Highly tunable flat-top thin-film lithium niobate electro-optic frequency comb generator with 148 comb lines

Electro-optic (EO) frequency combs offer distinct advantages, such as high flexibility in tuning the central wavelength and line spacing, insensitivity to input light power, and good spectral flatness, compared to other broadband microcombs and mode-locked lasers. EO combs are a perfect match for data communication requirements due to their lower power fluctuations per comb line and flexible frequency spacing. To date, flat EO combs demonstrate limited bandwidth and line numbers. Here, we present a Mach-Zehnder modulator cascade with three phase modulators with only a 3 V RF half-wave voltage at 25 GHz on a thin-film lithium niobate (TFLN) on silicon. The device is fabricated using a wafer-scale deep ultraviolet lithography process and is packaged with fiber pigtails and RF connectors for robust and stable testing. The TFLN-based packaged frequency comb generator produces 148 comb lines at a 25-GHz repetition rate with a power variation of 10 dB. The central wavelength is tuned to enable the frequency comb to cover the S, C, L, and U bands.