Mee-suk Jung

Development of Microlens for High-Density Small-Form-Factor Optical Pickup

A microlens of numerical aperture (NA) 0.85 a small-form-factor optical pickup, following the specifications of the Blu-ray disc (BD), was designed, fabricated and evaluated. To avoid difficulties in the fabrication of a high-NA objective lens and to obtain a low chromatic aberration, a new hybrid lens unit was designed to have a refractive lens and a diffractive lens. The micro-plano-aspheric refractive lens was fabricated using glass molding technology, and the diffractive lens was fabricated in a two-dimensional array using the electron beam mastering and consecutive UV embossing process. For the evaluation of the developed lens unit, diffraction efficiency was measured with the proposed diffraction efficiency measurement method, and the wavefront error of the lens unit was evaluated using a modified Mach–Zehnder interferometer. The measured average efficiency of the diffractive lens was approximately 85% and the RMS wavefront error of the lens unit was 0.0376 λrms.

Diffraction limit of the focusing waveguide grating coupler for optical probe information storage

A focusing waveguide grating coupler (FWGC) has been applied to an optical information storage element. To achieve minimum diffraction, focusing and high-coupling efficiency with high power, several fabrication and design difficulties have to be overcome. In this work, we report some new strategies to improve the fabrication and design, and greatly improve the pattern quality in defining curved gratings in the nanometre range using single-step electron-beam lithography with a conventional exposure mode. We also present the optimum fabrication conditions for the FWGC and the minimum diffraction limit (1.1 µm) obtained for the structure, which is optically the smallest diffraction spot size obtainable from diffraction gratings focusing beams into a spot in air.