Observation of Photon Echoes From Evanescently Coupled Rare-Earth Ions in a Planar Waveguide

We report the measurement of the inhomogeneous linewidth, homogeneous linewidth, and spin-state lifetime of Pr3+ ions in a novel waveguide architecture. The TeO2 slab waveguide deposited on a bulk Pr3+: Y2SiO5 crystal allows the H-3(4) <-> D-1(2) transition of Pr3+ ions to be probed by the optical evanescent field that extends into the substrate. The 2-GHz inhomogeneous linewidth, the optical coherence time of 70 +/- 5 mu s, and the spin-state lifetime of 9.8 +/- 0.3 s indicate that the properties of ions interacting with the waveguide mode are consistent with those of bulk ions. This result establishes the foundation for large, integrated, and high performance rare-earth-ion quantum systems based on a waveguide platform.