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In this study, we evaluated the read-out signal quality from narrow track patterns, utilizing linearly arranged slender track patterns, while changing the track width from 10 to 0.1 μm and the pattern density from 200 nm line-and-space (L/S) to 120 nm L/S. To acquire narrow track readout signals, we adjusted the aperture’s in-plane position to cross a linear track at shallow angles of less than 1°, and we could successfully transform directly acquired signals into those of an aperture crossing tracks at a right angles. The results of an experiment utilizing a 10-μm-wide track (which is thought to represent an infinitely wide track) clarified that the stationary field was spread to an approximately 1.2–1.6 times larger region than the typical aperture size of 330 nm. The results also clarified that the “field spread” depended on the pattern density, that is, the case in which polarization direction θ equals 0 or 45°, and that the field spread increased monotonically as the line or space width became smaller. When the polarization direction equals 90°, the field spread had its local maximum when the line or space width was approximately 150 nm. An approximate prediction of the read-out signal amplitude was based on the rule that the signal amplitude was proportional to the net field spread that passed across the track pattern, and this prediction corresponded well to the experimental results, except when the interaction between the stationary field and the track side walls was not taken into account.

In near-field optical recording, the combination of a triangular aperture and a polarized illuminating light is thought to be one of the most promising breakthroughs for improving both spatial resolution and signal-to-noise ratio. In light of this, we have already fabricated a triangular-aperture mounted optical head slider and demonstrated its superior performance while clarifying the influence of the polarization direction on the spatial resolution in the circumferential direction. When the polarization direction was perpendicular to the bottom side (which is parallel to the slider trailing edge) of the aperture, the highest spatial resolution and signal contrast were obtained, in spite of the usage of a fairly large aperture, indicating the presence of clear readout signal waveforms corresponding down to 100 nm line-and-space (L/S) patterns. In this study, we tried to experimentally clarify the influence of the polarization direction of the illuminating light on an aperture's field spread in the radial direction. In order to concretely evaluate the field spread, we prepared 1-mm-long linearly arranged (in the circumferential direction) L/S patterns on a metal-layered medium, and a piezo-electric actuator combined positioner. Intersecting the aperture at two portions of the tracks, directly acquired signal waveforms could be successfully transformed into the waveforms that would be obtained if the aperture had crossed the track at right angles. The field spreads in the radial direction were estimated to be approximately 250 nm when the polarization direction was perpendicular to the bottom side. In contrast, when the polarization direction was 45 degrees, the stationary field spread in the radial direction was estimated to be approximately 350 - 370 nm. It could be confirmed experimentally that both the highest spatial resolution in the circumferential direction and the smallest field spread in the radial direction were realized with the combination of the triangular aperture and the illuminating polarized light whose direction was perpendicular to the bottom side. Based on these results, the signal-to-noise ratio will be evaluated and discussed in the future with respect to the above-mentioned optimum aperture structure and conditions.

The continual advancement of the digital network society demands higher density and higher data transfer rates for all sorts of data storage. Optical memory based on the “near-field” principle is considered one of the most promising ones because it has no apparent physical density limit such as that due to the thermal instability encountered in magnetic recording. In light of this, we have previously demonstrated the superior readout performance of an optical head slider which is mounted on a non-circular aperture, specifically a triangular aperture having a bottom side size of 330 nm irradiated by polarized light, with this scheme indicating a clear signal response corresponding to a 70-nm-long single slit pattern. In order to fully realize the superior potential of the triangular aperture’s high spatial resolution and high signal output, it is essential to minimize aperture-to-medium spacing. In this paper, we introduce a protruded aperture mounted on a 1.5-mm-long miniaturized optical head slider whose aperture protrudes approximately 20 nm from an air-bearing surface level based on nano-step lithography technology. Utilizing a triangular aperture of 140 nm per side, a readout experiment was carefully performed at an aperture-to-medium spacing down to approximately 30 nm, corresponding to a circumferential velocity of 2.18 m/s. The influence of the incident light’s polarization direction (in relation to the bottom side of the triangular aperture) on the readout signals was evaluated by flying the aperture above a chromium patterned medium having single-space or line-and-space patterns whose line lengths ranged from 300 to 50 nm.

Optical memory based on the “near-field” principle is considered one of the most promising technological breakthroughs because it has no apparent physical density limit such as that due to the thermal instability encountered in magnetic recording. In light of this, we have demonstrated the superior readout performance of an optical head slider mounted on a triangular aperture with a typical side size of 140 nm irradiated by polarized light. With this scheme, we have indicated a clear signal response corresponding to a 150-nm line-and-space (L/S) pattern. In this paper, we introduce a protruded aperture mounted on a 1.5-mm-long miniaturized optical head slider whose aperture protrudes approximately 25 nm from an air-bearing surface. Utilizing a triangular aperture irradiating polarized violet laser light, we performed a readout experiment at an aperture-to-medium spacing down to approximately 29 nm. A clear readout signal was obtained corresponding to the pattern down to 100-nm line width, in spite of the usage of a fairly large side size of 330 nm. We also evaluated the influence of the incident light’s polarization direction on the readout signals while changing the line width of the L/S patterns from 300 to 100 nm. A polarization direction perpendicular to the bottom side of the aperture provided both higher spatial resolution and better signal contrast. We also observed a “spike phenomenon” when the aperture passed through the boundaries between the metal portion and the space (or line-and-space) portion. We believe this phenomenon is the cause of the enhancement or suppression of specific L/S pattern or period signals.

The near-field principle combined with thin-film gas-lubricated slider bearing technology is thought to be one of the most promising breakthroughs to overcome the difficult optical diffraction limit (or wavelength shortening limit), which governs traditional optical recording performance. In light of this, we have demonstrated high linear density (150 nm pattern length) and high speed 10 MHz readout signals using the combination of a tapered circular aperture and a planar lens mounted on a quartz slider, flying above a metal patterned medium. In order to further improve both the spatial resolution and signal-to-noise ratio of this device, it is essential to minimize the spacing and laser power throughput of an aperture. Also investigated was the effectiveness of a non-circular aperture, which has approximately triangular configuration in combination with polarized light in simultaneously improving spatial resolution and increasing signal output. In this paper, we confirmed the predicted effectiveness on more practical condition of both high speed and compactness of head construction using a sub-micrometer size non-circular aperture, which was mounted on a 1.5-mm-long miniaturized optical head slider, flying above a ROM medium having sub-100-nm-long chromium patterns. The influence of the electric-field direction of the incident light and aperture to medium spacing on the readout signal are carefully evaluated by flying the aperture at spacing down to less than 50 nm.

Recent rapid progress in a digital network society necessitates storage devices with higher-density and faster transfer rates. In optical storage, a novel recording principle is eagerly awaited that will drastically improve recording density without being restricted by a wavelength shortening limit or a numerical aperture (NA) limit of the optics utilized. Storage based on the “near-field” principle is thought to be one of the most promising breakthroughs for overcoming various limitations governing traditional optical recording. We have already proposed an integrated optical head slider assembly that relies on the novel near-field principle for its operation; it is mounted on a minute tapered aperture and has a planar focusing lens and a micro silicon mirror. Readout signals corresponding to a 200-nm-long bit have demonstrated a frequency band up to approximately 10 MHz, using a chromium patterned medium. In this study, we have investigated the accuracy of the tracking characteristics of an aperture-mounted head slider by using linearly arranged 1-mm-long line-and-space patterns. Based on the step or inverse step responses that occur when an aperture flies obliquely across the linearly arranged pattern region boundary, we present a simple method of predicting accurate tracking characteristics in detail, and also by using a 350-nm line-and-space pattern signal, we were able to predict both tracking characteristics and tracking sensitivities of arbitrary wide tracks to a track width of 100 nm.

Recent rapid progress in a digital network society necessitates storage devices with higher-density and faster transfer rates. In optical storage, a novel recording principle is eagerly awaited that will drastically improve recording density without being restricted by a wavelength shortening limit or a numerical aperture (N.A.) limit of the optics utilized. Storage based on the "near-field" principle is thought to be one of the most promising breakthroughs for overcoming various tough limitations governing traditional optical recording. From this perspective, we have already proposed an integrated optical head slider assembly that relies on the novel near-field principle for its operation; it is mounted on a minute tapered aperture and has a planar focusing lens and a micro silicon mirror. Readout signals corresponding to a 200-nm-long bit have demonstrated a frequency band up to approximately 10 MHz, using a chromium patterned medium. In this study, we have investigated a tribological (glide height) property and flying stability of a miniaturized 1.5-mm-long optical head slider by using acoustic emission sensor signal and readout signal from the medium. We have also evaluated detecting performance separately using traditional 3.2-mm-long slider and a chromium patterned medium whose bit patterns are accurately scored with bit lengths less than 100 nm using electron beam lithography including reactive ion etching. We have confirmed stable flying performance of 1.5-mm-long slider assembly and furthermore, ability of detecting sub-100-nm long bit patterns.

Advances in a digital network society require both higher densities and higher transfer rates in all sorts of storage devices. In optical recording, the trend toward higher recording density and larger storage capacity requires novel surface recording technologies that would drastically improve recording density. To satisfy these severe requirements, we have already proposed a compact integrated optical head slider assembly for proximity optical recording based on the "near field principle". Using the optical head slider, we have successfully demonstrated readout signals from 200 to 150-nm-long bit patterns at frequency bands up to approximately 10 MHz. However, from the practical point of view, it is quite necessary to evaluate readout signals from patterns of smaller (sub-micron to sub-sub-micron) track width in order to prove high-density recording potential. In this paper, we have investigated tracking accuracy characteristics utilizing sub-micron sized alternate patterns of 1-mm length formed in a straight line in the circumferential direction of the medium. Arranging precisely the head's relative position to these recorded patterns, we have successfully obtained readout signals just crossing the sub-micron line-and-space pattern's boundaries. Assuming that an aperture runs along an accurate trajectory of the arc of a circle, readout signal amplitude variations when crossing the pattern edge at a right angle have precisely predicted. Also, the influences of track width on maximum readout signal intensity and tracking sensitivity are discussed in detail.

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.