JPH04315825A - Optical head - Google Patents

Abstract

PURPOSE:To obtain an optical head capable of easy adjustment and high speed scanning by combining a galvanomirror type scanning means and a push-pull type recording area detection means without complicating a construction. CONSTITUTION:First and second relay lens 5 and 6 are arranged between an objective lens 2 and a rotary mirror 3 of a galvanomirror type scanning means 30 so that the focus on the side of a light source 7 of the objective lens 2 can coincide with the focus on the side of a recording medium 1 of the first relay lens 5, that the focus on the rear side of the first relay lens 5 can coincide with the focus on the front side of the second relay lens 6 and that the focus on the rear side of the second relay lens 6 can coincide with the rotating center of the rotary mirror 3. A reflection beam from the recording area forming surface of a recording medium 1 is returned to the rotary mirror 3 through the same light path at the time of irradiation, reflected by a beam splitter 9 and made incident on a light receiving element (splitting light receiving surfaces 10a and 10b) of a push-pull type recording area detection means 30.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical head for an optical recording/reproducing apparatus that records or reproduces information by following the relative position of a beam spot and a recording medium.

0002

2. Description of the Related Art Various types of recording media have been proposed for recording and reproducing information using light, such as a read-only type, a write-once type, and a rewritable type. These recording media have strip-shaped recording areas (tracks), and in order to record and reproduce information, it is necessary to align the beam spot with a predetermined recording area with high precision (tracking). It is. For this reason, the optical head of the optical reproducing device is provided with beam scanning means for scanning the recording area forming surface of the recording medium with a beam spot and recording area detection means for detecting a predetermined recording area. There is.

Conventionally, a galvano mirror system has been known as a beam scanning means for an optical head. This galvano mirror method places a rotating mirror (galvano mirror) between the light source of the optical head and the objective lens, and by rotating the mirror, the beam spot is moved in a direction perpendicular to the scanning direction (track extension direction). This enables faster scanning than methods that move the objective lens itself.

Further, a push-pull (PP) method is known as a method for detecting a predetermined recording area. In this push-pull method, the reflected beam from the recording area is received by a light-receiving element whose light-receiving surface is divided in a direction perpendicular to the scanning direction, and the difference between the signals corresponding to the light intensity on the light-receiving surface from each of the divided light-receiving surfaces is calculated. This method detects the recording area by In other words, if the center of the beam spot and the center of the recording area do not match, the light intensity distribution of the reflected beam becomes asymmetrical and a signal difference occurs, and by detecting this signal difference, a tracking error signal can be obtained.

[0005]

However, in the conventional optical head, there are the following problems when employing a galvano-mirror type beam scanning means or a push-pull type recording area detection means.

The push-pull recording area detection means described above has the advantage of being simple in configuration and easy to adjust, but the center of the reflected beam from the recording area is polarized in a direction perpendicular to the dividing line of the light receiving element. As a result, asymmetry occurs in the light amount distribution on the light receiving surface, and an offset occurs in the tracking error signal corresponding to the difference in light amount between the two divided light receiving surfaces.

However, in a general galvano-mirror type scanning means, the center of the reflected beam from the recording area forming surface is shifted by rotating the mirror. For this reason, an optical head cannot be constructed by simply combining a galvano-mirror type scanning means and a pull-pull type recording area detection means.

Here, as a configuration for avoiding deviation of the beam center in the galvano-mirror type scanning means,
Conventionally, an arrangement of an optical system as shown in FIG. 3 is known. In FIG. 3, a recording medium 101 is held horizontally above an objective lens (focal length f0) 102;
A rotating mirror 103 is arranged below the mirror 02. This rotating mirror 103 is rotatable in the direction in the plane of the paper with reference to a position forming an angle of 45° with respect to the horizontal direction (the direction of incidence of the beam center 104).

[0009] Also, a recording medium 101, an objective lens 102
The positional relationship between the rotating mirror 103 and the objective lens 102 is
The focal point on the recording medium 101 side (hereinafter referred to as the front focal point) and the recording area forming surface 101a of the recording medium 101 (the upper surface of the recording medium 101 in the case of FIG. 3) match, and the focal point on the light source side of the objective lens 102 (hereinafter, the light source side focal point will be referred to as the rear focal point) and the rotation center 103a of the rotating mirror 103 are arranged so that they coincide with each other.

In such a configuration, the rotating mirror 10
3 is at the reference position, rotating mirror 103 from the horizontal direction
The center 104 of the incident beam is reflected by the rotation center 103a of the rotating mirror 103, travels straight on the optical axis of the objective lens 102, and is focused on the recording area forming surface 101a. Then, the reflected beam reflected by the recording area forming surface 101a returns to the rotating mirror 103 through the optical axis again, and the beam center is reflected by the rotation center 103a and proceeds in the horizontal direction.

On the other hand, when the rotating mirror 103 rotates as shown by the dotted line in the figure, the rotating mirror 10
The angle of incidence of the beam relative to 3 will change. However, in FIG. 3, since the rear focus of the objective lens 102 and the rotation center 103a of the rotating mirror 103 match,
The beam center 104a (in the figure, the optical path of the beam center when the mirror 103 rotates is shown by a dashed line at one end) is reflected by the rotating mirror 103 at an angle with respect to the optical axis of the objective lens 102, and then the beam center 104a is reflected by the rotating mirror 103 at an angle to the optical axis of the objective lens 102. The beam is emitted from the beam in a direction parallel to the optical axis. That is, even if the rotating mirror 103 rotates, the beam center 104a is always aligned with the recording area forming surface 10.
1a, the reflected beam from the recording area forming surface 101a returns to the rotating mirror 103 through the same optical path as during irradiation, and is directed horizontally in the same way as when the rotating mirror 103 is at the reference position. reflected. Therefore, Figure 3
With this configuration, theoretically, it is possible to prevent the beam center of the galvano-mirror type scanning means from shifting.

However, as a practical matter, the focal length f0 of the objective lens 102 used in the optical head is usually about 4 mm, and the objective lens 102, rotating mirror 103, and mirror actuator are arranged in a positional relationship as shown in FIG. (not shown) is not possible due to space considerations.

In addition to the configuration shown in FIG. 3, there is a method disclosed in Japanese Patent Laid-Open No. 177648/1983 as a method for avoiding deviation of the beam center. In this method, an actuator for the objective lens is provided in addition to the actuator for the rotating mirror, and the two actuators are interlocked so that the optical axis always passes through the rear focal point of the objective lens.

In this method, deviation of the beam center is avoided by moving the objective lens following the rotation of the rotating mirror, but the configuration for interlocking the two actuators is complicated, Manufacturing costs will also increase.

The present invention has been made in view of the above points, and provides an optical head that can realize high-speed scanning with a simple configuration and that does not cause recording area detection errors due to deviation of the beam center. The purpose is to

[0016]

[Means for Solving the Problems] An optical head of the present invention includes a light source and an objective lens, and includes a beam scanning means for scanning a recording area forming surface of an optical recording medium with a beam spot, and a beam scanning means for scanning a recording area forming surface of an optical recording medium with a beam spot; and recording area detection means for detecting the recording area of the recording area.
The beam scanning means includes a rotating mirror that moves the beam spot in a direction perpendicular to the scanning direction, and the recording area detection means includes a rotating mirror that moves the beam spot in a direction perpendicular to the scanning direction. a push-pull type recording area detection means for detecting the recording area based on a signal, and at least one pair of relay lenses between the objective lens of the beam scanning means and the rotating mirror, and the recording medium side The first relay lens and the second relay lens on the light source side are arranged so as to satisfy the following conditions a to c. a. The light source side focal point of the objective lens matches the recording medium side focal position of the first relay lens. b. A focus of the first relay lens on the light source side and a focus of the second relay lens on the recording medium side match. c. The light source side focal point of the second relay lens and the rotation center of the rotary mirror match.

[0017]

[Operation] The operation of the present invention will be explained with reference to FIG. 2, which shows the basic structure of the scanning means in the optical head according to the present invention. In the figure, below the recording medium 1 held horizontally, there are
In order from the recording medium 1 side, objective lens 2 with focal length f0
, a first relay lens 5 with a focal length f1 and a focal length f1
2 second relay lenses 6 are arranged so that their optical axes are perpendicular to the recording area forming surface 1a. Further, the lower part of the second relay lens 6 is provided with a diameter of 45 mm with respect to the horizontal direction (the direction of incidence of the beam from the light source (not shown) on the right side of the page).
A rotating mirror 103 is provided that can rotate in the direction in the plane of the paper with reference to a position forming an angle of .degree.

The positional relationship of the above-mentioned components is as follows: the front focus of the objective lens 2 and the recording area forming surface 1a, the back focus of the objective lens 2 and the front focus of the first relay lens 5, and the rear focus of the first relay lens 5. a side focus and a front focus of the second relay lens 6;
The positional relationship is such that the rear focal point of the second relay lens 6 and the rotation center 3a of the rotary mirror 3 coincide with each other.

In other words, f0 from the recording area forming surface 1a
Objective lens 2 is placed in a separated position, and from objective lens 2 (
f0 + f1) The first relay lens 5 is placed at a separated position.
, a second relay lens 6 is located at a position separated by (f1 + f2) from the first relay lens 5, and a second relay lens 6 is located at a position separated from the first relay lens 5 by f1 + f2.
2. Each component is arranged so that the rotation center 3a of the rotating mirror 3 is located at a separated position, and the front focus A1 of the objective lens 2 and the front focus A1 of the second relay lens 6 (the rear side of the first relay lens 5) focus) A2 forms a conjugate relationship,
And the back focus B1 of the objective lens 2 (the front focus of the first relay lens 5) and the back focus B2 of the second relay lens 6
(rotation center 3a of rotating mirror 3) form a conjugate relationship.

Next, the optical path at the beam center in the galvano-mirror type scanning means shown in FIG. 2 will be explained. In the figure, the optical path of the beam center 4 when the rotating mirror 3 is at the reference position is shown by a solid line, and the optical path of the beam center 4a when the rotating mirror 3 is rotated is shown by a chain line.

First, when the rotating mirror 3 is at the reference position, the center 4 of the beam incident horizontally on the rotating mirror 3 is reflected in the vertical direction by the rotation center 3a of the rotating mirror 3, and the beam is reflected in the first direction. The light then travels straight on the optical axes of the second relay lenses 5 and 6 and the objective lens 2, and is perpendicularly incident on the recording area forming surface 1a. The center 4 of the beam reflected by the recording area forming surface 1a passes on the optical axis again and reaches the rotation center 3 of the rotating mirror 3.
It returns to point a and is reflected in the horizontal direction.

On the other hand, when the rotating mirror 3 rotates as shown by the dotted line in the figure, the following occurs. The beam enters the rotating mirror 3 from the horizontal direction, as in the case where the rotating mirror 3 is at the reference position. At this time, the angle of incidence of the beam becomes smaller as the rotating mirror 3 rotates to the right in the drawing, and the beam center 4a is tilted with respect to the optical axis and reflected to the right.

However, in the configuration of the present invention, the rear focal point of the second relay lens 6 coincides with the rotation center 3a of the rotating mirror 3, and the beam center 4a passes through the rear focal point B2 of the second relay lens 6. The light then enters the second relay lens 6. Therefore, after the beam center 4a passes through the second relay lens 6, it travels parallel to the optical axis and enters the first relay lens 5. The beam center 4a that is perpendicularly incident on the first relay lens 5 is bent by the first relay lens 5 so as to pass through the front focal point of the first relay lens. As mentioned above, the front focus of the first relay lens 5 matches the back focus of the objective lens 2 (point B1
), the beam center 4a enters the objective lens 2 through the rear focal point of the objective lens 2, and is emitted from the objective lens 2 in a direction parallel to the optical axis. The beam center 4a emitted from the objective lens 2 is perpendicularly incident on a point C that is offset to the left in the drawing from the optical axis of the recording area forming surface 1a. The center 4a of the beam reflected at this point C returns to the rotation center 3a of the rotating mirror 3 through exactly the same optical path as during irradiation. The beam center 4a is
It is reflected by the rotation center 3a of the rotating mirror 3, and is reflected in the horizontal direction in the same way as when the rotating mirror 3 is at the reference position.

As mentioned above, in the present invention, the rotating mirror 3
Even when the beam is rotated from the reference position, the beam center 4a always passes through the rear focus of the objective lens 2 and is incident perpendicularly to the recording area forming surface 1a. The center 4a of the reflected beam returns to the rotating mirror 3 through the same optical path as when it was incident, and is reflected in the same direction as when the rotating mirror 3 is at the reference position. Therefore,
In the present invention, the center 4a of the reflected beam from the recording area forming surface 1a does not deviate due to the rotation of the rotating mirror 3.

Now, the distance from the recording medium 1 of the beam scanning means to the rotating mirror 3 in the present invention is (2f0 +2f1 +2f2) as shown in FIG. 2, which is shorter than the conventional example shown in FIG. (2f1 +2f2) corresponding to the focal length of the first and second relay lenses 5, 6
), the distance is longer. That is, in the present invention, by appropriately selecting the focal length of the relay lens provided between the objective lens 2 and the rotating mirror 3, the distance between the recording medium 1 and the rotating mirror 3 can be adjusted without causing deviation of the beam center. can be set to a desired length, and sufficient space is secured for arranging the rotating mirror 3 and an actuator (not shown).

Note that in FIG. 2, a pair of relay lenses 5 and 6 are arranged between the objective lens 2 and the rotating mirror 3;
It goes without saying that the number of relay lenses may be increased as necessary. However, since the optical system of the galvano-mirror type scanning means is usually configured with a parallel system, if a single relay lens is provided between the objective lens 2 and the rotating mirror 3, the beam incident on the relay lens will not reach the objective lens. Since the beam is focused between the relay lenses and not on the recording area forming surface, at least one pair of relay lenses is arranged to focus the beam between the two relay lenses, and the beam is focused between the focus point and the front side of the objective lens. It is necessary to focus on the conjugate relationship.

[0027]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is an optical path diagram of essential parts showing the structure of an optical head according to an embodiment of the present invention. In this embodiment, a case will be explained in which a read-only optical disk on which a spiral track consisting of a row of pits is formed is used as a recording medium.

In the figure, a storage medium 1 (only tracks are shown in FIG. 1) is held horizontally with the recording area forming surface facing upward (with the pit openings facing upward), and a beam scanning means of an optical head. 20 is arranged below the recording medium 1.

In the beam scanning means 20 , a beam (beam center 4 ) emitted from a light source 7 made of a semiconductor laser or the like is converted into a parallel beam by a collimator lens 8 and reaches a polarizing beam splitter 9 . This beam splitter 9 is configured to transmit the beam from the light source 7, and the beam transmitted through the beam splitter 9 continues in the horizontal direction, passes through a quarter wavelength plate (not shown), and is directed to the rotating mirror 3. reach.

The rotating mirror 3 is arranged so that the center 4 of the beam from the beam splitter 9 and the center of rotation 3a coincide with each other, and an angle of 45° with respect to the incident beam center 4 is set as a reference position by an actuator (not shown). As a result, it is rotatable in a plane including the center of the incident beam and the center of the reflected beam at the reference position.

An objective lens 2 and first and second relay lenses 5 and 6 are provided between the rotating mirror 3 and the recording medium 1 so that their optical axes are perpendicular to the recording area forming surface. The rear focal point of the objective lens 2 and the front focal point of the first relay lens 5, the rear focal point of the first relay lens 5 and the front focal point of the second relay lens 6, and the rotation center of the second relay lens 6 and the rotating mirror 3. 3a are matched. Further, the front focus of the objective lens 2 almost coincides with the recording area forming surface (strictly speaking, the opening surface of the pit) of the recording medium 1, and a well-known focus servo means (not shown) such as a knife edge method is used. The position of the front focal position of the objective lens 2 in the optical axis direction is adjusted.

In FIG. 1, the rotating mirror 3 is at the reference position, and a parallel beam incident from the horizontal direction is reflected in the vertical direction. First and second relay lenses 5, 6 and objective lens 2
The optical system composed of is a parallel system, and the parallel beam reflected by the rotating mirror 3 is once focused on the optical axis by the second relay lens 6, and then enters the first relay lens 5. , is again emitted from the first relay lens 5 as a parallel beam. The parallel beam incident on the objective lens 2 from the first relay lens 5 is focused by the objective lens 2 onto the recording area forming surface. That is, when the rotating mirror 3 is at the reference position, the center 4 of the beam reflected by the rotating mirror 3 travels straight on the optical axis and is perpendicularly incident on the recording area forming surface.

The center 4 of the reflected beam on the recording area forming surface returns to the rotation center 3a of the rotary mirror 3 through the same optical path (ie, on the optical axis) as when it was incident, and is reflected in the horizontal direction here. The beam reflected by the rotating mirror 3 passes through a quarter-wave plate (not shown) and returns to the beam splitter 9. The reflected beam has its polarization state changed by the quarter-wave plate, is reflected by the beam splitter 9, and enters the light receiving element 10 of the recording area detection system 30.

The light receiving element 10 provided in the recording area detection system 30 has a light receiving surface divided in a direction perpendicular to the scanning direction (specifically, a pair of light receiving elements are joined).
The beam spot is arranged so that the dividing line 10c and the center of the beam spot coincide with each other. Among the reflected beams from the recording area forming surface, the zero-order diffracted light (regularly reflected light) becomes a spot centered on the dividing line 10c of the light-receiving surface, and the first-order diffracted light becomes a spot centered on the dividing line 10c.
There are two spots whose centers are separated from c in the dividing direction. The second-order and higher-order diffraction light is passed through the objective lens 2.
The light is blocked by an aperture stop (not shown).

[0035] Here, the light intensity distribution of the reflected beam on the light-receiving surface of the light-receiving element 10 will be considered. As mentioned above, the front focus of the objective lens 2 is aligned with the pit aperture surface of the recording area forming surface, so the intensity of the beam reflected from the pit bottom surface is smaller than the intensity of the beam reflected from the pit aperture surface. Become.

First, when the center of the beam spot from the objective lens 2 coincides with the center line of the recording area, the area occupied by pits when the beam spot is divided in the direction perpendicular to the scanning direction is equal on both sides of the dividing line. becomes. For this reason,
The light quantity distribution on the light receiving surface of the light receiving element 10 is symmetrical with respect to the dividing line 10c, and the light quantities on the divided light receiving surfaces 10a and 10b are equal.

On the other hand, when the center of the beam spot deviates from the recording area, the area occupied by the pits within the beam spot increases on one side of the dividing line. Therefore, the light amount distribution on the light receiving surface of the light receiving element 10 becomes asymmetrical with respect to the dividing line 10c, and the light amount on the side of the divided light receiving surfaces 10a, 10b that receives more light reflected from other than the pits becomes larger.

Divided light-receiving surfaces 10a, 10b of light-receiving element 10
Signals corresponding to the amount of light are sent to the +input terminal and -input terminal of the amplifier, respectively, and a tracking error signal proportional to the difference in the amount of light between the divided light-receiving surfaces 10a and 10b is obtained from the output terminal of the amplifier. As mentioned above, when the center of the beam spot and the center of the recording area are aligned, the light intensity of the divided light receiving surfaces 10a and 10b is equal, and when the center of the beam spot and the center of the recording area are shifted, the light intensity of the divided light receiving surface 1 is equal.
Since there is a difference in the light intensity of 0a and 10b, if the movement of the rotating mirror 3 is controlled so that the tracking error signal output from the amplifier 11 is below the allowable range, the relative positions of the beam spot and the recording area can be matched. I can do that.

At this time, when the center of the reflected beam from the recording area forming surface deviates due to the rotation of the rotating mirror 3, as in the conventional galvano mirror type scanning means, the light receiving element 1
The beam spot moves in the direction perpendicular to the dividing line 10c on the 0 light receiving surface. For this reason, the divided light receiving surface 1
A difference occurs between the light amounts of 0a and 10b, and an offset occurs in the tracking error signal.

In contrast, in the present invention, as explained above, the beam always passes through the rear focal point of the objective lens 2 and is irradiated onto the recording area forming surface, so that the center of the reflected beam does not shift. There is no offset in the tracking error signal.

Next, a method for reproducing information recorded on the recording medium 1 in this embodiment will be briefly explained. If the recording medium 1 is a read-only optical disk in which pits are formed along a spiral track as in this embodiment, information can also be read using the recording area detection means 30. As mentioned above, objective lens 2
The front focus of the pit is aligned with the pit opening surface, and the intensity of the reflected light from the bottom surface of the pit is weaker than the intensity of the reflected light from a surface other than the pit (the pit opening surface). Therefore, when the recording medium 1 held horizontally is rotated by a motor (not shown) and a predetermined track is scanned with a beam spot, the amount of light of the reflected beam decreases corresponding to the pit portion, and the total amount of the reflected beam decreases. A reproduction signal can be obtained by detecting the amount of light. That is, in the recording area detection means 30, during tracking, the amplifier 11 calculates the difference between the signals corresponding to the light intensity of each of the divided light receiving surfaces 10a and 10b, and when reproducing information, the sum of the signals corresponding to the light amount of each of the divided light receiving surfaces 10a and 10b is calculated. If the configuration is such that a tracking error signal and a reproduction signal can be obtained from the output terminal of the amplifier 11.

The recording medium 1 may also be a magneto-optical disk in which information is recorded by, for example, changing the direction of magnetization of the recording film (when the beam irradiation area is raised to around the Curie temperature, the direction of magnetization of that area changes). If it is,
Since the pits are not concave, the tracking error signal uses reflected light from the guide grooves carved on the disc surface.
Tracking is performed using the same principle as described above. In addition, a second beam splitter (not shown) is arranged between the rotating mirror 3 and the beam splitter 9 in FIG. (not shown) and detect the vibration direction of the reflected beam to obtain a reproduced signal.

In the above embodiment, the recording medium 1 was described as an optical disk on which tracks were formed in a spiral shape. However, the recording medium in the present invention does not necessarily have to be in the shape of a disk, and may be in the shape of a card, for example. It may be. The tracks do not necessarily have to be continuous, and may be arranged in stripes.

Further, the light receiving element provided in the recording area detecting means 30 does not necessarily have to be divided into two as long as it is divided in the direction perpendicular to the scanning direction;
It goes without saying that b may be further divided.

[0045]

As described above, in the present invention, at least one pair of relay lenses are arranged in a specific positional relationship between the rotating mirror of the galvano-mirror type beam scanning means and the objective lens. It prevents deviation of the center of the reflected beam on the recording area forming surface due to the rotation of the rotating mirror without complicating the configuration of the scanning means, and uses a galvano-mirror type beam scanning means that can perform high-speed scanning and is easy to adjust. This makes it possible to combine push-pull type recording area detection means. That is, according to the present invention, high-precision and high-speed scanning is possible, and the number of parts of the optical head can be reduced and the adjustment process can be simplified.

[Brief explanation of drawings]

FIG. 1 is a main part optical path diagram showing the configuration of an optical head according to an embodiment of the present invention.

FIG. 2 is an optical path diagram showing the basic configuration of a beam scanning means in the present invention.

FIG. 3 is an optical path diagram of a conventional example of a galvano-mirror type scanning means known as a structure for avoiding deviation of the beam center.

[Explanation of symbols]

1 Recording medium 2 Objective lens 3 Rotating mirror 4,4a　Beam center 5 First relay lens 6 Second relay lens 7. Light source 8 Condenser lens 9 Beam splitter 10 Photo receiving element 10a, 10b split light receiving surface 11 Amplifier

Claims (1)

[Claims] 1. Beam scanning means that includes a light source and an objective lens and scans a recording area forming surface of an optical recording medium with a beam spot; Recording area detection means that detects a predetermined recording area of the optical recording medium. In the optical head, the beam scanning means includes a rotating mirror that moves the beam spot in a direction perpendicular to the scanning direction, and the recording area detection means includes a light receiving surface divided in a direction perpendicular to the scanning direction. a push-pull type recording area detection means for detecting the recording area according to a signal from a light receiving element having a light receiving element, and at least one pair of relay lenses between the objective lens of the beam scanning means and the rotating mirror. The first relay lens on the recording medium side and the second relay lens on the light source side are as follows a to c.
An optical head characterized in that the optical head is arranged to satisfy the following conditions. a. The light source side focal point of the objective lens matches the recording medium side focal position of the first relay lens. b. A focus of the first relay lens on the light source side and a focus of the second relay lens on the recording medium side match. c. The light source side focal point of the second relay lens and the rotation center of the rotary mirror match.