Re-modulation WDM-PON Based On Coherent Detection Using 3×3 Coupler

With the rapid development of broadband services, especially the explosive development of streaming media technology, high-definition television, cloud computing and peer to peer(P2P)service, the operator’s access network bandwidth demand continues to grow. Optical fiber access network is the most attractive option to solve this problem. WDM-PON is recognized as a best networking model for next-generation PONs due to its high transmission bandwidth, data transparency and network security. The WDM-PON based on the reflective semiconductor optical amplifier(RSOA) is one of the most promising candidates. It is wavelength-agnostic, the simplest structure for single fiber access, and avoiding stabilized laser use. Meanwhile, the coherent detection technique of high receiver sensitivity has been introduced to WDM-PON. Because the access network is extremely sensitive to cost, we used a 3×3 fiber coupler as a 120-degree optical hybrid in place of using the bulky 90-degree optical hybrid in coherent receiver. In this dissertation,the remodulation technology based on RSOA and coherent detection technology using a 3×3 fiber coupler in WDM-PON have been investigated.The key technical issue of the coherent receiver using 3×3 fiber coupler is how to reduce the impact of the unbalances in the splitting ratios of the real 3×3 coupler. In this dissertation, a new demodulation theory is formulated for deriving the I&Q components from the output signals of the asymmetric 3×3 coupler. Via the QPSK simulation system, the new I&Q components demodulation theory has been verified.Finally, in order to verify if the coherent receiver using asymmetric 3×3 coupler can be introduced in WDM-PON system based on RSOA, the remodulation WDM-PON system is constructed on the virtual optical instrument(VPI) simulation platform. And with the compensation of the new I&Q demodulation algorithm, when the optical fiber transmission length is 80 km, the sensitivity of the coherent receiver using asymmetric 3×3 coupler is-41.5dBm. And its performance is identical with the coherent receiver using 90° optical hybrid. Also this paper analyzes the limitations of the coherent receiver using asymmetric 3×3 coupler.