The laser operations at U-band (1625-1675 nm) have found numerical applications in telecommunication, Doppler wind LIDAR and gas sensing. Among the laser sources, Er³⁺ activated fiber lasers show many advantages in compactness, good beam quality and low cost. However, the Er-doped fiber lasers at wavelengths longer than 1600 nm face challenges of excited-state absorption and low gain coefficient.

Most recently, a research team led by Shanghai Institute of Optics and Fine Mechanics (SIOM) of the Chinese Academy of Sciences (CAS), has succeeded in broadening the emission band of Er³⁺ ions by manipulating the local structures around Er³⁺ ions in phosphate fiber. The study was published in Optics Letters on Jan. 15, 2023.

In their experiment, more than 260 nm band width (1420-1680 nm) has been achieved in self-developed Er doped phosphate fiber. The laser wavelength of Er-phosphate fiber was extended to 1630 nm. The maximum output powers and slope efficiencies of the lasers at 1627 nm and 1630 nm reached up to 44 mW/12.5% and 16.5 mW/5.6%, respectively, in a 30-cm phosphate fiber. These are the highest output powers and slope efficiencies at 1627 nm and 1630 nm from an Er³⁺-doped all-fiber laser configuration.

For the phosphate fiber, the core and cladding had diameter of 6 μm and 125 μm, respectively. The numerical aperture is 0.17, the concentration of Er₂O₃ in the fiber core is 3.5 wt%, and the background loss is 0.5 dB/m@1300 nm, using a length of 30 cm.

Moreover, compared with Er-silica fiber, the studied Er-phosphate fiber has much higher concentration of Er, shorter length of fiber and high spectroscopic flatness of gain, indicating an excellent fiber host for U-band fiber lasers.

This research leads to a host material for fiber lasers operated at U-band wavelengths.

Manipulating glass structure for extending emission wavelength. (Image by SIOM)

Optical spectra of a 15-cm Er-phosphate fiber laser at 1600, 1609, 1627 and 1630 nm(Image by SIOM)

Article website:
https://doi.org/10.1364/OL.480921

Contact:
WU Xiufeng
General Administrative Office
Shanghai Institute of Optics and Fine Mechanics, CAS
Email: xfwu@siom.ac.cn
Web: http://english.siom.cas.cn/