Question 18M.3.SL.TZ1.9c.iii
| Date | May 2018 | Marks available | [Maximum mark: 3] | Reference code | 18M.3.SL.TZ1.9c.iii |
| Level | SL | Paper | 3 | Time zone | TZ1 |
| Command term | Explain | Question number | c.iii | Adapted from | N/A |
A ray of light travelling in an optic fibre undergoes total internal reflection at point P.
The refractive index of the core is 1.56 and that of the cladding 1.34.
The input signal in the fibre has a power of 15.0 mW and the attenuation per unit length is 1.24 dB km–1.
Explain how the use of a graded-index fibre will improve the performance of this fibre optic system.
[3]
refractive index near the edge of the core is less than at the centre
speed of rays which are reflected from the cladding are greater than the speed of rays which travel along the centre of the core
the time difference for the rays that reflect from the cladding layer compared to those that travel along the centre of the core is less
OR
the signal will remain more compact/be less spread out/dispersion is lower
bit rate of the system may be greater
[3 marks]
