  The simultaneous existence of coherent perfect absorption (CPA) and lasing is
one of the most intriguing features of non-Hermitian photonics. However, the
link between CPA lasing and PT symmetry breaking at the exceptional point (EP)
needs clarification. In this paper, we study the manifestations of the
CPA-laser effect in a PT-symmetric multilayer loss-gain structure using both
the transfer-matrix method and numerical simulations of the Maxwell-Bloch
equations. We show that the maximal contrast between absorption and
amplification at different phase relations between the input waves is reached
well below the EP and therefore is not connected to true lasing. In this
regime, there is a good qualitative agreement between both computational
approaches. Above the EP, the system demonstrates lasing regardless of the
parameters of the input waves. Thus, the maximal contrast between the
absorption and amplification rather corresponds to the CPA amplifier than to
the CPA laser.
