Second harmonic generation from zero-diffraction-order AlGaAs metasurfaces

Dielectric metasurfaces lend themselves to intracavity mode shaping in external-cavity semiconductor lasers thanks to their ability of creating distributions of high-contrast membranes on the same epitaxial growth [1]. In this... [ view full abstract ]

Dielectric metasurfaces lend themselves to intracavity mode shaping in external-cavity semiconductor lasers thanks to their ability of creating distributions of high-contrast membranes on the same epitaxial growth [1]. In this context, an intriguing option is represented by using the metasurface to generate harmonic frequencies inside the laser cavity. While χ⁽³⁾effects were reported in silicon-on-insulator nanoantennas [2], the AlGaAs-on-insulator platform has recently enabled the demonstration of second harmonic generation (SHG) in χ⁽²⁾nanoantennas [3]. Their excitation at normal incidence results in efficient SHG driven by Mie-type magnetic dipole resonance at the pump frequency in the near infrared and a polarisation behaviour dominated by a high-order multipole resonance at the second harmonic (SH) [4]. 

Here we focus on SHG from MOCVD-grown monolithic metasurfaces of Al_0.18Ga_0.82As-on-AlOx nanoantennas, where AlOx is obtained from selective wet oxidation of µm-thick aluminium-rich AlGaAs layer. As a prototype example, we report the case of a set of coupled nanocylinders with height h = 400 nm, radius r = 122 nm and 300 to 900 nm periodicity, which we excite with a pump beam at λ = 1064 nm linearly polarized along the [100] AlGaAs axis. The related SHG efficiency is low for periodicities smaller than the array diffraction limit, where SH modes stay confined in the metasurface plane. Conversely, for greater periodicities the SH modes are coupled into the zero-diffraction order. In this case, the SH fields generated from neighbouring nanoantennas constructively interfere, with a strong enhancement with respect to the case of the SHG from an isolated nanoantenna. This result paves the way to dielectric intracavity metasurfaces for SHG with an arbitrary wavefront.

REFERENCES

[1] M. S. Seghilani et al., Opt. Expr. 22, 5962 (2014).

[2] M. R. Shcherbakov et al., Nano Lett. 14, 6488 (2014).

[3]V. F. Gili et al., Opt. Expr. 24, 15965 (2016).

[4] L. Ghirardini et al., Opt. Lett. 42, 559 (2017).