JP2005316065A - Light condensing optical element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a light condensing optical element by which miniaturization and low price of an optical apparatus using a light condensing optical system can be attained. <P>SOLUTION: In the light condensing optical element 10 which has a plurality of optical operating faces including at least an incident face 16 and an emission face 19 and which condenses incident light from the incident face 16 and emits the light from the emission face 19, at least one of the optical operating faces is formed of a rotationally asymmetric curved surface and a center of gravity 25 is on an optical axis of emission light 15 or on a prolonged line of the optical axis of the emission light 15 or near the prolonged line. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a condensing optical element, for example, a condensing optical element used for an optical pickup provided in an optical disc drive apparatus for optically recording / reproducing information.

  Optical recording / reproducing devices are being used for CDs that use lasers with a wavelength of 780 nm, DVDs that use lasers with a wavelength of 660 nm, and discs that use lasers with a wavelength of 405 nm. ing. As for NA, the density has been increased by increasing CD from 0.45 to DVD to 0.6.

  As described above, when the wavelength is shortened and the NA is increased, the tolerance for various optical characteristics is reduced, and the demand for an objective lens that is a condensing optical element for condensing laser light on a recording medium is severe. Become. For example, although a semiconductor laser is used as the laser, the occurrence of chromatic aberration due to the wavelength variation becomes unacceptable, and in order to cancel the chromatic aberration, the objective lens needs to be configured with a plurality of positive and negative lenses.

  However, if the objective lens is composed of a plurality of lenses, the assemblability deteriorates, such as the need to align their optical axes. Moreover, since the number of parts increases, it tends to be disadvantageous in terms of cost.

  In order to avoid or reduce such an inconvenience, an objective lens made up of a so-called free-form surface lens having a rotationally asymmetric curved surface as shown in FIG. There is known an optical pickup in which the number of sheets can be reduced by using 101 even when the wavelength is short and the NA is high (see, for example, Patent Document 1). In FIG. 11, in order to align the direction with the other figures, the figure shown in Patent Document 1 is rotated 180 degrees so that the recording medium 102 faces up.

The objective lens 101 refracts incident light 103 on a surface 105, then sequentially reflects the light on a surface 106 and a surface 107, and further refracts the light on a surface 108, thereby condensing the emitted light 104 on the recording medium 102. The surfaces 105 to 108 are rotationally asymmetric curved surfaces.
Japanese Patent Laid-Open No. 2002-245331

  In the objective lens 101 disclosed in Patent Document 1, the center of gravity of the objective lens 101 is in the vicinity of the center 109, which is different from the optical axis of the emitted light 104, unlike a general coaxial lens.

  On the other hand, the objective lens 101 is mounted in a mechanism called a lens actuator in order to follow the surface shake of the recording medium 102 and the shake of the recording track. In this lens actuator, the objective lens 101 is fixed to a holder, and the holder is used for recording. In many cases, it is elastically supported by a wire spring or the like so as to be movable in the surface runout direction of the medium or in the direction crossing the track.

  However, in an elastically supported holder system, resonance that causes the holder to rotate may be a problem. This resonance is a movement that rotates around the axis passing through the center of gravity. Strictly speaking, it is influenced by the support point, but since the eigenvalue of the wire spring used for the support is small, the influence of the support point is small, and the center of rotation is closer to the center of gravity than the support point.

  For this reason, if the distance between the emitted light of the objective lens and the center of gravity is large, the movement of the emitted light becomes large by the lever principle, and the influence of resonance becomes larger. Therefore, in order to reduce the influence of this resonance, it is desirable to align the center of gravity and the optical axis of the emitted light. In the lens actuator, the objective lens is placed at the center of the holder as viewed from the direction of the emitted light (Z direction). In many cases, the center of gravity of the holder system coincides with the center of the emitted light. In order to prevent resonance, it is desirable to make the driving point coincide with the center of gravity, and therefore, a magnetic circuit for generating a driving force is often arranged symmetrically around the light emitted from the objective lens.

  However, in the objective lens 101 disclosed in Patent Document 1, the center of gravity of the objective lens 101 is not located on the optical axis of the emitted light 104 and its extension line. For this reason, in order to set the position of the emitted light 104 to the center of gravity of the holder system, a balancer for balancing the mass is required in addition to the objective lens 101. This increases the number of parts and increases the size of the apparatus. There is concern about inviting.

  As a variation of the lens actuator, there is a lens actuator that is held at the end in the track direction and the Y direction of the recording medium instead of the center of the holder. However, even in this case, in the X direction (the direction crossing the track), since it is common to align the positions of the emitted light and the center of gravity, the mass in addition to the objective lens 101 is the same as in the case of the central arrangement. There is a concern that a balancer for balancing will be required, resulting in an increase in cost due to an increase in the number of parts and an increase in the size of the apparatus.

  Accordingly, an object of the present invention made in view of the above circumstances is to provide a condensing optical element appropriately configured so that an optical device using a condensing optical system can be reduced in size and cost. .

The invention according to claim 1, which achieves the above object, has a plurality of optical action surfaces including at least an entrance surface and an exit surface, and condenses the light incident from the entrance surface by condensing from the exit surface. In the optical element,
At least one of the optical action surfaces is a rotationally asymmetric curved surface, and the center of gravity is on the optical axis of the emitted light or an extension of the optical axis of the emitted light.

The invention according to claim 2 has a plurality of optical action surfaces including at least an entrance surface and an exit surface, and a condensing optical element that collects and emits light incident from the entrance surface from the exit surface,
At least one of the optical action surfaces is a rotationally asymmetric curved surface, and the center of gravity is in a circle having a radius of 1 mm centered on the optical axis of the emitted light or an extension line of the optical axis of the emitted light. .

The invention according to claim 3 is the condensing optical element according to claim 1 or 2,
It has the convex part for mass balance in areas other than the said optical action surface, It is characterized by the above-mentioned.

The invention according to claim 4 is the condensing optical element according to any one of claims 1 to 3,
A fixing portion to another member is provided asymmetrically with respect to the optical axis of the emitted light.

The invention according to claim 5 is the condensing optical element according to any one of claims 1 to 4,
The optical action surface has at least one reflection surface in addition to the incident surface and the exit surface.

The invention according to claim 6 is the condensing optical element according to claim 5,
The reflective surface is a rotationally asymmetric curved surface.

The invention according to claim 7 is the condensing optical element according to claim 5 or 6,
The optical path from the entrance surface to the exit surface is crossed.

The invention according to claim 8 is the condensing optical element according to any one of claims 5 to 7,
When divided into two regions by a plane passing through the optical axis of the emitted light, the incident surface and the at least one reflecting surface are in different regions.

The invention according to claim 9 is the condensing optical element according to any one of claims 1 to 8,
The incident surface is a surface having no power.

  According to the present invention, in a condensing optical element using a so-called free-form surface lens, the center of gravity is on the optical axis of the emitted light, on the extended line of the optical axis of the emitted light, or in the vicinity thereof, so that the condensing optical system Therefore, it is possible to obtain a condensing optical element that can reduce the size and the price of an optical device that uses the optical device.

  Hereinafter, embodiments of a condensing optical element according to the present invention will be described with reference to the drawings.

(First embodiment)
FIGS. 1 to 8 show a first embodiment of the present invention. FIGS. 1 and 2 are perspective views of an optical pickup including a condensing optical element, FIG. 3 is a top view, and FIG. FIG. 5 is an exploded perspective view, FIGS. 6 and 7 are perspective views of an objective lens that is a condensing optical element, and FIG. 8 is a top view of the holder.

  1 to 5, an objective lens 10, which is a condensing optical element, focus coils 1a to 1d, and tracking coils 2a and 2b are bonded to a holder 30 made of a synthetic resin such as a liquid crystal polymer.

  The objective lens 10 is a so-called free-form surface lens. As shown in FIG. 4, light enters the objective lens 10 from the optical path 11, and the incident light is refracted by the incident surface 16, travels along the optical path 12, and then is reflected by the reflecting surface 17. The light travels along the optical path 13, further reflects on the reflecting surface 18, travels along the optical path 14, and finally refracts on the exit surface 19, travels along the optical path 15, and forms a spot on the recording medium 20. In addition, the optical paths 11-15 have shown the center optical axis, respectively. Further, for the exit surface 19, since the optical axis of the optical path 14 is perpendicularly incident and is not refracted, the optical path 14 and the optical path 15 are shown in a straight line in FIG. Since it is incident, it is refracted.

  Here, the optical action surfaces of the incident surface 16, the reflecting surface 17, the reflecting surface 18, and the exit surface 19 are curved surfaces that are not rotationally symmetric and are free-form surfaces. The optical axes that are the centers of the optical paths 11 to 15 are in the same ZX plane, and the incident surface 16, the reflecting surfaces 17 and 18, and the exit surface 19 are curved surfaces that are not rotationally symmetric, but ZX that passes through the optical axis. Regarding the plane, it has a plane-symmetric shape.

  As shown in FIGS. 4, 6, and 7, a fixing portion 23 is provided at the end of the objective lens 10 in the X-direction so as to protrude greatly. The fixing portion 23 serves as a balancer, and thereby the center of gravity 25 of the objective lens 10 is positioned on the optical axis extension line of the optical path 15 of the emitted light as shown in FIGS.

  The objective lens 10 is attached to the holder 30 with an adhesive at the fixing portion 23. The holder 30 is provided with receiving portions 36a to 36c as shown in FIG. 8 for receiving the surfaces 21a to 21c parallel to the XY plane of the fixing portion 23 of the objective lens 10, and these receiving portions 36a to 36c. The objective lens 10 is fixed to the holder 30, and the position in the Z direction is also determined. Further, the position of the objective lens 10 in the XY plane with respect to the holder 30 is determined by the ends 22 a to 22 c of the fixing portion 23 facing the walls 35 a to 35 c of the holder 30. Further, the position of the objective lens 10 in the X direction is positioned by applying the end 22b of the fixed portion 23 to the wall 35b of the holder 30, and the position in the Y direction is determined between the wall 35a and the wall 35c of the holder 30. The distance is slightly larger than the distance between the end 22a and the end 22c of the objective lens 10 and is positioned by fitting the ends 22a and 22c of the objective lens 10 between the walls 35a and 35c of the holder 30. .

  Further, as shown in FIG. 4, in order to prevent the objective lens 10 from vibrating like a cantilever at the fixing portion 23, the X + end of the objective lens 10 is also fixed to the holder 30 by the adhesive 38. Yes.

  As shown in FIGS. 3 and 4, the holder 30 is provided with a cover 40 on the side where the fixing portion 23 of the objective lens 10 is not formed. Similar to the objective lens 10, the cover 40 is positioned by the receiving portions 36 a and 36 c and the walls 35 a, 35 c and 35 d and is fixed to the holder 30. Further, on the side where the cover 40 is not provided, a portion other than the exit surface 19 of the objective lens 10 is a rough surface. This prevents unnecessary light from entering the objective lens 10 from the Z + side and emission of unnecessary light from the objective lens 10 to the Z + side. That is, the reflecting surface 17 on the cover 40 side is an optical action surface and cannot be a rough surface, so the cover 40 is provided to prevent unnecessary light from entering and exiting.

  On the bottom of the Z-end of the holder 30 to which the objective lens 10 is fixed, as shown in FIGS. 4 and 8, an aperture 37 that serves as an aperture limit for limiting the incident light 11 is provided.

  The focus coils 1a to 1d are bonded so as to be sandwiched between the protrusions 31a and 31b provided on the holder 30 and the protrusions 34a to 34d, and the rigidity after bonding is increased. The tracking coils 2a and 2b are bonded to the surfaces of the focus coils 1a to 1d so that their central holes 4a and 4b enter the protrusions 31a and 31b of the holder 30, respectively. For this reason, the dimension in the Z direction of the protrusions 31a and 31b is slightly smaller than the dimensions of the holes 4a and 4b, and the tracking coils 2a and 2b are positioned by the protrusions 31a and 31b.

  The holder 30 is provided with protrusions 32a and 32b at both ends in the X direction. The protrusions 32a and 32b are provided with holes 33a to 33c and 33d to 33f, into which six wire springs 6a to 6f made of beryllium copper are inserted and bonded. The cross-sectional shape of the wire springs 6a to 6f is a circle, and six springs having the same dimensions. Substrate 5a, 5b is also bonded to holder 30, and six wire springs 6a-6f, focus coils 1a-1d and tracking coils 2a, 2b are soldered to these substrates 5a, 5b. That is, both ends of the tracking coils 2a and 2b connected in series are connected to the two wire springs, and both ends of the focus coils 1a and 1c connected in series are connected to the other two wire springs. The two ends of the focus coils 1b and 1d connected in series are connected to the two wire springs, and the focus coils are divided into two sets, unlike the case of the known four-wire support.

  The ends of the six wire springs 6a to 6f in the Y + direction are fixed to the spring pocket 7, and are further inserted into the holes 43a to 43f of the substrate 41 and soldered. Concave portions 8a and 8b are formed in the spring spring 7, and the portions are filled with silicone gel to damp the wire springs 6a to 6f. Although not shown, holes corresponding to the bottoms (Y + direction) of the recesses 8a and 8b are formed with holes through which the wire springs 6a to 6f are passed in the same manner as the holder 30 and the substrate 41. The substrate 41 is positioned by fitting the hole 42 to the circular convex portion 9 provided in the spring spring 7.

  As described above, the holder 30 is supported by the spring spacer 7 by the six wire springs 6a to 6f so as to be movable in a direction substantially perpendicular to the recording medium 20 (Z direction) and in a direction crossing the track of the recording medium 20 (X direction). Will be. The substrate 41 is connected to an external electric circuit, whereby the focus coils 1a to 1d and the tracking coils 2a and 2b are connected to the external electric circuit through six wire springs 6a to 6f.

  Here, as described above, the center of gravity 25 of the objective lens 10 coincides with the optical axis of the optical path 15 of the emitted light on the XY plane, but the center of gravity of the entire movable part fixed to the holder 30 is also XY. It coincides with the position of the center of gravity 25 in the plane. For this reason, in the Y direction, the shape of each component is symmetric with respect to the ZX plane, except for the substrates 5a and 5b. The substrates 5a and 5b are balanced in mass by providing the holder 30 with lightening or the like. In the X direction, the objective lens 10 is not symmetrical with respect to the YZ plane, but the centroid 25 is located on the optical axis extension line of the optical path 15 of the emitted light as already described. Furthermore, the cover 40 exists only on the X + side, and the mass on the X + side is correspondingly increased. However, the holder 30 is provided with a thickness reduction or the like so as to achieve a mass balance. The thickness of the X direction both ends 28a and 28b of the holder 30 to which the objective lens 10 is attached is different in one of the balances of the cover 40. Other parts are symmetrical with respect to the YZ plane.

  The spring 7 is fixed to an iron base 44. The base 44 is formed with raised portions 45c and 45d, and the raised portions 45c and 45d position the X direction and the Y direction of the spring 7 so that the Z direction of the spring 7 extends in the bottom surface of the base 44 (XY direction). Positioning).

  The base 44 is also formed with rising portions 45a and 45b having the same shape as the rising portions 45c and 45d, and magnets 47a to 47d are bonded to the rising portions 45a to 45d. Further, the base 44 is formed with rising portions 46a to 46d at portions facing the magnets 47a to 47d. The base 44 is manufactured by press working, but the rising portions 46a to 46d are not bent with the plate thickness at the time of press working, but are processed to be longer than before being bent by being crushed slightly. By processing in this way, the distance between the rising portions 46a and 46c and the distance between the rising portions 46b and 46d are narrow, but the height (Z dimension) of the rising portions 46a to 46d can be secured. For this reason, the thickness (Y dimension) of the rising parts 46a to 46d is smaller than the thickness (Y dimension) of the rising parts 45a to 45d bent with the plate thickness.

  The magnets 47a to 47d have the polarity shown in FIG. 3, for example, and the direction of the magnetic field is reversed on the opposite sides 3a and 3b (see FIG. 5) of the tracking coil 2a as indicated by arrows. However, since the directions of the currents are reversed in the sides 3a and 3b, the direction of the force received from the magnetic field is the same. As a result, the tracking coil 2a generates a driving force in the tracking direction (X direction). Moreover, since the driving force is generated by the two sides 3a and 3b of the tracking coil 2a, the force can be increased and the driving force can be increased with respect to the magnitude of the current flowing through the coil. The same applies to the sides 3c and 3d of the tracking coil 2b. Although the direction of the magnetic field extending to the focus coils 1a and 1b is also reversed, since the coils are independent, it is only necessary to pass a current so that a driving force is generated in the same direction, and there is no particular problem. The same applies to the focus coils 1c and 1d.

  The magnetic circuit forming portions of the focus coils 1a to 1d, the tracking coils 2a and 2b, the magnets 47a to 47d, and the base 44 are symmetric with respect to the YZ plane and the ZX plane passing through the optical axis of the optical path 15 of the emitted light, and the focus direction The driving point in the tracking direction coincides with the optical axis of the emitted light, that is, the center of gravity 25 in the XY plane.

  As described above, the focus coils 1a to 1d are configured such that the focus coils 1a and 1c are connected in series and the focus coils 1b and 1d are connected in series so that current can flow independently. Therefore, when the current is applied so that the focus coils 1a and 1c and the focus coils 1b and 1d generate the same driving force, the holder 30 moves in response to the driving force in the focus direction (Z direction). Further, if the driving force generated by the focus coils 1a and 1c is different from the driving force generated by the focus coils 1b and 1d, the larger driving force moves greatly, and the holder 30 rotates around the Y axis. . By utilizing this, it is possible to make a movement for adjusting the tilt of the objective lens 10. Therefore, the driving force generated by the focus coils 1a and 1c and the focus coils 1b and 1d may be reversed in some cases.

  The drive mechanism of the objective lens 10 configured as described above is referred to as a lens actuator. Although not shown, the lens actuator is fixed to an optical pickup body including an optical system including a laser diode, a photodetector, a prism, and the like as a light source.

  Next, the operation of the present embodiment configured as described above will be described.

  Laser light emitted from a laser diode of an optical system (not shown) passes through several prisms and the like, passes through an optical path 11, and unnecessary light is removed by a squeezing 37 formed on the holder 30, so that it is applied to the objective lens 10. Incident light is emitted from the optical path 15 to form a spot on the recording medium 20. The reflected light from the recording medium 20 passes through the objective lens 10 again, returns to the optical system (not shown), passes through several prisms, etc., and is received by the photodetector to detect the focus error, tracking error, and recording signal. Done. Further, the inclination of the objective lens 10 around the Y axis with respect to the recording medium 20 is also detected.

  When a focus error is detected, the holder 30 is driven in a direction perpendicular to the recording medium 20 by passing a current through the focus coils 1a to 1d. When a tracking error is detected, current is passed through the tracking coils 2a and 2b to drive the holder 30 in a direction crossing the track of the recording medium 20, or in the radial direction when the recording medium 20 is a circular disk. It will be. When accessing different tracks, the holder 30 together with the main body including the lens actuator is driven in a direction crossing the track of the recording medium 20 by a driving means (not shown). As described above, the holder 30 and the objective lens 10 fixed thereto are subjected to focus control, tracking control, and access control.

  Further, when the light emitted from the objective lens 10 to the optical path 15 is not perpendicular to the recording medium 20 due to the bending of the recording medium 20, and the inclination about the Y axis is detected as a result, as described above, By adjusting the currents flowing through the coils 1a and 1c and the focus coils 1b and 1d, the holder 30 is rotated around the Y axis so that the optical path 15 is perpendicular to the recording medium 20. Here, the inclination adjustment is only in the direction around the Y axis, but when the recording medium 20 is a circular disk, there is no problem because the deflection around the Y axis in the direction from the center side toward the outer periphery side is the main.

  Here, as described above, since the center of gravity 25 of the entire movable part fixed on the holder 30 and the drive point coincide with each other when viewed from the direction of the optical path 15, the holder 30 is used during the above control. Unnecessary resonance that rotates is not generated. Further, even if a slight deviation occurs due to component tolerances or assembly errors and a small resonance occurs, the optical axis of the optical path 15 and the center of gravity 25 coincide with each other, and the holder 30 rotates about that, Resonance prevents the emitted light from moving greatly, and the influence of resonance can be reduced.

  In this embodiment, since the center of gravity 25 of the objective lens 10 is positioned on the optical axis extension line of the emitted light, the center of gravity of the entire movable part fixed on the holder 30 can be obtained by using this objective lens 10. It can be easily matched with the optical axis extension line of the emitted light. Therefore, it is not necessary to enlarge the holder 30 or provide a separate balancer to achieve balance, and the optical pickup can be reduced in size and price.

  In the present embodiment, the center of gravity 25 of the objective lens 10 does not necessarily have to be completely coincident with the optical axis extension line of the emitted light, and there may be a slight deviation. For example, in FIG. 3, even if the center of gravity 25 of the objective lens 10 is positioned within a circle 24 with a radius of 1 mm centered on the optical axis of the optical path 15, the center of gravity 25 is not within that range. Since balancing is much easier and the balancer can be made smaller, the apparatus can be sufficiently reduced in size and price. If the center of gravity 25 of the objective lens 10 deviates from the circle 24 having a radius of 1 mm centered on the optical axis of the optical path 15, it becomes difficult to balance and the balancer becomes large, making it impossible to reduce the size and cost of the apparatus. .

  Similarly, it is needless to say that the center of gravity and the driving point of the entire movable part fixed on the holder 30 need only be close to a level where the resonance can be suppressed to a level that is not problematic in use, even if they are not completely matched. .

(Second Embodiment)
FIG. 9 is a cross-sectional view of an objective lens according to the second embodiment of the present invention.

  The objective lens 50 is also a so-called free-form surface lens as in the first embodiment. Light enters the objective lens 50 from the optical path 51, and the incident light is refracted by the incident surface 57, travels along the optical path 52, is then reflected by the reflective surface 58, travels along the optical path 53, and Reflected by the reflecting surface 59, travels along the optical path 54, further reflects by the reflecting surface 60, travels along the optical path 55, and finally refracts at the exit surface 61, travels along the optical path 56, and is spotted on the recording medium 20. Form. The optical paths 51 to 56 each indicate the central optical axis.

  Here, the optical action surfaces of the entrance surface 57, the reflection surface 58, the reflection surface 59, the reflection surface 60, and the exit surface 61 are curved surfaces that are not rotationally symmetric and are free-form surfaces. The optical axes that are the centers of the optical paths 51 to 56 are in the same ZX plane, and the entrance surface 57, the reflection surfaces 58 to 60, and the exit surface 61 are curved surfaces that are not rotationally symmetric, but ZX that passes through the optical axis. Regarding the plane, it has a plane-symmetric shape. Further, the center of gravity 63 of the objective lens 50 is on the optical axis extension line 62 of the emitted light.

  The objective lens 50 is held by a holder, for example, as in the first embodiment, and is mounted on a lens actuator. In this case, similarly to the first embodiment, the holder is formed with a support portion having a shape that follows the outer shape of the objective lens 50, and the objective lens 50 is held by the support portion. Other configurations and operations are substantially the same as those in the first embodiment.

  In the present embodiment, the optical paths 51 to 56 are in the ZX plane, but the optical path 53 and the optical path 55 are crossed in the objective lens 50. Here, when the optical paths in the same plane are not crossed, the light incident on the end of the objective lens is emitted from the other end while repeating reflection or the like, but the optical path as in the present embodiment If 53 and the optical path 55 are crossed, the exit location can be near the center of the X direction instead of the end of the objective lens 50 in the X direction, so that the center of gravity 63 of the objective lens 50 is on the center line of the optical path 56. That is, it can be easily matched with the optical axis extension line 62 of the emitted light. As a result, it is not necessary to provide a convex portion for balancing the mass, and even when a convex portion for balancing is provided, a small convex portion can be used, so that the objective lens 50 can be reduced in size and weight. Can be planned.

  Further, when the objective lens 50 is divided into two regions on the YZ plane passing through the optical axis of the optical path 56, the incident surface 57 is in the X + direction region, and the reflecting surface 59 is in the X− direction region without the incident surface 57. From this point, the center of gravity 63 of the objective lens 50 can be easily aligned with the optical axis extension line 62 of the emitted light. As a result, it is not necessary to provide a convex portion for balancing the mass, and even if a convex portion for balancing is provided, a small convex portion can be used, so the objective lens 50 can be reduced in size and weight. I can plan.

  Therefore, if this objective lens 50 is used for an optical pickup or the like, the apparatus can be reduced in size and price.

(Third embodiment)
FIG. 10 is a cross-sectional view of an objective lens according to the third embodiment of the present invention.

  The objective lens 70 is also a so-called free-form surface lens as in the first embodiment. Light enters the objective lens 70 from the optical path 71 to the incident surface 75. Here, the incident surface 75 is a flat surface and has no power. Further, the incident light 71 enters the incident surface 75 perpendicularly and travels on the same optical path 71 as it is without being refracted.

  In the objective lens 70, the light traveling along the optical path 71 is then reflected by the reflecting surface 76, travels along the optical path 72, further reflected by the reflecting surface 77, travels along the optical path 73, and finally exits 78. Are refracted and travel along the optical path 74 to form spots on the recording medium 20. In addition, the optical paths 71-74 have shown the center optical axis, respectively.

  Here, the reflecting surfaces 76 and 77 and the exit surface 78 excluding the entrance surface 75 of the objective lens 70 are curved surfaces that are not rotationally symmetric and are free-form surfaces. The optical axes that are the centers of the optical paths 71 to 74 are in the same ZX plane, and the reflection surfaces 76 and 77 and the exit surface 78 are curved surfaces that are not rotationally symmetric. It has a symmetrical shape. Further, the center of gravity 80 of the objective lens 70 is on the optical axis extension line 79 of the emitted light.

  The objective lens 70 is held by a holder and mounted on a lens actuator, for example, as in the first embodiment. In this case, similarly to the first embodiment, the holder is formed with a support portion having a shape that follows the outer shape of the objective lens 70, and the objective lens 70 is held by the support portion. Other configurations and operations are substantially the same as those in the first embodiment.

  Also in the present embodiment, the optical path 71 and the optical path 73 are crossed within the objective lens 70 as in the second embodiment. Further, when the objective lens 70 is divided into two regions on the YZ plane passing through the optical axis of the emitted light, the incident surface 75 is in the region in the X + direction, and the reflecting surface 76 is in the region in the X− direction without the incident surface 75. Therefore, the center of gravity 80 of the objective lens 70 can be easily matched with the optical axis extension line 79 of the emitted light. As a result, it is not necessary to provide a convex portion for balancing the mass, and even when a convex portion for balancing is provided, a small convex portion can be used, so the objective lens 70 can be reduced in size and weight. Can be planned.

  Further, since the incident surface 75 is a surface having no power, even if the position of the incident surface 75 is moved in the direction of the arrow 81, the optical characteristics are not affected. Therefore, the center of gravity 80 of the objective lens 70 can be easily aligned with the optical axis extension line 79 of the emitted light by adjusting the position of the reflecting surface 75 to achieve mass balance.

  Therefore, if this objective lens 70 is used for an optical pickup or the like, the apparatus can be reduced in size and price.

  It should be noted that the present invention is not limited to the above-described embodiment, and many variations or modifications can be made. For example, the objective lens that is a condensing optical element may have various shapes other than those described above, and may have a shape that is not plane-symmetric, for example. Moreover, the number of reflective surfaces can also be set arbitrarily. Furthermore, the curved optical surface of the objective lens is not limited to a rotationally asymmetric curved surface, and may include a rotationally symmetric curved surface. Furthermore, a diffraction grating may be formed on the optical action surface.

  In the above embodiment, the optical axes of all the optical paths in the objective lens are in the same plane, but they may not be in the same plane. In this case, the crossing of the optical paths shown in the second embodiment and the third embodiment may not cross the optical axes but may cross the light beams.

  Further, in order to make the center of gravity of the objective lens coincide with or substantially coincide with the exit optical axis or its extension line, various convex portions may be provided in addition to the optical action surface, and the convex portions are the first embodiment. In this way, it is not necessary to serve as a fixing part to the holder.

  Moreover, the condensing optical element according to the present invention can be used not only for an optical pickup but also for various optical devices.

It is a perspective view of an optical pick-up provided with the condensing optical element which concerns on 1st Embodiment of this invention. Similarly, it is a perspective view of an optical pickup. Similarly, it is a top view of an optical pickup. It is AA sectional drawing of FIG. It is a disassembled perspective view of an optical pick-up. It is a perspective view of the objective lens which is a condensing optical element. Similarly, it is a perspective view of an objective lens. It is a top view of a holder. It is sectional drawing of the objective lens which concerns on 2nd Embodiment of this invention. Similarly, it is sectional drawing of the objective lens which concerns on 3rd Embodiment. It is a figure which shows the conventional objective lens.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Objective lens 11-15 Optical path 16 Incident surface 17, 18 Reflective surface 19 Ejection surface 20 Recording medium 25 Centroid 50 Objective lens 51-56 Optical path 57 Incident surface 58-60 Reflective surface 61 Ejection surface 62 Optical axis extension line 63 Centroid 70 Objective Lenses 71 to 74 Optical path 75 Incident surface 76, 77 Reflecting surface 78 Ejecting surface 79 Optical axis extension line 80 Center of gravity

Claims (9)

In a condensing optical element having a plurality of optical action surfaces including at least an entrance surface and an exit surface, and condensing and exiting light incident from the entrance surface from the exit surface,
A condensing optical element characterized in that at least one of the optical action surfaces is a rotationally asymmetric curved surface, and the center of gravity is on the optical axis of the emitted light or an extension of the optical axis of the emitted light. In a condensing optical element having a plurality of optical action surfaces including at least an entrance surface and an exit surface, and condensing and exiting light incident from the entrance surface from the exit surface,
At least one of the optical action surfaces is a rotationally asymmetric curved surface, and the center of gravity is in a circle having a radius of 1 mm centered on the optical axis of the emitted light or an extension of the optical axis of the emitted light. element.   3. The condensing optical element according to claim 1, further comprising a convex portion for balancing the mass in a region other than the optical action surface.   The condensing optical element according to any one of claims 1 to 3, wherein a fixing portion to another member is provided asymmetrically with respect to the optical axis of the emitted light.   5. The condensing optical element according to claim 1, wherein the optical working surface has at least one reflecting surface in addition to the incident surface and the exit surface.   6. The condensing optical element according to claim 5, wherein the reflecting surface is a rotationally asymmetric curved surface.   The condensing optical element according to claim 5, wherein optical paths from the incident surface to the exit surface intersect each other.   When divided into two regions on a plane passing through the optical axis of the emitted light, the incident surface and the at least one reflecting surface are in different regions. The condensing optical element as described.   The condensing optical element according to claim 1, wherein the incident surface is a surface having no power.

Images