AN OPTICAL DEVICE

An optical device comprising: a light routing element coupled to a first optical path and a second optical path such that light received by the light routing element is directed into one of the first optical path or the second optical path; a combiner coupling the first optical path and second optical path into a single output path; a controller applying a control signal to said light routing element, the control signal indicating whether a portion of the light received by the light routing element is directed into the first optical path or into the second optical path; a phase controlling element provided in the first optical path such that there is provided a pre-determined fixed phase difference between a light pulse routed through the first optical path and a light pulse routed through the second optical path.