Further i would like to mention that Optical code division multiple accessm(OCDMA) technique, which allows multiplemusers share the same transmission mediamby assigning different optical codes (OCs)mto different users, is an attractive candidatemfor next generation broadband access networks . The basic architecture and the working principle of an OCDMA passive optical network (PON) network. Partricularly，coherent OCDMA technique is receiving much attention for the overall superior performance over incoherent OCDMA and the development of compact and reliable en/decoders (E/D) like spatial light phase modulator (SLPM), superstructured fiber Bragg grating (SSFBG) and multi-port array waveguide grating (AWG)-type E/D . Previously, on-off-key (OOK) is mostly used as modulation format for payload data in OCDMA system, which is refered as OOKOCDMA. In a multi-user asynchronous coherent OOK-OCDMA system, the major noise sources are the coherent signalinterference (SI) beat noise (coherent noise) and the incoherent MAI (incoherent noise), which limit the number of active users in a network. Therefore, it is essential to combat the SI beat and MAI noises in such a network. Time gating and optical thresholding techniques can be used to suppress the MAI enabling data-rate detection.
Here i am providing with various papers you may consult. These will be very helpful.
http://ieeexplore.ieee.org/xpl/login.jsp?tp=&arnumber=4290311&url=http%3A%2F%2Fieeexplore.ieee.org%2Fiel5%2F35%2F4290299%2F04290311
http://file.scirp.org/pdf/JEMAA_2013022815384836.pdf
https://optics.synopsys.com/rsoft/application-gallery/optsim-optical-code-division-multiple-access.html
https://www.eng.tau.ac.il/~tur/pdfs/112.pdf
http://home.eps.hw.ac.uk/~xw66/News%20and%20highlights_files/AOE-invited-xw.pdf
The last paper is about different modulation schemes used in OCDMA. It may be very helpful to you.
Thanks