Studies On Photonic RF Phase Shift Technique Of Microwave Photonic Signal Processing

With the development of broadband wireless access networks, sensor networks, radar, satellite communication, instrumentation, warfare systems and astronomical detection for high frequency, high-bandwidth, large dynamic range and broad geographical distribution, it is a new challenge to improve the performance of the millimeter wave devices. Microwave photonics is an interdisciplinary area that studies the interaction between microwave and optical signals for microwave and millimeter-wave signal generation, distribution, control and processing by means of photonics. It is generally regarded as an effective way to deal with the aforementioned challenges and the consequent scientific issue has become cutting-edge research of the microwave photonics. Microwave photonic signal processing is a photonic subsystem designed with the aim of processing microwave and millimeter-wave signal, bringing supplementary advantages inherent to photonics such as low loss, high bandwidth, immunity to electromagnetic interference, and also providing features which are difficult to achieve with traditional technologies, such as fast tunability and reconfigurability.These works are supported by the National Basic Research Program of China (973Program). The dissertation focuses on the technology of optical true-time-delay and photonic RF phase shifter in microwave photonics photonic signal processing. The main contributions of the dissertation are as follows: (1) Research on optical true-time-delay (OTTD) in optical beam-forming network (OBFN). OTTD, with key advantages such as immunity to electromagnetic interference (EMI), low loss, small size and light weight, are being considered as a promising alternative for wideband phased array antennas. A two-dimensional (2D) OTTD beam-forming system using a compact fiber grating prism (FGP) for a planar phased array antenna (PAA) is proposed. The optical beam-forming system mainly consists of the OTTD units based on the same compact FGP, one tunable laser for elevation beam steering, and a wavelength-controlled converter for azimuth beam steering. A planar PAA using such2D optical TTD unit has advantages such as compactness, low bandwidth requirement for tunable laser sources, and potential for large-scale system implementations. The proof-of-concept experiment results demonstrate the feasibility of the proposed scheme.(2) Research on the balance and control of optical power in OBFN. In actual OBFN, the responses of the various optical devices are inconsistent, for instance, coupling coefficients of optical coupler at the different wavelength signals are different, the gain of optical amplifier at the different wavelength signals is inconsistent, the insertion losses of optical filters at different wavelengths are different, and the impact of non-linear devices. All these will inevitably lead to the optical signal power differences, which could deteriorate the performance of the OBFN. The problem is serious especially in the large-scale optical-controlled phased array antenna. A method for the banlence and control of optical power is proposed to achieve the balance and control of the different channels. The improvement of the performance with the control of the optical power is proved by simulation.(3) Research on the photonic RF phase shifter. The requirements of phase shifter include the ability to achieve full phase-shift range of0～360°while keeping the amplitude of the RF signal constant, fine tuning resolution, operation over a wide bandwidth, simple implementation, low cost, lightweight, and small size. A new photonic RF phase shifter based on homodyne mixing principle is proposed. It can achieve a full360°phase shift with very little RF signal amplitude variation, and which can operate over very wide frequency range of22-70GHz.(4) Research on the photonic RF phase shifter based on Fourier-domain optical processor (FD-OP). Optical spectrum processing (OSP) is a general method for microwave photonic signal processing, which represents signal in Fourier-domain and explores the spectrum evolution of an arbitrary signal in the process of electro-optical/optical-electric conversion and transmission. It can carry out operations for any spectral components to achieve the functions of microwave photonic signal processing. Programmable RF photonic phase shifter that can achieve a full360°phase shift with little RF signal amplitude variation and low noise is presented. It is based on a two-dimensional (2D) FD-OP comprising an array liquid crystal on silicon (LCoS) pixels to control the amplitude and phase of the multiple RF modulation sidebands by programming and realize multiple photonic RF phase shifters simultaneously applied in optical controlled phased array antennas. Experimental results show the RF phase shifter can achieve a continuous0～360°phase shift with low amplitude variation of <2.5dB and a phase deviation of<2°at15GHz.