Fig. 3: A 53 km free-space optical (FSO) link with high-speed data transmission.
From: Tbit/s line-rate satellite feeder links enabled by coherent modulation and full-adaptive optics
a Experimental setup; First, a dual-polarized complex-modulated signal is generated by an arbitrary waveform generator (AWG) and mixed onto an optical carrier fc (1550 nm) by means of a DP IQ-modulator. Afterwards it is optically equalized by a wavelength selective switch (WSS) and fed to the space terminal (ST). Subsequently, the signal is transmitted over a FSO distance of 53 km through a turbulent atmospheric channel. At the receiver side, the phase-distorted wavefront is corrected in an adaptive optics system consisting of a wavefront sensor (WS) and a deformable mirror (DM), and coupled to a single mode fiber. After pre-amplification in low-noise amplifiers (LNA), the data signal is mapped back to baseband in the optical coherent receiver consisting of a local oscillator, a 90°-Hybrid and balanced photodetectors (B-PD). Finally, the digital signal is assessed by a standard offline digital signal processing stage. b Received constellation diagrams of high-speed data transmission are shown, achieving single-carrier symbol-rates of up to 126 GBaud. This results line rates of up to 1.008 Tbit/s by means of advanced modulation formats. (Amp amplifier, Atm atmosphere, AWG arbitrary waveform generator, B-PD balanced photodetector, BPF band pass filter, Col collimator, DM deformable mirror, DSP digital signal processing, DP dual polarization, DSO digital sampling oscilloscope, IQ-mod in-phase quadrature modulator, EDFA erbium-doped fiber amplifier, HPOA high-power optical amplifier, HWP half wave plate, LNA low noise amplifier, OGS optical ground station, OPM optical power meter, Rx receiver, ST space terminal, WS wave-front sensor, WSS wavelength-selective switch.)
