JP2011113632A - Optical pickup - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To enhance accuracy in adjusting a wavefront phase of a liquid crystal element without increasing the number of spring members in an optical pickup. <P>SOLUTION: The optical pickup has a fixed part 24 including a laser beam emitting device for emitting an optical beam; and a movable part 25 including an objective lens 14 for condensing the optical beam on an optical recording medium, a liquid crystal element 11 located between the laser beam emitting device and objective lens 14 for adjusting the wavefront phase of the optical beam, and a liquid crystal control element 26 for controlling a voltage or current to be applied to the liquid crystal element 11. The movable part 25 is movable relative to the fixed part 24 in the direction substantially orthogonal to a light axis C along which the optical beam passes through the objective lens 14. The liquid crystal control element 26 is electrically connected to the fixed part 24 by input lines 34, and is electrically connected to the liquid crystal element 11 by output lines 35. The number of the input lines 34 is smaller than that of the output lines 35. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an optical pickup, and more particularly to an arrangement of a liquid crystal control element that controls a liquid crystal element for adjusting a wavefront phase of a light beam.

  The optical pickup is required to accurately irradiate a predetermined position on the optical recording medium with laser light. In order to increase the irradiation accuracy of the laser beam, it is necessary to control the position of the objective lens provided at the position closest to the optical recording medium with high accuracy. The position of the objective lens is always corrected by a plurality of servo mechanisms. The tracking servo controls the position of the objective lens in the lateral direction (direction orthogonal to the optical axis), and the tilt servo controls the tilt of the objective lens with respect to the optical recording medium. Further, the position of the objective lens in the optical axis direction is controlled by a focus servo. For this reason, the objective lens is accommodated in the movable housing, and is elastically supported by the spring member with respect to the fixed portion of the optical pickup.

  Recent optical pickups are required to be compatible with many optical recording media having different specifications such as DVD (Digital Versatile Disc) -ROM, CD (Compact Disc). However, since the depth position of the signal recording surface of the optical recording medium from the surface of the recording medium varies depending on the optical recording medium, there is a problem that spherical aberration and wavefront aberration vary depending on the type of optical recording medium. Therefore, for each type of optical recording medium, the wavefront phase of the light beam incident on the objective lens is optimized by a liquid crystal element, and spherical aberration and wavefront aberration are minimized. Since it is necessary to supply a control voltage or a control current to the liquid crystal element, a liquid crystal control element that supplies the control voltage or the control current to the liquid crystal element is provided in the fixed portion, and the liquid crystal element and the liquid crystal control element are formed by the above-described spring member. It is connected.

  The spherical aberration correction pattern in the liquid crystal element is generally divided into a plurality of concentric segments, and the wavefront phase of the light beam is individually adjusted for each segment. Therefore, the adjustment accuracy of the wavefront phase of the liquid crystal element increases as the number of segments increases. However, since a control voltage or control current is individually supplied from the liquid crystal control element to each segment, it is necessary to increase the number of means for supplying the control voltage or control current according to the number of segments in order to increase the adjustment accuracy. is there. Although this problem can be dealt with relatively easily by using a flexible wiring board (hereinafter referred to as FPC), there is a high possibility that the reaction force of the FPC will adversely affect the response characteristics of the tracking servo and tilt servo. Therefore, Patent Document 1 describes that the number of spring members is increased to improve the adjustment accuracy of the wavefront phase of the liquid crystal element.

Japanese Patent Laid-Open No. 2005-4826

  The spring member is not the movable part itself, but moves together with the movable part. For this reason, when the number of spring members increases, (1) the weight of the spring member relatively increases and the operation sensitivity of the movable part decreases, (2) the left-right symmetry of the movement of the movable part and the entire movable part It becomes difficult to control the vibration characteristics. (3) Unnecessary resonance occurs because the degree of freedom of vibration increases. (4) Transmission characteristics (high frequency characteristics) of the tracking servo and tilt servo deteriorate. It becomes difficult to secure a place for placement, which causes problems such as an obstacle to downsizing and weight reduction of the movable part.

  SUMMARY OF THE INVENTION An object of the present invention is to provide an optical pickup capable of increasing the accuracy of adjusting the wavefront phase of a liquid crystal element without increasing the number of spring members.

  According to one embodiment of the present invention, an optical pickup includes a fixing unit including a laser beam emitting device that emits a light beam, an objective lens that focuses the light beam on an optical recording medium, and a laser beam emitting device and an objective lens. And a movable part including a liquid crystal element that adjusts a wavefront phase of the light beam and a liquid crystal control element that controls an applied voltage or an applied current to the liquid crystal element. The movable part is movable with respect to the fixed part in a direction substantially perpendicular to the optical axis of the light beam passing through the objective lens. The liquid crystal control element is electrically connected to the fixed portion by an input line and electrically connected to the liquid crystal element by an output line, and the number of input lines is smaller than the number of output lines.

  Since the liquid crystal control element is conventionally provided in the fixed portion, the output line of the liquid crystal control element and the liquid crystal element are connected via a spring member. However, since the output lines of the liquid crystal control element correspond to each segment of the liquid crystal element on a one-to-one basis, the number of output lines increases as the number of segments increases. On the other hand, the number of input lines of the liquid crystal control element does not correspond one to one with the number of segments. In this embodiment, since the liquid crystal control element is accommodated in the movable part and the number of input lines of the liquid crystal control element is smaller than the number of output lines, the total number of lines connecting the fixed part and the movable part is smaller than the conventional one. Can be reduced. In other words, if the total number of lines connecting the fixed part and the movable part is the same, the number of output lines of the liquid crystal control element can be increased without increasing the number of spring members. In general, in the case of a liquid crystal driving system that sends digital information to an IC, the number of input lines of a liquid crystal element driver IC is often five, and it is necessary to increase the number of output lines as the number of segments of the liquid crystal element increases. .

  As described above, according to the present invention, it is possible to provide an optical pickup capable of improving the adjustment accuracy of the wavefront phase of the liquid crystal element without increasing the number of spring members.

It is the schematic which shows the structure of the optical system of an optical pick-up. FIG. 2 is a schematic perspective view of the optical pickup shown in FIG. 1. It is a schematic diagram which shows the whole shape of FPC. It is a mimetic diagram showing the state where a part of FPC was bent. It is a schematic diagram which shows the state by which all the FPC was bent. It is a schematic diagram which shows the state by which FPC was inserted in the housing. It is a schematic diagram which shows the state which the assembly of the movable part was complete | finished.

  Hereinafter, embodiments of an optical pickup according to the present invention will be described with reference to the drawings. FIG. 1 is a schematic diagram showing a configuration of an optical system of an optical pickup. The optical pickup 1 is configured such that digital information can be recorded or reproduced on each of three types of optical recording media 2 (2a to 2c) having different physical track pitches.

  The first optical recording medium 2a is an optical recording medium having a current DVD-ROM, DVD ± R / RW, and a structure and storage capacity equivalent to these. The second optical recording medium 2b is an optical recording medium having a CD-ROM, CD-R / RW, and a structure and storage capacity equivalent to these. The third optical recording medium 2c is a BD (Blu-ray Disc (registered trademark)) or CB-HD (China High Density Optical Recording Medium Standard) that performs high-density recording / reproduction using blue laser light having a wavelength of about 405 nm. This is an optical recording medium exclusively for reproduction or for both recording and reproduction.

  The optical pickup 1 includes semiconductor lasers 3 and 4 that are light sources (laser light emitting devices) that emit a light beam having a predetermined wavelength. The semiconductor laser 3 includes a first light emitting region that emits a light beam having a wavelength of 650 nm (first light beam) for recording and reproducing a current DVD, and a light beam having a wavelength of 780 nm for recording and reproducing a CD (first light beam). 2nd light emission area | region which light-emits (2 light beams). These light emitting regions are formed at a predetermined distance and are accommodated in one package. On the other hand, the semiconductor laser 4 emits a light beam (third light beam) having a wavelength of 405 nm for recording / reproducing a high-density optical recording medium such as BD or CB-HD.

  The semiconductor lasers 3 and 4 are provided so that the optical axis of the first or second light beam emitted from the semiconductor laser 3 and the optical axis of the third light beam emitted from the semiconductor laser 4 are orthogonal to each other. It has been.

  A diffraction grating 5 is disposed at a predetermined position on the light emitting side of the semiconductor laser 3. On one side of the diffraction grating 5, the first and second light beams emitted from the semiconductor laser 3 are each divided into three light beams (0th-order main beam and ± 1st-order subbeams; not shown). Thus, an optimized diffraction grating pattern is formed. The diffraction grating 5 is a semiconductor on the signal recording surface of the optical recording medium 2 so that ± 1st order sub beams are condensed at symmetrical positions separated by a predetermined distance in the track line direction around the main beam condensing position. The first and second light beams emitted from the laser 3 are divided.

  A diffraction grating 6 is also disposed at a predetermined position on the light emitting side of the semiconductor laser 4. On one side of the diffraction grating 6, the third light beam emitted from the semiconductor laser 4 is optimally divided into three light beams (0th-order main beam and ± 1st-order subbeams; not shown). A diffraction grating pattern is formed. The diffraction grating 6 is a semiconductor on the signal recording surface of the optical recording medium 2 so that the ± first-order sub-beams are condensed at symmetrical positions separated by a predetermined distance in the track line direction around the condensing position of the main beam. The third light beam emitted from the laser 4 is split.

  A substantially cubic dichroic prism 7 is provided at a position where the light beam from the semiconductor laser 3 and the light beam from the semiconductor laser 4 intersect. The dichroic prism 7 transmits the first and second light beams almost completely and reflects the third light beam substantially totally.

  The light beam that has passed or reflected through the dichroic prism 7 enters the polarization beam splitter 8. About 90% of the light beam incident on the polarizing beam splitter 8 is reflected by the polarizing beam splitter 8 and enters the rising mirror 9. The remaining 10% of the light beam incident on the polarization beam splitter 8 passes and enters the front monitor photodetector 15. The front monitor photodetector 15 measures the light intensity of the first to third light beams emitted from the semiconductor lasers 3 and 4. The outputs of the semiconductor lasers 3 and 4 are adjusted based on the output of the front monitor photodetector 15.

  The light beam incident on the rising mirror 9 is reflected by the rising mirror 9 and enters the collimating lens 10. The light beam is a diverging beam until it enters the collimating lens 10 after being emitted from the semiconductor lasers 3 and 4, but is converted into substantially parallel beam light by the collimating lens 10. That is, the collimating lens 10 is a parallelism conversion lens that is disposed on the optical path between the semiconductor lasers 3 and 4 and the objective lens 14 and converts the parallelism of the light beam.

  The light beam that has passed through the collimator lens 10 enters the liquid crystal element 11. The liquid crystal element 11 is located between the semiconductor lasers 3 and 4 and the objective lens 14 and adjusts the wavefront phase of the light beam. The liquid crystal element 11 includes a transparent electrode (not shown) divided into a predetermined shape, and a control voltage or a control current is applied from the liquid crystal control element 26 for each divided segment. When a voltage or current is applied to each segment of the liquid crystal element 11, the refractive index of the segment changes, an appropriate phase difference is given to the passing light beam, and various wavefront aberrations occurring on the optical path are corrected and optimized. Can be The transparent electrode is made of, for example, tin-doped indium oxide (ITO) or tin oxide.

  The liquid crystal element 11 is preferably arranged slightly inclined with respect to the optical axis C. When the element surface of the liquid crystal element 11 is arranged in a direction that is completely orthogonal to the optical axis C, part of the reflected light from the element surface becomes stray light and enters the light receiving element 17, causing noise or an output electric signal. Cause offset. In order to prevent this phenomenon, it is desirable to arrange the liquid crystal element 11 slightly inclined with respect to the optical axis C so that stray light does not enter the light receiving element 17.

  The light beam that has passed through the liquid crystal element 11 is incident on the quarter-wave plate 12, and the main beam and the ± 1st-order sub beam (hereinafter referred to as “outward light beam”) are changed from linearly polarized light to circularly polarized light. Converted. The quarter-wave plate 12 in this example is a composite element integrated with the liquid crystal element 11 and is an active element that can control the phase difference corresponding to the three wavelengths by controlling the applied voltage. The half-wave plate 12 may be provided separately from the liquid crystal element 11 as a passive type for sharing three wavelengths.

  A wavelength compatible element 13 is provided adjacent to the quarter wave plate 12. The wavelength compatible element 13 has a specific lens power corresponding to the wavelength of the light source to be used, changes the wavefront (angle) of incident light on the objective lens 14, and converts the magnification of the objective lens 14.

  The light beam that has passed through the wavelength compatible element 13 enters the objective lens 14 and is focused on the signal recording surface of the optical recording medium 2. At the time of recording, the focused light beam writes a record to a predetermined bit on the signal recording surface, and the recording operation is completed.

  At the time of reproduction, the light beam condensed on the optical recording medium 2 is reflected by the signal recording surface and further proceeds in the reverse direction. First, the light beam reflected by the optical recording medium 2 is converted into a substantially parallel beam by the objective lens 14. The light beam continues to enter the quarter-wave plate 12 through the wavelength compatible element 13, and is converted from circularly polarized light into linearly polarized light in a direction orthogonal to the polarization direction of the forward light beam. The light beam that has passed through the quarter-wave plate 12 enters the collimating lens 10 through the liquid crystal element 11, and is converted into a convergent beam. The light beam that has passed through the collimating lens 10 is reflected by the rising mirror 9 and enters the polarization beam splitter 8. The polarization beam splitter 8 causes the return light from the collimating lens 10 to pass through the internal joint surface and enter the anamorphic lens 16. The anamorphic lens 16 gives astigmatism for detecting a defocus error to the light beam incident from the polarization beam splitter 8 and forms an image on the light receiving element 17. The light receiving element 17 photoelectrically converts the received light beam for each divided light receiving region (not shown) and outputs an electrical signal.

  FIG. 2 is a conceptual perspective view of the optical pickup. The housing 21 accommodates the liquid crystal element 11, the quarter-wave plate 12, the wavelength compatible element 13, the objective lens 14, and the liquid crystal control element 26, and constitutes a movable portion 25 together with these containers. In the figure, the liquid crystal element 11, the quarter-wave plate 12, the wavelength compatible element 13, and the liquid crystal control element 26 are shown in a state of being taken out from the housing 21. Other elements of the optical pickup including the semiconductor lasers 3 and 4 constitute a fixed portion 24.

  The movable portion 25 is supported with respect to the fixed portion 24 by an elastic wire 31. Five elastic wires 31 are provided on each outer surface side of the first surface 32 and the second surface 33 facing each other of the housing 21. Of the five elastic wires 31 provided on the surfaces 32 and 33, two are main elastic wires 31a having a relatively large diameter and high rigidity, and the movable portion 25 is mainly supported by the main elastic wires 31a. ing.

  Referring to FIG. 1, a tracking coil 23 for tracking servo and a tilt coil 22 for tilt servo are provided around the objective lens 14. Magnets (not shown) are provided at positions facing the coils 22 and 23. By energizing the coils 22 and 23, a magnetic action (Lorentz force) is generated between the magnet and the current flowing through the coils 22 and 23, and the movable part 25 can move in a desired direction by this force. As a result, as shown in FIG. 2, the movable portion 25 can move in the direction substantially perpendicular to the optical axis C passing through the objective lens with respect to the fixed portion 24 by the tracking servo (arrow A), and the tilt servo. Thus, tilting with respect to the normal direction of the recording medium 2 is possible (arrow B). The main elastic wire 31 a also functions as a conductor that supplies power to the tilt coil 22 and the tracking coil 23.

  Of the five elastic wires 31 provided on the respective surfaces 32 and 33, the remaining three are relatively thin wires having a small rigidity and also serve as an input line 34 to the liquid crystal control element 26 ( Hereinafter, it is referred to as an input line combined wire 31b). In this embodiment, since there are a total of five input lines, one of the input line combined wires 31b is a spare. However, by providing three input line combined wires 31b on each of the surfaces 32 and 33, the left-right symmetry of the movement of the movable portion 25 can be easily ensured. For the same purpose, it is desirable that five elastic wires 31 are provided at symmetrical positions on each of the surfaces 32 and 33.

  The input line combined wire 31b is attached to the movable portion 25 via tabs 38a and 38b provided on the FPC 36, as will be described later. The tabs 38a and 38b are provided at positions that do not interfere with the attachment and operation of the main elastic wire 31a.

  The number and rigidity of the elastic wires 31 are not limited to those in the present embodiment, and can be appropriately determined in consideration of the number of input lines, desired servo characteristics, and the like.

  The liquid crystal control element 26 is electrically connected to the fixing unit 24 via the input line 34 and the input line combined wire 31b, and is electrically connected to the liquid crystal element 11 via the output line 35. The number of input lines 34 is smaller than the number of output lines 35. In the present embodiment, the number of input lines 34 is five, whereas the number of output lines 35 is 14. In general, a liquid crystal control element has a function to individually generate a control voltage or control current for each segment of the liquid crystal element based on an input signal received from the outside via an input line. The number of lines does not increase accordingly. For this reason, by installing the liquid crystal control element 26 in the movable portion 25, the number of lines connecting the movable portion 25 and the fixed portion 24 can be reduced as compared with the case where the liquid crystal control element 26 is installed in the fixed portion 24. it can.

  For example, in the case of the present embodiment, there may be five control lines for the liquid crystal element 11 between the movable portion 25 and the fixed portion 24, but when the liquid crystal control element 26 is installed on the fixed portion 24, the control line is movable. Fourteen lines are required between the portion 25 and the fixed portion 24. This means that at least 14 input line combined wires 31b are required, and the influence on the operating characteristics of the movable portion 25 cannot be ignored. On the other hand, in the present embodiment, since the input line combined wire 31b needs to be at least five (actually six), the influence on the operation characteristics of the movable portion 25 is limited.

  The liquid crystal control element 26 is located in the vicinity of the inner wall of the housing 21 (actually, it is fixed on the FPC 36 extending along the inner wall of the housing 21), and the center of gravity of the liquid crystal element 11 is liquid crystal with respect to the centroid of the movable portion 25. It is located on the opposite side to the control element 26. This makes it possible to make the center of gravity of the movable part 25 coincide with the centroid within a plane including the moving direction of the movable part 25, and the movable part 25 has an undesirable movement (for example, has a tilt component during tracking servo operation). Can be prevented from occurring.

  3A to 3E are schematic views showing specific configurations of the input line and the output line. As the input line 34 and the output line 35, a known flexible wiring means such as an FPC can be used.

  FIG. 3A is an external view when the FPC 36 is unfolded, and an arrow Y shown in the drawing indicates that the mountain is folded according to the direction of the arrow, and an arrow T indicates that the valley is folded. The liquid crystal control element 26 is fixed to one end side of the FPC 36, and a band-shaped portion 37 extends leftward therefrom. A first tab 38 a is provided in the middle of the belt-shaped portion 37, and a second tab 38 b is provided at the end of the belt-shaped portion 37. The first and second tabs 38a and 38b are each formed with three pads 39 connected to the input line / wire 31b (one of the six pads 39 is a spare pad). Although illustration is omitted, inside the FPC 36, there are three in total from the vicinity where the liquid crystal control element 26 is provided toward the first tab 38a and two toward the second tab 38b. An input line 34 is embedded. Accordingly, the liquid crystal control element 26 can be supplied with an input voltage or an input current from a power supply unit (not shown) provided in the fixing unit 24 via these tabs 38a and 38b.

  FIG. 3B shows a state in which the end portion of the FPC 36 on which the liquid crystal control element 26 is provided is folded according to the direction of the arrow shown in FIG. Note that for convenience of illustration, the belt-like portion 37 is twisted 90 degrees toward the front side in the vicinity of portion A in the drawing. A third tab 38c and a fourth tab 38d are provided at the right end of the FPC 36 (see also FIG. 3A), and these sandwich the liquid crystal element 11 from both sides. Although not shown, a total of 14 output lines 35 are embedded in the FPC 36 from the vicinity of the liquid crystal control element 26 toward the third tab 38c and / or the fourth tab 38d. Yes. Therefore, the liquid crystal element 11 can be supplied with an applied voltage or an applied current from the liquid crystal control element 26 through these tabs 38c and 38d.

  FIG. 3C shows a situation where the belt-like portion 37 is folded into a quadrangle. FIG. 3D shows a state in which the folded FPC 36 is inserted into the housing 21. The FPC 36 is fixed to the inner wall of the housing 21 by an appropriate method such as an adhesive. It should be noted that the housing 21 is schematically shown in a simple box shape in FIG. 3D and is different from the actual shape.

  As apparent from FIGS. 3A to 3D, the input line 34 embedded in the FPC 36 extends from the liquid crystal control element 26 along the inner wall of the housing 21, and partly branches at the first surface 32 of the housing 21. It goes out to the outer surface side and is connected to the input line combined wire 31a, and the remaining input line 34 further extends along the inner wall of the housing 21 and goes out to the outer surface side of the housing 21 by the second surface 33 of the housing 21 and remains. Are connected to the input line combined wire 31b. As can be seen from FIG. 3D, since the liquid crystal element 11 is provided so as to bridge between the opposing long sides of the housing 21, the long side portion of the structurally weak housing 21 is reinforced, and the housing 21 Can be suppressed.

  FIG. 3E shows a situation when the movable part 25 is assembled. As the elastic wire 31, only the elastic wire provided on the first surface 32 is illustrated. The first and second tabs 38a and 38b are further bent 90 degrees in the same direction from the outer side of the housing 21 shown in FIG. 3D and fixed to the outer surface of the housing 21 (second tabs). The illustration of 38b is omitted.). As a result, the pads 39 provided on the first and second tabs 38a and 38b are positioned along the outer surface of the housing 21, and the input line / wire 31b can be connected.

  As described above, according to the present embodiment, since the liquid crystal control element 26 is installed in the movable portion 25, the number of lines connecting the movable portion 25 and the fixed portion 24 depends on the number of input lines of the liquid crystal control element 26. It is decided. In general, since the number of input lines of the liquid crystal control element is smaller than that of the output lines, the number of elastic wires can be reduced accordingly. For this reason, the deterioration of the operating characteristics of the movable part due to the restraint of the elastic wire can be prevented, and obstacles to miniaturization and weight reduction can be removed.

DESCRIPTION OF SYMBOLS 1 Optical pick-up 2 Optical recording medium 3,4 Semiconductor laser 11 Liquid crystal element 12 1/4 wavelength plate 13 Wavelength compatible element 14 Objective lens 21 Housing 22 Tilt coil 23 Tracking coil 24 Fixed part 25 Movable part 26 Liquid crystal control element 31 Elastic wire 31a Main elastic wire 31b Input line combined wire 32 First surface 33 Second surface 34 Input line 35 Output line 36 FPC
37 Band-shaped portions 38a to 38d First to fourth tabs 39 Pad C Optical axis of laser light

Claims (3)

A fixed portion including a laser beam emitting device for emitting a light beam;
An objective lens that focuses the light beam on an optical recording medium; a liquid crystal element that is positioned between the laser light emitting device and the objective lens; and that adjusts a wavefront phase of the light beam; and a voltage applied to the liquid crystal element Or a movable part including a liquid crystal control element for controlling an applied current;
Have
The movable part is movable with respect to the fixed part in a direction substantially perpendicular to an optical axis of the light beam passing through the objective lens,
The optical pickup, wherein the liquid crystal control element is electrically connected to the fixed part by an input line and electrically connected to the liquid crystal element by an output line, and the number of the input lines is smaller than the number of the output lines. The movable part is supported with respect to the fixed part by an elastic wire, and a part of the elastic wire is an input line combined wire that also serves as the input line,
The movable part has a housing that houses the objective lens, the liquid crystal element, and the liquid crystal control element,
The input line combined wire is located at least one on each outer surface side of the first and second surfaces facing each other of the housing,
The input line extends from the liquid crystal control element along the inner wall of the housing, partly branches at the first surface of the housing, and exits to the outer surface side of the housing, to part of the input line combined wire. Connected, the remaining input line further extends along the inner wall of the housing, exits on the outer surface side of the housing on the second surface of the housing, and is connected to the remaining input line combined wire, The optical pickup according to claim 1.   The liquid crystal control element is located in the vicinity of the inner wall of the housing, and the center of gravity of the liquid crystal element is located on the side opposite to the center of gravity of the liquid crystal control element with respect to the centroid of the movable part. The optical pickup according to claim 2, wherein the center of gravity of the movable part and the centroid coincide with each other in a plane including a moving direction of the part.

Images