Abstract: A transceiver is herein described. The transceiver comprises an optical source providing an optical signal, a modulator receiving the optical signal and configured to encode data into the optical signal, a transmitter module to receive data to be encoded into the optical signal and having at least one drive circuit supplying driver signals to the modulator to cause the modulator to encode data into a carrier having a frequency band and a tone signal outside of the frequency band into the optical signal, a narrowband filter operable to receive a portion of the optical signal via an optical loopback, the optical signal having the encoded data and a first tone reflection of the tone signal at a first instant of time and to pass the first tone reflection, a polarimeter operable to receive the first tone reflection and determine a first tone polarization of the first tone reflection.