Research On Ultra-Compact And Low Loss Fiber-Silicon-Based Waveguide Edge Coupler

With the rapid development of silicon-based photonic integrated chip technology and the continuous improvement of optical interconnection and communication technology,people have put forward higher requirements for integrated optical communication network technology.Fast transmission rate,large information load,ultra-low loss and ultra-low cost are the development directions of various information processing systems and silicon-based photonic integrated circuits(PICs).Silicon-based photonic integrated devices are compatible with the standard complementary metal-oxide-semiconductor(CMOS)technology at the same time.They also have a series of significant advantages such as superior performance,high integration,small size,low loss and low cost.They play an important role in on-chip optical communication,data transmission and system information technology computing.In order to realize high-speed interconnection between silicon-based photonic chips and optical fibers,couplers are needed as the bridge for optical signal transmission between them.At present,the low loss coupling from fiber to chip can be roughly divided into two directions: grating coupler and edge coupler.The edge coupler is widely used because of its low coupling loss,large working bandwidth,small size and other advantages.In this thesis,three different types of silicon-based edge couplers have been studied and designed.In order to improve the coupling performance,the Subwavelength Grating(SWG)structure has been introduced in the design.The specific research contents are as follows:1.Based on the design concept of silicon-based edge coupler,a trident edge coupler based on Subwavelength Grating is designed.The structure is relatively simple and the performance is superior.The key conversion region consists of SWG to form a variety of Taper structures,which are combined with silicon photonic chips.After optimization and simulation,the insertion loss is 0.45 d B at 1.55 μm,the overall length of the device is 54 μm,and the bandwidth is up to 400 nm when the insertion loss is less than 1 d B.The paper has carried out detailed parameter design analysis for the proposed device,such as SWG length analysis,SWG duty cycle analysis,etc.2.An innovative edge coupler combining taper waveguide and Subwavelength Grating is proposed,which is based on multiple groups of symmetrical Taper waveguide structure and Subwavelength Grating area to reduce the insertion loss of the device.At the standard wavelength of 1.55 μm,the insertion loss of the edge coupler is 0.39 d B,and its total length is60 μm.The bandwidth is 470 nm when the insertion loss is less than 1 d B.If the standard is raised,the bandwidth is 360 nm when the insertion loss is less than 0.6 d B.3.A hybrid edge coupler of taper waveguide and trident Subwavelength Grating is designed.The key conversion area consists of a trident SWG in the center and a matched strip waveguide on both sides.In order to realize the high matching between the optical fiber mode and the silicon-based waveguide mode,and realize the low loss transmission on the chip,the conversion region is divided into three parts,and its optimal size is optimized.After design and simulation,the proposed edge coupler has excellent performance.At 1.55 μm,the insertion loss is only 0.23 d B,and the overall length of the device is only 60 μm.The operating bandwidth is390 nm when the insertion loss is less than 1.5 d B.If the standard is raised,the bandwidth is240 nm when the insertion loss is less than 1 d B.The manufacturing tolerance of the device is also analyzed in detail.