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Definition: the control of the overall chromatic dispersion of a system by adding optical elements with a suitable amount of dispersion
Dispersion compensation essentially means canceling the chromatic dispersion of some optical element(s). However, the term is often used in a more general sense of dispersion management, meaning the control the overall chromatic dispersion of some system. The goal can be, e.g., to avoid excessive temporal broadening of ultrashort pulses and/or the distortion of signals. Dispersion compensation is applied mainly in mode-locked lasers and in telecommunication systems, but also sometimes in optical fibers transporting light e.g. to or from some fiber-optic sensor.
Dispersion Compensation in Mode-locked Lasers
In a mode-locked laser for femtosecond pulse generation, the chromatic dispersion introduced by the gain medium and other optical components in the laser resonator is often not desirable, because it tends to broaden and chirp the generated pulses. While the naturally occurring chromatic dispersion is often in the normal dispersion regime, the desired dispersion may either be close to zero or even anomalous (for the formation of quasi-soliton pulses in the resonator). Such dispersion values can be achieved by introducing optical components with anomalous dispersion. In the case of bulk lasers, such components are usually either special dispersive dielectric mirrors (e.g. in the form of monolithic Gires-Tournois interferometers or chirped mirrors), or prism pairs. For mode-locked fiber lasers, the dispersion can be compensated with special dispersive fibers (e.g. photonic crystal fibers or multimode fibers where a higher-order mode is used), with chirped fiber Bragg gratings, or sometimes with bulk components such as pairs of diffraction gratings.
For pulses with durations below roughly 30 fs, it is necessary to control not only the second-order dispersion but also the dispersion of higher orders. It may then be important e.g. to select the appropriate material for a prism pair, or an optimized geometry of a prism compressor. Also, there are special devices called GRISMs, with a grating structure on a prism, which make possible an optimized ratio of the strength of second- and third-order dispersion.
Dispersion Compensation in Fiber Communication Links
Dispersion compensation can also be used outside laser resonators, for example to compensate the dispersion of long fiber links in systems for optical fiber communications. In that case, the required dispersion may be normal (rather than anomalous). It can be provided with sections of fibers with different designs, or with dispersion compensation modules (DCMs) which can contain, e.g., long pieces of dispersion-shifted fibers or chirped fiber Bragg gratings. The latter have the advantage of compactness and comparatively low insertion losses.
To some extent, the effects of dispersion in a system for optical data transmission can also be mitigated by electronic dispersion compensation.
Bibliography
| [1] | R. L. Fork et al., "Negative dispersion using pairs of prisms", Opt. Lett. 9 (5), 150 (1984) |
| [2] | J. Kuhl and J. Heppner, "Compression of femtosecond optical pulses with dielectric multilayer interferometers", IEEE J. Quantum Electron. 22 (1), 182 (1986) |
| [3] | R. L. Fork et al., "Compression of optical pulses to six femtoseconds by using cubic phase compensation", Opt. Lett. 12 (7), 483 (1987) |
| [4] | D. Garthe et al., "Adjustable dispersion equaliser for 10 and 20 Gbit/s over distances up to 160 km", Electron. Lett. 30 (25), 2159 (1994) |
| [5] | G. Tempea et al., "Dispersion control over 150 THz with chirped dielectric mirrors", IEEE J. Sel. Top. Quantum Electron. 4 (2), 193 (1998) |
| [6] | N. Matuschek et al., "Theory of double-chirped mirrors", IEEE J. Sel. Topics in Quantum Electron. 4, 197 (1998) |
| [7] | B. Golubovic et al., "Double Gires-Tournois interferometer negative-dispersion mirrors for use in tunable mode-locked lasers", Opt. Lett. 25 (4), 275 (2000) |
| [8] | N. M. Litchinitser et al., "Fiber-based tunable dispersion compensation", J. Opt. Fiber Commun. Rep. 4, 41 (2007) |
| [9] | R. Jones et al., "Silicon photonic tunable optical dispersion compensator", Opt. Express 15 (24), 15836 (2007) |
See also: chromatic dispersion, dispersion compensation modules, mode locking, solitons, optical data transmission, prism pairs, Gires-Tournois interferometers, fiber Bragg gratings, chirped mirrors, electronic dispersion compensation, pulse compression
Categories: communications, methods, pulses
