El-Nahal, F. (2016) “Bidirectional OFDM-WDM-PON System Employing 16-QAM Intensity Modulated OFDM Downstream and OOK Modulated Upstream”, Photonics Letters of Poland, 8(2), pp. pp. 60–62. doi: 10.4302/photon. lett. pl.v8i2.636.