Ultra-short embedded long-period waveguide grating for broadband mode conversion

摘要

We propose a novel embedded long-period waveguide grating (LPWG) for the implementation of a broadband mode conversion. The proposed LPWG is formed in the inner of waveguide where the two coupled modes have the largest field overlap and, hence, features an ultra-short length and a wide bandwidth. Besides, the bandwidth of the proposed LPWG is further increased by manipulating its phase-matching curve. Our proof-of-principle device, fabricated with polymer for the conversion between the E-11 and E-21 modes, contains only two periods and achieves a mode conversion efficiency larger than 98.2% (99.2%) for the x (y) polarization over the C + L band. The proposed LPWG could find applications as an ultra-compact and broadband mode converter in mode-division-multiplexing system.