A Study On The Phase Noise In Microwave Photonic Links

Microwave photonics is an interdisciplinary area that combines microwave technology and optical fiber technology. Microwave photonics links(MPLs) are one of the core research areas in microwave photonics and it contains the generation, processing,control and transmission of optical signal. MPLs have the advantages of large bandwidth, immunity to electromagnetic interference and low loss which has nothing to do with the signal frequency.Therefore, MPLs have a huge superiority in long distance transmission and high frequency signal transmission. Phase noise is an important figure of merit of MPLs. Therefore, research on designation and implementation of MPLs with low phase noise is in the highlight of the industry.Firstly, this thesis introduced the theoretical principle of microwave photonics links, especially introduced the working principle and main parameters of the sources,modulators and photodetector. The noise properties of MPLs are analyzed in detail. On the basis of introducing and analyzing thermal noise, shot noise and laser RIN noise of the link, the thesis mainly focused on the characteristics in phase noise and direct modulation and external modulation links. Secondly, transmission experiments of platform, and a comparison of the phase noise between of transmission 10 MHz, 400 MHz and 2GHz RF signals are made in external modulation and direct modulation links, respectively. Experimental results show that the phase noise of direct modulation links is better than external modulation links when the frequency of the RF signal is 10 MHz. The phase noise of the two links are nearly identical when the frequency of the RF signal is 400 MHz or 2GHz. Thirdly, we reduce the link phase noise by choosing proper devices, using narrow band filters and amplitude limited devices.The results show that using low phase noise devices can reduce link phase noise obviously. Using amplitude limited devices can reduce phase noise by 10 d B@10KHz frequency offset. Simulation results show the link phase noise can be reduced by 20 to 30 d B when the PD is operating under the high saturation status.