Hello Shaid,I have seen your system and just replaced a photo detector with default one .I have used a besel filter selecting one wasvelength 1546 and i observed better performance of the system .BER resuced to 10^-16 to 10^-18-19 .So i would like you to use optical filter .Rest your system is good.You may increase no. of users by splitting each wavelength 1:n for total supported users.