JPS62177734A - Optical head - Google Patents

Abstract

PURPOSE:To make parts constituting an astigmatism system unnecessary by emitting a laser beam on the returning path obliquely to the side face of a beam splitter to generate astigmatism. CONSTITUTION:The exit light from a semiconductor laser 11 is focused on an optical disc D, and its return light is converged by a collimator lens 13 and is reflected on a beam splitter 12. A reflecting face 121 of the splitter 12 is inclined at an angle theta0 smaller than 45 deg. to the optical axis of the exit light from the laser 11, and the angle of the return light reflected on the reflecting face 121 is set to an acute angle theta1 (90 deg.>theta1>48.2 deg.) to said optical axis. The return light reflected on the reflecting face 121 is converged in only the direction parallel with the optical path of the going path by the side face of the splitter 12, and astigmatism occurs in the return light thereby,,and it reaches a photodetector 15 and is received and detected. Thus, optical parts constituting the astigmatism system are made unnecessary and the optical path length is shortened.

Description

[Detailed Description of the Invention] Industrial Application Field The present invention is applicable to the reproduction or recording of information signals such as audio and video.
Conventional technology related to optical heads that optically perform reproduction Conventionally, the optical system of an optical head has an optical axis between a semiconductor laser that emits a laser beam and an objective lens that converges the laser beam and focuses it on an optical disk. A cube-shaped beam splitter is installed above the beam, which deflects the return light from the optical disk by 90 degrees and guides it to a detection system equipped with a photodetector (
It is common to do this.

In this type of optical head, the optical axis of light emitted from the semiconductor laser is set in the SV line with respect to the optical disk surface.
The optical disc player is designed to be deflected 90 degrees through a 5-degree mirror and guided to an objective lens, and an optical disc player with a built-in optical nozzle is made thinner.

However, as described above, the returning light is deflected by 90 degrees through a beam splitter, resulting in beam splitting.

In the optical head, which forms the return path optical system that guides the light to the photodetector placed in a direction 90 degrees perpendicular to the light beam, the photodetector is attached to the long sword-shaped block that forms the outward path from the semiconductor laser to the objective lens. The optical path length between the beam splitter and the photodetector is sufficient to obtain a focal length of [- minutes and to improve detection sensitivity. This would result in a large optical system block.Also, the beam spot from the objective lens of the optical head should be set from the outermost recording trunk of the optical disk to the innermost recording track of the optical disk. To move in the L radial direction,
Sufficient movement space is required for the optical head to move back and forth, and when the disc player housing structure is miniaturized to the minimum size according to the disc diameter, the structure protrudes from the outer periphery of the optical disc, making the disc player device more compact. This is a hindrance to achieving this goal.

Therefore, as a measure for downsizing, the optical system of the optical head is constructed as shown in FIG. 4. In the optical system shown in FIG. 4, a laser beam emitted from a semiconductor laser 1 passes through a beam shifter 2 and is converted into a working beam via a collimator lens 3. This parallel beam reaches the objective lens 4 and focuses on the optical disk I] via the objective lens 4. And optical disc D
The beam splitter 2 is formed so that the optical axis in the backward direction, which reflects the return light from the beam splitter 2 through the beam splitter 2, is at an acute angle with respect to the forward optical axis. Therefore, the beam splitter 2 is formed into a modified pentagonal shape with one corner of the rectangular beam splitter cut out, and the returning light is guided perpendicularly to the cutout. A cylindrical lens 5 that produces astigmatism in this return path optical axis direction
When in just focus (in focus), a circle?
, a four-split photodetector 6 is disposed at a position where the astigmatism caused by the lens 5 becomes a perfect circle.

In this way, the return path that forms the photodetection system is provided at an angle with respect to the outbound path, and the optical head is miniaturized, and the optical head is moved back and forth parallel to the direction of the return path to move the outbound optical system block. It has been proposed to reduce the size of the optical disc player by configuring the space to be in the shape of a rectangular rectangle so that the moving space does not protrude from the outer periphery of the optical disc.

Problems to be Solved by the Invention However, the above-mentioned optical head
There are two methods for processing ivy into a modified pentagonal shape, but the processing is difficult and unsuitable for mass production, and the processing cost increases by the amount of processing, resulting in high costs.

In addition, since the structure uses an optical component such as a cylindrical lens to generate astigmatism and detect a focus error, an optical component for generating astigmatism is required. If a cylindrical lens is used as this component, in order to make the image formed on the photodetector a perfect circle when the image is just focused, a predetermined distance τ must be set as the return optical path length.
shall be. In order to improve the focus error detection sensitivity, a magnifying optical component is required, and the distance to the destination detector becomes larger. For this reason, the structure has not always been fully satisfactory in terms of reducing the size and cost of the optical head.

The present invention was made in view of the above points, and it is possible to make the return optical axis of the laser beam at an acute angle with respect to the outgoing optical axis, and to detect a focus error due to astigmatism without using optical parts such as a cylindrical lens. The purpose of this is to reduce the size and cost of the optical head main body.

In order to achieve an objective that is more than just a means to solve the problem, the present invention aims to direct a laser beam emitted from a semiconductor laser to an objective lens through a collimator lens that converts it into a parallel beam, and to convert the laser beam into a parallel beam through the objective lens. A beam splitter is provided between the semiconductor laser and the collimator lens, and a beam splitter is provided between the semiconductor laser and the collimator lens, and the beam splitter focuses the light on the optical disk and directs the return light from the optical disk to a return path different from the outbound path from the single conductor laser. At the throat, a photodetector is installed in the return direction guided by the optical system to detect the optical modulation signal.
The optical axis of the laser beam traveling on the return trip is made to be oblique to the optical axis of the return trip at an acute angle, and the optical axis is adjusted so that astigmatism occurs due to the laser beam passing through the beam spot on the return trip. was configured.

According to the present invention, the return light from the optical disk is converged via the collimator lens, reflected by the beam blur and the reflective surface, and guided on the return path to the photodetector. At this time, the returning laser beam is emitted with its leading axis inclined with respect to the side surface of the beam splitter, obliquely obliquely at an acute angle with respect to the optical axis, and is emitted as refracted light. As a result, astigmatism occurs in the laser beam on the return path, and the laser beam is focused on the photodetector, thereby detecting a focus error using the astigmatism method.

Therefore, there is no need for an optical component such as a cylindrical lens for producing astigmatism in the returning laser beam. In addition, the optical path length from the beam splitter to the photodetector is minimized, and the size of the lateral protrusion from the optical head to the photodetector is reduced to 1 minute while maintaining sufficient focus error detection sensitivity. Can be set small.

Embodiments Hereinafter, embodiments of the present invention will be described with reference to the drawings.

1 and 2 show the basic optical system of the optical head according to the present invention. A collimator lens 13 converts the laser beam into a parallel beam, an objective lens 14 converges the laser beam converted into a parallel beam and focuses it on the optical disk D, and a beam splitter 12 converts the returned light from the optical disk D. Light detection Z15 arranged in the direction of guiding through
It is roughly composed of.

The beam splitter 12 disposed on the optical path between the semiconductor laser 11 and the collimator lens 13 has a reflective surface 121 of the beam splitter 12 at an angle of less than 45 degrees with respect to the optical axis of the emitted light of the semiconductor laser 11. The angle O1 between the outgoing optical axis of the laser beam and the incoming optical axis of the return light reflected on the reflective surface 121 of the beam splitter 12 is smaller than 90 degrees, and the beam splitter 12 is formed from 90 degrees. Critical angle I of prism (41°8°)
(90°〉θl
〉90°−I (41,8°)=48.2°). Therefore, the beam splitter 12 uses triangular prisms 122 and 123 in the shape of a right triangle, in which one side parallel to the outgoing optical axis is longer than the one side perpendicular to the outgoing optical axis.
They are integrally formed so that the outer surfaces facing each other are parallel to each other. Further, the prism 123 located on the side facing the photodetector 15 is formed of a triangular prism in the shape of a right triangle that is similar in shape and size to the other prism 122 and is larger than the other prism 122, and is located on the side facing the semiconductor laser 11. The beam splitter 12 is formed by extending the corner portion further from the end of the prism 122, and as shown in the figure, the beam splitter 12 has a shape in which the return optical axis side protrudes greatly. By doing this, all of the returning laser beam reflected by the reflective surface 121 of the beam splitter 12 is reliably emitted from the long-side side surface 124 of the triangular prism 123 of the beam splitter 12, and light leaking from the splitter is prevented. It disappears.

The return light that is converged through the collimator lens 13 and reflected through the beam splitter 12 is incident on one side surface 124 of the beam splitter 12 at an angle smaller than the critical angle and larger than 0 degrees, and is refracted. It is emitted. At this time, the converging backward laser beam is converged only in a direction parallel to the forward optical axis on the side surface 124 of the beam splitter 12, and this causes astigmatism in the backward laser beam. The laser beam with this astigmatism reaches the photodetector 15 and is detected. This photodetector 15 is a photodetector in which the photodetecting section is divided into four parts, and the optical axis is the center of division, and the dividing line is 45
It is constructed at an angle. When the focus of the beam spot converged by the objective lens 14 is just in focus with respect to the optical disk D, the beam spot focused on the photodetector 15 is arranged at a position where it becomes a perfect circle. As a result, depending on the distance of the optical disk D with respect to the objective lens 14, an image is formed on the photodetector 15 as an elliptical spot with different vertical and horizontal directions, and a focus error is detected.

Each photodetector section 151, 152. of the photodetector 15 divided into four parts.
If the respective detected amounts of 153.154 are A, B, C, and D, then the diagonals are (A+C)-(B+D). A focus error signal is detected by differentially amplifying the sum of the amounts of light detected by the detection section. And (A+B)-(C
A tracking error signal is detected by taking the difference in the amount of light detected by the left and right detection sections as shown in +D). The objective lens actuator supporting the objective lens 14 is controlled by the focus error signal and the tracking error signal, and the objective lens 12 is servoed. As a result, the beam spot of the laser beam is controlled to follow the recording focus surface of the optical disk D correctly.

Then, the total sum (A+B
+C+D), detection of the lff raw RF signal is performed.

In this way, it is possible to generate astigmatism in the returning laser beam and detect a focus error signal using the astigmatism method without providing an optical component such as a cylindrical lens that causes astigmatism.

Further, since there is no need to dispose an optical component between the beam splitter 12 and the photodetector 15, the optical path length from the beam splitter 12 to the photodetector 15 can be shortened to perform photodetection. Furthermore, the laser beam on the return path emitted from the beam splitter 12 is refracted and the angle with the optical axis on the outgoing path becomes smaller, and it can be brought closer to the optical axis side on the outgoing path. The size of the protruding portion of the block of the photodetection system on the return path can be made smaller than that of the optical system block forming the outward path. Therefore, the main body of the optical head can be downsized. Furthermore, beam splitter 1
2 is composed of two triangular prisms, which can be easily processed and mass-produced, and because optical parts that cause astigmatism are not required, costs can be reduced.

FIG. 3 shows another embodiment of the optical head according to the present invention. In the figure, the same parts as in the embodiment described above are denoted by the same reference numerals, and detailed description thereof will be omitted.

In FIG. 3, the beam subwoofer 12 disposed on the optical path between the semiconductor laser 11 and the collimator lens 13 includes a triangular prism 122 in the form of a right isosceles triangle;
The semiconductor laser 1 is integrated with the triangular prism 122 and the triangular prism 123 whose diagonals are obtuse.
It is formed into a trapezoidal shape in which two surfaces perpendicular to the optical axis of light emitted from the device are parallel to each other.

As a result, on the optical axis of the return path where the return light from the optical disk D is polarized at right angles to the reflective surface 121 of the beam splitter 12, the angle of incidence on the side surface 124 of the beam splitter 12 in the prism exit direction is changed. It is made to be smaller than the critical angle I. Astigmatism is thereby produced in the laser beam on the return path emitted via the beam splitter 12, and light detection is performed by the astigmatism method. That is, light detection is performed by the photodetector 15 disposed in the direction in which the laser beam is emitted from the prism 12, and focus error signal detection is performed using the astigmatism method.

Even if the beam splitter 12 is formed as shown in FIG. 3, the protrusion rjk of the optical head from the beam splitter to the photodetector can be made sufficiently small, and the cost and size can be reduced. Of course, it is possible to achieve this.

In the above-described embodiment, the objective lens 15 is aligned in a straight line parallel to the optical axis direction emitted from the semiconductor laser 11.
In the explanation above, a 45-degree mirror is installed in the optical axis direction of the hF conductor laser, and the laser beam is irradiated at a 90-degree angle by this mirror.
The present invention can also be applied to an optical system having a structure in which the optical system is reflected and guided to the objective lens 14.In practice, when constructing an optical system, the optical system can be used as an optical disk.
When placed on a horizontal opto base in line with NI, it becomes optical.

This would be of great benefit in making the card smaller and thinner. In that case, it is better to adopt the configuration of the above embodiment.

In addition, in the -1 two-legged embodiment, a 1-beam type optical head was explained, but the present invention is also applicable to a so-called 3-beam type optical head.As described in detail of the invention, According to the optical head of the present invention, when the returning laser beam reflected on the reflective surface of the beam splitter is emitted from the beam splitter, it is emitted at an angle with respect to the side surface of the beam splitter. This action can produce astigmatism.

Therefore, there is no need to separately provide optical parts constituting the astigmatism system, the number of parts can be reduced, and at the same time, the length of the optical path to the photodetector can be shortened to the minimum.

Furthermore, since the return optical axis is oblique to the outgoing optical axis at an acute angle, the amount of protrusion of the photodetection system block from the main body can be minimized. Therefore, the optical head body can be made smaller and
Cost reduction can be achieved.

In addition, when the above-mentioned optical configuration is applied to an optical disc player, the return optical axis is oblique to the outgoing optical axis at an acute angle, and when linearly feeding, the optical disc is moved in a direction perpendicular to the radial direction of the optical disc. Instead, only diagonal feeding obliquely intersecting the radial direction of the disk parallel to the return optical axis is possible, which minimizes the occupied plane area and allows the player to be stored in the player with the highest efficiency.

[Brief explanation of drawings]

FIG. 1 is an optical system diagram showing the optical system of the optical head according to the present invention, FIG. 2 is an exploded perspective view showing the main parts thereof, and FIG. 3 is an optical system diagram showing the optical system of another embodiment according to the present invention. , 4th
The figure is an optical system diagram of an optical system showing a conventional example. DESCRIPTION OF SYMBOLS 11... Semiconductor laser, 12... Beam splitter, 13... Collimator lens, 14... Objective lens, 15... Photodetector, D... Optical disk. Patent applicant Nippon Electric Hot, Electronics Co., Ltd.;2

Claims (1)

[Claims] (1) A laser beam emitted from a semiconductor laser is guided to an objective lens through a collimator lens that converts it into a parallel beam, and is focused on an optical disk through this objective lens, and the return light from this optical disk is directed to the semiconductor laser. A beam splitter is provided between the semiconductor laser and the collimator lens to guide the laser to a return path different from the forward path, and a photodetector is provided in the direction of the return path guided via the beam splitter to detect the optical modulation signal. In the optical head, the optical axis of the laser beam reflected by the beam splitter and traveling in the backward path is made to be oblique at an acute angle to the optical axis of the laser beam traveling in the forward path, and the laser beam traveling in the backward path is An optical head characterized in that astigmatism is caused by passing through the beam splitter.