US Patent 10320478 Optical channel sounder

The present invention relates to an optical channel sounding transmitter apparatus, comprising an optical signal generator for generating an optical carrier signal; an optical modulator for modulating the optical carrier signal with a predetermined training sequence to obtain an modulated optical signal; a first optical transmitter for transmitting the optical carrier signal; and a second optical transmitter for transmitting the modulated optical signal. Further the present invention relates to a coherent optical channel sounding receiver apparatus, comprising a first optical receiver for receiving an optical carrier signal over a first optical channel; a second optical receiver for receiving a modulated optical signal over a second optical channel; an optical down converter for down converting the modulated optical signal using the received optical carrier signal to obtain a down converted signal; and a channel estimator for estimating a channel characteristic of the second optical channel.