Research On Photonic Downconversion With Tunable Wideband Wideband Phase Shift System

With the rapid development of Internet technology, Now people come to a new era,which is been called Big Data Era. Communication between people also transition from a single text to graphics, and even to live video. The amount of information transmitted grows from Kbps to Gbps. The emergence of microwave photonics makes people see the future, it has been apply to many aspects of people's lives.In the field of microwave photonics,millimeter-wave phased-array beamforming networks and phase-coded radar systems are very important research direction. All these systems need photonic downconversion and phase shift. All the schemes mentioned above can only achieve one function either frequency downconversion or phase shift.However,combining both of the functions into a simple compact configuration is quite promising but has not been reported. The phase modulator to have stability and high linear advantages than traditional intensity modulator, but the phase modulation signal can not be detected,need to be transformed into intensity signal. This will produce another problem, intermodulation distortion. According to the practical application requirements, a method of restraining link distortion and simultaneously frequency conversion phase shift is proposed. The main research points are as follows:1.Research on intermodulation distortion suppression technology.adding compensation path strategy is firstly achieved on PM-MPL by bi-directional phase modulation. Two lightwaves at different wavelengths are injected into a traveling-wave phase modulator in opposite direction.After FBG, up sidebands of a lightwave and down sidebands of another lightwave are filtered out. Remained optical sidebands of the wavelengths will generate two electrical signals with natural and accurate ? phase differences between them. Thus, IMD3 can be counteracted by adjusting the optical power ratio and modulation depth of the two lightwaves. Experimental results demonstrate that IMD3 can be suppressed by 28.6 dB, compared with the traditional single sideband phase modulation system2.Research on photonic downconversion and phase shift. A microwave photonic frequency downconversion system with wideband and continuous phase shift function is proposed and experimentally demonstrated. In proposed system, radio frequency (RF) and local oscillator (LO) signal drive two arms of a dual-drive Mach-Zehnder modulator (DMZM), respectively.A fiber Bragg grating (FBG) is used for reflecting the 1 st order sidebands of both RF and LO signals. Due to phase independence between RF and LO optical sidebands,phase-shifting operation for output intermediate frequency (IF) signal can be implemented either by adjusting the bias voltage of DMZM or by controlling optical wavelength of laser. Experimental results demonstrate a full 0°to 3600° phase shift while RF signal between 12 GHz to 20 GHz is downconverted to IFs below 4 GHz. Phase deviation ismeasured less than 2° and fluctuation of magnitude response is measured less than ±1dB over a wideband frequency range.