Multiple visible emissions by means of up-conversion process in a microstructured tellurite glass optical fiber

Physico-chemical and optical properties of Er3+-doped and Er3+/Yb3+-co-doped Ge25Ga9.5Sb0.5S65 chalcogenide glass

We investigated the physicochemicаl properties, structure and optical properties of the Ge25Ga9.5Sb0.5S65: Er3+/Yb3+ glasses. The Judd-Ofelt theory was used to calculate the intensities of the intra-4f electronic transitions of Er3+ ions. We observed the upconversion photoluminescence (UCPL) at 530, 550, 660 and 810 nm under 980 nm excitation. In the Ge25Ga9.5Sb0.5S65: 0.1 at.% Er3+, we found that the Stokes photoluminescence (PL) at the green spectral region excited by the 490 and 532 nm laser is only ≈5 times higher than the UCPL emission under 810 or 980 nm excitation making these materials attractive for UCPL applications. The addition of 0.1–1 at.% of Yb3+ into Ge25Ga9.5Sb0.5S65: 0.1 at.% Er3+ glass reduces the UCPL as well as the Er3+ ≈1.5 μm emission intensity probably due to the reabsorption processes of the excitation light and concentration quenching. However, the observed Er3+: 4 S 3/2→4 I 13/2 (≈850 nm) emission in the Ge25Ga9.5Sb0.5S65: 0.1 at.% Er3+ sample populates the 4 I 13/2 level, which promises the using of this material for the 1.5 μm optical amplification.

Ligand-Driven and Full-Color-Tunable Fiber Source: Toward Next-Generation Clinic Fiber-Endoscope Tomography with Cellular Resolution

In many biomedical applications, broad full-color emission is important, especially for wavelengths below 450 nm, which are difficult to cover via supercontinuum generation. Single-crystalline-core sapphires with defect-driven emissions have potential roles in the development of next-generation broadband light sources because their defect centers demonstrate multiple emission bands with tailored ligand fields. However, the inability to realize high quantum yields with high crystallinity by conventional methods hinders the applicability of ultra-broadband emissions. Here, we present how an effective one-step fiber-drawing process, followed by a simple and controllable thermal treatment, enables a low-loss, full-color, and crystal fiber-based generation with substantial color variability. The broad spectrum extends from 330 nm, which is over 50 nm further into the UV region than that in previously reported results. The predicted submicrometer spatial resolutions demonstrate that the defect-ligand fields are potentially beneficial for achieving in vivo cellular tomography. It is also noteworthy that the efficiency of the milliwatt-level full-color generation, with an optical-to-optical efficiency of nearly 5%, is the highest among that of the existing active waveguide schemes. In addition, direct evidence from high-resolution transmission electron microscopy together with electron energy loss spectroscopy and crystal-field ligands reveals an excellent crystalline core, atomically defined core/cladding interfacial roughness, and significant enhancements in new laser-induced electronic defect levels. Our work suggests an inexpensive, facile, and highly scalable route toward achieving cellular-resolution tomographic imaging and represents an important step in the development of endoscope-compatible diagnostic devices.

Simple and efficient defect-tailored fiber-based UV-VIS broadband white light generation

We propose and demonstrate a facile approach for ultraviolet-visible broadband generation from a sapphire crystal core-borosilicate glass cladding hybrid fiber using a laser-heated pedestal growth technique. Considerable formation of F- and F(2)-type color emitters is effectively facilitated by Ti(4+) ions and Al(3+) vacancies, retaining efficient luminescence and high crystallinity of the sapphire core. These color centers intensify the ultraviolet, blue, and green emissions at 370, 450, and 540 nm, whereas the 650-nm red emission is contributed by Cr(3+) in the octahedral sites of the corundum structure. Over 1-mW white light with an optical-to-optical efficiency of up to nearly 5% and 1931 Commission International de l'Eclairage chromaticity coordinate of (0.287, 0.333) is achieved under 325-nm excitation.