Press ReleaseAll colours of light within free space travel at the same speed, this speed is known to be three million meters per second. However when different colours of light travel along any medium that isn’t free space, the speeds of the different colours of light are no longer the same. The aim of this project is measure what causes this effect, and how this effect changes when different colours of light are travelling along the fibre.

Measure How Different Colors of Light Travel in Optical Fibre at Different Speeds

By: Gruffydd Page Roberts | Supervisor: Dr Chao Wang1. Introduction

As different colours of light travel along a fibre the colours will spread out. The spreading effect caused by different colours of light travelling at different speeds is called chromatic dispersion.

2. Measuring Chromatic DispersionThis project will measure chromatic dispersion using two methods.

Modulation phase shift - measures the phase of the light signal before and after the fibre. Compares the difference between the measured phases. The phase difference has been caused by chromatic dispersion and thus can be used to calculate the chromatic dispersion.

3. ResultsThe results for the chromatic dispersion present within a optical fibre are shown below.

The results shown above show small differences in the methods, these differences are expected as each method has slightly different accuracy. The results show that the chromatic dispersion within fibre decreases as the wavelength decreases.

A second optical device was tested, the device is a Fibre Bragg Grating (FBG). The results are shown below.

The FBG has drastically changed the chromatic dispersion, a huge drop has been measured and could be used in applications to reduce the spreading of the light.

The aim of this project is to measure the chromatic dispersion in optical fibre and see how chromatic dispersion changes as the colour of the light travelling through the fibre changes.

Wavelength to time mapping -compares the frequency domain of the light signal with it’s time domain. Due to chromatic dispersion the time domain of the waveform spread and mimic the spectrum domain.

Fibre Time Domain

Chromatic Dispersion

Spectrum

Fibre Phase After

Chromatic Dispersion

Phase Before

Phase Difference