A Pulse-Duration Compensation Scheme for GHz Electro-Optic Frequency Comb

Electro-optic frequency combs, generated by cascaded intensity and phase modulators, are known for their frequency agility. However, frequency detuning induced pulse distortion significantly hinders their applicability in asynchronous optical sampling. In this letter, we propose a scheme where a motor-driven optical delay line between the phase and intensity modulators serves as an effective pulse-duration compensation mechanism. A 10 GHz flat-topped optical frequency comb (OFC) at a central wavelength of 1552 nm is first optimized to output a 7.2 ps pulse. It is seen that the temporal pulses experience dramatic distortion and elongation (up to 130 ps) when frequency offset is present. Interestingly, the output pulse duration is periodically modulated by the frequency offset, and the associated period is inversely proportional to a system delay time (<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\tau $ </tex-math></inline-formula>) that is fundamentally linked to the phase retardation between the intensity and phase modulators. In this scheme, we derive an algorithm that can drive the optical delay line in a deterministic way to counter the effect of frequency detuning, and successfully demonstrate an OFC tunable across 8- 12 GHz, with a constant pulse duration (<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\sim ~7$ </tex-math></inline-formula> ps). Our approach provides a practical solution for stabilizing pulse duration for repetition rate-tunable OFCs and can bring new capabilities in optical sensing and sampling.