Saturable plasmonic metasurfaces for laser mode locking

Abstract

Metamaterials are artificial materials made of subwavelength elementary cells that give rise to unexpected wave properties that do not exist naturally. However, these properties are generally achieved due to 3D patterning, which is hardly feasible at short wavelengths in the visible and near-infrared regions targeted by most photonic applications. To overcome this limitation, metasurfaces, which are the 2D counterparts of metamaterials, have emerged as promising platforms that are compatible with planar nanotechnologies and thus mass production, which platforms the properties of a metamaterial into a 2D sheet. In the linear regime, wavefront manipulation for lensing, holography, and polarization control has been achieved recently. Interest in metasurfaces operating in the nonlinear regime has also increased due to the ability of metasurfaces to efficiently convert incident light into harmonic frequencies with unusual polarization properties. However, to date, the nonlinear absorption of metasurfaces has been mostly ignored. Here, we demonstrate that plasmonic metasurfaces behave as saturable absorbers with modulation performances superior to the modulation performance of other 2D materials and exhibit unusual polarimetric nonlinear transfer functions. We quantify the link between saturable absorption, the plasmonic resonances of the unit cell and their distribution in a 2D metasurface, and finally provide a practical implementation by integrating the metasurfaces into a fiber laser cavity operating in pulsed regimes driven by the metasurface properties. As such, this work provides new perspectives on ultrathin nonlinear saturable absorbers for applications where tunable nonlinear transfer functions are needed, such as in ultrafast lasers or neuromorphic circuits.

Strongly Coupled Systems for Nonlinear Optics

“…Wang et al investigated the SA properties of 2D plasmonic metasurfaces under the radiation of intensive laser by tailoring the input polarization and geometric parameters of metasurfaces. [239] When the nanorod arrays were embedded into the cavity, one could acquire a fairly stable modelocked lasing. This ultrathin saturable absorber can provide a versatile platform for supporting ultrafast laser.…”

Plasmonic Saturable Absorbers

“…Recently, plasmonic metasurfaces made of an array of GNRs for which plasmonic properties are well established are designed and fabricated, as shown in Figure a. [ 105 ] According to the measurements of NLO response, this plasmonic metasurface demonstrated saturable absorption in the NIR region and the NLO response is polarization dependent. The authors further demonstrated that the plasmonic metasurfaces could be used as SAs with modulation performances superior to that of other 2D materials, which can reach values as high as M d = 60%, as shown in Figure 7c.…”

Pseudo‐Waveform‐Selective Metasurfaces and their Limited Performance

“…[26,27] These capabilities can be further extended or improved by introducing nonlinearity into metamaterials and metasurfaces. [28][29][30][31] For example, nonlinear metasurface absorbers [32][33][34][35] permit the transmission of low-amplitude signals used for antenna communications while effectively absorbing strong electromagnetic noise that may affect sensitive electronics even at the same frequency, as opposed to linear metasurface absorbers, which accept both types of waves. Recently, circuit-based metasurfaces containing nonlinear Schottky diodes have been reported to discriminate particular electromagnetic waves at the same frequency depending on their waveforms, or more specifically, their pulse widths.…”