Research On Local Oscillator Generation Of Radio-over-Fiber And Its Key Technologies

With the rapid development of radar,satellite,electronic reconnaissance and next generation wireless communication,there is an increasing demand for working bandwidth and signal frequency.However,it is difficult to meet the future needs due to the electronic bottleneck of traditional electronic technology.Radio-over-Fiber is an emerging technology that coalesces the merits of both radio communication and optical fiber communication.It not only has the advantages of large working bandwidth,small transmission loss and low cost,but also has the characteristics of mobile and flexible.It has obvious advantages over traditional electronic technology.As the carrier transmission information of the ROF system,the generation and transmission of microwave local oscillator signal is of great importance to the system performance.It is an extremely important technology in ROF.In this paper,the key research on microwave local oscillator signal generation technology in ROF system is carried out.The following research tasks were completed:1.This paper analyzes the basic principle,practical application and key technologies of microwave photonics and ROF technology,and summarizes the generation methods of microwave local oscillations in ROF system and the research situation in domestic and overseas.The merit and demerit of the existing methods of generating microwave local oscillations are compared.The structure of ROF,the key devices used in the system and several indicators for measuring the local oscillator signal are described.Several relatively classic schemes for microwave generation with frequency doubling,quadrupling,sextupling and octupling are introduced.2.A tunable frequency sextupled optoelectronic oscillator based on cascading a Sagnac loop with a phase modulator(PM)and a dual-parallel Mach-Zehnder modulator(DPMZM)is proposed and simulated.The scheme effectively suppresses the optical carrier and other spurious harmonics,which can generate pure sextupling microwave local oscillator signal.The local oscillator signals of 5GHz,6GHz and 8GHz are simulated respectively to verify the frequency tunability of the system.3.A tunable frequency 12-tupling optoelectronic oscillator based on cascaded dual-parallel Mach-Zehnder modulator(DPMZM)and Mach-Zehnder modulator(MZM)is presented and simulated.The scheme utilizes the reflection and transmission mechanisms of FBG to form an optoelectronic oscillator loop and a microwave 12-tupling link respectively,and generates a pure 12-tupling microwave local oscillator signal.The scheme achieves high frequency multiplication factor and the frequency is tunable in a certain range.And the frequency tunability is verified.4.A photonic frequency-octupling scheme based on cascaded dual Sagnac loops is proposed and simulated.The scheme is simple in structure,avoids the use of any filter,and has a large tunable range.Spurious harmonics are suppressed by using the characteristics of the Sagnac loop,and a pure octupling microwave local oscillator signal can be generated.The performance of frequency tunability is also implemented in the simulation.