Optical channel sounder

A coherent optical channel sounding receiver apparatus, comprising:

• a first optical receiver for receiving an optical carrier signal over a first optical channel, wherein the optical carrier signal is received at different carrier frequencies at different time instants according to a predetermined time-frequency grid;
• a second optical receiver for receiving a modulated optical signal over a second optical channel, the modulated optical signal comprising a received copy of the optical carrier signal modulated with a predetermined constant-amplitude zero auto-correlation (CAZAC) training sequence, the received copy of the optical carrier signal being affected by the optical channel;
• an optical down converter, separately connected to the first optical receiver and the second optical receiver, 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 upon the basis of the down converted signal and the predetermined CAZAC training sequence, wherein the channel estimator uses a CAZAC sequence flat spectrum property to measure the channel frequency response of the second optical channel.

An optical channel sounder, comprising:

• an optical channel sounding transmitter apparatus, comprising:
• an optical signal generator for generating a first optical carrier signal, wherein the optical signal generator is configured to generate the first optical carrier signal at different carrier frequencies at different time instants according to a predetermined time-frequency grid,
• an optical modulator for modulating the first optical carrier signal with a predetermined constant-amplitude zero auto-correlation (CAZAC) training sequence to obtain a first modulated optical signal,
• a first optical transmitter for transmitting the first optical carrier signal, and
• a second optical transmitter for transmitting the first modulated optical signal;
• and
• a coherent optical channel sounding receiver apparatus, comprising:
• a first optical receiver for receiving a second optical carrier signal over a first optical channel,
• a second optical receiver for receiving a second modulated optical signal over a second optical channel, the second modulated optical signal comprising a received copy of the second optical carrier signal modulated with a predetermined training sequence, the received copy of the second optical carrier signal being affected by the optical channel,
• an optical down converter for down converting the second modulated optical signal using the second received optical carrier signal to obtain a down converted signal, and
• a channel estimator for estimating a channel characteristic of the second optical channel upon the basis of the down converted signal and the predetermined CAZAC training sequence, wherein the channel estimator uses a CAZAC sequence flat spectrum property to measure the channel frequency response of the second optical channel.