US20010010583A1 - Optical pickup device - Google Patents
Optical pickup device Download PDFInfo
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- US20010010583A1 US20010010583A1 US09/824,037 US82403701A US2001010583A1 US 20010010583 A1 US20010010583 A1 US 20010010583A1 US 82403701 A US82403701 A US 82403701A US 2001010583 A1 US2001010583 A1 US 2001010583A1
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- pickup device
- light beam
- optical element
- beam shaping
- optical pickup
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- 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
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- 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
- G11B7/1398—Means for shaping the cross-section of the beam, e.g. into circular or elliptical cross-section
Abstract
An optical pickup device in which a light beam radiated from a semiconductor laser element is converted by a collimator lens into collimated light beam which is converged by an objective lens so as to be illuminated on an optical disc. A beam shaping element having a hologram pattern on its incident surface and/or its radiating surface is provided on a divergent optical path of the radiated light beam from the semiconductor laser element between the semiconductor laser element and the collimator lens for shaping the light beam radiated from the semiconductor laser element for forming a beam spot of an optimum shape on the optical disc.
Description
- This invention relates to an optical pickup device employing a semiconductor laser element as a light source for radiating a light beam. More particularly, it relates to an optical pickup device configured for shaping a light beam for reducing the beam spot of the light beam radiated from the semiconductor laser device so as to be converged on the recording medium.
- Up to now, attempts have been made to elevate the recording density of, for example, an optical disc, used as a recording medium for a disc-shaped recording medium for the audio information or the picture information, by a recording/reproducing apparatus used for recording data processed by the computer system. For elevating the density of this sort of the recording medium, the recording track formed on the recording medium for recording information signals is reduced in pitch, and the recording pit is also reduced in size, for elevating the recording density per unit area.
- For recording and/or reproducing the information signals for an optical disc improved in the recording density, it is required to use an optical pickup device capable of reducing the spot size of the light beam illuminated on the optical disc.
- The optical pickup device for illuminating a converged light beam on an optical disc employs a semiconductor laser element as a light source and shapes the light beam radiated by this semiconductor laser element by an optical component to split the light beam into plural light beam portions which are condensed on the optical disc. This optical pickup device includes a photodetector for detecting a return light beam reflected from the optical disc and detects the return light beam by this photodetector to detect the information signals recorded on the optical disc in order to reproduce the information. The optical pickup causes the light beam radiated from the semiconductor laser element to be converged and illuminated as fine-sized beam spot on the optical disc.
- The beam spot diameter of the light beam illuminated on an optical disc is given by the wavelength λ of the light beam and the numerical aperture NA of an objective lens of the optical pickup device configured for condensing the light beam on the optical disc. Specifically, the beam spot diameter of the light beam illuminated on the optical disc is given by λ/NA. Therefore, if the wavelength λ of the light beam used is constant, it is necessary to increase the numerical aperture NA of the objective lens used for converging the light beam.
- Meanwhile, in a light beam radiated from a semiconductor laser element used as a light source of the optical pickup device, there is produced a change in the radiation angle between the TE direction (direction of the electrical field) and the TM direction (direction of the magnetic field). That is, the radiation angle of the light beam radiated from the semiconductor laser element is not uniform when seen from the light-emitting point, and differs from one light beam radiated from each light emitting point to another. If the light beams having different radiation angles are converged by the objective lens to form a beam spot on the optical disc, the beam spot formed on the optical disc becomes elliptically-shaped or is not converged to a desired size but is increased in spot diameter because the radiation angle of the light beam radiated from each light-emitting point is not constant.
- For overcoming these inconveniences, there is mounted a beam shaping element on the light path of the light beam radiated from the semiconductor laser element for enlarging or narrowing the light beam radiated from the semiconductor laser element in one direction.
- As the beam shaping element, a lens termed an anamorphic lens is usually employed. If this anamorphic lens is placed on a divergent light path of the light beam radiated from the semiconductor laser element, there is produced aberration, such as astigmatic aberration or coma aberration. It is therefore necessary to provide the anamorphic lens in the light path of the light beam collimated by, for example, a collimator lens. That is, in the optical pickup device employing the anamorphic lens as the beam shaping element used for shaping the light beam, it is necessary to provide a collimator lens for collimating the light beam radiated as a divergent light beam from the semiconductor laser element. Thus, not only can the optical path length from the semiconductor laser element to the anamorphic lens not be reduced, but also it is difficult to reduce the size of the device.
- For shaping the shape of the beam spot formed on the optical disc, there is proposed an optical pickup device in which a cylindrical lens is arranged on the optical path of the light beam radiated from the semiconductor laser element and in which a plan-parallel glass plate is arranged at a pre-set angle relative to the optical axis of the light beam. With this optical pickup device, it is difficult to remove completely the aberration in the beam spot of the light spot converged on the optical disc.
- It is an object of the present invention to provide an optical pickup device whereby the information signals recorded on an optical disc designed for high density recording of information signals can be read out correctly.
- It is another object of the present invention to provide an optical pickup device whereby the light beam radiated from the semiconductor laser element can be shaped without producing aberration in the light beam to enable the light beam to be converged with a fine-sized beam spot on the optical disc.
- It is yet another object of the present invention to provide an optical pickup device whereby the optical path length for the light beam from the semiconductor laser element radiating the light beam to an objective lens converging the light beam to illuminate the converged light beam on the optical disc can be reduced to enable the device itself to be reduced in size.
- For accomplishing the above object, an optical pickup device according to the present invention includes a beam shaping element arranged on a divergent optical path of a light beam radiated from a semiconductor laser element. By this beam shaping element, the light beam is shaped to fall on the objective lens. In this manner, the light beam is shaped without producing aberration and is converged highly accurately so as to be illuminated on the optical disc.
- The beam shaping element has an incident surface and an outgoing surface at least one of which carries a hologram pattern.
- Alternatively, the beam shaping element is flat-plate-shaped and has a hologram pattern and a cylindrical lens unit on one of the incident surface and the outgoing surface and on the other of the incident surface and the outgoing surface, respectively.
- An optical pickup device according to the present invention includes a semiconductor laser element, a collimator lens for collimating a light beam radiated from the semiconductor laser element, an objective lens for converging the collimated light from the collimator lens and beam shaping means arranged on a divergent optical path of a light beam radiated from the semiconductor laser element on a light path between the semiconductor laser element and the collimator lens.
- With this optical pickup device, a beam splitter is arranged between the beam shaping element and the collimator lens. The beam splitter separates the light beam radiated from the semiconductor laser element from the light beam incident via the objective lens.
- Other objects and advantages of the present invention will become more apparent from the following description.
- FIG. 1 is a side view showing an example of an optical pickup device according to the present invention.
- FIG. 2 shows the state of a light beam radiated from the semiconductor laser element.
- FIG. 3 illustrates light intensity distribution in the X- and Y-directions of the light beam radiated from the semiconductor laser element.
- FIG. 4 illustrates the state of the light beam condensed in an aperture of an objective lens.
- FIG. 5 is a plan view showing an example of a hologram pattern formed on a beam shaping element.
- FIG. 6a is a schematic side view showing, on an XZ plane, how the light beam traverses the beam shaping element constituting an optical pickup device according to the present invention, and
- FIG. 6b is a schematic side view showing, on a YZ plane, how the light beam traverses the beam shaping element constituting an optical pickup device according to the present invention.
- FIG. 7 is a schematic side view showing, on the XZ plane, how the light beam traverses the beam shaping element constituting an optical pickup device according to the present invention.
- FIG. 8a is a schematic side view showing, on the XZ plane, how a light beam traverses a beam shaping element according to a modification, and
- FIG. 8b is a schematic side view showing, on the YZ plane, how a light beam traverses the beam shaping element according to the modification.
- FIG. 9a is a schematic side view showing, on the XZ plane, how a light beam traverses a beam shaping element according to a still another modification, and
- FIG. 8b is a schematic side view showing, on the YZ plane, how a light beam traverses the beam shaping element according to this modification.
- FIG. 10a is a schematic side view showing, on the XZ plane, how a light beam traverses a beam shaping element according to yet another modification, and
- FIG. 10b is a schematic side view showing, on the YZ plane, how a light beam traverses a beam shaping element according to this modification.
- FIG. 11 is a plan view showing the state of the light beam on the lens aperture surface of an objective lens and a signal recording surface of an optical disc.
- FIG. 12 is a plan view showing the state of the light beam on the lens aperture surface of an optical pickup device not having a beam shaping element and on the signal recording surface of the optical disc.
- FIG. 13 is a schematic side view for illustrating the spherical aberration produced on the XZ plane by the light beam traversing the beam shaping element.
- FIG. 14 is a schematic side view for illustrating the spherical aberration produced on the YZ plane by the light beam traversing the beam shaping element.
- FIG. 15 is a side view showing on the YZ plane an example of using a beam shaping element having both surfaces as columnar lenses and having coincident radii of curvature of the incident surface and the radiating surface.
- FIG. 16 is a side view showing on the YZ plane an example of using a beam shaping element having both surfaces as columnar lenses and adapted for freeing the light beam traversing the element of aberration.
- FIG. 17a is a schematic side view showing, on the XZ plane, an example of using a beam shaping element in the form of a cylindrical lens at least one surface of which is a non-spherical surface in the YZ plane, and
- FIG. 17b is a schematic side view showing, on the YZ plane, an example of using a beam shaping element in the form of a cylindrical lens at least one surface of which is a non-spherical surface in the XZ plane.
- FIG. 18a is a schematic side view showing, on the XZ plane, an example of using a beam shaping element in the form of a cylindrical lens both surfaces of which are non-spherical surfaces in the YZ plane, and
- FIG. 17b is a schematic side view showing, on the YZ plane, an example of using a beam shaping element in the form of a cylindrical lens both surfaces of which are non-spherical surfaces in the XZ plane.
- An optical pickup device according to the present invention is hereinafter explained with reference to the drawings.
- The
optical pickup device 1 includes, as a light source, asemiconductor laser element 2, as shown in FIG. 1. Thesemiconductor laser element 2 radiates a light beam as a divergent light beam radiated at a pre-set radiation angle from an oscillation area. - The
optical pickup device 1, having thesemiconductor laser element 2, includes abeam shaping element 3, abeam splitter 4, acollimator lens 5 and anobjective lens 7, in this order, looking from the side of thesemiconductor laser element 2 radiating the light beam. - The
beam shaping element 3 is arranged on an optical path of the divergent light radiated from thesemiconductor laser element 2, because the beam shaping element is arranged between thesemiconductor laser element 2 and thebeam splitter 4. - The light beam radiated from the
semiconductor laser element 2 is transmitted through thebeam shaping element 3 to fall on thebeam splitter 4. The light beam transmitted through thebeam splitter 4 is collimated by acollimator lens 5 to fall on theobjective lens 7 so as to be thereby converged and illuminated on asignal recording surface 6 a of anoptical disc 6. - The light beam illuminated on the
signal recording surface 6 a of theoptical disc 6 is reflected by thesignal recording surface 6 a to fall on theobjective lens 7. The return light beam from theobjective lens 7 is transmitted through theobjective lens 7 and thecollimator lens 5 and subsequently falls on thebeam splitter 4 so that it has its optical axis bent 90° by apolarizing film 4 a provided on thebeam splitter 4. Thebeam splitter 4 permits the light beam radiated from thesemiconductor laser element 2 to be transmitted therethrough, while bending the optical axis of the light beam reflected by thesignal recording surface 6 a of theoptical disc 6 by 90°. Thus, thebeam splitter 4 operates as an optical element for separating the light beam reflected by thesemiconductor laser element 2 from the light reflected from thesignal recording surface 6 a of theoptical disc 6. - The return light beam from the
optical disc 6, having its optical axis bent 90° by the lightpolarizing film 4 a of thebeam splitter 4, falls on anoptical analyzer 8 which plane-polarizes this light beam. The light beam, plane-polarized by theoptical analyzer 8, is incident on a photodetector 9 whereby it is detected. The photodetector 9 is designed as, for example, a four-segment detector, and detects the focusing error based on detection outputs of the detector segments. - Meanwhile, the light beam radiated by the
semiconductor laser element 2 used in thisoptical pickup device 1 exhibits difference in spreading of the radiation angles θ⊥ and θ// in the TE direction (direction of the electrical field) and in that in the TM direction (direction of the magnetic field), such that it is radiated in the form of an ellipsis from theobjective lens 7, as shown in FIG. 2. Specifically, the light beam is radiated by a radiation angle θ⊥ to undergo spreading in the Y-direction, while being radiated by a radiation angle θ// to undergo spreading in the X-direction, as a result of which the light intensity of the light radiated by thesemiconductor laser element 2 is distributed with a Gauss distribution centered about the optical axis. This light beam undergoes differential spreading in the X- and Y-directions due to the radiation angle θ of thesemiconductor laser element 2, with the spreading in the Y-direction being larger than that in the X-direction. Of this light beam, the portion having a light intensity not less than 1/e2 representing the lowest point usable as a spot is incident at alens aperture 7 a of theobjective lens 7, as shown in FIG. 4, thus forming a spot on theoptical disc 6. - The
beam shaping element 3, arranged on the divergent light path of the light beam radiated as the divergent light from thesemiconductor laser element 2, shapes the light beam radiated from thesemiconductor laser element 2 such that the light beam radiated on thesignal recording surface 6 a of theoptical disc 6 is converged to high precision by theobjective lens 7 to form a beam spot of a true circular shape. - The
beam shaping element 3 forms ahologram pattern 10 on anincident surface 3 a on which the light beam radiated from thesemiconductor laser element 2 is incident and a radiatingsurface 3 b from which the light beam is radiated. Thehologram pattern 10 is formed so as to be symmetrical in both the Y and X directions in the XY plane which is the surface perpendicular to the Z-direction of the light beam radiated from thesemiconductor laser element 2, as shown in FIG. 5. Preferably, thehologram pattern 10 is inclined from theincident surface 3 a or the radiatingsurface 3 b by a pre-set angle to form grooves of a lattice having a smooth planar surface, by way of blazing, for maximizing the diffraction efficiency of the first-order light of the light beam incident on thebeam shaping element 3. With thebeam shaping element 3, having thehologram pattern 10 formed on both theincident surface 3 a and the radiatingsurface 3 b of the light beam, it is possible not only to shape the light beam but also to remove astigmatic aberration of the light beam radiated from thesemiconductor laser element 2. - The
beam shaping element 3, having thehologram pattern 10 formed on each of theincident surface 3 a and the radiatingsurface 3 b, spreads the light beam incident from theincident surface 3 a in the X-direction, as shown in FIG. 6a. That is, the light beam incident from theincident surface 3 a is enlarged in diameter when transmitted through thebeam shaping element 3, and is radiated form the radiatingsurface 3 b. Thebeam shaping element 3, each of theincident surface 3 a and the radiatingsurface 3 b of which carries thehologram pattern 10, is higher in diffraction efficiency than the beam shaping element only one surface of which carries thehologram pattern 10. Meanwhile, the light beam is not spread by thisbeam shaping element 3 in the YZ plane, as shown in FIG. 6b. - In view of the diffraction efficiency, only one of the
incident surface 3 a on which falls the light beam radiated from thesemiconductor laser element 2 and the radiatingsurface 3 b radiating this light beam may be provided with thehologram pattern 10. - Preferably, the
beam shaping element 3 of thisoptical pickup device 1 is designed so that, with the thickness t in the XZ plane and the refractive index n of thebeam shaping element 3, the separation S between an object point A and an image point B is given by - S=t(1-1/n) (1)
- By designing the
beam shaping element 3 in this manner, the light beam can be correctly collimated after passing through thecollimator lens 5. It is noted that thecollimator lens 5 is designed to correct the spherical aberration of the light beam produced in the YZ plane by thebeam shaping element 3. - On the other hand, the
beam shaping element 3 is preferably designed so as to satisfy the condition shown in the above equation (1) and so as not to produce the spherical aberration of the light beam transmitted through thecollimator lens 5. Since thecollimator lens 5 is formed so as to correct the spherical aberration for the XZ plane, thebeam shaping element 3 is formed so that the radiated light beam undergoes spherical aberration to be corrected by thecollimator lens 5 even in the XZ-plane. - The
optical pickup device 1 provided with thebeam shaping element 3 according to a modification is explained. For removing the astigmatic aberration, there is provided acylindrical lens unit 13 on the side of theincident surface 3 a of thebeam shaping element 3 shown in FIG. 8. Thehologram pattern 10 is formed on the side of the radiatingsurface 3 b of thebeam shaping element 3. Meanwhile, thecylindrical lens unit 13 is formed as-one with thebeam shaping element 3 so as to be swollen out from the side of the i3 a towards the radiatingsurface 3 b of thebeam shaping element 3, by forming a cylindrical recess in theincident surface 3 a. - Similarly to the beam shaping element shown in FIG. 6, the
beam shaping element 3 shown in FIG. 8 spreads the light beam in the XZ plane to emit the spread light beam from the radiatingsurface 3 b, by the light beam from thesemiconductor laser element 2 being transmitted through thebeam shaping element 3, as shown in FIG. 8a. However, the light beam is not spread by thebeam shaping element 3 in the YZ plane, as shown in FIG. 8b. - For enlarging the light beam diameter in the XZ plane, the
hologram pattern 10 and acylindrical lens unit 23 may be provided on theincident surface 3 a and on the radiatingsurface 3 b of thebeam shaping element 3, as shown in FIGS. 9a and 9 b. Thiscylindrical lens unit 23 is formed as-one with thebeam shaping element 3 by forming a cylindrical protrusion on the radiatingsurface 3 b of thebeam shaping element 3. - Similarly to the beam shaping element shown in FIG. 5, the
beam shaping element 3 shown in FIG. 9 spreads the light beam in the XZ plane to emit the spread light beam from the radiatingsurface 3 b, by the light beam from thesemiconductor laser element 2 being transmitted through thebeam shaping element 3, as shown in FIGS. 9a and 9 b. However, the light beam is not spread by thebeam shaping element 3 in the YZ plane, as shown in FIG. 8b. - Moreover, the
beam shaping element 3 may be constituted by ahologram plate 11 as a flat plate-shaped first optical element having thehologram pattern 10, and acylindrical lens 33 as a second optical element, as shown in FIGS. 10a, 10 b. The first and second optical elements are formed independently of each other. In this case, thehologram plate 11 is arranged on the side of thebeam shaping element 3 on which falls the light beam radiated by thesemiconductor laser element 2, while thecylindrical lens 33 is arranged on the light beam radiating side of thebeam shaping element 3. Thehologram plate 11 has the hologram pattern formed for facing theincident surface 3 a, while thecylindrical lens 33 is arranged with the cylindrical surface facing the light beam radiating surface. - Similarly to the beam shaping element shown in FIG. 6, the
beam shaping element 3 shown in FIG. 10 spreads the light beam in the XZ plane to emit the spread light beam from the radiatingsurface 3 b, by the light beam from thesemiconductor laser element 2 being transmitted through thebeam shaping element 3, as shown in FIG. 10a. However, the light beam is not spread by thebeam shaping element 3 in the YZ plane, as shown in FIG. 10b. - The
collimator lens 5 collimates the light transmitted through thebeam shaping element 3 and thebeam splitter 4. On thiscollimator lens 5 falls the divergent light beam radiated from thesemiconductor laser element 2. The light beam is collimated by thecollimator lens 5 so as to be radiated towards theobjective lens 7. - The
objective lens 7 converges the light beam transmitted through thecollimator lens 5 to thesignal recording surface 6 a of therecording medium 6. Thisobjective lens 7, on which falls the light beam collimated by thecollimator lens 5, converges the light beam so that a beam spot will be formed on thesignal recording surface 6 a of therecording medium 6. - The
optical analyzer 8, on which falls the light beam reflected by thesignal recording surface 6 a of therecording medium 6 and transmitted through theobjective lens 7,collimator lens 5 and thebeam splitter 4, plane-polarizes this light beam. The light beam transmitted through thisoptical analyzer 8 is incident on the photodetector 9. - With the above-described
optical pickup device 1, the light beam having the intensity distribution as shown in FIG. 3 is sent from thesemiconductor laser element 2 and transmitted through the above-described optical elements so as to be converged on thesignal recording surface 6 a of therecording medium 6. Of the light beam radiated from thesemiconductor laser element 2, the component of the light beam in the Y-direction is spread more significantly than the light beam component in the X-direction. In theoptical pickup device 1 having thebeam shaping element 3, the light beam exhibits significant spreading in the X-direction in the XZ plane, so that, by passing the light beam through thebeam shaping element 3, as shown in FIG. 11, the size of the light beam corresponding to the intensity of the light beam L equal to 1/e2 can be made larger in size on thelens aperture surface 7 a of theobjective lens 7 than the diameter of the pupil of theaperture 7 a. - If the light beam L is converged on the
signal recording surface 6 a of therecording medium 6, the beam spot S as shown in FIG. 11 is formed. This beam spot S has approximately the same shape as a diffractionlimit beam spot 12 determined by the wavelength of the light beam radiated from thesemiconductor laser element 2 and the numerical aperture of theobjective lens 7. - Conversely, with an optical pickup device not having the above-described beam shaping element, the size of the light beam corresponding to the intensity of the light beam L not less than 1/e2 as shown in FIG. 12 exhibits more significant spreading in the Y-direction than that in the X-direction on the XY plane on the lens aperture surface. If the light beam L is spread in this manner more significantly in the Y-direction than in the X-direction, the light beam L is not incident in the X-direction in the opening pupil of the
lens aperture 11. - If the light beam L is condensed on the
signal recording surface 6 a of therecording medium 6, there is formed a beam spot S having intensity distribution as shown in FIG. 12. The beam spot S formed by the light beam L is of an elliptical shape in contradistinction from the true circular intensity distribution of the diffractionlimit beam spot 12 determined by the wavelength λ of the light beam radiated from thesemiconductor laser element 2 and the numerical aperture of theobjective lens 7. If the beam spot formed on thesignal recording surface 6 a of the recording medium is elliptically-shaped, the beam spot is increased in size. - Thus, with the
optical pickup device 1, a light spot of approximately true circular shape can be formed in a manner different from that formed in the prior art device, even if the light beam is elliptically-shaped and has an intensity distribution as shown in FIG. 3. In addition, a beam spot can be formed on thesignal recording surface 6 a of therecording medium 6 with reduced light beam aberration. - Moreover, since the
beam shaping element 3 is arranged in the divergent light path, the device itself can be reduced in size. Since the light beam can be shaped by one or two optical elements, there is no necessity of shaping the light beam using a conventional anamorphic lens, thus reducing the cost. - A further example of the
optical pickup device 1 is explained. - Specifically, the
beam shaping element 3 is not limited to the above-described embodiment in which thehologram pattern 10 is formed on at least one of theincident surface 3 a and the radiatingsurface 3 b of thebeam shaping element 3. That is, the beam shaping element may be formed as-one with a firstcylindrical lens unit 43 and a secondcylindrical lens unit 53 on theincident surface 3 a and the radiatingsurface 3 b of the light beam radiated from thesemiconductor laser element 2, as shown in FIGS. 13 and 14. Thebeam shaping element 3, thus having the non-spherical first and secondcylindrical lens units incident surface 3 a and the radiatingsurface 3 b of the light beam, is easy to manufacture because there is no necessity of forming complicated hologram patterns. - Meanwhile, the first
cylindrical lens unit 43 is formed for being swollen out from theincident surface 3 a towards the radiatingsurface 3 b. Specifically, the firstcylindrical lens unit 43 is formed as-one with thebeam shaping element 3 by forming a cylindrically-shaped swollen-out portion on theincident surface 3 a. radiatingsurface 3 b of thebeam shaping element 3. On the other hand, the secondcylindrical lens unit 53 is formed as-one with thebeam shaping element 3 by forming a cylindrically-shaped swollen-out portion on the radiatingsurface 3 b of thebeam shaping element 3. - In the above-described embodiment, the lens operation is accorded in the XZ plane to the
beam shaping element 3 for increasing the spreading of the light beam whilst the lens operation is not accorded in the YZ direction. Alternatively, the lens operation may be accorded in the YZ plane for increasing the beam spreading in the YZ plane, without according the lens effect in the XZ plane, as shown in FIGS. 13 and 14. - That is, the
beam shaping element 3 is designed so as to have the lens operation in the XZ plane shown in FIG. 13 and so as not to have the lens operation in the YZ plane shown in FIG. 14. If thebeam shaping element 3 has a thickness t, a plan-parallel plate with a thickness equal to t is equivalently arranged in the XZ plane. Meanwhile, thecollimator lens 5 is designed to correct the spherical aberration generated by thebeam shaping element 3 in the XZ plane. Thus, the light beam which has traversed thecollimator lens 5 in the XZ plane is freed of aberration even if the light beam is subjected to spherical aberration by being passed through thebeam shaping element 3. - It should be noted that the
collimator lens 5 is designed to correct the spherical aberration generated by thebeam splitter 4 as well ifsuch beam splitter 4 is arranged between thecollimator lens 5 and thebeam shaping element 3 as shown in FIG. 1. - In the XZ plane, the light beam traversing the
beam shaping element 3 as the equivalent plan-parallel plate has an offset component due to a pre-set aberration of the plan-parallel plate. This offset component α is the distance between the radiating point A of the light beam and the point B of intersection of a line of extension of an outer contour line of the light beam which has traversed the plan-parallel plate in the XZ plane and the optical axis. - On the other hand, this
beam shaping element 3 increases the spreading of the light beam in the YZ plane, due to the lens operation of thelens 3, as shown in FIG. 14. The light beam which has traversed thecollimator lens 5 needs to be free of spherical aberration in the YZ plane as well. As a condition in this case, the separation S between the object point A and an image point D needs to be equal to an error ascribable to aberration of the plan-parallel plate in the above-mentioned XZ plane, that is an offset component α between the object point A and the image point D, for the thickness t of thebeam shaping element 3. If the refractive index of thebeam shaping element 3 is n, the condition for the light beam to be a collimated light beam after traversing thecollimator lens 5 is - S=t(1-1/n) (1)
- as above. That is, if the separation S between the object point A and the image point D is equal to the offset component α ascribable to aberration, the light beam is collimated after traversing the
collimator lens 5. In the YZ plane, theincident surface 3 a and/or the radiatingsurface 3 b of thebeam shaping element 3 is preferably non-spherical. For example, thebeam shaping element 3 is preferably a non-spherical cylindrical lens. In this case, the light beam which has traversed thebeam shaping element 3 and thecollimator lens 5 is radiated with suppressed spherical aberration in the YZ plane and in the XZ plane. - In place of at least one of the
incident surface 3 a and the radiatingsurface 3 b of thebeam shaping element 3 being non-spherical in the YZ plane as described above, both theincident surface 3 a and the radiatingsurface 3 b of thebeam shaping element 3 may be spherical. With thebeam shaping element 3, having both surfaces as the spherical surfaces, it is desirable that not only the condition of the equation (1) is met, but also that the center of curvature of theincident surface 3 a is coincident with that of the radiatingsurface 3 b at the same point E, as shown in FIG. 15. In addition, with thebeam shaping element 3, shown in FIG. 15, having the thickness t in the Z-direction, refractive index n and the separation S between the objet point A and the image point B, the above equation (1) is desirably met. This enables the light beam having passed through thecollimator lens 5 to be collimated light free of aberration. - Moreover, in order to minimize the spherical aberration of the light beam having passed through the
collimator lens 5, not only is the above equation (1) to be satisfied, but also is the center of curvature of the incident surface to be coincident in the XZ direction with that of the radiating surface. For minimizing the spherical aberration, the separation between the center position of the incident surface and that of the radiating surface of thebeam shaping element 3 is preferably not larger than 3% of the lens thickness t. - Meanwhile, if an object point F and an image point G of the optical system are aplanatic points of the
incident surface 3 a and the center of curvature of the radiatingsurface 3 b is coincident with the aplanatic points, thebeam shaping element 3 represents a lens free of aberration, as shown in FIG. 16. However, thecollimator lens 5, on which falls the light beam having traversed thebeam shaping element 3, is designed as having spherical aberration caused by thebeam shaping element 3 having a thickness t. Therefore, the light beam, having traversed thecollimator lens 5, is subjected to spherical aberration on traversing thecollimator lens 5, even if the light beam having traversed thebeam shaping element 3 is free of aberration. Thus, thebeam shaping element 3 shown in FIG. 16 is designed so that the light beam passed therethrough undergoes pre-set spherical aberration associated with the thickness t. - An embodiment in which the
incident surface 3 a or the radiatingsurface 3 b of thebeam shaping element 3 represents a non-spherical cylindrical lens or theincident surface 3 a and the radiatingsurface 3 b represent non-spherical cylindrical lenses, is hereinafter explained. - The
beam shaping element 3 represents a cylindrical lens having the radiatingsurface 3 b as acylindrical portion 53 in the YZ plane, as shown in FIGS. 17a and 17 b. In this case, thebeam shaping element 3 has a multiplication factor of approximately 1.7, a refractive index of approximately 1.86, a separation between the radiatingsurface 3 b and theincident surface 3 a of approximately 2 mm, a radius of curvature of theincident surface 3 a of approximately 2 mm, a radius of curvature of the radiatingsurface 3 b of approximately 6.07 mm and a thickness t of approximately 3 mm. At this time, the separation S between an object H and an image point I in FIG. 17b is approximately 1.3857 mm. - On the other hand, an offset component α caused by the aberration in case the
beam shaping element 3 is regarded as a plan-parallel plate is 3×(1-1/1.86)=1.3857 mm, as found from the equation (1). Thus, with the presentbeam shaping element 3, the separation S between the object point H and the image point I is of the same value as the offset component α caused by the aberration proper to the plan-parallel plate. Therefore, the presentbeam shaping element 3 satisfies the above equation (1) not only in the YZ plane but also in the XZ plane. - It is noted that, with the
beam shaping element 3, the separation between the center of curvature of theincident surface 3 a and that of the radiatingsurface 3 b in the YZ plane is approximately 1.98 mm which is of the order of 66% of the thickness t. - The light beam having traversed the
beam shaping element 3 and thecollimator lens 5 has the wavefront aberration of approximately 0.11 λ and thus undergoes spherical aberration. If thebeam shaping element 3 is of a non-spherical shape, without changing the curvature of the radiatingsurface 3 b, thebeam shaping element 3 has the wavefront aberration of approximately 0.03 λ thus enabling reduction in the spherical aberration. - The
beam shaping element 3 can be designed by setting four of six conditions, namely the multiplication factor, refractive index, separation between the object point and theincident surface 3 a, radius of curvature of theincident surface 3 a, radius of curvature of the radiatingsurface 3 b and the thickness t, as described above. With thisbeam shaping element 3, the aberration proper to the traversing light beam can be set to pre-set value by having at least one of theincident surface 3 a and the radiatingsurface 3 b formed as a non-spherical surface. - An embodiment in which both the
incident surface 3 a and the radiatingsurface 3 b of thebeam shaping element 3 represent spherically-shaped cylindrical lenses in the YZ plane, as shown in FIG. 18, is hereinafter explained. - If the
beam shaping element 3 is a cylindrical lens, having its both surfaces spherically-shaped in the YZ plane, as shown in FIGS. 18a, 18 b, the multiplication factor, refractive index, separation between the object point (light-emitting point) H and theincident surface 3 a, radius of curvature of theincident surface 3 a, radius of curvature of the radiatingsurface 3 b and the thickness t, are approximately 1.7, approximately 1.86, approximately 2 mm, approximately 0.6 mm, approximately 1.78 mm and approximately 2 mm, respectively. In this case, the separation S between the object point H and the image point I in FIG. 18b is approximately 0.5543 mm. On the other hand, the offset component α due to the aberration proper to a plan-parallel plate when thebeam shaping element 3 in FIG. 18a is regarded as being a plan-parallel plate in the XZ plane is of the order of 3×(1-1/1.86) =0.5543 mm, as found from the equation (1). Therefore, with thisbeam shaping element 3, the separation S between the object point H and the image point I is equal in magnitude to the offset component α ascribable to aberration. Therefore, thisbeam shaping element 3 satisfies the above equation (1) both in the YZ plane and in the XZ plane. - It is noted that, with this
beam shaping element 3, the separation between the center of curvature of theincident surface 3 a and that of the radiatingsurface 3 b is approximately 0.02 mm which is of the order of 1.7% of the thickness t. - The light beam having traversed the
beam shaping element 3 and thecollimator lens 5 is of the wavefront aberration of approximately 0.002 λ which is of a magnitude smaller than the light beam having traversed thebeam shaping element 3 of the first embodiment. - The
beam shaping element 3 can be designed so as to have the aberration smaller than that of the above-described embodiment of thebeam shaping element 3 by setting three of six conditions, namely the multiplication factor, refractive index, separation between the object point and theincident surface 3 a, radius of curvature of theincident surface 3 a, radius of curvature of the radiatingsurface 3 b and the thickness t, as described above. - Although the beam shaping element in the
optical pickup device 1 of the present invention is arranged upstream of thebeam splitter 4 as described above, it may, of course, be arranged in the divergent optical path upstream of thecollimator lens 5. - In the above-described embodiment, the
optical pickup device 1 has thebeam shaping element 3 and thecollimator lens 5. However, the optical pickup device may also not be provided with thecollimator lens 5. - Although the above-described
optical pickup device 1 is of the type of directing the light beam having traversed thecollimator lens 5 to theobjective lens 7, with the aperture diameter of the light beam having traversed thecollimator lens 5 as the opening pupil diameter, the aperture determining the opening pupil of the light beam having traversed thecollimator lens 5 may, of course, be arranged upstream of theobjective lens 7. - Although the above-described
optical pickup device 1 is of the type of converging the light beam on thesignal recording surface 6 a of theoptical disc 6, the present invention may, of course, be applied to an optical pickup device adapted for recording/reproducing signals by converging the light beam on a tape-shaped or card-shaped recording medium. - With the optical pickup device according to the present invention, as described above, the incident light beam can be shaped since the beam shaping element for shaping the light beam is arranged on the divergent optical path of the light beam. Therefore, with the present optical pickup device, the beam spot converged on the signal recording surface of the recording medium is not elliptically-shaped but is of the substantially true circular shape for recording/reproducing information signals to high density. In addition, with the present optical pickup device, the optical path length can be shortened to reduce the size of the device since the beam can be shaped solely on arranging the beam shaping element on the divergent optical path.
Claims (22)
1. An optical pickup device comprising:
a semiconductor laser element;
an objective lens for converging a light beam radiated from said semiconductor laser element; and
beam shaping means arranged in a divergent optical path of a light beam radiated from said semiconductor laser element.
2. The optical pickup device as recited in wherein said beam shaping means includes an incident surface, an radiating surface and a hologram pattern provided on at least one of the incident surface and the outgoing surface.
claim 1
3. The optical pickup device as recited in wherein said hologram pattern has a pattern of extending substantially parallel to the long axis direction of the light beam radiated from said semiconductor laser element.
claim 2
4. The optical pickup device as recited in wherein said hologram pattern is blazed for maximizing the diffraction efficiency of the first-order light.
claim 3
5. The optical pickup device as recited in wherein said beam shaping means is a flat-plate-shaped optical element the incident surface and the radiating surface of which are both provided with hologram patterns.
claim 2
6. The optical pickup device as recited in wherein said beam shaping means is a flat-plate-shaped optical element the incident surface or the radiating surface of which is provided with the hologram pattern and the radiating surface or the incident surface of which is provided with a cylindrical lens unit.
claim 2
7. The optical pickup device as recited in wherein said optical element satisfies
claim 4
s=t(1-1/n)
where t, n are a thickness and a refractive index of the optical element, respectively, and s is a separation between an objet point and an image point.
8. The optical pickup device as recited in wherein said beam shaping means includes a flat-plate-shaped first optical element having said hologram pattern on its incident surface and a second optical element having a cylindrical lens unit on its radiating surface.
claim 2
9. The optical pickup device as recited in wherein said beam shaping means includes an optical element the incident surface and the radiating surface of which are formed as non-spherical surfaces and wherein said optical element satisfies
claim 1
s=t(1-1/n)
where t, n are a thickness and a refractive index of the optical element, respectively, and s is a separation between an objet point and an image point.
10. The optical pickup device as recited in wherein said beam shaping means includes an optical element the incident surface and the radiating surface of which are formed as spherical surfaces having a coincident center of curvature and wherein said optical element satisfies
claim 1
s=t(1-1/n)
where t, n are a thickness and a refractive index of the optical element, respectively, and s is a separation between an objet point and an image point.
11. The optical pickup device as recited in wherein said beam shaping means includes an optical element the incident surface and the radiating surface of which are formed as spherical surfaces and wherein said optical element satisfies
claim 1
s=t(1-1/n)
where t, n are a thickness and a refractive index of the optical element, respectively, and s is a separation between an objet point and an image point, the distance between the centers of curvature of the incident and radiating surfaces being not larger than 3% of the thickness of the optical element.
12. An optical pickup device comprising:
a semiconductor laser element;
a collimator lens for collimating a light beam radiated from said semiconductor laser element;
an objective lens for converging the collimated light from said collimator lens; and
beam shaping means arranged on a divergent optical path of a light beam radiated from said semiconductor laser element on a light path between said semiconductor laser element and the collimator lens.
13. The optical pickup device as recited in further comprising:
claim 12
a beam splitter arranged between said beam shaping means and said collimator lens for separating a light beam radiated from the semiconductor laser element from an incident light beam via said objective lens.
14. The optical pickup device as recited in wherein said beam shaping means includes an incident surface, an radiating surface and a hologram pattern provided on at least one of the incident surface and the radiating surface.
claim 12
15. The optical pickup device as recited in wherein said hologram pattern is blazed for maximizing the diffraction efficiency of the first-order light.
claim 14
16. The optical pickup device as recited in wherein said beam shaping means is a flat-plate-shaped optical element the incident surface and the radiating surface of which are both provided with hologram patterns.
claim 14
17. The optical pickup device as recited in wherein said beam shaping means is a flat-plate-shaped optical element the incident surface or the radiating surface of which is provided with the hologram pattern and the radiating surface or the incident surface of which is provided with a cylindrical lens unit.
claim 14
18. The optical pickup device as recited in wherein said optical element satisfies
claim 16
s=t(1-1/n)
where t, n are a thickness and a refractive index of the optical element, respectively, and s is a separation between an objet point and an image point.
19. The optical pickup device as recited in wherein said beam shaping means includes a flat-plate-shaped first optical element having on its incident surface said hologram pattern and a second optical element having a cylindrical lens unit on its radiating surface.
claim 14
20. The optical pickup device as recited in wherein said beam shaping means includes an optical element the incident surface and the radiating surface of which are formed as non-spherical surfaces and wherein said optical element satisfies
claim 12
s=t(1-1/n)
where t, n are a thickness and a refractive index of the optical element, respectively, and s is a separation between an objet point and an image point.
21. The optical pickup device as recited in wherein said beam shaping means includes an optical element the incident surface and the radiating surface of which are formed as spherical surfaces having a coincident center of curvature and wherein said optical element satisfies
claim 12
s=t(1-1/n)
where t, n are a thickness and a refractive index of the optical element, respectively, and s is a separation between an objet point and an image point.
22. The optical pickup device as recited in wherein said beam shaping means includes an optical element the incident surface and the radiating surface of which are formed as spherical surfaces and wherein said optical element satisfies
claim 12
s=t(1-1/n)
where t, n are a thickness and a refractive index of the optical element, respectively, and s is a separation between an objet point and an image point, the distance between the centers of curvature of the incident and radiating surfaces being not larger than 3% of the thickness of the optical element.
Priority Applications (1)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
US09/824,037 US6337774B2 (en) | 1997-05-07 | 2001-04-03 | Optical pickup device |
Applications Claiming Priority (6)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
JP11718797 | 1997-05-07 | ||
JP09-117187 | 1997-05-07 | ||
JPP09-117187 | 1997-05-07 | ||
PCT/JP1998/002036 WO1998050913A1 (en) | 1997-05-07 | 1998-05-07 | Optical pickup device |
US09/214,255 US6252686B1 (en) | 1997-05-07 | 1998-05-07 | Optical pickup device |
US09/824,037 US6337774B2 (en) | 1997-05-07 | 2001-04-03 | Optical pickup device |
Related Parent Applications (3)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
US09/214,255 Division US6252686B1 (en) | 1997-05-07 | 1998-05-07 | Optical pickup device |
PCT/JP1998/002036 Division WO1998050913A1 (en) | 1997-05-07 | 1998-05-07 | Optical pickup device |
JPPCT/JP98/07036 Division | 1999-05-07 |
Publications (2)
Publication Number | Publication Date |
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US20010010583A1 true US20010010583A1 (en) | 2001-08-02 |
US6337774B2 US6337774B2 (en) | 2002-01-08 |
Family
ID=14705567
Family Applications (4)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
US09/214,255 Expired - Fee Related US6252686B1 (en) | 1997-05-07 | 1998-05-07 | Optical pickup device |
US09/824,039 Expired - Fee Related US6335836B2 (en) | 1997-05-07 | 2001-04-03 | Optical pickup device |
US09/824,037 Expired - Fee Related US6337774B2 (en) | 1997-05-07 | 2001-04-03 | Optical pickup device |
US09/824,038 Expired - Fee Related US6347015B2 (en) | 1997-05-07 | 2001-04-03 | Optical pickup device |
Family Applications Before (2)
Application Number | Title | Priority Date | Filing Date |
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US09/214,255 Expired - Fee Related US6252686B1 (en) | 1997-05-07 | 1998-05-07 | Optical pickup device |
US09/824,039 Expired - Fee Related US6335836B2 (en) | 1997-05-07 | 2001-04-03 | Optical pickup device |
Family Applications After (1)
Application Number | Title | Priority Date | Filing Date |
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US09/824,038 Expired - Fee Related US6347015B2 (en) | 1997-05-07 | 2001-04-03 | Optical pickup device |
Country Status (3)
Country | Link |
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US (4) | US6252686B1 (en) |
CN (1) | CN1123874C (en) |
WO (1) | WO1998050913A1 (en) |
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EP1441334A2 (en) * | 2003-01-22 | 2004-07-28 | Matsushita Electric Industrial Co., Ltd. | Optical head, optical information recording/reproducing apparatus, computer, video recording/reproducing apparatus, server and car navigation system |
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JP2003188452A (en) * | 2001-12-14 | 2003-07-04 | Minolta Co Ltd | Light source device and optical pickup |
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US7180644B2 (en) * | 2002-04-03 | 2007-02-20 | Inphase Technologies, Inc. | Holographic storage lenses |
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JP2004288346A (en) * | 2002-10-18 | 2004-10-14 | Konica Minolta Holdings Inc | Optical element for optical pickup device, coupling lens, and optical pickup device |
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- 1998-05-07 WO PCT/JP1998/002036 patent/WO1998050913A1/en active Application Filing
- 1998-05-07 US US09/214,255 patent/US6252686B1/en not_active Expired - Fee Related
- 1998-05-07 CN CN98800906.4A patent/CN1123874C/en not_active Expired - Fee Related
-
2001
- 2001-04-03 US US09/824,039 patent/US6335836B2/en not_active Expired - Fee Related
- 2001-04-03 US US09/824,037 patent/US6337774B2/en not_active Expired - Fee Related
- 2001-04-03 US US09/824,038 patent/US6347015B2/en not_active Expired - Fee Related
Cited By (3)
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EP1441334A2 (en) * | 2003-01-22 | 2004-07-28 | Matsushita Electric Industrial Co., Ltd. | Optical head, optical information recording/reproducing apparatus, computer, video recording/reproducing apparatus, server and car navigation system |
EP1441334A3 (en) * | 2003-01-22 | 2006-02-01 | Matsushita Electric Industrial Co., Ltd. | Optical head, optical information recording/reproducing apparatus, computer, video recording/reproducing apparatus, server and car navigation system |
US7453788B2 (en) | 2003-01-22 | 2008-11-18 | Panasonic Corporation | Optical head, optical information recording/reproducing apparatus, computer, video recording/reproducing apparatus, video reproducing apparatus, server and car navigation system |
Also Published As
Publication number | Publication date |
---|---|
US6337774B2 (en) | 2002-01-08 |
CN1123874C (en) | 2003-10-08 |
US6252686B1 (en) | 2001-06-26 |
US20010019435A1 (en) | 2001-09-06 |
CN1231052A (en) | 1999-10-06 |
US6335836B2 (en) | 2002-01-01 |
US20010021043A1 (en) | 2001-09-13 |
US6347015B2 (en) | 2002-02-12 |
WO1998050913A1 (en) | 1998-11-12 |
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