Complex modulation of light in polarization and space using laser-written multiplane light conversion

We present a compact and efficient realization of Multi-Plane Light Conversion (MPLC) for full vectorial light modulation, enabling control over polarization, phase, and amplitude. Conventional MPLC implementations based on phase-only modulation suffer from losses and limited polarization control, while metasurface-based solutions require complex nanofabrication processes. Our approach employs laser-written birefringent waveplates in silica slides, each with fixed retardance and a spatially varying optical axis orientation. The structures are fabricated using direct laser writing of nanogratings in silica, achieving ~90% transmission and ~1–2 µm spatial resolution. We demonstrate high-dimensional quantum gates and a polarization-controlled single-photon CNOT gate using spatial and polarization degrees of freedom. This cleanroom-free platform shows strong potential for high-dimensional quantum processing, optical communication, and beam shaping, with future prospects for extending modulation into the frequency domain.