Research On Digital Linearized Microwave Photonics Link Based On Coherent Optical Detection

With the progress of technology,the development of society,the demand in communication capacity has also been gradually increasing.The pursuit for long-distance transmission of broadband signal and high-performance parallel processing has promoted the research on related technologies no matter in radar,electronic warfare or communication systems.Microwave photonic technology,as a newly emerging technology that combines photonics and microwave technology,can realize many advantages of signal transmission and processing such as low-loss in ultra-high-frequency signals,channel parallel without interference,anti-electromagnetic interference and so on.The frontier research on microwave photonic technology is to realize a large dynamic range,ultra-broadband microwave photonics links to meet today's information processing needs of high-speed,high-capacity and integration.In response to this demand,this paper studies and designs a digital linearized microwave photonics link system based on coherent optical detection,which makes the spurious free dynamic range(SFDR)greatly improved.This scheme uses coherent optical link which provides greater SFDR than the conventional intensity modulation direct detection(IMDD)link.This scheme uses carrier-suppressed single-sideband modulation combined with coherent optical balanced detection to reduce common mode noise and increase system gain.As for the digital nonlinear compensation algorithm,a universal nonlinear compensation model is constructed by acquiring the third-order interrupt point,and taking it as the distortion compensation signal.Compared with the traditional analog linearization algorithm,the complexity of distortion compensation is reduced to a great extent,without constructing extra nonlinear compensation link,and also the matching delay between optical link and compensation optical link need not to be considered.Compared with the traditional digital linearization algorithm,it also does not need to estimate parameters of the distorted link in the digital domain accurately,such as the operating point of the modulator,the half-wave voltage of the radio frequency,and the gain of the link,which greatly reduces the dependence on link parameters and the complexity of algorithm implementation.In view of the proposed system,this paper has carried out the theoretical derivation and mathematical simulation,and set up an experimental platform for feasibility verification.The experimental results show that the SFDR of the link in the 12-36GHz wideband range is better than the traditional IMDD link,improved nearly 15dB.The proposed system overcomes the technical shortcomings of the traditional nonlinear compensation scheme based on the additional construction of the distorted optical link,which not only simplifies the implementation of the linearized optical link,but also has universal applicability.