Complete optical isolation created by indirect interband photonic transitions

Abstract

Achieving on-chip optical signal isolation is a fundamental difficulty in integrated photonics [1]. The need to overcome this difficulty, moreover, is becoming increasingly urgent, especially with the emergence of silicon nano-photonics [2- 4], which promise to create on-chip optical systems at an unprecedented scale of integration. In spite of many efforts, there have been no techniques that provide complete on-chip signal isolation using materials or processes that are fundamentally compatible with silicon CMOS process. Here we introduce an isolation mechanism based on indirect interband photonic transition. Photonic transition, as induced by refractive index modulation [5], has been recently observed experimentally in silicon nanophotonic structures [6]. Here we show that a linear, broad-band, and nonreciprocal isolation can be accomplished by spatial-temporal modulations that simultaneously impart frequency and wavevector shifts during the photonic transition process. We further show that non-reciprocal effect can be accomplished in dynamically-modulated micron-scale ring-resonator structures.