An electro-optical memory cell having a non-volatile programmable refractive index and a method of making. The memory cell includes: a waveguiding structure having a transition metal oxide with oxygen vacancies; a plurality of electrodes for applying an electrical field; and an optical detector for detecting a state of the memory cell. The method includes: fabricating a waveguiding structure having a transition metal oxide with oxygen vacancies; positioning a plurality of electrodes for application of an electric field; arranging the transition metal oxide and the electrodes such that when an electric field is applied, the oxygen vacancies migrate in a direction that has a component which is radial relative to a center of the beam path; applying the electric field thereby programming the refractive index to set a state of the memory cell; and detecting the state of the memory cell using an optical detector.