  Magneto-optical effects (MOE), interfacing the fundamental interplay between
magnetism and light, have served as a powerful probe for magnetic order, band
topology, and valley index. Here, based on multiferroic and topological bilayer
antiferromagnets (AFMs), we propose a layer control of MOE (L-MOE), which is
created and annihilated by layer-stacking or an electric field effect. The key
character of L-MOE is the sign-reversible response controlled by ferroelectric
polarization, the Neel vector, or the electric field direction. Moreover, the
sign-reversible L-MOE can be quantized in topologically insulating AFMs. We
reveal that the switchable L-MOE originates from the combined contributions of
spin-conserving and spin-flip interband transitions in spin-valley splitting
AFMs, a phenomenon not observed in conventional AFMs. Our findings bridge the
ancient MOE to the emergent realms of layertronics, valleytronics, and
multiferroics and may hold immense potential in these fields.
