Research On High Order Modulation Of Quantum Dot Semiconductor Optical Amplifiers

Compared with TDM-PON,WDM-PON is a high-performance optical access method with symmetrical upstream and downstream bandwidth,no dynamic bandwidth allocation,low optical power loss in optical distribution network,transparent and efficient protocol.But it increases the the complexity and cost of the system to configure of differernt wavelenths of semiconductor lasers for each ONU node.The RSOA-based reconfiguration scheme avoids configuring the laser for each client in the WDM-PON to achieve a colorless ONU.As the RSOA modulation bandwidth is limited(about 0.6 ~ 3.2GHz),however it can achieve modulation bandwidth of 10 GHz by the means of using R-QDSOA instead of RSOA.In addition,higher order modulation than OOK has higher spectral efficiency,and higher bit rate transmission can be realized under the same bandwidth.Therefore,the high-order modulation and re-modulation based on R-QDSOA are studied in this paper.The main contents are as follows :(1)A multi-segment simulation method of R-QDSOA is proposed.In order to ensure that the simulation accuracy is required in a single method,which leads to the problem of large sparse martix dimension and long simulation time,a multi-segmentation method is proposed to reduce the dimension of the sparse matrix and improve the simulation speed by reducing the number of single segments and re-segmenting on the previous segment.The results show that when the total number of segments is 163,the time of quadratic and cubic sub-simulation is 90% lower than that of the first segment,and the simulation error is 10-7.(2)The high-order modulation performance of R-QDSOA is studied.The simulation model of R-QDSOA high-order modulation is set up and the R-QDSOA is modulated by the 16 QAM signal with the bit rate of 20Gb/s and the carrier center frequency of 10 GHz.The simulation results show that the bit error rate is less than the FEC limit(3.8×103)when the input optical power is 0dBm,The impacts of input optical power,modulation coefficient and bias current value on the 16 QAM modulation performance are analyzed.The rusults show that the bit error rate benefits from moderate input optical power since lower input optical power reduces the molulation bandwidth of R-QDSOA and higher input optical power makes the gain recovery slower.Increasing modulation coefficient and bias current can improve the performance bit error rate.(3)Researching on the re-modulation of R-QDSOA.The NRZ downlink signal is re-modulated by 4QAM signal and the influence of the downlink optical power,ectinction ratio and the upstream and downstream signal bit rates on the re-modulation performance are analyzed,the simulation results show that the bit rates of upstream and downstream signal can reach 20Gb/s and 5Gb/s respectively when the the re-modulation bit error rate is below the FEC limit(3.8×103).The 10Gb/s 4QAM downstream signal is re-modulated by 15Gb/s NRZ signal.When the initial phase of the carrier in the downstream 4QAM symbol is ?/4,the residual interference at the junction of symbol is minimal.The influence of the input optical power and modulation coefficient on the eye opening degree of the re-modulated output signal show that increasing the downstream signal optical power and reducing the modulation coefficient can improve the R-QDSOA's suppression on the downstream signal,therefore the re-modulation performance will be improved.