Experimental demonstration of coherent receiver with photonic lantern and digital signal processing

In free-space optical communications in which the signal is coupled into a single-mode fiber, atmospheric distortion leads to loss of signal and reduced receiver sensitivity. We demonstrate a coherent receiver system in which a dual polarization quadrature phase shift-keying (DP-QPSK) signal is coupled into a photonic lantern, which efficiently separates the light from a large multimode core into single mode fibers. Outputs from the lantern are passed to off-the-shelf integrated coherent receivers and digitized, and the resulting signals are coherently combined with optimal weight coefficients. The reconstructed signal exhibits reduced sensitivity to atmospheric distortion and demonstrates improved performance.