Hi Alisthu,there are very major role of these techniques for spectrum broadning.In case of OCDMA due to security concern and to increase the degree of security,these scehmes widely used.You can convert your signal wavelength with the help of soa EAM or HNLF to broad spectrum and then convert wavelength so that jamming and effect of evasdropping cant intrupt the system.Howevere with this systems performance decreases due to phase change ,but it depends for what purpose you are designing.if it is for millitory applications then security is very much important otherwize you can go for high perfoemance.So finally it is basically a trade off in performance and security.