Optical polarizability of erbium-oxygen complexes in sol-gel-based silica films

Abstract

For erbium (Er)-doped amorphous oxides, such as those that are used in compact lightwave devices interfaced with silicon, values of the refractive indices are commonly obtained empirically. This work, combining experimental and theoretical studies, examines silica as the exemplary host and the influence of Er doping on the refractive index. Analysis of data is presented for the spectral refractive index in the ultraviolet to near infrared wavelength range of heavily Er-doped silica thin films prepared by spin coating a sol-gel precursor on silicon and subsequent vacuum annealing. Effective medium Lorentz–Lorenz data analysis determines that the dopant component has a refractive index of 1.76 ± 0.24 with wavelength dispersion constrained to within 2%. Considering the dopant as a localized ErO6 impurity complex, a corresponding theoretical refractive index of 1.662 is derived by calculating the optical polarizability and volume of the impurity. Data presented for room-temperature (∼293 K) photoluminescence in the vicinity of 1.54 μm are shown to be consistent with random variability in impurity sites. Inherent advantages of studying colloid-based materials are discussed. To the best of the authors’ knowledge, such a detailed study of the refractive index associated with Er impurities in silica is being reported for the first time in the literature.

Synthesis and Characterization of Erbium-Doped Silica Films Obtained by an Acid–Base-Catalyzed Sol–Gel Process

“…The samples could be divided in two groups depending on the doping concentration. It was expected that the higher Er concentration increased the films optical parameters appreciably [20], and this is clearly shown for erbium doping concentrations of 3% and 6%. The Sellmeier model utilized did not show the same results for lower doping concentrations (i.e., 0.2, 0.5 and 0.75%).…”

“…These studies focused mainly on relating the emission to radiative recombination across the Si-band [15][16][17][18] and on understanding the activation mode of Er as in reference [19]. In a subsequent study, the same group concentrated on understanding the pertaining effect of the dopant on the optical parameters utilizing the effective medium theorem [20]. All of these studies were limited to one doping concentration of erbium and to using a single catalyst for the sol-gel preparation.…”

Simultaneous ultraviolet, visible, and near-infrared continuous-wave lasing in a rare-earth-doped microcavity

“…Here, the refractive index of doped silica is set to the same as that of pure silica for the calculation, which should bring a permissible deviation. 48 One of the characteristics of the lasing onsets is distinct spectral linewidth narrowing around the lasing threshold. However, in our scheme, the linewidths of the lasers and the Purcell enhanced spontaneous emission peaks are too narrow to be resolved by the spectrometer.…”