Nonreciprocal optically induced transparency created in an asymmetric double microrings structure

Electromagnetically induced transparency (EIT) which forms an optical transparent transmission window for the opaque ones has widely use in optical operation, such as slow light and all-optical switching. Recently, optically induced transparency process based on nonlinear effects such as Stimulated Brillouin scattering has been studied deeply, and this type of OIT needs the high power of input pump light. Moreover, the study of optical nonreciprocal transmission employing the thermo-optic effect suggests that using asymmetric waveguide structure [3–5], it can cause different optical energy storing in the function unit of the structure. This effect can lead to the different intensity of nonlinear effect. In this paper, We realize nonreciprocal OIT effect through the wavelength conversion of stimulated four-wave mixing (SFWM) in an asymmetric double-ring structure which uses two silicon microrings with their radiuses respectively are 100 and 90 µm. The principle of our design is shown in the Fig. 1. The all-pass ring resonance conditions lead to opaque dips to the transmission spectrum, but SFWM effect in it can cause inner optical gain which transfers the opaque dips to transparent windows. Meanwhile, we employ the filter effect of the add-drop ring to ban the pump light of SFWM so that the transmission direction of the pump light can cause the different input power to the all-pass ring, which can open or close the inner gain of the SFWM. We show our nonreciprocal OIT result in Fig. 2, the 3 dB bandwidth of the OIT window is 13 pm, and the isolation radio of the referenced idler light between forward and backward transmission can be 20.03 dB in the input pump power is 875 µW with the wavelength of 1554.257 nm.