(INVITED)Investigation of intense visible defect luminescence from visible and infrared pumped barium fluorosilicate glass-core fiber

Optically active defects in silica have been studied for decades and are often indicators of network irregularities such as those that might result from optical or mechanical damage. They are well-known to be weak emitters and are usually present in relatively low concentration, thus precluding their use in a wide range of applications, including sensing and laser gain. Here, a new paradigm in intense defect emission in the visible wavelength range from a nominally passive optical fiber is presented. Optical fiber starting with 100 mol % BaF2 precursor core material and a pure silica cladding was successfully drawn utilizing the molten core method. These fibers demonstrate an intense, yet unexpected, green photoluminescence peaking near 537 nm (in addition to a second, weaker band near 704 nm) arising from relatively low-power CW pumping in the near-infrared at 976 nm. To understand the origins of this emission, absorption across the optical spectrum is analyzed and photoluminescence via excitation in both the visible and near-infrared wavelength ranges is studied. In addition, Raman spectra, decay lifetimes, magnetization curves, and temperature dependence measurements were collected. The emission spectra maintained a Pekarian-like spectral shape, suggesting an optically active defect as the mechanism behind the green emission. The results presented herein point towards the most likely origin being silanone or dioxasilyrane groups usually associated with surface defects. Importantly, such fibers, fabricated through less conventional methods and possessing novel compositions, may prove to be key in further extending the range of possibilities in defect engineering to well beyond what was previously thought possible