US Patent 7965941 Multichannel optical transport network time domain reflectometry calibration

A system and method are provided for controlling time delay in a multichannel optical transport network (OTN) transmission device using time domain reflectometry (TDR) measurements. The method accepts a pair of 2n-phase shift keying (2n-PSK) modulated signals via Ix and Qx electrical signal paths, where n>1. Likewise, a pair of 2p-PSK modulated signals are accepted via Iy and Qy electrical signal paths where p>1. Using TDR modules, signal reflections are measured from an output port for each signal path. The method minimizes time delay differences in the signal reflections for the Ix, Qx, Iy, and Qy signals paths by using the signal reflection measurements to adjust time delay modules in each signal path.