Mode scrambler
telecommunications device for handling signals on optical fibers
In telecommunications, a mode scrambler or mode mixer is a device for inducing mode coupling in an optical fiber, or a device that, itself, exhibits a uniform output intensity profile independent of the input mode volume or modal excitation condition. Mode scramblers are used to provide a modal distribution that is independent of the optical source for purposes of laboratory, manufacturing, or field measurements or tests. Mode scramblers are primarily used to improve reproducibility of multimode fiber bandwidth measurements.
Overview
If multimode fiber bandwidth is measured using a laser diode directly coupled to its input, the resulting measurement can vary by as much as an order of magnitude. This measurement variability is due to the combination of differences in laser output characteristics (emitted mode power distribution) and the differential mode delay of the fiber. Differential mode delay is the difference in the time delays amongst the fiber's propagating modes caused by imperfections or nonideality of the fiber refractive index profile.
The primary purpose of a mode scrambler is to create a uniform, overfilled launch condition that can be easily reproduced on multiple measurement systems, so that measurement systems have essentially the same launch conditions and can measure approximately the same bandwidth despite having different laser sources. These were used for this purpose in the first U.S. NIST round-robins on multimode fiber. The overfilled launch (OFL) was created to reduce measurement variability, and improve concatenation estimates for multimode fibers, used at that time for telecom 'long haul' (e.g., 7–10 km 850 nm or 20–30 km 1300 nm) systems.
When the telecom industry converted to near-exclusive use of single-mode fiber ca.
“Mode scrambler” enters the record as telecommunications device for handling signals on optical fibers. Crown Archives preserves that source wording while asking what Mode, scrambler and telecommunications can confirm, complicate or overturn.
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