Distinguish between single mode and multimode optical fiber.

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Distinguish between single mode and multimode optical fiber.

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A single-mode fibre has a very thin core and carries only one mode (one path) of light; a multimode fibre has a wider core and carries many modes. PointSingle-mode fibreMultimode fibre Core diameterVery small, about 5–10 µmLarger, about 50–200 µm Number of modesOnly oneMany (hundreds) V-number V < 2.405 V > 2.405 ; number of modes ≈ V²/2 (step index) Refractive index difference Δ Very smallLarger Numerical apertureSmallLarge Intermodal dispersionAbsentPresent (less in graded index) Bandwidth / data rateVery highLower DistanceLong distance (tens of km and more)Short distance (LAN, within buildings) Light sourceLaser diodeLED or laser Coupling and splicingDifficult, needs precise alignmentEasier Cost of systemHigherLower Index profileStep indexStep index or graded index

Distinguish between single mode and multimode optical fiber.

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Point	Single-mode fibre	Multimode fibre
Core diameter	Very small, about 5–10 µm	Larger, about 50–200 µm
Number of modes	Only one	Many (hundreds)
V-number	\(V < 2.405\)	\(V > 2.405\); number of modes \(\approx V^2/2\) (step index)
Refractive index difference \(\Delta\)	Very small	Larger
Numerical aperture	Small	Large
Intermodal dispersion	Absent	Present (less in graded index)
Bandwidth / data rate	Very high	Lower
Distance	Long distance (tens of km and more)	Short distance (LAN, within buildings)
Light source	Laser diode	LED or laser
Coupling and splicing	Difficult, needs precise alignment	Easier
Cost of system	Higher	Lower
Index profile	Step index	Step index or graded index