Dual-band control of bound states in the continuum with pairwise positioning of singularities in metasurfaces

Controlling the quality (Q) factor and far-field polarization response of a metasurface is critical for many applications in classical and quantum optics with new applications driving the creation of increasingly sophisticated devices with multi-dimensional control. In particular, one emerging need is the ability to create and control nearly degenerate pairs of high-Q modes while robustly shaping the frequency splitting, Q-factors, and polarization responses across two bands simultaneously. Here, we solve this challenge with a design paradigm for pairwise control of symmetry-guaranteed pairs of symmetry-protected bound states in the continuum and their corresponding polarization singularities. We experimentally demonstrate dual band control over mode splitting, Q-factors, and polarization responses in dielectric metasurfaces. Building upon this demonstration, we will conclude by expanding the design methodology to enable narrowband wavefront shaping without deeply sub-wavelength features.