Patent ID: 7872738

Claim:
A method of monitoring an optical communication system using differential optical time domain reflectometry (OTDR), said optical communication system including first and second optical paths, said first and second optical paths being coupled together, said method comprising: optically loading at least said first optical path; transmitting a first OTDR test signal on said first optical path at a first test wavelength; transmitting a second OTDR test signal on said first optical path at a second test wavelength; detecting first and second reflected OTDR signals on said second optical path to produce first and second sets of OTDR test data, said first and second reflected OTDR signals corresponding to said first and second OTDR test signals being reflected from at least one reflecting element in said first optical path; determining a difference between said first and second sets of OTDR test data to produce difference data representing gain tilt in at least one of said optical paths; and monitoring a condition of said at least one of said optical paths using said difference data.