JPH02199632A - Hologram optical head - Google Patents

Abstract

PURPOSE:To prevent the spread of a tracking error signal to a focusing error signal by disposing the line for parting the 1st region and 2nd region of a hologram element so as to intersect orthogonally with the progressing direction of disk tracks. CONSTITUTION:The return light reflected by a disk signal surface 4 is diffracted by the hologram element 2 and is detected by a photodetector 5 disposed in the diffraction direction thereof. The hologram element 2 is divided to the 1st region I and 2nd region II of such grating patterns at which the diffracted light focuses at different two points and the 3rd region II of such grating patterns at which the diffracted light focuses between the two focal positions. In addition, the line parting the 1st region I and the 2nd region II is so disposed as to intersect orthogonally with the progressing direction Q of the disk tracks. The signal detection to prevent the spread of the tracking error signal to the focusing error signal is executed in this way.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a hologram optical head using a hologram element.

[Prior Art] In recent years, a hologram optical head using a hologram element has been developed as an optical head in an optical disk device. As shown, the first area of the lattice pattern with different pitches
It has a structure in which the diffracted light is divided into two parts: and a second region (2), and the diffracted light is focused on two different points.

An example of the configuration of an optical head using the hologram element 2 is as follows:
To explain with reference to FIG. 7, the laser diode 1, the hologram 2, and the objective lens 3 are arranged in order on the optical axis,
A photodetector 5 is arranged in the direction of the first-order diffracted light at the hologram 2 of the return light reflected on the signal surface of the optical disk 4.
It is composed of a four-division photodiode consisting of four segments A, B, C, and D. The arrangement of each part is as follows.
As shown in Figs. 9 to 9, the photodetector 5 is arranged in the same direction (as seen from the top) with the disk track traveling direction (arrow Q), and the two areas <i> of the hologram element 2 are , (II) is along the track traveling direction Q.

In the optical head described above, the laser beam emitted by the laser diode 1 passes through the hologram 2, and the light beam that passes through the hologram 2 is focused by the objective lens 3, and then the optical disc 4
A spot is formed on the signal surface. The light beam reflected by the disk 4 returns to the hologram 2 along the same optical path, but the first-order light diffracted by the hologram 2 reaches the photodetector 5.
heading towards. At this time, the light that has passed through the two regions 1 and 2 of the hologram 2 is focused at positions 1 and 2 on the photodetector 5, respectively, as shown in FIG.

At that time, focusing error signals (F, E) by the double knife method, tracking error signals (T, E) by the push-pull method, and reproduced RF signals (R, F
) is obtained by the following equation.

F, E= (A+C)-(B+D) T, E= (A+B)-(C+D) R, F=A+B+C+D [Problems to be Solved by the Invention] The above-mentioned conventional hologram optical head has a first region I and a It consists of two areas, the second area (■), and since these two areas have the functions of focusing error detection and tracking error detection, the dividing line l between the two areas is the same as the track traveling direction Q. Because of this, the tracking error signal always loops into the focusing error signal during focus search or in the servo state, causing major problems such as skipping and servo failure.

The present invention has been made in order to eliminate the above-mentioned conventional drawbacks, and an object of the present invention is to obtain a hologram optical head in which a tracking error signal does not overlap with a focusing error signal.

[Means for Solving the Problems] A hologram optical head of the invention according to claim 1 which solves the above problems diffracts the return light reflected on the disk signal surface by a hologram element, and a photodetector is arranged in the direction of the diffraction. A holographic optical head for detecting returned light, wherein the hologram element has a first region I and a second region II formed with grating patterns having different pitches so that the diffracted light focuses on two different points; The first region has a symmetrical shape with respect to the dividing line l that divides the first region and the second region, and
and a third region (2) in which a grating pattern with a different pitch is further formed so as to focus between the two focal positions of the second region, and the hologram element includes:
The hologram optical head according to claim 2, wherein the dividing line is arranged to be substantially perpendicular to the disk track traveling direction, wherein the hologram element is a reflection type hologram element in which a reflection film is formed on a grating pattern surface. This is what I used.

In the hologram optical head according to claim 3, in the hologram optical head according to claim 1 or 2, the photodetector is constituted by a 4-split photodiode, and the 3 diffracted lights corresponding to the 3 regions of the hologram element of the returned light are divided into 4 parts, respectively. When the photodiode is made to enter a predetermined position and a tracking error signal is obtained, by canceling the signals from the first region (■) and the second region (■), only the signal from the third region III is taken out and the tracking error signal is obtained. It is designed to perform detection.

[Function] In the hologram optical head having the above configuration, the three areas i of the hologram element of the return light reflected on the disk signal surface,
The light diffracted at different angles at n and m is divided into four photodiodes A, B, and C.

Spots are formed at three predetermined locations on the photodetector consisting of D.

At this time, the focusing error signals (F, E) are obtained by the double knife method, and the tracking error signals (T, E) are obtained by the Ashpull method using the following equations.

F, E= (A+C)-(B+D) T, E= (A+B)-(C+D) In this case, the dividing line between the first area and the second area of the hologram element is almost perpendicular to the disk track traveling direction. Therefore, even if servo is applied using the above formulas F and H, the tracking error signal will not wrap around the focusing error signal during focus search or in the servo state.

[Example] Hereinafter, an example of the present invention will be described with reference to FIGS. 1 to 6.

FIG. 1 shows a schematic configuration of a hologram optical head according to an embodiment of the present invention. A laser diode 1, a hologram element 2, and an objective lens 3 were arranged in order on the optical axis, and a photodetector 5 was arranged in the direction of the first-order diffracted light at the hologram element 2 of the return light reflected on the signal surface of the optical disk 4. The configuration itself is the same as the conventional example shown in FIG.

As shown in FIG. 2, the hologram element (hereinafter referred to as hologram) 2 has a first region formed with a grating pattern with different pitches so that the diffracted light focuses on two different points!
and a dividing line that separates the second area II from the first area (■) and the second area (■)! has a symmetrical shape with respect to the first
The hologram 2 includes a third area (2) in which a grating pattern with a different pitch is formed so as to focus between the two focal positions of the area (I) and the second area (2), and the dividing line (I) It is arranged so as to be orthogonal to the truck traveling direction Q.

Further, the photodetector 5 has four segments A.

It is the same as the conventional one in that it is composed of four-divided photodiodes consisting of B, C, and D, but in the present invention, FIGS.
As shown in FIG. 3, they are arranged in a direction (viewed from the top) perpendicular to the disk track advancing direction (arrow Q). Note that the disk center is indicated by M.

Next, the operation will be explained. The laser light emitted from the laser diode 1 passes through the hologram 2 and heads toward the objective lens 3. At this time, the +1st order light that passes through the hologram 2 is guided outside the objective lens 3, and only the 0th order light is used. The laser beam incident on the objective lens 3 is condensed, and the optical disc 4
A spot is formed on the signal surface. The light beam reflected by the disk 4 returns to the hologram 2 again along the same optical path, but the +1st order light (or -1st order light) that has been diffracted by the hologram 2 at a predetermined angle is transmitted to the photodetector 5. Head towards.

At this time, the light that has passed through the two regions (1) and (2) of the hologram 2 is focused on the position 1 and the position (2) on the photodetector 5, respectively, as shown in FIG.
The light that passes through I[[ is focused at its central position ■.

At this time, focusing error signals (F, E) by the double knife method, tracking error signals (T, E) by the push-pull method, and reproduction RF signals (R, F) are generated.
) is obtained by the following equation.

F, E= (A+C)-(B+D)...
■T, E= (A+B) -(C+D)...
・・■R,F=A+B+C+D ・・・・
...■These detection signals will be explained.

The tracking error signals T and E of (2) are substantially obtained as push-pull detection signals in the area (2).

In other words, since the light intensity changes in area 1 and area ■ due to tracking error occur in exactly the same phase, the information in area ■ and area ■ is completely canceled in equation 0, and from equation 0, The obtained signal is exactly a push-pull detection signal based on information only in region III.

Focusing error signals F and E in (2) also include signals from area III, but the 4-split photodiodes A, B,
Focusing error signals F and E by crossing C and D
Therefore, the information in area III is canceled in equation 0, and the focusing error signals F and E are based only on the signals in area I and area (2). That is,
As mentioned above, this region III, which has tracking error information, is not affected at all, so the above
Even if the servo is applied using the formula, the tracking error signal will not wrap around the focusing error signal during focus search or in the servo state.

Furthermore, since the reproduced RF signal (R, F) of (2) is the sum of the amount of light incident on the entire area of the hologram 2, an output level equivalent to that of the conventional system can be obtained.

Next, a second embodiment is shown in FIG. In this embodiment, the third area (■) in the hologram 2 is divided into the first area (■) and the second area (W).
4. It is formed in a ring shape around the outer periphery of area (3). The signal detection procedure in this embodiment is exactly the same as in the previous embodiment, and the equations (1), (2), and (2) above are applied as they are.

Next, a third embodiment is shown in FIGS. 5 and 6.

In this embodiment, a reflective hologram element 2A in which a reflective film is formed on the grating pattern surface is used as the hologram element. At this time, the laser diode 1 is arranged so that the laser beam emission direction is parallel to the disk 4 surface, the reflective hologram element 2A is arranged facing the objective lens 3 at an angle of 45 degrees, and the photodetector 5 the laser diode 1
The configuration is such that it is placed laterally in the same plane as the

In this hologram optical head, the laser beam from the laser diode 1 is reflected by the reflective hologram element 2A and directed toward the objective lens 3, and the return light that is reflected by the signal surface of the disk 4 and transmitted through the objective lens 3 is The difference is that the light is reflected by the hologram element 2A and directed toward the photodetector 5, but the other points are the same as in the transmission type hologram element 2 described above.

Note that the dividing line r between the first region and the second region in the hologram element does not necessarily have to be strictly orthogonal to the track traveling direction.

[Effects of the Invention] As explained above, according to the present invention, the hologram element is arranged in the first region and the second region of the grating pattern such that the diffracted light focuses on two different points, and the diffracted light focuses on two different points. Since the third area is divided into a grid pattern that connects the focal point between the focal positions and the dividing line between the first area and the second area is arranged to be almost perpendicular to the disk track advancing direction, focusing errors can be avoided. Signal calibration is now possible to prevent tracking error signals from entering the signal.

[Brief explanation of the drawing]

FIG. 1 is a front view showing a schematic configuration diagram of a hologram optical head showing an embodiment of the present invention, FIG. 2 is an explanatory diagram of the hologram element and photodetector in FIG. 1, and FIG. FIG. 4 is an explanatory diagram of the positional relationship of the detector in the optical disk device. FIG. 4 is an explanatory diagram of a hologram element and a photodetector showing another embodiment. FIG. 5 is an explanatory diagram of a hologram optical head showing another embodiment. 6 is a front view of the same, FIG. 7 is a front view of the schematic structure of a conventional hologram optical head, and FIG. 8 is an explanatory diagram of the hologram element and photodetector in FIG. 7; FIG. 9 is an explanatory diagram of the positional relationship of the hologram element and the photodetector in the optical disk device. 3... Hologram element, 6... Photodetector, A, B,
C, D, E, F...Photodiode, ■...1st
area, ■...second area, ■...third area.

Claims (1)

[Claims] 1. A hologram optical head that diffracts return light reflected from a disk signal surface by a hologram element and detects the return light by a photodetector arranged in the direction of the diffraction, wherein the hologram element has a diffraction direction. A first region I and a second region II formed with a lattice pattern with different pitches so that the light focuses on two different points, and a symmetrical shape with respect to a dividing line l separating the first region and the second region, And the first
and a third region III in which a grating pattern with a different pitch is formed so as to focus between the two focal positions of the second region, and the dividing line is in the disk track traveling direction. A holographic optical head characterized in that it is arranged substantially perpendicular to the holographic optical head. 2. The hologram optical head according to claim 1, wherein the hologram element is a reflection type hologram element in which a reflection film is formed on a grating pattern surface. 3. The photodetector is composed of a 4-split photodiode, and the three diffracted lights corresponding to the three regions of the hologram element of the returned light are respectively incident on predetermined positions of the 4-split photodiode to generate a tracking error signal. When obtaining the tracking error signal, the tracking error signal is detected by canceling the signals of the first region I and the second region II, thereby extracting only the signal of the third region III. 3. The hologram optical head according to 1 or 2.