A new scheme of Er-doped phosphate fiber as U-band fiber laser proposed by Shanghai Institute of Optics and Mechanics

Recently, the High Power Laser Unit Technology Laboratory of Shanghai Institute of Optics and Precision Mechanics, Chinese Academy of Sciences, proposed a new scheme based on Er-doped phosphate fiber as a U-band laser. The relevant research results were published online in Optics Letters under the title of "Extending laser wavelengths to 1630nm in center-scale Er-phase fiber".

U-band (1625-1675 nm) laser has important application value in laser communication, Doppler laser radar and other fields. At present, the gain matrix for the realization of U-band lasers basically depends on semiconductors and crystals. Due to the large volume, high cost and poor beam quality, the practical application is limited. In contrast, Er-doped fiber laser materials have the advantages of compactness, miniaturization, high beam quality and low cost, and are the most promising laser substrate materials for commercial use. However, Er-doped fiber lasers are limited by the absorption of excited states of Er ions, which makes the laser gain greater than 1600 nm insufficient. Therefore, how to improve the long-wave gain of Er-doped fiber materials is a key scientific problem that needs to be solved in the field of U-band laser at present.

The research team proposed a new method of phosphate glass structure regulation for Er ion local environment regulation and spectral shaping. The phosphate fiber is proved to be the long-wave gain enhancement matrix of Er ion from both theoretical and experimental aspects. In this scheme, 1420-1680 nm broadband luminescence is obtained in Er-doped phosphate fiber, which is much better than 1420-1633 nm in P-doped quartz fiber.

At the same time, the team broke through the limit of laser wavelength in the self-developed Er-doped phosphate fiber with a length of 15 cm, expanded the laser wavelength to 1630 nm in the U band, and achieved the longest laser wavelength, the highest efficiency and the maximum output power. The output power and slope efficiency of the laser at 1627nm and 1630nm are 44mW/12.5% and 16.5mW/5.6% respectively. The background loss of the optical fiber is 0.5 dB/m @ 1300 nm, and the use length is only in the order of centimeters. Compared with quartz fiber, this fiber has high doping concentration, short service length, and is the most likely active fiber material to realize the application of U-band laser.

This work has been supported by the National Natural Science Foundation and national key projects.

Fig. 1 Wavelength extension mechanism of Er-doped phosphate fiber laser

Fig. 2 Er-doped phosphate fiber U-band laser signal

Source: Shanghai Institute of Optics and Precision Machinery, Chinese Academy of Sciences