Spiral waveguide Bragg grating modulator on thin-film Z-cut lithium niobate

Abstract

Next-generation photonic integrated circuits require compact electro-optic modulators (EOMs) that achieve high performance and efficient use of the on-chip area simultaneously. We demonstrate a compact EOM based on a spiral-shaped waveguide Bragg grating on thin-film lithium niobate. The modulator utilizes the grating’s optical filter characteristics along with electro-optic tuning of the central Bragg wavelength to achieve simple and efficient intensity modulation. The spiral Bragg gratings were realized on Z-cut lithium niobate and modulated using top and bottom electrodes. The integrated design wrapped a 2.2 mm long grating into a 120×120µm2 area. The modulator bandgap, with an extinction ratio of over 35 dB at 1550 nm, could be efficiently tuned with a sensitivity of 8.36 pm/V and a 3 dB operating bandwidth of 25 GHz.