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Mode Volume
In fiber optics, mode volume is the number of bound modes that an optical fiber is capable of supporting. The mode volume ''M'' is approximately given by V^2 \over 2 and \left(\right), respectively for step-index and power-law index profile fibers, where ''g'' is the profile parameter, and ''V'' is the normalized frequency, ''which must be greater than 5 for this approximation to be valid''. See also *Equilibrium mode distribution *Mode scrambler *Mandrel wrapping In multimode fiber optics, mandrel wrapping is a technique used to preferentially attenuate high-order mode power of a propagating optical signal. Consequently, if the fibre is propagating substantial energy in affected modes, the modal distr ... References * Fiber optics {{optics-stub ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Fiber Optics
An optical fiber, or optical fibre in Commonwealth English, 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 (data transfer rates) 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. O ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Transverse Mode
A transverse mode of electromagnetic radiation is a particular electromagnetic field pattern of the radiation in the plane perpendicular (i.e., transverse) to the radiation's propagation direction. Transverse modes occur in radio waves and microwaves confined to a waveguide, and also in light waves in an optical fiber and in a laser's optical resonator. Transverse modes occur because of boundary conditions imposed on the wave by the waveguide. For example, a radio wave in a hollow metal waveguide must have zero tangential electric field amplitude at the walls of the waveguide, so the transverse pattern of the electric field of waves is restricted to those that fit between the walls. For this reason, the modes supported by a waveguide are quantized. The allowed modes can be found by solving Maxwell's equations for the boundary conditions of a given waveguide. Types of modes Unguided electromagnetic waves in free space, or in a bulk isotropic dielectric, can be described as a super ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Optical Fiber
An optical fiber, or optical fibre in Commonwealth English, 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 (data transfer rates) 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. ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Step-index Profile
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. A step-index fiber is characterized by the core and cladding refractive indices ''n1'' and ''n2'' and the core and cladding radii a and b. Examples of standard core and cladding diameters 2a/2b are 8/125, 50/125, 62.5/125, 85/125, or 100/140 (units of µm). The fractional refractive-index change \triangle \, = \frac \ll \ 1. The value of n1 is typically between 1.44 and 1.46, and \triangle is typically between 0.001 and 0.02. Step-index optical fiber is generally made by doping high-purity fused silica glass (SiO2) with differe ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Power-law Index Profile
For optical fibers, a power-law index profile is an index of refraction profile characterized by : n(r) = \begin n_1 \sqrt & r \le \alpha\\ n_1 \sqrt & r \ge \alpha \end where \Delta = , and n(r) is the nominal refractive index as a function of distance from the fiber axis, n_1 is the nominal refractive index on axis, n_2 is the refractive index of the cladding, which is taken to be homogeneous (n(r)=n_2 \mathrm r \ge \alpha), \alpha is the core radius, and g is a parameter that defines the shape of the profile. \alpha is often used in place of g. Hence, this is sometimes called an alpha profile. For this class of profiles, multimode distortion is smallest when g takes a particular value depending on the material used. For most materials, this optimum value is approximately 2. In the limit of infinite g, the profile becomes a step-index profile. See also *Graded-index fiber A graded-index or gradient-index fiber is an optical fiber whose core has a refractive ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Normalized Frequency (fiber Optics)
In an optical fiber, the normalized frequency, ''V'' (also called the V number), is given by :V = \sqrt\quad = \mathrm, where ''a'' is the core radius, λ is the wavelength in vacuum, ''n''1 is the maximum refractive index of the core, ''n''2 is the refractive index of the homogeneous cladding, and applying the usual definition of the numerical aperture ''NA''. In multimode operation of an optical fiber having a power-law refractive index profile, the approximate number of bound modes (the mode volume), is given by : \left( \right)\quad, where ''g'' is the profile parameter, and ''V'' is the normalized frequency, which must be greater than 5 for the approximation to be valid. For a step-index fiber, the mode volume is given by ''V''2/2. For single-mode operation, it is required that ''V'' < 2.4048, the first root of the ''J'' ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Equilibrium Mode Distribution
The equilibrium mode owerdistribution of light travelling in an optical waveguide or fiber, is the distribution of light that is no longer changing with fibre length or with input modal excitation. This phenomenon requires both mode filtering and mode mixing to occur in the fibre to produce a state that is independent of the mode power distribution launched by the light source. At propagation distances exceeding the equilibrium length, intramodal pulse distortion increases (bandwidth decreases) as the square root of length. The term ''equilibrium length'' is sometimes used to describe a ''stationary'' mode distribution, which is the length of multi-mode optical fiber necessary to attain a static mode distribution from a specific excitation condition. Equilibrium length is, strictly, the longest such length, as would result from a widely variable range of input excitation. Other terms for equilibrium length are ''equilibrium coupling length'' and ''equilibrium mode distribution ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Mode Scrambler
In telecommunications, a mode scrambler mode mixer is a device for inducing mode coupling in an optical fiber, or a device that, itself, exhibits a uniform output intensity profile independent of the input mode volume or modal excitation condition. Mode scramblers are used to provide a modal distribution that is independent of the optical source for purposes of laboratory, manufacturing, or field measurements or tests. Mode scramblers are primarily used to improve reproducibility of multimode fiber bandwidth measurements. If multimode fiber bandwidth is measured using a laser diode directly coupled to its input, the resulting measurement can vary by as much as an order of magnitude. This measurement variability is due to the combination of differences in laser output characteristics (emitted mode power distribution) and the differential mode delay of the fiber. Differential mode delay is the difference in the time delays amongst the fiber's propagating modes caused by imperfections ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Mandrel Wrapping
In multimode fiber optics, mandrel wrapping is a technique used to preferentially attenuate high-order mode power of a propagating optical signal. Consequently, if the fibre is propagating substantial energy in affected modes, the modal distribution will be changed. A cylindrical rod wrap consists of a specified number turns of fiber on a mandrel of specified size, depending on the fibre characteristics and the desired modal distribution. It has application in optical transmission performance tests, to create a defined mode power distribution or to prevent multimode propagation in single mode fibre. If the launch fibre is fully filled ahead of the mandrel wrap, the higher-order modes will be stripped off, leaving only lower-order modes. If the launch fibre is underfilled, for example as a consequence of being energized by a laser diode The laser diode chip removed and placed on the eye of a needle for scale A laser diode (LD, also injection laser diode or ILD, or dio ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
