What Is a Forward Echo?

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  • Written By: Mal Baxter
  • Edited By: Daniel Lindley
  • Last Modified Date: 06 October 2019
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Forward echo refers to the reflection of optical data transmission, typically laser light, that propagates in the same direction along a fiber optic line as the traveling signal. The scattering effect can create interferences as well as data loss, or attenuation, as it's referred to technically. Dispersion of a single or multiple light wave can be caused by numerous factors. Problems with connection, polishing of the fiber optic glass tip, or network component configurations outside of recommended product specifications all contribute.

Referring to fiber optical signals, forward echo occurs through mismatched cable splices through the many connections and components the light wave may travel. The network systems can span the length of a room or continent. Preservation of the pulsing light signal through cable channels, repeaters, and multiplexers requires careful maintenance and troubleshooting through the entire length of the system. These signal dispersions can accumulate and compound over the span of a network; other faults may result, reducing efficiency and creating troubleshooting issues in the field.


Fiber optic lines transmit communication signals that carry data and voice transmissions. Simplex fiber optic lines carry signals in one direction, and duplex lines allow bidirectional transmissions. The light wave is contained in the optical channel through careful manufacture of an optical core and cladding that compel light wavelengths forward. Single-mode fiber optic lines have a tighter glass core and are used with more powerful lasers over long distances. Multimode fiber optic lines combine short-range multiple signals and commonly have more complex networks to maintain.

Specifically, forward echo occurs when a discontinuity in the channel or connection point reflects the otherwise forward moving wavelength back. If this reflection finds itself meeting another such discontinuity, it may then bounce forward once again. This issue can create imperceptible interferences or notable degradations in signal quality. Such degradations manifest as line interference or even dropouts, as during a long-distance telephone call. The issue requires the maintenance of a technician to detect the origin points of both involved discontinuities and take corrective action.

In metallic lines, forward echo may also occur in impedance mismatches. These may take place between an electrical source or load and whatever impedance characterizes the transmission line. Forward echo degradations occurring in fiber optic networks can happen over numerous types of transmission channels and waveguides. Such types include most transmission configurations, twisted pair, and coaxial tubes. When a light signal reflects in one direction only, this is typically referred to as backscatter.


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