## 5 Discussion  
Our recent work has been focused on the application of SOAs for improving the performance of incoherent OCDMA systems that are based on a 2D-WH/TS coding scheme using multi-wavelength picosecond code carriers. In [19], we reported for the first time the use of an SOA on the receiver site to continuously compensate for the broadening of the OCDMA auto-correlation due to the temperature induced dispersion in the optical fibre (the temperature induced dispersion coefficient \(D_{\text{T}}<0\) in SMF-28). The SOA compensation was applied directly on the distorted OCDMA auto-correlation composed of multi-wavelength code carriers sitting on top of each other. We have shown that the broadening of the OCDMA auto-correlation width due to the fibre temperature induced dispersion can be mitigated using the twin SOA by controlling its chirp through bias current adjustments once  
Figure 8: Compensation of the impact of \(\beta_{2}\) on OCDMA auto-correlation width changes by using an SOA to control code carriers’ chirp at \(T=50\)\({}^{\circ}\)C.  
Figure 7: Simulations of the recovered OCDMA auto-correlation envelope \(S_{\text{L=19.5,T=50}}\) for OCDMA code propagation distance \(L=19.5\) km, \(T=50\)\({}^{\circ}\)C, and \(C\) equals to (a) 5 resulting FWHM width = 14.2 ps; (b) 3 resulting FWHM width = 13 ps; and, (c) 1 resulting FWHM width = 12 ps, respectively.  
the OCDMA auto-correlation is recovered by the OCDMA decoder. In [18], we investigated the use of an SOA that was also placed on the receiver site for a continuous manipulation of the broadened OCDMA auto-correlation due to fibre link CD (chromatic dispersion coefficient \(D_{\text{CD}}>0\) in SMF-28). The SOA compensation was applied directly on the distorted OCDMA auto-correlation composed of four multi-wavelength code carriers sitting on top of each other. In this configuration, we had to use a picosecond optical pulse called a holding beam (OP/HB) synchronized with the OCDMA auto-correlation at the SOA input to be able to demonstrate that the OCDMA auto-correlation that was broadened by the fibre chromatic dispersion can be continuously 'compressed'. In [20], we reported the use of an SOA on the transmitter site (right after the OCDMA encoder) to compensate the OCDMA auto-correlation broadening due to the fibre chromatic dispersion (\(D_{\text{CD}}>0\)), we observed on the OCDMA receiver site by controlling the chirp of the individual multi-wavelength OCDMA code carriers spread over a bit period before the code is launched into a fibre link.  
In this paper, we have investigated for the first time how controlling the chirp of the OCDMA code carriers by the SOA prior to entering the fibre transmission link that was exposed to varying temperature (20 \({}^{\circ}\)C to 50 \({}^{\circ}\)C) will influence the recovered OCDMA auto-correlation and its width at the receiver site. We have shown both experimentally and by using simulations that the distorted OCDMA auto-correlation due to temperature induced fibre dispersion (\(D_{\text{T}}<0\)) can be corrected by manipulating the chirp of OCDMA code carriers when traversing the biased SOA before entering the transmission link. In addition, the effects of varying values of GVD (parameter \(\beta_{2}\)) on the OCDMA auto-correlation width were also investigated. We have shown that the impact of a changing \(\beta_{2}\) (0.03-0.06) ps\({}^{2}\)/nm when the fibre link was exposed to 50 \({}^{\circ}\)C could be compensated by controlling the code carriers' chirp by placing an SOA on the transmitting site. Our simulation results are in very good agreement with experimental observations.