Chromatic dispersion arises because individual mode includes light consisting of different wavelength each travelling along the fiber at different velocity causing dispersion.

1. A narrow band tunable optical source is intensity modulated by an electrical signal generator.

2. A vector voltmeter is used to measure the phase of the modulation of the received signal.

3. The signal is detected by a photodiode receiver and the phase of its modulation is compared with the electrical modulation source.

4. The phase measurement is repeated at intervals of ∆λ.

1. Using measurements at the two adjacent wavelengths, the change in group delay is found out by equation.

   $$∆τ_λ = ∅_λ+\frac{∆λ}2-∅_λ-\frac{∆λ}2{360f_m} \times 10^6$$

   where λ is the wavelength at the center of the interval

   $f_m$ is the modulation frequency in MHz

   $\phi$ is the phase of the measured modulation in degrees