In a new study published in Nanophotonics, researchers developed a design for a programmable metasurface that uses projected light to switch diffraction channels and polarization states. In simulations, its best single-channel modes achieved diffraction efficiencies of about 45%, with polarization fidelity above 0.99.

The study was led by researchers from the Changchun Institute of Optics, Fine Mechanics and Physics of the Chinese Academy of Sciences, in collaboration with researchers from the Hunan Academy of Agricultural Sciences, Qualcomm Inc., and Soleilware Photonics LLC.

Programmable optical routing is necessary when optical signals must be redirected among several ports while preserving their polarization. While conventional metasurfaces offer compact control of light, many remain fixed after fabrication. Tunable designs often require dense electrical connections across the device.

The new approach shifts the control function to an external illumination pattern. This allows one planar surface to access several predefined optical states without dense nanoscale wiring.

The metasurface consists of a nested array of mode regions, each containing a nanostructured pattern optimized through Fourier coefficient design. Each region is assigned a target diffraction direction and polarization state. A digital light processing module projects a selected pattern onto the surface, activating the corresponding regions. Changing the projected pattern switches the selected routing state.

The design separates two optical tasks. The local pattern determines the primary beam direction and polarization, while the larger nested array governs the spacing and distribution of neighboring diffraction orders. This arrangement clusters useful sidebands around the intended output angle so that more redirected light can enter the angular window of a receiver.

Unlike other methods that adjust each nanoscale element individually, this platform adjusts an entire functional region simultaneously. This reduces the spatial resolution required from the projector while retaining optimized combinations of output angle and polarization. The trade-off is that each routing state must be designed in advance rather than generated freely after fabrication.

The researchers assessed four routing modes covering single-, dual-, and four-channel operation. Far-field calculations placed the outputs at their intended angular positions and reproduced the assigned polarization states, with controlled leakage into unintended channels. Link-level simulations also kept the error rate below the hard-decision forward error correction threshold at 25 gigabits per second across the tested telecommunications band. 

Additional calculations using different nested-array arrangements indicated that the receiver could continue to collect a stable share of the redirected power as the number of spatial regions increased.

These findings remain a numerical demonstration. Its link model describes the metasurface response but does not include losses from the digital micromirror device, projection optics, finite addressing contrast, aperture clipping, or alignment errors. Experimental work is therefore needed to establish end-to-end efficiency and switching performance. 

Scaling the design to support more simultaneous modes will also require careful management of crosstalk and the optical power allocated to each channel.

Within these limits, the study provides a design framework for controlling propagation direction and polarization using a single planar optical element. This approach could enable compact optical interconnects, programmable Fourier optical processing, and nanophotonic systems that use projected light to select among predefined functions.