Spacing and Wavelength Tunable Frequency Comb

Optical frequency combs (OFCs) are becoming increasingly prevalent in applications such as optical communications, radio signal processing and dual-comb spectroscopy. Many of these applications require a broad and flat spectrum with flexibility in tuning the center wavelength and the tone spacing with a maintained spectral profile. However, most OFC generators are either not tunable or cannot maintain their spectral profiles while tuning. In this paper, we demonstrate tone spacing tunability over 25-32 GHz and wavelength tunability from 1548 to 1568 nm using a cavity-less OFC based on electro-optic comb and parametric expansion. Our comb features high power (>2 W), wideband (>90 nm), high optical signal-to-noise ratio (OSNR, >25 dB), and, importantly, a maintained spectral profile. We show that a maintained spectral profile can be achieved by primarily adjusting the power of the RF driving signal and the gain of optical amplifiers. We also quantitatively study the changes in the spectral profile.