We present a study on the feasibility of extending our current experimental cover-incident near-field recording system to a 4-layer system promising 500 GB storage capacity on a single sided 12 cm disc. We calculated the electromagnetic field inside a 4-layer disc of which the design was optimized to have a minimum in the irradiance near recording layers other than the one that the light is focused on. Furthermore an objective lens and compensation device were designed to accommodate writing and reading from all four layers.
KEYWORDS: Servomechanisms, Near field, Actuators, Polymers, Solids, Signal detection, Scanning probe lithography, Near field optics, Control systems, Tolerancing
We present our progress on the development of a single-wavelength near-field recording system with a blue-violet laser and a NA=1.45 Solid Immersion Lens in a conventional 3D actuator. We will introduce our near-field optical recorder and present good recording results achieved on discs with a 3 μm thick spin-coated protective polymer cover-layer using a channel bit length of 43.7 nm. Furthermore, we will show recent results on high-speed near-field readout, up to 3xBD speeds, through a cover-layer using feed-forward control in the air gap servo system.
Progress is reported on cover-layer incident Near-Field Recording. Very good recording results are obtained on a CuSi disc demonstrating excellent signal quality with modulation corresponding to the full effective numerical aperture of 1.45. Comparing the Near-Field system with Blu-ray Disc further shows that an extension to at least 4 data layers should be possible. In addition, a method for dynamic tilt control is presented. Controlling the tilt between the solid immersion lens and the disc surface improves the system robustness and relaxes media manufacturing tolerances for a roadmap towards 500 GB capacity on a single-sided, 4-layer disc which is protected by a polymer cover-layer.
We present read-out results of a 50 GB disk with a blue laser and a NA=1.9 Solid Immersion Lens in a conventional focus and tracking actuator. Furthermore, we show a light path and a disk design that enable cover-layer incident near field recording on dual-layer disks with a capacity of 300 GB on a double-sided disk.
A 10 μm free working distance recording head for blue, cover-layer incident MO recording has been developed with NA=0.95 and integrated high bandwidth MFM coil. ZF-MAMMOS recording experiments are described.
We present a magneto-optical recording head designed for a 400 nm laser with a 0.85 numerical aperture doublet objective lens and a thin film Magnetic Field Modulation coil integrated in a flying slider.
We present an experimental set-up for systematical studies of optical near-field coupling phenomena using a solid immersion lens (SIL) to surpass the conventional far field diffraction limit. The set-up incorporates a microscope objective lens with NA equals 0.80 in combination with a hemispherical SIL manufactured from glass with refractive index n equals 1.887 and a laser with a wavelength of 430 nm. Test samples are positioned within the evanescent decay distance from the bottom surface of the SIL using a closed- loop-controlled piezo actuator. The laser spot can be scanned over the sample enabling a study of the push-pull signal of pregrooved samples on a split photodiode. The intensity distribution and polarization state of the light reflected from the sample in the exit pupil of the microscope objective lens is studied on a CCD camera. The reflected light can be combined with a reference beam into an interferogram used for alignment purposes. We present measurements of evanescent coupling of light to a glass sample and the push-pull signal of a reflective phase grating with a groove pitch of 300 nm as a function of thickness of the air gap between de SIL and the sample. The evanescent coupling to a glass sample can accurately be described by thin-film optics theory. Experiments show that the push-pull signal amplitude depends on the polarization state of the irradiating beam.
In optical design verification and interferometric lens testing, wavefront aberrations are expanded in orthogonal Zernike circle polynomials. Due to the continuity of these polynomials, they are less suitable for expanding discontinuous wavefronts. Examples of lenses that contain phase discontinuities are DVD objective lenses that are CD compatible. One of such compatibility solutions is a lens comprising a central pupil zone with one or more concentric annular pupil zones, separated by phase or intensity discontinuities. We have derived an expression that relates the Strehl intensity of the diffraction focus of such discontinuous pupil to the coefficients of the Zernike circle polynomial expansion in the central pupil zone and the Zernike annular polynomial expansion in the concentric annular pupil zones. Furthermore, we have developed a formalism to optimize the Strehl intensity by subtracting piston, tilt and defocus from the wavefront by correcting the coefficients of the Zernike circle and annular polynomials. Numerical calculations have shown that the approximation for the Strehl intensity of discontinuous wavefronts results in deviations from the actual intensity at the diffraction focus, that are comparable to the classical approximation for continuous wavefronts.
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