Research On Silicon-based Integrated Grating Coupler And Its Polarization-Independent Characteristic

With the rapid development of integrated optics and silicon photonics, the micro/nano grating device has attracted increasing interest due to its compactness, multifunction and easy fabrication. As a coupling device in integrated optics, grating coupler has many advantages, such as high coupling efficiency, loose coupling alignment, low cost of fabrication and packaging, no necessity of face polishing, support for wafer-scale testing, etc. Thus it has become the most promising method for integrated optics.The micro/nano scale of integrated optics results in polarization sensitivity of many integrated optical devices which may reduce the working stability of integrated optical system. Researches on polarization independence of integrated optical devices have attracted increasing attention and there has been much progress on it. However, polarization independent grating coupler is still a hard task to accomplish.Supported by"National Natural Science Foundation of China", theoretical and experimental studies on silicon-based integrated grating couplers are implemented and some researches and creative proposals on silicon-based integrated polarization -independent grating coupler are also achieved as following:(1) In this thesis, the theories and the fabrication and testing methods of grating couplers are introduced. A vertically-coupled input grating coupler and an output grating coupler are designed and optimized. Some results on the fabrication and testing of grating couplers are shown and discussed. Using thermal oxidation reduced the roughness of etched grating surface from 11 nm to 5 nm. The application of grating couplers in silicon-based hybrid integration and some fabrication results on it are presented.(2) A highly compact T-shaped polarization-independent grating coupler is proposed. Over a broad band of 1510 nm-1580 nm, the polarization dependence loss (PDL) of the device is lower than 0.05 dB and the coupling efficiencies for both TE and TM modes are higher than 50%. High-efficiency polarization-independent coupling is achieved.(3) A compact polarization-independent silicon-based hybrid integrated photodetector is accomplished by using the T-shaped grating coupler. Over a broad band of 1490 nm -1560 nm, the PDL of the device is lower than 0.05 dB and the coupling-in-active-layer efficiencies for both TE and TM modes are higher than 80%. Polarization independence of the photodetector is achieved.(4) Another method of realizing polarization independence, polarization beam splitting is introduced. A polarization beam splitter (PBS) based on a slot-groove grating is proposed. Over a broad band of 1530 nm-1630 nm, the extinction ratio (ER) of the PBS is higher than 15 dB and the device has accomplished polarization beam splitting function.