KR100700509B1 - Tracking device of near-field recording and reproducing system - Google Patents

Abstract

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a tracking device of a near field optical recording and reproducing system, comprising: means for generating a light source, an objective lens that refracts the light generated by the means and forms a grating in a critical angle region, and light that is reflected and diffracted from the objective lens A tracking device of a near field optical recording and reproducing system, comprising a detecting means for detecting a light source, and generating light from a light source, and injecting the light generated from the light source into an objective lens having a grating formed in a critical angle region of the surface. It provides a tracking method of a near field optical recording and reproducing system, which comprises detecting light reflected or transmitted and diffracted by grating of a lens with light detecting means, and performing tracking by comparing the amount of light detected by the light detecting means with a reference value. do. According to the present invention, it is possible to simply track by forming a grating in the critical angle inner beam area of the objective lens without using a conventional tracking method or configuring a separate tracking method. In particular, tracking can be done more accurately and in a very high density recording and reproducing system such as near field optics.

Description

TRACKING DEVICE OF NEAR-FIELD RECORDING AND REPRODUCING SYSTEM}

BRIEF DESCRIPTION OF THE DRAWINGS It is a schematic diagram explaining the tracking method by the conventional 3-beam method.

2 is a schematic diagram illustrating a tracking device and method of a near field optical recording and reproducing system according to the present invention.

3 is a plan view illustrating a grating formed on the objective lens of FIG. 2.

*** Explanation of symbols for main parts of drawing ***

6: laser diode 7: photodiode

8: SIL 9: Disc

10: objective lens 11: grating

The present invention relates to a tracking device of a near field optical recording and reproducing system.

These days, recording capacity of computer hard disks and auxiliary storage devices of computer peripherals is rapidly developing. This is due to the rapid development of the network and the development of scientific civilization, which is due to the database of recording and retaining a large amount of image information and data information that was not previously thought. In the case of hard disks, the annual growth rate is about 60% compared to the previous year's record capacity, and optical disc drives for computer-assisted storage devices have a capacity of several to tens of gigabytes. However, storage capacity at the same level as hard disks and optical disk drives for computer auxiliary storage has limitations in terms of storage capacity. Based on these technical backgrounds, near-field recording, which is emerging as a next-generation data storage device these days, is not only able to accommodate a large amount of data information as a future information storage device, but also sufficient for a future lifestyle. It is settled as a technology to cope with. For example, it is a technology that can be easily applied to all products that pursue miniaturization, mobility and convenience. In advanced countries such as the US and Japan, research on this is being actively conducted, while in Korea, technical research is not even at the beginning stage. However, since a global unified standard for such high density technology, especially near field recording technology, has not yet been prepared, it is very important and urgent to provide a foundation to lead the technology in the specification establishment by preempting important technology. Therefore, it is necessary to secure the fundamental technology such as recording and reproducing the near field recording technology as soon as possible, and to prepare technology for each part such as recording head, media, and operation method so that it can be commercialized as soon as possible.

In the near field optical recording and reproducing optical system, maintaining the gap between the disc and the optical head is very important and keeping the gap constant at about 1/4 wavelength (tens of nanometers) or less. If the gap is not kept constant, in the near field optical recording / reproducing optical system, the intensity of light decreases exponentially and the spot diameter of the beam increases greatly, making high density recording and reproduction of near field light difficult. This gap-keeping gap between discs and optical heads is the next generation for ultra-high-density recording and playback, such as scanning probe microscopes or atomic force microscopes, as well as the near field optical recording and playback commonly referred to. This is a very important part of the recording method.

In addition, in an ultra high density optical recording and reproducing system including near field optical recording, a precision tracking method capable of accurately reading tracks of data for high density recording and reproducing is very important and researches have been actively conducted.

Tracking methods of conventional optical recording and reproducing apparatuses include a three beam method, a push pull method, a heterodyne method, and the like. Among them, the three-beam method is shown in FIG. The tracking detection dedicated subbeams 1b and 1c are arranged on both sides of the main beam 1a for reading out signals, so that signal detection and tracking detection are independently performed. The three beams are arranged so that the line connecting the center has some offset value with respect to the track direction. As shown in FIG. 1, when the track is correctly hitted, when the returning light is detected by the photodiodes 3a, 3b, and 3c, the images of the pits 2 formed on the photodiodes 3b and 3c are equally applied to the subbeams 1b and 1c. It becomes bright. However, when the main beam 1a deviates to the right or to the left, a tracking error signal of + or-is obtained to the differential amplifier 4. Unlike the three-beam method, the push-pull method and the heterodyne method perform signal and tracking detection using one beam.

In the tracking method of the ultra-high density optical recording and reproducing system, various methods such as improving the precision have been continuously proposed in the conventional tracking method, but it is difficult to accurately track when recording and reproducing at high density in the near field and the like. There are many technical issues to solve.

It is therefore an object of the present invention to provide an apparatus for tracking in a simpler, more efficient and accurate way in an ultra high density optical recording and reproducing system such as near field.

The present invention provides an optical head including a light source, an objective lens refracting light generated from the light source and a grating formed on a surface thereof, detection means for detecting light reflected and diffracted from the objective lens; There is provided a tracking device of a near field optical recording and reproducing system including a piezoelectric element which drives the optical head and performs tracking in accordance with the amount of light detected by the detecting means.

The grating is formed in the critical angle region of the objective lens. A photodiode is installed in the optical head drive as a means for detecting a beam incident from the light source as parallel light and reflected and diffracted by the grating of the objective lens.

In addition, the present invention generates light from the light source, the light generated from the light source is incident to the objective lens having a grating formed in the critical angle region of the surface, the light is reflected or transmitted by the grating of the objective lens and the light detection means And tracking by comparing the light amount detected by the light detecting means with a reference value.

The light detecting means detects a first diffracted beam of light that is reflected or transmitted by the grating of the objective lens to be diffracted.

The principle of the near field optical recording and reproducing optical system will be described as follows. Light entering the lens at an angle greater than or equal to the critical angle is totally reflected inside the light instead of traveling to the next path as it progresses from a dense refractive index to a small area. At this time, due to total reflection of light, very small intensity of light exists on the surface of the lens. This is called an evanescent wave. Using this evernet wave, it is possible to achieve high resolution, which is impossible because of the diffraction limit, which is an absolute limit of resolution due to diffraction of light in the far-field. Basically, near-field light is confined to an area much smaller than the wavelength of light, so the uncertainty principle makes its physical properties completely different from the remote field. The near field optical recording and reproducing optical system totally reflects the light in the lens to generate an Evernet wave on the surface of the lens, and records and plays back by coupling the Evernet wave to a disk.

In the near field optical system for recording and reproducing in such a manner, the tracking device and method according to the present invention will be described with reference to the accompanying drawings.

2 is a schematic diagram illustrating the present invention. Block B, which represents the optical head, is provided with a semicircular SIL (Solid Immersion Lens, Terastor) 8 having a small gap on the upper surface of the disk 9 and generating an Evernest wave. The objective lens 10 for refraction is located. Among the beams refracted by the objective lens, the beams of the regions θ1 at both sides of the critical angle θ of the objective lens generate an Evernescent wave on the surface facing the disk of the SIL. The objective lens 10 has a grating 11 formed on an opposite surface of the SIL. The grating 11 is formed in the critical angle region of the objective lens 10 and has a predetermined thickness d and a width p. 3 shows an enlarged objective lens with a grating.

Meanwhile, block A of FIG. 2 includes a laser diode 6 as a light source, and the light generated by the laser diode 6 is refracted or transmitted through the grating 11 of the objective lens 10 to detect light diffracted. There is a photodiode 7 as a means. The photodiode is divided into four and can detect the amount of light incident on each region.

Block A is physically fixed to the upper surface of the disk and has a separate configuration from block B. The optical head of block B can move a small distance to maintain a gap or track with the disk.

Referring to the specific tracking method by the tracking device having such a configuration as follows.

The beam collimated from the block A is incident on the grating 11 portion of the objective lens 10 of the block B. Since the grating 11 is formed in a region corresponding to the critical angle of the objective lens 10, the beam emitted from the laser diode 6 is grating 11 of the objective lens 10 as a parallel beam through various optical components in the block A. When incident on the beam, the reflected or transmitted beam causes diffraction. At this time, the diffraction beam is detected by the photodiode 7 installed in the drive using the next-order reflection (or transmission) diffraction beam, preferably the first-order diffraction beam 22, not the zero-order diffraction beam 20. do. At this time, the angle θ2 of the primary diffraction beam is a function of the thickness d and the width p of the grating of the objective lens, and the following relationship is satisfied with the wavelength λ of light generated from the light source.

± λ = P sin θ2

When the position of the objective lens 10 changes during tracking of the optical head, the amount of light of the beam diffracted by the grating of the objective lens and incident on the photodiode 7 is changed accordingly. Computing two outputs of a + c and b + d, which combines the outputs of two diagonal portions of the amount of light incident on the respective portions a, b, c, and d of the quadrant photodiode 7, and compares them with the reference value. The difference is fed back to block A.
Then, power is applied to the piezoelectric element PZT (not shown) fixed to the block A or another fixture according to the feedback difference value. When power is applied to the piezoelectric element, the piezoelectric element performs tracking by moving the optical head which is the block B connected to the piezoelectric element while the displacement thereof is changed. Since the structure and principle thereof for driving the optical head of the block B using the piezoelectric element are obvious to those skilled in the art, a detailed description thereof will be omitted.
In this embodiment, a piezoelectric element is used as the driving means for driving the block B, but various known driving means of the optical pickup device may be used.

According to the present invention, it is possible to simply track by forming a grating in the critical angle inner beam area of the objective lens without using a conventional tracking method or configuring a separate tracking method. In particular, tracking can be done more accurately and in a very high density recording and reproducing system such as near field optics.

Claims (7)

Light source, An optical head having an objective lens refracting the light generated from the light source and having a grating formed in a region within a critical angle of the surface; Detection means for detecting light diffracted by the grating formed on the surface of the objective lens; And a piezoelectric element which drives the optical head to perform tracking in accordance with the amount of light detected by the detection means. delete The tracking device of claim 1, wherein the detecting means is a photodiode. 4. The tracking device of claim 3, wherein the photodiode is a quad split photodiode. delete delete Light source; An optical head having an objective lens refracting light generated from the light source and having a grating formed in a region within a critical angle of the surface; Detection means for detecting light diffracted by the grating formed on the surface of the objective lens; And And driving means for driving the optical head to perform tracking in accordance with the amount of light detected by the detecting means.

Images