Design of lateral-modes filter based on high-index contrast waveguide

The design of a compact mode filter (with a total length of 90 μm) using laterally tapered ridge waveguide is proposed. The mode filter comprises a down-taper waveguide and a single-mode waveguide for higher order modes discrimination, followed by a mode-size expander that restores the original fundamental mode size. The insertion loss for the fundamental mode could be as small as 0.02 dB. The operation is found to be insensitive to many of the device's dimensions. The mode filter can be integrated with any ridge waveguide device, irrespective of the waveguides cross-section, material system and operating wavelength.