Ultra-broadband Raman gain media for photonics device applications

摘要

A study was initiated to understand requirements to widen and flatten the gain coefficient spectra of tellurite-based glasses for their application as new gain media for photonic devices. Rationale of broadening was found to be generating Raman active structural elements such as WO_4, MoO_4 and PO_4 tetrahedra in appropriate concentrations in suitable base glasses. Suitable base glass with best compromise between glass formations, optical and thermal properties were determined. Raman active WO_4 and PO_4 tetrahedra were generated either separately or jointly in a TeO_2-Nb_2O_5-BaO (TNB) glass system. The Raman spectral response to this addition was studied by exciting the samples at four wavelengths, 488, 532, 633, and 785 nm. The Raman intensity and bandwidth increased when WO_3 and P_2O_5 were jointly added in TNB. Pure non-resonant Raman gain coefficient spectra of the new glasses were derived by comparing with the gain spectrum of fused silica. The bandwidth of the gain spectra of the present tellurite glasses were more than twice that of a conventional TeO_2-Bi_2O_3-ZnO-Na_2O glass and 70% larger than silica glass. However, gain coefficient of glasses with broader bandwidths was not impressive. This made us to use transition metal oxides as a network modifier in place of the alkaline earth oxide and use them as base glasses. By doing so, higher gain coefficients and broader bandwidths were achieved in a single glass.