90° Optical Hybrid with Lower Loss and Higher Balance Based on a Tapered 2×4 MMI Coupler and a 2×2 MMI Coupler

We propose an optimized 90° optical hybrid based on a tapered 2×4 MMI coupler and a 2×2 MMI coupler. Simulations indicate that the hybrid yields the excess loss and imbalance of 0.2dB and 0.06dB, respectively.