We investigate the transport characteristics of a four-port gyrotropic photonic structure with mirror-time reversal symmetry. The structure consists of two coupled cavities with balanced amplification and attenuation. The cavities are placed on top of a gyrotropic substrate and are coupled to two bus waveguides. Using detail simulations in the microwave domain we demonstrate a strong non-reciprocal intra-guide port transport and an enhanced inter-guide port transmittance. The non-reciprocal features are dramatically amplified in the gain–loss parameter domain where an exceptional point degeneracy, for the associated isolated set-up, occurs. These results are explained theoretically in terms of an equivalent lumped circuit.
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