An apparatus comprising a planar optical structure that includes an input coupler, first and second planar waveguides and an output coupler, all on a planar substrate. The input coupler is configured to divide an incoming light into two input light beams. Each of the first and second waveguides is configured to receive one of the two input light beams. The first waveguide has a first core with a width that is greater than a width of a second core of the second waveguide. At least one of the first or second planar waveguides is birefringent. The output coupler is configured to receive the light beams after passage through the first and second waveguides. A first output light beam from the output coupler is substantially TE polarized light and a second output light beam from the output coupler is substantially TM polarized light.