JPH07334851A - Optical head and adjusting method therefor - Google Patents

Abstract

PURPOSE:To provide an optical head and an adjusting method therefor capable of easily determining the cylindrical axis of a cylindrical single lens and moreover reducing the deviation between the incident light flux to the lens and a lens optical axis accompanying the fixing of the cylindrical single lens. CONSTITUTION:A cylindrical single lens 6 has a lens first surface 6c having positive power and a toric surface 6c including a cylindrical surface inside an effective diameter and cylindrical axis angle determining parts 6h around an axis which is inclined by an angle alpha with respect to a cylindrical axis outside the effective diameter at a lens second surface 6d having a negative power. The lens 6 is adjusted and positioned by engaging an engaging means with the cylindrical axis determining parts 6h and by rotating them.

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 recording and reproducing by irradiating a recording medium with a light beam and a method of adjusting the same.

[0002]

2. Description of the Related Art A conventional optical head will be described below with reference to the drawings. FIG. 7 is a perspective view of a conventional optical head, 1 is a light source such as a semiconductor laser, 2 is a collimating means exemplifying a collimating lens, 3 is a light beam separating means exemplifying a beam splitter, and 4 is an objective lens. Is a recording medium, 5 is a recording medium, 7 is a first focal point, and 8
Is a second focal point, 9 is a four-division light receiving element, 9a, 9b, 9c,
Reference numeral 9d is a light receiving area of the four-division light receiving element, 9e, 9f and 9g are light spots connected on the four-division light receiving element, 10 is an optical base, and 10a is a reference plane for assembling the optical head.
d is a hole through which a light beam is provided on the optical base, and 15 is a first
A lens surface of which is a positive power surface and a second lens surface of which is a cylindrical surface; 15a is a cylindrical axis;
Is a lens holder.

The operation of the conventional example thus constructed will be described. The light emitted from the light source is converted into a parallel light flux by the collimating means 2, is reflected by the light flux separating means 3, and the reflection component of the parallel light flux is integrated into an objective lens driving device (not shown). Thus, the light is condensed on the reflection surface of the recording medium 5. The reflected light beam from the recording medium 5 is substantially transmitted through the light beam separating means 3, and the first lens surface, which serves as the focus error detecting means rotated about the lens optical axis by 45 ° about the cylindrical axis, is the second surface with a positive power. Astigmatism occurs due to the lens 15 whose lens surface is a cylindrical surface.

That is, in a plane perpendicular to the cylindrical axis and including the lens optical axis, the optical path becomes a solid line and converges on the first focal point 7 in front of the four-divided light receiving element to form an astigmatic spot 9e on the four-divided light receiving element 9. In the plane that coincides with the cylindrical axis, the optical path becomes a broken line and converges on the second focal point 8 behind the four-divided light receiving element to form an astigmatic spot 9f on the four-divided light receiving element 9. The light receiving surface of the four-division light receiving element 9 is located approximately in the middle between the first focus 7 and the second focus 8, and the focus error signal is detected by the astigmatism method and the tracking error signal is detected by the push-pull method. The information signal is detected by taking the sum.

The lens 15 whose first lens surface has a positive power and whose second lens surface has a cylindrical surface is fixed to the lens holder 16 by rotating the cylindrical axis 15a about the lens optical axis by 45 °. Lens holder 16
Are fixed to the optical base 10.

However, this conventional optical head is
Let L2 be the distance from the lens surface to the four-division light receiving element 9, the focal length of the objective lens, the S-shaped range of the focus,
Since L2 becomes long due to the optical constants such as the spot diameter,
There is a drawback in that the optical head has a long optical path length and its shape becomes large.

Therefore, in order to shorten the optical path length, the lens 15
If the focal length of is shortened, the light spot on the 4-division light-receiving element 9 becomes smaller, and the influence of the distance variation is overwhelmed by the positional deviation of the 4-division light-receiving element 9 and the temperature characteristics between the lens 15 and the 4-division light-receiving element 9. There is a problem that it is easily received.

On the other hand, in order to solve these problems, the lens 15
As a plurality of lenses, for example, the first lens surface has a positive power and the second lens surface has a negative power, and either the first lens surface or the second lens surface A so-called telefocus lens having a surface including a cylindrical surface is also implemented.

However, due to the deviation between the optical axes of the lenses, the mounting error between the lens 15 and the lens holder 16 and the mounting error between the lens holder 16 and the optical base 10,
Since spherical aberration and coma are likely to occur in the light spot formed on the light receiving surface of the four-division light receiving element 9, there is a possibility of destabilizing the focus error control.

On the other hand, FIG. 8 is a schematic view of an recently proposed optical head (Japanese Patent Application No. 4-287334),
The first lens surface having positive power and the lens surface having negative power are arranged in this order from the side on which the light beam is incident, and
Either one of the lens surface of the second lens surface and the lens surface of the second lens surface has a cylindrical axis in a plane perpendicular to the incident light beam to generate astigmatism. Except for the cylindrical single lens 6, the optical head has the same configuration as that of the optical head shown in FIG.

In this optical head, the telefocus system lens, which has been conventionally realized by a plurality of lenses, is realized by a cylindrical single lens, so that the optical axis shift between the lenses when a plurality of lenses are not caused can be realized. The distance L1 from the incident surface of the single lens 6 to the incident surface of the four-division light receiving element 9 can be significantly shortened, and the optical head can be downsized.

The cylindrical single lens 6 can be obtained, for example, by press molding a glass material with a mold shown in FIG. 1
Reference numeral 7 is an upper mold, 18 is a barrel mold, 19 is a lower mold, and 20 is a cavity in which a lens is molded.

[0013]

However, in the optical head having the above-described structure, in order to determine the cylindrical axis of the cylindrical single lens, the light spot formed on the four-divided light receiving element is observed and the first focal point is set. The rotation adjustment must be performed so that the astigmatic inclination angle of the second focal point falls within a predetermined range, and an increase in assembly and adjustment man-hours cannot be avoided.

In view of this conventional problem, an object of the present invention is to easily determine the cylindrical axis of a cylindrical single lens, and to let the incident light beam on the lens and the lens optical axis when the cylindrical single lens is fixed. An object of the present invention is to provide an optical head capable of reducing the deviation and an adjusting method thereof.

[0015]

An optical head according to the present invention comprises a light source such as a semiconductor laser, a collimating means for converting a light beam emitted from the light source into a parallel light beam, and an objective for converging the parallel light beam on a recording medium. Condensing means such as a lens, luminous flux separating means for separating the parallel luminous flux and reflected luminous flux from the recording medium, a light receiving element on which the separated luminous flux from the luminous flux separating means is incident, the separating means and the luminous flux separating means. A first lens surface having a positive optical power and a second power having a negative power in order from the incident side of the separated light flux.
And a cylindrical single lens having a cylindrical surface in a plane perpendicular to the lens optical axis of the second lens surface, and the cylinder parallel to the reference surface and the separated light beam and orthogonal to each other. At least 2 for abutting and fixing the side surfaces of the single lens
An optical head having an optical base having two lens fixing surfaces, the optical head having a predetermined angle with respect to a reference surface of the optical base outside the effective diameter of the lens surface having the cylindrical axis of the cylindrical single lens. It is characterized by having a cylindrical axis angle determining unit for positioning.

An optical head according to a second aspect is the optical head according to the first aspect, characterized in that the cylindrical axis angle determining portion of the cylindrical single lens is constituted by at least one substantially flat taper portion.

An optical head adjusting method according to a third aspect of the present invention has a first lens surface having a positive power and a second lens surface having a negative power, and the optical axis of the second lens surface is located on the optical axis. An optical base having a cylindrical single lens having a cylindrical axis in a vertical plane, and at least two lens fixing surfaces for abutting and fixing side surfaces of the cylindrical single lens parallel to the reference surface and orthogonal to each other in the separated light flux. A method of adjusting the cylindrical single lens at a position where the cylindrical axis forms a predetermined angle with respect to a reference plane of the optical base, which comprises a table, and a cylindrical axis angle determining unit of the cylindrical single lens. It is characterized in that it has an engaging means for engaging with, and a rotating means for adjusting the rotation of the cylindrical single lens engaged with the engaging means.

[0018]

According to the optical head of the first aspect, since the cylindrical axis angle determining unit is formed in the mold on the second surface side of the cylindrical single lens, the angle error of the angle determining unit with respect to the cylindrical axis is suppressed to a very small value. be able to.

Further, the side surface of the cylindrical single lens is brought into contact with at least two lens fixing surfaces of the optical base, and the cylindrical single lens is rotated to set the cylindrical axis to a predetermined plane with respect to the reference surface of the optical base. By positioning the lens at an angle and fixing the cylindrical single lens to the lens fixing surface in this state, the lens optical axis of the cylindrical single lens becomes parallel to the reference surface of the optical base, and the cylindrical axis is relative to the reference surface. It is fixed so that it is inclined at a predetermined angle. Therefore, by shortening the focal length by using the tubular single lens, the distance between the tubular single lens and the light receiving element can be shortened, so that the optical head can be downsized and the cylindrical axis of the tubular single lens can be easily positioned. Moreover, it is possible to reduce the deviation between the light flux incident on the cylindrical single lens and the optical axis of the lens due to the fixing of the cylindrical single lens, and it is possible to achieve high accuracy and high reliability.

According to the optical head of claim 2, claim 1
In the above, in the cylindrical single lens, the cylindrical axis angle determining portion is configured by a substantially flat taper portion.

According to the optical head of the third aspect, the cylindrical axis angle determining portion of the cylindrical single lens is engaged with the engaging means, and the cylindrical single lens is rotated together with the engaging means by the rotating means, and the optical base is rotated. By rotating and fixing the cylindrical single lens until it becomes a predetermined angle with respect to the reference surface of the table,
Conventionally, the adjustment can be performed faster than the case where the light spot is observed and adjusted.

[0022]

Embodiments of the present invention will be described with reference to FIGS. 1, 2, 3, 4, 5, and 6. 1 is a perspective view of an optical head in an embodiment of the present invention, FIG. 2 is a perspective view of a mold for molding the second surface of a tubular single lens, FIG. 3 is a sectional view of the tubular single lens 6, and FIG. Is a front view of the second surface side of the cylindrical single lens 6, FIG. 5 is a front view showing an adjusting method of the optical head of this embodiment, and FIG. 6 is a side view showing an adjusting method of the optical head of this embodiment. .

In FIG. 1, since it has basically the same configuration as the optical system of the conventional optical head shown in FIG. 7, the same components are designated by the same reference numerals and detailed description thereof will be omitted. In addition, 6a is a cylindrical axis of the cylindrical single lens 6,
a and 10b are surfaces for abutting and fixing the tubular single lens, 10e is a step for restricting the position of the tubular single lens 6 in the optical axis direction, 1
1 is a cylindrical single lens 6 which is a lens fixing surface 10b of an optical base,
It is a spring for pressing and fixing to 10c.

In FIG. 2, 19 is the lower die of the mold for molding the tubular single lens 6 of this embodiment, and 19a is the tubular single lens 6.
Of the second surface, a transfer surface for molding a toric surface including a cylindrical surface within the effective diameter, 19b for transferring a conical taper portion outside the effective diameter of the cylindrical single lens 6, and 19c for forming an angle from the cylindrical axis 19e. A transfer surface for molding the α-rotated cylindrical axis angle determining section, 19d is a center line of the cylindrical axis angle determining section of the cylindrical single lens 6, and 19e is a cylindrical axis of the mold.

The cylindrical single lens 6 is a lower mold 16 of the conventional example shown in FIG.
Is molded by using the lower mold 19 shown in FIG.

3 and 4, 6a is a cylindrical axis, 6b is a lens optical axis, 6c is a first lens surface having positive power, 6d is a second lens surface having negative power, and 6e.
Is a toric surface that is an effective surface of the lens second surface and includes a cylindrical surface, 6f is a knuckle surface configured as the first surface, 6g is a central axis of a cylindrical axis angle determining unit rotated by an angle α with respect to the cylindrical axis 6a, and 6h Is a tapered flat surface which is a cylindrical axis angle determining portion formed outside the effective diameter of the second surface, and 6i is a conical tapered portion formed outside the effective diameter of the second surface.

In the optical head configured as described above, the optical operation from the focusing system to the detection system is the same as that of the conventional example shown in FIG. 7, and therefore its explanation is omitted, and only the operation of the cylindrical single lens 6 will be described.

The cylindrical single lens 6 is pressed and fixed to the lens fixing surfaces 10b and 10c of the optical base 10 by the spring 11, and is positioned so that the cylindrical shaft 6a is at a predetermined angle α with respect to the reference surface 10a. . Cylindrical single lens 6
Is located between the light beam separating means 3 and the four-division light receiving element 9, and the light beam from the light beam separating means is the first surface 6 of the cylindrical single lens 6.
It is incident on c and sharply narrowed down. The light flux that has reached the toric surface 6e of the second surface 6d is widened and given astigmatism, so that a spot is formed on the four-division light receiving element 9 and a signal is detected.

Next, the cylindrical single lens 6 of this optical head
A method of adjusting the positioning with respect to the optical base 10 will be described with reference to FIGS.

In FIGS. 5 and 6, 12 is an engaging means for engaging with the tapered flat surface 6h of the cylindrical single lens 6, 13 is a supporting means for supporting the engaging means 12, and 14 is the cylindrical single lens 6.
It is a rotating means for rotating the engaging means 12 engaged with the lens around the optical axis of the lens.

The tapered flat surface 6h, which is the cylindrical axis angle determining portion of the cylindrical single lens 6, and the cylindrical axis 6a of the toric surface 6e form a constant angle α. α = 4
When the angle is 5 °, the cylindrical axis 6a can be fixed at an angle of 45 ° with respect to the optical base 10a by stopping the rotation of the cylindrical axis angle determination unit 6g at a position perpendicular to the reference surface 10a of the optical base. As a result, the recording medium 5
When the reflected light flux from is incident on the cylindrical single lens 6, the light receiving surface of the four-divided light receiving element 9 disposed approximately in the middle of the first focal point 7 and the second focal point 8 of the cylindrical single lens 6 is properly astigmatic. And an error signal is obtained.

According to the optical head of this embodiment, the side surface of the cylindrical single lens 6 is brought into contact with at least two lens fixing surfaces 10b and 10c of the optical base 10, and the cylindrical single lens 6 is rotated to rotate the cylindrical lens. The shaft 6a is positioned at a predetermined angle α with respect to the reference surface 10a of the optical base 10, and in this state, the cylindrical single lens 6 is fixed to the lens fixing surfaces 10b and 10c. The shaft 6b and the reference surface 10a of the optical base 10 are parallel to each other, and the cylindrical axis 6a can be fixed so as to be inclined at a predetermined angle α with respect to the reference surface 10a. Therefore, by shortening the focal length by using the tubular single lens 6,
Since the distance L1 between the light receiving element 9 and the four-division light receiving element 9 can be shortened, the optical head can be downsized, and the incident light flux to the cylindrical single lens 6 and the deviation of the optical axis from the lens axis 6b due to the fixation of the cylindrical single lens 6 can be reduced. It is possible to reduce the number, and it is possible to achieve high accuracy and high reliability.

Further, according to the method of adjusting the optical head, the cylindrical axis 6a of the cylindrical single lens 6 and the angle α of the cylindrical axis angle determining portion 6h can be accurately manufactured by using a mold, so that the cylindrical single lens 6 has a cylindrical shape. Positioning is possible only by engaging the tapered flat surface 6h, which is the axial angle determining portion, with the engaging means 12, and restricting the rotation angle of the rotating means 14. Therefore, the positioning in the rotational direction can be performed more accurately and in a shorter time and more easily than the conventional positioning that is performed while observing the signal from the light receiving element and the light spot on the light receiving element.

In this embodiment, the tapered flat surface portion is 2
Although it is composed of one surface, it may be one surface or three or more surfaces.

Further, in this embodiment, the focus error signal is detected from the recording medium 5 in which the information signal is formed by the pits by the astigmatism method, the tracking error signal is detected by the push-pull method, and the information signal is detected. The optical head detects the sum of four divided areas, but the focus error is detected by the astigmatism method in the optical head that detects the tracking error signal by the three-beam method or the optical head that detects the magneto-optical signal. It goes without saying that it can be applied to an optical head to be used.

[0036]

According to the optical heads of the first and second aspects, the cylindrical axis angle determining portion is formed outside the effective diameter of the second surface of the cylindrical single lens by inclining the cylindrical axis at a predetermined angle with respect to the cylindrical axis. Thus, by fixing the cylindrical axis angle determination unit to the optical base, the cylindrical axis of the cylindrical single lens can be easily positioned,
Moreover, it is possible to reduce the deviation of the light flux incident on the cylindrical single lens and the optical axis of the lens due to the fixation of the cylindrical single lens, and it is possible to achieve high accuracy and high reliability.

According to the optical head of claim 3, claim 1
In, the cylindrical single lens is detected by engaging the tubular single lens with engaging means that engages with the cylindrical axis angle determining portion formed outside the effective diameter of the second surface and rotating the tubular single lens. Instead, the cylindrical shaft can be rotationally positioned and fixed with high accuracy with respect to the reference surface of the optical base. Further, a force can be applied to the cylindrical single lens in the optical axis direction at the same time, and the cylindrical single lens can be positioned in the optical axis direction at the same time, so that the cost can be reduced.

[Brief description of drawings]

FIG. 1 is a perspective view of an optical head according to an embodiment of the present invention.

FIG. 2 is a perspective view of a mold for molding the second surface of the cylindrical single lens according to the embodiment of the present invention.

FIG. 3 is a sectional view of a cylindrical single lens according to an embodiment of the present invention.

FIG. 4 is a front view of the second surface side of the cylindrical single lens in the example of the present invention.

FIG. 5 is a front view showing an adjusting method of the optical head according to the embodiment of the invention.

FIG. 6 is a side view showing an adjusting method of the optical head according to the embodiment of the invention.

FIG. 7 is a perspective view of a conventional optical head.

FIG. 8 is a schematic explanatory view of another conventional optical head.

FIG. 9 is a view showing a molding die for a cylindrical single lens of an optical head of another conventional example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 light source 2 collimating means 3 light flux separating means 4 light collecting means 5 recording medium 6 cylindrical single lens 6a cylindrical axis 6b lens optical axis 6c positive lens 1st surface 6d negative lens 2nd surface 9 4 Split light receiving element 10 Optical base 12 Engaging means 14 Rotating means

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Toru Nakamura 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd.

Claims (3)

[Claims] 1. A light source such as a semiconductor laser, a collimating means for converting a light flux emitted from the light source into a parallel light flux, a condensing means such as an objective lens for converging the parallel light flux on a recording medium, and the parallel light flux. A light beam separating means for separating the light beam reflected from the recording medium, a light receiving element on which the separated light beam from the light beam separating means is incident, and an optical axis of the separated light beam positioned between the separating means and the light beam separating means. And a second lens surface having a positive optical power and a second lens surface having negative power in order from the side on which the separated light flux enters. A cylindrical single lens having a cylindrical axis in a plane perpendicular to the lens optical axis of the surface, and at least two abutting and fixing side surfaces of the cylindrical single lens that are parallel to the reference plane and the separated light flux and are orthogonal to each other. Len An optical head having an optical base having a fixed surface, which is positioned at a predetermined angle with respect to a reference surface of the optical base outside the effective diameter of the lens surface having the cylindrical axis of the cylindrical single lens. An optical head having a cylindrical axis angle determining unit for performing the operation. 2. The optical head according to claim 1, wherein the cylindrical axis angle determining portion of the cylindrical single lens is a substantially flat taper portion including at least one surface. 3. A cylindrical axis having a first lens surface having a positive power and a second lens surface having a negative power and having a cylindrical axis in a plane perpendicular to the optical axis of the second lens surface. An optical base having a cylindrical single lens having the same, and an optical base having at least two lens fixing surfaces for abutting and fixing a side surface of the cylindrical single lens parallel to the reference surface and orthogonal to each other to the separated light flux. Is an adjusting method for positioning the cylindrical single lens at a position where the cylindrical axis forms a predetermined angle with respect to the reference surface, and engaging means for engaging with the cylindrical axis angle determining unit of the cylindrical single lens. An adjusting method for an optical head, comprising: an engaging means and a rotating means for adjusting the rotation of the cylindrical single lens engaged with the engaging means.