1-Tb/s/3.9-km FSO Propagations With WDM-PAM4 Technique and Telescope-Type Four-Lens System

The implementation of 1-Tb/s/3.9-km free-space optical (FSO) propagation with wavelength-division-multiplexing (WDM)-four-level pulse amplitude modulation (PAM4) technique and telescope-type four-lens system is successfully achieved. The WDM-PAM4 technique greatly increases the transmission rate, while a telescope-type four-lens system substantially extends the FSO propagation distance. By utilizing two tandem phase modulator-optoelectronic oscillators, a total wavelength of 20 wavelengths is generated, each modulated by a 50-Gb/s PAM4 signal. This enables FSO propagation with a total data rate of 1 Tb/s (50 Gb/s/λ × 20 λs). At the receiver side, the micro-electromechanical system-based telescope-type four-lens with a control unit dynamically adjusts the tilt (vertical) or pan (horizontal) angle to precisely realign and couple the laser beam onto the fiber ferrule input. This demonstrated 1-Tb/s/3.9-km FSO propagation, leveraging WDM-PAM4 technique and telescope-type four-lens system, establishes a milestone in achieving high transmission rate over long-distance free-space transmission.