Study Of Graphene Assisted Integrated Optical Devices On Glass

With the rapid development of the high-speed, large-capacity optical communication systems, the optoelectronic devices, especially the integrated optical devices, used in the systems are confronted with grim situations. The glass-based optical devices are widely used in the fabrication of wavelength division multiplexer (WDM), optical power splitters, optical amplifiers and so on, owing to its advantages such as low cost, simple process, easy to mass production. However, the weak electro-optical and thermal-optical properties of the glass subsrate make it difficult to realize the active optical device which limits its application in the integrated optical devices.In recent years, graphene, which demonstrates excellent physical properties, has attracted enormous scientific interest. Graphene, the two-dimensional crystal material, is a monolayer of carbon atoms packed into honeycomb lattice. Its extraordinal electron mobility, the exceptional optical absorption independent of frequency over a wide range and high transmittance make gaphene a potential material for integrated optical devices. Furthermore, graphene hybrid waveguide based integrated optical devices, such as modulator, polarizer, photodetector and so on, showed exceptional properties.In summary, the main research of this dissertation focused on combing the excellent properties of graphene with glass to realize integrated high-performance and low-cost graphene assisted integrated optical devices on glass. Both theoretically and experimentally, mainly including graphene/glass hybrid waveguide polarizer and photoconductive detector were studied. A resolution is proposed to realize active optical devices on glass substrate, which has a potential application in the integrated optical devices. The main contents and innovations are listed as follows:1. An improved backside mask fabrication process of the selectively buried waveguide was proposed. To realize the hybrid integration of the graphene and the glass waveguide, the selectively buried waveguide is necessary owing to its low insertion loss and consisting of surface waveguide. Therefore, an improved fabrication process is proposed in this dissertation, in which the backside electrode film is used to accurately control the structure of the waveguide and the backside dielectric mask is used to shield the electrical field. A selectively buried waveguide with the transition portion loss of only 0.28 dB at the wavelength of 1550 nm is fabricated by this process. The improved process is more stable and more accurate in controlling the waveguide structure. And the model of the selectively buried waveguide was proposed by analyzing enormous experimental results. This model is the basis of the graphene/glass hybrid waveguide and the selectively buried waveguide optical sensors such as temperature and refractive index optical sensors.2. A broadband graphene/glass hybrid waveguide polarizer was proposed. The graphene has an opacity of 2.3% which is independent of frequency over a wide range. The polarizing effect of the polarizer is based on the difference in the attenuation between the fundamental TE mode and the TM mode. And the deference between them will increase if the chemical potential of the graphene decreases. In this dissertation, the hybrid waveguide polarizer is demonstrated and the PMMA is used to decrease the chemical potential of the graphene, which will increase the extinction ratio of the polarizer. The polarization extinction ratio of the polarizer is about 27 dB in the telecommunication band with about 4-mm graphene coating length along the propagation direction. This improved the operating wavelength range of the polarizer based on glass.3. A graphene/glass hybrid waveguide photoconductive detector was proposed. In highly doped graphene, the photoabsorption leads to an increase of the temperature of the electrons, which will decrease the effective Fermi energy. And this leads to a decrease of the effective carrier density, therefore, the conductivity of the graphene will decrease. The measurement results indicate the responsivity of 0.75 A/W at 0.1 V bias voltage at the wavelength of 1510-1630 nm with about 4-mm graphene coating length along the propagation direction. This provides a new way to realize the active optical devices based on glass substrate.