Probing material absorption and optical nonlinearity of integrated photonic materials

Abstract

Abstract Optical microresonators with high quality ( Q ) factors are essential to a wide range of integrated photonic devices. Steady efforts have been directed towards increasing microresonator Q factors across a variety of platforms. With success in reducing microfabrication process-related optical loss as a limitation of Q , the ultimate attainable Q , as determined solely by the constituent microresonator material absorption, has come into focus. Here, we report measurements of the material-limited Q factors in several photonic material platforms. High- Q microresonators are fabricated from thin films of SiO 2 , Si 3 N 4 , Al 0.2 Ga 0.8 As, and Ta 2 O 5 . By using cavity-enhanced photothermal spectroscopy, the material-limited Q is determined. The method simultaneously measures the Kerr nonlinearity in each material and reveals how material nonlinearity and ultimate Q vary in a complementary fashion across photonic materials. Besides guiding microresonator design and material development in four material platforms, the results help establish performance limits in future photonic integrated systems.