Nature Commun. 5, 5337 (2014)

The electrical control of light polarization in hybrid electronic–photonic systems is desirable because it could allow a dynamic rotation of the polarization. However, achieving this control in an on-chip, planar structure is challenging. Ronald Reano and colleagues at the Ohio State University have now shown that the rotation of light polarization can be dynamically tuned by electrical means in a silicon-on-insulator photonic chip.

The rotation is achieved by leveraging on the Berry phase, which is a phase of geometrical origin that can be acquired by light that is travelling along a closed path in momentum space. To attain a non-zero Berry phase in momentum space, the light is made to travel into a three-dimensional waveguide that has out-of-plane sections. The angle of deflection in real space of the out-of-plane portions determines the Berry phase and, in turn, the angle of rotation of light polarization. The researchers fabricate the out-of-plane waveguide in a silicon–silicon dioxide chip; the dynamic tuning of polarization rotation is enabled by electrically controlling a microheater that regulates the coupling of light to the waveguide. An almost-full rotation of polarization, from transverse electric to transverse magnetic mode, is demonstrated as a function of the electrical power through the heater.