The Key Technology Research On Medium-and Short-distance Optical Transmission Systems Based On Stokes Vector Direct Detection

In recent years,with the development of information technology and emergency of various novel Internet services like cloud-based services,live videos and so on,short to medium reach transmission systems which include metro networks,access networks and datacenter networks are facing more and more challenges to meet the ever-increasing traffic demand.Therefore,novel short to medium reach optical transmission schemes with low cost and high capacity are attracting much research interest.Stokes vector direct detection(SV-DD)is a novel direct detection scheme where polarization de-multiplexing is possible by direct detection.Therefore,higher spectral efficiency than intensity modulation direct detection(IMDD)systems can be achieved at relatively low cost in SV-DD systems and SV-DD becomes a candidate for novel short to medium reach optical transmission schemes.This thesis focuses on SV-DD systems and carries out researches on related key techniques.The main research outcomes are as follows:(1)Starting with the principles of SV-DD systems,the effect of birefringence induced polarization states change on signal demodulation is analyzed theoretically.Besides,the importance of polarization de-multiplexing under the influence of chromatic dispersion(CD)is elaborated for SV-DD systems.(2)To address the above issue,an improved adaptive polarization de-multiplexing algorithm is proposed in this thesis.The proposed algorithm utilizes signals' distribution in Stokes space and is supposed to have strong robustness towards CD and good suitability for different modulation formats.As shown in simulations results,after 100 km transmission in single mode standard fiber(SSMF),the proposed algorithm can track rotation of state of polarization of 20 Mrad/s and 8 Mrad/s for SV-DD systems with 28 GBaud 4-QAM and 16-QAM signal,respectively,meeting the requirement of short to medium reach transmission systems.(3)Based on water pouring theorem and the noise equalization effect of pre-coding techniques,the influence of pre-coding techniques on the channel capacity is studied in theory.After derivation,a conclusion is drawn that the channel capacity of systems with pre-coding will decrease when noise equivalent power over different sub-channels is not equal.Through simulations,the above conclusion is verified and further research is carried out.The simulation results show that when difference of noise equivalent power over different sub-channels is significant,the introduce of pre-coding will cause considerable degradation of channel capacity.Moreover,the loss of channel capacity caused by pre-coding could be negligible for minor difference of noise equivalent power.At this point,the merits of pre-coding techniques can be fully utilized.