Two-octave-spanning dichroic integrated photonic filters on thin-film lithium niobate

Integrated optical filters are essential devices for spectral shaping and suppression of optical waves in photonic systems. We present an ultrabroadband dichroic filter with a potential operation range spanning more than two octaves (500–2100 nm). The integrated filters are based on directional coupling between adiabatic slot waveguides and standard ridge waveguides on thin-film lithium niobate. We experimentally demonstrate geometrically tuned cutoff wavelengths across the telecommunication C-band, with a dichroic contrast up to 25 dB and a filtering roll-off of about 0.5 dB/nm. We also validate the filter operation in the O-band and the visible (red) range. The filters provide power splitting and wavelength multiplexing solutions for advanced nonlinear and quantum photonic integrated systems with wide separation between pump and signal wavelengths.