JP3455399B2 - Optical disk sensor system - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical disk sensor system for detecting a focusing error signal by a spot size method and a tracking error signal by a push pull method.

[0002]

2. Description of the Related Art An optical system of an optical disk device that uses a medium such as an optical disk and a magneto-optical disk is provided with
It is equipped with an objective lens that converges a light beam emitted from a light source onto a medium to form a spot, and is equipped with a sensor system that receives reflected light from the medium and detects a recording signal, a focusing error signal, and a tracking error signal. . When the spot size method is used to detect the focusing error signal, the sensor system includes a condenser lens that condenses the reflected light and a hologram element that separates the light flux converged by the condenser lens into two components. , And a first sensor and a second sensor that receive the separated light beams.

The first sensor and the second sensor are arranged at positions corresponding to the front and the rear of the focal point of the condenser lens. The hologram element has the effect of a positive lens for the + 1st order diffracted light and the effect of a negative lens for the −1st order diffracted light, and converges the ± 1st order diffracted light to different degrees. The + 1st order diffracted light is received by the first sensor arranged on the side farther from the converging position than the converging position, and the −1st order diffracted light is detected by the second sensor arranged on the side closer to the condensing lens than the converging position. Received light. 0th order light here
(Transmitted light) is not used.

Since the size of the spot formed on these two sensors changes depending on the focus state of the objective lens, the difference in the size of the spots on both sensors is detected to detect the size of the objective lens. A focusing error signal indicating the in-focus state can be obtained.

Since the focusing error signal is detected by the spot size method and the tracking error signal is detected by the push-pull method, the hologram element directs the light beam in the tangential equivalent direction Y (the disc tangential direction of the spot on the disc). (The direction within the spot on the sensor), and the first and second sensors are each divided into four regions A separated by a dividing line along the tangential equivalent direction Y as shown in FIG. , B, C, D, and E, F, G, H. If the signal from each area is represented by the same symbol,
The focusing error signal FE and the tracking error signal TE are calculated by the following equations. FE = A-B-C + D-E + F + G-H TE = A + B-C-D-E-F + G + H

Since the diffraction angle of the hologram element changes depending on the wavelength, when the emission wavelength of the light source changes, the spot on the sensor is separated in the tangential direction Y.
Is displaced to. By arranging the boundary line of the light receiving area parallel to the tangential direction Y as shown in FIG. 6, it is possible to prevent the displacement of the spot due to the wavelength variation from giving noise to the signal.

[0007]

However, in the above-described conventional sensor system, when the spot on the disc crosses the track across the track when searching for data, the focus of the objective lens coincides with the disc. Even if there is no focusing error,
A change in brightness occurs at the center of the radial equivalent direction X of the spot on the sensor (the direction within the spot on the sensor corresponding to the disc radial direction of the spot on the disc),
There is a problem that the focusing error signal changes.

FIG. 7 shows a state in which the objective lens is focused on the disk by using the objective lens of NA 0.6, the condenser lens having the focal length of 27 mm, and the conventional sensor system shown in FIG. Center of land for disc information recording (X =
Tracking error signal (solid line, 1/10 scale) and focusing error signal (dashed line) output when the spot is moved from 0) to the center of the adjacent land (X = 1.0)
And indicates. X = 0.5 indicates a groove having a mountain-shaped cross section formed between adjacent lands. As shown in FIG. 7, it can be understood that there is noise in the focusing error signal, which should be flat, depending on the radial movement position of the spot on the disc.

In this specification, the noise of the focus error signal generated by the radial movement of the spot on the disc is defined as T / F (Track / Focus) crosstalk.

In order to find out what kind of phenomenon the T / F crosstalk occurs based on, the light quantity distribution of the returning light on the first and second sensors when the spot on the disk crosses the track is simulated. did. The results of the simulation of the light amount distribution on each sensor along the radial equivalent direction X are shown in FIGS. FIG. 8 shows the light amount distribution when the spot on the disk is located at the center of the land, the broken line shows the distribution on the first sensor, and the solid line shows the distribution on the second sensor. The light amount is a value obtained by integrating the light amount within the effective range in the tangential equivalent direction Y for each coordinate in the radial equivalent direction X that is the horizontal axis. FIG. 9 shows a similar light amount distribution when the spot on the disc is located on the groove.

From these results, when the spot on the disk is located at the center of the land on the first sensor, as shown in FIG.
A region that is long in the tangential equivalent direction Y at the center of the radial equivalent direction X on the sensor as shown by hatching
It was found that the inside of the (crosstalk area) became bright and the inside of the crosstalk area became dark when the spot on the disk was located on the groove. It was also found that, on the second sensor, the crosstalk area was dark at the center of the land and bright on the groove, contrary to the first sensor.

On the other hand, the result of the simulation of the light amount distribution on each sensor along the tangential equivalent direction Y is
It is shown in FIGS. FIG. 11 shows the light amount distribution when the spot on the disc is located at the center of the land, and the broken line indicates the first
On the sensor, the solid line shows the distribution on the second sensor. The amount of light is
It is a value obtained by integrating the amount of light within the effective range in the radial equivalent direction X for each coordinate in the tangential equivalent direction Y that is the horizontal axis. FIG. 12 shows a similar light amount distribution when the spot on the disc is located on the groove.

According to FIGS. 11 and 12, in the tangential direction, the light quantity distributions on the first and second sensors are almost equal, and there is no deviation in the distribution that causes T / F crosstalk. be able to. Therefore, FIG.
If the boundary line between the light-receiving areas of the first and second sensors is made parallel to the radial equivalent direction X with this configuration, the effect of T / F crosstalk can be eliminated, but in that case a tracking error signal cannot be obtained. Moreover, there arises a problem that the displacement of the spot on the sensor due to the wavelength variation of the light source becomes noise for the focusing error signal.

The present invention has been made in view of the above-mentioned problems of the prior art, and detects the tracking error signal even when the T / F crosstalk is removed by using the spot size method for detecting the focusing error. An object of the present invention is to provide an optical disk sensor system capable of preventing the fluctuation of the wavelength of the light source from becoming a noise for the focusing error signal.

[0015]

According to a first optical disk sensor system of the present invention, a condensing lens for condensing reflected light from an optical disk, and a light beam condensed by the condensing lens are zero-order diffracted light. , A n-th order diffracted light (n ≠ 0) is separated in the radial equivalent direction, and a hologram element having a predetermined power for the n-th order diffracted light and a 0th order diffracted light separated by the hologram element are received. At a position away from the convergent position of the 0th-order diffracted light, and at the center of the radial equivalent direction, one boundary line parallel to the tangential equivalent direction and at least two boundaries parallel to the radial equivalent direction. A first sensor having a plurality of light-receiving regions separated by lines and a position for receiving the n-th order diffracted light separated by the hologram element, and the convergence position of the n-th order diffracted light. It disposed away al position, and a second sensor having a plurality of absorption regions separated by at least two boundary lines parallel to the radial direction corresponding, first
A focusing error signal by the spot size method is generated using signals from the light receiving regions of the sensor and the second sensor, and a tracking error signal by the push-pull method is generated by using the signal from the first sensor. To do.

In the first structure, the first sensor is
It can be arranged on the side closer to the condensing lens than the converging position of the 0th-order diffracted light, in which case the second sensor is arranged on the side farther from the condensing lens than the converging position of the n-th order diffracted light.
By using the hologram element, the first sensor and the second sensor
The sensor and the sensor can be arranged at the same distance from the condenser lens, that is, on the same plane. The hologram can be configured to have a shape that efficiently produces 0th order diffracted light and + 1st order diffracted light, in which case the second sensor is +1.
It is desirable to be arranged at a position for receiving the second-order diffracted light.

A second optical disk sensor system according to the present invention has a condensing lens for condensing the reflected light from the optical disk and a light beam condensed by the condensing lens to 0.
At least three components of the diffracted light of the nth order and the diffracted light of the nth order (n ≠ 0) are separated in the radial equivalent direction, and ± n
The hologram element having different powers for the 0th order diffracted light and the position for receiving the 0th order diffracted light separated by the hologram element are arranged at positions apart from the converging position of the 0th order diffracted light, and the tanger is arranged at the center in the radial equivalent direction. A first sensor having a plurality of light receiving regions separated by one boundary line parallel to the direction corresponding to the vertical direction, and a position for receiving the + n-th order diffracted light separated by the hologram element, and collecting from the convergence position of the + n-th order diffracted light. Located on the side far from the optical lens,
A second sensor having a plurality of light receiving regions separated by at least two boundary lines parallel to the radial equivalent direction, and a position where the -nth order diffracted light separated by the hologram element is received, and the -nth order diffracted light converges. A third sensor provided on the side closer to the condenser lens than the position and having a plurality of light receiving regions separated by at least two boundary lines parallel to the radial equivalent direction, and each of the second sensor and the third sensor A focusing error signal is generated based on a difference in spot size on each sensor using a signal from the light receiving region, and a tracking error signal is generated using a signal from the first sensor.

In the above second structure, the first sensor is
It can be arranged closer to the condenser lens than the convergent position of the 0th-order diffracted light. By using a hologram element,
The first sensor, the second sensor, and the third sensor can be arranged at the same distance from the condenser lens, that is, on the same plane. The hologram can be configured to have a shape that efficiently generates 0th-order diffracted light and ± 1st-order diffracted light,
In that case, it is desirable that the second sensor is arranged at a position for receiving the + 1st order diffracted light and the third sensor is arranged at a position for receiving the −1st order diffracted light.

[0019]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of an optical disk sensor system according to the present invention will be described below. As shown in FIG. 1, the optical system of the optical disk device includes a laser light source 1, a collimator lens 2 that converts a light beam emitted from the laser light source 1 into a parallel light beam, and converges the light beam on an optical disk D to form a spot. And a beam splitter 4 for separating the reflected light from the optical disc D from the incident optical path, and the reflected light from the optical disc reflected by the beam splitter 4 to receive a recording signal, a focusing error signal, and a tracking error. The sensor system 10 which detects a signal is provided.

An optical disk such as a magneto-optical disk has a mountain-shaped groove in a cross section in the radial direction, and an information recording land located between the grooves. When recording / reproducing information, the objective lens 3 is positioned so that a spot is formed at the center of the land in the radial direction.

First, the first embodiment will be described with reference to FIGS. In the first embodiment, a focusing error signal by the spot size method is detected by using two light fluxes of a 0th-order diffracted light and a + nth-order diffracted light, here a + 1st-order diffracted light, and a push error is detected by using only the 0th-order diffracted light. A tracking error signal is detected by the pull method.

The sensor system 10 of the first embodiment is
In order to enable detection of the focusing error signal by the spot size method, as shown in FIG. 2, the condenser lens 11 that condenses the reflected light and the light flux converged by the condenser lens 11 in the radial equivalent direction X. At least 0 along
Hologram element 1 that separates into first-order diffracted light and + 1st-order diffracted light
2 and the first sensor 13 that receives the separated 0th order diffracted light
And a second sensor 14 that receives + 1st order diffracted light. Reference numeral 15 is an element provided in the second embodiment described later, and is omitted in the first embodiment. In the example of FIG. 2, the condenser lens 11, the hologram element 12, and the sensor are arranged in this order from the light incident side, but the hologram element 12, the condenser lens 11, and the sensor may be arranged in that order.

The hologram element 12 has no power for the 0th order diffracted light and has the effect of a positive lens for the + 1st order diffracted light. The first sensor 13 and the second sensor 14 are indicated by a broken line 0 in the figure so that the spot sizes of the 0th-order diffracted light and the + 1st-order diffracted light become equal when the objective lens is focused.
It is arranged at the convergent position of the secondary diffracted light, that is, on the side closer to the condenser lens 11 than the focal point of the condenser lens. This allows
The first sensor uses the condenser lens 1 from the converged position of the 0th order diffracted light.
The second sensor is arranged on the side closer to 1, and the second sensor is arranged on the side farther from the condenser lens 11 than the convergence position of the + 1st order diffracted light.
However, these perspectives are based on the convergence position of the light flux, and in an actual arrangement, the sensors are arranged side by side on the same plane.

Since the focusing error signal is detected by the spot size method and the tracking error signal is detected by the push-pull method, the hologram element 1 is used.
2 is set so as to separate the light beam in the radial equivalent direction X. Further, as shown in FIG. 3, the first sensor 13 has a tangential equivalent direction Y at the center of the radial equivalent direction X.
The six light-receiving areas A, B, which are separated by one boundary line parallel to the radial direction and two boundary lines parallel to the radial equivalent direction X.
Equipped with C, D, E and F. On the other hand, the second sensor 14 includes three light receiving regions G, H, I which are separated by two boundary lines along the radial direction X.

Since the diffraction angle of the hologram element 12 changes depending on the wavelength, when the emission wavelength of the laser light source 10 changes, the spot on the second sensor is displaced in the separated radial direction X. For example, as the wavelength becomes longer, the position moves to the outside as shown by the broken line. However, by making the boundary line of the light receiving area parallel to the radial direction X as shown in FIG. 3, it is possible to prevent the spot displacement caused by the wavelength variation from giving noise to the signal. Since the 0th-order diffracted light is not diffracted by the hologram element, the spot on the first sensor 13 is not displaced even if the wavelength of the light source changes.

The focusing error signal FE by the spot size method is obtained by using the outputs of both sensors, and the tracking error signal TE by the push-pull method is obtained only by the output of the first sensor. If the signals from the respective areas of the sensor are represented by the same symbols, the focusing error signal FE and the tracking error signal TE are
It is calculated by the following formula. FE = A−B + C + D−E + F−G + H−I TE = A + B + C−D−E−F

FIG. 4 is a plan view of the sensor portion of the optical disk sensor system according to the second embodiment of the present invention. In the second embodiment, the tracking error signal by the push-pull method is detected by using the 0th order diffracted light, and the focusing error signal by the spot size method is detected by using the ± 1st order diffracted lights. Condensing lens 1
1. The arrangement of the hologram element 12 is the same as that of the first embodiment shown in FIG.

In the second embodiment, the hologram element 12 is used.
Separates the 0th-order diffracted light and the ± 1st-order diffracted light in the radial direction, and functions as a positive lens for the + 1st-order diffracted light and a negative lens for the -nth-order light. The 0th order diffracted light is received by the first sensor 13 ′, the + 1st order diffracted light is received by the second sensor 14, and the −1st order diffracted light is received by the third sensor 15. The first sensor 13 ′ is arranged closer to the condenser lens 11 than the convergent position of the 0th-order diffracted light, and the second sensor 14 ′.
Is arranged on the side farther from the converging lens 11 than the converging position of the + nth order diffracted light, and the third sensor 15 is arranged on the side closer to the condensing lens 11 than the converging position of the −nth order diffracted light.

First sensor 13 'for receiving 0th order diffracted light
Has two light receiving regions D and E separated by one boundary line parallel to the tangential equivalent direction Y at the center of the radial equivalent direction X. The configuration of the second sensor 14 is the same as that of the first embodiment, and the second sensor 14 is parallel to the radial equivalent direction X.
It is provided with three light receiving regions F, G, H separated by the boundary line of the book. Since the first and second sensors 13 ', 14 are arranged so that spots of the same size are formed when the objective lens is focused, they are formed of the same size as in the first embodiment. On the other hand, since the third sensor 15 is arranged at a position where the defocus of the light flux is larger than that of the first and second sensors, it is formed larger than the other two sensors. The third sensor 15 has a radial equivalent direction X.
It has three light receiving areas A, B and C separated by two boundary lines parallel to.

The focusing error signal FE by the spot size method is obtained as follows using the outputs of the second and third sensors 14 and 15, and the tracking error signal TE by the push-pull method is obtained by the first sensor 13 '. It is calculated based on the output only as follows. Since the + 1st-order diffracted light and the -1st-order diffracted light have different rates of change in spot diameter due to defocus, the third sensor 15
The output of is multiplied by a coefficient k to be electrically corrected. FE = k (A-B + C) -F + G-H TE = D-E

The configuration of FIG. 5 can also detect the focusing error signal by the spot size method and the tracking error signal by the push-pull method without T / F crosstalk, and moreover, by the fluctuation of the wavelength of the laser light source. Even if the spots on the second and third sensors 14 and 15 are displaced as shown by the broken line, the displacement is in the radial equivalent direction parallel to the boundary line of the light receiving region and therefore does not affect the focusing error signal. Further, since the tracking error signal is detected by the 0th-order diffracted light that is not diffracted, it is not affected by the wavelength fluctuation.

FIG. 6 shows the objective lens 3 with respect to the disk D, which uses the objective lens 3 with NA of 0.6, the condenser lens 11 with the focal length of 27 mm, and the sensor system 10 of the embodiment shown in FIG. A tracking error signal (solid line, 1/10 scale) output when the spot is moved from the land center (X = 0) of the disc to the adjacent land center (X = 1.0) in the focused state Focusing error signal
(Dashed line). X = 0.5 indicates on the groove. As shown in FIG. 5, it can be understood that the focusing error signal is almost flat, that is, the T / F crosstalk is almost removed, regardless of the radial movement position of the spot on the disc. .

[0033]

As described above, according to the present invention, the first sensor receives the 0th-order diffracted light, and the tracking error signal is detected based on the output of the first sensor. , Or the third sensor receives diffracted light of another order, and the first sensor and the second sensor,
Alternatively, by configuring the focusing error signal to be detected based on the outputs of the second sensor and the third sensor, it is possible to remove the T / F crosstalk and prevent the influence of the wavelength fluctuation of the light source. It becomes possible to detect a focusing error signal and a tracking error signal.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing an outline of an optical system of an optical disc device.

FIG. 2 is an enlarged view of a sensor system of the device shown in FIG.

FIG. 3 is a plan view showing an arrangement of light receiving regions of a first sensor and a second sensor according to the first embodiment of the present invention.

FIG. 4 is a plan view showing an arrangement of light receiving areas of a first sensor, a second sensor, and a third sensor according to a second embodiment of the present invention.

FIG. 5 is a graph showing changes in a tracking error signal and a focusing error signal with a radial movement of a spot when the sensor system of the embodiment is used.

FIG. 6 is a first sensor in a conventional sensor system,
It is a top view which shows arrangement | positioning of the light-receiving area of a 2nd sensor.

FIG. 7 is a graph showing changes in a tracking error signal and a focusing error signal due to movement of a spot in a radial direction when a conventional sensor system is used.

FIG. 8 is a graph showing a light amount distribution in a radial equivalent direction when a spot on a disc is located at the center of a land.

FIG. 9 is a graph showing a light amount distribution in a radial equivalent direction when a spot on a disc is located on a groove.

FIG. 10 is a plan view showing a crosstalk region on the sensor.

FIG. 11 is a graph showing a light quantity distribution in a direction corresponding to a tangential when a spot on a disc is located at the center of a land.

FIG. 12 is a graph showing a light amount distribution in a tangential equivalent direction when a spot on a disc is located on a groove.

[Explanation of symbols]

10 sensor system 11 Condensing lens 12 Hologram element 13 First sensor 14 Second sensor 15 Third sensor

Claims (8)

(57) [Claims] 1. A condensing lens for condensing reflected light from an optical disc, and a light beam condensed by the condensing lens as 0th-order diffracted light,
At least two components of n-th order diffracted light (n ≠ 0) are separated in a radial equivalent direction, and a hologram element having a predetermined power for the n-th order diffracted light and a 0th-order diffracted light separated by the hologram element are provided. At the light receiving position, it is arranged at a position away from the convergent position of the 0th-order diffracted light, and one boundary line parallel to the tangential equivalent direction at the center of the radial equivalent direction and at least two boundary lines parallel to the radial equivalent direction. A first sensor having a plurality of light-receiving regions separated by a boundary line; and a position at which the n-th order diffracted light separated by the hologram element is received and a position apart from the convergence position of the n-th order diffracted light, A second sensor having a plurality of light-receiving regions separated by at least two boundary lines parallel to the corresponding direction, the first sensor and the second sensor Using signals from the light receiving regions to generate a focusing error signal by a spot size method, a sensor system for a optical disc and generating a tracking error signal by the push-pull method using signals from the first sensor. 2. The first sensor is arranged closer to the condenser lens than the convergent position of the 0th order diffracted light, and the second sensor is farther from the condenser lens than the convergent position of the nth order diffracted light. The optical disc sensor system according to claim 1, wherein the optical disc sensor system is disposed on the side. 3. The optical disk sensor system according to claim 2, wherein the first sensor and the second sensor are arranged at an equal distance from the condenser lens. 4. The hologram has a shape for efficiently generating 0th-order diffracted light and + 1st-order diffracted light, and the second sensor is arranged at a position for receiving the + 1st-order diffracted light. The optical disk sensor system according to claim 1. 5. A condenser lens for condensing the reflected light from the optical disk, and a light flux condensed by the condensing lens as 0th-order diffracted light,
A hologram element which is separated into at least three components of ± n-order diffracted light (n ≠ 0) in the radial equivalent direction and has different power with respect to the ± n-order diffracted light, and a 0-th order diffracted light separated by the hologram element A plurality of light-receiving regions which are arranged at a position for receiving the 0th-order diffracted light and apart from the converging position of the 0th-order diffracted light and which are separated by one boundary line parallel to the tangential-equivalent direction at the center in the radial-equivalent direction. 1 sensor and at least two boundaries parallel to the radial equivalent direction, which are arranged at a position where the + n-th order diffracted light separated by the hologram element is received and farther from the converging position of the + n-th order diffracted light. A second sensor having a plurality of light receiving regions separated by lines, and a position for receiving the −nth order diffracted light separated by the hologram element, a third sensor disposed on a side closer to the condensing lens than a converging position of the n-th order diffracted light, and having a plurality of light-receiving regions separated by at least two boundary lines parallel to the radial equivalent direction; A focusing error signal is generated based on a difference in spot size on each sensor using signals from the light receiving regions of the sensor and the third sensor, and
A sensor system for an optical disc, wherein a tracking error signal is generated by using a signal from the sensor. 6. The optical disk sensor system according to claim 1, wherein the first sensor is arranged closer to the condenser lens than a convergence position of the 0th-order diffracted light. 7. The first sensor, the second sensor, and the third sensor
7. The optical disk sensor system according to claim 6, wherein the sensor is arranged at an equal distance from the condenser lens. 8. The hologram has a shape for efficiently generating 0th-order diffracted light and ± 1st-order diffracted light, and the second sensor is arranged at a position for receiving + 1st-order diffracted light, and the third sensor is provided.
7. The optical disc sensor system according to claim 6, wherein the sensor is arranged at a position for receiving the −1st order diffracted light.