Toward a10†dB net-gain waveguide amplifier in an Er3+-Yb3+ co-doped phosphate glass.

High-gain materials and high-quality structures are the two main conditions that determine the amplification performance of optical waveguides. However, it has been hard to balance each other, to date. In this work, we demonstrate breakthroughs in both glass optical gain and optical waveguide structures. We propose a secondary melting dehydration technique that prepares high-quality Er3+-Yb3+ co-doped phosphate glass with low absorption loss. Additionally, we propose a femtosecond laser direct-writing technique that allows controlling the cross section, size, and mode field of waveguides written in glass with high accuracy, leveraging submicron-resolution multi-scan direct-writing optical waveguide technology, which is beneficial for reducing insertion loss. As a proof of concept demonstration, we designed and fabricated two kinds of waveguides, namely, LP01- and LP11-mode waveguides in the Er3+-Yb3+ co-doped phosphate glass, enabling insertion loss as low as 0.9 dB for a waveguide length of 2 mm. Remarkably, we successfully achieved an optical amplification for both the waveguides with a net gain of >7 dB and a net-gain coefficient of >3.5 dB/mm, which is approximately one order of magnitude larger than that in the Er3+-Yb3+ co-doped phosphate glass fabricated by the traditional melt-quenching method. This will open new avenues toward the development of integrated photonic chips.

Optical planar and ridge waveguides formed in Er3+-doped germanate glass by ion implantation and precise diamond blade dicing.

In this work, we report on the preparation and characterization of the planar and ridge optical waveguides in the Er3+-doped germanate glass by combining hydrogen ion implantation and precise diamond blade dicing. The nuclear energy loss and the implantation depth were calculated by the SRIM 2013 software. The refractive index profile was obtained by the reflectivity calculation method. The dark-mode spectrum and the near-field intensity distribution were measured by the prism coupling system and end-face coupling technique, respectively. This work has important reference significance for the development of Er3+-doped germanate glass active devices in the optical communication field.

High efficient and broadband ∼3.5 µm emission of Er3+:YAG crystal.

The YAG single crystals doped with 10 at.%, 20 at.% and 50 at.% Er3+ were successfully grown by the micro-pulling down method and spectroscopic properties of the crystals were investigated. The main interest was focus on the relation between the Er3+ concentration and ∼3.5 µm emission of Er3+:YAG crystals. Room temperature absorption spectra were analyzed by the Judd-Ofelt theory. The stimulated emission cross-sections were calculated by the Füchtbauer-Ladenburg equation. The fluorescence intensities and peak emission cross-sections of the crystals at ∼3.5 µm are slightly decreasing with the increase of Er3+ concentration. The trend of the emission properties in NIR and visible region with the Er3+ concentration was also discussed and compared. The results indicate that the highly doped Er3+ concentration is beneficial to realize the ∼3.5 µm laser output.

Concentration dependence of visible luminescence from Pr3+-doped phosphate glasses.

To clarify the concentration dependence of visible fluorescence of Pr3+, a series of phosphate glass samples with Pr3+ concentration from 0.05 to 3.0 mol% were fabricated. Steady and dynamic spectroscopic characteristics of Pr3+-doped phosphate glasses were systematically investigated. When the Pr3+ concentration was small, only one visible fluorescence band can be observed at 596 nm, which was ascribed to the transition of 1D2 → 3H4. With increasing Pr3+ concentration from 0.05 to 0.5 mol%, since the multi-phonon relaxation rate of 3P0 was largely quicker than that of 1D2. Increasing Pr3+ concentration from 0.5 to 3 mol%, increasing two other fluorescence bands at 612 nm and 640 nm, which were assigned to the transitions of 3P0 → 3H6 and 3P0 → 3F2, respectively. It was due to the cross relaxation probability between [1D2: 1G4] and [3H4: 3F4] increased, which results in quicker decay rate of 1D2. The fluorescence lifetime of 1D2 decreased from 173 to 6 µs with increasing Pr3+ concentration from 0.1 to 3 mol%, which due to the cross relaxation probability between [1D2: 1G4] and [3H4: 3F4] increased, resulting in quicker decay rate of 1D2. Fitting the concentration dependence of fluorescence lifetime demonstrated that the cross relaxation arising from dipole-dipole interactions between Pr3+ ions.

Fabrication of silica nano/micro-fibers doped with one-dimensional assembly of silver nanoparticles.

Nano/micro fibers doped with metal nanocrystals are of great interest both theorectically and practically. Nevertheless, the ordered assembly of metal nanocrystals with desired patterns in nano/micro fibers still remains a big challenge, which constrains the further development of the performance of the material. In this investigation, we propose a facile strategy based on the sol-gel and coaxial electrospinning technique to fabricate silica submicron fibers incorporating ordered 1D array of silver nanoparticles. The silver nanoparticles align strictly in a head-to-tail manner in silica fibers, and their size, shape and population are conveniently controlled through tailoring the properties of the precursor solutions and the electrospinning parameters. Therefore, the plasmon property of the obtained fibers is tuned with great freedom. The fabrication method applied here holds great potential for low-cost preparation of metal/glass composite fibers for nano/micro optical applications in general.

Comparative investigation on the spectroscopic properties of Pr³âº-doped boro-phosphate, boro-germo-silicate and tellurite glasses.

We report on the spectroscopic properties of Pr(3+)-doped boro-phosphate, boro-germo-silicate and tellurite glasses. The stimulated absorption and emission cross sections were estimated. Only one emission at 596 nm and 605 nm is observed in Pr(3+)-doped boro-phosphate and boro-germo-silicate glasses, respectively, while three emissions at 605 nm, 612 nm and 645 nm are observed in Pr(3+)-doped tellurite glass when excited at 467 nm. The fluorescence lifetime at 600 nm in Pr(3+)-doped boro-phosphate, boro-germo-silicate and tellurite glasses is 137 µs, 73 µs and 51 µs, respectively. The emissions from Pr(3+)-doped boro-phosphate, boro-germo-silicate and tellurite glasses show different decay behaviors and can be well explained by multiphonon relaxation theory.