JPH0237532A - Optical head device - Google Patents

Abstract

PURPOSE:To obtain a device equipped with a simple tilt detecting mechanism with a few number of components by utilizing an unrequired light beam out of the emitting light beams of a semiconductor laser, and making it incident on a convergence lens via a diffraction grating. CONSTITUTION:The diffraction gratings 90-1 and 90-2 are arranged in the unrequired light beams 8-1 and 8-2, and the light beams are passed through an aperture limiting means 7 by changing the progressive direction of them, and are set as the light beams for detecting tilt on an optical disk 6 as convergence spots 17-1 and 17-2. Since the spots 17-1 and 17-2 irradiate a position different from that of a spot 9 for recording and reproduction, the light beam for detecting tilt reflected from a disk 6 is image-formed at a different position, and is received at the area (14a-14d) of an optical detector 14. In such a way, inclination between the disk 6 and the optical axis of the convergence lens 5 is detected as a tilt signal 51. Therefore, it is possible to perform tilt detection with a few number of components and with simple structure without using another light source such as a LED, etc.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an optical head device used for recording/reproducing information on an optical information storage medium, and particularly relates to an optical head device used for recording/reproducing information on an optical information storage medium, and in particular, the present invention relates to an optical head device used for recording/reproducing information on an optical information storage medium. The present invention relates to an optical head device including means for detecting a relative angle between an axis and a recording surface of a storage medium.

[Conventional technology]

FIG. 6 shows a conventional optical head device. In FIG. 6 (a), a light beam (2) emitted from a semiconductor laser light source (hereinafter referred to as LD) (1), which is a light source, is diffracted by a diffraction grating (3). , a seven-plate beam splitter (4) that separates the beam into three beams reflects the light beam and makes it enter the condenser lens (5). (6) is an optical information storage medium (hereinafter referred to as an optical disk) that is covered near the convergence point of the light beam transmitted through the condenser lens (5), and (80) is an information string stored on the optical disk (6). An information recording surface (27)K is formed of tracks. (25) is the substrate of the optical disk (6),
The photodetector (10) receives the light beam [11] reflected by the disk (6)K and transmitted through the condenser lens (5) and the beam splitter (4), and photoelectrically converts it. (13)(
12') is a subtracter, (16) is an adder, (18) (19
) is a phase compensation circuit, focusing actuator (2
0) drives the condenser lens (5) in the optical axis direction C±t). The tracking actuator (21) is a condenser lens (
5) in the direction C±X) across the track (8). (2G) is a motor that rotates the optical disk (6);
(40) is the optical axis.

After being reflected by the surface of the beam sliver (4), three light spots (
The light is focused as 9a) (9e) (9f). A line connecting the centers of the three light spots (9a), (9e), and (9f) is positioned so as to be slightly inclined with respect to the direction of the track (80). The light thus focused on the information surface of the optical disk (6) is reflected, passes through the condensing lens (5) again, and then passes through the beam splitter (4), thereby eliminating astigmatism. photodetector (10) with given
incident on . When the light-condensing spot (9a) on the disk (6) is in focus, the photodetector (10) is positioned in the optical axis direction where the central beam (Ila), that is, the reflected luminous flux of the O-order diffracted light, has a circle of least confusion. placed in position. Photodetector (l
O) has a six-divided configuration as shown in the same figure (b), and the part that receives the central beam (11a) is ((transfer)(Bl).
(C) (Dl K It is divided into 4 parts.

In addition, the parts that receive the beams (11+1 (11f) on both sides are independent detectors (El (Fl).As is well known, K, the output of both side detectors fEl (Fl) is subtracted
By differentially calculating (EF) with (E-F), the positional deviation in the X direction between the center slot (9a') and the track (80) can be detected (tracking error signal). The tracking error signal is applied to the tracking actuator (21) K through an appropriate phase compensation circuit (18), and the condenser lens (5) is moved in a direction perpendicular to the track (8) (
±X direction) to drive the slot) (9a) to the track (
8) is used to correct the position in the center.

Furthermore, the output of the center quadrant detector is the diagonal component (Al(C
1 and (Bl (Di) are differentially calculated as (A + C) - (BlD) by the subtractor (12),
It is possible to detect the focus shift (9a) (focus error signal). This defocus detection method is called the astigmatism method, and when the spot on the disk (6) is in focus, the spot on the detector, which is approximately circular with a circle of least confusion, as shown by (lla), is on the disk. According to the distance and near focus shifts in (6), the deformation into an elongated ellipse in directions A, C and directions B and D, as shown by the broken lines, is converted into an electrical output.

The focus error signal is applied to the focusing actuator (2o) through a suitable phase compensation circuit (19), and is used to drive the condenser lens (5) in the optical axis direction (±2 directions) to correct the focus shift. .

Also, the sum output VHF from the adder (16) K of the 4-split detector obtained as the optical disc rotates is the sum output VHF of the optical disc (
6) is processed and used by a circuit (not shown) in the subsequent stage.

In the conventional optical head device, when recording/reproducing information is performed through the substrate (25) 7 as described above,
) may be warped or tilted when attached to the motor (26), so that the disc information surface (27) may no longer be perpendicular to the optical axis of the condenser lens (5). Typically the thickness l,
25 The dragon-sized substrate (25) is incorporated into the V-lens design as an element of the objective lens together with the condenser lens (5), but as mentioned above, if the substrate (25) is tilted, coma aberration will occur. There is a problem in that crosstalk from adjacent tracks (81) and (82) to the track (80) that should originally be recorded/reproduced increases. This phenomenon has been a major problem, particularly in optical video discs on which analog signals are recorded, deteriorating the image quality. In the conventional optical head device, in order to solve the above-mentioned problem, the perpendicularity of the condenser lens optical axis (40) and the substrate (25) was ensured by a tilt serge.

An example of a conventional tilt sensor will be described below with reference to FIG. In the figure, the sixth
The optical head device shown in the figure holds an optical system. The head housing (33) is rotated about a pivot point (34), and the pivot point (34) is supported by a support (35). The rotating shaft (37) of the motor (36) is processed into a salt screw shape and connected to the casing (33). (30) is the housing (33
) is a light emitting diode (LED) placed on the top surface of the information recording surface (27), and emits a light beam as shown by an arrow toward the information recording surface (27).

(3n, (32) is a photodetector, with the LED in between
They are arranged in one row in the direction (direction perpendicular to the track). (38) is a subtracter, and (39) is a phase compensation circuit.

Next, the operation of the conventional tilt servo will be explained. L
The light beam emitted from the ED (30) hits the information recording surface (27).
) and enters the photodetector (31''1.(32)) symmetrically placed on both sides of the LED (30'l).

The outputs of the photodetectors (31) and (32) are subtracted by a subtracter (38) as (32)-(31). The amount of light incident on the photodetectors (31) and (32) is set so that it is equal to the optical axis (40) of the condenser lens (5) shown in Fig. 6 when the substrate (25) is vertical. ing. Therefore, when the substrate (25) is tilted about the Y direction as shown in FIG. 8, the amount of light incident on the photodetectors (31) and (32) becomes unbalanced. Therefore, the output of the subtracter (38) changes between positive and negative depending on the tilt of the substrate (25) (tilt sensor). The output of the subtracter (38) is passed through a suitable phase compensator (
K is applied to the motor (36) through the screw (37)
), the housing (33) is rotated around the rotation fulcrum (34).

In conventional optical head devices, the occurrence of negative signals as described above is minimized to prevent an increase in crosstalk from adjacent tracks.

[Problem to be solved by the invention]

In the conventional optical head device as described above, the light emitted from the LED is received by a pair of photodetectors, and the tilt sensor output is obtained by differential calculation of the outputs of the photodetectors. However, this has caused the following problems.

■Additional optical components such as LEDs and photodetectors are required, which increases costs.

(2) There is not much space between the top surface of the casing and the substrate (25), and the arrangement of the LED and photodetector is a major constraint on the design of the optical head device.

This invention was made to solve the above problems, and it provides an optical head device that can obtain tilt sensor output without using a separate light source such as an LED in the conventional recording/reproducing optical system. ■The purpose is to obtain.

[Means to solve the problem]

The optical head device according to the present invention uses unnecessary light beams other than the effective light beams used for reproduction and recording out of the light beams emitted from the LD, uses the unnecessary light beams as light beams for a tilt sensor, and uses diffraction to change the traveling direction of the unnecessary light beams. By making the unnecessary light beam incident on the condensing lens using the grating means, it is reproduced on the optical disk.
The tilt sensor light beam is irradiated to a position different from the recording spot.

[For production]

In this invention, a light beam for tilt detection is obtained without using a separate light source such as an LED, and is irradiated onto the optical disk, and the reflected light beam is received to detect the tilt of the optical disk.

〔Example〕

A first embodiment of the present invention will be described below with reference to FIGS. 1 and 2. An aperture limiting means (7) is arranged close to the condenser lens (5). (8-1) (8-2) are unnecessary light beams, (3) is a diffraction grating, (3a) is a conventional diffraction grating area, (90-1) (90-2) is arranged in the unnecessary light beam. (14) is the second diffraction grating area for tilt detection.
It is a photodetector. Other parts and configurations are the same as the conventional device. Also play/record.

The focus and tracking servo mechanisms are the same as those of the conventional device, and illustrations of actuators, arithmetic circuits, etc. are omitted.

Here, the tilt detection method will be explained. The light flux emitted from the LD (1) is a divergent light flux with a Gaussian distribution with a full width half-width of approximately 20' to 40'';
uses only a part of the luminous flux (referred to as the effective luminous flux).

The effective luminous flux (2) is a luminous flux determined by the aperture limiting means (7) out of the diverging luminous flux of the LD (1), and typically has a full angle of spread of only 10'' to 15''. Therefore, other unnecessary light has traditionally not been used.

In this embodiment, diffraction gratings (90-) (90-2) are arranged in the unnecessary light beams (8-1) (8-2) to change the traveling direction of some of the unnecessary light beams, and the aperture limiting means ( 7) Press to pass. In FIG. 2, the diffraction grating (3) is the diffraction grating (3a) for the tracking sensor described in the conventional example, and the diffraction grating (90-) (90-) for the tilt sensor of the present invention.
-2) are formed in the same plane.

The effective light flux (2) passes through the grating area (3a), and the unnecessary light flux (8-
1 (8-2), each first-order diffracted light is changed in direction of propagation from the incident light and transmitted through the aperture limiting means (7). 1st
In the figure, this light flux (8-1) (8-F) is condensed onto the optical disk (6) by a condensing lens (5) (1)
7-) (17-2) and used as a light beam for tilt detection.

The focused spots (17-1) (1 2) are irradiated to a different position from the focused spot (9) for reproduction/recording.

Therefore, each reflected light beam from the optical disk (6) is imaged at a different position, and the tilt detection light beam is focused on the photodetector (
14). Then, the light beam (8-1) is sent to the two-divided detection area (1←a) (14-b).
2”1 is the two-divided detection area (14-CI (14-d)
The light is received by each. When the optical disk (6) is directly aligned with the optical axis of the condenser lens (5), the amount of received light of the tilt detection light beam (8-1) is in the areas (14a'l and (14b)).
The photodetector (14) is arranged so that the amount of light beam (8-2) received is equal in the areas (14C) and (x4d).

In FIG. 1, when the optical disk (6) is tilted with the y-axis as the rotation axis, the tilt detection light beam (8-N (8-2) moves in the ±X direction on the photodetector (14). Therefore, Arithmetic processing ((1
4a) + (14c)) - ((14b) + (14d))
By applying this, the tilt of the optical disc (S) 7) can be detected as a tilt signal (51).

In this way, the second diffraction grating (90-1) (90-2) is inserted into the unnecessary light beam of LD (1), which has not been used in the past.
By simply arranging the above, tilt detection can be achieved without using a separate light source such as an LED.

In the first embodiment, in order to obtain the tilt detection signal (51), the second optical detection signal is set to K when the optical disc (6) is not tilted, and K so that the output of the tilt detection signal (51) is zero. I had to adjust the position of the container (14).

Therefore, it was necessary to have a position adjustment mechanism independent of the first photodetector (10) for reproduction.

Therefore, as the second implementation issue, we will discuss the first. An example in which the second photodetectors (10) and (14) can be integrally fixed and configured on the same substrate will be described with reference to FIGS. 3 and 4. As shown in FIG. 4, the second diffraction grating (90-1) is made so that its grating period gradually changes depending on the position (in two directions). In the same figure (at), the unnecessary light (8-1) emitted from the LD (1) is diffracted by 00 degrees from the grating region (90-1'lK. Here, the 1st diffraction grating (3) K is adjusted in position in two directions. A device (55) is attached, as shown in the same figure (bl).
For example, when the diffraction grating (3) is moved in the −2 direction, the light beam (8-1) enters a region with a small grating period, producing a large diffraction angle θ1. That is, cl>θ0. on the other hand,
As shown in the same figure (cl), when the diffraction grating (3) is slightly moved in the +2 direction, the light beam (8-1") enters the grating region (90-1, a region with a large grating period, and the diffraction angle θ2 is θ
becomes smaller than 0.

As mentioned above, the grating period K differs depending on the location, and by providing the position adjustment mechanism (55) in the direction perpendicular to the grating direction, it is possible to adjust the diffraction angle of the unnecessary beam (8-1). can.

In Fig. 3, adjusting the diffraction angle of the unnecessary beam (8-1) means adjusting the angle of incidence on the condenser lens (5) and the position of the spot on the photodetector (14) in the ±X direction. i, 14
! I will be able to do it. In Figure 3, the tilt detection light flux is (
8-1), and the tilt detection signal (51
) is given by the calculation output of ((14-a)-(14-b)). In the first embodiment, a photodetector (toro ±
However, in this embodiment, the offset of the tilt detection signal (51) when the optical disk inclination angle is zero can be adjusted by adjusting the position of the diffraction mirror (3). As a result, 1. By integrally forming the second photodetectors (1G) and (14), for example, on the same semiconductor substrate, it is possible to realize miniaturization of the device. Also, in this second embodiment, the lattice region (
3a) may be set to a size such that all of the effective light beam (2) passes through the grating region (3a) even after the above adjustment, and there is no effect on the reproduction/recording characteristics.

Furthermore, in the first and second embodiments, a diffraction grating can be obtained and tilt detection sensitivity can be improved.

〔Effect of the invention〕

As described above, according to the present invention, the light beam of the part of the divergent light from the LD that is not used for reproduction/recording is used as the light beam for tilt detection without using a separate light source such as an LED.
This has the advantage that the device can be manufactured at a low cost, the number of parts can be reduced, and an optical head device equipped with a tilt detection mechanism of a simple structure can be obtained.

[Brief explanation of the drawing]

Figure 1 is an elevational view of the main part of the first embodiment of this invention, Figure 2 is a side view (a) and front view (b) of the diffraction grating in Figure 1, and Figure 3 is a second embodiment. An elevation view of the main part of the example, Figure 4 is the 3rd
5 is a partial side view of the deformation of the diffraction grating in the above embodiment, and FIG. 6 is a perspective view of (a) main parts of a conventional optical head device. (b) Detector connection diagram, FIG. 7 is a partial elevational view of the one shown in FIG. 6, and FIG. 8 is a partial elevational view for explaining the operation of the one shown in FIG. (1)-〇 Semiconductor laser light source, (2)・Φ divergent luminous flux, (
3) Diffraction grating consisting of first diffraction grating means (3a) and second diffraction grating means (90-1) (90-2), (4
)... Beam splitter (separation means), (5)... Condensing lens (condensing means), (6)... Information storage medium, (7)
・・Aperture limiting means, (8-1 (8-2)・Fist-free light flux,
(10) (14)... 1st. second photodetector, (40)
...Optical axis, (5N--Tilt signal (relative angle detection signal)
. In each figure, the same reference numerals indicate the same or corresponding parts. Boru 1 Figure 2: Sale 51: @Karaku Luo Reception Ifu Te (b)

Claims (1)

[Scope of Claims] A semiconductor laser light source that emits a diverging light beam, a first diffraction grating means that separates the light beam emitted from this light source into three light beams,
a condensing means for condensing and irradiating the three light beams onto the information storage medium; an aperture limiting means for restricting the aperture of the incident light beam to the condensing means; and a separation of the reflected light beam from the information storage medium from the output light beam. In an optical head device having a separation means and a first photodetector that receives the reflected light beam, unnecessary light beams other than the effective light beam that passes through the aperture restriction means and enters the condensing means among the output light beams are provided. a second diffraction grating means disposed in the light beam to change the traveling direction of a part of the unnecessary light beam and make it incident on the aperture limiting means; and reflection of the unnecessary light beam incident on the aperture limiting means from the information storage medium. 1. An optical head device comprising: a second photodetector that receives a light beam, and obtains an output of detecting a relative angle between the optical axis of the light condensing means and the information surface of the information storage medium.