Metasurface-stabilized optical microcavities

Abstract

Cavities concentrate light and enhance its interaction with matter. Confining to microscopic volumes is necessary for many applications but space constraints in such cavities limit the design freedom. Here we demonstrate stable optical microcavities by counteracting the phase evolution of the cavity modes using an amorphous Silicon metasurface as cavity end mirror. Careful design allows us to limit the metasurface scattering losses at telecom wavelengths to less than 2% and using a distributed Bragg reflector as metasurface substrate ensures high reflectivity. Our demonstration experimentally achieves telecom-wavelength microcavities with quality factors of up to 4600, spectral resonance linewidths below 0.4 nm, and mode volumes below $$2.7{\lambda }^{3}$$ 2.7 λ 3 . The method introduces freedom to stabilize modes with arbitrary transverse intensity profiles and to design cavity-enhanced hologram modes. Our approach introduces the nanoscopic light control capabilities of dielectric metasurfaces to cavity electrodynamics and is industrially scalable using semiconductor manufacturing processes.

Metasurface-Controlled Holographic Microcavities

“…This shift is caused by light penetration into the metasurface and the partial reflector, which changes the imaging condition. The effect has been previously observed for spherical microcavities. , Without a second partial reflector, i.e., without a cavity, the metasurface creates only a poor representation of the skier, because the spatial intensity profile is uncontrolled.…”

“…Assuming a flat phase in the imaging plane, the complex electric field amplitude of the mode is proportional to the square root of its intensity E IP ( x ′ , y ′ ) ∼ I IP ( x ′ , y ′ ) . We can then calculate the evolution of this mode along the propagation direction z using the Rayleigh–Sommerfeld diffraction integral: E ( x , y , z , k ) = prefix− i k 2 π ∫ ∫ normald x ′ .25em normald y ′ .25em E IP ( x ′ , y ′ ) normale ± i k r r .25em cos ( χ ) r = false( x − x ′ false) 2 + false( y − y ′ false) 2 + z 2 …”

“…Due to their ability for sub-wavelength phase control, metasurfaces have been predicted to allow intracavity microscale holography, i.e., stable cavity modes with a complicated spatial profile. So far, the idea has been theoretically explored only for infrared light.…”

“…Recently, two works have shown such transverse phase control using metasurfaces and have experimentally demonstrated stable Gaussian modes in microcavities. 23,24 For This article is licensed under CC-BY 4 Gaussian-shaped modes, the metasurface approaches have not yet exceeded the capabilities of state-of-the-art microscale spherical mirrors. 9 However, metasurfaces can realize considerably steeper phase gradients than microscale mirrors which are limited by cracks that form during their fabrication if their topography changes quickly.…”

“…9 However, metasurfaces can realize considerably steeper phase gradients than microscale mirrors which are limited by cracks that form during their fabrication if their topography changes quickly. 9 Due to their ability for sub-wavelength phase control, metasurfaces have been predicted to allow intracavity microscale holography, 24 i.e., stable cavity modes with a complicated spatial profile. So far, the idea has been theoretically explored only for infrared light.…”