one bit input signal power level 505 and a zero bit input signal power level 510 this ratio is referred to herein as an extinction ratio 515 the extinction ratio 515 is a measure of a contrast or a distinction between power levels of input signals designating a one bit input signal and a zero bit input signal for example if the extinction ratio 515 is large the distinction between a one bit input signal power level and a zero bit input signal power level is also large because the distinction between the power levels is large an optical receiver has an easier task in detecting an input signal as either a one bit input signal or a zero bit input signal in contrast if the extinction ratio 515 is small the distinction between a one bit input signal power level and a zero bit input signal power level is also small and an optical receiver has a more difficult task in detecting an input signal as either a one bit input signal or a zero bit input signal a similar ratio may be said to exist between the zero bit input signal power level 510 and a no input signal power level 520 this ratio is referred to herein as a no input extinction ratio 525 like the extinction ratio 515 the no input extinction ratio 525 is a measure of a contrast or a distinction between a power level of an input signal designating a zero bit input signal and a power level of a no input signal for example if the no input extinction ratio 525 is large the distinction between a zero bit input signal power level and a no input signal.