Abstract

The development of wireless communication services requires broader access bandwidth. To meet this requirement, unlicensed millimeter wave (mm-wave) band has been considered as a potential carrier for the next generation wireless communications. However, due to high attenuation loss in mm-wave signal transmission, the number of the picocell base station (BS) should be increased in the coverage area. Radio over fiber (RoF) transport scheme is a good option to face the challenge of mm-wave wireless distribution, because it takes advantages of long transmission distance, large bandwidth and immunity to electromagnetic interference. In RoF technique, optical mm-wave signal generation is one of the crucial issues. There are two major schemes to generate optical mm-wave signals, optical heterodyning technique and optical frequency multiplication (OFM) technique, in which OFM technique can provide simpler BS configuration. One of the most popular OFM techniques is optical harmonic generation using optical external modulators. There are mainly two options of external modulator: one is Mach-Zehnder Modulator (MZM) and the other is Electro-Absorption Modulator (EAM). The objective of this thesis is to propose a novel photonic frequency doubling and quadrupling technique for the generation of mm-wave signal using two cascaded EAMs. The two cascaded EAMs driven by a low frequency radio frequency (RF) signal and the phase shift between the two EAMs is 180 degree. Theory of techniques using two cascaded EAMs with identical characteristics and two cascaded EAMs with different characteristics is investigated and verified by simulation based on VPI Transmission Maker. Good agreement is achieved between theory and simulation. It is shown that power of doubling and quadrupling signal is increasing with RF modulation index, and bias voltages of EAMs also have a great impact on the performance of the system. It is found that by using cascaded EAMs with identical characteristics, odd-order optical harmonics are perfectly suppressed while even-order harmonics are maximized, and as a result high quality frequency doubling and quadrupling signals can be generated; by using cascaded EAMs with different characteristics, good system performance still can be achieve when phase shift, RF modulation voltage and bias voltages are optimized. Power fading induced by fiber chromatic dispersions is also investigated and an optical filter is adopted in order to make the system immune to chromatic dispersions at frequency quadrupling. Experiment is also carried out to verify the concept of the proposed technique. A low cost electro-absorption modulator integrated laser (EML) is used in experiment to achieve a cost-effective system. Good quality doubling signal and quadrupling signal are generated while noise level is reasonable. It suggests that the proposed technique is efficient for mm-wave generation using frequency doubling or quadrupling