2- $\mu$ m Free-Space Data Transmission Based on an Actively Mode-Locked Holmium-Doped Fiber Laser

We experimentally demonstrate a 2-μm free-space data transmission system in a simulated atmospheric turbulent device with an actively mode-locked holmium-doped fiber laser. The central wavelength can be adjusted from 2035.6 nm to 2050.2 nm with optional repetition rates of 1.01 GHz and 2.02 GHz, respectively, and the pulse is stabilized by adding a fiber Fabry-Perot filter in the laser cavity. The pulse sequence can be modulated by a digital signal and transmitted in a tunable simulated atmospheric turbulent channel. Compared with backto-back (BTB), the optical signal-to-noise ratio (OSNR) of 2-μm laser carrier reduces from 15.04 dB to 6.67 dB under the condition of C_n² = 5.71 × 10^-16m^-2/3, and the received power jitter increases from ±0.04 dB to ±0.74 dB. The sensitivity of the 2-μm data transmission system is -19.52 dBm. In addition, we compare the average receiving power standard deviation and power penalty between the 2-μm laser and a 1.55-μm laser under the same propagation conditions. The experimental results demonstrate that the 2-μm laser communication system realizes superior performance in a weak turbulent channel.