Research On Linearization Technology Of Broadband Analog Photonics Link

With the construction and development of the integrated information network covering the whole world, the communication demand for large capacity, high bandwidth and low loss is becoming more important. The microwave photonic technology, which combines the flexible advantage of microwave and the broadband of optics, can break through the electronic bottleneck of limited bandwidth, and realize the complicated function that is difficult to be done by traditional RF link, and provide the technical support for future integrated information processing. Now the analog photonics link system is developing in the direction of ultra-wideband, multi-carrier, high-performance, and promoting the analog photonics link to realize the goal of multi-band, large spurious-free dynamic range (SFDR), and high performance. However, the current technical challenges of linearized analog photonics link are as follows:Firstly, multi nonlinear distortions coexist, which seriously limit the SFDR of the link; Secondly, the ideal linear demodulation is difficult to be preserved due to the limited bandwidth of signal receiver and ADC; Thirdly, the low bias angle of modulator easily drifts away when the link is deeply modulated. Based on the above technical challenges, focusing on nonlinear distortions compensation, the ideal linear demodulation, and bias stabilization, a deep-in-sight research has been carried out in this dissertation. The innovative works of this dissertation are presented as follows:1. A novel simple dual wavelength linearization approach based on polarization modulator is put forward, which can eliminate the third-order intermodulation nonlinear distortion (IMD3) of narrow-band analog photonics link. In the scheme, the analog signal is intensity and orthogonally modulated on a pair of co-propagated photonic links, i.e. one of the two intensity modulations has a bias angle which is 90-degree difference from the other. At the digital signal processing (DSP) unit of analog photonics link, 26.8 dB suppression of the IMD3 distortion is achieved, and the SFDR is improved by 8 dB. The proposed scheme has a simple structure and flexible algorithm, and it meets the linearization requirement of narrow-band analog photonics link.2. An effective linearization approach is demonstrated, which can suppress the multi nonlinear distortions of broad-band analog photonics link. In the scheme, the nonlinear compensation information is directly obtained from hardware then the distortion compensation is carried out in the digital domain.And experiment results show that the cross-modulation distortions (XMD) and IMD3 distortions are suppressed with 36.6 dB and 25.8 dB, respectively, and the link dynamic range is improved by 25 dB. This scheme is expected to meet the linearization requirement of broadband analog photonics link.3. To realize ideal linear demodulation in high-carrier application, a novel photonic-bandpass-sampled polarization-modulated RF link with in-phase/quadrature (I/Q) demodulation is proposed, which is capable of multi-carrier down-conversion and digital linearization of multiple co-exist nonlinear spurs. When apply two dual-carrier RF signals as input, and 30 dB suppression of multiple nonlinear spurs is achieved, and the dynamic ranges of target IF signals are both 118 dB·Hz2/3. This approach is a promising candidate for achieving large SFDR of broadband analog photonics link.4. To overcome the bias angle drift issue of low biasing the Mach-Zehnder Modulator (MZM) for deeply modulated analog photonics link, a novel dither-free low bias control technique is presented. The scheme is based on reversely transmitting and power locking a lightwave in the MZM. When the input RF power is scanned from 0 dBm to 20 dBm, the proposed scheme still works well.MZM bias locking at a low-bias position (about -81 °) with phase deviations less than 2.6° is achieved even when the modulation depth is as high as 2. The proposed scheme is very simple and suitable for any bias points.In all, this dissertation solves the problem of nonlinear distortions and bias angle drift issue for deeply modulated analog photonics link, and release the pressure of limited bandwidth of the devices, which is expected to be used in cooperative communication system, signal processing and the integrated RF system.