Fabrication Optimisation Of Polymer Integrated Photonic Devices And Their Applications

The great potential of photonic integration has been recognized more and more by scientists and engineers. The micro chips that integrate photonic, electronic and possible fluidic functions are expected to play an important role in optical communication and optical biosensing, which will have a deep impact on the life of people. So far, photonic integration has been implemented on several material platforms. As one of them, polymer receives much attention due to some of its unique features such as low cost and easy processing. This thesis is dedicated to the development of an ideal platform, on which different kinds of integrated photonic devices with high performance can be fabricated in a fast and efficient way with the cheap polymer material. As a further step, several applications in optical communication and optical sensing are found for the devices obtained from this platform. In the following, we briefly summarize our work.Considering that many of the commercially avaible polymer photonic materials are expensive and some of their properties are still not satisfying, the aunthor and his group developed an innovative polysiloxane polymer material named PSQ-Ls. Easy synthesis is a big advantage for the polymer. The self-developed material exhibits good optical properties (e.g. low optical loss, low birefringence, high thermo-optical coefficient and so on) and thermal stability (e.g. high degradation temperature). Being UV curable and solvent-free are unique features of this material. These material characteristics enable polymer PSQ-Ls to be a good candidate for the further fabrication of polymer waveguides and devices.We explore different fabrication processes, trying to find an appropriate way to process the developed polymer PSQ-Ls into waveguides and devices. Conventional lithography and dry etching method is experimentally feasible, but is considered to be unsuitable because of the complicated fabrication process. Thus a simple UV-based soft imprint technique compatible with polymer PSQ-Ls is developed. Critical issues such as waveguide roughness and residual layer thickness are solved and discussed in detail. Different kinds of polymer-based optical devices can be fabricated in this fast and efficient way. The obtained devices exhibit good optical performances, which are highly desired for our subsequent applications. The Q value of the microring resonator is as high as5×104, which is among the highest reported value so far.Optical label-free biosensing is realized with the polymer microring resonator with high Q value. We discuss the sensing mechanisms, the interrogation methods and the design considerations for this kind of device. Special attention was paid to the performance of the microring resonator working in aqueous environment. A simple but efficient surface functionalization protocol based on physical adsorption is developed for the polymer microring resonator, avoding the multi-step modification process usually required by the devices of inorganic material. Both surface sensing and bulk sensing are realized with the solution delivering capability provided by the fluidic channel, which is assembled on the chip of polymer microring resonators with the "stamp-and-stick" method. For surface sensing, specific targeted analyte with a concentration as low as5μg/mL was detected. For bulk sensing, a sensitivity of around50nm/RIU is achieved with a NaCl solution.Considering the potential application of polymer integrated photonic devices on multiplexed sensing, we investigate a new coupling mechanism for polymer waveguides, surface coupling. We proposed a new structure, in which a thin layer of Si3N4with high refractive index is embedded between the waveguide core and the under cladding. By doing this, the coupling between the polymer waveguide and the single-mode fiber is demonstrated for the first time, with a coupling efficiency of around12%. Compared to the edge coupling route usually adopted for the polymer waveguide, the surface coupling regime is more flexible with relaxed alignment tolerance, which would be of great use for the further development of a multiplexed biosensing system with polymer-based photonic devices.The temperature problem for integrated photonic devices is considered and discussed. Special attention is paid to realize the athermalization for one of the most important WDM components, the arrayed waveguide grating (AWG). Taking advantage of a proper design, a state-of-the-art CMOS fabrication technique and a high thermo-optical coefficient of the PSQ-Ls polymer, the temperature dependence of the AWG is reduced to only-1.5pm/℃, while maintaining the good filtering property of the device. So far, we have realized athermalization for several key optical components, which include MZI, microring resonator and AWG. These optical components will play an important role in future high-level electrical-photonic integration systems.