JPS62257635A - Optical head - Google Patents

Abstract

PURPOSE:To obtain a small-sized and light weight optical head simplified in constitution and to reduce an access time by constituting incorporatedly a light source, an objective lens, a light split member and a photodetector. CONSTITUTION:An optical head 5 is constituted incorporately by a light source 61 generating converging light, an objective lens 18 collecting the light emitted from the light source 6 onto an information storage medium 1 having tracks, a light split member 65 splitting the light led from an objective lens 18 via the information storage medium 1 into light to detect the out of focus to the medium 1 and into the light to detect the deviation to the track of the light led to the medium 1 and a photodetector 14 converting the split light by the light split member into an electric signal by a support member. Since each section of the optical system is constituted incorporatedly, miniaturization is attained and the weight is reduced.

Description

[Detailed Description of the Invention] [Object of the Invention] (Industrial Application Field) The present invention relates to a memory device such as an additionally recordable compact disc, a video disc, or an erasable computer output memory. The present invention relates to an optical head that is applied to a laser card, etc., and is applied to an information recording/reproducing device for recording and reproducing at least information on an information storage medium using focused light.

(Prior art) =a, an optical head used in an optical disk device or the like converts laser light emitted from a semiconductor laser into a collimating lens (condensing lens), a polarizing beam splitter, and a polarizing beam splitter.
After successively passing through a 74-wavelength plate, the laser beam is focused by an objective lens onto an information storage medium (optical disk) having spiral or concentric tracks, and the laser beam reflected from this information storage medium is passed through the objective lens and a 174-wavelength plate. , a polarizing beam splitter, and a light projecting lens (condensing lens), the light is converted into an electrical signal by a photodetector and output. As a result, the output from the photodetector is used to read information recorded on the information storage medium, detect defocus of the objective lens on the information storage medium, and detect track deviation on the information storage medium. There is.

However, in the above-mentioned optical head, the semiconductor laser and the photodetector are provided at separate positions, so that the laser light guided from the semiconductor laser to the information storage medium and the laser light guided from the information storage medium to the photodetector are different. The disadvantage is that most of the laser light travels through optical paths consisting of components, making the optical head large and heavy. For this reason, there is a drawback that the access time of an optical disk device using this optical head becomes long.

(Problems to be Solved by the Invention) This invention eliminates the disadvantages of being large and heavy and requiring a long access time, and it is possible to simplify the configuration and make it smaller and lighter. An object of the present invention is to provide an optical head that can shorten access time.

[Structure of the Invention] (Means for Solving the Problems) The optical head of the present invention includes a light source that generates divergent light;
An objective lens is provided near the light source to focus light emitted from the light source onto an information storage medium having a track, and the objective lens is provided in the vicinity of the light source to direct the light guided from the objective lens through the information storage medium to the information storage medium. A light splitting member that splits light into light for detecting defocus and light for detecting a shift of the light guided to the information storage medium with respect to the track, and an electric A photodetector that converts into a signal is integrally formed with a support member, and the entire component moves to prevent track deviation.
It is designed to correct defocus.

(Function) In the present invention, a light source, an objective lens, a light splitting member, and a photodetector are integrated.

(Example) An example of the present invention will be described below with reference to FIGS. 1 to 4.

FIG. 4 shows an information recording and reproducing apparatus according to the present invention. In this figure, 1 is a disk-shaped information storage medium, which is placed on a turntable 3 that is rotationally driven by a drive shaft 2. and is pressed down by a pressing member 4 from above.

The information storage medium 1 has a recording area on at least one side thereof, which is provided with a recording layer on which information can be recorded, reproduced, and erased using a laser beam or the like. In this recording area, a tracking guide (track) by a pre-group is formed in a spiral shape or a concentric circle shape.

An optical head 5 is provided below the information storage medium 1, and is attached to a slide portion 7 provided on a fixed portion 6 so as to be slidable along the radial direction of the information storage medium 1.

Furthermore, the optical head 5 is movable in the vertical direction with respect to the slide portion 7 (the direction of approaching or moving away from the information storage medium 1).

Then, for access at the start of recording, reproducing, and erasing information, CPJJ8 creates a program for moving the optical head 5.
An optical head movement drive circuit 10 is operated via the D/A converter 9 to move the entire optical head 5 in the direction of arrow a in the figure.

Also, when accessing, the number of tracking guides provided on the information storage medium 1 is counted, and this causes the optical head 5 to
The current location of is now confirmed. That is, the output signal of the track deviation detection circuit 11 is
2, and when the optical head 5 crosses one tracking guide, one pulse is generated from the binarization circuit 12, and the number of pulses is counted by the counter 13 for counting the number of tracks. It has become.

Furthermore, after the access is completed, track deviation correction is started. That is, the photodetector 1 inside the optical head 5 will be described later.
The photoelectric signals obtained from 4 are sent to preamplifier array 1, respectively.
5 and is supplied to the track deviation detection circuit 11 via the arithmetic circuit 16, whereby a track deviation detection signal is obtained.

Then, when the analog switch 17 is activated, the signal is supplied to the optical head movement drive circuit 10,
As a result, the entire optical head 5 is moved to perform track deviation correction.

As mentioned above, the objective lens 1 is provided in the optical head 5.
8 is provided, and this objective lens 18 is integrated with the optical head 5, and the entire optical head 5 can also be moved in the vertical direction (the axial direction of the objective lens 18), that is, in the uniaxial direction toward and away from the information storage medium 1. It becomes. The focal position of the objective lens 18 is moved by moving the entire optical head 5 in the direction indicated by the arrow in the figure by an optical head moving drive circuit 20 in response to a signal from a defocus detection circuit 19, which will be described later. . Further, just before the defocus servo loop is closed, the analog switch 21 is switched, thereby activating the automatic retracting circuit 22 and moving the optical head 5, that is, the objective lens 18 to the initial position.

Further, the recording optical ffi setting section 24 outputs a recording signal according to the information recorded on the information storage medium 1, which is supplied from an external device (not shown) via the interface 32 and the recording signal processing circuit 23. light for reproduction.
The setting section 25 is for outputting an erasure signal, and is used for reproducing light! The setting section 26 outputs a reproduced signal, and the analog switch 27 switches the signals from each of the setting sections described above under the control of the CPU and outputs the signals to the laser light drive circuit 28. Note that 29 is an information signal reading circuit, 30 is a binarization circuit, 31 is a reproduced signal processing circuit that performs modulation, demodulation, error correction, etc. of the information signal, and 32 is an interface circuit.

The first factor schematically shows the optical head 5. The optical system shown in FIG. 1 is a multi-beam optical system that can form a plurality of focused spots on the information storage medium 1 when focusing, and one of them is used for recording and reproduction on the information storage medium 1. 1 to form a circular condensed spot, and another one for erasing to form an elliptical condensed spot on the information storage medium 1. That is, as shown in FIG. 2, the semiconductor laser array (light source) 61 includes a recording/reproducing semiconductor laser 61a that generates a recording/reproducing laser beam 1a and an erasing laser beam 1. -b. The semiconductor laser 61 for recording and recycling of this semiconductor laser array 61
The recording/reproducing laser beam La emitted from the laser beam a and the erasing laser beam Lb emitted from the erasing semiconductor laser 61b enter the prism section 63 as divergent light. The laser beam entrance surface of this prism portion 63 is a vertical surface 63a perpendicular to the optical axis. The erasing laser beam Lb generated from the front side of the semiconductor laser array 61 is transmitted to a beam state conversion member 61 constituted by a cylindrical lens.
1 allows the beam traveling direction or spot size to be changed. Thereby, the divergence and convergence states of the erasing laser beam Lb in one axis direction (a certain specific direction) are changed, and an elliptical focused spot is formed on the information storage medium 1. The beam state conversion member 611 is arranged near the exit of the light emitting point of the erasing laser beam Lb.

Almost 100% of the laser beams 1a and 1b incident on the vertical surface 63a of the prism section 63 are reflected by the polarized beam splitting surface 64 provided on the other surface of the prism section 63, and 1
The light passes through the /4 wavelength plate 70 and becomes circularly polarized light. After passing through the objective lens 18, this circularly polarized light is focused on the information storage medium 1.

The objective lens 18 has an aspherical entrance surface and an exit surface, and is made of a single optical component such as glass or plastic.

The recording and reproducing laser beam 1a emitted from the recording and reproducing semiconductor laser 61a of the semiconductor laser array 61 and the erasing laser beam Lb emitted from the erasing semiconductor laser 61b have a divergence angle β as shown in FIG. The direction parallel to the page (trajectory shown by a solid line) is different from the direction perpendicular to the page (trajectory shown by a broken line). Correspondingly, objective lens 1
The aspherical curved surfaces 18a and 18b of No. 8 can also be used to store information by changing their curvatures in the direction parallel to the page of FIG. The convergence angle α on the medium 1 is equal in the direction parallel to the plane of the paper and in the direction perpendicular to the plane of the paper. For this reason, the recording and reproducing laser beam 1
A is designed so that a substantially circular focused spot can be obtained on the information storage medium 1.

The divergence angle β of the recording and reproducing laser beam 1-a is usually ±
In contrast, in order to obtain a sufficiently small focused spot on the information storage medium 1, the convergence angle α is as narrow as 10 to ±20 degrees.
needs to be made larger. For this reason, the quarter wavelength plate 70
The aspherical curved surface 18b of the objective lens 18 after passing through changes the concave lens curvature and widens the divergence angle to a larger extent. Thereby, the curvature of the concave lens is changed in a direction parallel to and perpendicular to the plane of the paper in accordance with the difference in the divergence angle β of the recording and reproducing laser beams La, and the degree to which the divergence angle β is widened is changed.

Thereafter, the aspherical curved surface 18a of the objective lens 18 has a convex lens effect and changes the recording/reproducing laser beam 1a and the erasing laser beam 1b into convergent light. The ratio α/β of the divergence angle β and the convergence angle α at this time approximately indicates the imaging lateral magnification.

Laser beams La and Lb focused on the information storage medium 1
is reflected on this information storage medium 1 and is reflected again on the objective lens 1.
8. After passing through the 1/4 wavelength plate 70, the light enters the prism section 63 and returns to the polarized beam splitting surface 64. Here, the laser beam La.

1b travels back and forth through the 1/4 wavelength plate 70, so that the shooting direction is 9 compared to when the polarized beam is reflected by the split surface 64.
It becomes a linear leaking light rotated in the 0 degree direction. Therefore, the laser beams La and Lb returned to the polarized beam splitting surface 64 pass through this polarized beam splitting surface 64, and the light separating and reflecting member 65 that exists behind it and is superimposed on the polarized beam splitting surface 64. The light-reflecting planes 65a1, which are two light-reflecting surfaces adjacent to each other with inclinations, are too late to reach the light-reflecting cylindrical surface 65b. The laser beam reflected by the light reflecting member 65 passes through the polarized beam splitting surface 64 again and heads toward the photodetector 14.

Among the recording and reproducing laser beams 1a, a light reflective plane 6
The light reflected by 5a becomes a laser beam Lf for detecting defocus, and as shown in FIG. 2, it is focused between light detection cells 66a and 66b for detecting defocus when in focus. Further, the light reflected by the light reflective cylindrical surface 65b becomes a laser beam Lt for detecting track deviation, and when the light is focused, a light detection cell 67 for detecting track deviation on the photodetector 14 as shown in FIG.
a, 67b are irradiated. Since the light reflection between the light reflective plane 65a and the light reflective cylindrical surface 65b utilizes total reflection, a gap 65c for total reflection is provided on the rear side.

Note that the detection sensitivity of the defocus detection by the defocus detection laser beam Lf is proportional to the modulation ratio α/β of the information storage medium 1 onto the photodetector 14. Therefore, the objective lens 18 having an optical image with a large value of imaging lateral magnification α/β is also useful for improving the sensitivity of defocus detection.

The mechanical frame that holds each of the optical components described above is composed of a semiconductor element mount stand 68 that supports the semiconductor laser array 61 and the photodetector 14, and an optical component mount frame 71 that houses the remaining optical components. . The joint between the two is sealed with a hermetic seal 72 to protect the semiconductor element from environmental resistance. The inner wall of the optical component mounting frame 71 is machined with high mechanical precision, so that each optical component can be assembled by simply fitting. As a result, by using the structure shown in FIG. 1, the optical head 5 can be significantly downsized, with a diameter of φA-φ7 mm and a length of B=1.
It can be set to about 0 mm.

The structure of the photodetector 14 will be explained using FIG. 2. That is, the defocus detection principle uses the so-called Knifezi method, and the defocus detection laser beam If is focused on the photodetector 14 at a focused point. In addition, when the distance between the objective lens 18 and the information storage medium 1 becomes too close due to the out-of-focus condition, the defocus detection laser beam if
The light focusing position of is shifted to the rear of the photodetector 14, and the defocus detection light detection cell 66k) is mainly irradiated with the defocus detection laser light.

Conversely, when the distance between the objective lens 18 and the information storage medium 1 increases, the focal position of the laser beam If for defocus detection shifts to the front of the photodetector 14, and the light detection cell 66a for defocus detection shifts. The out-of-focus detection laser light is irradiated more towards the camera.

However, the amount of defocus became too large and the objective lens 18
When the distance between the information storage medium 1 and the information storage medium 1 becomes further, the focal position of the defocus detection laser beam 66f shifts significantly,
For example, it may shift to the γ point shown in FIG. Then, as shown in FIG. 3(b), the spot state of the laser beam on the photodetector 14 is more exposed to the defocus detection cell 66b. In this state, the objective lens 18
The situation remains the same as when the two are too close. Therefore, in order to distinguish between the above state and the state in which the objective lens 18 is out of focus and slightly approaches the information storage medium 1, a light detection cell 69 for detecting an abnormality as shown in FIG. 3 is provided. be.

Therefore, either one of the 2fi type laser beams Lf and Lt is detected by the out-of-focus or track deviation light detection cell 66.
a, 66b, 67a, 67b and reaches the abnormality detection light detection cell 69 arranged around them, it is assumed that the focus has become significantly out of focus, the defocus correction is temporarily interrupted, and the focus is refocused. Try searching for the location again. When defocus and track deviation are detected by each of the photodetection cells 66a, 66b, 67a, and 67b. Correction is made by moving the entire optical head 1 up and down and left and right.

In addition, 14 photodetection cells 66a, 66b, 6 of the photodetector
The portion other than 7a and 67b is a non-sensing area 14a.

A prism 81 and a photodetector 82 are provided on the back side of the semiconductor laser array 61 to adjust the amount of laser light 1a, lb emitted by the semiconductor laser array 61. Since this light emission amount control is explained in Japanese Patent Application No. 61-40710, the details thereof will be omitted here.

Further, the semiconductor element mount table 68 includes a photodetector 1.
While taking out the output of 4.82, the semiconductor laser 61a
, 61 drive signals are supplied to the electrical terminal connector 68a.
is provided.

Next, a method of assembling and adjusting the optical system shown in FIG. 1 will be explained. That is, the important part during adjustment is the occurrence of comatic aberration in the objective lens 18 due to the deviation of the optical axis. For this reason, as described above, a frame is created with high precision and each optical component is fitted into the frame. Therefore, if the light emitting point of the semiconductor laser array 61 is set at the ideal position,
This ensures that coma aberration does not occur.

For this reason, first, the far field pattern of the laser beams La and Lb emitted from the semiconductor laser array 61 is measured, and those whose patterns have an asymmetric intensity distribution are rejected as defective products. Next, a mirror is placed near the position where the information storage medium 1 is to be set through a transparent substrate having birefringence, and the mirror is moved up and down. During focusing, a portion of the laser light returns to the semiconductor laser array 61 through the transparent substrate with birefringence, making the light emission of the semiconductor laser array 61 unstable. As a result, noise is added to the light emission from the semiconductor laser array 61, and when the light is unstable, it is considered to be in focus.

As shown in FIG. 1, there are three directions in which the semiconductor element mount table 68 can be adjusted: X, Y, and .theta..

That is, by moving in the above-mentioned X direction, the light amount ratio between the laser beam lf for defocus detection and the laser beam Lt for tracking deviation detection can be changed. By moving in the Y direction, the optical detection cells 67a and 67b for detecting track deviation are
The upper track deviation detection laser beam Lt moves. In this case, the center of rotation of the semiconductor element mount table 68 is made to coincide with the recording/reproducing laser light emitting point of the semiconductor laser array 61. Furthermore, when the semiconductor element mount base 68 is rotated in the θ direction, the defocus detection photodetection cell 6
A defocus detection laser beam moves on 6a and 66b.

In addition, in order to prevent the track deviation detection system from being adversely affected during rotation in the θ direction, a photodetection cell 67a for tracking deviation detection,
The boundary line between the areas 67b and 67b has a structure in which an arc is drawn around the recording/reproducing laser emission point. Therefore, X-
Adjustment is completed by simply moving in the Y-θ direction. Finally, a piece of the information storage medium 1 that can be moved vertically and horizontally is placed at the position of the information storage medium 1 for confirmation. As a result, the fragments of the information storage medium 1 are moved up and down using the defocus detection signal, and a servo for defocus correction is applied. Further, the fragments of the information storage medium 1 are further shaken left and right, and the state of the track deviation detection signal is checked.

Therefore, except when erasing information on the information storage medium 1, that is, when recording or reproducing, the recording and reproducing semiconductor laser 6
Only 1a lights up, and each cell 66a, 66b of the photodetector 14
, 67a, 67b are irradiated with only the recording and reproducing laser beam la, which is used for defocus detection and track deviation detection.

As described above, since each part of the optical system is integrally constructed, the optical system can be miniaturized.

Furthermore, since the number of optical parts is reduced, that is, no collimator lens is used, the ml can be reduced, and the overall weight can be reduced. This speeds up the access of the information recording/reproducing device and shortens the access time.

In addition, in the above embodiment, a light source that generates a laser beam for recording and reproduction and a laser beam for erasing was explained, but the present invention is not limited to this. The same operation as described above can be carried out when using a light source changed to a recording laser.

In addition, although we have explained the case where a light reflective plane and a light reflective cylindrical surface are used as the light reflective surface, the invention is not limited to this, and an aspherical reflective surface is used, and an astigmatism method is used to detect defocus. You can do it like this.

[Effects of the Invention] As described in detail above, according to the present invention, it is possible to provide an optical head which can be made smaller and lighter by simplifying the structure, and which can shorten the access time due to the lighter weight.

[Brief explanation of drawings]

The drawings show an embodiment of the present invention, in which Fig. 1 is a sectional view showing the overall configuration of an optical head, Fig. 2 is a plan view showing a semiconductor laser array and a photodetector, and Fig. 3 is a photodetector. FIG. 4 is a plan view showing the structure of the device, and FIG. 4 is a block diagram showing the straight path structure of the information recording/reproducing apparatus. 1a... Laser light for recording and reproduction, 1b... Laser light for erasing, 1... Information storage medium, 14... Photodetector,
18... Objective lens, 61... Semiconductor laser array (light source), 61a... Recording and reproducing laser, 61b...
. . . Erasing laser, 65 . . . Light separation and reflection member (light division member), 65a . Detection cells, 67a, 67b... Light detection cells for detecting track deviation. Applicant's agent Patent attorney Takeshi Suzue Guo 1 Figure

Claims (10)

[Claims] (1) a light source that generates diverging light; an objective lens that focuses the light emitted from the light source onto an information storage medium having a track; Light splitting that splits the light guided through the medium into light for detecting defocus with respect to the information storage medium and light for detecting a shift of the light guided to the information storage medium with respect to the track. What is claimed is: 1. An optical head comprising: a member; and a photodetector that converts the light split by the light splitting member into an electrical signal, and each of the above parts is integrally formed by a support member. (2) The optical head according to claim 1, wherein the diverging light from the light source has a circular shape. (3) The optical head according to claim 1, wherein the light splitting member has a polarizing surface and a light reflecting surface. (4) The light splitting member is divided into a plurality of surfaces in which either one of the polarizing surface and the light reflecting surface is inclined at different angles from each other. optical head. (5) The optical head according to claim 1, wherein the objective lens expands the diverging light from the light source into light with a wide divergence angle, and then converts it into convergent light. . (6) The optical head according to claim 1, wherein one surface of the objective lens is constituted by an aspherical lens having asymmetrical points. (7) The optical head according to claim 1, wherein the two curved surfaces of the objective lens have different curvatures. (8) The optical head according to claim 1, wherein each of the above-mentioned parts is constituted by an external frame consisting of an optical component mount stand and a semiconductor element mount stand. (9) A light source and a photodetector are built in the optical component mounting frame, and an objective lens and a light splitting member are built in the semiconductor element mount base. optical head. (10) The optical head according to claim 8, wherein a hermetic seal is formed between the optical component mounting frame and the semiconductor element mounting stand.