Research On All-fiber Modulating Components Based On Graphene Materials

The optical modulator is the core device in the high-speed optical communications and also has great applications in the fields of wireless communications, sensing detect systems and integrated optics. According to the principle, modulators can be divided into different categories:electro-optic modulator, acousto-optic modulator, thermo-optic modulator and all-optic modulator, etc. By adjusting the voltage or electrical field onto the electro-optic material, the optical properties of electro-optic modulator will experience the according change, such as the index, loss and phase, etc. Within all the electro-optic material, LiNbO3 outstanding with advantages of high operation bandwidth and zero chirp. However, with the rapid development of the high-speed communications, modulators are required with higher modulation bandwidth, lower half-wave voltage and more compact size, thus modulators with new material has attracted a lot of interest.This dissertation has made in-depth research on the all-fiber devices based on the new material graphene. First it gives a detailed conclusion about the conventional modulators and their applications in the RoF system, and propse a novel technique to realize the high modulation bandwidth with current conventional LiNbO3 modulator by using it in the 40GHz millimeter-wave communication system. However, in the future RoF system, to further reduce the size and half-wave voltage of the modulator as well as increase the modulation efficiency, the new material graphene has come into sight, after studying the optical properties of graphene and the graphene waveguide modulators, we have a detailed analysis about the graphene-based modulator. Based on this, we have proposed graphene-based phase and absorption modulator with all-fiber structure, and demonstrated it in both theoretical and experimental way. Besides, we have also proposed an all-fiber graphene tunable polarizer, it owns the advantages of large extinction ratio, broad bandwidth and unaffected by the temperature, and it is the first ever designed to realize the tunable polarization states. The major contributions and innovations are listed as follows:1. To meet the requirements of higher bandwidth, lower half-wave voltage and better integrated with photonic circuits, research on the application of the new material graphene in the modulator area has been conducted and some drawbacks have been pinpointed. The difference caused by the choice of anisotropic or isotropic property of graphene is especially discussed, to make it more precise, graphene is treated as the anisotropic material.2. Graphene-based all-fiber modulator is proposed with the combinative integration of graphene and all-fiber structure, by using the change of the real and imaginary part of the effective mode index, and we also have the analytical and numerical calculations of the proposed model. Besides, two dimensional and three dimensional simulation are both conducted to ensure the accuracy. Analytical method is also employed to ensure the accuracy of the simulation results. It is the first ever reported that under some conditions, phase and chemical potential display the quasi-linear relationship; Compared with conventional absorption modulators,our proposed absorption modulator outstands with higher extinction ratio and compact size.3. We demonstrated the proposed all-fiber graphene modulator in experiments, including all the detailed steps such as the structue design of the proposed modulator, the transfer of the graphene and the design of the electrode. A RoF system is set up and signal is successfully modulated. Results discussion and optimizing methods are both given.4. A graphene-based all-fiber tunable polarizer is proposed, graphene is coated onto the fiber surface, by changing the direction of the voltage onto the graphene, either a horizontal-pass or perpendicular-pass polarizer is achieved. It is the first time ever reported that a all-fiber structure polarizer can be made polarization-selective tunable. Besides, compared with other polarizer, our proposed one outstands with higher extinction ration, broad operation waveband and unaffected by the temperature.This dissertation is mainly focused on the all-fiber modulating components based on graphene materials, proposing two kinds of all-fiber graphene modulators and one kind of all-fiber graphene polarizers. In the aspect of the research method, theoretical modelling, simulation analysis, experimental demonstration and results discussions are used, some achievements are obtained, however, limited by the current experiment conditions, some achievements are still to be experimentally investigated.