In-line Dispersion Control of Femtosecond Laser Pulses by Multilayer Huygens' Metasurfaces

Abstract

Dispersion is a key limiting factor in ultrafast systems as it modifies the temporal structure of ultrashort optical pulses. Conventional dispersion compensation techniques, though widely used, rely on a combination of several bulky optical components and complex, long propagation paths, posing challenges for integration into compact photonic platforms. All-dielectric resonant metasurfaces operating in the Huygens' regime of spectrally overlapping electric and magnetic dipolar resonances offer a promising route to low-loss dispersion control at the sub-wavelength scale; however, the achievable dispersion from a single layer remains fundamentally limited by its phase gradient and spectral bandwidth. Here, we experimentally demonstrate in-line dispersion control of femtosecond laser pulses using a multilayer architecture of dielectric Huygens' metasurfaces, without requiring spatial separation of their spectral components, as typically employed in Fourier-plane dispersion compensation schemes. The phase dispersion accumulates across stacked layers approaching a total of 8pi, corresponding to a maximum group delay dispersion of around 3969 fs2. This enables efficient compensation of the input chirp and results in a significant compression of femtosecond laser pulses in the telecom wavelength range. Importantly, the metasurface stack functions as a single compact transmissive element, which is simply inserted into the beam path. Overall, our results establish a compact, scalable platform for integrated pulse compression and ultrafast dispersion engineering.