Single-frequency fiber lasers have drawn intense attention for their extensive applications from high-resolution spectroscopy and gravitational wave detection to materials processing due to the outstanding properties of low noise, narrow linewidth, and the resulting long coherence length. In this paper, the recent advances of single-frequency fiber oscillators and amplifiers are briefly reviewed in the broad wavelength region of 1–3 μm. Performance improvements in laser noise and linewidth are addressed with the newly developed physical mechanisms. The solution to achieving higher power/energy is also discussed, accompanied by the start-of-the-art results achieved to date.

In this letter, a temperature sensor based on a fiber ring laser with a reflective Sagnac loop is proposed. The reflective Sagnac loop inserted into the fiber ring laser through a download optical fiber is used as the filter and sensing head to supply high temperature sensitivity. As the temperature varies, the transmission spectrum of Sagnac loop changes, leading to the shift of emission wavelength of a fiber ring laser. We obtain a temperature sensor system with a high temperature sensitivity of 1.739 nm/°C, a narrow 3-dB bandwidth less than 0.05 nm, and a high signal-to-noise ratio ~50 dB. Moreover, it is convenient to achieve the remote sensing by changing the length of the download optical fiber.

A novel passively Q-switched all-fiber laser using a single mode-multimode-single mode fiber device as the saturable absorber based on the Kerr effect of multimode interference is reported. Stable Q-switched operation of an Er³⁺/Yb³⁺ co-doped fiber laser at 1559.5 nm was obtained at a pump power range of 190-510 mW with the repetition rate varying from 14.1 kHz to 35.2 kHz and the pulse duration ranging from 5.69 μs to 3.86 μs. A maximum pulse energy of 0.8 μJ at an average output power of 27.6 mW was achieved. This demonstrates a new modulation mechanism for realizing Q-switched all-fiber laser sources.

We report a single-frequency distributed Bragg reflector (DBR) fiber laser at 930 nm for the first time, to the best of our knowledge. A $\sim 2.5\mathrm{cm}$ long commercial highly neodymium-doped silica fiber was utilized as the gain medium to achieve $\sim 1.9\mathrm{mW}$ laser output. The single longitudinal mode operation of this laser was verified by a scanning Fabry–Perot interferometer. This fiber laser is suited for seeding high-power 930 nm narrow-linewidth laser amplifiers, which can be used to generate coherent single-frequency pure blue light through frequency doubling.

A single-frequency fiber laser operating at 1950 nm has been demonstrated in an all-fiber distributed Bragg reflection laser cavity by using a 1.9 cm commercially available thulium-doped silica fiber, for the first time, to the best of our knowledge. The laser was pumped by a 793 nm single-mode diode laser and had a threshold pump power of 75 mW. The maximum output power of the single longitudinal mode laser was 18 mW and the slope efficiency with respect to the launched pump power was 11%. Moreover, the linewidth and relative intensity noise at different pump power have been measured and analyzed.