Experimental 2.5-Gb/s QPSK WDM Phase-Modulated Radio-Over-Fiber Link With Digital Demodulation by a $K$ -Means Algorithm

Highest reported bit rate of 2.5 Gb/s for optically phase-modulated radio-over-fiber (RoF) link, employing digital coherent detection, is demonstrated. Demodulation of 3×2.5 Gb/s quadrature phase-shift-keying modulated wavelength-division-multiplexed RoF channels is achieved after 79 km of transmission through deployed fiber. Error-free performance (bit-error rate corresponding to 10^-4) is achieved using a digital coherent receiver in combination with a K-means algorithm for radio-frequency phase recovery.