JPH1139676A - Sensor system for optical disk - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical disk sensor system capable of detecting, even when T/F(track/focus) crosstalk is eliminated by using a spot size method for detection of a focusing error, a tracking error signal and preventing the wavelength fluctuation of a light source from being noises to the focusing error signal. SOLUTION: A first sensor 13 has six light receiving areas A, B, C, D, E and F divided by one order line parallel to a tangential equivalent direction Y in the center of a radial equivalent direction X and two border lines parallel to the radial equivalent direction X, and a second sensor 14 has three light receiving areas G, H and I divided by two border lines along the radial equivalent direction X. If signals from the respective areas of the sensors are expressed by identical symbol, a focusing error signal FE is obtained by FE=A-B+C+ D-E+F-G+H-I, and a tracking signal TE is obtained by TE=A+B +C-D-E-F.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a sensor system for an optical disk which detects 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 apparatus using a medium such as an optical disk and a magneto-optical disk includes a laser light source,
An objective lens that forms a spot by converging a light beam emitted from a light source onto a medium is provided, and a sensor system that receives reflected light from the medium and detects a recording signal, a focusing error signal, and a tracking error signal is provided. . When the spot size method is used to detect a focusing error signal, the sensor system includes a condensing lens for condensing reflected light, and a hologram element for separating a light beam converged by the condensing lens into two components. And a first sensor and a second sensor that receive the separated light beams.

[0003] The first sensor and the second sensor are arranged at positions corresponding to the front and rear sides of the focal position of the condenser lens. The hologram element has a positive lens effect on + 1st-order diffracted light and a negative lens effect on -1st-order diffracted light, and converges ± 1st-order diffracted light to different degrees. The + 1st-order diffracted light is received by a first sensor disposed farther from the converging lens than the convergence position, and the -1st-order diffracted light is received by a second sensor disposed closer to the converging lens than the convergence position. Received. Here is the 0th order light
(Transmitted light) is not used.

Since the size of the spot formed on these two sensors changes according to the in-focus state of the objective lens, the difference between the spot sizes on the two sensors is detected to determine 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 converts the light beam into a tangential direction Y (corresponding to the disk tangential direction of the spot on the disk). (The direction within the spot on the sensor), and the first and second sensors are each divided into four areas A divided by a dividing line along the tangential direction Y as shown in FIG. , B, C, D and E, F, G, H. Expressing the signal from each area with the same symbol,
The focusing error signal FE and the tracking error signal TE are obtained 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 light emission wavelength of the light source changes, the spot on the sensor is separated in the tangential direction Y.
Is displaced. By making the boundary of the light receiving region 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 fluctuation from giving noise to the signal.

[0007]

However, in the above-described conventional sensor system, when a spot on the disk crosses the track when searching for data or the like, the focus of the objective lens coincides with the disk. If there are no focusing errors,
A change in lightness and darkness occurs in the central portion of the radial equivalent direction X of the spot on the sensor (the direction in the spot on the sensor corresponding to the disk radial direction of the spot on the disk),
There is a problem that the focusing error signal changes.

FIG. 7 shows a state in which the objective lens is focused on a disk using an objective lens having an NA of 0.6, a condenser lens having a focal length of 27 mm, and the conventional sensor system shown in FIG. Center of land for recording information on disc (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 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 noise is added to the focusing error signal which should be flat in accordance with the radial movement position of the spot on the disk.

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

[0010] In order to find out what phenomenon the T / F crosstalk is based on, the light amount distribution of the returning light on the first and second sensors when the spot on the disk crosses the track is simulated. did. Simulation results 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, with the broken line on the first sensor and the solid line on the second sensor. The light quantity is a value obtained by integrating the light quantity within the effective range in the tangential equivalent direction Y for each coordinate in the radial equivalent direction X, which is the horizontal axis. FIG. 9 shows a similar light amount distribution when the spot on the disk 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, it can be seen from 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 indicated by hatching
(Crosstalk area), and it became clear that the spot in the crosstalk area became dark when the spot on the disk was located on the groove. It was also found that the crosstalk area on the second sensor became darker at the center of the land, and became brighter on the groove, as opposed to the first sensor.

On the other hand, the simulation result of the light amount distribution on each sensor along the tangential direction Y is as follows.
This 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 is the first.
On the sensor, the solid line shows the distribution on the second sensor. The amount of light is
This value is obtained by integrating the light amount within the effective range in the radial equivalent direction X for each coordinate in the tangential equivalent direction Y, which is the horizontal axis. FIG. 12 shows a similar light amount distribution when the spot on the disk is located on the groove.

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

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

[0015]

A first optical disk sensor system according to the present invention comprises: a condenser lens for condensing light reflected from an optical disk; and a light beam condensed by the condenser lens as a zero-order diffracted light. A hologram element having a predetermined power with respect to the nth-order diffracted light while being separated in at least two components with the nth-order diffracted light (n ≠ 0), and a 0th-order diffracted light separated by the hologram element. One boundary line parallel to the tangential equivalent direction at the center in the radial equivalent direction and at least two boundary lines parallel to the radial equivalent direction at a position apart from the convergence position of the zero-order diffracted light. A first sensor having a plurality of light receiving regions separated by lines, and a convergence position of the n-th order diffracted light at a position for receiving the n-th order diffracted light separated by the hologram element 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
Generating a focusing error signal by a spot size method using a signal from each light receiving area of the sensor and the second sensor, and generating a tracking error signal by a push-pull method by using a signal from the first sensor. I do.

[0016] In the first configuration, the first sensor includes:
The second sensor can be arranged closer to the condenser lens than the convergence position of the 0th-order diffracted light. In this case, the second sensor is arranged farther from the condenser lens than the convergence position of the nth-order diffracted light.
By using a hologram element, the first sensor and the second
The sensor and the condenser can be arranged at an equal distance from the condenser lens, that is, on the same plane. The hologram can be configured to have a shape that efficiently generates the 0th-order diffracted light and the + 1st-order diffracted light, in which case the second sensor has a + 1st order
It is desirable to be arranged at a position for receiving the next-order diffracted light.

Further, a second optical disk sensor system according to the present invention includes a condensing lens for condensing light reflected from the optical disc, and a light beam condensed by the condensing lens.
And at least three components of ± nth order diffracted light and ± nth order diffracted light (n ≠ 0) in the radial equivalent direction.
A hologram element having different power with respect to the 0th-order diffracted light, and a position where the 0th-order diffracted light separated by the hologram element is received and located away from the convergence position of the 0th-order diffracted light. A first sensor having a plurality of light receiving areas separated by a single boundary line parallel to the direction corresponding to the tangential direction, and a position for receiving the + n-order diffracted light separated by the hologram element, and collecting from the converging position of the + n-order diffracted light. It is 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 a radial equivalent direction, and a convergence of the -n-order diffraction light at a position where the -n-order diffraction light separated by the hologram element is received. A third sensor disposed on a 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 a radial equivalent direction; and a second sensor and a 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 area, and a tracking error signal is generated using a signal from the first sensor.

In the second configuration, the first sensor includes:
It can be arranged closer to the condenser lens than the convergence position of the zero-order diffracted light. By using a hologram element,
The first sensor, the second sensor, and the third sensor can be arranged at an equal 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 this case, it is desirable that the second sensor is arranged at a position for receiving + 1st-order diffracted light, and the third sensor is arranged at a position for receiving -1st-order diffracted light.

[0019]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an embodiment of a sensor system for an optical disk according to the present invention will be described. As shown in FIG. 1, the optical system of the optical disk device includes a laser light source 1, a collimating lens 2 for converting a light beam emitted from the laser light source 1 into a parallel light beam, and converging the light beam on an optical disk D to form a spot. A beam splitter 4 for separating reflected light from the optical disc D from an incident optical path, and receiving a reflected light from the optical disc reflected by the beam splitter 4 to record a signal, a focusing error signal, and a tracking error. A sensor system 10 for detecting a signal is provided.

An optical disk such as a magneto-optical disk has a groove in a radial cross section and a land for recording information 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, a first embodiment will be described with reference to FIGS. In the first embodiment, a focusing error signal is detected by a spot size method using two light beams of a 0th-order diffracted light and a + nth-order diffracted light, here, a + 1st-order diffracted light, and a push is performed using only the 0th-order diffracted light. A tracking error signal is detected by the pull method.

The sensor system 10 according to the first embodiment includes:
To enable detection of a focusing error signal by the spot size method, as shown in FIG. 2, a condensing lens 11 for condensing reflected light, and a light beam converged by the condensing lens 11 in a radial equivalent direction X. At least 0 along
Hologram element 1 that separates light into first-order and + 1st-order diffracted light
2 and a first sensor 13 for receiving the separated zero-order diffracted light
And a second sensor 14 for receiving + 1st-order diffracted light. Reference numeral 15 denotes an element provided in a second embodiment described later, and is omitted in the first embodiment. Although the condenser lens 11, the hologram element 12, and the sensor are arranged in this order from the light incident side in the example of FIG. 2, the hologram element 12, the condenser lens 11, and the sensor may be arranged in this 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 arranged 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 on the convergence position of the next 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 is provided with a condenser lens 1 from the convergence position of the zero-order diffracted light.
The second sensor is disposed on the side closer to 1 and farther from the condenser lens 11 than the convergence position of the + 1st-order diffracted light.
However, these distances are based on the convergence position of the light beam, 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
Numeral 2 is set so as to separate the light beam in the radial equivalent direction X. The first sensor 13 has a tangential equivalent direction Y at the center of the radial equivalent direction X as shown in FIG.
, And six light receiving areas A, B, separated by one boundary line parallel to the radial direction and two boundary lines parallel to the radial equivalent direction X.
C, D, E, F are provided. On the other hand, the second sensor 14 includes three light receiving areas G, H, and I separated by two boundary lines along the radial equivalent 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, when the wavelength becomes longer, the position moves outward as indicated by a broken line. However, by making the boundary line of the light receiving region parallel to the radial direction X as shown in FIG. 3, it is possible to prevent the displacement of the spot due to the wavelength fluctuation from giving noise to the signal. Since the zero-order diffracted light is not affected by the diffraction effect of 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 using the outputs of both sensors, and the tracking error signal TE by the push-pull method is obtained based only on the output of the first sensor. When the signals from the respective regions of the sensor are represented by the same symbols, the focusing error signal FE and the tracking error signal TE are
It is obtained by the following equation. FE = AB + C + DE + FG + HITE = A + B + CDEF

FIG. 4 is a plan view of the sensor part of the optical disk sensor system according to the second embodiment of the present invention. In the second embodiment, a tracking error signal is detected by the push-pull method using the 0th-order diffracted light, and a focusing error signal is detected by the spot size method using the ± 1st-order diffracted light. 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
Separates the 0th-order diffracted light and the ± 1st-order diffracted light in the radial direction, functions as a positive lens for the + 1st-order diffracted light, and functions as 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 disposed closer to the condenser lens 11 than the convergence position of the zero-order diffracted light, and the second sensor 14 ′
Is located farther from the condenser lens 11 than the converging position of the + n-order diffracted light, and the third sensor 15 is arranged closer to the condenser lens 11 than the converging position of the -n-order diffracted light.

First sensor 13 'for receiving the zero-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.
It has three light receiving areas F, G, and H separated by book boundaries. Since the first and second sensors 13 'and 14 are arranged so that spots of the same size are formed when the objective lens is focused, they are formed in 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 beam is larger than the first and second sensors, the third sensor 15 is formed larger than the other two sensors. The third sensor 15 has a radial equivalent direction X
Are provided with 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 obtained as follows based only on the output. Since the rate of change of the spot diameter based on defocus differs between the + 1st-order diffracted light and the -1st-order diffracted light, the third sensor 15
Is electrically corrected by multiplying the output by a coefficient k. FE = k (AB + C) -F + GH TE = DE

The configuration shown in FIG. 5 can also detect a focusing error signal by the spot size method without T / F crosstalk and a tracking error signal by the push-pull method. Even if the spots on the second and third sensors 14 and 15 are displaced as indicated by broken lines, the displacement is in a radial equivalent direction parallel to the boundary 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 which is not affected by the diffraction effect, it is not affected by the wavelength fluctuation.

FIG. 6 shows an objective lens 3 having a NA of 0.6, a condenser lens 11 having a 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 center of the disc land (X = 0) to the center of the adjacent land (X = 1.0) in the focused state Focusing error signal
(Broken 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 eliminated irrespective of the radial movement position of the spot on the disk. .

[0033]

As described above, according to the present invention, the first sensor receives the zero-order diffracted light and detects the tracking error signal based on the output of the first sensor. Or a third sensor receives diffracted lights of other orders, and a first sensor and a second sensor,
Alternatively, by configuring so as to detect the focusing error signal based on the outputs of the second sensor and the third sensor, it is possible to eliminate the influence of the wavelength variation of the light source while eliminating the T / F crosstalk, thereby providing accurate It becomes possible to detect a focusing error signal and a tracking error signal.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing an outline of an optical system of an optical disk 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 regions 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 accompanying movement of a spot in a radial direction when the sensor system of the embodiment is used.

FIG. 6 shows a first sensor in a conventional sensor system,
It is a top view showing arrangement of a light sensing field of the 2nd sensor.

FIG. 7 is a graph showing changes in a tracking error signal and a focusing error signal accompanying a radial movement of a spot 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 disk 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 disk is positioned on a groove.

FIG. 10 is a plan view showing a crosstalk area on a sensor.

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

FIG. 12 is a graph showing a light amount distribution in a direction corresponding to tangential when a spot on a disk is positioned on a groove.

[Explanation of symbols]

 Reference Signs List 10 sensor system 11 condenser lens 12 hologram element 13 first sensor 14 second sensor 15 third sensor

Claims (8)

[Claims] A condenser lens for condensing reflected light from an optical disk; a light beam condensed by the condenser lens being a zero-order diffracted light;
A hologram element having a predetermined power with respect to the n-order diffracted light while separating the n-order diffracted light (n ≠ 0) into at least two components in a radial equivalent direction, and a 0-order diffracted light separated by the hologram element. At a light receiving position, a single boundary line parallel to the tangential equivalent direction at the center of the radial equivalent direction and at least two parallel lines parallel to the radial equivalent direction is disposed at a position apart from the convergence position of the zero-order diffracted light. A first sensor having a plurality of light receiving regions separated by a boundary line; a first sensor that receives the n-th order diffracted light separated by the hologram element; A second sensor having a plurality of light receiving regions separated by at least two boundary lines parallel to the corresponding direction, wherein 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 disposed closer to the condenser lens than the zero-order diffracted light converges, and the second sensor is farther from the condenser lens than the n-order diffracted light converges. The sensor system for an optical disk according to claim 1, wherein the sensor system is disposed on a side of the optical disk. 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 that efficiently generates a 0th-order diffracted light and a + 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 condensing lens for condensing light reflected from an optical disk, and a light beam condensed by the condensing lens being a zero-order diffracted light;
A hologram element that separates at least three components with ± n-order diffracted light (n ≠ 0) in a radial equivalent direction and has different powers with respect to the ± n-order diffracted light, and a 0-order diffracted light separated by the hologram element A plurality of light-receiving regions, which are arranged at positions distant from the convergence position of the 0th-order diffracted light and separated by a single boundary line parallel to the tangential direction at the center in the radial direction. A sensor and at least two boundaries disposed at a position for receiving the + n-order diffracted light separated by the hologram element, farther from the converging lens than a convergence position of the + n-order diffracted light, and parallel to a radial equivalent direction A second sensor having a plurality of light receiving regions separated by lines, and a position for receiving the −n-order diffracted light separated by the hologram element. a third sensor disposed on a side closer to the condenser lens than the convergence position of the n-th order diffracted light, the third sensor including a plurality of light receiving regions separated by at least two boundary lines parallel to a radial equivalent direction; A focusing error signal is generated based on a difference in spot size on each sensor using signals from the respective light receiving areas of the sensor and the third sensor, and
An optical disk sensor system for generating a tracking error signal using a signal from a sensor. 6. The optical disk sensor system according to claim 1, wherein the first sensor is disposed on a side closer to the condenser lens than a convergence position of the zero-order diffracted light. 7. The first sensor, the second sensor, and a third sensor.
7. The optical disk sensor system according to claim 6, wherein the sensor is disposed 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, the second sensor is arranged at a position for receiving + 1st-order diffracted light, and
The optical disk sensor system according to claim 6, wherein the sensor is arranged at a position for receiving the -1st-order diffracted light.