Extinction ratio shows how well a system tells strong signals from weak ones. Extinction ratio, when used to describe the performance of an optical transmitter used in digital communications, is simply the ratio of the energy (power) used to transmit a logic level '1', to the energy used to transmit a logic level '0'. For a graphical description, the eye-diagram is commonly. Eye diagram showing an example of two power levels in an OOK modulation scheme, which can be used to calculate extinction ratio. P1 and P0 are represented by (binary 1) and (binary 0) respectively. In addition, the variability of extinction ratio. One important parameter that is typically measured with an oscilloscope is extinction ratio (ER), which describes how efficiently laser transmitter power is converted to modulation power.