Ultra-broadband mode filters based on graphene-embedded waveguides.

We propose spatial-mode filters based on embedding graphene films in optical waveguides. To demonstrate the effectiveness and the flexibility of this approach, we design and fabricate several mode filters where graphene films of different widths and lengths are placed in different locations of polymer waveguides. Our mode filters are easy to make and can provide high mode extinction ratios that are insensitive to the operation wavelength. Such mode filters could find applications in broadband mode-division-multiplexing transmission systems and other areas that involve mode selection or stripping.