JPS59175041A - Optical head device - Google Patents

Abstract

PURPOSE:To eliminate the generation of an offset even in the shift of a lens by shifting a half mirror and a total reflection mirror after fixing them to an objective and providing a means to detect the displacement to a pit. CONSTITUTION:A half mirror 3 is set opposite rectangularly to a total reflection mirror 10, and both lenses are fixed to an objective 4 and shifted together with the lens 4. The luminous flux sent from a light source is condensed to a piy 6, and the reflected light 7 is made incident to a detector 8. The lens 4 is fixed to mirrors 3 and 10 and shifted in case the lens 4 has a delta shift of the direction A to the flux 2 and irradiate correctly the pit 6. Therefore, the coincidence is obtained between the center luminous flux 7 reflected by the mirror 10 and the luminous flux 7' having no shift. Then these fluxes 7 and 7' reach a point C on a 2-split line of the detector 8. As a result, an offset is optically eliminated even in the shift of a lens.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an optical head device for optically writing and/or reading information, and in particular to an optical head device equipped with a tracking sensor for detecting the position of an information track on an optical disk. This invention relates to a head device.

2. Description of the Related Art Optical head devices for optical video disks, PCM audio disk devices, etc. that optically write and/or read information have been widely known.

FIG. 1 is a schematic diagram showing an optical system of a conventional optical head device. The optical head device is fixedly provided with a frimate light source 1 that emits a collimated light beam for detecting information signals and the like. From the collimated light source 1, a beam of light (in particular, the central beam is indicated by reference numeral 2) passes through a half mirror 3 and is focused by an objective lens 4 in the direction of, for example, a disk 5 as an information recording carrier. 5. A bit 6 is formed on the disk 5, and the light beam is reflected and diffracted by the bit and enters the objective lens 4 again. The luminous flux thus returning home (the central luminous flux is indicated by reference number 7) is
After passing through the objective lens 4, its optical path is bent by the half mirror 3, and then enters the two-split detector 8.

The detector shown here as an example is divided into two parts and has divided parts 8a and 8b. The sum output of the signal light incident on the detector 8 in this way is electrically processed and used as an information signal. In addition, in an actual rotating disk, the positional relationship between the bit 6 and the focused spot is not constant and varies relatively due to, for example, the eccentricity of the disk itself. A mechanism is required. As a method for this, there is a method in which the objective lens 4 is displaced in the direction of the arrow AB force by the actuator 9 to correct the position of the focused spot.

At that time, a tracking sensor is required to detect the positional deviation m of the bit in the arrow AB force direction, and in the optical head device shown in FIG.

This is done by detecting the asymmetry of the reflected analytical light from bit 6 incident on each of bits 8b, 21 and 22, respectively. That is, the divided portion 8a of the detector 8 divided into two
The tracking sensor output can be obtained by taking the difference between the outputs of 8b and 8b. In this way, the collimated light m1, the half mirror 3, and the photodetector 8 are fixedly attached to the optical head device, and the objective lens 4 is fixedly attached to the optical head device.
However, based on the tracking sensor output, the actuator 9
movably mounted.

Next, the operation of the tracking sensor of the conventional optical head device described above will be explained. FIG. 2 shows changes in the luminous flux distribution on the detector 8 due to changes in the positional relationship between the bit 6 and the focused spot in three cases (a), (b),
It is shown separately in (c). FIG. 3 is a graph showing the tracking sensor output corresponding to each case in FIG. First, as shown in FIG. 2(b), when the positional relationship between the bit 6 and the focused spot is symmetrical, the light analyzed by the bit 6 is also symmetrical. Therefore, the luminous flux distribution 21,22 on the detector 8 is also symmetrical as shown with respect to the bisecting line of the detector 8. Next, as shown in FIG. 2(a), when the bit 6 is slightly shifted in the A direction, the diffracted light becomes asymmetrical. Since the spot portion covering the bit 6 is subjected to stronger diffraction, the light flux distribution on the detector 8 is such that the light flux distribution 21 on the dividing portion 8a side is stronger than the light flux distribution 22 on the dividing portion 8b side. Conversely, if bit 6 deviates in the direction of arrow B compared to FIG. 2(b) as in the second factor (C), the light flux distribution of detector 8 is It becomes stronger than the part 8a side. Based on the principle described above, when the detector division parts 8a and 8b are differentially operated, a sensor output as shown in FIG. 3 can be obtained. Points a, b, and c in the figure are respectively (a), (b), and
The output for case (c) is shown. In this way,
When the spot and the bit are misaligned as shown in FIGS. 2(a> and (C)), the actuator 9 (FIG. 1) is driven by the servo mechanism using the sensor output shown in FIG. 3 as an error signal. By changing the digit of the lens, the relationship between the bit 6 and the focused spot was made symmetrical as shown in FIG. 2(b).

However, the tracking system of the conventional optical head device has a fundamental defect in that an offset occurs in the sensor characteristics when the objective lens 4 moves in the direction of arrow A or B. This drawback will be explained with reference to FIG. FIG. 4(a) shows a situation in which the bit 6 is correctly irradiated with the center line 31 of the objective lens 4 coinciding with the central beam 2 of the emitted light from the collimated light source 1, and FIG. 4(b) shows the situation where the bit 6 is correctly irradiated. A situation is shown in which the bit 6 is correctly irradiated with the center line 31 of the objective lens 4 displaced by δ from the central beam 2 of the emitted light from the collimated light source 1. Figure 4 (
In a), the reflected central beam 7 from the bit 6 reaches a point C on the bisecting line on the detector 8. On the other hand, Fig. 4 (
In b), the central luminous flux 2 is located between the lens center line 31 and δ
After being reflected from the bit 6, it returns to a point on the objective lens 4 that is separated from the central beam 2 by 2δ. After being further reflected by the half mirror 3, such a central light beam 7 reaches a point on the detector 8 which is 26 points away from the dividing line. Through the mechanism described above, the objective lens 4
When is moved, the diffracted light flux distribution on the detector 8 is moved by a distance @2δ in the direction perpendicular to the dividing line.

As a result, as can be seen from FIG. 4(b), the line of symmetry of the luminous flux on the detector 8 does not coincide with the two divided parts of the detector 8, and the sensor takes a differential between the divided parts 8a and 8b. An offset will occur in the output.

As described above, in conventional optical head devices, when the objective lens moves, an offset occurs in the sensor characteristics in principle. It was a hindrance.

An object of the present invention is to provide an optical head device that optically eliminates the above-mentioned offset and does not generate offset even when the lens is moved.

An embodiment of the present invention will be described below with reference to the drawings. Fifth
The figure is a schematic diagram showing an embodiment of the present invention, and the same parts as in FIG. 1 are designated by the same reference numerals, and the explanation thereof will be omitted. Simply put, in this embodiment, a half mirror 3 and a total reflection mirror 10 are arranged facing each other at a right angle, and are fixed to an objective lens 4.
It is configured to move together with the objective lens 4. Specifically, the half mirror 3 and the objective lens 4 are fixed via a support 11. half mirror 3
, total reflection mirrors 10 are fixed at right angles with their reflection surfaces facing each other. That is, the objective lens 4, the half mirror 3, and the total reflection mirror 1
0 are moved together by the actuator 9.

Briefly explaining the optical path from the collimated light source 1 to the detector 8, the light beam emitted from the collimated light N1 passes through the half mirror 3 and enters the objective lens 4. The light beam is condensed by the objective lens 4 and irradiated onto the bit 6, where it is reflected and diffracted, enters the objective lens 4 again, and is returned to a parallel light beam. The light beam is reflected by the half mirror 3, further reflected by the total reflection mirror 10, and enters the detector 8.

Next, the operation of the tracking sensor of the optical head device according to an embodiment of the present invention will be explained as shown in FIGS. 6(a) and 6(b).
This will be explained with reference to (c). First, FIG. 6(b) shows the center #! of the objective lens 4! This is a case where A31 and the central light beam 2 match, and corresponds to FIG. 2(b) shown in the conventional example. Figure 6(b).

The situation when the pit 6 is displaced in the direction of arrow A or B from the state shown in FIG. 6 (a) or FIG. 6 (
C), and these are the conventional example shown in FIG. 2(a) and
The situation is the same as in (C). Referring to FIG. 6(a), a case will be described in which the objective lens 4, half mirror 3, and total reflection mirror 10 move in six directions to correctly illuminate the pits 6. In this case, the objective lens 4, the half mirror 3, and the total reflection mirror 10 have moved by δ in the direction of the arrow, and the central light beams 2 and 7 are separated by 2δ on the objective lens 4. In the figure, dotted lines indicate the half mirror 3', the total reflection mirror 10', and the central light beam 7' before movement. As is clear from the figure, the central beam 7 that is 2.delta. away from the central beam 2 and exits from the objective lens 4 is reflected by the half mirror 3. but,
Since the half mirror 3 also moves by δ together with the objective lens 4, the central beam 7 reflected by the half mirror 3 is the same as the central beam 7' in the case of no movement (the central beam 7 in FIG. 6(b)).
(equivalent to). This central light beam 7 is further reflected by the total reflection mirror 10, but since the total reflection mirror 10 has also moved by δ,
The central beam 7 after reflection coincides with the central beam 7' in the case of no movement.

Therefore, the central beam 7 reaches a point C on the dividing line of the detector 802. On the other hand, as shown in FIG. 6(C), the objective lens 4, the half mirror 3, and the total reflection mirror 10 are
Even when moving by δ in the direction of arrow B, Fig. 6(a)
As in the case of , the central light beam 7 reaches the point C on the dividing line of the detector 8 .

FIG. 7 is a schematic diagram showing another embodiment of the invention.

In this embodiment, the half mirror 3 of the embodiment shown in FIGS. 5 and 6 is replaced with a half mirror joint surface 23 formed by joining the right angle prisms 12 and 13.
In addition, the total reflection mirror 10 is replaced with a total reflection mirror surface 30 formed on a surface perpendicular to the eight-point mirror joining surface 23 of the right-angle prism 13. Even in such a configuration, no offset occurs in the detector 8 as explained using FIG. 6.

FIG. 8 is a schematic diagram showing still another embodiment of the invention. In this embodiment, the collimated light source 1 and detector 8 of the embodiment shown in FIG. 7 are replaced by W. It can be understood from the reversibility of the optical path that the above-mentioned offset can be removed even in such a configuration. In this way, collimated light 8
! The fact that 1 and detector 8 can be replaced reversely means that
The same applies to the embodiment shown in FIG. 5 described above or the embodiment shown in FIG. 9 described below.

FIG. 9 is a schematic diagram showing yet another embodiment of the invention. In this example, three right angle prisms 12.13
．． 14, the half-mirror joint surfaces 23 of the prisms 12 and 13 constitute a half-mirror □ means, and the half-mirror joint surfaces 40 of the right-angle prisms 13 and 14 constitute a mirror means. Also,
A portion of the prism 13 is made into a total reflection mirror surface 15 by, for example, vapor deposition of a reflective metal, so as to send a central beam 7 to a detector 8 provided on the same side as the collimated light source 1, as shown. has been done. In this embodiment, the collimated light source 1 and the detector 8 can be arranged on the same side with respect to the objective lens 4.

As described above, according to the present invention, it is possible to optically compensate for the movement of the central light beam on the photodetector, which occurs with the conventional optical diameter, and it is possible to prevent the occurrence of offset of the tracking sensor, thereby making it possible to An optical head device that can extremely stably write and/or read information on a record carrier is obtained.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram showing an example of a conventional optical head device. FIG. 2 is a diagram showing the positional relationship between the pit and the focused spot in FIG. 1 and the luminous flux distribution on the detector. FIG. 3 is a graph showing the output of the tracking sensor corresponding to FIG. FIG. 4 is a diagram illustrating the offset that occurs on the detector when adjusting the position of the condensed spot of the optical head device of FIG. 1. FIG. 5 is a schematic diagram of an embodiment of the present invention. FIG. 6 is a diagram for explaining the offset compensation effect in the embodiment of FIG. 5. FIG. 7 is a schematic diagram showing another embodiment of the invention. FIG. 8 is a schematic diagram showing a rough example of the present invention. FIG. 9 is a schematic diagram showing still another embodiment of the present invention. In the figure, 1 is a collimated light source, 2.7 is a central luminous flux,
3 is a half mirror, 110 is a total reflection mirror, 4 is an objective lens, 5 is a disk, 6 is a bit, 8 is a detector, 9 is an actuator, 12, 13, 14 is a right angle prism, 23.
40 is a half mirror joint surface, and 15.30 is a total reflection mirror surface. Agent Shin Kuzuno - (1 other person) Figure 5 Figure 6 (a) (b) (C)B<
- Ichiga A Figure 7 Calculation 8 Figure 9 Self-motivated to write procedural amendment] Showa 5% June 22nd, Mr. Commissioner of the Patent Office 1, Indication of the case, 1986-58-5O No. 2, Name of the invention Optical head Apparatus 3, Representative Hitoshi Katayama of the person making the amendment Section 5, Claims column of the specification to be amended and Detailed explanation column 6 of the FIJj, Contents of the amendment (1) Claims attached. As of. (2) "Analyzed light" on page 5, line 18 of the specification is corrected to "diffracted light." (3) "Servo mechanism" in lines 15 and 16 of page 7 of the specification is corrected to "servo mechanism, although not particularly shown in FIG. 1." (4) Mei II, page 9, line 6: “It will occur.”
, and regardless of whether the center of the condensed spot and the center of the bit match, the servo til! structure produces an output that drives the lens. Correct it to J. (5) Meiji M, page 11 In the 6th and 7th lines, [Situation J when displaced is corrected to [Situation of luminous flux distribution on detector 8 when displaced]. (6) Detailed value on page 11, line 7 and line 8: “These are shown in Figure 6 (a) or Figure 6 (C), respectively.”
Delete. (7) "They are the same." on page 11, line 9 of the specification is corrected to "Since they are the same, illustrations are omitted." (1) An information record carrier including optically readable bits, a light source that generates light that is irradiated onto the information record carrier, and a lens that focuses the light from the light source onto the information record carrier. , an actuator that displaces the lens in a direction across the bit; and an actuator located on an optical path from the light source to the lens, from which light enters the lens and is irradiated onto the information recording carrier.
a half mirror means for separating the light reflected from the information recording carrier and emitted from the lens; and a half mirror means for receiving the light reflected from the information recording carrier and detecting the displacement of the lens with respect to the bit. divided light detection means, the light source, a half mirror means, a lens, an information recording carrier,
In an optical head device in which an optical path is formed that sequentially passes through a lens, a half-mirror means, and a photodetector, either an optical path from the light source to the half-mirror means or an optical path from the half-mirror means to the photodetector. a mirror means disposed on one side and having a reflective surface facing the reflective surface of the half mirror means at a right angle and changing the direction of the optical path by reflection; an optical head device which is fixed relative to said lens together with means and moves together with said lens; (2) The optical head device according to claim 1, wherein the half mirror means is a half mirror, and the mirror means is a total reflection mirror. (3) The optical head device according to claim 1, wherein the reflecting surface of the half mirror means and the reflecting surface of the mirror means are mutually orthogonal surfaces of u, 1(7)7-rhythm. (4) The reflecting surface of the half mirror means is the front 1LiL.
A half-mirror joint surface formed by joining another prism on one of the orthogonal surfaces of Yu J and Zuism,
The optical head device according to claim 3, wherein the reflective surface of the mirror means is a total reflection mirror surface formed on the other orthogonal surface of the first prism. (5) The reflecting surface of the half mirror means and the reflecting surface of the mirror means are each a half mirror joint surface formed by joining another prism on the orthogonal surface of the first Δ1 rhythm. The optical l\rad position described in item 3. (6) A total reflection mirror surface is formed on a part of the surface of the first prism, and the total reflection mirror surface reflects the light beam in the direction of the half mirror joint surface, and the light beam is transmitted through the half mirror joint surface. The optical head device according to claim 5, wherein the optical head device sends the luminous flux to a photodetector.

Claims (6)

[Claims] (1) an information record carrier including about one optically readable bit; a light source that generates light that is irradiated to the information record carrier; and a lens that focuses the light from the light source onto the information record carrier; an actuator that displaces the lens in a direction across the bit; and an actuator located on an optical path from the light source to the lens, from the light that enters the lens and irradiates the information recording carrier.
a half-mirror means for separating light reflected from the information recording carrier and emitted from the lens; and a light detection means for receiving the light reflected from the information recording carrier and detecting displacement of the lens with respect to the bit, The light source, a half mirror means, a lens, an information recording carrier,
In an optical head device in which an optical path is formed that sequentially passes through a lens, a half-mirror means, and a photodetector, an optical path from the light source to the half-mirror means and an optical path from the half-mirror means to the photodetector is provided. a mirror means disposed on either side, having a reflective surface facing at a right angle to the reflective surface of the half mirror means, and changing the course of the optical path by reflection; the mirror means: An optical head device that is fixed to the lens together with the half mirror means and moves together with the lens. (2) The optical head device according to claim 1, wherein the half mirror means is a half mirror, and the mirror means is a total reflection mirror. (3) The reflecting surface of the half mirror means and the reflecting surface of the mirror means are mutually orthogonal surfaces of the prism;
An optical head device according to claim 1. (4) The reflective surface of the half mirror means is a half mirror joint surface formed by joining another prism to one of the orthogonal surfaces of the prism, and the reflective surface of the mirror means is a The optical head device according to claim 3, wherein the optical head device is a total reflection mirror surface formed on the other orthogonal surface of the prism. (5) The reflective surface of the half mirror means and the reflective surface of the mirror means are each a half mirror joint surface formed by joining another prism on the orthogonal surface of the prism. The optical head device according to item 3. (6) A total reflection mirror surface is formed on a part of the surface of the prism, and the total reflection mirror surface reflects the light beam in the direction of the half mirror joint surface, and the light beam is transmitted through the half mirror joint surface. The optical head device according to claim 5, which transmits data to a photodetector.