In telecommunications, optical modulation amplitude (OMA) is the difference between two optical power levels, of a digital signal generated by an optical source, e.g., a laser diode.

It is given by

${\displaystyle {\text{OMA}}=P_{1}-P_{0}\,}$

where P₁ is the optical power level generated when the light source is "on," and P₀ is the power level generated when the light source is "off." The OMA may be specified in peak-to-peak mW.

The OMA can be related to the average power ${\displaystyle P_{\text{av}}=(P_{1}+P_{0})/2}$ and the extinction ratio ${\displaystyle r_{e}=P_{1}/P_{0}}$

${\displaystyle {\text{OMA}}=2P_{\text{av}}{\frac {r_{e}-1}{r_{e}+1}}}$

In the limit of a high extinction ratio, ${\displaystyle {\text{OMA}}\approx 2P_{\text{av}}}$. However, OMA is often used to express the effective usable modulation in a signal when the extinction ratio is not high and this approximation may not be valid.