Transmission characteristics of 1.55 and 2.04 µm laser carriers in a simulated smoke channel based on an actively mode-locked fiber laser

We experimentally demonstrate a free-space data transmission system in an indoor simulated smoke chamber with a laser carrier of an erbium-doped actively mode-locked fiber laser and a holmium-doped actively mode-locked fiber laser. Two additional semiconductor lasers operating at 0.85 and 1.06 µm are used to calibrate the visibility of a smoke channel using the Ijaz model and compare smoke attenuation with 1.55 and 2.04 µm lasers. The eye patterns and bit error rates of 1.55 and 2.04 µm laser carriers with a data rate of 4.04 Gbps are investigated experimentally at 0.5, 0.05, and 0.005 km visibilities. The experimental results show that the smoke attenuation is wavelength dependent for V < 0.5 km. As the visibility decreases, the long wavelength laser is less affected by the attenuation and power fluctuation caused by Mie scattering. The measured optical signal-to-noise ratios of the 1.55 and 2.04 µm laser carriers for V = 0.005 km are 4.83 and 8.62 dB, respectively. The corresponding link sensitivities are -14.59 and -17.74 dBm, respectively, indicating that the 2.04 µm data transmission system is more reliable under an extremely dense smoke condition.