Ultra-fast tuning of refractive index in Lithium Niobate slab by GHz acoustic wave

Abstract

Refractive index modulation in optical materials facilitates dynamic control on electromagnetic waves. Ultra fast tuning of both refractive index and its spatial distribution in Y−Z Lithium Niobate slab via strain employed through GHz acoustic perturbation has been simulated and studied. To create acoustic disturbance in taken 500 nm thick slab, the fundamental symmetric Lamb mode at 5 GHz acoustic frequency is excited. Displacement field patterns generated by longitudinal and transverse disturbances of perturbing fundamental symmetric Lamb mode are analyzed under reinstate limits of optical material to create elastic strain. Modification in optical index of Lithium Niobate due to strain generated by longitudinal and transverse acoustic disturbance is then examined. The sinusoidal modulation in refractive index with maximum change of 0.070 along nz and 0.036 along ny is observed. The modulated refractive index has a periodic distribution over space with period equals to wavelength of acoustic disturbance created by fundamental Lamb mode. This acoustically induced ultra-fast change in refractive index and in its spatial distribution depends on perturbing acoustic frequency and thickness of slab. Thus, the slab can optimize dynamically, to control electromagnetic wave for various optical applications. © 2018 Elsevier GmbH