The refractive index of the at least one photonic structure having two separate photonic bands is modulated, so that light supplied to the at least one photonic structure and initially in one of the two photonic bands of the traveling along a forward direction in the at least one photonic structure is converted to light in a second one of the photonic bands, and light in the one photonic band traveling along a backward direction opposite to the forward direction in the at least one photonic structure is not converted and remains in the one photonic band, achieving non-reciprocity.