Rare earth-doped photonic crystals via sol–gel

Erbium/ytterbium-doped photonic bandgap materials and structures have been prepared by sol–gel processing, in the form of 1-D structures of the single (Fabry–Perot) and coupled (double) microcavity types, consisting of multilayer stacks of silica and titania. Such multilayers were deposited by spin-coating on silica glass substrates and their reflection spectra were measured in the near infrared range. It was found that, by varying the detection angle, it is possible to broaden the Er³⁺ emission at 1.5 μm, irrespective of the excitation wavelength (514.5 or 980 nm), which is important for applications where broadband emission is necessary, for example for all-optical amplification in dense wavelength division multiplexing (WDM) systems. A remarkable full width at half maximum (FWHM) of 52 nm was achieved for the Er³⁺ emission peak at 1.5 μm, when this rare-earth (RE) dopant was incorporated in a pure silica glass cavity layer. Other described phenomena include Er³⁺ photoluminescence enhancement from microcavities, compared with doped Bragg mirrors and films and enhanced Yb³⁺→Er³⁺ energy transfer in co-doped photonic crystal structures.