JPH0334133A - Optical pickup - Google Patents

Abstract

PURPOSE:To reduce the generation of track offset with simple constitution by making the central axis of a beam of light from a rotary movable mirror conform to the optical axis of an entire optical system at the incident side focusing position at the intermediate position of the stroke of a movable optical system. CONSTITUTION:A relay lens system 9 is arranged between the rotary movable mirror 4 and the movable optical system. It can be seen that the relay lens system 9 is comprised of a positive lens system A and a positive lens system B, and it is set as an aforcal system by conforming their focusing positions, and the beam of light made incident as parallel beams is emitted as the parallel beams similarly. Meanwhile, as a synthesizing system, an image on the reflecting plane of the rotary movable mirror 4 is image-formed at the incident side focusing position of the objective lens 6. Thereby, no deviation of the position of the beam of light made incident on the objective lens is generated even when the movable mirror 4 is turned to perform tracking at that position. Also, an aperture diaphragm 10 which limits the beam of light is arranged at the beam of light incident side focusing position of the objective lens.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to the improvement of optical pickups for optical discs, etc., particularly linear separation type optical pickups. In order to achieve this, it is known that a tracking means is provided in a fixed optical system (for example, 1985 Japan Society of Precision Machinery Spring Conference Academic Lecture Kanawa Bunshu No. 146). Its configuration is shown in FIG.

In FIG. 2, the light beam from the light source 1 passes through the beam splitter 2 and the collimator lens 3, and becomes a parallel light beam.
A spot is focused on the disk 7 while the imaging position is controlled by the rotatable ta4, the reflector 15, and the objective lens 6. The reflected light follows the same path and enters the photodetector 8 via the beam splitter 2. Here, a light source 1, a beam splitter 2, a collimator 3, and a photodetector 8 are fixed on the main body of the apparatus, and a reflecting mirror 5 and an objective lens 6 are attached to a portion near the center and the outer periphery of the disk 7 during reproduction. It is a movable part that moves in the radial direction between nearby parts, and is rotatably movable.
4 is located between these, and the rotation angle is controlled for tracking.

In this type of pickup, the amount of tracking is determined by the deflection angle of the light beam incident on the objective lens. The amount of track offset when this pre-angle is kept constant is proportional to the amount of deviation of the light beam on the illumination plane on the light beam incidence side of the objective lens. As shown in FIG. 3a, the deviation of the luminous flux caused by the rotation of the rotatable movable 1IIt4 increases with the distance from the rotary reflecting mirror, and becomes particularly large at the end of the stroke. for example,
Rotation movement when the movable part is at the outer circumferential position! ! The distance between 4 and the reflector 5 is 30 m, the stroke length of the movable part is 30 m,
When the distance between the reflecting mirror 5 and the objective lens 6 is 19nn, and the focal length of the objective lens is 4-, the distance from the rotary movable 1!4 to the illumination plane on the light beam incidence side of the objective lens is 45 to 75nw.
Therefore, the amount of deviation of the light beam on the illumination plane on the light beam incidence side of the objective lens 6 is per 101-rack (0,016 aa),
It extends to 0.18m at the outer circumference position and 0.3+lll+ at the inner circumference position.

(Problems to be solved by this invention) As mentioned above,
In the method of simply separating a rotary movable mirror whose center of rotation is near the mirror surface to a fixed optical system side, a large track offset occurs particularly when the movable optical system moves away from the rotary movable mirror.

Further, a method of using another movable means such as a parallel plane plate rotary actuator for this offset correction requires a control means for the same, and the configuration becomes complicated.

The present invention aims to obtain an optical pickup in which the occurrence of track offset is so small that there is virtually no problem with a simple configuration.

(Means for Solving the Problem) In the optical pickup of the present invention, the central axis of the light beam from the rotary movable mirror and the optical axis of the entire optical system are at the focal point on the incident side of the objective lens at the midpoint of the stroke of the movable optical system. This is done so that they match in position.

in particular.

1. A fixed optical system that has a light source, a beam splitter, and a photodetector and a movable mirror that rotates once and is fixed on the main body, and a movable optical system that has an objective lens and moves linearly in the radial direction of the disk-shaped information recording medium. In an optical pickup consisting of, the intersection position of the central axis of the light beam deflected by the rotating movable mirror or its extension and the optical axis of the entire optical system, and the incident side of the objective lens when the movable optical system is at the mid-stroke point. A relay lens whose focal position is in a conjugate relationship is provided between the rotatable movable mirror and the movable optical system. Here, the radial direction does not have a strict meaning, but means the direction passing through the track from the inner circumference to the outer circumference or vice versa.

2. A fixed optical system fixed on the main body, which includes a light source, a beam splitter, a photodetector, and a rotating movable mirror.

In an optical pickup consisting of a movable optical system that has an objective lens and moves linearly in the radial direction of a disk-shaped information recording medium, the intersection point between the central axis of the light beam deflected by a rotating movable mirror and the optical axis of the entire optical system. The rotational center position of the rotatably movable mirror is set so that the position of the focal point on the incident side of the objective lens coincides with the position of the focal point on the incident side when the movable optical system is at the midpoint of the stroke.

This can be achieved by

(Example) An example of the optical pickup of the present invention is shown below, and a second example is shown below.
Components that are the same as in the figures are designated by the same reference numerals.

The optical system shown in FIG. 1 is the optical system shown in FIG. 2 in which a relay lens system 9 is disposed between the rotary movable #I4 and the movable optical system.

As shown in Fig. 4, this relay lens system can be seen as consisting of a positive lens system A and a positive lens system B, and by matching their focal positions, it becomes an afocal system, and a parallel light beam The light beam that enters as a parallel light beam also exits as a parallel light beam. On the other hand, as a synthetic thread, an image of the reflective surface of the rotatable movable t44 is formed at the focal position on the incident side of the objective lens when the movable optical system is at the midpoint of the stroke.

In this way, at this position, even if the rotatable movable tIt4 is rotated for tracking, the position of the light beam incident on the objective lens 6 will not shift, and no track offset will occur.

Of course, if it deviates from this intermediate point, as shown in FIG. 3, the light beam incident position will shift and an offset will occur. However, in a pickup similar to the conventional example described above, even at the stroke end of the movable optical system, the amount of movement from the position where the deviation of the incident light beam is zero remains at ±15 mm, so the amount of deviation of the incident light beam that occurs is ±0. It falls within the range of .06am,
The overall size can be made extremely small.

In addition, in this embodiment, it is desirable to install an aperture diaphragm 10 that limits the light beam at the focal position on the light beam incidence side of the objective lens.In this position, the light beam incident on the objective lens is also reflected from the information recording medium. The light beam that returns through the objective lens also passes through the same position on the aperture stop surface, and no vignetting occurs in the returned light beam.

Furthermore, the positive lens system B in this embodiment is arranged so that the negative lens system precedes it in the traveling direction of the light beam, thereby shortening the overall length of the lens. Furthermore, this increases the distance between the principal points, making it possible to increase the distance from the relay lens system to the focal point on the light beam incidence side of the objective lens.

In the embodiment shown in FIG. 5, the light beam emitted from the light source is made to enter the rotary movable mirror and the relay lens as diverging light. In this case, the relay lens also functions as a collimator, and the optical system can be made smaller.

If it is desired to increase the coupling efficiency of the light beam emitted from the light source, a suitable coupling lens may be inserted between the light source and the rotary movable mirror.

Furthermore, when a semiconductor laser is used as a light source and the light beam emitted from the light source is elliptical, the relay lens can have the function of shaping the cross-sectional shape of the light beam by using an appropriate cylindrical lens.

In short, this invention requires that the point where the center of the light beam deflected by the one-rotation movable mirror intersects the optical axis of the entire optical system is constant, and that this point and the illumination plane on the incident side of the objective lens have a conjugate relationship. The configuration of the relay lens also changes as the above-mentioned intersection moves depending on the rotation center position of the rotatable mirror.

Any suitable relay lens can be used, such as not only positive and positive systems but also negative and positive systems.

Furthermore, it is clear that the light beam may be deflected around the focal position on the incident side of the objective lens without using the relay lens. in particular.

As shown in Fig. 6, when the optical distance from the objective lens's light beam incidence measurement point plane to the rotary movable mirror when the movable optical system is at the midpoint of its stroke, the light reflected from the rotary movable mirror is The rotary movable mirror may be rotated about a point located at a distance of two distances in the traveling direction of the light beam as the center of rotation. Such a rotatable mirror can be realized using a swing arm type or two non-parallel link types. Namely.

In the embodiment shown in FIG. 7a, the one-turn movable mirror 4 is
It is fixed at the top of the rotating shaft 12 or 62Q, and is rotated and opened by a coil 13 provided at its tip. In the figure, 14 is a magnet, and 15 is a yoke. In the embodiment shown in the figure, the rotary movable mirror 4 is fixed on a mirror holder 16 held by a non-parallel link 17, and is driven by a magnetod and a coil as in the previous embodiment.

(Effects of the Invention) As described above, in the optical pickup of the present invention, when the movable optical system is at the midpoint of the stroke, the central axis of the light beam from the rotary movable mirror and the optical axis of the entire optical system are aligned with the objective lens. By satisfying the extremely simple condition of matching at the incident-side focal position, it was possible to reduce the track offset to a level that causes no practical problems in the entire reproduction range. The means for achieving this can be as simple as adopting a simple relay lens or selecting the center of rotation of a rotatable mirror, making it possible to obtain an extremely practical optical pickup.

[Brief explanation of drawings]

Fig. 1 is an optical configuration diagram showing one embodiment of the optical pickup of the present invention, Fig. 2 is an optical configuration diagram of a conventional optical pickup, Fig. 3 is an explanatory diagram of the deflection state of the light beam, and Fig. 4 is a relay diagram. FIG. 5 is an explanatory diagram of the lens system, FIG. 5 is an optical configuration diagram of the second embodiment, FIG. 6 is a conceptual diagram of the configuration of the third embodiment without using a relay lens, and FIG. 7 is a plan view showing the configuration. l; Light source 2: Beam splitter 3: Collimator lens 4: Rotating movable mirror 5: Reflection I! 6: Objective lens 7: Disk 8; Photodetector 9: Relay lens system 10: Aperture stop 11 Nilever 12:
Rotating shaft 13: Coil 14: Magnet 15: Yoke 16: Mirror holder 17: Non-parallel link diagram

Claims (1)

[Claims] 1. A fixed optical system that includes a light source, a beam splitter, a photodetector, and a rotatable mirror and is fixed on the main body, and an objective lens that extends linearly in the radial direction of the disk-shaped information recording medium. In an optical pickup consisting of a moving movable optical system, the intersection position of the central axis of the light beam deflected by the rotating movable mirror or its extension and the optical axis of the entire optical system, and the objective when the movable optical system is at the mid-stroke point. Optical pickup 2, characterized in that a relay lens whose focal position on the incident side of the lens is in a conjugate relationship is provided between the rotatable movable mirror and the movable optical system. , an optical pickup 3 according to claim 1, characterized in that the optical pickup is provided at a focal position on the light beam incident side of the objective lens. 4. An optical pickup 4 according to claim 1, characterized in that the light beam exiting the fixed optical system is a diverging light. Consists of a fixed optical system that has a light source, a beam splitter, a photodetector, and a rotating movable mirror and is fixed on the main body, and a movable optical system that has an objective lens and moves linearly in the radial direction of the disk-shaped information recording medium. In an optical pickup, the intersection point between the central axis of the light beam deflected by the rotating movable mirror and the optical axis of the entire optical system coincides with the focal position on the incident side of the objective lens when the movable optical system is at the midpoint of the stroke. An optical pickup characterized in that the rotation center position of the rotary movable mirror is set as follows.