| Because of its so many advantages Ssuch as low loss,small electromagnetic interference,high bandwidth and so on,optical fiber communication has been more and more applied to contemporary transmission backbone network.There are more trends in optical fiber communication system such as faster speed,further distance and capacity of taking much more information;however it subsequently exposes some drawbacks.The most important one is the influence on optical link transmission caused by polarization instability which is due to polarization loss.It makes that signal produces jitters and power ups and downs.Therefore,to make the signal with more high quality and high fidelity through transmission,polarization stability is particularly significant.The polarization controller in overcoming polarization damage plays a crucial role,and it has fine precision on polarization control,fast response speed and low insertion loss,and can be achieved on the polarization in the link of automatic tracking and compensation.In terms of no dazzle,the three aspects of the principle of polarization controller adjustment,polarization tracking loop feedback system and the application of polarization stability in the long distance RF photonic frequency link are studied and carried out in this paper.Specific work is as follows:According to the principle of polarization controller adjustment,mathematical modeling and Matlab simulation are proved.The polarization controller used in this paper is a proprietary product which is researched and developed by OZ Optics Company in Canadian Ottawa.The work of this thesis includes that mathematical theory deduction of adjustment principle of the 4-channel voltage-controled polarization controller.It points out that the theoretical basis of the possibilities of algorithm design,which can be proved by simulation.It established a mathematical model of the polarization control and deduced the mathematical relationship between 4 waveplate retardation and feedback control signal and made the process of adjusting algorithm without introducing jitters.To build an experimental platform,an automatic tracking control algorithm is introduced for the polarization tracking closed-loop feedback system.Through the experiment it has verified the response speed and adjusting precision of whole polarization tracking system,compared anti?noise disturbance with the mature commercial devices POS-002 type of polarization tracking module in the market produced by general photonics company production,and by comparing the peak-peak value and the average value of the signal under the stable polarization state,further illustrated that the method and this polarization tracking system have an advantage of anti noise disturbance,and can ensure the expected polarization in a more stable Output.In view of the application of polarization stabilization in the RF photonic frequency conversion system,the polarization tracking system designed by this paper is placed in the long distance transmission of RF photonic frequency link.The experiment pointed out that in the long distance optical fiber transmission link,the impact of the change of polarization state will be greater,because it will change with the changes in the transmission process of time and space.Because photonic RF frequency link usually include some electro-optical modulation devices,when random changes of polarization through the polarization sensitive devices,the polarization jitters will transform into the intensity of the jitters,which results in larger noise.Therefore,to overcome the polarization sensitive of devices in the distant photonic RF frequency transmission system,ensuring the stable transmission of polarization is significant.Experiments show that the designed algorithm and polarization control system can be very well applied in the remote RF photonic frequency transmission system and the output signal power can remain stable,which means the difference between maximum and minimum power is very small,less than 0.71dB. |
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