Figure 3.

Purcell enhancement of Er³⁺: TiO₂ ensembles on Si photonic crystal cavities. (a) Resonant laser reflection spectrum of a photonic crystal cavity (T = 3.1 K) tuned near the rutile transition, showing a cavity Q near 53 000. The cavity has a corresponding line width (full-width half-maximum, FWHM) of 3.71(0.17) GHz (top axis). (b) Comparison of the ensemble lifetime of Er³⁺ ions coupled in a bare waveguide device (blue squares) versus the cavity-coupled device (red circles) shown in panel a. The corresponding fits give τ = 23(1) μs (black dashed line) and τ = 4660(20) μs (gray dashed-dot line), which is a 200-fold reduction in the decay time. (c) Plot of the increase in the ensemble decay rate as a function of the cavity-laser detuning (Δ) when the laser is fixed at 1520.56 nm. This is the same cavity as in panel a, which was measured at the start of the detuning experiment. The decay rate enhancement line shape is also fit to a Lorentzian with a FWHM line width of 5.06(0.17) GHz.