Complete optical isolation created by indirect interband photonic transitions

Achieving on-chip optical signal isolation is a fundamental difficulty in integrated photonics(1). The need to overcome this difficulty is becoming increasingly urgent, especially with the emergence of silicon nano-photonics(2-4), which promises to create on-chip optical systems at an unprecedented scale of integration. Until now, there have been no techniques that provide complete on-chip signal isolation using materials or processes that are fundamentally compatible with silicon CMOS processes. Based on the effects of photonic transitions(5,6), we show here that a linear, broadband and nonreciprocal isolation can be accomplished by spatial-temporal refractive index modulations that simultaneously impart frequency and wavevector shifts during the photonic transition process. We further show that a non-reciprocal effect can be accomplished in dynamically modulated micrometre-scale ring-resonator structures. This work demonstrates that on-chip isolation can be accomplished with dynamic photonic structures in standard material systems that are widely used for integrated optoelectronic applications.