A Recomfigurable D8PSK/8QAM Optical Modulator And Its Transmission Performance Analyse

In recent years, people now have an increasing demand for broadbandcommunication, because of the invention and the development of smartphones andInternet, expecially the broadband Internet. The media applications, such as the page forcommunication (the so-called social network) and the VOD (video on demand) system,spread all over the world. The approximately exponential increasing of network flowbrings unprecedented strong pressure to the core network. Therefore, finding anddesigning a solution for this "transmission capacity crisis", including the utilization ofhigher order modulation formats and coherent detection-digital equalization technique,becomes a hot tissue in the work of the researchers.Our work is mainly about the tissue of "transmission capacity crisis" and proposesa solution for improving the transmission efficiency. The specific research and analysisfor the linear damage effects of the optical fiber transmission systems is done, includingloss (internal loss and external lose) and fiber dispersion (mode dispersion andpolarization mode dispersion). Moreover, the fiber nonlinear effects (four-wave mixing,self-phase modulation and cross-phase modulation), the channel crosstalk and someother factors that can influence the performance of the fiber communication system arealso discussed in this work.Based on the discussion above, this paper proposes a reconfigurable8PSK/8QAMmodulator and describes the differential encoding rules of this modulation structure,comparing with the precoding rules of the DPSK and DQPSK modulation structure.Meanwhile, we also take advantage of the delay interferometer to control the systemresulting in two different modulation formats. Finally, we make further improvement ofthis modulation structure, and the new structure can generate four kinds of advancedmodulation formats, including QPSK, PM-QPSK,8PSK and8QAM. In practicalapplication environment, based on the link implementation and the specific demand ofthe transmission capacity, this reconfigurable modulator can choose a propermodulation format for transmission. Moreover, using the coherent detection-digitalequalization technique, we compensate for the damage in optical fiber transmissionnetwork. We discussed several significant algorithms in digital signal processing,including dispersion compensation algorithm, digital back propagation algorithm (DBP),constant modulus algorithm (CMA) and carrier phase estimation algorithm (CPE).The optical modulator structure proposed by us has a good noise tolerance which isin a reasonable range of error comparing with the theoretical value, according to ourresults of simulation. And the DSP algorithm can compensate for the damage in thefiber link efficiently, including fiber dispersion effects, nonlinear effects and laser phase noise. Finally, we use VPIsoftware to simulate transmission process of this flexiblereconfigurable optical modulator, and the captured data is then processed offline byDSP with Matlab. The results fully confirm the superiority of this flexible andself-adaptive optical modulation structure.In conclusion, the solution proposed in this paper can choose a proper modulationformat for transmission, based on actual link implementation and the detailedrequirement of the transmission capacity. This superiority not only helps to improve thespectral efficiency of the whole fiber communication system and the performance of thelink, but can also meet the requirements of the complex transmission link environmentin reality.