Nd³⁺-doped fiber lasers at around 900 nm based on the ⁴F_3/2 → ⁴I_9/2 transition have obtained much research attention since they can be used as the laser sources for generating pure blue fiber lasers through the frequency doubling. Here, an all-fiber laser at 915 nm was realized by polarization-maintaining Nd³⁺-doped silica fiber. A net gain per unit length of up to 1.0 dB/cm at 915 nm was obtained from a 4.5 cm fiber, which to our best knowledge is the highest gain coefficient reported in this kind of silica fiber. The optical-to-optical conversion efficiency varies with the active fiber length and the reflectivity of the output fiber Bragg grating (FBG), presenting an optimal value of 5.3% at 5.1 cm fiber length and 70% reflectivity of the low reflection FBG. Additionally, the linear distributed Bragg reflector short cavity was constructed to explore its potential in realizing single-frequency 915 nm fiber laser. The measurement result of longitudinal-mode properties shows it is still multi-longitudinal mode laser operation with 40 mm laser cavity. These results indicate that the Nd³⁺-doped silica fiber could be used to realize all-fiber laser at 915 nm, which presents potential to be the seed source of high-power fiber laser.

Bismuth (Bi)-doped photonic materials, which exhibit broadband near-infrared (NIR) luminescence (1000–1600 nm), are evolving into interesting gain media. However, the traditional methods have shown their limitations in enhancing Bi NIR emission, especially in the microregion. Consequently, the typical NIR emission has seldom been achieved in Bi-doped waveguides, which highly restricts the application of Bi-activated materials. Here, superbroadband Bi NIR emission is induced in situ instantly in the grating region by a femtosecond (fs) laser inside borosilicate glasses. A series of structural and spectroscopic characterizations are summoned to probe the generation mechanism. And we show how this novel NIR emission in the grating region can be enhanced significantly and erased reversibly. Furthermore, we successfully demonstrate Bi-activated optical waveguides. These results present new insights into Bi-doped materials and push the development of broadband waveguide amplification.

A noise-sidebands-free and ultra-low relative intensity noise (RIN) 1.5 μm single-frequency fiber laser is demonstrated for the first time to our best knowledge. Utilizing a self-injection locking framework and a booster optical amplifier, the noise sidebands with relative amplitudes as high as 20 dB are completely suppressed. The RIN is remarkably reduced by more than 64 dB at the relaxation oscillation peak to retain below 150 dB/Hz in a frequency range from 75 kHz to 50 MHz, while the quantum noise limit is 152.9 dB/Hz. Furthermore, a laser linewidth narrower than 600 Hz, a polarization-extinction ratio of more than 23 dB, and an optical signal-to-noise ratio of more than 73 dB are acquired simultaneously. This noise-sidebands-free and ultra-low-RIN single-frequency fiber laser is highly competitive in advanced coherent light detection fields including coherent Doppler wind lidar, high-speed coherent optical communication, and precise absolute distance coherent measurement.

Bismuth (Bi)-doped laser glasses and fiber devices have aroused wide attentions due to their unique potential to work in the new spectral range of 1 to 1.8 μm traditional laser ions, such as rare earth, cannot reach. Current Bi-doped silica glass fibers have to be made by modified chemical vapor deposition at a temperature higher than 2000°C. This unavoidably leads to the tremendous loss of Bi by evaporation, since the temperature is several hundred degrees Celsius higher than the Bi boiling temperature, and, therefore, trace Bi (～50 ppm) resides within the final product of silica fiber. So, the gain of such fiber is usually extremely low. One of the solutions is to make the fibers at a temperature much lower than the boiling temperature of Bi. The challenge for this is to find a lower melting point glass, which can stabilize Bi in the near infrared emission center and, meanwhile, does not lose glass transparency during fiber fabrication. None of previously reported Bi-doped multicomponent glasses can meet the prerequisite. Here, we, after hundreds of trials on optimization over glass components, activator content, melting temperature, etc., find a novel Bi-doped gallogermanate glass, which shows good tolerance to thermal impact and can accommodate a higher content of Bi. Consequently, we successfully manufacture the germanate fiber by a rod-in-tube technique at 850°C. The fiber exhibits similar luminescence to the bulk glass, and it shows saturated absorption at 808 nm rather than 980 nm as the incident power becomes higher than 4 W. Amplified spontaneous emissions are observed upon the pumps of either 980 or 1064 nm from germanate fiber.