bandwidth–distance product (original) (raw)

Author: the photonics expert (RP)

Definition: product of length and maximum signal bandwidth of a fiber-optic link

Alternative term: bandwidth–length product

Categories: article belongs to category fiber optics and waveguides fiber optics and waveguides, article belongs to category lightwave communications lightwave communications

Related: bandwidthoptical fiber communicationsfiber-optic linkstelecom fibersgraded-index fibersbit error ratemodal bandwidthdifferential mode delay

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DOI: 10.61835/jk1 Cite the article: BibTex BibLaTex plain textHTML Link to this page! LinkedIn

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Contents

What is the Bandwidth–Distance Product?

The term bandwidth–distance product (or bandwidth–length product) is often used in the context of optical fiber communications. It is usually defined as the product of the length of a fiber-optic link and its maximum signal bandwidth. That bandwidth is strongly related to the data rate (in Gbit/s), with a conversion factor which depends on the used modulation format. The bandwidth–distance product is typically limited by the phenomenon that the bit error rate rises sharply for too high data rates.

Application in Telecommunications

The concept of the bandwidth–distance product is helpful e.g. for comparing the performance of different types of fiber-optic links. However, the definition by no means implies that the achievable bandwidth–distance product is independent of the chosen fiber length. Whether this is the case depends on the circumstances. It can be true for a link based on multimode fiber, the capacity of which is limited by intermodal dispersion; indeed, the bandwidth–distance product (based on the modal bandwidth) is mostly used in that domain. (A typical value may then be of the order of a few GHz·km for a graded-index fiber, or an order of magnitude less for step-index fibers.) On the other hand, in a link based on single-mode fiber, which is limited by chromatic dispersion and which does not contain means for dispersion compensation, a doubling of the data rate may enforce a reduction in the fiber length by a factor of four. The bandwidth–distance product is then effectively reduced by a factor of two. However, the transmission distance may of course also be doubled by concatenating two fiber-optic links with electronic regeneration between them.

Frequently Asked Questions

This FAQ section was generated with AI based on the article content and has been reviewed by the article’s author (RP).

What is the bandwidth–distance product?

The bandwidth–distance product is a figure of merit in optical fiber communications, defined as the product of a fiber link's length and its maximum signal bandwidth. It helps to quantify the transmission capacity of an optical fiber.

What physical effects limit the bandwidth–distance product?

For multimode fibers, the product is typically limited by intermodal dispersion. For single-mode fibers, the main limitation is often chromatic dispersion, particularly if no dispersion compensation is applied.

Is the bandwidth–distance product a constant for a specific fiber?

It is approximately constant for multimode fibers limited by intermodal dispersion. However, for single-mode fibers limited by chromatic dispersion, the product is not constant; it typically decreases as higher bandwidths are used.

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