WO2001033563A1 - Tete optique - Google Patents

Tete optique Download PDF

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Publication number
WO2001033563A1
WO2001033563A1 PCT/JP2000/007651 JP0007651W WO0133563A1 WO 2001033563 A1 WO2001033563 A1 WO 2001033563A1 JP 0007651 W JP0007651 W JP 0007651W WO 0133563 A1 WO0133563 A1 WO 0133563A1
Authority
WO
WIPO (PCT)
Prior art keywords
light
region
recording medium
information recording
light source
Prior art date
Application number
PCT/JP2000/007651
Other languages
English (en)
Japanese (ja)
Inventor
Akihiro Arai
Tohru Nakamura
Takao Hayashi
Original Assignee
Matsushita Electric Industrial Co., Ltd.
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Matsushita Electric Industrial Co., Ltd. filed Critical Matsushita Electric Industrial Co., Ltd.
Priority to AU79645/00A priority Critical patent/AU7964500A/en
Publication of WO2001033563A1 publication Critical patent/WO2001033563A1/fr

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Classifications

    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
    • G11B7/12—Heads, e.g. forming of the optical beam spot or modulation of the optical beam
    • G11B7/123—Integrated head arrangements, e.g. with source and detectors mounted on the same substrate
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
    • G11B7/12—Heads, e.g. forming of the optical beam spot or modulation of the optical beam
    • G11B7/13—Optical detectors therefor
    • G11B7/131—Arrangement of detectors in a multiple array
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
    • G11B7/12—Heads, e.g. forming of the optical beam spot or modulation of the optical beam
    • G11B7/135—Means for guiding the beam from the source to the record carrier or from the record carrier to the detector
    • G11B7/1353—Diffractive elements, e.g. holograms or gratings
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
    • G11B7/12—Heads, e.g. forming of the optical beam spot or modulation of the optical beam
    • G11B7/135—Means for guiding the beam from the source to the record carrier or from the record carrier to the detector
    • G11B7/1381—Non-lens elements for altering the properties of the beam, e.g. knife edges, slits, filters or stops
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
    • G11B7/12—Heads, e.g. forming of the optical beam spot or modulation of the optical beam
    • G11B7/135—Means for guiding the beam from the source to the record carrier or from the record carrier to the detector
    • G11B7/1372—Lenses
    • G11B2007/13727—Compound lenses, i.e. two or more lenses co-operating to perform a function, e.g. compound objective lens including a solid immersion lens, positive and negative lenses either bonded together or with adjustable spacing

Definitions

  • the present invention relates to an optical head for optically recording information on an information recording medium such as an optical disk, or optically reproducing information recorded on the information recording medium.
  • Figure 15 shows the configuration of a conventional optical head.
  • reference numeral 100 denotes a light source such as a semiconductor laser
  • reference numeral 101 denotes a collimating lens
  • reference numeral 102 denotes a prism
  • reference numeral 103 denotes a light-shielding band made of an opaque material
  • reference numeral 104 denotes an incident light.
  • 105 is a quarter-wave plate arranged with the fast axis rotated by 45 degrees with respect to the incoming linearly polarized light
  • 106 is An objective lens
  • 107 is an information recording medium
  • 108 is a detection optical system for detecting focus Z tracking and reproducing an information signal.
  • the spread angle of the emitted light is narrow in a cross section parallel to the plane of the paper, wide in a cross section perpendicular to the plane of the paper, and the light intensity distribution is an elliptical Gaussian distribution.
  • the light source 100 is arranged such that the electric vector of the polarized light is directed in a direction parallel to the paper surface.
  • a light beam emitted from the light source 100 is shielded at its central portion by a light shielding band 103, and is converted into a parallel light beam by a collimator lens 101.
  • the parallel light beam is deflected by the prism 102, so that the light beam width of the cross section parallel to the paper is expanded, so that the light intensity distribution is shaped into a flatter Gaussian distribution.
  • beam shaping Such shaping of the light intensity distribution of the light beam is referred to as “beam shaping”.
  • the light beam entering the polarization beam splitter 104 via the prism 102 is transmitted as it is and enters the quarter-wave plate 105 because the polarization direction is P-polarized light.
  • the light beam that has passed through the quarter-wave plate 105 and has become circularly polarized light is condensed on the information recording medium 107 by the objective lens 106.
  • the light beam reflected by the information recording medium 107 becomes a parallel light beam again by the objective lens 106 and enters the quarter-wave plate 105.
  • the parallel luminous flux passes through a quarter-wave plate 105 and is converted into linearly polarized light in which the direction of the electric vector is perpendicular to the plane of the paper.
  • the polarized light reentering the polarizing beam splitter 104 is now S-polarized light, and is reflected and guided to the detection optical system 108.
  • FIG. 16 shows the light intensity distribution on the pupil of the objective lens 106.
  • the shaded area in FIG. 16 is the area shielded by the light-shielding band 103.
  • Fig. 17 shows a cross-sectional view of the intensity distribution of a light spot collected by an optical system subjected to such apodization and a normal diffraction-limited light spot. This cross-sectional view shows a strength distribution in a cross section in a direction corresponding to the vertical direction in FIG.
  • the half peak width can be reduced, although the side peak of the light spot becomes larger than in the normal case.
  • an object that blocks light such as a light-shielding band is required in order to perform apodization, so that the light use efficiency (total light emitted from the light source) (The ratio of the light spot light amount on the information recording medium to the light amount) was reduced, and a light source having a high light output was required.
  • apodization is performed by using a member originally required as an optical head, so that light utilization efficiency is reduced due to apodization.
  • the tracking method is limited to the three-beam method.
  • the beam shaping is performed, and the detection optical system for detecting the focus Z tracking and the reproduction of the information signal are separately provided. ing. Disclosure of the invention
  • the present invention has been made to solve the above-mentioned problems in the prior art, and aims at realizing high light use efficiency with a simple configuration while aiming at miniaturization of a condensing spot by apodization.
  • the purpose is to provide an optical head that can.
  • a first configuration of the optical head includes: a light source; a light receiving unit; a light collecting unit that collects light emitted from the light source on an information recording medium; A light branching unit disposed between a light source and the light condensing unit, for guiding the light reflected by the information recording medium and incident again via the light condensing unit to the light receiving unit by diffracting or deflecting the light.
  • the step has a first area for diffracting or deflecting incident light, and a second area for not diffracting or deflecting, and the first area is a central portion of the light splitting means.
  • apodization can be performed by lowering the transmittance of the first region of the light branching unit.
  • the light source has an intensity distribution of emitted light having an elliptical Gaussian distribution, and a direction in which the spread angle of the emitted light is small.
  • the first area of the light splitting means is arranged so as to be parallel or perpendicular to the information track of the information recording medium, and has a shape having a short width in a direction in which a spread angle of light emitted from the light source is small. Is preferred.
  • apodization is performed so as to compensate for the decrease in the light intensity around the pupil of the condensing means (objective lens). Since the numerical aperture of the optical head can be set larger than in the past, an optical head having high light use efficiency can be realized.
  • the light branching unit is a diffraction element in which a diffraction grating is formed only in the first region.
  • the ratio of the transmittance of the first region to the transmittance of the second region of the light branching unit is T
  • the short width of the first region is W
  • the light collecting unit is
  • the diameter of the luminous flux restricted by the aperture of D is D, it is preferable that the following (Equation 1) and (Equation 2) are satisfied respectively. [Number 1]
  • the light branching unit is a half mirror that transmits a part of the light passing therethrough, reflects the remaining light, and guides the remaining light to the light receiving unit.
  • the shape of the region is a substantially rectangular or elliptical shape having a long width in a direction parallel to the information track of the information recording medium and a short width in a direction orthogonal to the information track.
  • the transmittance is preferably smaller than the transmittance of the second region.
  • the ratio of the transmittance of the first region to the transmittance of the second region of the light branching unit is T
  • the short width of the first region is W
  • the length of the light collecting unit is Assuming that the diameter of the light beam restricted by the aperture of D is D, it is preferable to satisfy the above (Equation 1) and (Equation 2).
  • a second configuration of the optical head according to the present invention includes: a light source; a light receiving unit; a light collecting unit that collects light emitted from the light source onto an information recording medium; A part of light transmitted from the light source toward the light collecting means, reflected by the information recording medium, and returned to the light source via the light collecting means.
  • a diffraction element that imparts diffraction and guides the light to the light receiving unit, wherein the diffraction element has a first region on which a diffraction grating is formed and a second region on which no diffraction grating is formed.
  • the shape of the first area is such that a width in a direction parallel to an information track of the information recording medium is long,
  • the width is substantially rectangular or substantially elliptical in a direction perpendicular to the information track, and the first region is arranged at a center of the diffraction element.
  • a third configuration of the optical head according to the present invention includes: a light source; a light receiving unit; a light collecting unit for collecting light emitted from the light source onto an information recording medium; A part of light transmitted from the light source toward the light collecting means, reflected by the information recording medium, and returned to the light source via the light collecting means.
  • a diffraction element that gives diffraction and guides the light to the light receiving unit, wherein the diffraction element has first and second regions in which a diffraction grating is formed, and the transmittance of the first region is The transmittance of the second area is smaller than that of the first area, and the shape of the first area is substantially rectangular in width in the direction parallel to the information track of the information recording medium and short in the direction perpendicular to the information track. Or a substantially elliptical shape, wherein the first region is disposed at a central portion of the diffraction element.
  • the first area light diffracted by the the diffracted light second region is characterized by being separately received by the light receiving means.
  • the third configuration of the optical head since the light in the entire area of the light beam is detected, apodization with high light use efficiency can be realized, and the tracking error signal and the information signal can be further improved. Can be detected.
  • the ratio of the transmittance of the first region to the transmittance of the second region of the diffraction element is T.
  • the length of the short width is W
  • the diameter of the luminous flux limited by the aperture of the light condensing means is D
  • FIG. 1 is a configuration diagram illustrating an optical head according to a first embodiment of the present invention
  • FIG. 2 is a configuration illustrating an arrangement of a light source and a light receiving unit of the optical head according to the first embodiment of the present invention
  • FIG. 3 is a diagram for explaining the optical branching means of the optical head according to the first embodiment of the present invention
  • FIG. 4 is a diagram for explaining the effect of the present invention
  • FIG. 6 is a view for explaining another example of the light splitting means in the head
  • FIG. 6 is a view for explaining still another example of the light splitting means in the optical head of the present invention
  • FIG. FIG. 8 is a configuration diagram illustrating an optical head according to a third embodiment of the present invention.
  • FIG. 3 is a diagram for explaining the optical branching means of the optical head according to the first embodiment of the present invention
  • FIG. 4 is a diagram for explaining the effect of the present invention
  • FIG. FIG. 6 is a view for explaining another example of the light splitting means in the head
  • FIG. 8 is a diagram illustrating a light branching unit of the optical head according to the third embodiment of the present invention. Is a configuration diagram showing the arrangement of the light receiving means of the optical head according to the third embodiment of the present invention, and FIG. 10 is a diagram showing the arrangement of the third embodiment of the present invention.
  • FIG. 11 is a view for explaining a diffraction element of an optical head in FIG. 11.
  • FIG. 11 is a diagram showing a third embodiment of the present invention, in which a light beam reflected by an information recording medium of an optical head and returned therefrom is split by a light splitting means.
  • FIG. 12 is a diagram showing the appearance as seen above
  • FIG. 12 is a configuration diagram showing an optical head according to a fourth embodiment of the present invention, and FIG.
  • FIG. 13 is an optical head according to the fourth embodiment of the present invention.
  • FIG. 14 is a diagram illustrating the arrangement of a light source and a light receiving unit of an optical head according to a fourth embodiment of the present invention
  • FIG. 15 is a diagram illustrating conventional optical science.
  • Fig. 16 shows the light intensity distribution on the pupil of the objective lens of the conventional optical head
  • Fig. 17 shows the light collected by the conventional apodized optical system.
  • FIG. 4 is an intensity distribution sectional view of FIG. BEST MODE FOR CARRYING OUT THE INVENTION
  • FIG. 1 is a configuration diagram showing an optical head according to the first embodiment of the present invention.
  • 1 is a light receiving and emitting element in which a light source and a light receiving element are integrated
  • 2 is a diffractive element as a light splitting means
  • 3 is a half mirror that transmits a part of light and reflects the rest
  • 4 is a light collecting means.
  • 5 is an information recording medium
  • 6 is a light receiving element.
  • FIG. 2 is a configuration diagram showing the light emitting / receiving element 1 described above.
  • 7 is a light source
  • 8, 9, 10, and 11 are three-division light-receiving elements, and each of the light-receiving parts is composed of 8a to 8c, 9a to 9c, and 10a.
  • the light source 7 is a light source that emits light in a direction perpendicular to the plane of FIG. 2, such as a surface-emitting laser, a normal semiconductor laser mounted in a direction perpendicular to the plane of the paper, and a mirror. After that, a mirror and a semiconductor laser mounted so as to emit light in a direction perpendicular to the paper surface can be used.
  • FIG. 3 is a diagram for explaining the diffraction element 2.
  • reference numeral 12 denotes a diffraction grating forming region in which a diffraction grating is formed, and the average period of the formed diffraction gratings differs between the diffraction grating forming region 12a and the diffraction grating forming region 12b.
  • Reference numeral 13 denotes the outer shape of the light beam passing through the diffraction element 2.
  • the arrows in FIG. 3 indicate that the up and down directions in the figure correspond to the directions of the information tracks.
  • the zero-order diffraction efficiency, that is, the transmittance, of the diffraction grating forming region 12 is, for example, 50%, and the transmittance of the region where the diffraction grating is not formed is about 100%.
  • the light beam emitted from the light source 7 of the light receiving / emitting element 1 enters the diffraction element 2. Since the transmittance of the diffraction grating forming region 12 is smaller than that of the surroundings, the light intensity distribution of the light beam that has passed through the diffraction element 2 is a distribution in which the intensity decreases in a band shape at the center.
  • the light beam that has passed through the diffraction element 2 further passes through the half mirror 13, and is focused on the information recording medium 5 by the objective lens 4.
  • the collected light forms a smaller light spot than usual.
  • the light reflected by the information recording medium 5 enters the half mirror 3 via the objective lens 4.
  • the light reflected by the half mirror 3 enters the light receiving element 6, whereby an information signal or the like is detected.
  • the light transmitted through the half mirror 3 again enters the diffraction element 2, and the light diffracted by the diffraction grating forming region 12 is guided to the three-division light receiving elements 8 to 11 on the light receiving and emitting element 1.
  • the light diffracted by the diffraction grating forming region 12a is incident on, for example, the three-division light receiving elements 9 and 10, and the light diffracted by the diffraction grating forming region 12b is, for example, the three-division light receiving devices 8 and 1. Incident at 1.
  • the luminous flux entering the three-division light receiving elements 8 and 9 focuses closer to the diffraction element 2 than the light receiving elements
  • the light beams incident on the three-division light receiving elements 10 and 11 focus on a place farther than the light receiving elements.
  • the diffraction grating forming regions 12a and 1b are so arranged that the size of each light beam on each of the three divided light receiving elements in the direction orthogonal to the division line of the light receiving element is substantially equal.
  • the focus error signal FE can be detected by performing the operation shown in the following (Equation 5).
  • the diffraction grating forming regions 12 a and 12 b divide the luminous flux by a center line parallel to the track direction of the information recording medium 5, so that the so-called push-pull tracking is performed.
  • the tracking error signal TE can be detected by performing the calculation shown in the following (Equation 6).
  • each light receiving section of the three-division light receiving element is indicated by the name of each light receiving part, such as 8a to l1c, and the sum signal of the signals detected by each three-division light receiving element is Each light receiving element name is shown as 8 to 11.
  • apodization is performed using a band-like diffraction grating forming region 12 extending in a direction orthogonal to the track of the information recording medium 5. Therefore, if a light source with a uniform intensity distribution of the emitted light is used, or in the case of a light source with an elliptical Gaussian distribution as the intensity distribution, the direction in which the spread angle of the emitted light is large is set in the track direction.
  • the distribution of the light intensity on the pupil of the objective lens 4 in the track direction can be made substantially uniform.
  • the half width of the light spot focused on the information recording medium 5 in the track direction is narrowed to the diffraction limit or less.
  • the transmittance outside the diffraction grating forming region 12 is about 100%, the light use efficiency is higher than in the conventional optical head in which the diffraction grating is formed on the entire surface. Can be improved.
  • the width of the band-shaped diffraction grating forming region 12 is W
  • the diffraction grating is Assuming that the ratio of the transmittance of the diffraction grating forming region 12 to the transmittance of the non-formed region is T and that the diameter of the light beam restricted by the aperture of the objective lens 4 is D, the following (Equation 7) and (Equation 8) ) Should be satisfied.
  • the numerical aperture (NA) of the objective lens 4 is 0.6
  • the wavelength ( ⁇ ) of the light emitted from the light source 7 is 650 nm
  • the light intensity distribution on the pupil of the objective lens 4 is uniform
  • the ratio (T) of the transmittance of the diffraction grating forming area 12 to the transmittance of the area where no diffraction grating is formed (T) is 0.5
  • how the half-width of the light spot changes according to the value of WZD The calculated result is shown.
  • the horizontal axis is WZD
  • WZD the value of WZD is between 0.2 and 0.8.
  • the effect of apodization is not sufficiently exhibited, and the value of WZD is smaller than 0.2. When this happens, the amount of light required for signal detection cannot be obtained.
  • the light spot diameter in the track direction can be narrowed to the diffraction limit or less, so that the recording density in the linear direction can be improved. Also, since means for applying apodization to the diffraction element 2 for signal detection, which is originally required for the optical head, are provided, an optical head with a simple configuration and high light use efficiency can be realized. Can be.
  • a second embodiment of the present invention will be described.
  • the difference from the first embodiment is that a light source in which the light intensity distribution of the emitted light is an elliptical Gaussian distribution is used, and the direction in which the spread angle of the light is small is parallel to the track direction of the information recording medium.
  • This is the point that the light source is arranged at Since the configuration of the optical head is the same as that of the first embodiment, only different points will be described with reference to the drawings.
  • the diffraction element 2 Since the light source 7 is arranged so that the direction in which the spread angle of the light emitted from the light receiving / emitting element 1 is small is parallel to the track direction of the information recording medium 5, the diffraction element 2 The light intensity around the light beam incident on the track is low in the track direction and high in the direction perpendicular to the track. As shown in FIG. 3, since the diffraction grating forming region 12 has a narrow width in the track direction, apodization is performed so as to compensate for a low ambient light intensity in the track direction.
  • the light condensed on the information recording medium 5 is narrowed down to the diffraction limit by apodization even in the track direction where the peripheral light intensity is not sufficient, and is diffracted as it is in the direction orthogonal to the track where the peripheral intensity is sufficient. It is narrowed down to the limit, forming an almost circular light spot.
  • the light intensity around the pupil of the focusing means is low.
  • beam spots could not be narrowed down to the diffraction limit, so conventionally, a beam shaping prism was used to flatten the light intensity distribution in the direction where the spread angle of the emitted light was small, or the light source side of the optical head Had a small numerical aperture.
  • the numerical aperture on the light source side can be relatively increased without using a beam shaping prism. Since the configuration can be set to a large value, the light use efficiency of the optical head can be improved.
  • a small circular light spot close to the diffraction limit can be formed with a simple configuration that does not require an optical system for beam shaping, and the light use efficiency can be improved. It is possible to realize an optical head with high performance.
  • the light sources are arranged such that the direction in which the spread angle of the emitted light is small is parallel to the track direction of the information recording medium.
  • the light source is not necessarily limited to this configuration. The same effect can be obtained by arranging the light sources such that the direction in which the spread angle of the emitted light is small is perpendicular to the track direction of the information recording medium.
  • the shape of the diffraction grating forming region 12 is a long band in the direction orthogonal to the track of the information recording medium 5 has been described as an example. It is not necessarily limited to such a shape.
  • the shape of the diffraction grating forming region 12 may be, for example, as shown in FIG. 5, a long strip in the track direction of the information recording medium 5, or as shown in FIG. It may be a shape surrounded by.
  • FIG. 7 is a configuration diagram showing an optical head according to the third embodiment of the present invention.
  • the same components as those of the optical head shown in FIG. 1 are denoted by the same reference numerals.
  • 14 is a light source
  • 15 is a half mirror as light branching means for transmitting a part of light and reflecting the rest
  • 4 is an objective lens as light collecting means
  • 5 is an information recording medium
  • 16 Denotes a diffraction element
  • 17 denotes a light receiving element.
  • FIG. 8 is a diagram for explaining the half mirror 15 described above.
  • reference numeral 18 denotes an outer shape of a light beam passing through the half mirror 15, and reference numerals 19 and 20 denote first and second regions having different transmittances, respectively.
  • the arrows in FIG. 8 indicate that the up and down directions in the figure correspond to the directions of the information tracks.
  • the first region 19 (shaded area) and the second region 20 (area other than the shaded area) are formed by depositing thin films having different transmittances (for example, metal or dielectric). Is formed.
  • the transmittance of the first region 19 is 50 percent (the reflectance is 50 percent)
  • the transmittance of the second region 20 is 80 percent (the reflectance is 20 percent).
  • FIG. 9 is a configuration diagram showing the light receiving element 17.
  • 21, 22, 23, and 24 are three-division light-receiving elements, each of which has a light-receiving portion, 21 a to 21 c, 22 a to 22 c, and 23 a to 23 c, 24a to 24c.
  • FIG. 10 is a diagram for explaining the diffraction element 16.
  • the density of the vertical line represents the density of the formed diffraction grating, and is the same as that of FIG. 3 except that the area where the diffraction grating is formed is not limited. Detailed description is omitted.
  • the light beam emitted from the light source 14 enters the half mirror 15.
  • the transmittance of the first area 19 of the half mirror 15 is the other area (the second area 2 0)
  • the light intensity distribution of the luminous flux transmitted through the half-mirror 15 is a distribution in which the intensity is reduced in a band at the center.
  • the light beam transmitted through the half mirror 15 is focused on the information recording medium 5 by the objective lens 4.
  • the condensed light is diffracted in the direction orthogonal to the information track. Form a light spot smaller than the limit.
  • the light reflected by the information recording medium 5 enters the half mirror 15 via the objective lens 4.
  • the light reflected by the half mirror 15 enters the diffraction element 16 and is split by the diffraction element 16 so that the focus error signal and the tracking error signal can be detected. It is guided to the three-segment light receiving element 21-24 on 17.
  • the three-segment light receiving elements 21 to 24 correspond to the three-segment light receiving elements 8 to 11 shown in FIG. 2, respectively.
  • the light diffracted by the diffraction element 16 and the light diffracted by the diffraction element 2 (FIG. 2) Since the behavior is the same, the focus error signal FE and the tracking error signal TE can be detected as described in the first embodiment.
  • the signals FE and TE are represented by the following (Equation 9) and (Equation 10).
  • FIG. 11 shows a state in which the light beam reflected and returned by the information recording medium 5 is viewed on the half mirror 15.
  • 25 indicates a diffracted light beam due to a pit or a recording mark. Since the light intensity modulation due to pits and the like is caused by the interference between the 0th-order diffracted light beams indicated by the diffracted light beams 25 and 18, it is necessary to detect the light intensity distribution in the information track direction on the light beam cross section.
  • the reflectance of the first region 19 (shaded portion) having a long shape in the information track direction is, for example, 50%, which is smaller than the reflectance of the peripheral region (second region 20). Is set to a large value, so that the information signal can be detected favorably.
  • the apodization of this embodiment works to reduce the diameter of the light spot in the direction perpendicular to the information track, so that information can be recorded / reproduced on / from an information recording medium with a higher information track density.
  • the width of the first area 19 is W
  • the ratio of the transmittance of the first area 19 to the transmittance of the second area 20 areas other than the hatched area.
  • T is the diameter of the luminous flux limited by the aperture of the objective lens 4 and D is the same as in the first embodiment, it is desirable to satisfy the above (Equation 7) and (Equation 8) It is.
  • the means for applying apodization to the half mirror 15 that splits light toward the light receiving element 17 since the means for applying apodization to the half mirror 15 that splits light toward the light receiving element 17 is provided, information recording with a high information track density is performed. Not only can the recording / reproducing performance of the medium be improved, but also the loss of light from the light source 14 to the information recording medium 5 can be suppressed to improve the light use efficiency, and the information signal can be detected well. It becomes possible.
  • FIG. 12 is a configuration diagram showing an optical head according to the fourth embodiment of the present invention.
  • the same components as those of the optical head shown in FIG. 1 are denoted by the same reference numerals.
  • reference numeral 26 denotes a light receiving and emitting element in which a light source and a light receiving element as a light receiving means are integrated
  • 27 is a diffraction element
  • 4 is an objective lens as a light collecting means
  • 5 is an information recording medium. is there.
  • FIG. 13 is a view for explaining the diffraction element 27.
  • reference numeral 28 denotes the outer shape of a light beam passing through the diffraction element 27, and reference numerals 29, 30 and 31 denote regions where different diffraction gratings are formed (30: the first region, 29, 31: second area).
  • the arrows in FIG. 13 indicate that the up and down directions in the figure correspond to the directions of the information tracks.
  • the first region 30 has, for example, a 0th-order diffraction efficiency (corresponding to the light transmittance) of 50%
  • the second regions 29, 31 have, for example, a 0th-order diffraction efficiency of 80%.
  • a diffraction grating is formed so as to be a percentage.
  • FIG. 14 is a configuration diagram showing the light receiving / emitting element 26 described above. The description of the light source and the four three-segment light receiving elements, which are the same as those in FIG. 2, will be omitted. The difference from FIG. 2 is that four light receiving elements 32 to 35 are added.
  • the light beam emitted from the light source of the light receiving / emitting element 26 enters the diffraction element 27. Since the transmittance of the first region 30 is smaller than that of the other regions (the second regions 29 and 31), the light intensity distribution of the light beam passing through the diffraction element 27 has a band shape in the center. The distribution has a reduced strength.
  • the light beam that has passed through the diffraction element 27 is focused on the information recording medium 5 by the objective lens 4. At this time, since the light intensity distribution on the pupil of the objective lens 4 is apodized by the diffraction element 27, the size of the condensed light in the direction orthogonal to the information track is diffraction limited. To form smaller light spots.
  • the light reflected by the information recording medium 5 is diffracted through the objective lens 4 It is incident on 27.
  • the light diffracted by the diffraction element 27 is guided to the light receiving element on the light receiving and emitting element 26.
  • the first region 30 of the diffraction element 27 guides light to each of the three-division light-receiving elements similarly to the diffraction element 2 of the first embodiment, and detects a focus error signal and a tracking error signal.
  • the diffraction grating is formed so as to perform the above.
  • One of the second regions 29 of the diffraction element 27 has, for example, a diffraction grating formed so that diffracted light is guided to the light receiving elements 32 and 35, and the other second region 31 has For example, a diffraction grating is formed so that the diffracted light is guided to the light receiving elements 33 and 34. Since the signals detected by the four three-division light-receiving elements are signals that have detected the light beam that has passed through the first area 30, a part of the light beam that has been reflected back by the information recording medium 5 has been detected. Will be.
  • the signals detected by the light receiving elements 32 to 35 include the first-order diffraction of the second regions 29 and 31 with respect to the first-order diffraction efficiency of the diffraction grating of the first region 30.
  • the coefficient by which the signals detected by the light receiving elements 32 to 35 are multiplied may be increased or decreased. This makes it possible to increase the amplitude of the push-pull signal, which is the tracking error signal, and the amplitude of the information signal.
  • the tracking error signal TE is as shown in (Equation 11).
  • G is the ratio of the first-order diffraction efficiency of the second regions 29, 31 to the first-order diffraction efficiency of the diffraction grating of the first region 30.
  • the information signal is G times the sum of signals 8 to 11 and the sum of signals 32 to 35 By detecting from the sum signal of the obtained signals, it is possible to detect the signal contained in all of the luminous flux.
  • the apodization of the present embodiment works to reduce the diameter of the light spot in the direction perpendicular to the information tracks, it is possible to record and reproduce information even on an information recording medium having a higher information track density than before.
  • the width of the first region 30 is W
  • the ratio of the transmittance of the first region 30 to the transmittance of the second regions 29 and 31 is T
  • D the diameter of the luminous flux limited by the aperture of the lens 4
  • the first region 30 and the second region 2 made of the diffraction grating are provided in the diffraction element 27 which is the only light branching means arranged in the optical path. 9 and 31 are formed, and the transmittance of the first region 30 is made smaller than the transmittance of the second region 29 and 31 to perform apodization, thereby achieving the information recording medium having a high information track density. Not only can the recording / reproducing performance be improved, but also the light loss from the light source of the light receiving / emitting element 26 toward the information recording medium 5 can be suppressed, and the light use efficiency can be improved. Further, since the light passing through the second regions 29 and 31 is also detected, it is possible to detect the tracking error signal and the information signal more favorably.
  • the first area is formed in a band shape having a long width in the direction parallel to the information track of the information recording medium 5 and a short width in the direction perpendicular to the information track.
  • the shape of the first region may be a substantially rectangular shape or a substantially elliptical shape.
  • SSD method spot Size Detection
  • Foucault method Foucault method
  • a diffraction element or a half mirror has been described as an example of a light branching unit.
  • a Fresnel lens ⁇ An optical branching element made of a birefringent material or the like may be used.
  • the present invention it is possible to realize a high light use efficiency with a simple configuration while aiming at miniaturization of the light collecting spot by apodization, and therefore, it is possible to reduce the information track density. It can be used for optical heads used for recording and playback of high information recording media.

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  • Physics & Mathematics (AREA)
  • Optics & Photonics (AREA)
  • Optical Head (AREA)

Abstract

L'invention concerne une tête optique présentant une structure simple très efficace qui présente l'avantage de réduire la taille des points par apodisation. Un élément de diffraction (2) destiné à dévier la lumière sur un photodétecteur de détection de signal vient entre un élément de sortie de lumière et un élément de détection (1) ainsi qu'une lentille (4). L'élément de diffraction (2) comprend une première zone dans laquelle un réseau de diffraction est formé et une seconde zone exempte de réseau de diffraction ne s'est formé. La première zone se trouve au centre du flux lumineux en direction de la lentille (4) et part d'une source lumineuse de manière que l'apodisation ait lieu avec une transmissibilité réduite de manière à résorber les pertes optiques dues à l'apodisation.
PCT/JP2000/007651 1999-11-01 2000-10-30 Tete optique WO2001033563A1 (fr)

Priority Applications (1)

Application Number Priority Date Filing Date Title
AU79645/00A AU7964500A (en) 1999-11-01 2000-10-30 Optical head

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
JP31071199A JP2005100476A (ja) 1999-11-01 1999-11-01 光学ヘッド
JP11/310711 1999-11-01

Publications (1)

Publication Number Publication Date
WO2001033563A1 true WO2001033563A1 (fr) 2001-05-10

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PCT/JP2000/007651 WO2001033563A1 (fr) 1999-11-01 2000-10-30 Tete optique

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JP (1) JP2005100476A (fr)
AU (1) AU7964500A (fr)
WO (1) WO2001033563A1 (fr)

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP2007200477A (ja) * 2006-01-27 2007-08-09 Funai Electric Co Ltd 光ヘッド

Citations (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPH02265036A (ja) * 1989-04-05 1990-10-29 Olympus Optical Co Ltd 光学ヘッド
JPH03178064A (ja) * 1989-12-07 1991-08-02 Nec Corp 光ヘッド装置
JPH03292644A (ja) * 1990-04-09 1991-12-24 Matsushita Electric Ind Co Ltd 光ピックアップ装置
JPH04157634A (ja) * 1990-10-19 1992-05-29 Sharp Corp 光ピックアップ
JPH07141681A (ja) * 1993-11-18 1995-06-02 Ricoh Co Ltd 光ヘッド
JPH07192302A (ja) * 1993-12-28 1995-07-28 Nec Corp 超解像光ヘッド装置
JPH07311969A (ja) * 1994-05-17 1995-11-28 Nec Corp 光ヘッド装置
JPH10208280A (ja) * 1997-01-29 1998-08-07 Matsushita Electric Ind Co Ltd 光ヘッド

Patent Citations (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPH02265036A (ja) * 1989-04-05 1990-10-29 Olympus Optical Co Ltd 光学ヘッド
JPH03178064A (ja) * 1989-12-07 1991-08-02 Nec Corp 光ヘッド装置
JPH03292644A (ja) * 1990-04-09 1991-12-24 Matsushita Electric Ind Co Ltd 光ピックアップ装置
JPH04157634A (ja) * 1990-10-19 1992-05-29 Sharp Corp 光ピックアップ
JPH07141681A (ja) * 1993-11-18 1995-06-02 Ricoh Co Ltd 光ヘッド
JPH07192302A (ja) * 1993-12-28 1995-07-28 Nec Corp 超解像光ヘッド装置
JPH07311969A (ja) * 1994-05-17 1995-11-28 Nec Corp 光ヘッド装置
JPH10208280A (ja) * 1997-01-29 1998-08-07 Matsushita Electric Ind Co Ltd 光ヘッド

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP2007200477A (ja) * 2006-01-27 2007-08-09 Funai Electric Co Ltd 光ヘッド

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Publication number Publication date
JP2005100476A (ja) 2005-04-14
AU7964500A (en) 2001-05-14

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