Wide-angle low-loss waveguide branching for integrated optics

A new wide-angle, low-loss, symmetrical Y-branch waveguide is proposed. The waveguide configuration utilizes ribs for lateral confinement in the planar guiding region underneath. This Y-branch structure can be fabricated easily without an additional process step. Together with a utilization of the multimode interference effect, a local decrease of the waveguide ridge in the wedge part of the Y-branch reduces the radiation loss. When proper@ designed, the proposed Y-branch has a radiation loss as low as 2.2 dB at a branch angle of 6° with the index difference (Δn/n) as small as 7.1 × 10^-4 at a wavelength of 870 nm in the TE fundamental mode as compared to 12.6 dB for a conventional Y-branch. The proposed method yields corresponding advantages for waveguide designs with a higher Δn/n ratio and can also be adapted in combination with S-branch designs.