KR100417404B1 - Near-field optical recording system - Google Patents

Abstract

The present invention provides a light source for generating light used for optical recording or reproduction, a collimator lens for converting light generated from the light source in parallel, an optical head slider mounted with a focusing lens, and installed between the collimator lens and the focusing lens. And a wavefront aberration correction means for adjusting the divergence angle or convergence angle of the incident beam running in parallel. According to the present invention, it is possible to increase the tolerance during fabrication and assembly of various components of the optical recording system, thereby improving mass productivity and minimizing wave front aberration, thereby increasing the reliability of the system.

Description

Near-field optical recording system {NEAR-FIELD OPTICAL RECORDING SYSTEM}

The present invention relates to a near-field optical recording system, and more particularly, to a near-field optical recording system having means for adjusting the focal position through separate means and correcting the wave front aberration when the focusing lens is not accurately focused. will be.

Advances in computer and network technology have increased the need for recording devices that can store large amounts of information. Fixed disk drives are difficult to achieve an increase in recording density due to the limitations of the driver and its recording media.In order to safely store large amounts of information, it is necessary to develop a new concept of drivers and recording media. In order to stably store data, to operate a lot of time continuously, and to maintain a long time of operation and frequent input / output, technology development of an information storage device capable of high speed input / output and stable use is accelerating. Disc drivers of various concepts continue to be developed for the purpose of increasing the speed and mass of such information storage devices. Among them, the near field optical recording method is a representative technology that greatly improves the existing method and greatly improves the recording density. This is attracting attention.

Near-field optical recording is a method of placing optical pick-up at about 50-150 nm so close to an optical disk as compared to a far field recording method of a conventional optical disk system, thereby recording or reproducing ultra high density. to be. There are various optical techniques for realizing near-field light recording, but a method using a SIL (Solid Immersion Lens) or a SIM (Solid Immersion Mirror) as a focusing lens is considered to be practical.

1 is a perspective view showing an example of the near field optical recording device 10. In the deck 18, a central portion of the disk 11, which is a recording medium, is mounted on the spindle motor (not shown) so as to be rotatable, and a recording and reproducing apparatus is provided on the other side of the inside. The floating optical head slider 12 is supported by the suspension arm 14 on the upper surface of the disk, and one side of the suspension arm is connected to the pickup 17. A voice coil motor (VCM) 16 is installed below the pickup to allow the pickup to rotate at an angle within a certain range. On the other hand, a fixing arm 13 is supported on the upper surface of the optical head slider from the pickup, and a prism 15 is provided at the end of the fixing arm. Light generated by the light source (not shown) of the pickup part is changed in the prism, passes through a lens (not shown) mounted on the optical head slider, and finally enters the disk surface. It is possible to record or reproduce the optical information by the interaction of the incident light with the disk surface.

2 is an enlarged perspective view of an example of an optical head slider, in which an objective lens 27 is mounted with a flange 28 formed around the optical head slider 20 supported thereon, and the focusing lens 29 is an optical head. It is supported and mounted on the lower part of the slider, and the two lenses maintain a constant distance.

The optical head slider of the near field optical recording system should be assembled to achieve the correct focal length between the objective lens and the focusing lens in the near field optical system configuration. However, when assembling the objective lens and the focusing lens on the optical head slider equipped with the optical lens, the focusing error is caused by the processing error of the mounting base surface of the slider, the processing error of the focusing lens and the objective lens itself, the design deviation of the refractive index, and the shape error. It becomes difficult to focus accurately on the bottom of the lens. If this error is aggravated, the wavefront aberration value increases and the optical characteristics of the beam coming through the focusing lens are degraded.

In the near field optical recording system, the wavefront aberration change at the focal forming position of the bottom surface of the focusing lens according to the gap between the objective lens and the focusing lens mounted on the optical head slider is investigated and shown in FIG. 3. The parallel incident beam generated from the light source passes through the objective lens of the optical head slider to form a focal point near the bottom surface of the focusing lens. However, due to an error in the manufacturing process, the distance between the objective lens and the focusing lens is out of a desired constant interval. do. The distance between the objective lens and the focusing lens so that the focal point is correctly formed on the bottom surface of the focusing lens is set to 0, and the amount of change in the distance from the focusing lens is shown on the X axis. Is shown. As a measure of change in wave front aberration, wavefront error (WFE) at the focusing position of the bottom surface of the focusing lens is expressed as root-mean-square value (RMS). The acceptable wavefront error in the optical recording system is preferably 0.03 or less. As can be seen from the figure, in order for the wave front aberration error value to be 0.03 or less, the distance variation between the objective lens and the focusing lens should be 0.3 μm or less. However, it is very difficult for mass production to adjust the variation of the distance between the objective lens and the focusing lens to 0.3 占 퐉 or less, and the production efficiency is very low.

Accordingly, an object of the present invention is to provide a means for correcting wave front aberration by adjusting the focus formation position even if the focus is not accurately formed due to the process error of the lens mounted on the optical head.

Still another object of the present invention is to widen the process margin necessary for mass production of an optical recording system to improve productivity and yield.

1 is a perspective view showing a conventional near field optical recording device.

2 is a perspective view showing an optical head slider.

3 is a graph showing wavefront aberration change according to the change in the distance between the objective lens and the focusing lens.

4 is a graph showing the amount of change in the distance between the objective lens and the focusing lens according to the divergence of the incident beam.

5 is a graph showing wavefront error values according to the divergence of the incident beam.

6 is a block diagram showing an embodiment of a near-field optical system according to the present invention.

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

60: light source 61: collimator

62: beamspiller 64: wave front aberration correction means

64a: first component 64b: second component

66: objective lens 67: focusing lens

In order to achieve the above object, the present invention includes wavefront aberration correction means for compensating wavefront aberration caused by the manufacturing and assembly error of the focusing lens and the objective lens of the flying optical head used in the optical recording system. Provide an optical recording system.

In detail, a light source for generating light used for optical recording or reproduction, an optical pickup unit for converting light generated from the light source in parallel, and wavefront aberration correction for adjusting the divergence angle or convergence angle of the incident beam running in parallel. A means and a near field optical recording system comprising an optical head slider mounting a focusing lens is provided.

The wavefront aberration correction means includes a first component and a second component, and adjusts the divergence angle or convergence angle of the incident beam by adjusting a distance between the first component and the second component.

The optical head slider may mount only the focusing lens, or may mount the objective lens and the focusing lens together. In the former case, the focusing lens itself should be a lens capable of forming a light spot for optical recording and reproduction.

The wavefront aberration correction means of the present invention reduces the wavefront aberration at the focus forming portion of the focusing lens by adjusting the divergence / convergence of the beam generated in the light source and traveling in parallel through a collimator, and the bottom of the focusing lens. Compensate for the correct focus of the incident beam on the surface. It is also possible to compensate for wavefront aberrations caused by changes in external temperature or changes in light wavelength.

The optical recording system of the present invention includes a near field optical recording system, and can be applied to various optical memory devices as well as various optical recording systems such as a hard disk drive and a CD-ROM. Further, when applied to the near-field optical recording system, it is preferable to use SIL as the focusing lens, but it can also be applied to the case of using various other types of focusing lenses.

In general, the near field optical system uses a light transmission phenomenon that occurs near the focal point of the laser beam. For optical recording and reproduction, a distance between the bottom surface of the focusing lens of the optical head slider and the surface of the recording medium must be maintained at a very narrow distance within 100 nm. do. Therefore, in order to focus the beam incident from the light source on the bottom surface of the focusing lens, focus formation must be precisely controlled.

Theoretically, it may be easy to focus the beam incident on the bottom surface of the focusing lens, but in practice, focusing may occur due to manufacturing errors generated during the manufacture of the objective lens and the focusing lens and assembly errors generated during the assembly thereof. It is very difficult to shape the focus on the bottom surface of the lens.

In order to correct wavefront aberration caused by not being formed at the focal point on the bottom surface of the focusing lens, the present invention arranges wavefront aberration correction means inside the optical system.

As an example of wavefront aberration correcting means, the present invention includes an optical head slider comprising an objective lens and a focusing lens, a light source (for example, a laser diode), a light sensing means (for example, a photodiode), a beam splitter, and the like. A beam expander is inserted between the optical pickup unit and the objective lens of the optical head slider.

By adjusting the position on the optical axis of the beam expander, the degree of divergence or convergence of the incident beam incident on the objective lens from the light source can be controlled. The focal position of the incident beam formed near the bottom surface of the focusing lens may be changed by controlling the diffusion or convergence of the incident beam.

As an example of the beam expander, the present invention provides a pair of lenses composed of a concave lens and a convex lens having a very large focal length. In this case, the focal position of the incident beam formed on the bottom surface of the focusing lens may be changed by adjusting the relative position of the convex lens with respect to the concave lens.

When the incident beam is diverged by the wavefront aberration correction means without traveling in parallel, the focal point is formed at a position farther from the actual focusing position of the parallel beam. Alternatively, if the incident beam is converged instead of diverging, the focus is formed at a position closer to the actual focusing position of the parallel beam. Such an adjustment of the focus position is achieved by focusing on the bottom surface of the focusing lens through a separate means regardless of the distance when the focusing distance between the focusing lens and the objective lens is out of a predetermined position and focus is not formed on the bottom surface of the focusing lens. To be formed.

Hereinafter, the present invention will be described in more detail with reference to the drawings for clarity of understanding.

4 is a graph showing the amount of change Δd between the objective lens and the focusing lens according to the divergence control of the incident beam by the wavefront aberration correction means.

The degree to which the incident beam diverges with respect to the parallel beam is represented by a diverging angle θ. As a result of measuring the change in the distance between the objective lens and the focusing lens while changing θ from 0 ° to 1 °, it can be seen that the distance change amount Δd increases as the divergence angle increases. From the drawings, it can be seen that by changing θ within a range of 0.1 °, the gap change amount Δd can be adjusted within a range of 2 μm or less. In other words, if the divergence angle θ of the incident beam is changed within the range of 0.1 ° by the wavefront aberration correction means, even if an error occurs in the range between the objective lens and the focusing lens within a range of 2 μm or less according to the manufacturing process, the correction is not performed. It is possible. This process margin, or tolerance, not only increases the yield of product production, but also contributes greatly to the improvement of product quality.

FIG. 5 is a graph showing a wavefront error (WFE) value according to the divergence control of the incident beam by the wavefront aberration correction unit. As a result of measuring the wave front error value by changing θ from 0 ° to 1 °, it can be seen that the wave front error value increases as the divergence angle θ increases. It can be seen that.

The results of FIGS. 4 and 5 show that the wavefront aberration correction means according to the present invention can compensate for the change in the distance between the objective lens and the focusing lens or the wavefront aberration change accordingly by changing the divergence angle θ within a predetermined range.

Figure 6 is a schematic diagram showing an embodiment of a near field optical system according to the present invention. The beam generated from the light source 60 passes through the collimator lens 61 to be converted into parallel light, and then reaches the objective lens 66 and the focusing lens 67 via the beam splitter 62. The wavefront aberration correction means 64 according to the present invention is positioned between the beam splitter and the objective lens to adjust the divergence angle of the incident beam. The magnitude of the divergence angle is changed by adjusting the distance L between the first component 64a and the second component 64b. For example, when the first component and the second component are concave and convex lenses, the divergence angle is increased by increasing the distance between the two lenses, and the divergence angle is decreased by narrowing the interval. The optical path changing means 65 changes the optical path of the beam diverging (or converges) from the wavefront aberration correcting means so that the beam is incident on the objective lens. Reference numeral 63 denotes a light sensing means for sensing the reflected beam.

As another embodiment of the present invention, both the first component and the second component of the wavefront aberration correcting means may be constituted by convex lenses. Even in this case, it is possible to change the divergence angle of the incident beam by adjusting the distance between the two components.

According to the present invention, the tolerance in manufacturing an optical recording system, especially an optical recording system using a near field, and assembling various components used in such a system can be increased. Therefore, the mass production efficiency of a product can be improved. In addition, since the wave front aberration can be minimized, the optical characteristic is improved. Further, by adjusting the degree of divergence of the incident beam at the time of initial product assembly, subsequent servos are unnecessary, thus improving the operating characteristics of the optical recording system and reducing the power consumption.

Claims (9)

A light source for generating light used for optical recording or reproduction; A collimator lens for converting light generated from the light source in parallel, An optical head slider equipped with a focusing lens, And a wavefront aberration correction means installed between the collimator lens and the focusing lens and adjusting the divergence angle or convergence angle of the incident beam running in parallel. The near field light recording system according to claim 1, wherein the wavefront aberration correction means comprises a first component and a second component for adjusting the divergence angle or the convergence angle of the incident beam. 3. The near field light recording system according to claim 2, wherein the first component is a concave lens and the second component is a convex lens. 3. The near field light recording system according to claim 2, wherein the first component and the second component are convex lenses. 3. The near field light recording system according to claim 2, wherein the wavefront aberration correction means adjusts the divergence angle or the convergence angle of the incident beam by adjusting the distance between the first component and the second component. delete The near field light recording system of claim 1, wherein the optical head slider includes an objective lens mounted on an upper portion thereof. The near field light recording system according to claim 1, wherein the focusing lens is SIL. The near field optical recording system according to claim 1, further comprising an optical path changing means between the wavefront aberration correction means and the optical head slider.