Magnetically switchable metalens for polarization-dependent nonreciprocal forward-propagating wavefront manipulations

We propose a nonreciprocal hybrid-phase magnetically switchable metalens (MSM), in which the magnetic bias applied to the ferrite slab selects the handedness of the forward-propagating circularly polarized wave, while a nonreciprocal hybrid phase composed of both the geometric and propagation phases is introduced to tailor the phase response. Unlike Pancharatnam-Berry (PB) phase-only designs, whose phase response is strictly locked to the incident spin state, an additional propagation phase is introduced by adjusting the height of the top elliptical dielectric post, providing an extra degree of freedom for wavefront manipulation. This nonreciprocal hybrid-phase strategy overcomes the spin-locking constraint and enables cooperative focusing of both left-handed (LHCP) and right-handed (RHCP) circularly polarized waves under forward transmission. Moreover, the proposed MSM exhibits a pronounced spin-dependent nonreciprocal response, achieving an isolation ratio of up to 9.17 dB under ±10 mT magnetic bias, thereby enabling selective forward transmission for the designated circular polarization while suppressing the backward-propagating opposite-spin energy from the focal region. Notably, the ferrite material used in this work is commercially available, eliminating the need for any special custom fabrication. The proposed MSM provides a reconfigurable platform for polarization-dependent nonreciprocal wave manipulation, offering strong potential for adaptive microwave imaging and integrated nonreciprocal components.