Coherent backscattering in lithium niobate whispering-gallery-mode resonators

Splitting of high-Q whispering gallery modes into a doublet of counterpropagating modes was observed in a resonator fabricated from LiNbO(3). An energy-transfer rate of 10 MHz was calculated by measuring the frequency detuning of the doublet structure. The splitting rate is also used to calculate the maximum variation in the internal index of refraction over one wavelength, which is of the order of 10(-7). This shows that the mechanical process used to fabricate whispering-gallery-mode resonators from LiNbO(3) is sufficient to achieve material-limited quality factors.