by Yiannopoulos, K., Vyrsokinos, K., Tsiokos, D., Kehayas, E., Pleros, N., Theophilopoulos, G., Houbavlis, T., Guekos, G., Avramopoulos, H.
Published in IEEE journal of quantum electronics (01.02.2004)

by Kalyvas, Marios, Yiannopoulos, Kostas, Houbavlis, Thanassis, Avramopoulos, Hercules
Published in International journal of electronics and communications (2003)