In a first broad aspect the invention provides an optical hybrid. The optical hybrid has an input for receiving an incoming optical signal containing data and a local oscillator optical signal and an output for releasing first and second output optical signals having a known phase relationship between them. In a specific and non-limiting example of implementation the phase relationship is 90 degrees. In this specific case the output signals are described as an in-phase and quadrature signals. The optical hybrid has an optical processing entity for deriving the first and second output optical signals from the incoming optical signal and the local oscillator signal. The optical processing entity including a loss element and a phase delay element for subjecting at least a component of an optical signal that exists in the processing entity to a known degree of attenuation and phase delay. The phase relationship between the output optical signals is dependant at least in part on at least one of the degree of attenuation and phase delay.