This study aims to enhance the efficiency of an optical receiver system utilizing a silicon-photonics platform. Both the absorption efficiency of the photodetector and the coupling efficiency of the grating coupler are optimized. A slow light effect by photonic crystal is leveraged to significantly boost absorption efficiency and simulated using the finite-difference time-domain method, resulting in a 22-fold increase in absorption. The 1D and 2D grating couplers, based on SOI wafer and without a bottom mirror, are designed to achieve highly efficient and perfectly vertical coupling, and the fabrication is performed using DUV 248 nm lithography. A resonance induced by the corner mirror is utilized to reduce back-reflection and modify the mode profile. The measured coupling efficiency of the 1D and 2D grating couplers reaches up to -1.185 dB and -2.0 dB, respectively, demonstrating promising performance for various applications. Furthermore, an inverse design process utilizing a neural network is proposed to enhance the design and optimization of the apodization grating coupler. An apodization grating coupler based on single-mode waveguide is designed to achieve a coupling efficiency of -0.94 dB, which represents the highest record reported in the literatures for the case of single-mode waveguide and without a bottom mirror. Furthermore, the optimization result is verified using CMA-ES, demonstrating similar structural parameters and indicating the achievement of global optimization through the proposed inverse design process.

Chapter 1 Slow Light Waveguide Photodetector 1
1-1 Introduction 1
1-2 Formalism 4
1-3 Design Strategies 6
1-4 Results and Discussion 13
Chapter Completely Vertical Grating Coupler 18
2-1 Introduction 18
2-2 Grating Coupler Theory 21
2-3 Design 1D Grating Coupler 27
2-3-1 Design for High Coupling Efficiency 32
2-3-2 Design for Minimal Back-Reflection 37
2-3-3 Summary of 1D Grating Coupler 41
2-4 Design 2D Grating Coupler 42
2-4-1 Design with Unit-Cell Simulation 45
2-4-2 Full Structure Simulation 51
2-4-3 Results and Discussion 54
2-5 Grating Coupler Fabrication 60
2-5-1 Fabrication Layout 63
2-5-2 Fabrication Process and Results 74
2-6 Grating Coupler Measurement 84
2-6-1 Calibration Device Measurement 87
2-6-2 Measurement on Wafer-Level Testing 90
2-6-3 Measurement on Die-Level Testing 98
2-6-4 Results and Discussion 104
2-7 Grating Design with Neural Network 115
2-7-1 Materials and Methods 117
2-7-2 Results and Discussion 123
2-7-3 Neural Network and CMA-ES 130
Chapter 3 Conclusion 133
Reference 136

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