TIA/TR-1026

Description / Abstract: This part of IEC 61282, which is a technical report, applies to the accommodation and compensation of dispersion in fibre optic communication systems.

Generally, dispersion compensation and accommodation is used in the 1 550 nm region with cables incorporating conventional (dispersion-unshifted) single-mode category B1 fibre as shown in IEC 60793-1 and IEC 60793-2. In this wavelength region, the fibre has a positive dispersion coefficient that averages at about 17 ps/nm–km. There are two subcategories of such fibre. The cutoff wavelength of B1 fibre is low enough for the fibre to be used in either the 1 310 nm or the 1 550 nm region. Such fibre makes up the vast majority of installed fibre optic cable world wide. The cutoff wavelength of B1.2 fibre is high enough for the fibre to be used in the 1 550 nm region only. Such fibre is used in some submarine systems.

Smaller values of dispersion are attainable with dispersion-shifted category B2 fibre and with non-zero-dispersion category B4 fibre. Dispersion accommodation or compensation may sometimes be used with these fibre types as well, but only category B1 fibres will be discussed in this technical report.

Compensation refers to techniques or components that reduce the value of the dispersion or the dispersion slope of a fibre optic link to enable transmission at digital bit-rates and at analogue frequencies higher than would be possible without these techniques. Effectively, the cumulative zero-dispersion wavelength of the optical path is moved from the 1 310 nm region to somewhere in the 1 550 nm region. A link of dispersion-unshifted B1 fibre and an in-line dispersion compensator can be made to resemble, in some cumulative respects, a link of dispersion-shifted B2 fibre. Examples of passive dispersion compensating components include dispersion-compensating fibre, fibre Bragg gratings, and etalons.

Accommodation refers to techniques or components that utilize dispersion to enable transmission at digital bit-rates and at analogue frequencies higher than would be possible without these techniques. Examples of active dispersion accommodation include optical or electrical prechirping at the transmitter, dispersion-assisted transmission, midspan spectral inversion, and receiver signal processing. Accommodation will be treated in future revisions of this technical report.

Management referring to techniques that vary the dispersion coefficient along the optical path (both sign and magnitude) remains under study.