JPH0793797A - Optical head and disk device using the same - Google Patents

Abstract

PURPOSE:To obtain an optical head whose constitution is simple and small-sized and having a high light utilizing efficiency by generating an evanessent light beam by using a diffraction grating lens of a concentric circular shape. CONSTITUTION:The recording surface 301 of an optical disk 300 is irradiated with a laser beam from a semiconductor laser 20 through a collimetor lens 30 and a grating lens 50. The lens 50 is composed of concentric circular shaped diffraction gratings whose grating interval having an equal interval is smaller than a light wave length and generates evanescent light beam. Thus, the device becomes the optical head whose constitution is simple and small-sized and having the high light utilizing efficiency and then high density recordings, reproducings and erasings in which the diameter of a converged spot is smaller than a diffraction limit determine by the numerical aperture of the objective lens and the wave length of the light beam can be performed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical head for optically recording, erasing or reproducing information by irradiating light on an information recording medium and an optical disk device using the same, and more particularly to utilizing evanescent light. This enables high density recording,
The present invention relates to an erasable or reproducible optical head and an optical disk device using the same.

[0002]

2. Description of the Related Art The recording density on an optical disk is determined by the focused spot diameter, but in the conventional optical head, the focused spot diameter cannot be made smaller than the diffraction limit determined by the numerical aperture of the objective lens and the wavelength of the light source. Therefore, the recording density exceeding the diffraction limit could not be obtained. Therefore, in order to form a light spot below the diffraction limit and dramatically improve the recording density of the optical disc, for example, Applied. Physics. Letter (Appl. Phys. Lett.), 61.14
2 (1992), by sharpening the tip of an optical fiber, further providing a minute aperture having a diameter of a wavelength or less at the tip, and recording / reproducing on / from an optical disc by using evanescent light generated in the aperture, Techniques for achieving so-called super resolution exceeding the diffraction limit have been disclosed.

Evanescent light is an inhomogeneous, non-radiative wave that exponentially attenuates in the direction perpendicular to the traveling direction on the incident surface, exists as a localized wave without propagating property, and is below the diffraction limit. Can be focused on. Such evanescent light can be generated by a diffraction grating or a dielectric film.

[0004]

In the conventional method for producing evanescent light by providing a minute opening at the tip of the optical fiber, it is difficult to process the fiber, and the optical system for making the light incident on the fiber is complicated. Therefore, there is a problem that the integration is difficult and the optical head becomes large.

Further, there is a problem that the light utilization efficiency of the beam is low because the beam is guided to the tip of the thinned fiber and is taken out from the minute aperture.

An object of the present invention is to solve the above-mentioned problems of the prior art, and to perform recording / reproducing at a recording density higher than the recording density determined by the conventional diffraction limit, and to have a simple structure and a small size. It is an object of the present invention to provide an optical head that is easy to realize and has high light utilization efficiency, and an optical disk device using the same.

[0007]

In order to achieve the above object, the present invention provides an optical head in which an optical spot is formed on an information recording medium to optically record and reproduce information. As a means for forming the above, a concentric diffraction grating is characterized by using a grating lens in which the evanescent light is generated in the vicinity of the center surface thereof at substantially equal intervals.

[0008]

When the grating lens having the above structure is used, the light emitted from the light source can be converted into an evanescent light, and a light spot having a diameter shorter than the wavelength can be formed on the information recording medium. A dramatic increase in density is achieved.

[0009]

EXAMPLES First, a method of generating evanescent light in the present invention will be described. The evanescent light that exists as a localized wave without propagating properties has a lattice spacing Λ of wavelength λ.
It can be generated using shorter and equal concentric diffraction gratings.

Usually, the position r _m of the m-th grating of the grating lens having the focal length f is given by the following equation (1).

(R _m ² −f ² ) ^1/2 −f = mλ (1) Here, if the focal length is shortened to f = 0, the following equation is obtained.
(2) is obtained, and the gratings are equally spaced with a period λ.

R _m = mλ (2) Further, if the period of the lattice interval Λ is further shortened to make the intervals equal to or less than the wavelength, the beam incident on the grating lens forms evanescent light. At this time, the beam diameter does not depend on the wavelength and becomes approximately the same as the lattice spacing Λ.

The conventional spot diameter at the diffraction limit using an objective lens is λ / N, where NA is the numerical aperture of the objective lens.
Although it is about A, when an evanescent wave grating lens is used, the spot diameter becomes smaller than when the NA is "1" which is the maximum value, so that so-called super-resolution can be achieved. The light intensity of the spot formed on the information recording medium by the evanescent light becomes weaker from the central part to the outer peripheral part, but the diameter of the range where the light intensity is approximately 1 / e ^{2 of the} central part is It is desirable that the wavelength is equal to or less than the wavelength.

In the grating lens having such a structure, the beam can be received and used as a whole,
The efficiency of evanescent light can be increased as compared with the case of using a minute aperture. Moreover, since a technique for producing an integrated circuit such as photolithography can be applied to the production of the grating lens, the production is easy. Further, since the optical waveguide, the photodetector and the like can be formed by the same process, the grating lens can be easily integrated with the optical waveguide and the size can be reduced.

The embodiments of the present invention will be described in detail below.
FIG. 1 is a schematic configuration diagram of an optical head to which the present invention is applied. The light beam emitted from the semiconductor laser 20, which is the light source, passes through the half mirror 35, and collimates the lens 30.
Then, it becomes parallel light and is incident on the grating lens 50. The beam made evanescent by the grating lens 50 forms a spot on the recording surface 301 formed on the optical head side of the optical disc 300. Recording surface 301
The reflected light from (1) passes through the grating lens 50 and the collimating lens 30 again, is reflected by the half mirror 35, and is detected by the photodetector 90.

FIG. 2A shows the grating lens 50.
FIG. 2B is a cross-sectional view taken along the center line of FIG. The grating lens 50 has a concentric diffraction grating on a glass substrate with a pitch of 0.3 μm and a maximum diameter of 0.1 m.
It is composed by carving up to m. Each grating has about 45 so that the incident beam is diffracted toward the center.
Blazed to °. Grating lens 50
Photolithography or an electron beam drawing method which has been conventionally used for fine processing of semiconductors can be used for the above processing. Further, the track pitch of the optical disc 300 is set to 0.3 μm, and 2 G is used for an optical disc of 2.5 inch diameter.
B information can be recorded. This is a recording density of 0.55G / i
It corresponds to n ² .

A sample servo system can be used for tracking error detection. In the sample servo method,
Since the tracking error signal is obtained from the intensity difference between the reproduction signals of the two pre-pits formed so as to sandwich the track center of the optical disc, the optical head may reproduce the pre-pit signal.

The focus error can be detected by detecting the reflectance intensity by utilizing the fact that the intensity of the evanescent wave decreases exponentially with the distance. Therefore, in combination with the sample servo system, the optical head can obtain the data reproduction, the distance between the optical head and the optical disc, and the tracking error signal by only detecting the reflected light from the optical disc with one detector.

Since the intensity of the evanescent wave decreases exponentially with distance, the grating lens 5
The distance between 0 and the recording surface 301 needs to be about the beam diameter. Therefore, also in this embodiment, the grating lens 50
The distance between the recording surface 301 and the recording surface 301 needs to be as small as 0.3 μm or less, and the parallelism between the grating lens 50 and the recording surface 301 must be precisely adjusted so that the grating lens 50 does not come into contact with the recording surface 301. To alleviate this adjustment accuracy, it is desirable that the grating lens 50 be given a curvature so that the center surface of the surface on which the grating is formed is bulged. Alternatively, when a plastic substrate having plasticity or the like is used as the substrate of the optical disc 300, the same effect can be obtained by pressing the substrate from the side opposite to the optical head so as to have a curvature.

Further, the intensity of the evanescent light sharply decreases with distance from the grating lens, so that the beam cannot be incident through the substrate as in the conventional optical disk. Therefore, in this embodiment, the recording surface of the optical disk is directed to the optical head side. I decided to provide it.

When reproducing a reproduction-only optical disc in which concave and convex pits are formed on the optical disc in advance and a reflective film is formed thereon, the intensity of the evanescent light strongly depends on the distance, and therefore the concave and convex portions on the recording surface are shallow. Causes the reflection intensity to change significantly. Therefore, it is desirable that the depth of the pits is approximately 1/10 or more of the grating spacing of the grating lens.

FIG. 3 is a sectional view showing the structure of a rewritable phase change optical disk used in the present invention. On the optical disk substrate 405, the metal reflection film 404 (Al-Ti, 2
00 nm), a dielectric film 403 (ZnS-SiO2, 70
nm), recording film 402 (In3 SbTe2, 30n
m), dielectric film 401 (ZnS-SiO2, 70 nm)
Are sequentially stacked.

The evanescent light beam 1 is made incident from the side of the dielectric film 401. Recording is performed by heating the recording film 402 with incident light and reversibly changing the state between amorphous and crystalline. The reproduction is performed by utilizing the fact that the reflectance of the optical disc varies depending on the crystalline state of the recording film. In this example, recording / erasing was performed at a recording power of 0.5 mW and erasing power of 0.3 mW, and reproduction was performed at 0.04 mW. In addition, in order to guide the energy of the evanescent light to the recording film more efficiently, a metal film that is thin enough to transmit light may be formed on the dielectric film 401.

FIG. 4 is another schematic configuration diagram of an optical head to which the present invention is applied. The beam emitted from the semiconductor laser 20 of the light source passes through the hologram 70 formed on the back surface of the grating lens 50 and enters the grating lens 50 as diffused light. Grating lens 5
The beam converted to evanescent light by 0 is the optical disc 3
The recording surface 301 formed on the optical head side of No. 00 is irradiated. The reflected light from the recording surface 301 passes through the grating lens 50 again, is diffracted by the hologram 70, and is detected by the photodetector 90. In the grating lens 50 used in this embodiment, the period of the grating is made smaller toward the outer circumference in order to convert the diffused light into an evanescent light.

FIG. 5A is a structural view of the optical head according to the first embodiment of the present invention, and FIG. 5B is a perspective view from above.

A low refractive index transparent layer 43 is formed on a substrate 80, and a transparent high refractive index waveguide 4 is formed on the transparent layer 43.
0, 41, 42 are formed. Waveguides 40, 41,
On the 42, concentric or spiral grating couplers 60, 61, 62 are formed, respectively. The light beam emitted from the semiconductor laser 20 is coupled with the waveguide 40 by the grating coupler 60 and guided. Since the waveguide 40 and the waveguide 41 are formed of the material having the same refractive index, the beam is transmitted through the waveguide 41.
To reach the grating coupler 61. The beam emitted by the grating coupler 61 as substantially parallel light in a substantially vertical direction enters the grating lens 50 and becomes evanescent light. The grating coupler 60
Was formed in a position recessed from the grating lens 50 so that the beam converted into the evanescent light would not hit.

On the other hand, the beam reflected by the recording surface 301 of the optical disc 300 enters the grating lens 50 again, and is detected by the photodetector 90 via the grating coupler 61 and the waveguide 41. Also, the recording surface 301
Among the beams scattered by the pits formed in the above, the beam that reaches the grating coupler 62 is coupled with the waveguide 42 and detected by the photodetector 92.

In this embodiment, the distance between the semiconductor laser 20 and the grating lens 50 can be shortened by using the waveguides 40, 41 and 42. As a result, the grating lens, the waveguide, and the photodetector can be integrated, so that the optical head can be made thin and compact.

FIG. 6A is a configuration diagram of an optical head according to a second embodiment of the present invention, and FIG. 6B is a perspective view from above,
The same reference numerals as those used above denote the same or equivalent parts.

Waveguides 40 and 41 made of a transparent material having a high refractive index are formed on the substrate 80. Waveguides 40 and 41
Grating couplers 60 and 61 are respectively formed on the top. The semiconductor laser 20 is bonded to the end face of the waveguide 40, and the light beam emitted from the semiconductor laser 20 enters the waveguide 40. The beam that has traveled through the waveguide 40 is launched into a substantially parallel light by the grating coupler 60 and is incident on the grating lens 50 to generate evanescent light.

On the other hand, the beam reflected by the optical disk 300 passes through the grating lens 50 and the grating coupler 60, and then is coupled to the waveguide 41 by the grating coupler 61. The beam propagating through the waveguide 41 is incident on the photodetector 90 by the grating coupler 62 and detected.

The grating lens 50 has a period of 0.3.
It was formed by concentric grooves with a diameter of μm and a maximum outer diameter of 0.1 mm. The grating was blazed at about 45 ° so that the incident beam was diffracted toward the center. Waveguides 40, 4
1, the grating couplers 60, 61, 62, the grating lens 50, etc. were formed by sequentially forming and processing a transparent dielectric film on the substrate 80.

It is desirable to use a semiconductor such as Si or GaAs for the substrate 80, and Si is used in this embodiment. The detector 90 is a PIN photodiode formed on the substrate 80. Since the thickness of the waveguide formed on the substrate 80 is sufficiently smaller than the thickness of the substrate, the thickness of the optical head is almost determined by the thickness of the substrate. In this example, the thickness of the optical head could be suppressed to 0.5 mm.

In the above embodiment, the semiconductor laser 2
Although 0 is bonded to the waveguide 40 to form the optical head, the semiconductor laser 20 may be formed on the same surface as the substrate 80.

FIG. 7 is a block diagram of an optical head according to a third embodiment of the present invention. The present embodiment is characterized in that the photodetector 90 is not formed on the substrate 80, but is provided at a position facing the optical head with the optical disc 300 interposed therebetween.

The semiconductor laser 20 is bonded to the waveguide 40, and the beam is incident on the waveguide 40. The beam that has propagated through the waveguide 40 is raised by the grating coupler 60 and enters the grating lens 50 to become an evanescent wave. By making the optical disk 300 and the recording surface 301 have optical transparency, the beam that has interacted with the recording surface 301 to become propagating light is transmitted through the optical disk 300 and the recording surface 301 and detected by the photodetector 90.
As an optical disc, one having irregularities provided on a transparent substrate,
Alternatively, it is possible to use a material such as a phase change medium, which is made of a material having optical transparency and having different transmittances.

When detecting transmitted light as in this embodiment, an optical system for condensing the transmitted light on the detector side and detecting the polarization direction of the beam is provided so that the light is used as a recording medium. A magnetic film can be used.

FIG. 8 is a block diagram of an optical head according to a fourth embodiment of the present invention. In this embodiment, three optical heads are arranged side by side on the same substrate so that a tracking error signal can be obtained even in an optical disc having continuous grooves.

In this embodiment, the tracking error can be detected by the so-called three spot method. The grating lenses 50, 51A, 51B are arranged in a direction perpendicular to the track of the optical disc, and the focal point of the grating lenses 51A, 51B is on the inner circumference side of the track with the focal point of the grating lens 50 as the center. It is adjusted so that the light beam is shifted to the outer peripheral side by about 1/4 track.

The data is reproduced by the photodetector 90 by the focused spot by the grating lens 50. The signals from the grating lenses 51A and 51B are detected by the photodetector 9
1A and 91B are reproduced, and a tracking error signal is obtained from the difference signal of the signals from the photodetectors 91A and 91B.

FIG. 9 is a diagram showing a mechanical system of an optical disk device to which the present invention is applied. The optical head of the present invention is small
Since the weight can be reduced, the optical head can be driven by a swing arm type actuator.

In the figure, the optical head 10 is attached to an air slider 101. Air slider 101
Is a fulcrum 10 via the spring 102 and the arm 103.
It is possible to rotate around 5. Arm part 10
3 has a coil 104 on the opposite side of the air slider 101, and can generate a rotational force in the arm portion 103 by the interaction with the magnet on the apparatus side.

Thus, the optical head can be moved from the inner circumference to the outer circumference of the optical disc 300 by the rotation of the arm portion.
Further, by slightly driving this actuator, it becomes possible to perform tracking in which the beam follows the track.

The air slider 101 floats above the optical disc 300 by a certain distance due to the balance of the air pressure caused by the rotation of the optical disc 300 and the force of the spring 102. In this embodiment, the flying height is 30 nm. If the fluctuation of the flying height is kept within the range required for focusing, focus control becomes unnecessary. By using the swing arm type actuator as in the present embodiment, it is possible to reduce the thickness of the mechanism portion and thus the entire apparatus. The optical disc is 2.
Use a 5-inch diameter and use a spindle motor for 18
It was rotated at 00 rpm.

Although the focus control is not performed in this embodiment, even if the focus control needs to be performed, since the optical head is small, it is mounted on a conventional two-dimensional actuator for performing focus and tracking and integrally driven. be able to.

FIG. 10 is a system configuration showing up to the data processing unit of the optical disk device, and the same reference numerals as those used above denote the same or equivalent portions.

In the figure, recording / reproducing of information to / from the optical disc 300 is performed by rotating the optical disc 300 by a spindle motor 900 and irradiating the optical head 10 with evanescent light. Optical head 10
Moves in parallel to the optical disc 300 by the swing arm type course actuator 700, and accesses from the inner circumference to the outer circumference of the optical disc 300.

The drive microcomputer 600 controls the drive unit and performs signal processing. Drive microcomputer 600
Controls the spindle servo unit 611, the focus servo unit 612, the tracking servo unit 613, and the course actuator servo unit 614 as a mechanical system. The drive microcomputer 600 also controls the modulation signal processing unit 660 and the detection signal processing unit 662 of the optical head.

The control microcomputer 605 sends an operation command to the drive microcomputer 600, receives a reproduction signal from the optical disk 300, and performs error correction. Further, the control microcomputer 605 also controls the interface when connecting to another system. The control of the two-stage servo and the switching of control during recording and during reproduction were performed by the drive microcomputer 600.

The spindle servo unit 611 controls the number of revolutions of the spindle motor 900, and CAV (Constant Angular Velocity) control, CL
V (Constant Linear Velocity) control and MCLV
(Modulated Constant Linear Velocity) control, etc., and these can be appropriately selected according to the system.

In this embodiment, the optical disk device including the circuit board has a thickness of 10 mm, and can be mounted on a laptop or notebook personal computer or workstation. Also, since the storage capacity is large and the data transfer rate is high, it is possible to record and reproduce moving images.

[0052]

As described above, according to the present invention,
Since an evanescent light is generated using a diffraction grating type grating lens, an optical head with a simple and compact structure and high light utilization efficiency can be realized, and an optical disc with a recording density higher than the recording density determined by the diffraction limit can be realized. It is possible to record / playback / delete information of the above.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of an optical head to which the present invention is applied.

FIG. 2 is a configuration diagram of a grating lens used in the present invention.

FIG. 3 is a diagram showing a film structure of an optical disk used in the present invention.

FIG. 4 is another schematic configuration diagram of an optical head to which the present invention is applied.

FIG. 5 is a configuration diagram of an optical head that is a first embodiment of the present invention.

FIG. 6 is a configuration diagram of an optical head that is a second embodiment of the present invention.

FIG. 7 is a configuration diagram of an optical head that is a third embodiment of the present invention.

FIG. 8 is a configuration diagram of an optical head that is a fourth embodiment of the present invention.

FIG. 9 is a diagram showing a mechanism system of an optical disc device to which the present invention is applied.

FIG. 10 is a system configuration diagram of an optical disc device to which the present invention is applied.

[Explanation of symbols]

1 ... Beam, 10 ... Optical head, 20, 20A, 20B ...
Semiconductor laser, 30 ... Collimating lens, 35 ... Half mirror, 40, 41, 42 ... Waveguide, 43 ... Transparent layer, 50
... Grating lens, 51A, 51B ... Tracking grating lens, 60, 61, 62 ... Grating coupler, 70 ... Hologram, 80 ... Substrate, 9
0, 91A, 91B ... Photodetector, 100 ... Swing arm actuator, 101 ... Air slider, 102 ... Spring, 103 ... Arm, 104 ... Coil, 105 ... Support point,
106 ... Leaf spring, 300 ... Optical disk, 301 ... Recording surface, 401, 403 ... Dielectric film, 402 ... Recording film, 40
4 ... Reflective film, 405 ... Optical disk substrate, 600 ... Drive microcomputer, 605 ... Control microcomputer, 611 ...
Spindle servo unit, 613 ... Tracking servo unit,
614 ... Coarse actuator servo unit, 660 ... Modulation signal processing unit, 662 ... Detection signal processing unit, 700 ... Coarse actuator

Claims (14)

[Claims] 1. In an optical head for forming a light spot on an information recording medium to optically record and reproduce information, the means for forming the light spot has a concentric diffraction grating and a central surface thereof. An optical head comprising a grating lens arranged so that evanescent light is generated in the vicinity. 2. A grating lens for converting the light emitted from the light source into an evanescent light and condensing it on the information recording medium, a means for separating the reflected light from the information recording medium from the emitted light, and the separated reflected light An optical head comprising a detecting means. 3. The optical head according to claim 2, wherein the means for separating the reflected light from the emitted light is a hologram formed on the back surface of the grating lens on which the diffraction grating is formed. . 4. A grating lens for converting the light emitted from a light source into an evanescent light and condensing it on an information recording medium, and a grating lens arranged so as to face the grating lens with the information recording medium sandwiched therebetween. An optical head comprising a detecting means. 5. A substrate for forming first and second optical waveguides, a light source optically connected to the first optical waveguide, and a light source optically connected to the first optical waveguide to emit from the light source. And a grating lens for converting the emitted light propagating through the first optical waveguide into an evanescent light and condensing it on the information recording medium, and separating the reflected light from the information recording medium from the emitted light to the second optical waveguide. An optical head comprising: a guiding unit; and a unit that is optically connected to the second optical waveguide and that detects the separated reflected light. 6. The optical head according to claim 5, wherein the optical waveguide and the grating lens are the same member. 7. The optical head according to claim 5, wherein three grating lenses are arranged adjacent to each other, and a light source and a reflected light detecting means are provided for each grating lens. 8. The optical head according to claim 1, wherein the grating lens is formed by arranging diffraction gratings in concentric circles at substantially equal intervals. 9. The optical head according to claim 1, wherein a central portion of a surface of the grating lens on which the diffraction grating is formed is raised in a spherical shape. 10. The optical head according to claim 9, wherein the grating lens is formed by arranging concentric circular diffraction gratings so that the distance increases as the distance from the center of the grating increases. 11. The light spot formed on the information recording medium by the grating lens has an intensity distribution in which the light intensity decreases from the central portion toward the outer peripheral portion, and the light intensity is approximately 1 at the central portion. The diameter in the range of / e ² is equal to or less than the wavelength of the light source.
11. The optical head according to any one of 1 to 10. 12. The optical head according to claim 1, wherein an interval between the diffraction gratings is shorter than a wavelength of emitted light. 13. An optical head according to any one of claims 1 to 12, a drive mechanism for driving the optical head in a radial direction of an optical disc, and a spindle motor for rotating the optical disc. Characteristic optical disk device. 14. The gap between the optical head and the information recording medium is maintained at a predetermined distance by the optical head floating above the information recording medium due to the air pressure accompanying the rotation of the information recording medium. The optical disk device according to claim 13.