High-precision 1.5  µm band tunable single-frequency fluoro-sulfo-phosphate fiber laser based on a self-injection locking scheme

In this paper, a high-precision 1.5 µm band tunable single-frequency Er 3+ /Yb 3+ co-doped fluoro-sulfo-phosphate (EYFSP) fiber laser based on a self-injection locking scheme is experimentally demonstrated. A self-developed 4 cm long EYFSP fiber with a high gain coefficient (3.2–4.7 dB/cm) at the C-band serves as the gain medium for laser output. The single longitudinal mode (SLM) operation is realized via a 15 cm long commercial unpumped gain fiber and a self-injection locking scheme, while flexible wavelength tuning is controlled by a fiber Fabry–Perot tunable filter (FFP-TF). The laser wavelength is tuned from 1528.08 to 1555.55 nm, with a tuning precision of up to 10–18 pm and a tuning speed of 30 nm/s. Throughout the entire tuning range of 27.47 nm, the measured laser linewidth is less than 1.3 kHz, the relative intensity noise remains below −140dB/Hz at frequencies above 3 MHz, and the power fluctuation is as low as 1% over a measurement period of 2 h. These results demonstrate that the high-precision 1.5 µm band tunable single-frequency EYFSP fiber laser is a promising candidate for future coherent optical communication systems and optical fiber sensing.