This is the lowest value recorded during the current performance-monitoring interval of the actual optical carrier frequency measured at this port's output during the current performance-monitoring interval, expressed in MHz. The lowest transmit frequency recorded in the interval helps characterize how far the laser has drifted low, an early indicator of aging in the laser's wavelength-locking mechanism. For example, an admin investigating intermittent interference on a neighboring channel would check whether outOpticalFrequencyMin on the suspect transmitter dips into that neighbor's frequency band.