Polymer-based Optical Waveguide Devices

Polymers are emerging as an important material in the field of integrated optics. As the polymer materials are compatible with several simple fabrication processes, the cost of the optical devices is expected to be lowered down to meet economic criteria. Moreover, the molecular structure of the materials can be designed to fit some application requirements. Once the passive optical polymer technology is established, amplification and electro-optic effects can be easily achieved by selective doping. There are some kinds of optical polymers available in the market. However, the thermal stability is still hindering a wide application of polymer-based devices. Some aspects of the optical polymers still need to be improved for some applications. The objective of this work is to develop some kinds of optical polymers with appropriate properties and apply them in the optical applications.We have successfully developed two main kinds of polymer:PPESK series polymer and PSQ series polymer. The optical properties and other properties are investigated. As the synthesis technology of polymer PSQ-L is mature and the properties of this kind of polymer can meet the basic demands for optical applications, the fabrication technologies are investigated. Apart from the traditional fabrication process of lithography and RIE etching process for optical waveguides, new fabrication technologies like nanoimprint technology are explored here. We have developed a simple fabrication process for PSQ-L waveguides. Simple PSQ-L ring resonators are fabricated in this way. On the other hands, applications of polymer PSQ-L are also being explored. Athermal SOI (silicon-on-insulator) devices have been successfully achieved by overlaying a polymer PSQ-L cladding on top of narrowed waveguides.The thesis includes several parts below:1. We have successfully developed two main kinds of polymer:PPESK series polymer and PSQ series polymer. The polymers are synthesized by our group. Then the polymer films are prepared by the spin-coating process for property tests and further fabrications. The synthesis processes are adjusted to achieve better properties of the materials from the feedback of the property measurements. Finally both series polymer are developed with good optical properties and thermal stability.2. At the first stage the synthesis technology for polymer PSQ-L is mature and the properties of this kind of polymer can meet the basic demands for optical applications, therefore, the design of the polymer ring resonators is based on polymer PSQ-L. By theoretical calculation and simulation, the parameters of waveguides are optimized and PSQ-L ring resonators are designed.3. The fabrication technologies of this polymer are first investigated. Apart from the traditional fabrication process of photo-lithography and etching process for optical waveguides, new fabrication technologies like nanoimprint technology are explored here. A simple UV-based soft-lithography technology has been developed for fabrication of PSQ-L waveguides. Unlike in conventional imprint processes, the imprint step for structuring is done first on the cladding layer rather than on the core layer and is followed by a spin-coating step to fill the imprinted features with core layer material. This waveguide cross-section design smartly avoids controlling the thickness of the residual core layer. Simple PSQ-L ring resonators are fabricated in this way.4. The all-polymer PSQ-L microring resonators have been characterized after fabrication. The round trip loss and coupling coefficient can be extracted by fitting the transmission spectrum by Lorentz function. The estimated scattering loss of the ring waveguides fabricated by photo-lithography and etching process is about 1.6dB/cm. The estimated scattering loss of the ring waveguides fabricated by photo-lithography and etching process is about 1.8dB/cm. The nice resonance spectrum indicates the low absorption loss of the material and appropriate fabrication technique for this material. These devices have potential applications in the optical communications and sensing applications.5. Athermal SOI (silicon-on-insulator) devices, like ring resonators and MZ interferometers have been successfully achieved by overlaying a polymer PSQ-LH cladding on top of narrowed waveguides. The temperature dependence of the resonance wavelength of ring resonators is highly reduced below 5.0±1.0pm/℃, almost eleven time than normal silicon waveguides.