T-Branch Waveguide Mirror for Multimode Optical Splitter with Arbitrary Power Ratios

Mode-division multiplexing is an enabling technique for large-capacity on-chip optical interconnects. Multimode power splitter becomes the subject of interests which is highly desirable. However, challenges still exist for multimode splitter with arbitrary power ratio. Inspired by geometric optics, we demonstrate a series of power splitters based on T-branch waveguide mirrors which consist of subwavelength nanoholes. Arbitrary split ratio can be achieved by modifying the transmittance and reflectance of the waveguide mirrors. The devices can support up to 9 modes from TE0-TE8. For a proof-of-concept demonstration, we fabricate dual-mode splitters with power ratios of 40:60, 30:70 and 20:80. For both TE0 and TE1 modes, the measured excess losses are lower than 0.92 dB, and the crosstalk are all below-14.42 dB within the wavelength range from 1540 to 1580 nm.