Research On Photon Microwave Signal Generation Technology Based On Fiber-locked Cavity

Microwave photonics technology is a novel method to generate and process microwave signals with use of photonics technique. Compared with conventional microwave technology, this technique is strong to electromagnetic interference, low transmission loss and high bandwidth, which has been widely applied in many fields such as aerospace and communication. In microwave photonics technology, photonic generation of microwave signal has aroused wide attention and lots of research, for it is an important link and one of the determinants deciding the whole microwave photonics system's performance. In many generation methods, the fiber mode-locked cavity can not only generate microwave signal with high frequency but also simultaneously avoid difficult spectrum filter, which is thought to be a potential method. Our paper's work is mainly to generate high-repetition-frequency microwave signal, optimize system performance and expand functions with the use of national harmonic mode-locking(RHML) in the fiber mode-locked cavity.In the paper, we firstly summary the development situation and existing problems in microwave photonics and mode-locking technology. After analyzing the method of RHML in detail, we discover that main problem in RHML is uneven amplitude when mode-locked order is high, which is due to the existing super-mode noise and amplitude noise in the system. Aiming at this problem, we mainly start two researches:(1) To extend function of optical generation microwave system and output super-mode-suppressed multichannel microwave signal, we propose an novel RHML construction. In the scheme, two loops consists of two wavelength division multiplexers, in which the corresponding optical delay line is tuned to change the length of cavity to obtain microwave signal with different frequency. And due to the gain competition of two signals in the semiconductor optical amplifier, super-modes are suppressed. With no need of extra device, this structure can simultaneously output multiple microwave signals with different harmonic order and super-mode suppression.(2) A new scheme with use of a tunable fiber active optical ring filter to suppress amplitude noise is reported, in which mode-locked pulses are filtered and then output even pulses. MATLAB simulation and experimental verification are carried out respectively. This scheme has fine tunability and pulse amplitude equalization effect.Based on the research, we study on the principle of photonic generation microwave signal utilizing fiber mode-locking technique and the optimization method of system performance. Proposed schemes have simple structure, good performance, which provides new track for the optical generation technology of microwave signal.