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We advocate the use of a polymeric cover layer for protecting the data layer and the tip of the solid immersion lens in near-field optical recording system. With a cover on top of the data layer, the numerical aperture (NA) of the objective lens is limited to the refractive index of the cover material. This means that the maximum attainable NA of cover-incident near-field systems and therefore the maximum achievable storage density is lower compared to that for first surface systems. This lower storage capacity per layer can be more than compensated for by using multiple data layers which is not possible in first-surface systems with bare discs. In this paper we present first experimental results for near-field recording with a solid immersion lens that focuses through a cover layer and a spacer layer onto a data layer, as in a dual-layer near-field disc.

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.

We developed solid immersion lenses made of a KTaO3 monocrystal. The refractive index of KTaO3 is 2.382 at a wavelength of 405 nm. Using KTaO3 as the raw material of a solid immersion lens, we could design an effective numerical aperture of 2.20. We observed an eye pattern of a 150 GB capacity with a 130 nm track pitch and a 47.6 nm bit length. The areal density is 104.3 Gbit/in.2.

We have investigated high-density near-field readout using a solid immersion lens with a high refractive index. By using a glass material with a high refractive index of 2.08, we developed an optical pick-up with the effective numerical aperture of 1.8. We could observe a clear eye pattern for a 50 GB capacity disc in 120 mm diameter. We confirmed that the near-field readout system is promising method of realizing a high-density optical disc system.

We investigated high-density near-field readout using a diamond solid immersion lens (SIL). A synthetic single-crystal chemical vapor deposition diamond provides a high refractive index and a high transmission for a wide wavelength range. Since the refractive index at a wavelength of 405 nm is 2.458, we could design a solid immersion lens with an effective numerical aperture of 2.34. Using the diamond SIL, we observed the eye pattern of a 150-GB-capacity (104.3 Gbit/in.2) disk with a track pitch of 130 nm and a bit length of 47.6 nm.

A novel small lens of 0.221 mm diameter and 0.65 numerical aperture (NA) fabricated by using a new process which consists of a molded lens technology and a high refractive index thick film fabrication technology is presented.

We investigate improvements of the collection efficiency in fluorescence microscopy with a Weierstrass-sphere solid immersion lens (SIL). Using a Weierstrass-sphere SIL with refractive index n=1.845 and an objective lens with 0.55 numerical aperture, we demonstrate the high collection efficiency of fluorescence from 0.11-µm-diameter dye-doped microsphere bead samples, which is 21 times higher than that measured in conventional microscopy and is estimated to be 76%. Illumination uniformity and aberrations in Weierstrass-sphere SILs are also evaluated.

When an ultrasonic wave with sound pressure less than the threshold level of bubble destruction irradiates microbubbles, the microbubbles aggregate by an acoustic radiation force and form bubble clouds. The cavitation of bubble clouds produces a large number of microhollows (microdips) on the flow channel wall. In this study, microhollow production by bubble cloud cavitation is evaluated using a blood vessel phantom made of N-isopropylacrylamide (NIPA) gel. Microbubble dynamics in bubble cloud cavitation is observed by a microscope with a short pulse light emitted diode (LED) light source. Microhollows produced on the flow channel wall are evaluated by a confocal laser microscope with a water immersion objective. It is observed that a mass of low-density bubbles (bubble mist) is formed by bubble cloud cavitation. The spatial correlation between the bubble mist and the microhollows shows the importance of the bubble mist in microhollow production by bubble cloud cavitation.

Several types of objective lenses for blue laser optical pickup have been proposed. These objective lenses are composed of two lenses, and have a numerical aperture (NA) of 0.85 for high-density recording. We designed and fabricated a NA 0.9 lens for improvement of the technique. The objective lens is composed of two lenses. To achieve a precise wavefront, the objective lens was designed to use only one aspherical surface and to expand the tolerances of each lens.

We present the status of our efforts to demonstrate the feasibility of recording on a cover-layer protected dual-layer optical disc with a blue laser and NA=1.45 objective lens that is based on a solid immersion lens (SIL). We discuss the potential data density and some practical and theoretical considerations for the light path, the objective lens and the media. In particular, we show a lens design and results of prototype manufacturing for a NA=1.45 lens that focuses on the data layer of an optical disc through a sub-wavelength air gap and a 3 µm spin coated cover-layer that protects the data on the disc.

A solid immersion lens is combined with various aperture shapes in order to improve resolution. Both metallic and dielectric apertures are investigated, and optimum shapes for each are determined. Fabrication techniques for each type of combination probe are discussed and implemented, and a simple experiment with a dielectric combination probe scanning a reflective grating demonstrates improved resolution compared to a solid immersion lens alone.