Basic Study Of Silicon-based Mid-infrared Optical Waveguide Device

Mid-IR silicon photonic circuits, with broad mid-IR transparency (up to λ=8μm), CMOS compatibility, and robust mechanical/chemical properties, have attracted significant attention because of their potential for use in chemical sensing and environmental monitoring.Nowadays silicon integrated photonics is based mainly on conventional silicon-on-insulator (SOI) technology, in which a thin layer of silicon dioxide serves as an under-cladding between the top crystalline silicon and the bottom crystalline silicon substrate to prevent light waveguide leakage through the substrate. Though SOI is mature and suitable for near infrared (NIR) photonic circuits, it cannot be easily adopted for planar mid-IR (λ=3to8μm) devices since silicon dioxide becomes optically lossy at λ>3.6μm. Hence, designing photonic structures or finding undercladding materials that can enable silicon as a material for broad mid-IR applications remains a challenge.In this paper, we propose to use the commercial SOI but with the BOX locally etched way by hydrofluoric acid (HF) to form the suspended membrane waveguide for mid-IR applications. Generally speaking, the innovative work of this thesis can be summarized as follow:1. Invest the development of the mid-infrared optical waveguide devices. Propose a new suspended ridge waveguide structure, theoretically analyze the mid-infrared ridge waveguide single mode condition, and then combine with the laboratory’s existing process conditions to determine a feasible experimental program, and to carry out experiments.2. We designed and analyzed the MMI-MZI thermo-optic modulator based on SOI (Silicon-On-Insulator) single-mode mid-infrared low-loss suspended rib waveguide. Parameters of the single-mode suspended rib waveguide and the modulator based on it were analyzed, further more the realization method was given. At the wavelength5.4μm, we used3D-BPM (Beam Propagation Method) method to simulate the transmission characteristics of the thermo-optic modulator model. The results showed that when the heating electrode length was3000μm, a very small change of temperature5.3℃in the thermo-optic area could result in a extinction ratio of-40dB.3. Build a mid-infrared optical waveguide measure system at the wavelength of5.4μm. On the basis of the existing conditions of the laboratory, build a mid-infrared silicon-based optical waveguide device test system. The system consists of a5.4micron helium-neon laser, infrared lens, chopper, lock-in amplifier and detector.