Yoon Yong-Joong, Kim Wan-Chin, Park Kyoung-Su, Park No-Cheol, Park Young-Pil
Center for Information Storage Device, Yonsei University, Seoul, Korea.
J Opt Soc Am A Opt Image Sci Vis. 2009 Aug;26(8):1882-8. doi: 10.1364/josaa.26.001882.
Currently, data recording density in cover-layer-protected near-field-recording (NFR) and multiple-recording layered NFR optical data storage technology is limited by the difficulty in obtaining high-refractive-index cover layer materials. In addition, with the exception of improved resolution, the higher the numerical aperture (NA), the poorer the optical characteristics. However, in this study, we present novel cover-layer-protected solid immersion lens (SIL)-based NFR optics that provide superior optical performance with higher recording density, greatly enhanced focal depth, and less sensitivity to near-field air-gap-distance variation by modulating the amplitude and phase in the entrance pupil using annular pupil zones. Using an annular aperture consisting of three concentric annular zones to effect amplitude and phase modulation, the 1.45 NA cover-layer-protected SIL-based NFR optics achieved a data recording density as high as that of conventional 1.80 NA SIL-based NFR optics. These 1.45 NA optics yielded a full-width at half-maximum (FWHM) spot size of 0.315 lambda, a focal depth of 0.82 lambda, a focused beam spot sensitivity to air-gap-distance within the near-field region of 0.04 lambda, and a sidelobe intensity lower than 7%. In comparison with conventional 1.80 NA SIL-based NFR optics, the annular aperture optics achieved 3.5 times longer focal depth and much lower focused beam spot sensitivity to air-gap distance while maintaining the same high resolution. The introduction of this novel specially designed NFR optics could greatly improve data capacity in multiple-recording layered NFR.
目前，覆盖层保护近场记录（NFR）和多层记录NFR光数据存储技术中的数据记录密度受到难以获得高折射率覆盖层材料的限制。此外，除了分辨率提高外，数值孔径（NA）越高，光学特性越差。然而，在本研究中，我们提出了一种基于新型覆盖层保护固体浸没透镜（SIL）的NFR光学器件，通过使用环形光瞳区域调制入射光瞳中的幅度和相位，该光学器件具有更高的记录密度、大大增强的焦深以及对近场气隙距离变化更低的灵敏度等卓越光学性能。使用由三个同心环形区域组成的环形孔径来实现幅度和相位调制，基于1.45 NA覆盖层保护SIL的NFR光学器件实现了与传统1.80 NA基于SIL的NFR光学器件一样高的数据记录密度。这些1.45 NA光学器件产生的半高宽（FWHM）光斑尺寸为0.315λ，焦深为0.82λ，聚焦光束光斑对近场区域内气隙距离的灵敏度为0.04λ，旁瓣强度低于7%。与传统1.8 NA基于SIL的NFR光学器件相比，环形孔径光学器件在保持相同高分辨率的同时，焦深延长了3.5倍，聚焦光束光斑对气隙距离的灵敏度大大降低。这种新型特殊设计的NFR光学器件的引入可以大大提高多层记录NFR中的数据容量。
