Studies On Modulation Techniques And Performance Of Optical Beam-Forming Networks

Microwave Photonics is a discipline focused on the interaction of optical signals and electrical signals in the microwave and mm-wave band. The optical beam- forming networks (OBFN), as one of the important area in microwave photonics, is considered to be a promising key technology for future smart antennas and wideband phased array antennas (PAAs). By controlling the phase difference or time delay between different links in the array, the radiation from each microwave radiator has maximum interference at far field in certain directions, to achieve directional emission (receive) of the signal. OBFN offers many outstanding advantages, such as small size, low loss, electromagnetic immunity, large bandwidth and squint-free array steering. Based on the key technologies in the OBFN, this thesis proposed new ideas and methods aiming the dispersion induced power fading, suppression of modulation nonlinearity and expanding the dynamic range of the system. These works are supported by the National Natural Science Foundation and National Basic Research Program of China (973 Program).An integrated and stable subcarrier phase modulation technology is proposed to eliminate dispersion induced power fading. The analog phase modulation and digital phase modulation is achieved in the optical field, as well as simultaneous multi-channel differential phase shift keying (DPSK) of 1.25Gbps signal at 40GHz carrier. A carrier phase shifting technology is also proposed and demonstrated. By independently controlling the phase of the optical carrier in a modulated optical signal, the relationship between the carrier and sidebands are changed at the transmitter side. The carreier phase shifting (CPS) technique could give the system the best transmission band with small in-band flatness. Experiment verified that using CPS technique, a 0.5dB flatness is achieved for a 39-km link in the frequency band from 5.4GHz to 8.4GHz.A new modulation distortion cancelling technique is proposed. By controlling the biases in a single-drive dual parallel Mach-Zehnder modulator, the dispersion from two different origins cancel each other out, and lead to an excellent dynamic range. It is then combined with the up-conversion technique, to build a highly linearized up-conversion RoF link in mm-wave band. The SFDR of these techniques can reach 122 dB?Hz2/3. Considering the OBFN that utilizing broadband light source, the limitation on dynamic range is analyzed. A low-bias method is proposed to increase the signal-to-noise ratio and extend the dynamic range. Experimental results showed that an increase of SFDR of 10dB to 80.6 dB?Hz2/3 is achieved.An X-band OBFN that had 4 channels and 5-bit delay is also under-investigated. A prototype of the OBFN is made with a delay range of 1.6ns. The power and delay deviation between the 4 channels are below 0.5dB and 0.5ps, respectively. An automatic measurement platform is built to calibrate and measure the OBFN. The beam-sweep of the OBFN is also achieved using this platform. Based on the highly liniearized mm-wave modulation technique, a four-channel highly linearized mm-wave beam-forming network is designed. An experiment is demonstrated to verify this design by examining an mm-wave optical delay-line, which consists of 44 delay states with a maximum delay of 900ps. The SFDR of this system is 102.8 dB?Hz2/3.These specifications reach and surpass the requirement of the above projects, of which the National Natural Science Foundation project is completed and has been evaluated as level A with acceptance.