| Summary: | 碩士 === 國立中興大學 === 機械工程學系所 === 94 === In this study, we demonstrate the liquid crystal (LC) diffraction grating with multiple modes by using the technologies of polymer dispersion and electrode pattern design. It can be applied to a multi-mode 3-beam grating which is necessary for the tracking detection purpose of a rewritable optical pickup head with multi-wavelength. Based on the specifications of CDs, DVDs and future blue light disks, the diffractive effect of each mode can be respectively designed.
With the simulations by scalar diffraction theory, the difficulties of design and production of a traditional grating with fixed depth have been discussed. The optical design software was also applied to assist the grating designs. In fabrication, we proposed several configurations of dual-mode and triplex-mode liquid crystal gratings. A mixture of LC and UV-curable monomer RM257 was also adopted as the device material. The experiments show that the diffraction patterns projected on the screen can be switched under different diffraction modes. The grating gives the diffraction angle and the expanding direction of diffraction orders in accordance with its grating mode under operation. Besides, the diffraction efficiency is tunable by adjusting the applied voltage. In this research, we successfully combine different types of grating pattern in a diffractive element and make the multi-mode LC grating possible.
|
|---|
