Long-term mutual phase locking of picosecond pulse pairs generated by a semiconductor nanowire laser

TL;DR

This paper demonstrates that GaAs-AlGaAs nanowire lasers can produce phase-locked picosecond pulse pairs with long-term phase stability, enabling potential applications in on-chip ultrafast spectroscopy.

Contribution

It introduces a method to generate long-term phase-locked pulse pairs from nanowire lasers, overcoming previous nanoscale phase-locking challenges.

Findings

Phase locking persists beyond 30 ps, much longer than pulse duration.

Good agreement between experimental results and optical Bloch equation simulations.

Potential for on-chip ultrafast spectroscopy applications.

Abstract

The ability to generate phase-stabilised trains of ultrafast laser pulses by mode-locking underpins photonics research in fields such as precision metrology and spectroscopy. However, the complexity of conventional mode-locked laser systems, combined with the need for a mechanism to induce active or passive phase locking between resonator modes, has hindered their realisation at the nanoscale. Here, we demonstrate that GaAs-AlGaAs nanowire lasers are capable of emitting pairs of phase-locked picosecond laser pulses when subject to non-resonant pulsed optical excitation with a repetition frequency up to ~200GHz. By probing the two-pulse interference that emerges within the homogeneously broadened laser emission, we show that the optical phase is preserved over timescales extending beyond ~30ps, much longer than the emitted laser pulse duration (~2ps). Simulations performed by solving the optical Bloch equations produce good quantitative agreement with experiments, revealing how the phase information is stored in the gain medium close to transparency. Our results open the way to applications such as on-chip, ultra-sensitive Ramsey comb spectroscopy.