An optical pickup which is compatible with at least one high density recording medium that uses a blue-violet beam and at least one lower density recording medium, the optical pickup including: an optical unit to selectively emit one of a plurality of beams with different wavelengths onto one of the at least one high density recording medium and the at least one lower density recording medium, and to receive the respective beam reflected from the respective recording medium; and a holographic objective lens to focus the respective beams emitted by the optical unit on a recording surface of the respective recording medium, the holographic objective lens including a first holographic lens region and a second holographic lens region located inside the first holographic lens region, wherein holographic patterns of the first and second holographic lens regions respectively produce a first effective numerical aperture (NA) for the at least one high density recording medium and at least one additional effective NA suitable for the at least one lower density recording medium.

Compatible optical pickup

An optical scanning device for scanning an optical record carrier. The optical scanning device includes: a radiation source system (661; 761); an optical element (1; 101; 201; 301) comprising a first fluid (A) and a second fluid (B; C) separated from each other by a fluid meniscus (16; 116, 138; 216; 316) having an adjustable configuration; and a control system (20; 120; 220; 320) arranged to adjust the fluid meniscus configuration to introduce a first type of wavefront modification. The first type of wavefront modification causes the radiation beam to be redirected from an input radiation beam path (2; 102; 244; 348) onto one of a plurality of output radiation beam paths (24, 26; 140; 246; 350) which each have a different angular displacement (α, β, Ϝ, δ, e) from the input radiation beam path. The control system is further arranged to adjust the fluid meniscus configuration to introduce a second type of wavefront modification. The second type of wavefront modification is arranged to compensate a wavefront aberration of the radiation beam, the compensated wavefront aberration being adjusted in accordance with the angular displacement.

Optical Scanning Device

A compact optical head for reading or writing data on an optical disc is disclosed wherein the optical head comprises an integrated laser diode/photodetector package, a half-cube beamsplitter, and an objective lens. Light emitted from a diode laser is in transmitted to the beamsplitter and deflected towards the objective lens. The objective lens focuses the incident light on a focal point on the surface of the disc. A reflected beam travels along the same path as the incident light and is deflected by the beamsplitter toward a photodetector contained in the integrated package, wherein the photodetector is displaced from the laser diode. Other embodiments of the beamsplitter are disclosed which include a wedged plate for transmitting collimated light emitted from the laser diode, and a cylindrical lens for introducing astigmatism into the reflected beam. The present invention provides a substantial reduction in the size and volume required by the optical head, advantageously allowing the head to be easily integrated with an actuator for focussing and tracking the incident beam on the disc.

Compact optical head

A monolithically integrated optical disk pickup head is comprised of three-dimensional collimating focusing lenses, a beam splitter and 45-degree reflectors that define an optical axis in free-space using surface micromachining technology to fabricate hinged vertical optical structures.

Free-space integrated micro-pickup head for optical data storage and a micro-optical bench

With the progress of information technology (IT), we need more advanced storage devices to accommodate the unprecedented expansion of information and the rapidly changing IT environment. Magnetic and optical recording storage devices, such as hard disk drive (HDD) and optical disk drive (ODD), are the best candidates for satisfying these demands and requirements. For 10 Tb/in2 HDD magnetic recording, we need to develop several advanced and innovative technologies related to the head disk interface (HDI), head/media, servo, and signal processing in current perpendicular magnetic recording (PMR). And, several new read/write mechanisms, such as heat-assisted magnetic recording (HAMR) and bit-patterned media (BPM), are being investigated by many researchers at several institutes around the world. In optical data storage, the page-based holographic data storage system (HDSS) and micro-HDSS are expected to achieve a higher user capacity with beyond terabyte. The near field recording (NFR) system was developed to confirm the feasibility of achieving a multiple terabyte capacity, and currently, through the application of NF nanogap servo system using a flexible media, it is possible to enhance the recording density and data transfer rate together.

Prospect of Recording Technologies for Higher Storage Performance

A dual wavelength optical head for 0.6 mm and 1.2 mm substrate thicknesses, containing 635 nm and 785 nm laser diodes, has been developed. Holographic optical element (HOE) type optics and variable magnification type optics are described. For both types of optics, high light power efficiency is obtained, which is suitable for random access memory (RAM) applications. Moreover, the use of 785 nm light makes it possible to read compact disc-recordable (CD-R). A readout operation for a quadruple density CD and a conventional CD has been successfully demonstrated.

Dual wavelength optical head for 0.6 mm and 1.2 mm substrate thicknesses

A concept of a novel optical storage system has been proposed, which has the large-capacity characteristic because of three-dimensional recording and readout, and high-reliability and low-power-consumption characteristics achieved by controlling a light beam focused in a recording medium electrically instead of mechanically. On the basis of this concept, an optics for microholographic recording was constructed, and electrical beam control elements that vary the position of focused spots in the recording medium in both in-plane and vertical directions were incorporated into the optics. Liquid crystal deflectors and liquid crystal variable-focus lenses were used as the electrical beam control elements for in-plane and vertical beam control, respectively. Plural bits were recorded and read out in both in-plane and vertical directions of the recording medium, and the concept has been experimentally demonstrated.

https://iopscience.iop.org/article/10.1143/JJAP.48.03A056/pdf

Three-Dimensional Recording with Electrical Beam Control

A dual-wavelength optical head, believed to be new in design, for 0.6- and 1.2-mm-thick-substrate optical disks was developed by use of 650- and 780-nm-wavelength light and a wavelength-selective filter, which reduces the spherical aberration that is due to the difference in substrate thicknesses and restricts the numerical aperture for 780-nm-wavelength light. According to this configuration, both high light power efficiency and wide image field characteristics are obtained, which are suitable not only for read-only but also for recordable or rewritable optical disk systems. A reading operation for a digital video disc and for a compact disc and a recording operation for a phase change optical disk were successfully demonstrated.

Dual-wavelength optical head with a wavelength-selective filter for 0.6- and 1.2-mm-thick-substrate optical disks.

Microholographic recording with multiplexing of ten bits has been experimentally demonstrated by the combination of
wavelength multiplexing and angle multiplexing. The wavelength of the beams has been varied in two states and the
incident angle of the beams on the recording medium has been varied in five states. New coding methods to which these
technologies are applied have also been proposed. They lead to the effective use of the dynamic range of the recording
medium. It is expected that terabyte-order recording capacity would be achieved by further combining these
technologies with three-dimensional shift multiplexing technologies.

Microholographic recording with wavelength and angle multiplexing

In land/groove recording, it is necessary to detect both a land/groove signal and a differential push-pull signal for stabilization of the tracking servo. The former discriminates between land and groove during track pull-in operation, while the latter compensates for offset of the tracking error signal due to shift of the objective lens. This paper proposes an improved 3-beam method for detecting both signals with the same beam configuration. A 4-segment diffraction grating is employed, in which the grating patterns for two diagonal regions are π/2 out of phase. A land/groove signal is obtained from sub-beam signals, while a differential push-pull signal is obtained from the difference between the main beam and sub-beam signals. Features of this method are the applicability to disks with different track pitches and the robustness against disk eccentricity. A land/groove signal was observed, and the compensation of the tracking error signal offset with shift of the objective lens was confirmed experimentally. These results have demonstrated the validity of this method.

http://iopscience.iop.org/article/10.1143/JJAP.38.1761/pdf

Yuichi Komatsu

Papers

Dual wavelength optical head for 0.6 mm and 1.2 mm substrate thicknesses

Three-Dimensional Recording with Electrical Beam Control

Dual-wavelength optical head with a wavelength-selective filter for 0.6- and 1.2-mm-thick-substrate optical disks.

Microholographic recording with wavelength and angle multiplexing

Land/Groove Signal and Differential Push-Pull Signal Detection for Optical Disks by an Improved 3-Beam Method