# Development of New Spectral Amplitude Coding OCDMA Code by Using Polarization Encoding Technique
## 6 Conclusions  
In OCDMA systems, each user is assigned a sequence code that acts as their address. An OCDMA user modulates its code (or address) with each data bit and asynchronously initiates transmission. Hence, this affects its spectrum appearance in a way recognized only by the chosen receiver. The first OCDMA code is the Hadamard code, which experienced various hurdles during the field test. The performance of the OCDMA system degrades when the number of simultaneous users grows. This is connected to MAI, which results from the incomplete orthogonal of the employed signature codes. The DW family of codes was meant to relieve the difficulties discovered in the preceding codes, such as the number of simultaneous users supported and MAI. A good functional code must have low cross-correlation and strong autocorrelation for the system to have improved performance. FDW codes are the newest DW code family variations with variable weights bigger than two. The new polarization encoding technique has provided a better solution for achieving zero cross-correlation properties. The equation for the FDW code family was used for SNR and BER calculations to compare the performance of the code. FDW code with a polarization encoding technique has substantially greater performance compared to Hadamard, MFH, DW, MDW, and EDW codes. FDW can accommodate more than 220 simultaneous users. In the simulation, FDW code with the new polarization encoding technique can go up to 60 km distance for a 2.5 Gb/s bit rate and 40 km for a 10 Gb/s bit rate.  
Conceptualization, S.M.A., S.A.A. and N.A.; methodology, S.M.A. and S.A.A.; software, S.M.A., S.A.A. and N.A.; validation, S.M.A.; formal analysis, S.M.A.; investigation, S.M.A.; resources, S.M.A., S.A.A., R.E., M.N.S. and N.A.; data curation, S.M.A.; writing--original draft preparation, S.M.A.; writing--review and editing, S.A.A., N.A., R.E., A.M.A. and C.O.E.; supervision, N.A., M.N.S. and S.A.A. All authors have read and agreed to the published version of the manuscript.  
The author would like to acknowledge the support from the Long Term Research Grant Project under a grant number of LRGS/1/2020/UM/01/5/4 from the Ministry of Higher Education Malaysia (MOHE).  
Not applicable.  
Figure 5: Performance of FDW code with different bit rate.  
**Data Availability Statement:** Not applicable.  
**Acknowledgments:** Authors would like to acknowledge the support from the Centre of Excellence Advance Communication Engineering (ACE) Optics, especially the optic group team, for providing a place and technical support for the experimental setup.  
**Conflicts of Interest:** The authors declare no conflict of interest.  
**Abbreviations**  
The following abbreviations are used in this manuscript:  
\begin{tabular}{l l} SAC & Spectral Amplitude Coding \\ OCDMA & Optical Code Division Multiple Access \\ DW & Double Weight \\ MDW & Modified Double Weight \\ MWOOC & Multiwavelength Optical Orthogonal Code \\ EDW & Enhanced Double Weight \\ ZCC & Zero Cross-Correlation \\ FDW & Flexible Double Weight \\ OW & Odd Weight \\ EW & Even Weight \\ LAN & Local Area Network \\ MAN & Metropolitan Area Network \\ MFH & Modified Frequency Hopping \\ MAI & Multiple Access Interference \\ BER & Bit Error Rate \\ PIN & Phase-Induced Intensity Noise \\ OSNR & Optical Signal-To-Noise Ratio \\ SNR & Signal-To-Noise Ratio \\ PSD & Power Spectral Density \\ SPD & Single Photodiode Detector \\ \end{tabular}