Design and analysis of high resolution solid immersion lens based near field optics with annular aperture

다국어 초록 (Multilingual Abstract)

To achieve high resolution for the optical imaging systems such as fluorescent imaging microscopy, optical data storage and lithography have been required continuously. These demands can be met by means of solid immersion lens (SIL)-based near-field optics which is one of the strongest candidates to satisfy high resolution optics. By introducing SIL-based near-field optics, a numerical aperture (NA), a factor that defines optical resolution in an inversely proportional relation, can be increased to more than unity, which is the diffraction limit in free space. However, to realize SIL-based near-field optics for applying to high resolution advanced imaging optics, there are several critical problems should be solved. Moreover, higher resolution and longer focal depth than conventional SIL-based near-optics are continuously required to improve the optical performances in near-field optical systems. Therefore, it is inevitably required to solve the current status critical problems of conventional SIL-based near-field optics as well as to improve the optical performances by increasing resolution and focal depth.
In this thesis, I will introduce the possible solutions for the dominant problems related to the SIL optical head tolerances among the several problems which conventional SIL-based optics has. One of the critical problems is the fabrication of SIL itself, especially super-hemispherical SIL and the other problem is the assembly of a SIL optical head composed of an objective lens and a SIL. As the final end, I will show the improvement of the optical performances in SIL-based near-field optics by applying an aperture technique which is well known to optimize the intensity distribution of focused beam spot by modulating amplitude and phase.
Therefore, first, I will present the general diffraction integral formula for calculating the electric field structure in a focal region composed of a multilayered medium as well as at the exit pupil plane with an arbitrary NA for a finite number of annular aperture zones considering various polarized illumination. Based on the derived formula, it is possible to understand the electric field behavior in the focal region and at the exit pupil plane for the various optical conditions. The analysis based on the derived formula will be effectively used to verify proposed solutions and to design improved SIL-based near-field optics with an annular aperture through this thesis.
Second, I will introduce the hybrid SIL optical head design results as well as the conventional SIL optical heads of the hemispherical and super-hemispherical SIL. In the hybrid SIL optical head design, replicated surface is added on the top surface of a SIL to generate aspherical surface. Through the proposed design concept, the thickness tolerance of SIL, which is one of the critical technical barriers, can be increased by 30μm. In addition, through the vector field analysis I will show that the proposed hybrid SIL optical head has good optical performances to apply it to SIL-based near-field optics.
Third, I will show the assembly and evaluation results of SIL optical head for surface recording and cover-layer-protected recording types by means of Twyman-Green Interferometer. Interferometer system should be used when assembling and evaluating SIL optical head in order to confirm its optical performances repeatedly due to the severe distance tolerance between an objective lens and SIL. The evaluation results will be also compared with simulation ones. Further, to simplify the assembly and evaluation procedure for cover-layer-protected SIL optical head, I will propose the assembly and evaluation method without contact process between the SIL and the medium that was considered as essential requirement.
Finally, I will show high resolution SIL optical head for various polarization illuminations by introducing an annular aperture technique which can optimize interference between propagation and evanescent wave effectively to reduce focused beam spot size and to increase focal depth. By applying an optimized annular aperture to convention SIL optical head resolution can be increased by approximately 20%. This novel SIL-based near-field optics will be verified through experiments such as measuring focused beam spot profiles and observing the topology of a measurement sample.
The studied SIL-based near-field optics can be applicable to not only next generation optical storage device but also high resolution microscopy and pattering technologies.