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Glossary and Fiber Specification Notes

ATTENUATION :
A measure of how much of the light injected into an optical fiber actually reaches the other end, usually expressed in decibels per kilometre (dB/km). BEATLENGTH:
The length over which polarization rotates through 360 within an optical fiber and therefore a fundamental measure of the polarization maintaining ability of a polarization maintaining fiber. opp BL BIREFRINGENCE:
The fundamental principle by which Fibercore HiBi (Highly Birefringent) polarization maintaining fiber works. A birefringent material has two distinct indices of refraction. nnB fastslow CHROMATIC DISPERSION:
A pulse-broadening and therefore bandwidth-limiting phenomenon which occurs because different wavelengths of light travel at different velocities. CONVERSION EFFICIENCY :
In an erbium doped fiber amplifier (EDFA), the ratio between the amplified signal output power and the power input from the pump laser. CONCENTRICITY:
Core-cladding concentricity is the distance between the geometric center of the core and the geometric center of the cladding. Sometimes call ‘Eccentricity’ or ‘Concentricity Error’, CUT-OFF WAVELENGTH:
The wavelength at which an optical fiber becomes single-moded. Below cut-off, the fiber will transmit more than one mode. At increasing wavelengths above cut-off the strength of guidance is gradually reduced. EDFA:
Erbium Doped Fiber Amplifier. A device incorporating erbium doped fiber to provide direct amplification of optical signals when pumped at either 980 nm or 1480 nm. EXTINCTION RATIO:
In a polarization maintaining fiber, the ratio between the ‘wanted’ and ‘unwanted’ polarization states, expressed in decibels (dB). Highly dependent upon operating environment. FIBER LASER:
A laser in which the gain-element is a length of rare-earth doped optical fiber. FIBER GRATING:
A selective reflector formed by inducing a periodic variation of refractive index within the core of an optical fiber. FOG:
Fiber Optic Gyroscope. A solid-state replacement for the conventional ‘spinning mass’ gyroscopes used in direction sensing. Incorporates a coil of HiBi PM fiber as the sensing element. GAIN :
In an EDFA, the ratio between the amplified signal output and the (un-amplified) signal input, expressed in dB. H-PARAMETER:
In a PM fiber, the extinction ratio, expressed as a decibel, per unit length. Should not be used to compare fibers because H-parameter ratio is also determined by environment. HB:
Highly Birefringent (Hi-Bi). See Birefringence. The greater the difference in the indices of refraction, the higher the birefringence. The degree of PM is directly related to the degree of birefringence MODE FIELD DIAMETER (MFD ):
The diameter of the optical field within the fiber, specified at the 1/e or 1/e² point (the radial point at which the intensity has fallen to 1/e or 1/e² of its maximum value). NUMERICAL APERTURE:
A measure of the divergence of the light emitted from the fiber, determined by the refractive index difference between the core and the cladding. NA = 220sin nn PM:
Polarization Maintaining. In a PM fiber, a desired fixed polarization orientation is preserved along the entire fiber length. PMD:
Polarization Mode Dispersion. Dispersion associated with different waveguide characteristics for different polarization modes. QUANTUM EFFICIENCY:
In the EDFA, the actual conversion efficiency signal expressed as a percentage of the maximum possible conversion efficiency (equal to the ratio of the pump and sign wavelengths). SATURATION:
EDFA performance under conditions of total population inversion which occur at high input powers. SMF:
Singlemode Fiber. A fiber that only supports the propagation of a ‘single’ fundamental Gaussian mode above the cut-off wavelength V-VALUE:
Also called ‘Normalised Frequency’ – the fundamental relationship between numerical aperture, cut-off wavelength and core diameter. V = offcutatNAd .405.2)( FIBER SPECIFICATION NOTES: The speed of development of specialty fiber technology is such that the specifications of our fibers are subject to continuous review. Please contact Fibercore Limited for exact details of current specifications. 1. The Design Wavelength is the wavelength (or wavelengths) at which the fiber is typically used. In practice, the fiber will transmit the single mode at wavelengths of up to approximately 200 nm longer than the cut-off wavelength. 2. The Mode Field Diameter is a nominal, calculated value, estimated at the operating wavelength(s) using typical values for numerical aperture and cut-off wavelength. 3. Attenuation is a worst-case value, quoted for the shortest design wavelength. 4. Beat length is measured at 633 nm for all HB fiber types. To a first approximation, beat-length scales directly with operating wavelength. 5. Background loss is quoted at the minimum point of the spectrum (typically 1100 nm to 1200 nm for the Er-Doped fibers). Call us at +44 (0) 23 8076 9893 or Fax us at +44 (0) 23 8076 9895 to discuss your custom requirements Website: www.fibercore.com E-mail: info@fibercore.com