JPH0242640A - Optical head structure - Google Patents

Abstract

PURPOSE:To miniaturize the title structure and to reduce the weight without wasting a detected light interrupted with a knife edge by composing a turning means of the total reflecting surface of a prism provided in the optical path of the detected light and composing a knife edge means of the boundary peripheral part of the total reflecting surface. CONSTITUTION:The title structure is provided with the turning means to turn a part of a detected light 8 in a different direction, the knife edge means provided on one of optical paths for detecting a focus error condition, etc. The turning means is composed of a total reflecting surface 16 of a prism 15 provided in the optical path of the detected light 8, and the knife edge means is composed of a boundary peripheral part 17 of the total reflecting surface 16. Thus, since the turning means and knife edge means can be provided on the single prism 15, a part of the detected light cannot by interrupted by the knife edge means, and the optical head can be miniaturized and, simultaneously reduced in weight.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] <Industrial Application Field> The present invention relates to an optical head structure, and particularly to an optical head structure that can be made smaller and lighter in weight.

<Prior Art> Conventionally, high-density recording and reproducing apparatuses perform recording and reproducing by irradiating convergent light onto the recording surface of an optical disk as an optical head type recording medium and detecting the reflected light. There is. The optical disks used in this device generally have some warpage or distortion, as well as eccentricity due to errors in mounting the optical disk to the rotating shaft. Therefore,
In order to make the optical head follow the fine recording tracks of the optical disk without being affected by these, the position of the optical head is controlled by detecting each error in focus and tracking of the optical head.

As the detection light for each error detection, there is a type in which the direction of the reflected light from the optical disk is changed by a polarizing beam splitter, and this changed detection light is further divided into two directions through a half prism. Half of the detected light on one side is blocked by a knife edge, and the so-called knife edge method is used to detect, for example, two detection lights for focus error detection.
The focus is placed on the dividing line of the divided photodiode. In other words, if there is a shift in the focus direction, the focal position shifts to the front or back of the photodiode, so it is difficult to focus the light on one of the two split photodiodes and easily detect the shift. can. Also,
The other detection light separated by the half prism is focused on a dividing line of, for example, a two-split photodiode for tracking error detection. In this case as well, if there is a shift in the tracking direction, there will be a difference in brightness between the left and right sides of the condensing section, so the shift can be detected based on the difference in the output of the two-split photodiode.

According to the above structure, one of the detection lights split by the half prism is detected for focus error using a knife, but since half of the light beam incident on the focusing photodiode is blocked by the knife, the blocked light beam is is a waste. Also, half prism,
Since the optical head and two sets of photodiodes are provided separately, there are many parts and many parts to remove, and the optical head becomes larger and weighs more, which makes it disadvantageous to achieve a high-speed address. The problem arises.

<Problems to be Solved by the Invention> In view of the problems of the prior art, the main object of the present invention is to provide an optical head structure that uses the knife method to detect focus errors. It is an object of the present invention to provide an optical head structure that can be made smaller and lighter without wasting the blocked detection light.

[Structure 1 of the Invention <Means for Solving the Problems> According to the present invention, the object is to optically detect an error state in either tracking or focusing of an optical head. a first light-receiving element disposed in an optical path of light; a deflecting means for deflecting a portion of the detected light in a different direction; and optically detecting an error state in either tracking or focusing. an optical head having a second light receiving element disposed in the optical path of the deflected detection light to detect the focus error state; and a knife means disposed in either of the optical paths to detect the focus error state. In the optical structure, the deflection means comprises a total reflection surface of a prism provided in the optical path of the detection light, and the knife means comprises a boundary edge of the total reflection surface. This is achieved by providing a head structure.

In this way, by using the knife means consisting of the boundary edge of the total reflection surface of a prism having a total reflection surface for deflecting a part of the detected light, the 4-cass error can be solved by the knife method. In addition, since the direction changing means and the knife means can be provided in one prism, the number of parts and the number of parts for mounting them can be reduced, and a part of the detected light can be blocked by the knife means. Therefore, there is no wasted portion of the detection light.

<Embodiments> Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

FIG. 1 is a schematic diagram showing the main parts of an optical head to which the present invention is applied. As shown in FIG. 1, a polarizing beam splitter 2, a polarizing beam splitter 2,
and a λ/4 plate 3 are provided.

By the way, the output light 1 that has passed through the polarizing beam splitter 2
After passing through the λ/4 plate 3, it is reflected by the optical disk to become reflected light 4, which passes through the λ/4 plate 3 again and enters the polarizing beam splitter 2. In this case, the plane of polarization of reflected light 4 is different from the plane of polarization of output light 1 by 90 degrees. Therefore, the direction of the refracted light 4 is changed within the polarizing beam splitter 2 and is emitted as detection light 8 from the right side of the polarizing beam splitter 2 in the figure.

A condenser lens 6 and a photometric sensor 7 are coaxially arranged on the optical axis of the detection light 8, and the detection light 8 is arranged coaxially to detect errors in focus and tracking.
The light is condensed by a condensing lens 6 onto a photometric sensor 7 as convergent light. Although each of the components from the semiconductor ray 'f to the optical disk are arranged on the optical axis of the emitted light 1, the direction of the optical axis can be changed freely by arranging a mirror or the like on the optical axis. , the arrangement of each is not limited.

FIG. 2 is a side sectional view of the photometric sensor 7, and FIG. 3 is a side sectional view of the photometric sensor 7.
It is a diagram seen along the ■-m line in the figure. As shown in FIGS. 2 and 3, a photodiode 13 as a light receiving element for tracking error detection and a photodiode 14 as a light receiving element for focus error detection are integrated on the substrate 9 of the photometric sensor 7. It is set up as follows. A photodiode 13 for tracking error detection is placed in the optical path of the detection light 8, and a photodiode 14 for focus error detection is placed at a predetermined distance from the photodiode 13.

As shown in FIG. 3, each of these photodiodes 13 and 14 is constituted by a photodiode element divided into four parts by mutually orthogonal dividing lines. The tracking photodiode 13 is arranged so that one dividing line is orthogonal to the direction in which the optical axis of the detection light 8 shifts in the event of a tracking error, and the focusing photodiode 14 is arranged so that one dividing line is perpendicular to the direction in which the optical axis of the detection light 8 shifts in the event of a tracking error. is arranged so as to be located on an extension of the dividing line of the photodiode 13.

As shown in FIG. 2, a prism 15 is fixed on the substrate 9. The prism 15 has a parallelogram side cross section, covers only the photodiode 14 with its bottom surface 15a, and extends obliquely from the photodiode 14 side toward above the photodiode 13. The half of the luminous flux of the detection light 8 on the photodiode 14 side is made to enter the prism 15. Further, a surface 16 extending from the bottom surface 15a to the edge 17 of the extending end portion is formed at an angle such that the incident angle of the detection light 8 that enters the prism 15 and reaches 1016 is a critical angle or more. Detection light 8 reaching 16
forms a total reflection surface. The edge 17 of the surface 16 of the prism 15 serves as an edge in the Knifezi method that blocks half of the luminous flux, and the cross section of the reflected light totally reflected at the surface 16 is divided into half-moon shapes.

In this way, half of the detection light 8 is directly focused on the tracking photodiode 13 without being blocked by the prism 15, and the remaining half is focused on the opposing surface 25 parallel to the surface 16. After being reflected, the light is focused on the intersection of both dividing lines of the focusing photodiode 14. Note that each of the photodiodes 13 and 14 is electrically connected to a control circuit (not shown) via a lead wire (not shown) extending from the substrate 9.

Next, the procedure for detecting each error in tracking and focusing by each photodiode 13 and 14 will be described below.

As shown in FIG. 4, half of the detection light 8 is focused on the photodiode 13 in a half-moon shape as shown by the imaginary line, and if a tracking error occurs, it will be focused in the left and right direction in the figure. This results in a difference in light amount in either of the two cases.゛Also, from each photodiode element, detection signals E to 1 corresponding to each irradiation pattern are expressed as (E0F> and (G
+t-(>) is input to each amplifier 19.20, and the output value from each amplifier 19.20 is input to amplifier 21. Then, by amplifier 21, for example, from (E+F) (G + l) is subtracted and the calculated value is output to the control circuit.Therefore, if a tracking error occurs, the direction and error distance can be easily detected.

In addition, in FIG. 5, in the prism 15, the surface 16
The remaining half of the detection light 8 that was totally reflected and redirected at the opposite surface 25 is shown by an imaginary line on the intersection of the dividing lines of the four-divided photodiode 14. It is almost focused so that it is 7S-like, and
This shows a state where no focus error has occurred. Similarly to the above, detection signals A-D corresponding to each ζ irradiation pattern from each photodiode element of the photodiode 14 are inputted to each amplifier 22 and 23 so as to be divided into (A+B) and (C+D), respectively. Furthermore, each amplifier 22.2
The output value from 3 is input to the amplifier 24. and,
For example, the amplifier 24 subtracts (C0D> from (He1B>) and outputs the calculated value to the control circuit.

Note that the light beam for focusing is transmitted through the prism 1 as described above.
The cross section is divided into half-moon shapes by the edge 17 of the surface 16 of 5 and the surface 16.

When the focus changes and, for example, the focal position is in front of the photodiode 14, the light is concentrated in a half-moon shape on one side of the diodes 41 to 14 (upper half side in the figure), as shown in FIG. The focal point is the photodiode 14.
If it is located further back, as shown in FIG. 7, the light is focused on the other side of the photodiode 14 (lower half side in the figure). Therefore, when a focus error occurs, the direction and error can be determined by the output difference between (A+B> and (C+D>) of the detection signals of each pair of diode elements of the photodiode 14, similar to the so-called Naifezi method. m can be easily detected.The tracking signal is the sum of detection signals t to 1-1 of tracking photodiode]3 (
It can be detected by using E1F10+t-1>.

Furthermore, according to this embodiment, since the photodiodes for detecting errors in focus and tracking are provided on one substrate, wiring to the photodiodes is simplified and noise resistance can be improved. In addition, since the front shaft adjustment only needs to be done at one location, there is an effect that the adjustment time can be shortened.

Further, FIG. 8 shows a second embodiment of the invention based on the present invention.
3, the same parts as those in the previous embodiment are given the same reference numerals, and detailed explanation thereof will be omitted. This second
In the embodiment, the bottom surface 15a of the prism 15 is provided so as not to cover the photodiode 14, and the opposing surface 26 facing the surface 16 is not parallel to the surface 16, and the surface 16 is not parallel to the surface 16. The detection light 8 that has been totally reflected and redirected is emitted from the opposing surface 26 toward the outside of the prism 15 and is refracted in a direction to be focused on the photodiode 14. According to this second embodiment, the prism 15 can be made more compact.

Incidentally, the procedure for detecting each error by each photodiode 13, 14 is the same as that in the previous embodiment, so the explanation thereof will be omitted.

By the way, each of the photodiodes 13 and 14 is a four-divided photodiode, but the photodiode 13 is divided into (E1F> and (G+H)), and the photodiode 14 is divided into (A+B) and (C1D). A two-split photodiode may be used.Also, the photodiodes 13 and 14 may be replaced with each other. In this case, half of the detection light 8 is directly used for focus error detection. However, by focusing the remaining half of the redirected detection light 8 in the middle of its optical path and using the virtual image for tracking error detection,
Each error detection can be performed.

[Effects of the Invention] According to the present invention, errors in either tracking or focusing can be detected by the detection light whose direction is changed on the total reflection surface of the prism having the knife means for detecting focus errors. Since a part of the detection light is not blocked, there is no wasted part of the detection light. Furthermore, since the total reflection surface of the prism is used to change the direction of a portion of the detected light, there is no need to form a reflective film or the like as a direction changing means, and thus component costs can be reduced. Furthermore, since the direction changing means and the knife means are formed by one prism, the number of parts and the number of mounting points can be reduced, the optical head can be made smaller and lighter, and high-speed access is possible. , the effect is extremely large.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing the main parts of an optical head to which the present invention is applied. FIG. 2 is a side sectional view of the photometric sensor. FIG. 3 is a sectional view taken along the line ■-■ in FIG. 2. FIG. 4 is a schematic circuit diagram showing how to detect a tracking error. 5 to 7 are schematic circuit diagrams showing the focus error detection procedure. FIG. 8 is a diagram corresponding to FIG. 2 showing the second embodiment. 1... Outgoing light 2... Polarizing beam splitter 3... λ/4 plate 4... Reflected light 6... Condensing lens 7... Photometry sensor 8... Detection light
9...Substrate 13.14...Photodiode

Claims (1)

[Claims] a first light-receiving element disposed in the optical path of the detection light to optically detect an error state in either tracking or focusing of the optical head; and a first light-receiving element for redirecting a portion of the detection light in a different direction. a second light-receiving element disposed in the optical path of the deflected detection light for optically detecting an error state in either tracking or focusing; and a knife edge means provided in either of the optical paths for detecting the detection light, wherein the deflection means includes a knife edge means provided in either of the optical paths for detecting the detection light, wherein the deflection means directs the detection light from the total reflection surface of the prism provided in the optical path of the detection light. The optical head structure is characterized in that the knife edge means consists of a boundary edge of the total reflection surface.