Studies On Millimeter Wave Radio-over-Fiber Key Technology

Microwave photonics can be defined as the study of interactions between optical signals and electrical signals in the frequency range of microwave and millimeter-wave, and this field has been growing very rapidly since 1970s. There is much current interest in the use of fiber optical technology to support the generating, processing and distributing of millimeter-wave signals. Most of the applications for these systems are communications oriented. Research and development has already started on these systems, especially for radio-over-fiber systems with spectral allocations in the region of 60GHz.Optical millimeter-wave (mm-wave) generation is a key technique in radio over fiber systems. In this paper, a wideband continuously tunable mm-wave signal with sextuple-frequency multiplication of a microwave source is obtained by an optical LiNbO₃ intensity modulator cascaded with a semiconductor optical amplifier. And the mm-wave signal is high-spectrum-purity and low-phase-noise. Furthermore, we theoretically analyzed and experimentally demonstrated a novel mm-wave generation method for radio-over-fiber systems. By using optical carrier suppression (OCS) modulation scheme in two cascaded intensity modulators and a semiconductor optical amplifier, millimeter wave signals with 12-times frequency multiplication of a microwave source are optically generated. To enlarge the multiplication index, the thesis proposed another mm-wave generation method that mm-wave signals with 18-times frequency multiplication of a microwave source are generated by using intensity modulator and two cascaded semiconductor optical amplifiers. These methods were all experimentally proved, and a wideband continuously tunable mm-wave signals from 4GHz to 43GHz were obtained.After full study of optical fiber chromatic dispersion influence on the mm-wave signals, the paper proposed an optical mm-wave generation method in which the multiplication index was adjustable. By using optical phase modulator and an optical filter, mm-wave signals with quadruple frequency multiplication or sextuple frequency multiplication of a microwave source are optically generated. This simple method can make the optical mm-wave to be a reliable mm-wave source in radio-over-fiber system.On the basis of optical mm-wave generation technology, we studied the downlink transmission of mm-wave radio-over-fiber system. And the paper proposed that broadband data signals were transmitted in the downlink of radio-over-fiber system by using optical mm-wave signals with frequency multiplication. In the experiment, 2.5Gbps data signals were respectively transmitted over a long-distance single mode fiber without compensation of chromatic dispersion by using optical mm-wave signals with double frequency multiplication or sextuple frequency multiplication. The results of the experiments can be merited in the commercial mm-wave radio-over-fiber systems.All optical mm-wave up-conversion and all optical mm-wave down-conversion are also key techniques in mm-wave radio over fiber systems for wireless transmission. Based on the four-wave-mixing effect in the high nonlinear fiber, we proposed new schemes to optically up-convert the mm-wave and to optically down-convert the mm-wave. Both schemes were simulated by software and proved by experiments in this thesis. In the experiment, 2.5Gbps data signals were successfully up-converted to 30GHz radio frequency carrier, and transmitted over a long-distance single mode fiber. And moreover, the 2.5Gbps data signals were also successfully down-converted from 30GHz radio-frequency carrier to 6GHz intermediate frequency carrier in the experiment.