Q.8 Compare step index fibre and graded index fibre. (asked in MU Dec 2024)
Best answer
Answer: Step index has a constant core index with a sharp step at the cladding, light travels in zig-zag paths and dispersion is high; graded index has a core index that falls gradually from the axis, light travels in curved paths and dispersion is low.
| Point | Step index fibre | Graded index (GRIN) fibre |
|---|---|---|
| Refractive index of core | Constant (\(\mu_1\)) across the core; changes abruptly to \(\mu_2\) at the cladding | Maximum at the axis and decreases gradually (nearly parabolically) towards the cladding |
| Path of light | Straight lines, zig-zag by total internal reflection | Curved (helical/sinusoidal) paths due to continuous refraction |
| Modes | Single-mode or multimode | Usually multimode |
| Intermodal dispersion | High in multimode (rays travel very different path lengths) | Low: rays far from the axis travel faster in lower-index regions, so all rays arrive nearly together |
| Bandwidth | Lower (multimode) | Higher |
| Numerical aperture | Same for all points of the core end face | Highest at the axis, decreases away from it |
| Manufacture and cost | Simple, cheaper | Difficult, costlier |
| Typical use | Short links, illumination, (single-mode) long-haul links | Medium-distance data links, LANs |
Log in or create a free account to answer this question.
