This is the instantaneous, most-recently-sampled value of the received optical power measured on the higher-numbered optical lane of this multi-lane coherent port during the current performance-monitoring interval. A live per-lane reading matters on multi-lane coherent optics because the individual lanes can degrade independently, so checking this lane's power right now can isolate a problem to just one lane rather than the whole port. For example, if inOpticalPowerLaneHighInstant reads noticeably lower than the low-lane equivalent at the same moment, an admin would suspect an issue isolated to the high lane's optical path inside the module rather than a fiber-wide problem.