Fumihiro Tawa

Optical head with a butted-grating structure that generates a subwavelength spot for laser-assisted magnetic recording

Laser-assisted magnetic recording uses a subwavelength laser spot as its heat source. We devised a planar-type multilayer optical head with a butted-grating structure that combines dielectric materials. In this optical head, the spot size in the Y direction was reduced using a butted-grating structure, and the spot size in the X direction was reduced by multimode interference with the transmitted light. As a calculated result, a subwavelength spot of 88×82nm2 [full width at half maximum (FWHM)] at an optical efficiency of 17% is obtained. We experimentally demonstrated the subwavelength spot of 88×60nm2 (FWHM) by scanning near-field optical microscope.

Generation of nanosized optical beams by use of butted gratings with small numbers of periods

We have devised an optical high-throughput nanosized beam-generating structure consisting of butted gratings with small numbers of periods. We analyzed the structure of these grating by the transverse resonance method. We then demonstrated that it is possible to achieve a beam spot of 45 nm x 60 nm (FWHM) with this structure for the optical heads used in ultrahigh-density recording, such as those used in laser-assisted magnetic recording storage.

Flat Intensity Lens with High Optical Efficiency and Small Spot Size for Use in Optical Disc

The optical system in recordable optical discs must realize both, a smaller spot size for high data capacity, and an increased optical power for a high data transfer rate. We have devised a simple optical element that converts the Gaussian intensity distribution into a flat intensity distribution by refraction without optical power loss or aberrations.

High optical efficiency integrated head for use in magneto-optical disk drive

We explain the integrated magneto-optical (MO) head module that contains diffractive optical elements (DOE) and a beam-splitter (BS) with cylindrical surfaces. The optical system for servo signal detection is miniaturized by developing a multi-functional DOE. This system yields precise servo signals, and can eliminate the tracking error signal (TES) and focusing error signal (FES) independently. Power detection system is composed by using a multilevel DOE for high-speed automatic power control (APC). We suppress the distribution of the incidence angle on the BS surface, when divergent light is incident on the BS. It enables our integrated head to increase the coupling efficiency of a collimator without the deterioration of optical characteristics. When we test the head in a MO disk drive, the byte error rate (BER) of 10-6 is achieved. We confirm that this drive has the same commercial level performance for a 1.3 GB MO disk with magnetic super-resolution (MSR) technology.

High optical efficient integrated head for use in magneto-optical disk drive

We developed an integrated optical head for use with MO (magneto-optical) disks that makes it possible to adjust the focusing error signal (FES) and tracking error signal independently and to obtain high gain servo signals with a DOE (diffractive optical element). It prevents the changing of the FES caused by temperature changes by using a quasi-phase conjugate system. The cylindrical beam-splitter and the automatic power control-DOE achieve high optical efficiency and MO signal quality.