A guided ray is a ray of light in a multi-mode optical fiber, which is confined by the core.
In optics, the numerical aperture (NA) of an optical system is a dimensionless number that characterizes the range of angles over which the system can accept or emit light. By incorporating index of refraction in its definition, NA has the property that it is constant for a beam as it goes from one material to another, provided there is no refractive power at the interface. The exact definition of the term varies slightly between different areas of optics. Numerical aperture is commonly used in microscopy to describe the acceptance cone of an objective, and in fiber optics, in which it describes the range of angles within which light that is incident on the fiber will be transmitted along it.
The optical power budget in a fiber-optic communication link is the allocation of available optical power among various loss-producing mechanisms such as launch coupling loss, fiber attenuation, splice losses, and connector losses, in order to ensure that adequate signal strength is available at the receiver. In optical power budget attenuation is specified in decibel (dB) and optical power in dBm.
In an optical communications link, the optical power margin is the difference between the optical power that is launched by a given transmitter into the fiber, less transmission losses from all causes, and the minimum optical power that is required by the receiver for a specified level of performance. An optical power margin is typically measured using a calibrated light source and an optical power meter.
For an optical fiber or waveguide, a radiation mode or unbound mode is a mode which is not confined by the fiber core. Such a mode has fields that are transversely oscillatory everywhere external to the waveguide, and exists even at the limit of zero wavelength.
For an optical fiber, a step-index profile is a refractive index profile characterized by a uniform refractive index within the core and a sharp decrease in refractive index at the core-cladding interface so that the cladding is of a lower refractive index. The step-index profile corresponds to a power-law index profile with the profile parameter approaching infinity. The step-index profile is used in most single-mode fibers and some multimode fibers.
An optical telescope is a telescope that gathers and focuses light mainly from the visible part of the electromagnetic spectrum, to create a magnified image for direct visual inspection, to make a photograph, or to collect data through electronic image sensors.
In optical engineering, an objective is an optical element that gathers light from an object being observed and focuses the light rays from it to produce a real image of the object. Objectives can be a single lens or mirror, or combinations of several optical elements. They are used in microscopes, binoculars, telescopes, cameras, slide projectors, CD players and many other optical instruments. Objectives are also called object lenses, object glasses, or objective glasses.
In optics, an image-forming optical system is a system capable of being used for imaging. The diameter of the aperture of the main objective is a common criterion for comparison among optical systems, such as large telescopes.
Multi-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 800 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. The standard G.651.1 defines the most widely used forms of multi-mode optical fiber.
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.
An astronomical interferometer or telescope array is a set of separate telescopes, mirror segments, or radio telescope antennas that work together as a single telescope to provide higher resolution images of astronomical objects such as stars, nebulas and galaxies by means of interferometry. The advantage of this technique is that it can theoretically produce images with the angular resolution of a huge telescope with an aperture equal to the separation, called baseline, between the component telescopes. The main drawback is that it does not collect as much light as the complete instrument's mirror. Thus it is mainly useful for fine resolution of more luminous astronomical objects, such as close binary stars. Another drawback is that the maximum angular size of a detectable emission source is limited by the minimum gap between detectors in the collector array.
A fiber laser is a laser in which the active gain medium is an optical fiber doped with rare-earth elements such as erbium, ytterbium, neodymium, dysprosium, praseodymium, thulium and holmium. They are related to doped fiber amplifiers, which provide light amplification without lasing.
The Ohana project aims to use seven big telescopes on top of Mauna Kea, Hawaiʻi Big Island, in an interferometer configuration. Mauna Kea is a former volcano whose height is 13,600 ft. It is a good site for telescopes which probe the universe in the optical and infrared wavelengths because of its altitude and low levels of light pollution.
Cladding in optical fibers is one or more layers of materials of lower refractive index in intimate contact with a core material of higher refractive index.
The operation of a photon scanning tunneling microscope (PSTM) is analogous to the operation of an electron scanning tunneling microscope, with the primary distinction being that PSTM involves tunneling of photons instead of electrons from the sample surface to the probe tip. A beam of light is focused on a prism at an angle greater than the critical angle of the refractive medium in order to induce total internal reflection within the prism. Although the beam of light is not propagated through the surface of the refractive prism under total internal reflection, an evanescent field of light is still present at the surface.
Yerkes 41-inch reflector is a 40-inch aperture (101.6 cm) reflecting telescope at the Yerkes Observatory, that was completed in 1968. It is known as the 41 inch to avoid confusion with a 40 inch refractor at the observatory. Optically it is a Ritchey–Chrétien design, and the main mirror uses low expansion glass. The telescope was used as a testbed for an adaptive optics system in the 1990s.
A 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.
