JP2001023188A - Optical information recording/reproducing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To accurately align the center of an astigmatism generation element to a light axis by holding the astigmatism generation element while a side in parallel with an axis with lens operation butts against a butt surface. SOLUTION: Butt surfaces M1 and M2 for positioning and stopping the rotation of a toric lens 100 are formed at one end part of a lens barrel 101 so that the two faces orthogonally cross each other. The toric lens 100 is held while two sides in parallel with an axis with a lens operation butt against the butt surfaces M1 and M2 being formed at the low end part of the lens barrel 101, a light axis matches the center of the toric lens 100, and an axis with the lens operation is arranged in parallel with the butt surface. In this case, the butt surfaces M1 and M2 are used for aligning the toric lens 100, and the toric lens 100 is fixed to the lens barrel 101 by gluing another part of the toric lens to the lens barrel 101.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical information recording / reproducing apparatus for recording information on or reproducing recorded information from a recording medium while performing autofocusing control by an astigmatism method, and more particularly to an astigmatism generating astigmatism. The present invention relates to a holding structure for an aberration generating element.

[0002]

2. Description of the Related Art Various types of information recording media for recording and reproducing information using light, such as a disk, a card, and a tape, are conventionally known. These optical information recording media include those capable of recording and reproduction and those capable of only reproduction. In recording information on a recordable medium, information is recorded as an optically detectable information bit string by scanning an information track with a light beam modulated according to the recording information and narrowed into a minute spot.
When reproducing information from a recording medium, a light spot having a constant power enough to prevent recording on the medium is scanned on the information bit string of the information track, and reflected light or transmitted light from the medium is detected. The recorded information is reproduced by performing a predetermined signal processing using the detected signal.

An optical head used for recording and reproducing information on and from the recording medium described above is relatively movable with respect to the recording medium in the direction of the information track and in the direction crossing the track. Scan to the target track. As a lens for narrowing a light spot in the optical head, for example, an objective lens is used. The main body of the optical head is configured such that the objective lens can move independently in the optical axis direction (focusing direction) and in the direction (tracking direction) orthogonal to both the optical axis direction and the information track direction of the recording medium. Is held in. Such an objective lens is held through an elastic member, and the movement of the objective lens in the two directions is generally driven by an actuator utilizing magnetic interaction.

[0004] Among the above-mentioned optical information recording media, a card-shaped optical information recording medium (hereinafter referred to as an optical card) will be a large and small-sized information recording medium that is convenient to carry in the future. Demand is expected. FIG. 3 is a schematic plan view of the write-once optical card, and FIG. 4 is a partially enlarged view thereof. First, as shown in FIG.
A number of information tracks 2 are arranged in parallel in the LF direction on the information recording surface of (1). On the information recording surface of the optical card 1, a home position 3 serving as a reference position for accessing the information track 2 is provided.

[0005] The information tracks 2 are arranged in the order of 2-1, 2-2, 2-3,... In addition, as shown in FIG.
1, 4-2, 4-3,... Are sequentially provided. These tracking tracks 4 are used as a guide for automatic tracking (hereinafter, referred to as AT) for controlling a light spot so as not to deviate from a target information track during light spot scanning during information recording and reproduction.

This AT servo detects a deviation (AT error) of a light spot from an information track in an optical head and negatively feeds a detection signal back to a tracking actuator to move the objective lens relative to the optical head body in the tracking direction (D). Direction) to control the light spot to follow a desired information track. Further, when the light spot is scanned on the information track at the time of control recording / reproduction, an auto-focusing (hereinafter, referred to as AF) servo is performed to focus the light spot on the optical card surface. The AF servo detects a deviation (AF error) of a light spot from an in-focus state in an optical head, and negatively returns a detection signal to a focusing actuator to move an objective lens in a focusing direction with respect to the optical head main body. Control is performed so that the spot is focused on the optical card surface.

In FIG. 4, P ₁ , P ₂ , and P ₃ indicate light spots, and A ₁ is determined using the light spots of P ₁ and P _3.
Performs T control, AF control and recording of the recording time of the information pit, the reading of reproduction of information pit performed using the light spot P _2. In each information track, 6-1 and 6-
Reference numerals 2 and 7-1 and 7-2 denote a preformatted left address portion and a right formatted address portion, respectively, and the information track is identified by reading these address portions. 5
(Corresponding to 5-1 and 5-2 in the figure) indicate recorded pits.

FIG. 5 is a diagram showing an optical head optical system of a conventional optical card recording / reproducing apparatus. In FIG. 5, first, 2
Reference numeral 1 denotes a semiconductor laser as a light source. In this example, the semiconductor laser 21 is 830 polarized in a direction perpendicular to the track.
It emits light having a wavelength of nm. Further, 22 is a collimator lens, 23 is a beam shaping prism, 25 is a diffraction grating for splitting a light beam, and 26 is a polarization beam splitter. Further, 27 is a quarter-wave plate, 28 is an objective lens,
29 indicates a toric lens, and 31 indicates a photodetector. The photodetector 31 includes two light receiving elements 31a and 31c and a light receiving element 31b divided into four.

The light beam emitted from the semiconductor laser 21 is
A divergent light beam enters the collimator lens 22, is converted into a parallel light beam by the lens 22, and is further shaped by the beam shaping prism 23 into a beam having a predetermined light intensity distribution, that is, a circular intensity distribution. Beam shaping prism 2
The light beam emitted from 3 is split by the diffraction grating 25 into three light beams, and is incident on the polarizing beam splitter 26 as a P-polarized light beam. Further, this light beam passes through the polarizing beam splitter 26, enters the quarter-wave plate 27, and is converted into circularly polarized light when passing through the quarter-wave plate 27.

The light beam emitted from the quarter-wave plate 27 is irradiated as a minute light spot on the optical card 1 by the objective lens 28. The focused light is three as shown in FIG. 4 minute spot P ₁ (+1 order diffracted light), P ₂ (0-order diffracted light), P
₃ (-1st order diffracted light). P ₂ is recorded, reproduced, used in AF control, P ₁ and P ₃ are used for AT control. As shown in FIG. 4, the spot positions on the optical card 1 are such that the light spots P ₁ and P ₃ are located on the adjacent tracking track 4 and the light spot P ₂ is located on the information track 2 between the tracking tracks. I have. Thus, the reflected light of the light spot irradiated on the optical card 1 passes through the objective lens 28 again to be converted into a parallel light flux, and the quarter-wave plate 27
Is converted into a light beam whose polarization direction is rotated by 90 ° from that at the time of incidence. Then, the light enters the polarization beam splitter 26 as an S-polarized beam.

The detection optical system comprises a toric lens 29 which is an astigmatism generating element.
9, the AF control by the astigmatism method is performed. The three light beams reflected from the optical card 1 are respectively condensed by the detection optical system and detected by the respective light receiving elements of the photodetector 31 shown in FIG. The light receiving elements 31a and 31c are light spots P ₁ and P
The reflected light of No. ₃ is received, and AT control is performed using the difference between the outputs of these two light receiving elements. Also, the four-divided light receiving element 31
b is receives the reflected light of the light spot P _2, performs AF control by using the output, for reproducing recorded information.

Next, the relationship between the photodetector 31 and the incident light beam shown in FIG. 6 will be described. In the astigmatism AF method, the position of the photodetector 31 in the direction of the optical axis is generally the smallest position of an irregular circle at the time of focusing. At this time, the spot on the photodetector 31 has a shape close to a circle. The astigmatism AF method utilizes a shape change (a change in light amount distribution) on the four-segment photodetector 31b due to a displacement of the objective lens 28 in the optical axis direction, and accurately and stably detects the change. In order to achieve this, it is desirable that the center of the substantially circular spot on the photodetector 31b during focusing coincides with the center of the four-divided photodetector 31b (the intersection of the four-divided lines).

As an adjustment method, the four-divided photodetector 3
1b while detecting the outputs of the respective light receiving elements S1, S2, S3, and S4 (the outputs of the light receiving elements S1, S2, S3, and S4 are referred to as S1, S2, S3, and S4, respectively). The position is adjusted by a method of moving the four-divided photodetector 31b within the light beam cut plane with respect to the incident light beam so that S2 = S3 = S4.

[0014]

By the way, conventionally, in order to perform AF control by the astigmatism method, a toric lens is used as an astigmatism generating element. As shown in FIG. 7, the toric lens 29 has different lens functions in the A direction and the B direction. Point C is the intersection of the two axes that produce the two lens effects and generally coincides with the center of the lens.

FIG. 8 shows a conventional structure for holding a toric lens 29. FIG. 8A is a front view, and FIG.
Is a plan view (a view as seen from the optical axis direction). As shown in FIG. 8, the toric lens 29 is adhered to one end of a cylindrical lens barrel 50 by abutting the lens surface. Normally, the optical axis and the center of the lens barrel 50 and the optical axis and the center of the toric lens 29 (point C) are generally designed to coincide with each other. However, the fixing method of the toric lens 29 as in the conventional example is as follows. There is no guarantee that the center of the toric lens 29 coincides with the optical axis.

When the center of the toric lens 29 is displaced from the optical axis, the light beam that passes through the toric lens 29 and converges on the photodetector 31 has an inclination with respect to the ideal optical axis, and Incident on the vessel 31 obliquely. In the astigmatism AF method, as described above, the shape change of the light beam on the four-divided light receiving element 31b of the photodetector 31 is electrically detected, and the objective lens position is set in the AF direction so that the target output becomes a target. Is controlled.

However, when the light beam is obliquely incident on the photodetector 31, the shape of the light beam on the four-divided light receiving element 31b when the objective lens 28 is moved in the AF direction changes and the center of the light beam moves. This will be described with reference to FIGS. FIG. 9 shows a state where the toric lens 29 is displaced from the optical axis of the incident light. In this state, the transmitted light of the toric lens 29 is emitted obliquely. In addition, Y is the arrangement position of the photodetector 31 and is also the minimum circle of confusion.

FIG. 10B shows the relationship between the four-divided light receiving element and the light beam in that case. The light beam is located at the center of the four-divided light receiving element. On the other hand, in FIGS. 10A and 10C, the objective lens 28 moves in the defocus direction, and the light flux forms an image at the X and Z (first and second focal positions of the toric lens) in FIG. The light flux shape on the quadrant light receiving element at the time is shown. When the toric lens 29 is displaced from the optical axis, the center of the light beam becomes four as shown in FIGS.
It is shifted from the division center of the divided light receiving element. as a result,
In FIG. 11, the amplitude and the control gain of the AFS-shaped signal b when there is a shift indicated by the broken line are lower than the AFS-shaped signal a when there is no shift indicated by the solid line. Also, since the amount of reduction differs for each device, there is a problem that the compatibility between devices or the reliability of a single device is impaired.

In the prior art, since the toric lens 29 is not positioned in the rotational direction with respect to the center of the optical axis, the direction A or the direction B having the lens action is rotated and bonded to the ideal position. There was also a problem. FIG. 12 is a diagram in which the toric lens 29 is arranged in an ideal state with respect to the dividing direction of the four-divided light receiving element 31b. On the other hand, FIG. 13 shows that the toric lens 29 rotates in the rotation direction with respect to the optical axis center, and the direction A and the direction B
FIG. 7 is a diagram in which directions are located.

In the state shown in FIG. 13, the relationship between the direction of division of the four-divided light receiving element 31b and the direction A or B having a lens function is displaced in the rotation direction even if the light beam is incident perpendicularly on the photodetector 31. However, there is a problem that the amplitude and the control gain of the AFS signal for the AF control are reduced as in the AFS signal b shown in FIG. As a means to solve these problems, it is conceivable to provide a volume on the electric circuit and adjust the volume to adjust the amplitude and control gain to eliminate the machine difference of the device. And the number of adjustment steps also increases, resulting in a problem that the cost is greatly increased.

The present invention has been made in view of the above-mentioned conventional problems, and provides an optical information recording / reproducing apparatus capable of accurately aligning the center of an optical element generating astigmatism with an optical axis. The purpose is to:

[0022]

SUMMARY OF THE INVENTION An object of the present invention is to provide an astigmatism generating element for generating astigmatism, a holding member for holding the astigmatism generating element, and using the astigmatism generating element. In an optical information recording / reproducing apparatus for recording information on a recording medium while performing focusing control by an astigmatism method or reproducing recorded information, an axis having a lens function of the astigmatism generating element is provided on the holding member. Optical information, wherein the astigmatism generating element is held in a state in which a side parallel to an axis having a lens function is abutted against the abutting surface. This is achieved by a recording / reproducing device.

[0023]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 is a diagram showing a configuration of a main part of an optical information recording / reproducing apparatus of the present invention. That is, a toric lens 100 and a holding member 101 for holding the toric lens 100 are shown. FIG. 1A is a front view, and FIG.
Is a plan view. In the present embodiment, the optical card 1 shown in FIG. 3 is used as a recording medium, and the light from the semiconductor laser 21 is moved while the optical card 1 and the optical head optical system shown in FIG. By scanning the track of the optical card 1 with the beam, information is recorded or recorded information is reproduced. The toric lens of FIG. 1 is used as an astigmatism generating element as in the related art, and FIG.
In place of the toric lens 29 in the optical head optical system. However, the toric lens of FIG. 1 is different from the conventional example of FIG. 8 in the shape of the holding member and the holding structure, and the lens itself is the same as the conventional example.

Referring to FIG. 1, first, 100 is a toric lens, and 101 is a cylindrical lens barrel holding the toric lens. As described in the conventional example, the toric lens 100 has axes having a lens action in the A direction and the B direction, and the amounts of the lens actions are designed to be different from each other. Also, the toric lens 100
Is a quadrilateral having sides parallel to an axis having a lens function. Here, in this embodiment, abutting surfaces M1 and M2 for positioning and stopping rotation of the toric lens 100 are formed at one end of the lens barrel 101. The two abutting surfaces M1 and M2 are formed so as to be orthogonal to each other. This corresponds to the fact that the axes of the toric lens 100 having the two lens functions are orthogonal to each other.

The toric lens 100 is held in a state where two sides parallel to an axis having a lens action abut against abutting surfaces M1 and M2 formed at the lower end of the lens barrel 101, and the optical axis is The center of the toric lens 100 coincides, and the axis having the lens action is arranged parallel to the abutting surface. In this case, the abutting surfaces M1 and M2 are used for positioning the toric lens 100, and the other part of the toric lens 101 is bonded to the lens barrel 101, so that the toric lens 100 is fixed to the lens barrel 101.
If the lens barrel 101 itself rotates around the optical axis, the positional relationship between the direction of the axis having the lens action and the dividing line of the four-divided light receiving element is shifted. It is easy to prevent rotation by setting a pin on a part of the optical head body, forming a groove in the lens barrel, and aligning the pin with the groove.

Next, another embodiment of the present invention will be described. In the embodiment shown in FIG. 1, a case where a toric lens is used as the astigmatism generating element has been described. The same effect can be obtained by using a cylinder. FIG. 2 shows a holding structure in such a case.
FIG. 2A is a front view, and FIG. 2B is a plan view.

In FIG. 2, reference numeral 102 denotes a spherical lens, 10
Reference numeral 3 denotes a cylindrical lens. A spherical lens 102 is held at one end of the barrel 101, and butting surfaces M1 and M2 similar to FIG. 1 are formed at the other end of the barrel 101,
The cylindrical lenses 10 are provided on the abutting surfaces M1 and M2.
The lens is held in a state where the side parallel to the axis having the lens function of No. 3 abuts. The axis of the cylindrical lens 103 having a lens function is in one direction (the direction D in FIG. 2) of FIG. 2. For example, the side parallel to the axis having the lens function is abutted against the abutting surface M1 and bonded. If the luminous flux can be visually located so as to be located within the effective diameter of the lens, the abutting surface M2 is not necessarily required, and only one abutting surface is sufficient. Although a lens barrel is used as a holding member for the astigmatism generating element, although not shown, the same effect can be obtained even if a similar abutment surface is provided on a part of the optical head housing to satisfy the characteristics. Can be obtained.

[0028]

As described above, according to the present invention, the holding member is provided with an abutting surface in the direction parallel to the axis having the lens function of the element generating the astigmatism, and the astigmatism generating element is formed as a lens. By holding the side parallel to the axis having an action against the abutting surface, the center of the astigmatism generating element can be accurately aligned with the optical axis, and the stable A
An F control signal can be obtained. Therefore, there is no need for an electric circuit for adjusting the variation of the AF control signal amplitude and the control gain, and the adjustment man-hour for the adjustment can be eliminated. An optical information recording / reproducing device can be realized.

[Brief description of the drawings]

FIG. 1 is a diagram showing a main configuration of an optical information recording / reproducing apparatus according to an embodiment of the present invention.

FIG. 2 is a diagram showing a main configuration of another embodiment of the present invention.

FIG. 3 is a plan view of the optical card.

FIG. 4 is a view showing a state in which a light spot is applied to the optical card of FIG. 3;

FIG. 5 is a diagram showing an optical head optical system of a conventional optical card recording / reproducing apparatus.

6 is a diagram showing a photodetector of the optical head optical system of FIG.

7 is a diagram showing a toric lens of the optical head optical system of FIG.

FIG. 8 is a diagram showing a conventional structure for holding a toric lens.

FIG. 9 is a diagram showing a state in which the toric lens is arranged so as to be shifted from the optical axis of incident light.

FIG. 10 is a diagram illustrating a light beam shape of a four-division light receiving element when a light beam forms an image at X, Y, and Z positions in FIG. 9;

FIG. 11 is a diagram illustrating a change in the AFS-shaped signal when the center of the light beam is deviated from the center of the quadrant light receiving element.

FIG. 12 is a diagram showing a positional relationship between a toric lens and a four-divided light receiving element in an ideal state.

FIG. 13 is a diagram illustrating a positional relationship with a four-division light receiving element when a toric lens is rotated around an optical axis.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Optical card 100 Toric lens 101 Lens barrel 102 Spherical lens 103 Cylindrical lens M1, M2 Abutment surface 31b Quadrant light receiving element A, B, D Axes having lens action

Claims (5)

[Claims] 1. An astigmatism generating element for generating astigmatism,
An optical element that has a holding member that holds the astigmatism generation element, and that records information on a recording medium while performing focusing control by the astigmatism method using the astigmatism generation element, or reproduces recorded information. In the objective information recording / reproducing apparatus, the holding member has an abutting surface formed in a direction parallel to an axis having a lens function of the astigmatism generating element, and the astigmatism generating element has a side parallel to the axis having a lens function. Optical information recording / reproducing apparatus, wherein the optical information recording / reproducing apparatus is held in a state of being abutted against the abutting surface. 2. The optical information recording / reproducing apparatus according to claim 1, wherein the holding member has a cylindrical shape, and has an abutting surface formed at one end thereof. 3. The optical information recording / reproducing apparatus according to claim 1, wherein the holding member has a number of abutting surfaces equal to the number of axes having a lens function of the astigmatism generating element. apparatus. 4. The optical information recording / reproducing apparatus according to claim 1, wherein the astigmatism generating element is a toric lens. 5. The optical information recording / reproducing apparatus according to claim 1, wherein the astigmatism generating element comprises a spherical lens and a cylindrical lens.