Optical switch based on tunable perfect photon absorption

We investigate the manipulation of optical field within quantum electrodynamics (QED) scheme. In our proposal, the cold three-level atoms interact with a two-sided cavity driven by two coherent beams with a relative phase. Coherent perfect absorption (CPA) appears when the beams are in phase. However, the perfect outputs occur when the beams are out of phase. On the basis of the phase modulation, an optical switch can be operated at a high efficiency. With a coherent control laser, the excited and metastable levels of the atoms are coupled. Electromagnetically induced transparency (EIT) is produced at two-photon resonance, which leads to four-band CPA. By virtue of the control laser, the switching efficiency can be maximized in a weaker probe field, which provides advantages over two-level atoms on weak-signal switching.