In
telecommunications
Telecommunication is the transmission of information by various types of technologies over wire, radio, optical, or other electromagnetic systems. It has its origin in the desire of humans for communication over a distance greater than that fe ...
, a cutback technique is a destructive technique for determining certain
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 ...
transmission characteristic
The transmission curve or transmission characteristic is the mathematical function or graph that describes the transmission fraction of an optical or electronic filter as a function of frequency or wavelength. It is an instance of a transfer funct ...
s, such as
attenuation
In physics, attenuation (in some contexts, extinction) is the gradual loss of flux intensity through a medium. For instance, dark glasses attenuate sunlight, lead attenuates X-rays, and water and air attenuate both light and sound at variable att ...
and
bandwidth
Bandwidth commonly refers to:
* Bandwidth (signal processing) or ''analog bandwidth'', ''frequency bandwidth'', or ''radio bandwidth'', a measure of the width of a frequency range
* Bandwidth (computing), the rate of data transfer, bit rate or thr ...
.
Procedure
The measurement technique consists of:
#performing the desired measurements on a long length of the fiber under test,
#cutting the fiber under test at a point near the launching end,
#repeating the measurements on the short length of fiber, and
#subtracting the results obtained on the short length to determine the results for the residual long length.
The cut should be made to retain 1 meter or more of the fiber, in order to establish
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 ...
conditions for the second measurement. In a
multimode fiber
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 100 Gbit/s. Multi-mode fiber has a fairly large ...
, the lack of an equilibrium mode distribution could introduce errors in the measurement due to output coupling effects. In a
single-mode fiber
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 microwav ...
, measuring a shorter cutback fiber could result in significant transmission of cladding modes (light carried in the cladding rather than the core of the optical fiber), distorting the measurement. The errors introduced will result in conservative results (''i.e.'', higher transmission losses and lower bandwidths) than would be realized under equilibrium conditions.
Benefits
The benefit of this technique is that it allows measurement of the fiber characteristics without introducing errors due to variation in the launch conditions. For example, the
coupling efficiency of the light source is kept consistent between the initial and the cutback measurements.
Several characteristics may be determined using the same test fiber.
Attenuation measurement
Since the attenuation is defined as proportional to the logarithm of the ratio between
and
, where
is the
power
Power most often refers to:
* Power (physics), meaning "rate of doing work"
** Engine power, the power put out by an engine
** Electric power
* Power (social and political), the ability to influence people or events
** Abusive power
Power may a ...
at point
and
respectively. Using the cutback technique, the power transmitted through a fiber of known length is measured and compared with the same measurement for the same fiber cut to a length of
approximately.
Related techniques
A variation of the cutback technique is the
substitution method
In optical fiber technology, the substitution method is a method of measuring the transmission loss of a fiber. It consists of:
#using a stable optical source, at the wavelength of interest, to drive a mode scrambler, the output of which overfills ...
, in which measurements are made on a full-length of fiber, and then on a short length of fiber having the same characteristics (
core
Core or cores may refer to:
Science and technology
* Core (anatomy), everything except the appendages
* Core (manufacturing), used in casting and molding
* Core (optical fiber), the signal-carrying portion of an optical fiber
* Core, the central ...
size,
numerical aperture
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 proper ...
), with the results from the short length being subtracted to give the results for the full length.
References
{{FS1037C
External links
Optical Fiber Measurements
Fiber optics