Raman lasing and soliton mode-locking in lithium niobate microresonators

The recent advancement in lithium-niobite-on-insulator (LNOI) technology is opening up new opportunities in optoelectronics, as devices with better performance, lower power consumption and a smaller footprint can be realised due to the high optical confinement in the structures. The LNOI platform offers both large chi((2)) and chi((3)) nonlinearities along with the power of dispersion engineering, enabling brand new nonlinear photonic devices and applications for the next generation of integrated photonic circuits. However, Raman scattering and its interaction with other nonlinear processes have not been extensively studied in dispersion-engineered LNOI nanodevices. In this work, we characterise the Raman radiation spectra in a monolithic lithium niobate (LN) microresonator via selective excitation of Raman-active phonon modes. The dominant mode for the Raman oscillation is observed in the backward direction for a continuous-wave pump threshold power of 20 mW with a high differential quantum efficiency of 46%. We explore the effects of Raman scattering on Kerr optical frequency comb generation. We achieve mode-locked states in an X-cut LNOI chip through sufficient suppression of the Raman effect via cavity geometry control. Our analysis of the Raman effect provides guidance for the development of future chip-based photonic devices on the LNOI platform. Lithium niobate on insulator: the Raman effect Better understanding, and thus control, of lithium niobate interactions with light could guide the development of an optical device that measures time even more precisely than atomic clocks. Marko Loncar of Harvard University and colleagues studied how light scatters when laser light is pumped into an optical cavity made from lithium niobate, a synthetic crystal widely used in optical materials. Their findings suggested that changing the shape of the lithium niobate cavity could help them suppress 'Raman scattering', a type of energy transfer that happens when light interacts with the material's molecules. When laser light was shone through the specially tuned cavity, it exited in the form of light pulses of extremely short duration. The findings could guide the development of optical devices that can more precisely measure standard units such as distance and time.