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Dispersion Compensation Modules

Author: the photonics expert (RP)

Acronym: DCM

Definition: modules used for dispersion compensation

Categories: article belongs to category lightwave communications lightwave communications, article belongs to category light pulses light pulses

DOI: 10.61835/0xe   Cite the article: BibTex plain textHTML   Link to this page   LinkedIn

In optical fiber communications, dispersion compensation modules (DCM) (also called dispersion compensation units, DCU) can be used for compensating the chromatic dispersion of, e.g., a long span of transmission fiber. Typically, such a module provides a fixed amount of dispersion (e.g. normal dispersion in the 1.6-μm spectral region, with some wavelength dependence of the group delay dispersion), although tunable dispersion modules are also available. A module can easily be inserted into a fiber-optic link because it has fiber connectors for the input and output. The insertion losses may be significant, but may be compensated with a fiber amplifier, e.g. an erbium-doped fiber amplifier in a 1.5-μm telecom system. A dispersion-compensating module is often placed between two fiber amplifiers.

Dispersion compensation modules can be based on different technologies:

  • A simple and frequently used method employs a long piece of fiber, e.g. a dispersion-shifted fiber, wound up on a spool with a diameter of e.g. 100–200 mm. The fiber used can be optimized to provide dispersion for the compensation of e.g. a 100-km span of transmission fiber, while introducing an insertion loss of only a few decibels.
  • A more compact approach, also possibly presenting even lower insertion loss, is based on a chirped fiber Bragg grating. A large amount of dispersion can be compensated with relatively long fiber gratings (possibly tens of centimeters in length). By varying the device temperature (with built-in temperature gradients), the dispersion may be tuned.
  • For wavelength division multiplexing systems, virtually imaged phased arrays are sometimes used.

Key Performance Parameters

Various properties of dispersion compensation modules can be important:

  • A central aspect is of course the amount of group delay dispersion provided (e.g. in units of ps2, or ps/nm), which depends on the length of transmission fiber to be compensated, and on the type of transmission fiber. For example, dispersion-shifted transmission fibers usually require much less dispersion compensation.
  • The dispersion slope (higher-order dispersion) e.g. in units of ps/nm2 may strongly limit the usable bandwidth, which is important particularly in the case of wavelength division multiplexing. Depending on the type of transmission fiber, different relative dispersion slopes are required.
  • In some cases, tunable dispersion is desirable.
  • Optical insertion losses may result e.g. from absorption and scattering in a fiber, but also from splice and connector losses. Such losses should be low, since they require a high amplifier gain and lead to higher excess noise.
  • In some cases, the amount of optical nonlinearity (e.g. favoring four-wave mixing) can be relevant. This is minimized e.g. by using strongly dispersive fiber, where a shorter length is sufficient.
  • Compactness can be an important practical aspect. Tight winding of the compensating fiber can be a solution, but is limited by bend losses.

For very high single-channel data rates, compensation of polarization mode dispersion can also be required. This is substantially more complicated, since it is necessary for that purpose to monitor the state of the signal and correct the time delays accordingly.

More to Learn

Encyclopedia articles:

Suppliers

The RP Photonics Buyer's Guide contains 21 suppliers for dispersion compensation modules. Among them:

O-E Land

dispersion compensation modules

O/E Land's OEDCG-100 is a dispersion compensating module based on fiber Bragg gratings. It features a compact size, small insertion loss and customized dispersion slope. Our unique fiber grating apodization technology enables us to fabricate dispersion compensation grating filters with high isolation, low side lobes and low ripples.

APE

dispersion compensation modules

The APE femtoControl is a compact motorized dispersion compensation unit for optimization of the duration of femtosecond laser pulses in the spectral range of Ti:sapphire lasers.

femtoControl compensates for material dispersion by applying the inverse amount of dispersion to the pulse. This is generated by a pair of prisms on motorized translation stages allowing continuous adjustment of the pulse length.

For example, femtoControl can help to achieve more crisp and clearer microscope images especially for multi-photon microscopy.

Thorlabs

dispersion compensation modules

Thorlabs manufactures a suite of options for dispersion management, including a pre-compensation module, dispersion compensating fiber, chirped mirrors, and low GDD optics. For ultrafast applications where dispersion must be well known and managed, Thorlabs’ portfolio includes a robust benchtop white light interferometer for characterizing reflective and transmissive dispersive properties of optics and coatings. The Chromatis™ dispersion measurement system covers 500 – 1650 nm, providing a means for measuring optics used for common femtosecond systems, including Ti:Sapphire systems as well as 1 µm and 1550 nm oscillators. The Chromatis compliments our ultrafast family of lasers, amplifiers, and specialized optics including nonlinear crystals, chirped mirrors, low GDD mirrors/beamsplitters, and dispersion compensating fiber.

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