title: Ultra-low-loss CMOS-compatible waveguide crossing arrays based on multimode Bloch waves and imaginary coupling.
abstract: We experimentally demonstrate broadband waveguide crossing arrays showing ultralow loss of 0.0 4dB/crossing (0.9%) on average and converging to 0.033 dB/crossing (0.075%) matching theory and cross-talk suppression over 35 dB in a CMOS-compatible geometry. The principle of operation is the tailored excitation of a low-loss spatial Bloch wave formed by matching the periodicity of the crossing array to the difference in propagation constants of the first- and third-order TE-like modes of a multimode silicon waveguide. Radiative scattering at the crossing points acts like a periodic imaginary-permittivity perturbation that couples two supermodes, which results in imaginary (radiative) propagation-constant splitting and gives rise to a low-loss, unidirectional breathing Bloch wave. This type of crossing array provides a robust implementation of a key component enabling dense photonic integration.
authors.forename: Yangyang
authors.initials: Y
authors.lastname: Liu
authors.forename: Jeffrey M
authors.initials: JM
authors.lastname: Shainline
authors.forename: Xiaoge
authors.initials: X
authors.lastname: Zeng
authors.forename: Miloš A
authors.initials: MA
authors.lastname: Popović