Photorefractive coupling in ring resonators

The photorefractive coupling of the oppositely directed traveling waves in ring resonators is analyzed. The nonlocal response of the crystal gives rise to an asymmetrical coupling of the waves which results in unequal transmissivities and unequal phase shifts when the two waves traverse through the photorefractive material. The inequality in transmissivities and phase shifts removes the degeneracy and leads to a splitting in both oscillation frequency and intensity.