Passive PT -symmetric couplers without complex optical potentials

© 2015 American Physical Society. In addition to the implementation of parity-time-(PT-) symmetric optical systems by carefully and actively controlling the gain and loss, we show that a 2×2 PT-symmetric Hamiltonian has a unitarily equivalent representation without complex optical potentials in the resulting optical coupler. Through the Naimark dilation in operator algebra, passive PT-symmetric couplers can thus be implemented with a refractive index of real values and asymmetric coupling coefficients. This opens up the possibility to implement general PT-symmetric systems with state-of-the-art asymmetric slab waveguides, dissimilar optical fibers, or cavities with chiral mirrors.