray travels parallel to the length of the fiber, it is often called transverse mode since its electromagnetic oscillations occur perpendicular (transverse) to the length of the fiber. The 2009 Nobel Prize in Physics was awarded to Charles K. Kao for his theoretical work on the single-mode optical fiber. The standard G.652 defines the most widely used form of single-mode optical fiber.
WA 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.
WA tapered double-clad fiber (T-DCF) is a double-clad optical fiber which is formed using a specialised fiber drawing process, in which temperature and pulling forces are controlled to form a taper along the length of the fiber. By using pre-clad fiber preforms both the fiber core and the inner and outer cladding layers vary in diameter and thickness along the full length of the fiber. This tapering of the fiber enables the combination of the characteristics of conventional 8–10 µm diameter double-clad single-mode fibers to propagate light in fundamental mode with those of larger diameter (50–100 µm) double-clad multi-mode fibers used for optical amplification and lasing. The result is improved maintenance of pulse fidelity compared to conventional consistent diameter fiber amplifiers.By virtue of the large cladding diameter T-DCF can be pumped by optical sources with very poor brightness factor such as laser diode bars or even VECSELs matrices, significantly reducing the cost of fiber lasers/amplifiers.