On-chip amplification-free fCEO detection in parabolically width-modulated TFLN waveguides

On-chip carrier-envelope offset (fCEO) detection establishs a new benchmark for scalable, power-efficient, self-referenced frequency combs and quantum-enabled photonic systems. In this work, we demonstrate amplification-free fCEO detection in parabolically width-modulated z-cut thin-film lithium niobate (TFLN) waveguide. With 116 fs pulses at 1560 nm, the device generates more than two octaves broadband SCG spanning 600nm to beyond 2400 nm, enabling spectral overlap be-tween dispersive wave and second-harmonic generation near 780 nm for robust f\u20132f self-referencing. Most notably, we achieve the first fully amplification-free fCEO detection\u2014without optical or electronic amplifiers\u2014directly on-chip, obtaining 34 dB SNR at 100 kHz RBW and 57 dB at 100 Hz RBW, the highest reported to date under such conditions.