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

We experimentally demonstrate a 2-<inline-formula> <tex-math notation="LaTeX">$\mu \text{m}$ </tex-math></inline-formula> 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 back-to-back (BTB), the optical signal-to-noise ratio (OSNR) of 2-<inline-formula> <tex-math notation="LaTeX">$\mu \text{m}$ </tex-math></inline-formula> laser carrier reduces from 15.04 dB to 6.67 dB under the condition of <inline-formula> <tex-math notation="LaTeX">$\text{C}_{\mathrm {n}}^{2}=5.71 \times 10^{-16}\text{m}^{-2/3}$ </tex-math></inline-formula>, and the received power jitter increases from ±0.04 dB to ±0.74 dB. The sensitivity of the 2-<inline-formula> <tex-math notation="LaTeX">$\mu \text{m}$ </tex-math></inline-formula> data transmission system is −19.52 dBm. In addition, we compare the average receiving power standard deviation and power penalty between the 2-<inline-formula> <tex-math notation="LaTeX">$\mu \text{m}$ </tex-math></inline-formula> laser and a 1.55-<inline-formula> <tex-math notation="LaTeX">$\mu \text{m}$ </tex-math></inline-formula> laser under the same propagation conditions. The experimental results demonstrate that the 2-<inline-formula> <tex-math notation="LaTeX">$\mu \text{m}$ </tex-math></inline-formula> laser communication system realizes superior performance in a weak turbulent channel.