Theoretical framework for chip-scale wavefront shaping with transverse spatial mode modulation

Visible-wavelength applications such as quantum information systems, portable displays, and biological sensing and imaging devices require compact wavefront shaping capabilities. However, current chip-scale methods based on optical phased arrays require complex control of a large number of waveguides, leading to a large device footprint and limited field-of-view. Here, we propose an alternative framework for wavefront shaping using amplitude and phase control of transverse spatial modes within compact multimode waveguides. We show through analytical calculations and numerical simulations that changing the modal superposition of as few as 10 modes allows for dynamic control over the field both inside and outside of the waveguide. Grating-lobe-free beam steering over a 130° field-of-view is demonstrated with peak resolution below 5° and side lobe suppression levels up to -51 dB from a 5 µm aperture. Reconfigurable focusing of points in the waveguide and in the near field, coupling to free-space Hermite-Gaussian modes, and generation of non-diffracting Bessel and Airy beams are also demonstrated, showing the vast capabilities possible within near-term experimental reach.