We report the highest performance 640-Gb/s transmitter and receiver, based on cavity-less pulse generation and a novel sampling receiver constructed using a single fiber parametric gate capable of self-tracked 40-Gb/s tributary extraction. The performance of the transmitter and sampling receiver was measured with a 640-Gb/s return-to-zero on-off keying (RZ-OOK) signal. Error-free operation was achieved for all 16 tributaries of the 640-Gb/s input stream using the optical signal-to-noise ratio (OSNR) noise loading method. The error-free (bit-error rate (BER) =10-9 ) sensitivity of the sampling receiver was measured at an OSNR level of 33.5 dB, which is only 0.5 dB away from the practically achievable detection limit.