Phase noise compensation system, and method

A system comprising:

• a) a signal generator for providing a signal,
• b) a splitter for splitting the signal from the signal generator and directing it to a measurement path and a compensation path, wherein:
• i) the measurement path comprises a measurement interferometer having a splitter for splitting the signal into a first and a second part, the interferometer being arranged to transmit the first part to a remote target, and to receive reflections therefrom, and to combine the received reflections with the second part in a mixer, and
• ii) the compensation path comprises a compensation interferometer arranged to split its input signal into a first, delayed path, and a second, undelayed path, and to combine the first and second paths in a mixer to produce an output bearing information pertaining to a phase difference between the two paths, the relative delay between the first and second paths being a predetermined time Δt;
• c) sampling means for sampling the outputs of the measurement interferometer mixer and the compensation interferometer mixer
• d) processing means for calculating a phase compensation figure by summing a number n of the Δτ-induced phase difference samples from the compensation path to calculate a phase change over a time nΔτ, and for subtracting the calculated phase change from the output of the measurement interferometer.