Figure 2: Unidirectional invisibility of a *PT*-symmetric Bragg scatterer.

(A) The wave entering from the left does not recognize the existence of the periodic structure and goes through the sample entirely unaffected. On the contrary, a wave entering the same grating from the right experiences enhanced reflection. (B) Exact numerical evaluation [from Equation (1)] of transmission *T* and reflection *R* coefficients for a Bragg grating for *n*_{0}=1, *n*_{1}=10^{−3}, *L*=12.5 π, and *β*=100. In case of a *PT* grating, the system is at the EP when *n*_{1}=*n*_{2}. In this case, *R*_{L} is diminished (up to *n*_{1,2}^{2}~10^{−6}; see inset) for a broad frequency band, whereas *R*_{R} is enhanced [12].