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Method of Calculation of Trim Fiber Length

IP.com Disclosure Number: IPCOM000008639D
Publication Date: 2002-Jun-30
Document File: 8 page(s) / 35K

Publishing Venue

The IP.com Prior Art Database

Related People

Robert Hughes: INVENTOR [+2]

Related Documents

US 6,339,665: PATENT

Abstract

This publication deals with dispersion management, and in particular with a method for calculating the appropriate amounts of trim fiber and high order mode fiber required in a high order mode dispersion management device. The calculator is suitable for use with fundamental mode dispersion compensating fiber.

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METHOD OF CALCULATION OF TRIM FIBER LENGTH

                                                                                                                                                                                    By:  Robert Hughes

This publication deals with dispersion management, and in particular with a method for calculating the appropriate amounts of trim fiber and high order mode fiber required in a high order mode dispersion management device.

BACKGROUND

Optical fiber has become increasingly important in many applications involving the transmission of light.  When a pulse of light is transmitted through an optical fiber, the energy follows a number of paths which cross the fiber axis at different angles.  A group of paths which cross the axis at the same angle is known as a mode.  The fundamental mode, also known as the LP01 mode, is the mode in which light passes substantially along the fiber axis.  Modes other than the LP01 mode, are known as high order modes.  Fibers which have been designed to support only one mode with minimal loss, the LP01 mode, are known as single mode fibers.  A multi-mode fiber is a fiber whose design supports multiple modes, and typically supports over 100 modes.  A few-mode fiber is a fiber designed to support only a very limited number of modes.  For the purpose of this document, we will define a few mode fiber as a fiber supporting no more than 20 modes at the operating wavelength.  Fibers may carry different numbers of modes at different wavelengths, however in telecommunications the typical wavelengths are near 1310 nm and 1550 nm.

As light traverses the optical fiber, different group of wavelengths travel at different speeds, which leads to chromatic dispersion.  Chromatic dispersion is defined as the differential of the group velocity in relation to the wavelength in units of picosecond/nanometer (ps/nm).  Optical fibers are often characterized by their dispersion per unit length of 1 kilometer, which is expressed in units of picosecond/nanometer/kilometer (ps/nm/km).

The dispersion experienced by each wavelength of light is also different, and is primarily controlled by a combination of the material dispersion, and the dispersion created by the actual profile of the waveguide, known as waveguide dispersion.  The differential of the dispersion in relation to wavelength is known as the slope, or second order dispersion, and is in units of ps/nm2.  Optical fibers may be further characterized by their slope per unit length of 1 kilometer, which is expressed in units of picosecond/nanometer2/kilometer (ps/nm2/km).

Few mode fibers designed to have specific characteristics in a mode  other than the fundamental mode are also known as high order mode (HOM) fibers.  HOM fibers are particularly useful for compensating chromatic dispersion due to the large amount of negative dispersion which can be experienced by a signal traversing certain profiles in a high order mode.  Additionally, HOM fibers may compensate for much or all of the slope of a given transmission fiber. 

Single mode fibers (SMF) designed as dispersion compensating fibers (DCF) are well known in the art, and typically exhibit disp...