  In this work, we theoretically find that coherent perfect absorption (CPA)
and laser modes can be realized in a two-dimensional cylindrical structure
composed of conjugate metamaterials (CMs). The required phase factors of CMs
for achieving CPA and laser modes are determined by the geometric size of the
CM cylinder, which is a unique feature compared with other non-Hermitian
optical systems. Based on this property, we also demonstrate that CPA and laser
modes can exist simultaneously in a CM cylinder with an extremely large size,
where the excitations of CPA and laser modes depend on the angular momentum of
coherent incident light. Therefore, compared with the well known parity time
symmetry, our work opens up a brand-new path to obtaining CPA and laser modes,
and is a significant advance in non-Hermitian optical systems.

Optics