Femtosecond Pulse Generation via an Integrated Electro-Optic Time Lens

TL;DR

This paper demonstrates a chip-scale, integrated femtosecond pulse source using a time lens system on lithium niobate, achieving high efficiency, tunability, and stability for applications in ultrafast optics and quantum computing.

Contribution

It introduces a novel integrated electro-optic time lens system on lithium niobate for femtosecond pulse generation, surpassing previous integrated sources in efficiency and stability.

Findings

Femtosecond pulses of 520 fs duration achieved at 30 GHz repetition rate.

Optical spectra with 12.6 nm bandwidth and flat-top profile.

Pulse energies of 0.54 picojoules and individual comb-line powers above 0.1 mW.

Abstract

Integrated femtosecond pulse and frequency comb sources are critical components for a wide range of applications. The leading approaches for on-chip pulse generation rely on mode locking inside microresonator with either third-order nonlinearity or with semiconductor gain. These approaches, however, are limited in noise performance, wavelength tunability and repetition rates. Alternatively, sub-picosecond pulses can be synthesized without mode-locking, by modulating a continuous-wave (CW) single-frequency laser using a cascade of electro-optic (EO) modulators. This method is particularly attractive due to its simplicity, robustness, and frequency-agility but has been realized only on a tabletop using multiple discrete EO modulators and requiring optical amplifiers (to overcome large insertion losses), microwave amplifiers, and phase shifters. Here we demonstrate a chip-scale femtosecond pulse source implemented on an integrated lithium niobate (LN) photonic platform18, using cascaded low-loss electro-optic amplitude and phase modulators and chirped Bragg grating, forming a time-lens system. The device is driven by a CW distributed feedback (DFB) chip laser and controlled by a single CW microwave source without the need for any stabilization or locking. We measure femtosecond pulse trains (520 fs duration) with a 30-GHz repetition rate, flat-top optical spectra with a 10-dB optical bandwidth of 12.6 nm, individual comb-line powers above 0.1 milliwatt, and pulse energies of 0.54 picojoule. Our results represent a tunable, robust and low-cost integrated pulsed light source with CW-to-pulse conversion efficiencies an order of magnitude higher than achieved with previous integrated sources. Our pulse generator can find applications from ultrafast optical measurement to networks of distributed quantum computers.