Free-space optical delay line using space-time wave packets

TL;DR

This paper demonstrates a novel free-space optical delay line using space-time wave packets with tunable group velocities, achieving high delay-bandwidth products without fundamental bandwidth limits.

Contribution

It introduces a new approach using space-time wave packets for controllable optical delays in free space, surpassing previous dispersion-based methods.

Findings

Achieved delay-bandwidth products of ~100 for ~1 ps pulses.

Demonstrated tunable group velocity in free space.

No fundamental limit on system bandwidth.

Abstract

An optical buffer having a large delay-bandwidth-product -- a critical component for future all-optical communications networks -- remains elusive. Central to its realization is a controllable inline optical delay line, previously accomplished via engineered dispersion in optical materials or photonic structures constrained by a low delay-bandwidth product. Here we show that space-time wave packets whose group velocity in free space is continuously tunable provide a versatile platform for constructing inline optical delay lines. By spatio-temporal spectral-phase-modulation, wave packets in the same or in different spectral windows that initially overlap in space and time subsequently separate by multiple pulse widths upon free propagation by virtue of their different group velocities. Delay-bandwidth products of ~100 for pulses of width ~1 ps are observed, with no fundamental limit on the system bandwidth.