JP2009015974A - Optical pickup and optical disc apparatus - Google Patents

Abstract

An optical pickup can be miniaturized.
In the optical pickup 20 that irradiates an optical disc 100 with a light beam 40 emitted from a laser diode 21 via an objective lens 25, the light that is incident on the objective lens 25 by a rising prism 30 is provided. The light beam 40 incident with a light beam diameter (light beam vertical width Dv and light beam horizontal width Dh) smaller than the final light beam diameter Df which is the light beam diameter of the beam 40 is caused to travel as divergent light in a part of the rising prism 30. By adjusting the divergence angle of the light beam 40 that is stretched and incident by a plurality of free-form surfaces, the light beam vertical width Dv and the light beam horizontal width Dh of the incident light beam are adjusted to the final light beam diameter Df, and the incident light beam 40 is emitted as parallel light.
[Selection] Figure 3

Description

  The present invention relates to an optical pickup and an optical disc apparatus, and is suitable for application to an optical disc apparatus compatible with various systems such as a CD (Compact Disc) and a DVD (Digital Versatile Disc).

  Conventionally, as shown in FIG. 1, as an optical pickup 1 in an optical disc apparatus, laser light is emitted from a laser diode 2, and the vertical and horizontal widths of the light beam are the beam widths of the light beam when entering the objective lens 6. A light beam is incident on the rising prism 5 in a state where the incident light beam width Td is expanded, and the angle of the laser beam is changed by 90 ° by the rising prism 5 to rise perpendicularly to the optical disc 100. There are some which are configured to irradiate the signal recording layer 100 a of the optical disc 100 with the light beam through the objective lens 6.

  In the optical pickup 1 having such a configuration, the rising prism 5 and the objective lens 6 are arranged side by side in a direction perpendicular to the optical disc 100, so that the thickness Tt in the vicinity of the objective lens (from the optical disc 100 to the bottom of the rising prism). ) Tends to be thick, and the thickness Tt near the objective lens often determines the thickness of the entire optical pickup 1.

  The thickness Tt in the vicinity of the objective lens is the working distance Ta, the thickness Tb of the objective lens 6, and the distance between the objective lens 6 and the rising prism 5 secured as a driving range of the objective lens 6 in the focus direction. This is the sum of the lens / prism interval Tc and the incident beam width Td that determines the thickness of the rising prism 5.

Here, a rising prism is proposed in which the optical pickup is made thin by reducing the lens / prism distance Tc by emitting the light beam from a position lower than the upper part of the light beam of the incident light beam. (For example, refer to Patent Document 1).
JP-A-11-134701

  Incidentally, the optical pickup is required to be further downsized. However, since the optical pickup 1 described above enters the rising prism 5 with a light beam having a light beam width equal to the incident light beam width Td, the size of the optical component on the optical path cannot be made smaller than the incident light beam width Td. Therefore, there is a problem that it is impossible to meet the demand for further downsizing the optical pickup.

  The present invention has been made in consideration of the above points, and intends to propose an optical pickup that can be miniaturized and an optical disk apparatus using the optical pickup.

  In order to solve such a problem, in the present invention, in an optical pickup that irradiates an optical disk with a light beam emitted from a light source, the light beam is reflected multiple times to the objective lens. A rising prism that raises and emits a light beam to be vertical and an objective lens that collects the light beam emitted from the rising prism and irradiates the optical disk is provided. The rising prism is incident on the objective lens. A light beam incident with a light beam diameter smaller than the final light beam diameter, which is the light beam diameter of the light beam, is extended as a divergent light in a part of the rising prism and is incident on a plurality of free-form surfaces. By adjusting the divergence angle of the light beam, a light beam meeting the incident conditions required when entering the objective lens is emitted.

  Accordingly, a light beam having a light beam diameter smaller than the final light beam diameter may be incident on the rising prism, so that the optical component on the optical path can be reduced in size.

  In an optical disk device that irradiates an optical disk with a light beam emitted from a light source, the light beam is raised so as to be perpendicular to the objective lens by reflecting the light beam multiple times. A rising prism, and an objective lens that collects the light beam emitted from the rising prism and irradiates the optical disk, and the rising prism has a beam diameter of the light beam when entering the objective lens By adjusting the divergence angle of the incident light beam by a plurality of free-form surfaces by extending the light beam incident with a beam diameter smaller than the final beam diameter as a diverging light in a part of the rising prism. A light beam that meets the incident conditions required when entering the objective lens is emitted.

  Accordingly, a light beam having a light beam diameter smaller than the final light beam diameter may be incident on the rising prism, so that the optical component on the optical path can be reduced in size.

  According to the present invention, since it is sufficient that a light beam having a light beam diameter smaller than the final light beam diameter is incident on the rising prism, the optical component on the optical path can be reduced in size, and thus the optical pickup capable of being reduced in size An optical disk device using an optical pickup can be realized.

  Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings.

(1) First Embodiment (1-1) Overall Configuration of Optical Disc Device In FIG. 2, reference numeral 10 denotes an optical disc device as a whole. The optical disc apparatus 10 is controlled in a centralized manner by a system controller 11 and executes playback processing and recording processing for the optical disc 100.

  The system controller 11 sends a data read command to the drive control unit 13 together with address information for specifying data to be read from the optical disc 100 during the reproduction process.

  The drive control unit 13 controls the spindle motor 14 in accordance with a data read command from the system controller 11 to rotate the optical disc 100 at a predetermined rotational speed, and also uses the thread motor 15 based on the data read command and address information. Is controlled to move the optical pickup 20 in the radial direction of the optical disc 100. The system controller 11 causes the optical pickup 100 to irradiate the optical beam 100 with a light beam on the track corresponding to the address information in the information recording layer of the optical disc 100.

  At this time, the optical pickup 20 receives the reflected light beam reflected from the light beam irradiated on the optical disc 100 and sends a light reception signal corresponding to the amount of light to the signal processing unit 16. Based on the received light signal, the signal processing unit 16 performs a tracking error signal according to the amount of deviation of the irradiation position of the light beam with respect to a desired track and a focus error according to the amount of deviation of the focus of the light beam with respect to the information recording layer of the optical disc 100. A signal is generated and sent to the drive control unit 13, and a reproduction RF signal is generated based on the received light signal and sent to an external device (not shown).

  The drive control unit 13 generates a tracking control signal and a focus control signal based on the tracking error signal and the focus error signal, and sends them to the optical pickup 20. In response to this, the optical pickup 20 performs tracking control and focus control so that the focal point of the light beam coincides with a desired track of the optical disc 100.

  The system controller 11 generates a laser power signal based on the reproduction RF signal and sends it to the optical pickup 20. The optical pickup 20 generates a laser power control signal based on this laser power signal, thereby controlling the intensity of the light beam to be emitted so as to match the intensity suitable for reproduction.

  Further, the system controller 11 sends a data write command to the drive control unit 13 together with address information for designating a location for recording data on the information recording layer of the optical disc 100 during the recording process.

  Further, the system controller 11 sends write data input from an external device (not shown) or the like to the optical pickup 20. The drive control unit 13 controls the position of the optical pickup 20 based on the address information.

  In response to this, the optical pickup 20 focuses the light beam on the track corresponding to the address information in the information recording layer of the optical disc 100, and irradiates the writing with the light beam adjusted to an intensity suitable for data recording. Embedded data is recorded on the optical disc 100.

  As described above, the optical disc apparatus 1 can record and reproduce data by irradiating a desired light beam on the desired recording track in the information recording layer of the optical disc 100 from the optical pickup 20. .

(1-2) Configuration of Optical Pickup FIGS. 3 and 4 show the configuration of the optical pickup 20. 3 is a side view of the optical pickup 20 viewed from the X direction orthogonal to the Y and Z directions, and FIG. 4 is a top view of the optical pickup 20 viewed from the Y direction. Some of the optical parts that are shown are omitted.

  The optical pickup 20 (FIG. 3) has, for example, a small package type laser diode 21.

  The laser diode 21 emits laser light in the Z direction parallel to the information recording layer 100a (XZ plane) of the optical disc 100 in accordance with the laser power signal supplied from the system controller 11 (FIG. 2), and as a light beam 40, a collimator The light enters the lens 22 (FIG. 3). The collimator lens 22 converts the light beam 40 composed of divergent light into parallel light and enters the beam splitter 23.

  Here, since the laser diode 21 is disposed so as to be thin in the Y direction, the light beam 40 emitted from the laser diode 21 has a small divergence angle in the horizontal X direction with respect to the optical disc 100, and It has a large elliptical luminous flux in the vertical Y direction.

  The optical pickup 20 sets the focal length of the collimator lens 22 to be shorter than the collimator lens 3 in the conventional optical pickup 1 (for example, about 3 mm), and before the light beam 40 diverges greatly, that is, in the vertical direction of the light beam 40. Both the vertical beam width Dv, which is the width, and the horizontal beam width Dh, which is the width in the horizontal direction, are converted into parallel light in a state that is smaller than the final beam diameter Df that is the diameter of the light beam 40 when entering the objective lens 25. As a result, it is possible to prevent an increase in the thickness of the optical component on the optical path due to the large luminous flux width Dv of the light beam 40, and to reduce the thickness of the entire optical pickup 20.

  The beam splitter 23 transmits the incident light beam 40 and makes it incident on the rising prism 30. The rising prism 30 extends the light beam vertical width Dv and the light beam horizontal width Dh of the incident light beam 40 to the final light beam diameter Df, shapes the light beam 40 into a perfect circle (FIG. 4), and also changes the light beam 40. It is bent at 90 ° (perpendicular) with respect to the objective lens 25 and enters the objective lens 25 (FIG. 3).

  At this time, the rising prism 30 is different from the conventional rising prism 5 (FIG. 1) in which the light beam having the final light beam diameter Df is bent by 90 ° by one-time reflection, and the incident light beam 40 is multiple times. Since the light beam 40 is reflected and bent by 90 ° from when the light beam 40 is finally incident, the light beam 40 stretched to the final light beam diameter Df does not travel in the Z direction, and the light in the rising prism 30 The height of the beam 40 can be limited. The detailed configuration of the rising prism 30 will be described later.

  The objective lens 25 collects the incident light beam 40 and irradiates the optical disc 100 with it.

  The objective lens 25 receives a reflected light beam 50 formed by reflecting the light beam 40 on the optical disc 100 and enters the rising prism 30. The rising prism 30 contracts the incident reflected light beam 50 to convert it from a perfect circle to an ellipse (FIG. 4) and makes it incident on the beam splitter 23.

  The beam splitter 23 reflects the reflected light beam 50 and bends it by 90 ° so that the reflected light beam 50 is incident on the photodetector 28 via the multi-lens 27 that adds astigmatism. The photodetector 28 photoelectrically converts the reflected light beam 50 to generate a light reception signal and supplies it to the signal processing unit 16 (FIG. 2).

  Thus, in the optical pickup 20, the light beam 40 having a large divergence angle emitted by the laser diode 21 in the Y direction (vertical direction) is converted into parallel light by the collimator lens 22 before being expanded to the final light beam diameter Df. By doing so, the light beam vertical width Dv of the light beam 40 is kept small. In the optical pickup 20, the vertical beam width Dv of the light beam 40 is extended to the final beam diameter Df by the rising prism 30 that is the front stage of the objective lens 25, and at the same time, the light beam 40 is reflected in the rising prism 30 a plurality of times. By doing so, the light beam 40 in the Z direction is deflected upward (Y direction). Thus, the optical pickup 20 can position the upper end of the light beam 40 at a low position over the entire optical path of the optical pickup 20 without causing the light beam 40 having the final light beam diameter Df to travel in the Z direction. Therefore, the optical pickup 20 can be thinned.

(1-3) Configuration of Rising Prism Next, the above-described rising prism 30 will be described. As shown in FIGS. 3 and 4, when the rising prism 30 receives the light beam 40 from the incident free curved surface 30A, the first free curved surface 30B, the reflective region 30Ca of the reflective / transmissive surface 30C, and the second free curved surface 30D are arranged in this order. After the light beam 40 is reflected, the light beam 40 is transmitted toward the objective lens 25 located above by transmitting the light beam 40 through the emission region 30Cb of the reflection / transmission surface 30C.

  The rising prism 30 has an incident free curved surface 30A and a first free curved surface 30B among four surfaces (incident free curved surface 30A, first free curved surface 30B, reflection / transmission surface 30C, and second free curved surface 30D) on the optical path. For example, as shown in FIG. 5, the second free-form surface 30D is formed as a so-called free-form surface that has no rotational symmetry and is expressed by a mathematical expression such as a bicubic curve, a Coons curve, or a Bezier curve. Further, in the rising prism 30, a part of the reflection area 30Ca and the emission area 30Cb are overlapped, and the reflection / transmission surface 30C is formed as a flat surface so as not to generate aberration.

  The rising prism 30 is made of, for example, various plastics such as acrylic resin or polycarbonate resin, glass, or the like, and is formed by a method such as injection molding or polishing.

  Accordingly, the rising prism 30 is disposed below the objective lens 29 so that the light beam 40 is incident at substantially the center of the incident free curved surface 30 </ b> A and the emission region 30 </ b> Cb of the upper surface 30 faces the objective lens 25.

  The rising prism 30 is configured to extend the light beam vertical width Dv and the light beam horizontal width Dh of the light beam 40 to the final light beam diameter Df by appropriately combining the curvatures of these free-form surfaces as described above.

Here, as shown in FIG. 6, the laser diode 21 has an elliptical shape that is small in the Y direction (θ _// direction) and large in the X direction (θ _⊥ direction) from the active layer 21A arranged so as to be parallel to the XZ plane. The light beam 40 is emitted.

7 this time, in the theta _⊥ direction of the light beam 40 while the position of the beam waist BWθ _⊥ (7 (A)) coincides with the LD end surface 21B of the laser diode 21, in the theta _// direction position of the beam waist BDθ _// (FIG 7 (B)) inside the laser diode 21, [Delta] Z than LD end surface 21B (e.g. 6 [μm]) by Z (-) will be located in the direction side, the [Delta] Z Only an astigmatic difference will be generated.

  Therefore, in the present embodiment, the rising prism 30 generates astigmatism in the light beam 40, thereby canceling and correcting the astigmatic difference generated in the light beam 40. Curvature is selected.

  FIG. 8 shows a state of an experiment for confirming astigmatism generated by the rising prism 30. In FIG. 8, a light beam 45 having no astigmatism is incident on the rising prism 30 from the emission side opposite to the optical pickup 20 (FIG. 3). Light is received by the photodetector 46 through the collimator lens 22 arranged at the same position.

  At this time, the shape of the spot received by the photodetector 46 is shown in FIG. FIG. 9A shows the spot shape obtained in the same manner for the conventional upright prism (FIG. 1).

  As shown in FIG. 9A, the conventional rising prism 5 does not consider any correction for astigmatism, so astigmatism is not generated and the photodetector 46 matches the focal position Zp. The spot becomes large when the focal point position Zp is shifted by 3 [μm] in the Z (±) direction.

On the other hand, as shown in FIG. 9B, the rising prism 30 generates astigmatism in the light beam 45, thereby 3 [μm] in the Z (−) direction from the reference focal position Zp. The focus is set in the θ _{結 び} direction at the shifted position, and the focus is set in the θ _// direction at a position shifted by 3 [μm] in the Z (+) direction from the focus position Zp.

  That is, the rising prism 30 is non-directional in the opposite direction to the astigmatic difference by 6 [μm], which is the same as the astigmatic difference, by the three free curved surfaces with respect to the light beam 40 incident from the incident free curved surface 30A in the optical pickup 20. By generating astigmatism, when the light beam 40 having astigmatism is incident, this astigmatism can be canceled by astigmatism to correct the astigmatism.

  Specifically, the rising prism 30 (FIG. 3) transmits the light beam 40 incident through the beam splitter 23 by the incident free curved surface 30A. In this incident free-form surface 30A, the incident angle with respect to the light beam 40 is set to 10 ° to 40 °, and the light beam 40 is refracted downward toward the first free-form surface 30B and the light beam 40 has a vertical beam width. Dv and the light beam lateral width Dh are stretched. Further, the incident free-form surface 30A converts the light beam 40, which was parallel light before incidence, into divergent light.

  The first free-form surface 30B reflects the light beam 40 upward toward the reflection region 30Ca (FIG. 4) of the reflection / transmission surface 30C. At this time, the first free-form curved surface 30B (FIG. 3) is in a state in which the light beam 40, which has been once refracted downward and moved to a position where the entire light beam has been lowered, is lowered to a position lower than the lower end of the light beam 40 before incidence. The divergence angle of the light beam 40 is adjusted so that the light beam vertical width Dv and the light beam horizontal width Dh become the final light beam diameter Df when the light beam 40 reaches the second free-form surface 30D.

  Since the incident angle of the light beam 40 reflected by the first free curved surface 30B is greater than or equal to the critical angle, the reflecting region 30Ca reflects the light beam 40 downward toward the second free curved surface 30D.

  The second free-form surface 30D reflects the light beam 40 toward the emission region 30Cb of the reflection / transmission surface 30C so as to be perpendicular to the objective lens 25, and is light that is divergent light reflected by the reflection region 30Ca. The light beam 40 is converted into parallel light by adjusting the divergence angle of the beam 40 to zero. At this time, the second free-form curved surface 30D can set the light beam vertical width Dv and the light beam lateral width Dh of the light beam 40 to the final light beam diameter Df by adjusting the divergence angle of the light beam 40 by the first free-form curved surface 30B.

  The three free-form surfaces (incidence free-form surface 30A, first free-form surface 30B, and second free-form surface 30D) are generated by the laser diode 21 by generating astigmatism according to the combination of the curvatures of the three free-form surfaces. Correct the astigmatic difference that occurs.

  Since the incident angle of the light beam 40 reflected by the second free-form surface 30D is less than the critical angle, the emission region 30Cb transmits the light beam 40 and emits the light beam 40 from the rising prism 30.

  As a result, since the rising prism 30 can reduce the thickness Td (FIG. 3) of the rising prism 30 determined by the vertical beam width Tv at the time of incidence, the working distance Ta and the thickness Tb of the objective lens 25 can be reduced. The thickness Tt in the vicinity of the objective lens represented by the sum of the lens / prism interval Tc, which is the interval between the objective lens 25 and the rising prism 30, which is secured as a driving range in the focus direction of the objective lens 25, is reduced. The entire thickness of the optical pickup 20 determined by the thickness Tt in the vicinity of the objective lens can be reduced.

  For example, since the thickness Td of the rising prism 30 can be reduced to about half that of the conventional rising prism 5 (FIG. 1), for example, a DVD (Digital Versatile Disc) having an aperture ratio NA of about 0.65. When the present invention is applied to the optical pickup of the system, the thickness of the optical pickup 20 determined by the thickness Tt in the vicinity of the objective lens can be reduced to about 70% of the conventional optical pickup 1.

  As described above, in the rising prism 30, the light beam 40 having the final light beam diameter Td in the rising prism 30 is reflected in the rising prism 30 a plurality of times in order to deflect the light beam 40 by 90 °. Thus, the optical pickup 20 can be made thinner.

  Further, in the rising prism 30, by using three free curved surfaces as described above, light that is incident as parallel light by the incident free curved surface 30A using the optical path in the rising prism 30 for deflecting by 90 °. The beam 40 is converted into divergent light, and both the light beam vertical width Dv and the light beam horizontal width Dh of the light beam 40 are simultaneously extended to the final light beam diameter Df, and the astigmatic difference is also corrected.

  As a result, the rising prism 30 can reduce the number of components in the optical pickup 20 by omitting the beam expander for expanding the light beam of the light beam 40 and the optical element for correcting the astigmatic difference. The pickup 20 can be downsized.

(1-4) Operation and Effect In the above configuration, the optical pickup 20 has a light beam diameter smaller than the final light beam diameter Df that is the light beam diameter of the light beam 40 when it enters the objective lens 25 by the rising prism 30 ( The light beam 40 incident with the vertical beam width Dv and the horizontal beam width Dh) is extended as a divergent light in a part of the rising prism 30, and the divergence angle of the light beam 40 incident by a plurality of free-form surfaces is increased. Light at the time of entering the objective lens 25 by adjusting the light beam vertical width Dv and light beam horizontal width Dh of the adjusted light beam to the final light beam diameter Df and emitting the incident light beam 40 as parallel light. The light beam 40 is emitted according to the incident condition of the beam 40.

  As a result, the optical pickup 20 can obtain a desired final light beam diameter Df if a light beam 40 having a light beam vertical width Dv and a light beam horizontal width Dh smaller than the final light beam diameter Df is incident on the rising prism 30. The optical components on the optical path in the optical pickup 20 can be reduced in size, and the entire optical pickup 20 can be reduced in size.

  Further, the optical pickup 20 receives the light beam 40 having an elliptical light beam by the rising prism 30 and emits the light beam of the incident light beam 40 with a perfect circular shape and a final light beam diameter Df. Since the shape of the light flux of the beam 40 can be adjusted, an optical component such as a beam shaper that shapes the light beam 40 into a perfect circle can be omitted, and the optical pickup 20 can be downsized.

  The rising prism 30 includes, as a plurality of free-form surfaces, a first free-form surface 30B that reflects the light beam 40 and a second free-form surface 30D that reflects the light beam 40 so as to be perpendicular to the objective lens 25. And the first free-form curved surface 30B reflects the light beam 40 by adjusting the divergence angle, and the reflected light beam 40 is reflected by the reflection region 30Ca of the reflection / transmission surface 30C, which is a flat reflection surface. When the reflected light beam 40 is reflected by the second free-form surface 30D, the reflected light beam 40 is converted into parallel light, so that the optical path length from the first free-form surface 30B to the second free-form surface 30D. Secure.

  As a result, the rising prism 30 uses the optical path length from the first free-form surface 30B to the second free-form surface 30D, and only adjusts the divergence angle of the light beam 40 so that the vertical beam width Dv of the light beam 40 is reduced. In addition, the light beam lateral width Dh can be sufficiently extended.

  At this time, the rising prism 30 has a first free curved surface 30B having a negative power for diverging the light beam 40 and a second free curved surface 30D having a positive power for condensing the light beam. Using the optical path length from the first free-form surface 30B to the second free-form surface 30D, the light beam vertical width Dv and the light beam horizontal width Dh of the light beam 40 can be sufficiently extended, and astigmatism and aberration can be corrected freely. it can.

  Further, the rising prism 30 reflects the light beam 40 first and third times within the rising prism 30, and forms a first free curved surface 30 </ b> B and a second free curved surface 30 </ b> D constituting the lower surface of the rising prism 30 as a free curved surface. Thus, the transmission / reflection surface 30C constituting the upper surface side of the rising prism 30 can be formed flat, compared with the case where free curved surfaces are formed on both the upper surface side and the lower surface side of the rising prism 30. Thus, the manufacturing process can be simplified.

  Further, the optical pickup 20 can correct the astigmatism generated by the laser diode 21 as the light source by generating astigmatism in the light beam 40 by the first free curved surface 30B and the second free curved surface 30D. Optical components for correcting the point difference can be omitted, and the optical pickup 20 can be downsized.

  According to the above configuration, in the optical pickup 20, when the diverging light beam 40 is reflected in the rising prism 30 a plurality of times, the light beam 40 is caused by the refractive index difference and the angle change from the conventional air. Unlike the beam expander that adjusts the light beam diameter, the light beam 40 is diverged to expand the light beam diameter, and the light beam diameter of the light beam 40 is adjusted using the first free curved surface 30B and the second free curved surface 30D that are free curved surfaces. By doing so, the beam diameter of the light beam 40 can be freely adjusted in any direction on the XY plane, and the rising prism 30 can be made thin by suppressing the beam of the light beam 40 at the time of incidence, and the light beam can be reduced in thickness. An optical pickup capable of omitting an optical component for shaping the light beam shape of 40 and thus miniaturizing, and an optical disk apparatus using the optical pickup It can be realized.

(2) Second Embodiment (2-1) Configuration of Optical Pickup In the second embodiment, as shown in FIG. 10 (A), the same reference numerals are given to the corresponding parts to FIG. 3 and FIG. The optical pickup 120 has a configuration partially different from the optical pickup 20 in the first embodiment. This optical pickup 120 is different in that it has a free-form curved surface prism 31 having a collimator lens function for converting divergent light into parallel light instead of the rising prism 30. The configuration of the optical disc apparatus 10 is the same as that shown in FIG.

  In this optical pickup 120, a microprism 32 having a polarization surface 32A on the lower surface is bonded to the flat upper surface 31A of the free-form surface prism 31, and a photodetector 28 is bonded to the upper surface of the microprism 32 and integrated. .

  The laser diode 21 emits the light beam 40 with an inclination of about 40 ° upward from the Z direction, and enters the free-form surface prism 31 as divergent light.

  When the light beam 40 is incident from the incident surface 31A, the free-form surface prism 31 transmits and reflects the transmission / reflection region 31Cc on the transmission / reflection surface 30C, the lower first free-form surface 31B, and the reflection region 31Ca (not shown, but on the transmission / reflection surface 30C). After the light beam 40 is reflected in the order of the second free-form surface 31D from the center portion to the right side portion), the light beam 40 is reflected from the emission region 31Cb of the transmission / reflection surface 30C (not shown, but the right side portion of the transmission / reflection surface 30C). ), The light beam 40 is emitted toward the objective lens 25 positioned above.

  The free-form surface prism 31 has two free-form surfaces (a first free-form surface 31B and a second free-form surface 31D). By selecting the curvature of the two free-form surfaces, the collimator lens function and the above-described astigmatism difference are obtained. It is made to have a correction function.

  Thereby, the free-form surface prism 31 extends the light beam vertical width Dv and the light beam horizontal width Dh of the light beam 40 to the final light beam diameter Df, converts the light beam 40 into parallel light, and converts the light beam 40 to the objective lens 25. The light is emitted so as to be vertical.

  The objective lens 25 collects the incident light beam 40 and irradiates the optical disc 100 with it.

  The objective lens 25 receives a reflected light beam 50 formed by reflecting the light beam 40 on the optical disc 100 and enters the free-form surface prism 31. The free-form surface prism 31 contracts the incident reflected light beam 50 so as to enter the microprism 32.

  The microprism 32 transmits the reflected light beam 50 through the polarization plane 32 </ b> A and makes the reflected light beam 50 incident on the photodetector 28. The photodetector 28 photoelectrically converts the reflected light beam 50 to generate a light reception signal and supplies it to the signal processing unit 16 (FIG. 2).

  In FIG. 10B, the curvatures of the first free curved surface 31B and the second free curved surface 31D are shown three-dimensionally, and the sag amount of the first free curved surface 31B and the second free curved surface 31D is small. It can be seen that the free-form surface prism 31 can be easily manufactured.

(2-2) Operation and Effect In the above configuration, the optical pickup 120 is a flat second that reflects the light beam 40 incident on the free curved surface prism 31 as the rising prism toward the first free curved surface 31B. A reflection region 31Cc that is a reflection / transmission surface is provided, and a microprism 32 is provided in contact with the reflection region 31Cc. The light beam 40 is reflected on the interface between the free-form surface prism 31 and the microprism 32 to reflect the reflection light beam 50. By providing a polarizing surface 32A that is a deflection film that transmits the reflected light, the reflected light beam 50 is guided to the photodetector 28 that detects the amount of the reflected light beam 50.

  As a result, the optical pickup 120 can finally convert the light beam 40, which is divergent light, into parallel light by the free-form curved prism 31, and can emit the parallel light. Therefore, the collimator lens can be omitted, and the optical pickup 120 can be reduced in size. Can be

  Further, in place of the beam splitter 23 (FIG. 3), the optical pickup 120 is brought into contact with the microprism 32 (FIG. 10) smaller than the beam splitter 23 in the reflection region 31Cc, so that the objective lens 25 is disposed above the reflective area 31Cc. The microprism 32 can be arranged in the Y direction which becomes a dead space for securing the thickness Tt in the vicinity of the objective lens in the reflection / transmission region 31Cc which is not performed, and the optical pickup 120 can be downsized as compared with the case where the beam splitter 23 is used. can do.

  According to the above configuration, the optical pickup 120 does not need to convert the parallel light into the divergent light by directly entering the light beam 40 that is the divergent light emitted from the laser diode 21, so that the incident surface 31A is flattened. Compared to the case where the incident surface 31A is formed as a free-form surface, the manufacturing process of the free-form surface prism 31 can be facilitated, and the reflection region 31Cc that reflects the light beam 40 has a PBS film. By providing the microprism 32 integrally and guiding the reflected light beam 50 to the photodetector 28, the number of optical components of the optical pickup 120 can be reduced, and thus an optical pickup that can be reduced in size and an optical disk using the optical pickup. A device can be realized.

(3) Other Embodiments In the above-described embodiment, the rising prism 30 or the free curved prism 31 having a free curved surface is used for the optical pickup 20 or the optical pickup 120 shown in FIGS. Although the case has been described, the present invention is not limited to this. For example, the free-form surface prism 33 may be used in the optical pickup 130 having the configuration shown in FIG.

  In this case, the optical pickup 130 uses the beam splitter 23 to guide the reflected light beam 50 to the photodetector 28 as in the optical pickup 20, while the free-form surface prism 33 performs the collimator function in the same manner as the free-form surface prism 31 (FIG. 10). To have.

  Further, in the above-described second embodiment, the case where the laser beam 21 emits the light beam 40 while being inclined with respect to the Y direction and the Z direction has been described, but the present invention is not limited thereto. Instead, the laser diode 21 may emit the light beam 40 in the Z direction horizontal to the optical disc 100.

  Further, in the above-described embodiment, the case where the rising prism 30 and the free-form surface prism 31 correct the astigmatism due to the laser diode 21 has been described. However, the present invention is not limited to this, and the astigmatism is not necessarily limited. Need not be corrected.

  Furthermore, in the above-described embodiment, the rising prism 30 emits the light beam 40 so that the final light beam diameter Df, which is an incident condition when the light beam 40 is incident on the objective lens 25, and a parallel light state are obtained. Although the present invention is described above, the present invention is not limited to this. For example, as an incident condition, the rising prism 30 is placed in the light beam 40 so that the light beam 40 has a predetermined aberration or a predetermined convergence state. May be emitted.

  Further, in the above-described embodiment, the case where the optical pickup 20 as the optical pickup is configured by the rising prism 30 as the rising prism and the objective lens 25 as the objective lens has been described. However, the optical pickup according to the present invention may be configured by a rising prism having various configurations and an objective lens.

  Further, in the above-described embodiment, the case where the optical disk apparatus 10 as the optical disk apparatus is configured by the rising prism 30 as the rising prism and the objective lens 25 as the objective lens has been described. However, the present invention is not limited to this, and the optical disk device of the present invention may be configured by a rising prism having various other configurations and an objective lens.

  The optical pickup and the optical disk apparatus of the present invention can be used for various optical disk apparatuses corresponding to various systems, for example.

It is a basic diagram which shows the structure of the conventional optical pick-up. 1 is a schematic diagram illustrating an overall configuration of an optical disc device. It is a basic diagram which shows the structure (side view) of the optical pick-up by 1st Embodiment. It is a basic diagram which shows the structure (top view) of the optical pick-up by 1st Embodiment. It is a basic diagram with which it uses for description of generation | occurrence | production (1) of astigmatism. It is a basic diagram with which it uses for description of generation | occurrence | production (2) of astigmatism. It is a basic diagram which shows an example of a free-form surface. It is an approximate line figure used for explanation of amendment of astigmatism. It is a basic diagram which shows the spot shape of a focus position vicinity. It is a basic diagram which shows the structure of the optical pick-up by 2nd Embodiment. It is a basic diagram which shows the structure of the optical pick-up by other embodiment.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ... Optical disk apparatus, 20 ... Optical pick-up, 21 ... Laser diode, 22 ... Collimator lens, 25 ... Objective lens, 30 ... Rising prism, 30A ... Incident surface, 30B ... First free-form surface , 30C... Reflection / transmission surface, 30Ca... Reflection region, 30Cb... Output region, 30Cc... Reflection / transmission region, Dv. …… Free-form surface prism, 32 …… Micro prism, 32A …… PBS surface.

Claims (11)

In the optical pickup that irradiates the optical disk with the light beam emitted from the light source through the objective lens,
A rising prism that raises and emits the light beam so as to be perpendicular to the objective lens by reflecting the light beam a plurality of times;
An objective lens for condensing the light beam emitted from the rising prism and irradiating the optical disc,
The rising prism is
The light beam incident with a light beam diameter smaller than the final light beam diameter, which is the light beam diameter of the light beam when entering the objective lens, is advanced and diverged in a part of the rising prism. An optical pickup that emits a light beam that meets an incident condition required when entering the objective lens by adjusting a divergence angle of the incident light beam by a plurality of free-form surfaces. The rising prism is
2. The optical pickup according to claim 1, wherein the light beam having an elliptical light beam is incident, and the light beam of the incident light beam is emitted with a perfect circle shape and the final light beam diameter. The plurality of free-form surfaces are
The optical pickup according to claim 1, wherein astigmatism generated by the light source is corrected by generating astigmatism in the light beam. The rising prism is
The plurality of free-form surfaces include a first free-form surface that reflects the light beam and a second free-form surface that reflects the light beam so as to be perpendicular to the objective lens. Item 4. The optical pickup according to Item 1. The rising prism is
The divergence angle of the light beam is adjusted and reflected by the first free curved surface, the reflected light beam is reflected by a flat reflecting surface, and then the reflected light beam is reflected by the second free curved surface. The optical pickup according to claim 1, wherein the reflected light beam is converted into a light beam that meets an incident condition required when entering the objective lens. The rising prism is
The first free-form surface has a negative power for diverging the light beam, and the second free-form surface has a positive power for condensing the light beam. Optical pickup. The rising prism is
The incident light beam is reflected by the first free-form surface, the reflected light beam is totally reflected by a flat reflecting surface, and then the reflected light beam is reflected by the second free-form surface. The optical pickup according to claim 4. The rising prism is
The plurality of free curved surfaces include a first free curved surface that reflects the light beam and a second free curved surface that reflects the light beam so as to be perpendicular to the objective lens, The divergence angle of the light beam is adjusted and reflected by a free-form surface, the reflected light beam is reflected by a flat reflecting surface, and then the reflected light beam is reflected by the second free-form surface. The optical pickup according to claim 2, wherein an optical path length from the first free curved surface to the second free curved surface is secured by converting the reflected light beam into parallel light. The rising prism is
The optical pickup according to claim 1, wherein the light beam made of divergent light is incident on a flat incident surface. The rising prism is
The plurality of free-form surfaces include a first free-form surface that reflects the light beam and a second free-form surface that reflects the light beam so as to be perpendicular to the objective lens. When the light beam is reflected by a flat reflection / transmission surface, reflected by adjusting the divergence angle of the reflected light beam by the first free-form surface, and reflected by the second free-form surface To convert the reflected light beam into parallel light,
The above optical pickup
A photodetector for detecting the amount of reflected light beam reflected by the optical disc;
A microprism provided in contact with the reflection / transmission surface,
2. The reflected light beam is guided to the photodetector by providing a polarizing film that reflects the light beam and transmits the reflected light beam at an interface between the rising prism and the microprism. The optical pickup described in 1. In an optical disc apparatus that irradiates an optical disc with a light beam emitted from a light source via an objective lens,
A rising prism that raises and emits the light beam so as to be perpendicular to the objective lens by reflecting the light beam a plurality of times;
An objective lens for condensing the light beam emitted from the rising prism and irradiating the optical disc,
The rising prism is
The light beam incident with a light beam diameter smaller than the final light beam diameter, which is the light beam diameter of the light beam when entering the objective lens, is advanced and diverged in a part of the rising prism. An optical disc comprising: adjusting a divergence angle of the incident light beam with a plurality of free-form surfaces, and emitting a light beam that meets an incident condition required when entering the objective lens. apparatus.