JPH0337837A - Tilt detector for optical disk - Google Patents

Abstract

PURPOSE:To attain the miniaturization and lighten the weight of an optical head by simplifying constitution by forming diffracted light by providing a diffraction grating for tilt beam formation at the signal detection optical system of an optical disk, and using the diffracted light in tilt detection. CONSTITUTION:A laser beam 24 is made incident on a diffraction grating 26 for tracking beam formation, and 0th-order light emitted from the grating 26 is further made incident on the diffraction grating 28 for tilt beam formation, then, a tilt beam is formed. Beam groups emitted from the gratings 26 and 28 are made incident on the recording plane of a disk 18. Reflected light from the disk 18 is reflected on a half mirror 30, and is made incident on an octopartite photodetector 36. Photodetectors (g) and (h) for tilt are arranged at the detector 36 in a radial direction. The reflected light from the disk is received with the detectors (g) and (h), respectively. A tilt error detection signal can be obtained by subtracting the light reception signals of the detectors (g) and (h) with a subtractor, then, it is used in tilt servo. By employing such constitution, no means such as a LED for the formation of the tilt beam, etc., is required.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention is aimed at preventing tilt errors (the optical axis of the optical head relative to the disk surface) in optical disk devices such as CDs (compact discs) and LDs (laser vision discs). The present invention relates to a tilt detection device for detecting tilt errors, and achieves tilt error detection with a simple configuration.

[Conventional technology]

In optical disc devices such as CD players and LV players, the center of the objective lens of the optical head is designed to be perpendicular to the disc. However, if the disk is warped into an umbrella shape, even if the amount is small, the relationship between the disk and the objective lens is no longer perpendicular, which has a serious effect on the signal reading performance of the optical head (crosstalk interference). etc.).

In order to prevent such inconveniences, a tilt servo is provided to adjust the tilt of the entire optical head. In the conventional tilt servo, a tilt sensor 10 as shown in FIG. 2 is attached to the optical head in order to detect tilt errors.

The tilt sensor 10 is configured to irradiate a disk 18 with light rays emitted from an LED 12 and to receive the reflected light by photodiodes 16 provided on both sides of the LED 12. If the optical axis of the optical head is not tilted with respect to the disk 18, the amounts of light received by the photodiodes 14 and 16 are the same, but if there is a tilt, there will be a difference in the amount of light received. Therefore, by controlling the tilt angle of the optical head according to this difference, the optical axis of the optical head is always kept perpendicular to the disk surface.

[Problem to be solved by the invention]

According to the conventional tilt detection device, the tilt sensor 10 shown in FIG. 2 must be provided separately from the optical disk signal detection optical system, which increases the number of parts and is disadvantageous in reducing the size and weight of the optical head.

The second invention aims to solve these problems in the conventional technology and provide an optical disc tilt detection device that achieves tilt detection with a simple configuration and reduces the size and weight of the optical head. be.

[Means to solve the problem]

This invention relates to a tilt beam forming diffraction grating that is provided in a signal detection optical system of an optical disk and forms diffracted light in the disk radial direction and irradiates the disk surface with the diffraction grating, and a tilt light receiving device that detects the disk reflected light of the diffracted light. The device includes a tilt error detection means for detecting a tilt error based on the detection output of the tilt light receiving element.

[For production]

According to this invention, the signal detection beam is incident on the tilt beam forming diffraction grating to form diffracted light in the disk radial direction, and this diffracted light is irradiated onto the disk surface as a tilt beam. Then, the reflected light is received by the tilt light receiving element, and a tilt error is detected by the tilt error detection means based on the detection output of the light receiving element.

According to this, a diffraction grating for forming a tilt beam is provided in the signal detection optical system of an optical disk to form a diffracted light, and this diffracted light is used as a tilt beam for tilt detection. This eliminates the need for means such as LEDs, simplifies the configuration, and allows the optical head to be made smaller and lighter.

〔Example〕

An embodiment of this invention is shown in FIG. In the optical head 20, a laser beam 24 emitted from a laser diode 22 is incident on a tracking beam forming diffraction grating 26 to form a tracking beam. The zero-order light output from the diffraction grating 26 is further incident on the tilt beam forming diffraction grating 28 to form a tilt beam.

The grating pattern of the tilt beam forming diffraction grating 28 is formed at right angles to the grating pattern of the tracking beam forming diffraction grating 26. These diffraction gratings 26.28
In addition to arranging individual gratings with their grating patterns at right angles, it is also possible to form an integral structure by forming diffraction gratings 26 and 28 on the front and back surfaces of a flat glass body 27, respectively, as shown in FIG. can.

The tilt-forming diffraction grating 28 has a size that allows the light beam to pass through, and the grating patterns of the two diffraction gratings 26 and 28 have a beam spot interval on the disk of 20 to 20 degrees with respect to the information reading beam spot. The thickness is adjusted to about 30 μm.

The grating pattern of the diffraction gratings 26 and 28 can be formed into a volume phase type groove in which irregularities are formed on two flat glass bodies, as shown in FIG. 4, for example.

The pitch of the grating depends on the sunspot distance of the objective lens 34 and collimator lens 32, the wavelength used by the laser diode, the distance between the diffraction grating 26, 28 and the light emitting point, etc., but if the wavelength used is 0.78 μm, it is around 20 μm. . Further, the duty of the unevenness is approximately a:b-1:1.

The diffracted light formed by the diffraction gratings 26 and 28 is shown enlarged in FIG. The zero-order light when the first-order light of the diffraction grating 26 is diffracted again by the diffraction grating 28 is indicated by "0-0". Similarly, the 0th order light (tracking beam) when the +1st order light and the -1st order light of the diffraction grating 26 are diffracted again by the diffraction grating 28 are shown as "+1-0" and "-1-0", respectively. In addition, the diffraction grating 26
+1st order light when the 0th order light of is diffracted by the diffraction grating 28.

The primary light (tilt beam) is "0-+1" and "0-" respectively.
Shown at -1°.

The beam group outputted from the diffraction gratings 26 and 28 is irradiated onto the recording surface of the disk 18 via a half mirror 30, a collimator lens 32, and an objective lens 34, which constitute a signal detection optical system. The state of irradiation of the beam group onto the recording surface of the disk 18 is shown in an enlarged scale in FIG. The 0-0 order light is irradiated onto the recording track as an information reading beam. +
The 10th order light, -1-0th order light is 0 as a tracking beam.
The light is irradiated at the front and back positions of the -0th-order light slightly to the left and right from the center of the recording track. The O-+ first-order light and the 01-order light are irradiated as tilt beams onto positions in the radial direction of the disk 18 at the left and right positions of the 0-50th order light. 0-0 order light and O-+1
The distance between the beam spots of the order light and the 0th to 1st order light is set, for example, to about 20 to 30 μm.

The reflected light from the disk 18 passes through the objective lens 34 and the collimator lens 32, is reflected by the half mirror 30, and enters the eight-divided light receiving element 36. 8 division light receiving element・
In 36, four-divided light receiving elements a to d are arranged in the center for information signal reading and focus control, tracking light receiving elements e and f are arranged tangentially across this, and a tilting light receiving element g is arranged in the radial direction. , h are arranged. These eight-divided light receiving elements are constructed on the same substrate. The 0-0 order light reflected from the disc is received by the four-divided light receiving elements a to d. +1- for tracking light receiving elements e and f
The 0th-order light and the -1-0th order light beams opposite the disk are each received. Tilt light receiving element g.

The disk reflected light of the 0-+1st order light and the 0--1st order light are received at h.

FIG. 5 shows a signal processing circuit for the light-receiving signal of the eight-divided light-receiving element 36. The light-receiving signals of the four-divided light-receiving elements a to d at diagonal positions are added by adders 40 and 42. The addition outputs are further added in an adder 44 to obtain an HF signal, which is used for information reproduction. Further, the above addition output is subtracted by a subtracter 46 to obtain a focus error detection signal, which is used for focus servo.

The light reception signals of the tracking light receiving elements e and f are sent to a subtracter 48.
The tracking error detection signal is obtained by subtracting
Used for tracking servo.

The light reception signals of the tilt light receiving elements g and h are subtracted by a subtracter 50 to obtain a tilt error detection signal, which is used for tilt servo.

Regarding the tilt error detection operation by the device shown in Figure 1, Section 6
This will be explained with reference to the figures. If the optical axis of the optical head 20 (the optical axis of the 0-0th order light) is perpendicular to the recording surface of the disk 18 and has no inclination, the 0-0th order light (1? is the coarse reading beam) and the 0-+1 The order light, 0--first order light (tilt beam) is shown in Figure 6 (
As shown in a), the recording surface of the disk 18 is irradiated with light (
The beam spot interval is about 20 to 30 μm). At this time, the reflected light of the tilt beam from the disk 18 is shown in FIG.
The light is now shown by the dotted line in b), and the shaded portions are received as reflected light by the light receiving elements g and h, respectively (the portions outside the shaded areas are not received because they are outside the #1@ of the objective lens 34). . If the optical axis of the optical head 20 is perpendicular to the recording surface of the disk 18 and is not tilted, the areas of the two shaded areas are equal, so the amount of light received by the light receiving elements g and h is equal, as shown in FIG. The level of the tilt error detection signal output from the subtracter 50 becomes zero.

On the other hand, when the optical head 20 is deviated from perpendicular to the recording surface of the disk 18, the reflected light of the tilt beam becomes as shown by the dotted line in FIG.
The area of the two parts increases on one side and decreases on the other. As a result, the amount of light received by the light receiving element gh becomes unbalanced, and the subtracter 50 in FIG. 5 outputs a tilt error detection signal corresponding to the difference. The tilt servo operates so that this tilt error detection signal becomes zero, and controls the optical axis of the optical head to be perpendicular to the disk surface. If the direction of the tilt is reversed, the polarity of the tilt error detection signal is reversed, and the optical axis of the optical head is controlled to be perpendicular to the disk surface.

Note that the influence of adjacent track bits on the amount of reflected light of each tilt beam is of a level that poses no problem in practice for the following reasons.

First, the tilt beams are radiated symmetrically to both the left and right sides of the main beam, which is aligned to a predetermined track, and one of these tilt beams is on the track, and the other is located completely outside the track. There are no such situations, and no major asymmetries arise based on them.

Next, there are differences in individual changes in track bits, etc. at each tilt beam irradiation position, but this is because the time constant of tilt detection control is generally slow, ranging from several seconds to several tens of seconds, making it difficult to sufficiently integrate the amount of tilt detection light. This makes it possible to completely avoid these individual track bit differences.

[Example of change]

In the above embodiment, the tracking beam forming diffraction grating 2
Although the tilt beam forming diffraction grating 28 is disposed after the tilt beam forming grating 28, the opposite may be used.

Furthermore, the arrangement of the signal detection optical system to which this invention is applied is as follows:
The arrangement is not limited to that shown in FIG. 1, and can be applied to various arrangements.

Further, the present invention can be applied to optical heads other than the 3-beam type.

〔Effect of the invention〕

As explained above, a tilt beam forming diffraction grating is provided in the optical disc signal detection optical system to form diffracted light.
Since this diffracted light is used as a tilt beam for tilt detection, means such as an LED for forming a tilt beam are not required, and the configuration can be simplified and the optical head can be made smaller and lighter.

[Brief explanation of drawings]

FIG. 1 is a diagram showing an embodiment of the present invention, and is a diagram showing an example of the configuration inside an optical head. FIG. 2 is a front view and a plan view showing a conventional tilt sensor. FIG. 3 is a perspective view showing an example of the configuration of the diffraction gratings 26, 28 in FIG. 1. FIG. 4 is a perspective view showing an example of the grating pattern of the diffraction gratings 26, 28. FIG. 5 is a block diagram showing an example of the configuration of a signal processing circuit for a light reception signal of the eight-divided light receiving element 36 of FIG. FIG. 6 is a diagram showing a tilt error detection operation by the apparatus of FIG. 1. ]8... Optical disk, 20... Optical head, 28...
- Diffraction grating for tilt beam formation, 36... 8-division light receiving element, a - d... Light receiving element for information reading and focusing, e, f... Light receiving element for tracking, g, h.
...Tilt light receiving element, O...Subtractor (tilt error detection means)

Claims (2)

[Claims] (1) A tilt beam forming diffraction grating that is installed in the signal detection optical system of the optical disc and forms diffracted light in the disc radial direction and irradiates it onto the disc surface, and a tilt light receiving element that detects the disc reflected light of this diffracted light. and tilt error detection means for detecting a tilt error based on the detection output of the tilt light receiving element. (2) The signal detection optical system of the optical disk is of a three-beam type, the grating pattern of the tilt beam forming diffraction grating is formed in a direction substantially perpendicular to the tracking beam forming diffraction grating, and the tilt light receiving element are arranged in two elements in a direction substantially perpendicular to the arrangement direction of the tracking light-receiving elements, and together with the four information reading and focusing light-receiving elements and the two tracking light-receiving elements, the same light-receiving element is divided into eight parts in total. 2. The optical disk tilt detecting device according to claim 1, wherein the optical disc tilt detecting device is arranged on a substrate.