JP4490842B2 - Optical pickup device - Google Patents

Description

  The present invention relates to an optical pickup device in which a multi-layer liquid crystal optical element having a plurality of liquid crystal layers by laminating a plurality of transparent substrates is disposed at a predetermined angle with an optical axis of a laser light source.

  In recent optical pickup devices, the wavelength used for a laser light source is set to a short wavelength of 790 nm or 655 nm to 400 nm used for a CD or DVD, and the numerical aperture of the lens is set to 0.6 or more so that the recording density on the optical disk is increased. It has become something that raises.

  As described above, when the wavelength used in the laser light source becomes a short wavelength, the generation of coma aberration due to the tilt with respect to the optical axis of the optical disk increases. In addition, since the optical pickup device having the above specifications needs to have a high numerical aperture for the lens, spherical aberration is likely to occur due to uneven thickness of the optical disc. For this reason, the light condensing characteristics fluctuate in the light receiving element, and information on the optical disc may not be read accurately.

  Therefore, in order to suppress the fluctuation of the condensing characteristic obtained by these light receiving elements (the influence of wavefront aberration) as much as possible, the two-layer liquid crystal optical elements (first and second liquid crystal optical elements) are integrated. An optical pickup device equipped with a multilayer liquid crystal optical element has been proposed (see, for example, Patent Document 1).

  In this optical pickup device, the wavefront aberration of the laser beam in the forward path from the laser light source to the optical disk is corrected by the first liquid crystal optical element, and the wavefront aberration of the laser beam in the backward path that is reflected light from the optical disk is corrected by the second liquid crystal. Correction can be made with an optical element. In the first and second liquid crystal optical elements according to this proposal, the liquid crystal layer is arranged orthogonal to the laser beam, and the center of the electrode pattern formed in each element is the laser beam incident on the element. It is arranged so as to coincide with the optical axis.

  There is also a proposal for an optical pickup device in which a liquid crystal optical element is disposed at a predetermined angle with respect to the optical axis of laser light emitted from a laser light source (see, for example, Patent Document 2).

  Normally, the liquid crystal of the liquid crystal optical element is arranged with a predetermined pretilt angle when no voltage is applied, so even if laser light orthogonal to the liquid crystal layer is incident, accurate deflection cannot be achieved. As a result, the light utilization efficiency of the laser light is reduced. Further, the laser light reflected from the transparent substrate constituting the liquid crystal optical element and the surface of the electrode film enters the light receiver as stray light, which also causes a decrease in light utilization efficiency.

  Therefore, if the liquid crystal optical element is arranged so as to be inclined by the pretilt angle with respect to the optical axis of the laser light source, the above-described reduction in light utilization efficiency can be prevented.

JP 2002-319172 (page 2-4, Fig. 1-3) Japanese Patent No. 3271890 (page 3-4, FIG. 2-7)

In a small-sized optical pickup device that needs to correct aberrations for both the forward path and the backward path described in Patent Document 1 described above, downsizing of optical components is desired, and the number of transparent substrates is reduced. A small and thin multilayer liquid crystal optical element in which two liquid crystal optical elements are integrated (for example, as shown in FIG. 4, two layers of liquid crystal optical elements are constituted by first to third transparent substrates 1 to 3) is preferable. It is said that.

  When this multilayer liquid crystal optical element is tilted with respect to the optical axis of the laser light source and incorporated in the optical pickup device as shown in Patent Document 2, the center of the electrode pattern for applying a voltage to each liquid crystal layer is provided. Some deviation occurs and accurate control cannot be performed.

  As shown in FIG. 4, a technique for increasing the light utilization efficiency, which was possible with the single-layer liquid crystal optical element described in Patent Document 2, is applied to the configuration described in Patent Document 1 as it is, and the second liquid crystal optical This is because if the electrode pattern center 16 of the element is aligned with the laser optical axis 14, the electrode pattern center 15 of the first liquid crystal optical element will be shifted according to the angle at which it is assembled.

  The amount of deviation differs depending on the angle at which the multilayer optical element 10b is incorporated and the pretilt angle to be set. Even if the amount of deviation is small, the numerical aperture is increased with a short wavelength laser light source, and a plurality of layers of liquid crystal In an optical pickup device using a high-functional multi-layer liquid crystal optical element 10b that can correct the wavefront aberration of both forward and backward laser beams using layers, the amount is not negligible.

  Therefore, an object of the present invention is to provide a multi-layer liquid crystal optical element in which a plurality of liquid crystal layers are stacked, so that each liquid crystal layer can accurately correct the desired wavefront aberration and further improve the light utilization efficiency. An optical pickup device that can be improved is provided.

The optical pickup device of the present invention includes a laser light source and a wavefront of the laser light, which is arranged at a predetermined angle with respect to the laser light emitted from the laser light source and is formed by integrating a plurality of liquid crystal layers. An optical pickup device comprising: a multilayer liquid crystal optical element for correcting aberration; and a light receiver that transmits the laser light through the multilayer liquid crystal optical element and receives reflected light from the optical disk. The center of the optical axis of the transparent electrode sandwiching each of the plurality of liquid crystal layers is shifted from each other according to the tilt angle with respect to the laser light of the multilayer liquid crystal optical element, and coincides with the optical axis of the laser light. It is characterized by being arranged.

In the optical pickup device of the present invention, the multilayer liquid crystal optical element described above is a first liquid crystal optical element for correcting the wavefront aberration of the forward laser light emitted from the laser light source and reaching the optical disc; It is characterized by comprising a second liquid crystal optical element for correcting the wavefront aberration of the laser beam that is reflected from the optical disk and reaches the light receiver.
Furthermore, the plurality of liquid crystal layers in the optical pickup device according to the present invention are sandwiched between the transparent substrates, and the offset amount shifted and arranged according to the tilt angle is the transparent substrate located between the plurality of liquid crystal layers. Is preferably determined based on the following formula, where n is the refractive index of n, t is the thickness of the transparent substrate, and θ is the angle of attachment relative to the center of the optical axis.
t × tan (sin−1 (sin θ / n))

  If a multi-layer liquid crystal optical element in which a plurality of liquid crystal layers are stacked is mounted on the optical head device of the present invention, each liquid crystal layer can accurately correct the desired wavefront aberration and improve the light utilization efficiency. it can.

  Further, when the multilayer liquid crystal optical element is configured so that aberration correction can be performed for both the forward and backward laser beams, the effect can be obtained more.

  The configuration and operation of the optical pickup device of the present invention will be described with reference to FIGS. First, the apparatus configuration will be described. FIG. 1 shows an optical pickup device of the present invention.

  The optical pickup device of the present invention includes a laser light source 50, a collimator lens 52, a polarizing beam splitter 54, a multilayer liquid crystal optical element 10a for correcting aberrations, a quarter phase plate 66, an objective lens 56, a collecting lens. The optical lens 60 and the light receiver 62 are configured as shown in the figure. The multilayer liquid crystal optical element 10a is arranged with a predetermined angle (for example, an angle inclined by the pretilt angle of the liquid crystal) with respect to the optical axis of the laser light source 50 in order to improve the light utilization efficiency. .

  Further, as shown in the drawing, the forward laser beam 64 emitted from the laser light source 50 is converted into P-polarized parallel light by the collimator lens 52 and passes through the polarization beam splitter 54 and the multilayer liquid crystal optical element 10a. The laser beam 64 has a ¼ phase difference after the wavefront aberration including coma aberration, spherical aberration, or astigmatism of parallel light incident by the multilayer liquid crystal optical element 10 a is corrected by the first liquid crystal optical element 11. The light is converted into circularly polarized light by the plate 66, and a beam is irradiated onto the disk 58 by the objective lens 56.

  Further, the backward laser beam reflected from the disk 58 passes through the objective lens 56, is converted into S-polarized light by the ¼ retardation plate 66, and then passes through the multilayer liquid crystal optical element 10 a. The laser beam 64 is corrected by the second liquid crystal optical element 12 for wavefront aberration including coma aberration, spherical aberration, or astigmatism of parallel light incident by the multilayer liquid crystal optical element 10a, and then is applied to the polarization beam splitter 54. The laser beam reflected from the disk 58 is collected by the light receiver 62 after changing the optical path and passing through the condenser lens 60. Based on the data, information recorded on the disk 58 can be read or written on the disk surface.

  FIG. 2A is a drawing showing the operation of the multilayer liquid crystal optical element 10a mounted on the optical pickup device of the present invention, and FIG. 2B shows an upper plan view and a sectional view of the element.

  The first liquid crystal optical element 11 and the second liquid crystal optical element 12 are each provided with an electrode pattern (not shown) for driving the liquid crystal to correct the aberration. FIG. 2A shows an example in which the center of the electrode pattern is enlarged and clearly shown.

  According to this drawing, the multilayer liquid crystal optical element 10a is installed with a predetermined inclination with respect to the laser optical axis 14, and the electrode pattern centers 15 and 16 formed on the first and second liquid crystal optical elements 11 and 12 are arranged. Is located on the optical axis 14 of the laser.

  Further, each electrode pattern center 15, 16 calculates the shift amount (offset amount) of the electrode pattern formed in advance on the element from the angle at which the multilayer liquid crystal optical element 10 a is attached to the optical pickup device. An electrode pattern (not shown) of the second liquid crystal optical element 12 is formed at a position where an offset is placed on the electrode pattern (11) (not shown).

  That is, the multilayer liquid crystal optical element 10a of the present invention includes an electrode pattern 31 corresponding to the first liquid crystal optical element 11 and an electrode pattern 32 of the second liquid crystal optical element 12 as shown in FIG. In the form of being overlaid at a position shifted by the offset amount 33.

The offset amount 33 shown here is given by assuming that the refractive index of the second transparent substrate 2 is n, the thickness shown in FIG.
t × tan (sin−1 (sin θ / n))
It is represented by

For example, when glass of t = 0.5 mm is used and the mounting angle (angle corresponding to the pretilt angle) is θ = 2 degrees, the offset amount 33 obtained based on the above formula is about 11 μm. If the electrode pattern centers 15 and 16 of the electrode patterns 31 and 32 are shifted according to this value, the target multilayer liquid crystal optical element 10a can be obtained.

  The multilayer liquid crystal optical element 10a configured in this way suppresses a decrease in light utilization efficiency including the problem that the laser light is stray light and enters the light receiver due to the above-described action. At the same time, for example, it is possible to accurately correct the wavefront aberration of the laser beam in the forward path and the return path, or to correct multiple types of wavefront aberrations in one optical path, using the multilayer liquid crystal optical element 10a.

  Next, a method for manufacturing the multilayer liquid crystal optical element 10a mounted on the optical pickup device of the present invention will be described with reference to FIG. FIG. 3A is a drawing for explaining a process of superimposing the first to third transparent substrates 1 to 3 constituting the multilayer liquid crystal optical element 10a, and FIG. It is drawing which showed and overlapped the alignment mark to be used.

  As shown in FIG. 3 (a), the first transparent substrate 1 is formed with, for example, an electrode pattern 24 for correcting coma and astigmatism of the laser beam on the return path, and a first alignment mark 21. In addition, on one surface of the second transparent substrate 2, for example, an electrode pattern 25 and a second alignment mark 22 for correcting spherical aberration of the laser beam in the return path are formed. Then, based on the first and second alignment marks 21 and 22 shown in FIG. 3 (b), the first transparent substrate 1 and the second transparent substrate 2 are overlapped to return the return path. A second liquid crystal optical element 12 for correcting the wavefront aberration of the laser light is created. In this way, the center positions of the electrode patterns 24 and 25 can be aligned with the electrode pattern center 15.

  On the other surface of the second transparent substrate 2, for example, an electrode pattern 26 for correcting the spherical aberration of the forward laser beam is formed. The electrode pattern 26 is provided at a position shifted from the electrode pattern 25 for correcting the laser beam in the return path by 11 μm corresponding to the offset amount 33 described above. Note that no alignment mark is provided on the other surface of the second transparent substrate 2.

  Further, on the third transparent substrate 3, for example, an electrode pattern 27 and a third alignment mark 23 for correcting coma and astigmatism of the forward laser beam are formed, as shown in FIG. Based on the first and third alignment marks 21, 23, the second liquid crystal optical element 12 and the third transparent substrate 3 are bonded together, and the first liquid crystal optical element integrated with the first liquid crystal optical element After the liquid crystal optical element 11 is formed, each element is filled with liquid crystal to obtain a multilayer liquid crystal optical element 10a.

  In this way, the center positions of the electrode patterns 26 and 27 are aligned with the electrode pattern center 15, and the center positions of the electrode patterns 26 and 27 are shifted to the electrode pattern center 16 by being shifted from the electrode pattern center 15 by the offset amount 33. They can be arranged together.

  As shown in the drawing, a first alignment mark 21 provided on the first transparent substrate 1 or a second alignment mark 22 provided on the second transparent substrate 2 and a third alignment mark 22 For superimposing the first to third transparent substrates 1 to 3 performed using the third alignment mark 23 provided on the transparent substrate 3, each alignment mark is enlarged and observed with a multifocal microscope 28. If a technique for aligning is applied, the multilayer liquid crystal optical element 10a can be easily formed.

In the above description, the offset amount 33 is set to 11 μm. However, the offset amount 33 of the electrode patterns 31 and 32 is determined from the size of the optical pickup device and the restriction of the mounting part of the optical component incorporated in the device. It is optional depending on the specifications of the device.

It is a schematic diagram for demonstrating the structure of the optical pick-up apparatus of this invention. It is drawing which shows the effect | action and structure of the multilayer liquid crystal optical element used for the optical pick-up apparatus of this invention. It is process drawing which shows the manufacturing method of the multilayer liquid crystal optical element of this invention. 6 is a diagram illustrating an operation of a conventional multilayer liquid crystal optical element.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 1st transparent substrate 2 2nd transparent substrate 3 3rd transparent substrate 10a, b Multi-layer liquid crystal optical element 11 1st liquid crystal optical element 12 2nd liquid crystal optical element 14 Laser optical axis 15, 16 Electrode Pattern center 21 First alignment mark 22 Second alignment mark 23 Third alignment mark 24-27 Electrode pattern 28 Multi-focus microscope 31, 32 Electrode pattern 33 Offset amount 50 Laser light source 52 Collimator lens 54 Deflection beam splitter 56 Objective lens 58 disc 60 condensing lens 62 light receiver 64 laser light 66 1/4 phase difference plate

Claims (3)

A laser light source;
A multilayer liquid crystal optical element for correcting wavefront aberration of the laser light, which is arranged at a predetermined angle with respect to the laser light emitted from the laser light source and in which a plurality of liquid crystal layers are integrated. When,
A light receiving device for transmitting the multilayer liquid crystal optical element and irradiating the optical disc with the laser light and receiving reflected light from the optical disc,
Centers of the optical axes of the transparent electrodes that sandwich the plurality of liquid crystal layers are shifted from each other according to an inclination angle of the multilayer liquid crystal optical element with respect to the laser light, and are aligned with the optical axis of the laser light. An optical pickup device characterized by being arranged. The multilayer liquid crystal optical element includes: a first liquid crystal optical element for correcting wavefront aberration of a laser beam emitted from the laser light source and reaching the optical disk;
2. The optical pickup according to claim 1, comprising a second liquid crystal optical element for correcting wavefront aberration of a laser beam reflected from the optical disk and reaching the light receiver. apparatus. The plurality of liquid crystal layers are sandwiched between transparent substrates,
The offset amount that is shifted according to the tilt angle is n for the refractive index of the transparent substrate located between the plurality of liquid crystal layers, t for the thickness of the transparent substrate, and the center of the optical axis. T × tan (sin−1 (sin θ / n) )
The optical pickup device according to claim 1, wherein:

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