An optical device comprises first and second waveguide phase arms (20, 30) and a tunable element. Each of first and second waveguide phase arms (20, 30) has optically coupled parallel sections of waveguides. The parallel sections of each one of the first and second waveguide phase arms (20, 30) being dissimilar to lessen crosstalk. The tunable element applies a phase shift to an optical signal traversing the first waveguide phase arm.
