what block should be used for creating optical fiber channel in designing ocdma system in simulink? sir please answer it.......

i am designing optical code division multiple access (OCDMA) system and i got stuck while designing channel because it should be optical fiber link but in simulink there is no such type of block. so please tell me which block can work same as optical fiber channel. i am waiting for your favourable reply. please reply as soon as possible because its very urgent for me.