The Basic Research On Fabricating Arrayed Waveguide Grating By The Combination Of Sol-gel And UV Writing

With the development of modern telecommunication and internet, more and more attention has been paid to dense wavelength division multiplexing (DWDM) systems. And an N×N arrayed waveguide grating multiplexer is very attractive in optical DWDM networks since it is capable of increasing the aggregate transmission capacity of single strand optical fire. So, it becomes one of the key technologies in studying DWDM systems to fabricate AWG device and develop its performance. The arrayed waveguide grating consists of input/output waveguides, two focusing slab regions and a phase-array of multiple channel waveguides with the constant path length difference ? L between neighboring waveguides. It can work as grating and complete the function of multiplexing and demultiplexing for light with different wavelength. Based on the optical waveguide theory and combining with our experiments, we designed single-mode transmission condition and waveguide dimension fabricated by Sol-Gel and reactive ion etching (RIE) or UV-writing technology. For 1mol%Sn-doped SiO₂ RIE-etched waveguide, the refractive index of cladding and core are 1.4222 and 1.4368, respectively, and the designed single-mode dimension is 2.4×3.6μm². For 1mol%Sn-doped SiO₂ UV-written waveguide, the refractive index of upanddown, left right and core are 1.4222, 1.4368 and 1.4467, respectively, and the designed single-mode dimension is 2×3μm². This result provides a good foundation for fabrication of Si-based AWG. Optical waveguides is important for integrated optics. SiO2waveguides can be widely used in integrated optics. For fabricating AWG used for WDM, we carried out the study of growing SiO2 waveguide material on Si by sol-gel. We fabricated SiO2 and Sn-doped silica waveguide material by sol-gel and studied the influence of diversified experimental conditions to the film. Sn-doped SiO2 is smooth and uniform and is suitable for core of waveguide with a few-μms thickness and small roughness, 10-6 in the extinction coefficient. Its loss is less than 0.1dB/cm. In the experiment, we have analyzed the samples by SEM, AFM, XPS, XRD and VASE. It can be concluded that we have fabricated smooth SiO2 and Sn-doped SiO2 glass film. This work is important for the research on silica-on-silicon planar waveguide device, such as AWG. The effect of photoinduce refractive index changes in Sn-doped SiO2 material by UV writing has a potential advantage in integrated optical circuit and photonics devices. We have studied the photosensitivity of this materal through KrF excimer laser operating at 248nm. The relative refractive index change of 1mol% Sn-doped SiO2 film is 0.69% after exposure, which is the reported result in this research field. We have obtained the dependence of irradiation time and irradiation energy on the refractive index changes through a series of experiments. We use uv-absorption spectrum, XPS, EPR, and Photoluminescence to analyze the photorefractive mechanism of Sn-doped SiO2 waveguide material. Sn atom is in a substitutive site of Si atom in SiO2 network. We have found SnE'signals in irradiated SnO2-SiO2. It indicate sp3 unpaired electrons in threefold coordinated Sn sites is formed in SnO2-SiO2. This is the main reason of photorefractivity. The typical technology to fabricate AWG is to combine flame hydrolysis deposition (FHD) or plasma enhanced chemical vapor deposition (PECVD) and reactive ion etching (RIE). But this technology has much shortcoming, such as the complicated processing step, the expensive cost, the shift of center wavelength, the waveguide birefringence, and so on. The effect of photoinduced refractive index changes has been widely applied in fabricating planar waveguide devices and improving performance of typical RIE-etched AWG. Based on these, we put forward to writing AWG device in silica planar waveguide by UV writing, designedfabrication process and basic parameter and discussed some possible optimized means. We have designed and fabricated Cr-plating quartz amplitude mask used for exposure under KrF excimer laser by ourselves, and successfully written planar waveguide grating in SiO2 using this mask (1460mJ/cm2/pulse,9Hz,15min). We also have groped the threshold of the energy density of this mask is 1530mJ/cm2/pulse from the damage of mask. And the AWG fabricated by UV writing will have many good characteristics comparing with RIE technology, such as low insertion loss, polarization-insensitive, low cross-talk, precise center wavelength, and so on. The innovation of this dissertation has embodied in some aspects as followed: (1) It is the first time to put forward to UV writing AWG optical waveguide devices in optical communication system using the effect of photoinduce refractive index changes in germanosilicate glass under UV light. Because the typical AWG etched process is more difficult, we can make use of the higher laser photon energy and induced UV light to fabricate AWG replacing typical etched technology, and this photon processing will obtain very high precision. This UV writing AWG technology is innovative. We have applied patent and be authorized. (2) We use KrF excimer laser to irradiate the SnO2-SiO2 material fabricated by sol-gel method. The refractive index changed after irradiation The refractive index changed of 1mol% Sn-doped SiO2 material reached 0.69%, which is the reported results in this research field. (3) We have important breakthrough in mask fabrication technology. We find applicable strong UV mask material, design and fabricate amplitude mask used for UV exposure by ourselves, choosing bar Cr-plating quartz amplitude mask. Comparing with existing UV mask technology, this means avoid repeated plating and simplify the experiment. Whats more, it has enhanced the threshold of energy density of UV exposure mask (1530mJ/cm2/pulse) and increased the change in refractive index. At the same time, we successfully fabricated planar waveguide grating using this mask (1460mJ/cm2/pulse,9Hz,15min) andobserved obvious diffracted facula.