Research On Key Technologies Of Microwave Photonic Receiving Front End

The communication technology based on microwave photonics,with its advantages of multifrequency band,large bandwidth,light weight,small size,and anti-electromagnetic interference,is expected to be applied in many fields such as radar,reconnaissance,satellite communication,broadband wireless communication and so on.This article has launched an in-depth study on the important part of the wireless communication system-the receiving front-end part.Due to the limitation of the electronic bottleneck of the traditional electronic receiving front-end,the signal reception of high frequency band and large bandwidth often requires a very complicated receiving structure,large volume and weight,high power consumption,and poor system reconfigurability.Although the reception front-end based on microwave photons has inherent advantages for the above factors,most of the currently reported solutions also have obvious shortcomings.In terms of function: most mixing schemes have a single function and cannot adapt to complex receiving environments,such as radars and reconnaissance receivers that require beamforming;in terms of performance,multi-dimensional considerations are required,such as system gain,noise figure,nonlinear optimization,etc.This article focuses on these issues and studies the technical points involved in the reception front-end such as mixing,phase shifting,linear optimization and dispersion compensation,and has achieved the following innovative results:Aiming at the front-end mixing technology of microwave photon receiver,a new scheme of microwave photon mixing and phase-shifting is proposed.In this scheme,an integrated dual polarization quadrature phase shift keying modulator is used to realize the double sideband modulation for raido frequency signals and the single sideband modulation for local oscillator signals,and the polarization multiplexing is realized for both.Based on the principle of introducing phase difference to the orthogonal polarization state by the polarization controller,a tunable phase shift is introduced to the mixed signal in the range of0 to 360 degrees.It realizes the organic combination of microwave photon mixing and phase shifting,and has potential application value in beamforming network,vector signal in-phase(I)and quadrature(Q)demodulation and other directions.Because of the single sideband modulation of local oscillator signal,the system overcomes the problem of power periodic fading caused by fiber dispersion,and makes the system more compatible with fiber transmission.At the same time,the effectiveness of the scheme in the vector signal IQ demodulation is verified by experiments.The quaternary phase shift keying and hexadecimal quadrature amplitude modulation signals are demodulated,and the demodulation constellation is obtained.Aiming at the optimization technology of microwave photonic receiving front-end and transmission link,a scheme of simultaneous linear optimization and fiber dispersion compensation based on polarization modulator is proposed.The odd and even order polarization separation of modulation sideband is realized by using polarization modulator.The generation mechanism of nonlinear optical sideband and the phase change caused by fiber dispersion to different sidebands are analyzed,and the phase difference of orthogonal polarization state is introduced by using polarization controller By optimizing the nonlinearity and dispersion,the spurious free dynamic range of the system can be improved by at least 10 dB;a comprehensive optimization scheme based on dual polarization MachZehnder modulator is proposed,which significantly optimizes the gain and noise of the system by controlling the direct current bias voltage of the modulator,the phase difference of the orthogonal polarization state and the polarization direction of the polarizationmultiplexed signal,as well as the dispersion,nonlinearity and carrier sideband ratio The system optimization is applied to the front end of the receiver,and the optimal values of radio frequency attenuation and polarization angle are obtained by using Lagrange extremum method at the same time of down conversion,so as to complete the optimization of nonlinearity.By adjusting the direct current bias voltage of the main modulator,the fiber dispersion is compensated.By adjusting the sub modulation bias voltage,the system gain is improved.Aiming at the disadvantages of traditional channelized receiver,such as poor channel isolation,poor channel consistency and low demodulation efficiency,a super-efficient channelized receiver based on signal polarization multiplexing is proposed.The proposed scheme uses 4-wire radio frequency optical comb and 3-wire local oscillator optical comb to realize 12 channels demodulation.Compared with the traditional scheme,the utilization ratio of optical comb is increased to 2-4 times;due to the polarization multiplexing of signal,the occupied spectral range is reduced to more than half of the traditional scheme.Using dual output image suppression demodulation structure and integrated dual polarization coherent receiving board,not only reduces the use of devices,reduces the cost and complexity of the system,but also makes the system more stable.Finally,the scheme uses a simple digital signal processing algorithm to effectively solve the difficulty of IQ amplitude and phase imbalance in the case of broadband signal IQ demodulation reception,and improves the channel isolation,spurious suppression and other indicators.In order to solve the problem of poor isolation between channels caused by poor polarization isolation,the polarization beam splitter(polarization extinction ratio is 50 dB,bandwidth is 60 nm)or silicon polarization beam splitter(polarization extinction ratio is up to 40 dB)of dual core photonic crystal fiber is proposed to replace the polarization beam splitter with poor polarization extinction ratio in the original system,so as to improve the isolation index.The system has simple structure and strong scalability,which provides a theoretical basis and key technical support for the future microwave photonic channelization reception.