Noise-suppressed femtosecond electro-optic comb synthesis via soliton self-frequency shift

Optical frequency combs have revolutionized numerous fields of modern science, particularly precision metrology and molecular spectroscopy. Electro-optic (EO) modulation of light provides a novel approach to optical comb generation, circumventing the need for mode-locking and active phase stabilization. However, EO combs are inherently limited by electronic and optical noise, which restricts their coherent spectral extension into the critical mid-infrared (mid-IR) and terahertz (THz) regimes. Here, we introduce a passive noise suppression technique for EO comb generation based on the soliton self-frequency shift (SSFS) in optical fibers. Our method spectrally shifts the EO comb to a low-noise region, effectively isolating it from spontaneous emission noise. As a result, we achieve a frequency-shifted, 30-fs EO comb with a 20-dB reduction in phase noise and a 15-dB reduction in intensity noise. This comb is then extended into the 6–13 μm mid-IR range via difference-frequency generation in a GaSe crystal and into the 0.1–5 THz range through optical-to-THz conversion in a photoconductive antenna. The demonstrated EO comb and its mid-IR and THz extensions hold significant potential for advancing molecular spectroscopy and gas sensing applications.