Research On Grating Devices For Silicon-Based Photonic Integration

The research and application of grating has a long history. With the rapid development of the modern integrated optics and especially the development of silicon photonics, the novel micro-nano grating device has attracted increasing interest due to its compactness, multifunction and easy fabrication. Gratings play an important role in modern integrated optics. In this dissertation, researches are focused on grating devices with different functions. The transmission direction, strength and shape of wavefront as the main targets to find out the primary factors for affecting light transmission in the gratings, and the relationship between influencing factors and micro-nano structures. We proposed and fabricated the grating coupler with the tailored artificial refractive index based on the equivalent refractive index method, and designed a high efficiency vertical grating coupler and wavefront manipulation devices, etc. The study can be summarized as follows:(1) We propose and fabricate the apodized grating coupler with the tailored artificial refractive index. With circular and rectangular micro-nano structures, based on the equivalent index method we design the apodized grating that the structure is non-uniform along propagation direction. This can be used to eliminate the mode mismatch between the exponentially decreased diffraction field and the Gaussian profile of the optical fiber for the uniform grating couplers. Our calculation shows the maximum coupling efficiency of 68.2% and a 3 dB bandwidth of 74 nm for the apodized grating coupler and the maximum coupling efficiency coupling e?ciency of 59.4% at 1550 nm and a 3 dB bandwidth of 80 nm for the grating coupler with uniform refractive index. Experiments on the implementation of grating grooves with equivalent refractive index use both subwavelength rectangular holes and subwavelength photonic crystal circular holes. The measurement results show that the peak coupling e?ciency of 47.5% and 49.5%, and 3 dB bandwidth of 67 nm and 69 nm for apodized grating couplers with subwavelength rectangular and circular holes respectively. The measurement results show that the peak coupling e?ciency of 41.8% and 45.2%, and 3 dB bandwidth of 69 nm and 73 nm for uniform grating couplers with subwavelength rectangular and circular holes respectively. With respect to the uniform grating coupler, the coupling efficiency of apodized grating coupler is improved significantly. The improving of coupling efficiency of the apodized grating couplers benefit from the better mode matching between the diffraction field distribution of apodized grating couplers and the mode field distribution of fiber.(2) We propose grating coupler structures for vertical coupling. To resolve vertical coupling between the vertical cavity surface emitting laser and grating, we design a grating coupler structure for vertical coupling based on the metal bonding. The simulation results show that the peak coupling e?ciency of 89.5% is achieved. Furthermore, we design both mirror and grating coupler for vertical coupling based on a subwavelength high contrast grating. the reflectivity of 99% and vertical coupling e?ciency of 0.3% at wavelength 1550 nm are achieved. These works offer two possibilities for the realization of the silicon-photonics light source.(3) We obtain the wavefront shape control method based on rigorous coupledwave analysis, and design the wavefront manipulation devices that are difficult to fabricate in micro-optics field, including a convex lens, an axicon and a serrated blazed grating. The transmittances are 97%, 97.9% and 97.5%, respectively, and these devices achieve good focus and blazing effect.