Step-index profile

For an optical fiber

Optical fiber

An optical fiber is a glass or plastic fiber that carries light along its length. Fiber optics is the overlap of applied science and engineering concerned with the design and application of optical fibers...

, a step-index profile is a refractive index

Refractive index

The refractive index of a medium is a measure of how much the speed of light is reduced inside the medium. For example, typical soda-lime glass has a refractive index close to 1.5, which means that in glass, light travels at 1 / 1.5 = 2/3 the speed of light in a vacuum...

 profile characterized by a uniform refractive index within the core and a sharp decrease in refractive index at the core-cladding

Cladding

Cladding is the covering of one material with another. It has different meanings depending on the context.-Metal:In metallurgy, cladding is the bonding together of dissimilar metals. It is distinct from welding or gluing as a method to fasten the metals together...

 interface so that the cladding is of a lower refractive index. The step-index profile corresponds to a power-law index profile

Power-law index profile

For optical fibers, a power-law index profile is an index of refraction profile characterized bywhereand is the nominal refractive index as a function of distance from the fiber axis, is the nominal refractive index on axis, is the refractive index of the cladding, which is taken to be...

 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.

For an optical fiber

Optical fiber

An optical fiber is a glass or plastic fiber that carries light along its length. Fiber optics is the overlap of applied science and engineering concerned with the design and application of optical fibers...

, a step-index profile is a refractive index

Refractive index

The refractive index of a medium is a measure of how much the speed of light is reduced inside the medium. For example, typical soda-lime glass has a refractive index close to 1.5, which means that in glass, light travels at 1 / 1.5 = 2/3 the speed of light in a vacuum...

 profile characterized by a uniform refractive index within the core and a sharp decrease in refractive index at the core-cladding

Cladding

Cladding is the covering of one material with another. It has different meanings depending on the context.-Metal:In metallurgy, cladding is the bonding together of dissimilar metals. It is distinct from welding or gluing as a method to fasten the metals together...

 interface so that the cladding is of a lower refractive index. The step-index profile corresponds to a power-law index profile

Power-law index profile

For optical fibers, a power-law index profile is an index of refraction profile characterized bywhereand is the nominal refractive index as a function of distance from the fiber axis, is the nominal refractive index on axis, is the refractive index of the cladding, which is taken to be...

 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 . The value of n₁ is typically between 1.44 and 1.46, and is typically between 0.001 and 0.02.

Step-index optical fiber is generally made by doping

Doping (semiconductor)

In semiconductor production, doping is the process of intentionally introducing impurities into an extremely pure semiconductor to change its electrical properties. The impurities are dependent upon the type of semiconductor. Lightly- and moderately-doped semiconductors are referred to as extrinsic...

 high-purity fused silica glass (SiO₂) with different concentrations of materials like titanium, germanium, or boron.

See also

• Graded-index fiber
  Graded-index fiber
  In fiber optics, a graded-index or gradient-index fiber is an optical fiber whose core has a refractive index that decreases with increasing radial distance from the fiber axis ....
  
  
• Critical Angle
• Numerical aperture
  Numerical aperture
  In optics, the numerical aperture of an optical system is a dimensionless number that characterizes the range of angles over which the system can accept or emit light...