Why graded-index fibre is better than multimode step-index fibre?

Comparison between Graded-Index Fibre and Multimode Step-Index Fibre

Graded-index fibre and multimode step-index fibre are two types of optical fibers used in telecommunications and networking. The primary difference between them lies in their internal structure and how they manage light propagation, which significantly impacts their performance in data transmission. Below, we delve into why graded-index fibre is often considered superior to multimode step-index fibre for many applications.

1. Reduction in Modal Dispersion

Graded-index fibre features a refractive index that gradually decreases from the core center towards the cladding. This design minimizes modal dispersion, a phenomenon where light rays travel at different speeds, causing signal distortion over long distances. In contrast, multimode step-index fibre has a uniform refractive index in the core and a sudden change at the cladding, leading to higher modal dispersion and reduced signal quality over distance.

2. Higher Bandwidth

The reduction in modal dispersion allows graded-index fibres to support higher bandwidths compared to multimode step-index fibres. This makes graded-index fibres more suitable for high-speed data transmission over longer distances without significant signal degradation.

3. Improved Signal Quality

Due to the gradual change in the refractive index, graded-index fibres can focus light rays more efficiently towards the center of the core. This focusing effect reduces signal attenuation and maintains higher signal quality over longer distances, unlike in multimode step-index fibres where light rays can spread out and weaken the signal.

4. Application Versatility

Graded-index fibres are versatile and can be used in a wide range of applications, from short-haul connections within buildings to long-distance telecommunications networks. Their superior performance characteristics make them suitable for both digital and analog signal transmissions, whereas multimode step-index fibres are often limited to shorter, less demanding applications.


In summary, graded-index fibre offers significant advantages over multimode step-index fibre, including reduced modal dispersion, higher bandwidth, improved signal quality, and greater application versatility. These benefits make graded-index fibre a preferred choice for modern telecommunications systems and high-speed data networks.

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