UNDERSTANDING LAUNCHED OPTICAL POWER WITHOUT INPUT TO TRANSMITTER

This is term that is used in Passive Optical Network Technology (PON). PON devices consist of : OLT and ONU/ONU. Downstream is direction from OLT to ONU/ONT, while upstream is direction from ONU/ONT to OLT.

Launched optical power without input to transmitter is different from mean launched optical power.

The mean launched power at OLT and ONU/ONT is the average power of a pseudo-random data sequence coupled into the fibre by the transmitter. It is given as a range to allow for some cost optimization and to cover all allowances for operation under standard operating conditions, transmitter connector degradation, measurement tolerances, and ageing effects.

In operating state, the lower figure is the minimum power which shall be provided and the higher one is the power which shall never be exceeded.

NOTE - The measurement of the launched power at the ONU/ONT optical interface shall take into account the bursty nature of the upstream traffic transmitted by the ONU/ONT.

In the upstream direction, the ONU transmitter shall launch no power into the fibre in all slots which are not assigned to that ONU. The ONU shall also launch no power during the Guard time of slots that are assigned to it, with the exception of the last Tx Enable bits which may be used for laser pre bias, and the Tx Disable bits immediately following the assigned cell, during which the output falls to zero. The launched power level during laser pre-bias must be less than 0.1 of the one level.

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