An optical device includes an interferometer having a first optical coupler, a second optical coupler and at least three arms optically coupling the first optical coupler to the second optical coupler; and a phase-shifting arrangement associated with the arms, at least one among the first and second optical couplers including a first optical input port, two first optical output ports and a second optical output port. An optical power coupling is implemented such that optical power received at the first optical input port is coupled, a first fraction into each of the first optical output ports, and a second fraction into the second optical output port. The at least one among the first and second optical couplers further includes a second optical input port and a third optical input port, and the at least one among the first and second optical couplers implements an optical power coupling such that optical power received at either one of the first or second optical input ports is coupled, the first fraction into each of the first optical output ports, and the second fraction into the second optical output port, whereas optical power received at the third optical input port is coupled, a third fraction into each of the first optical output ports, and a fourth fraction into the second optical output port, wherein the first fraction is different from the third fraction.