| dc.description.abstract | In recent years, lithium niobate thin film has emerged, and countries are actively engaging in research and development of optical or optoelectronic devices based on these lithium niobate thin film. In this thesis, we first compare the differences and advantages of lithium niobate thin films with traditional lithium niobate substrates, and discuss the challenges of the thin film fabrication process. We will then develop an electro-optic polarization mode converter device on the thin film. To start, we will introduce the concepts of waveguides, electro-optic effects, and solc filters, integrating these three concepts to form the electro-optic polarization converter.
In terms of simulation, we will first simulate the waveguide structure, including waveguide width, etching depth, and sidewall angle. These three parameters will affect single-mode conditions and the effective refractive index. We will then calculate the required poling period using the effective refractive index obtained from the simulation. Regarding the electro-optic effect, we will simulate the actual working voltage needed to achieve the corresponding electric field.
In the fabrication process, we will compare the waveguide smoothness produced by different etching methods. We will then use the final chosen etching method to simulate the single-mode conditions, effective refractive index, and required poling period. Following this, we will test the poling parameters and measure the results to find the most suitable poling parameters, which will then be combined with the waveguide to form a periodically poled inverted waveguide. Finally, we will use semiconductor processing to fabricate electrodes on the top and sides of the waveguide to facilitate voltage application during measurements.
In terms of measurement, we will first measure the waveguide loss. The waveguide loss produced in this thesis is 3.62 dB/cm (TE) and 2.41 dB/cm (TM), which is the lowest loss recorded in our laboratory to date. Next, we will measure the electro-optic polarization mode converter (EOPMC). At 80°C, we achieved a conversion efficiency of 94%, and the highest efficiency, approximately 99%, was observed at 92°C. We will also measure the shift in the central wavelength at different temperatures.
Unlike traditional passive devices, the electro-optic polarization mode converter developed in this thesis serves as an active device, offering advantages such as a compact size and the ability to actively adjust the conversion between TE and TM modes. This device represents a significant advancement in the optical research and development of lithium niobate thin films. | en_US |