  A software-defined optical receiver is implemented on an off-the-shelf
commercial graphics processing unit (GPU). The receiver provides real-time
signal processing functionality to process 1 GBaud minimum phase (MP) 4-, 8-,
16-, 32-, 64-, 128-ary quadrature amplitude modulation (QAM) as well as
geometrically shaped (GS) 8- and 128-QAM signals using Kramers-Kronig (KK)
coherent detection. Experimental validation of this receiver over a 91~km
field-deployed optical fiber link between two Tokyo locations is shown with
detailed optical signal-to-noise ratio (OSNR) investigations. A net data rate
of 5 Gbps using 64-QAM is demonstrated.
