JPH04319539A - Optical information recording/reproducing device - Google Patents

Abstract

PURPOSE:To reduce the track offset by providing a converging means for a reflected light before a photodetecting means, and positioning the photodetecting means behind a focus. CONSTITUTION:A light beam emitted from a laser diode 1 is converted to parallel rays by a collimator lens 2, and thereafter, made incident on a galvanomirror 3 and deflected in the vertical direction, and made incident on a beam splitter 4. The light beam which transmits through the beam splitter 4 is made incident on a start mirror 5 and reflected in the direction of an objective lens 6. The light beam is converged by transmitting through the objective lens 6, and radiates a light spot onto an optical disk 7. The light beam reflected by the optical disk 7 transmits through the objective lens 6 and is reflected by the mirror 5. The light beam which is made incident on the beam splitter 4 is deflected in the vertical direction, and made incident on a focusing lens 8. The light beam forms the focus, and thereafter, is made incident on a 2-split PD 9.

Description

[Detailed description of the invention]

0001

[Field of Industrial Application] The present invention relates to an optical information recording/reproducing device that optically records, erases, reproduces, etc., using a laser beam, and is particularly characterized by tracking error detection. It is something.

0002

2. Description of the Related Art Information recording and reproducing apparatuses for optical discs and the like that optically record and reproduce information by irradiating a light spot onto a recording medium such as an optical disc have been widely used in recent years. In this information recording and reproducing device, tracking is performed by making a light spot follow an information track of a recording medium.
It is necessary for proper recording and reproduction of information. and,
For proper tracking, it is necessary to optically detect the positional deviation between the spot and the track (tracking error signal).

[0003] Generally, in optical discs that record information in addition to reproducing information, uneven grooves for tracking are formed in advance on the optical disc surface, and the reflected light from the grooves is formed in advance on the optical disc surface. A method is used in which a tracking error signal is detected by a detector based on changes in the diffraction pattern. The light intensity distribution in the far field of reflected light is
The push-pull method detects using a split photodetector.
It belongs to this.

[0004] Further, as a method for performing tracking based on the detection of the tracking error signal, there is a method in which a light spot is moved to a predetermined track by moving an objective lens that converges a light beam on a recording medium; There is a method of moving a light spot to a predetermined track by driving a galvanometer mirror that deflects a light beam toward an objective lens and tilting the optical axis of the light beam incident on the objective lens.

[0005]

However, as shown in FIG. 7, among the above-mentioned conventional methods, there are two methods in which a tracking error signal is detected by the push-pull method and tracking is performed by moving the objective lens 30. Since the light beam incident on the divided PD (photodetector) 31 is shifted (arrow) due to the movement of the objective lens 30 (arrow), there is a problem in that an offset occurs in the tracking error signal. In other words, the light beam emitted from the laser diode 32 is collimated by the collimator lens 33, passes through the beam splitter 34, and is transmitted to the mirror 3.
5 and is converged by the objective lens 30 to irradiate the optical disc 36 with a light spot. Then, the reflected light reflected by the optical disk 36 passes through the objective lens 30 again, is reflected by the mirror 35 and the beam splitter 34, and is guided to the PD 31.However, the objective lens 30 moves in the direction of the arrow. As a result, the reflected light flux also moves while reaching the PD 31 and shifts on the PD 31, resulting in a tracking error due to the difference in light intensity between the two light receiving areas.
This results in an offset in the signal.

[0006] The above-mentioned disadvantages also apply to the configuration of an optical system using a galvanometer mirror 37 as a reflecting member for guiding a light beam to an objective lens 30 as shown in FIG. In other words, this optical system tilts the optical axis of the light beam incident on the objective lens 30 while driving the galvanometer mirror 37 in the direction of the arrow. The light also moves while reaching the PD 31 and is shifted on the PD 31.

The problems encountered in the optical system provided with the galvano mirror 37 become even more problematic in the so-called separation optical system. That is, in recent years, in order to perform high-speed seeking, there has been a method of separating the optical head into a movable part and a fixed part, and providing a galvanometer mirror or the like on the fixed part to perform tracking. For example, Japanese Unexamined Patent Publication No. 2-76135 discloses the configuration of a separating optical system as shown in FIG. this is,
A light beam from an optical member 39 such as a light source provided in a fixed optical system 38 is transmitted to a deflecting prism 40 and then to a galvano mirror.
37 and guided to a movable optical system 41, further reflected by a deflection prism 42 provided in the movable optical system 41, transmitted through the objective lens 30, and a light spot is irradiated onto the optical disk 36. There is. The reflected light is received by the detector of the optical system 39 via the objective lens 30, the deflection prism 42, the galvanometer mirror 37, and the deflection prism 40. In such a separation optical system, the fixed optical system 3
The longer the distance between the optical system 8 and the movable optical system 41, the greater the degree of shift and the greater the amount of track offset.

Among the separation optical systems, a swing arm type separation optical system as shown in FIG.
7. A light emitting unit such as a collimator lens 33 and a light receiving unit such as a beam splitter 34, PDs 31, 43, and 44 are provided in a fixed optical system, and the optical axis of the objective lens 30 and the fixed optical system and the objective lens 30 is Optical members such as the parallelogram prism 45 for connecting the
This is the system provided in the system. In this swing arm type, the optical path length at the inner and outer circumferences of the optical disk is constant, but the drive of the galvanometer mirror 37 causes a track offset depending on the amount of drive.

Therefore, as a method for reducing this track offset, a separation optical system having a galvano mirror as shown in FIG. 11 has been proposed. Fixed optics include
Laser diode 32, collimator lens 33, beam splitter 46, 47, various PD48, galvanometer mirror
37, a rotating parallel plate 51, etc. are provided, and the movable optical system is provided with a mirror 49, an objective lens 22, a focus actuator 50, etc. And laser diode
The light beam emitted from the door 32 is separated into two, the amount of shift caused by driving the galvanometer mirror 37 is detected by one of the light beams, and the parallel plate 51 is rotated based on this detected amount. The track offset is canceled by correcting the optical axis deviation. However, with such a configuration, the number of parts increases, the configuration becomes complicated, and there are problems in that detection of shift amount, adjustment for canceling track offset, and control are difficult.

The present invention is proposed to solve the above-mentioned problems, and in order to perform high-speed seek, a separate optical system is used.
It is an object of the present invention to provide an information recording/reproducing apparatus which reduces the track offset of a push-pull signal in a tracking method using a galvanometer mirror and is capable of detecting a good tracking error signal.

[0011]

[Means for Solving the Problems] In order to achieve the above object, the present invention provides a deflection means for deflecting a light beam in order to cause a light spot to follow a predetermined track on an optical disk; an optical path dividing means disposed between an objective lens for converging a light spot on an optical disk; a converging means for converging reflected light from the optical disk split by the optical path dividing means; and convergence by the converging means. The optical information recording and reproducing device is characterized in that it is provided with a light receiving means disposed behind the focal point of the light and detecting the difference in the light quantity distribution in the direction perpendicular to the track to generate a tracking error signal.

0012

[Operation] In this way, the convergence means for the reflected light is provided in front of the light receiving means, and the light receiving means is positioned behind the focal point. This reduces the amount of movement of the light beam on the light receiving means and utilizes the fact that the intensity distribution of the light beam shifts in the opposite direction with respect to the direction of movement, thereby reducing changes in the difference signal of the two-split PD. Therefore, track offset can be reduced.

[0013]

Embodiments Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 shows an outline of an optical head used in the information recording/reproducing apparatus of the present invention. The light beam emitted from the laser diode 1 is made into parallel light by a collimator lens 2 provided in the emission direction, and then
The parallel light enters the galvanometer mirror 3 provided in the traveling direction, is deflected in the right angle direction (to the left in the paper), and enters the beam splitter 4 provided in the reflection direction. The light beam transmitted through the beam splitter 4 enters a rising mirror 5 provided in the direction of travel and is reflected by an objective lens 6.
reflected in the direction. The light beam is converged by passing through the objective lens 6 and illuminates the optical disk 7 with a light spot. In addition, mirror 5, objective lens 6
The part having . is the movable optical system.

The light beam reflected by the optical disk 7 passes through the objective lens 6 again and is reflected by the mirror 5 in the direction of the beam splitter 4, and the light beam incident on the beam splitter 4 is directed toward the beam splitter 4. The light beam is separated from the optical path of the light beam, is deflected in the right angle direction (downward in the plane of the paper), and enters the condenser lens 8 provided in the reflection direction. The light beam incident on the condenser lens 8
After focusing, the beam enters the two-part PD 9. The two-part PD 9 is a light-receiving element for detecting a tracking error signal, and the detection is performed by taking the difference in the amount of light between two light-receiving areas (push-pull method).

In order to perform tracking using the optical head configured as described above, the galvanomirror 3 is driven in the direction of the arrow based on the tracking error signal detected by the two-part PD 9, and the beam enters the objective lens 6. This is done by tilting the optical axis of the light beam. However, when driving the galvano mirror 3 as described above, the two-divided PD
The light beam incident on 9 is shifted. A method for reducing the track offset caused by this shift will be described below.

FIG. 2 shows the distribution of the amount of light beam incident on the objective lens 6 when the galvanomirror is driven. The upper row shows a state in which the optical axis of the light beam is tilted by driving the galvano mirror, and the lower row shows the light amount distribution in each state. The intensity distribution of the light beam emitted from the laser diode is generally a Gaussian beam, and the intensity decreases as it moves away from the center. Therefore, when the optical axis of the light beam is not tilted as shown in FIG. 2A, when a cross section is taken along the broken line, the intensity peak will be at the center as shown in the lower part. Also, the optical axis of the light beam is on one side (towards the left in the paper) as shown in Figure 2B.
, the intensity peak will be incident on the objective lens 6 with a shift to the left in the plane of the paper with respect to the center of the objective lens 6, as shown in the lower row. Furthermore, if the optical axis of the light beam is tilted to the other side (to the right in the paper) as shown in Figure 2C, the intensity peak will be in the opposite direction with respect to the center of the objective lens, as shown in the bottom row. The incident is shifted to the right of a certain page.

Therefore, the center of the intensity distribution of the reflected light beam after passing through the objective lens 6 and being irradiated onto the optical disk also shifts depending on the inclination of the optical axis. Therefore,
After the reflected light enters the beam splitter, it is deflected and enters the two-part PD 9 as shown in FIG. 3. That is, when the optical axis of the light beam is not tilted, the intensity distribution of the light incident on the two-part PD 9 has an intensity peak on the center line, as shown in the lower part of FIG. 3A. Furthermore, when the optical axis of the light beam is tilted to one side as shown in FIG. 3B and enters the two-part PD 9, the intensity peak shifts to one side (toward the right in the paper) as shown in the lower row. Furthermore, when the optical axis of the light beam is incident on the two-part PD 9 with its optical axis tilted to the other side as shown in FIG. 3C, the intensity peak shifts to the other side (toward the left in the paper) as shown in the lower row. In this way, on the two-divided PD 9, the moving direction of the light beam and the moving direction of the peak in the intensity distribution are the same,
The amount of track offset of the push-pull signal becomes large.

However, in the present invention, before the two-part PD9 (
A condensing lens 8 is provided between the beam splitter 4 and the two-part PD 9, and the light beam deflected by the beam splitter 4 is once focused, and then enters the two-part PD 9. It looks like this. FIG. 4 shows the state of the light beam incident in this manner. In other words, when the optical axis of the light beam is not tilted, the intensity distribution of the light incident on the two-part PD 9 has an intensity peak on the center line, as shown in the lower part of FIG. 4A.
Ku is coming. Further, when the optical axis of the light beam is tilted to one side as shown in FIG. 4B, the intensity peak is moved by the condenser lens 8 in the opposite direction to the tilt and enters the two-divided PD 9. Furthermore, even if the optical axis of the light beam is tilted in the other direction as shown in FIG. . Furthermore, as the optical axis tilts, the light incident on the condenser lens 8 moves laterally, and the light that passes through the end of the condenser lens 8 is strongly refracted, so that the amount of movement on the two-part PD 9 also becomes smaller.

As described above, in the conventional example, the moving direction of the light beam on the two-divided PD 9 is the same as the moving direction of the peak in the intensity distribution, but in the present invention, the intensity in the intensity distribution is adjusted by the condenser lens 8. The direction of movement of the peak is in the opposite direction, and the amount of movement is also small. Therefore, the two-part PD
This means that the track offset caused by the shift of the light beam incident on the optical system 9 can be reduced.

FIG. 5 shows a second embodiment of the present invention, which is an embodiment applied to a magneto-optical pickup of a separation optical system. Note that FIG. 5B is an X-arrow view of the movable optical system in FIG. 5A. The same reference numerals are given to parts corresponding to those in the above embodiment. The light beam emitted from the laser diode 1 is directed to a collimator lens 2 provided in the emission direction.
The parallel light is made into parallel light by passing through the light, and enters the galvanometer mirror 3 provided in the traveling direction of the parallel light. The galvanometer mirror 3 has its drive axis Z in a direction of approximately 45° in the plane of the paper, and is configured to swing its optical axis in a direction perpendicular to the plane of the paper by driving. The light beam deflected by the galvanometer mirror 3 in the right angle direction (to the left in the drawing) enters and passes through the beam splitter 4, and then enters the beam shaping prism 10 provided in the traveling direction. As a result, the elliptical intensity distribution of the light beam is shaped into a substantially perfect circle. The light beam transmitted through the beam shaping prism 10 is incident on a rising mirror 5 of a movable optical system provided in the traveling direction and is reflected in the direction of an objective lens 6. The light beam is converged by passing through the objective lens 6 and illuminates the optical disk 7 with a light spot.

The light beam reflected by the optical disk 7 passes through the objective lens 6 again, is reflected by the mirror 5, passes through the beam shaping prism 10 of the fixed optical system, and then enters the beam shaping prism 4. The light enters and is reflected in the right angle direction (upward in the drawing), passes through the λ/2 plate 11 (or the λ/4 plate), and then enters the condenser lens 8 provided in the traveling direction. The light beam transmitted through the condenser lens 8 enters a PBS (functioning as an analyzer) 12 provided in the traveling direction. P.B.
The light beam transmitted through the S12 is received by the PD 9a provided in front of the focal point, and the light beam reflected by the PBS 12 is further reflected by the total reflection surface of the PBS 12 and then received by the PD 9a provided behind the focal point. The light is received by the PD 9b. Note that the light receiving element 13 provided near the beam shaping prism 4 is a PD for APC.

The PDs 9a and 9b are adjusted so that the sizes of the light beams incident thereon are approximately the same. Furthermore, these PDs 9a and 9b are each divided into six parts as shown in FIG. A signal is obtained, and the reproduction signal of the magneto-optical disk is transmitted to both PDs 9a and 9b.
It is detected by calculating the difference in the total amount of light incident on the two. In addition, 1 to 12 of both PD9a and 9b are as follows:
Shows the light receiving area. In other words, Fo=[(1+4)+(3+6)-(2+5)]-[(
7 + 10) + (9 + 12) - (8 + 11)] Tr = (7 + 8 + 9) - (10 + 11 + 12)
RF=(1+2 +3 +4 +5 +6) −(7
+8 +9 +10+11+12+)

In this embodiment configured as above, when the galvanometer mirror 3 is driven, the PD 9a,
The light beam incident on 9b is shifted. but,
Since the PD9b receives the light after it has been converged by the condenser lens, the movement of the light beam can be reduced, and the movement direction of the peak of the intensity distribution can be set in the opposite direction. Track offset can be reduced by detecting the track error signal.

[0024] In the case of a separation optical system, the optical path length becomes long and also changes at the inner and outer peripheries of the optical disc. Therefore, conventionally, when detecting a tracking error signal, the longer the optical path length, the greater the amount of track offset.However, according to the present invention, the longer the optical path length, the more the shift amount of the center of the intensity distribution of the light beam increases. Since it becomes larger, the correction effect also becomes larger and the track offset amount becomes smaller.

[0025]

As described above, according to the present invention, by transmitting the light beam through the condensing lens before the light beam is incident on the PD, the light beam can be adjusted in the direction of movement of the light beam on the PD. The moving direction of the intensity peak of the intensity distribution of the beam can be set in the opposite direction, and even in a tracking method using a galvanomirror in which a large track offset of a push-pull signal occurs, the amount of track offset that occurs can be reduced. Can be done. This effect is particularly large in optical heads that require high-speed access because the track offset reduction effect is greater when the optical path length is longer, such as in a separation optical system. In order to obtain these effects, there is no need to particularly complicate the configuration, and there is no need to perform electrical correction.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram of an optical head according to a first embodiment of the present invention.

FIG. 2 is an explanatory diagram showing changes in the intensity distribution of a light beam.

FIG. 3 is an explanatory diagram showing changes in the intensity distribution of a light beam received by a two-part PD.

FIG. 4 is an explanatory diagram showing a state in which track offset is reduced.

FIG. 5 is a schematic diagram of an optical head (for magneto-optical use) according to a second embodiment of the present invention.

FIG. 6 is an explanatory diagram showing a light receiving area of a PD.

FIG. 7 is a schematic diagram of an optical head according to a conventional example.

FIG. 8 is a schematic diagram of an optical head according to a conventional example.

FIG. 9 is a schematic diagram of an optical head (separation optical system) according to a conventional example.

FIG. 10 is a schematic diagram of an optical head (separation optical system) according to a conventional example.

FIG. 11 is a schematic diagram of an optical head (separation optical system) according to a conventional example.

[Explanation of symbols]

1 Laser diode 2 Collimator lens 3 Galvano mirror 4 Beam splitter 5 Mirror 6 Objective lens 7 Optical disc 8 Condensing lens 9 2-split PD

Claims (1)

[Claims] Claim 1: A deflection means for deflecting a light beam to make the light spot follow a predetermined track on an optical disk; and an objective lens for converging the light spot on the optical disk; a converging means for converging the reflected light from the optical disk split by the optical path dividing means; and a converging means for converging the reflected light from the optical disk divided by the optical path dividing means; What is claimed is: 1. An optical information recording/reproducing apparatus comprising: a light receiving means for detecting a difference in light quantity distribution and generating a tracking error signal.