The Study Of Optical Signal-To-Noise Monitoring Method Based On Coherent Optical System And The Multiplexing Of Orbital Angular Momentum Mode

With the rapid development of Mobile Internet, cloud computing and Internet of Things and the popularity of personal wireless terminals, global network traffic and bandwidth show an explosive growth trend, which makes10G system can’t meet the communication capacity demands. With the commercial use of1OOG technology, which undoubtedly made a higher demand of optical transmission network, the management and maintenance of wavelength division multiplexing (WDM) layer face the challenges. The real-time online optical performance monitoring (OPM) becomes indispensable.Optical signal-to-noise ratio (OSNR) is one of the key parameters of OPM, which is directly related to the terminal bit error ratio (BER) and the quality of signal. OSNR can be used to the setup, optimization and alert of optical networks. Some novel and effective OSNR monitoring methods need to be researched when considering the fact that the monitoring methods of10G direct detection system can’t continue to be applied in100G coherent detection system.This paper also made some research and exploration of the brand new multiplexing method, orbital angular momentum (OAM) multiplexing, to further increase the transmission rate and the channel capacity. In the free space optical (FSO) communications, the main factor limiting the OAM modes multiplexing is atmospheric turbulent disturbance, which can cause the mode crosstalk, restrict the interval and the number of OAM modes, and decrease the transmission capacity of FSO. This paper is mainly about OSNR monitoring methods in coherent detection system and the analysis of OAM mode crosstalk in FSO communication system. The main work is as follows:1. This paper analyzed the mainstream OSNR monitoring methods of10G optical network, including out-of-band and in-band methods, and discussed the advantages and disadvantages of each option and the monitoring error of optical fiber channel impairments. The OSNR monitoring methods of100G coherent receiver system are also discussed.2. This paper proposed a modified OSNR monitoring method based on higher-order statistical moments, proved the feasibility of this method with theoretical analysis.112Gbit/s polarization multiplexing quadrature phase shift keying (PM-QPSK) coherent transmission system is built to further validate the method. The simulation results show the monitoring accuracy of0.5dB the OSNR range is from5dB to30dB in back-to-back system and high tolerance of optical fiber linear channel impairments when the reference OSNR is set to14dB.3. This paper proposed a pilot-aided OSNR monitoring method applied in Nyquist-WDM coherent transmission systems, analyzed and derived the feasibility of this method. A VPITM simulation platform is built to verify the monitoring accuracy. The simulation results show that the method is insensitive to chromatic dispersion (CD) and polarization mode dispersion (PMD).4. This paper demonstrated the orthogonality of OAM modes, made the experiment of the generation of OAM modes with the use of space optical phase modulator, simulated the distortion of OAM mode with Kolmogorov atmospheric turbulence model and the mode distribution scheme under different turbulence intensity. The simulation results show that continuous OAM modes multiplexing can be used as a scheme in short distance free space optical communication (FSO) under weak atmospheric turbulence. However, when moderate atmospheric turbulence is introduced, in order to ensure that the signal extraction not be influenced by the crosstalk at receiver, the multiplexing interval of OAM modes is at least equal to3.