Research On Wideband Highly-linear Analog Photonic Link For Distributed System

With the development of RF information system towards broadband and high-frequency,it becomes an important trend for the central office in connection with the remote base station by using Analog photonic link(APL)in the distributed system.Due to the advantages of low loss,wide working bandwidth,light weight and immunity to electromagnetic interference,APL is suitable for wideband and highly-linear transmission which can improve spurious free dynamic range(SFDR).APL in the distributed system is reconfigurable for signal and has advantages of rich wavelength resources and parallel processing ability which makes the system update convenient.The nonlinear distortions falling into the working band limit the system performance.Thus wideband highly-linear APL is important for the performance improvement in the distributed system.The research direction of this paper is the wideband highly-linear APL for distributed system,and new methods are proposed in wideband highly-linear APL and building analytical model.The main research contents of this paper include the following three aspects:1.A linear phase-modulated photonic link based on optical carrier band processing is investigated.Considering the chromatic dispersion and by using a programmable spectral processor to impose appropriate phase shift to the optical carrier band,the IMD3 term is power faded and suppressed after transmitting over 20 km fiber.Meanwhile the fundamental signal is reserved.The SFDR is improved to 103.04 dB·Hz2/3 at central frequency of 14.1 GHz,showing that an improvement of 10.96 dB higher than the traditional phase modulated link.At central frequency of 18 GHz,an improvement of 12.25 dB is achieved,leading the SFDR of the proposed link to 102.25 dB·Hz2/3.2.A multi-octave highly-linear analog photonic link with simultaneous suppression of second-order intermodulation distortion(IMD2)and third-order intermodulation distortion(IMD3)is proposed and demonstrated based on a single integrated polarization-multiplexing dual-parallel Mach-Zehnder modulator(PM-DPMZM).An experiment is carried out.Simultaneous suppression of IMD2 and IMD3 is achieved.The second-order spurious free dynamic range(SFDR2)and third-order spurious free dynamic range(SFDR3)are 82 dB·Hz1/2 and 110 dB·Hz2/3,respectively,indicating an improvement of 12 dB in SFDR2 and 13 dB in SFDR3 as compared with the low-biased Mach-Zehnder modulator(MZM)based analog photonic link,or an improvement of 3 dB in SFDR2 and 16 dB in SFDR3 as compared with the quadrature-biased MZM based photonic link.3.The analytical models to characterize the performance of polarization-modulation-based APL is proposed and the expressions of arbitrary order harmonics and intermodulation products of the received signal under single tone and two tone transmission are derived.The cases of intensity modulation,phase modulation and polarization modulation with compensation of the dispersion induced power fading are analyzed and the differences of the key parameters including gain,noise,noise figure,input intercept point and SFDR in these cases are compared.The developed analytical models provide an accurate mathematical tool in designing high-performance polarization-modulation-based APL.