Manabu Oumi

High Spatial Resolution and Throughput Potential of an Optical Head with a Triangular Aperture for Near-Field Optical Data Storage

A near-field optical head with a triangular aperture has been precisely analyzed on the basis of a three-dimensional finite-difference time-domain method in order to obtain both higher spatial resolution and signal output performance for a near-field optical data storage system. The numerical analysis revealed that in contrast to a conventional aperture, this triangular-shaped aperture can successfully enhance energy distribution intensity at only the side perpendicular to the incident polarization direction, generating an extremely small optical spot not limited by its entire aperture size. The read-out performance was also simulated for the aperture passing over a space-patterned metal medium, resulting in both superior spatial resolution and signal output.

Improvements in near-field optical performance using localized surface plasmon excitation by a scatterer-formed aperture

Near-field optical performance is greatly improved using our proposed near-field structure, in which a metal scatterer formed in an aperture enhances localized surface plasmon (LSP) excitation and functions as an alternative near-field light source. Based on the design through a finite-difference time-domain method, the scatterer-formed aperture is fabricated with an electron beam technique, and its near-field optical distribution is observed using a scanning near-field optical microscope. The scatterer-formed aperture enhances the near-field optical energy due to LSP excitation, thereby realizing a significant and simultaneous improvement in throughput and spatial resolution.

Numerical Simulation on Read-Out Characteristics of the Planar Aperture-Mounted Head with a Minute Scatterer

Recently, various researches on optical recording based on near-field optical principles have been conducted for higher data storage density. However, there is a problem of the trade-off between signal output and spatial resolution, especially when an aperture-type near-field optical head is utilized for high speed data-readout. In order to solve this problem, we propose a novel near-field optical head, the planar aperture-mounted head with a minute scatterer, and analyze its read-out performance through the three-dimensional finite-difference time-domain (3D-FDTD) method. Our simulations reveal that the Silver scatterer placed at the center of the planar aperture strongly enhances optical energy due to the local surface plasmon excitation, and that this head has the potential to realize high resolution and high signal output simultaneously.

Light Delivery System for Heat-Assisted Magnetic Recording

Heat-assisted magnetic recording (HAMR) technology needs a light delivery system with an incorporated near-field transducer (NFT) as a minute heat generator. A novel system for light delivery with a triangular spot size converter (SSC) and an optical fiber is proposed. The advantages of using a triangular SSC are optical efficiency and integration tolerance between the optical fiber and the NFT. It also has good affinity to conventional head fabrication process. The optical fiber enables flexible laser location. It was confirmed that fabricated triangular SSC can propagate light and reduce beam spot. Computer simulations and experiments demonstrated possibility of integration of light delivery system between NFT, SSC, and optical fiber. Flyability of a pico slider with an optical fiber was also demonstrated. It shows that the optical fiber does not have a big impact on flyability below 10 nm flying height and off-track vibration.

Near-Field Optical Flying Head with Protruding Aperture and Its Fabrication

One of the most important parameters related to the near-field readout principle is aperture-to-media spacing (effective spacing). We proposed a near-field optical head with a protruding aperture that can reduce the effective spacing beyond the mechanical limit of the flying height and localize the near-field on the medium. Using nanostep lithography, we fabricated the protruding aperture, whose extension is 20 nm with 5 nm accuracy, so that the effective spacing is successfully reduced to 50 nm on a 3.2×3.6 mm flying head. We demonstrated signal readout with a 150 nm-long line-and-space pattern in chromium with the head. The flying height was estimated to be 75 nm, so that the effective spacing was 54 nm. The circumferential speed was 2.7 m/s and the signal frequency was 9.1 MHz. We also propose a promising structure for an optical head of higher density.

Signal Readout Using Small Near-Field Optical Head with Horizontal Light Introduction Through Optical Fiber

We have developed a small near-field optical head for high-recording-density data storage applications, to overcome the disadvantage of conventional near-field optical heads, such as large light introduction, low optical throughput, and difficulty in controlling the aperture-medium distance. The optical head structure has miniaturized light introduction using an optical fiber placed horizontally. To decrease the optical loss, an integrated microlens focuses on the aperture tip that has a shortened cut-off region. The fabricated optical head (3.2×3.6×0.9 mm3) with a 200 nm aperture of the same height as the sliders shows a clear readout signal of a 200-nm-wide line and space pattern at a speed of 5.2 MHz. We show that the optical head has the ability to read 4 times the recording density by simulations of the finite difference time domain (FDTD).

Simulation of Simultaneous Tracking/Data Signal Detection Using Novel Aperture-Mounted Surface Recording Head

Recently, near-field surface recording based on near-field optical principles has been vigorously studied for higher data storage density. In near-field optics which utilizes an aperture, in addition to the high spatial resolution property, there is another characteristic that the shape of the optical spot can be arbitrarily controlled by the aperture configuration, and its application to various technologies in the optical disk drive is possible. From this perspective, we propose a novel tracking method utilizing an asymmetric configured aperture head which could provide continuous signal of readout data and tracking error simultaneously, and analyze its data read-out and tracking detection performance through the three-dimensional finite-difference time-domain (3D-FDTD) method. Our simulations reveal that this novel tracking head has sufficient data readout performance and high tracking sensitivity, and has the potential to readout both a data signal and a tracking signal simultaneously.

High-speed readout using small near-field optical head module with horizontal light introduction through optical fiber

Near-field optics, a super-resolution technique, is expected for optical data storage with high recording density (E. Betzig et al., Appl. Phys. Lett. vol. 61, p. 142, 1992; S. Hosaka et al, Nanotechnology vol. 8, p. A58, 1997). Recently, near- field optical heads using sliders, which can keep the distance between an aperture and a medium surface in proximity, were proposed, and reading from 110-250 nm pattern at the speed of 1.5-7.5 MHz was demonstrated (H. Yoshikawa et al., Opt. Lett. vol. 25, p. 67, 2000; F. Issiki et al., Appl. Phys. Lett. vol. 76, p. 804, 2000; K.T. Yatsui et al., Opt. Lett. vol. 25, p. 1279, 2000). These optical heads use an objective lens above sliders separately, to introduce the focused light to the aperture. However, this large light introduction using the objective lens leads optical heads with actuators to be large. From this perspective, we had proposed a small near-field optical head module with miniaturized light introduction (K. Kato et al., Tech. Dig. ISOM2000, p. 188, 2000). In this paper, we fabricated the proposed optical head module with air-bearing surface, and high speed reading from 200 nm chromium pattern formed on an SiO/sub 2/ disk medium was demonstrated.

Numerical simulation of the near-field optical head with a triangular aperture

1. Introduction Recent rapid advances in information society demand large-capacity and high-speed access capabilities even for optical data storage. Near-field surface recording technology, which utilizes an aperture-mounted head slider, has been vigorously studiedp3 due to its high density recording potential. One of the problems of near-field recording system is its low signal-to-noise ratio, and an optical aperture is required to realize high signal output and high spatial resolution simultaneously. Recently, in order to solve this problem, various configurations of novel near-field aperture have been proposed and their performances are validated in numerical simulationq6. In this paper, we propose a new aperture configuration, a near-field optical head with a triangular aperture, and perform numerical simulations to reveal its optical performance through our developed three-dimensional finite-difference time-domain (3D-FDTD) method. 2. Analysis Model Figure 1 shows the schematic diagram of the analysis model including a triangular aperture head and a metal-coated medium. The shape of the triangular aperture head is a pyramid of an equilateral triangle with a taper angle of 45 degrees, and its shading material is Aluminum. The length of the side of the triangular aperture at the end of the head is 200 nm. Incident light of the linearly polarized plane wave with a wavelength of 680 nm normally illuminates the triangular aperture head. A recording medium, which consists of glass substrate and 40-nm thick Chromium layer having a 100-nm wide space, is placed a few tens of nm (separation: h) apart from the aperture, and moves in lateral direction. The electric energy distribution (=I El *) i s calculated for a measure of the near field energy, and the transmitted optical energy is obtained by integrating the normal Poynting vector component, considering it as a far-field sensed signal. 3. Simulation Results without a Recording Medium First we performed calculations, without considering head-medium interactions to reveal fundamental characteristics of the triangular aperture head. Figure 2 shows the energy distributions of the triangular aperture for X-polarization and Ypolarization on the XY plane just below and 30 nm apart from the aperture. We can see that the energy distribution of the triangular aperture strongly depends on the polarization state, and especially in the case of X polarization, the energy is enhanced at the only one side of the triangular aperture due to the edge enhancement effect. While the circular and rectangular aperture usually show the energy enhancement at both edges of the …

Integration of light delivery for heat assisted magnetic recording

Light delivery with spot size converter (SSC) and optical fiber for heat assisted magnetic recording is proposed. It has an advantage in optical efficiency and integration tolerance. SSC was fabricated and confirmed its operation. Fly-ability of pico slider with optical fiber was also demonstrated.