Quasi-Single-Sideband Modulation With Tunable OCSR Based On Polarization Maintaining Fiber Grating

Microwave photon technology involves two disciplines,and the two disciplines are microwave and photonic.Microwave photon technology not only can provide wider spectrum resources for wireless communication by using microwave frequency band,but also has the characteristics of wide bandwidth,low consumption and anti-electromagnetic interference by taking advantage of optical fiber.This technology has important applications in military,satellite and wireless communication.In this paper,a series of theoretical and simulation studies on the transmission of optical microwave signal are carried out on the basis of ROF(Radio-Over-Fiber).In order to solve the problem of transmission of optical microwave signal in long distance analog photonic link,this paper proposes a single sideband modulation with tunable OCSR(Optical-Carrier-To-Sideband-Ratio)based on polarization maintaining fiber grating.The feasibility of the scheme is verified by the qualitative discussion about its theory and the simulation.The name of simulation software is Optisystem.The main purpose of the scheme in this paper is to solve two major problems in analog photonic link:1)The transmission of traditional optical double sideband modulation signal in optical fiber is influenced by dispersion,so that there is periodic fading after beat frequency;2)Optical carrier power is much larger than modulation sideband with small signal modulation,which means the OCSR is too high to lead to low receiver sensitivity of photonic link.Firstly,the paper makes a detailed analysis of the causes and effects of the above problems,then the principle and performance of the electro-optic modulator and fiber grating used in the scheme are analyzed.On this basis,the scheme of this paper is put forward.In this scheme,the fast and slow axis reflection spectrum of polarization maintaining fiber grating are firstly used to achieve the purpose of separating the optical carrier and the upper sideband/lower sideband,and then the tunable OCSR is obtained by adjusting the polarizing angle,and the conversion from optical double sideband to quasi-single sideband can be completed simultaneously.The obtained research efforts are listed as follows:(1)The application of polarization maintaining fiber grating in optical double to single sideband conversion is analyzed and studied,and the corresponding relationship between OCSR and polarization angle is obtained by using the spectrum and polarization characteristics of fiber grating.The dynamic tunable OCSR can be realized by adjusting the polarizing angle,and the tuning range is-9dB?72dB.It can ensure that the modulated signal always has the optimal OCSR under the condition of small signal and multi-subcarrier modulation.So it can achieve the goal of improving the receiver sensitivity of analog photonic link.(2)The relationship between the optimal OCSR and the power of the received RF signal under the condition of small signal and multi-subcarrier modulation is analyzed and studied.Through system simulation,the relationship between the power of the received RF signal and OCSR is verified through a modulation with a single subcarrier frequency of 30 GHz,and the simulation result is consistent with the theory.(3)The transmission characteristics of optical carrier modulation signal with different OCSR in analog photonic link are analyzed and studied.The data transmission(rate 512MBps)and the characteristics of bit error in the case of OCSR=OdB and OCSR=15dB are compared.It is found that when OCSR=OdB,the receiver sensitivity of the corresponding photonic link is higher.