JPS61162830A - Optical head - Google Patents

Abstract

PURPOSE:To detect the position shift of an objective lens by detecting the quantity of luminous flux from the objective lens in a light quantity detection area and detecting luminous flux striking a part other than the light quantity detection area according to the movement of the objective in a position shift detection area. CONSTITUTION:When a light reflecting surface 7 is on the rear focal plane of the objective lens 3 at any time, laser luminous flux as reflected light illuminates the light quantity detection area 8a of a photodetector 8 if the objective lens 3 is at a fixed position. Then, if the objective lens 3 shifts from the fixed position, the luminous flux illuminates either of the 1st and the 2nd position shift detection areas 8b and 8c provided adjacently at both sides of the light quantity detection area 8a. For the purpose, the difference between photodetection signals obtained from the 1st and the 2nd position shift detection areas 8b and 8c is calculated to detect the position of the objective 3. Consequently, tracking operation is entered stably; without reference to the oscillation of the objective and the optical head of extremely structure having good reliability is manufactured at low cost.

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention uses focused light to read information on an information storage medium such as a DAD or video disk, or to read information on an information storage medium such as a document file or COM. The present invention relates to an optical head that is applied to an information reproducing device or an information recording/reproducing device capable of additionally recording information, or an information recording/reproducing device capable of erasing already recorded edge information.

[Technical background of the invention and its problems]

At present, most of the above-mentioned information storage media are disk-shaped, and information is recorded concentrically or spirally along the circumference.

The above-mentioned optical head that reads information from such an information storage medium needs to read or record information along the tracks in which the information is lined up one by one even if the information storage medium itself is eccentric. Therefore, the above optical head usually has a structure in which an objective lens that focuses light onto an information storage medium can be moved in parallel in the radial direction of the information storage medium.

As for this drive mechanism, the objective lens is often supported by a spring so as to be movable by electric force, such as a linear motor type or a voice coil type.

By the way, in such an optical head, at the time of access, the entire optical head is moved by detecting the position of the entire optical head, and then precise positional correction is performed by tracking. When changing the position of the optical head, no particular detection is performed regarding the position of the objective lens. However, if this access is performed at a high speed, the swing of the objective lens in the access direction will increase accordingly. I was unable to track it and ended up flying off. As a result, precise position correction cannot be performed, and the total access time cannot be increased.

Therefore, a means is needed that allows immediate tracking by feedback from detecting the position of the objective lens. However, if such a means is added to the objective lens itself, it is difficult to miniaturize the optical head, and the weight of the lens itself increases. increases, and problems such as frequency characteristics are likely to occur.

[Purpose of the invention]

The present invention has been made based on the above-mentioned circumstances, and its object is to provide an optical head that can stably shift to a tracking operation regardless of the shaking of the objective lens.

[Summary of the invention]

In order to achieve the above object, the present invention provides an optical head that is capable of reading at least information from an information storage medium using focused light. Convert it into a luminous flux of
A part of the converted light beam is transferred to the information storage medium by an objective lens that has an inner diameter smaller than the spot size of the converted light beam and is movable at least in a direction orthogonal to the optical axis of the converted light beam. The light beam is condensed upward, reflected from the information storage medium and passed through the objective lens again, and projected onto a photodetector having a light amount detection area and a positional deviation detection area. The amount of light from the objective lens is detected in the detection area, and the positional deviation of the objective lens is detected by detecting the amount of light that protrudes from the light amount detection area as the objective lens moves in the positional deviation detection area. It is characterized by the following.

[Embodiments of the invention]

First, the lens position detection means applied to the optical head according to the present invention will be explained with reference to FIGS. 1 and 2.

Reference numeral 1 in FIG. 1 is a semiconductor laser (light source), and a laser beam generated from this semiconductor laser 1 is converted into a parallel beam through a collimating lens 2. Here, the laser beam converted into the parallel beam has a spot size that is sufficiently larger than the inner diameter of the objective lens 3, which will be described later. Next, the laser beam converted into a parallel beam passes sequentially through a polarizing beam splitter 4 and a quarter-wave plate 5, and is converted into circularly polarized light. A portion of the laser beam converted into circularly polarized light is focused onto the light reflecting surface 7 of the information storage medium 6 by the objective lens 3. The laser beam reflected by the light reflecting surface 7 is again made into a parallel beam by the objective lens 3, passes through the 174-wavelength plate 5, and is returned to the polarizing beam splitter 4. Here, by reciprocating through the quarter-wave plate 5, the plane of polarization of the laser beam is rotated by 90 degrees compared to when it passes through the polarizing beam splitter 4, and this polarized beam does not pass through the polarizing beam splitter 4. It will be reflected by the splitter 4. Then, this reflected laser beam is transmitted to the light amount detection area 8a and the first
The light is projected onto a photodetector 8 having second positional deviation detection areas 8b and 8c. Note that even if a half prism is used instead of the polarizing beam splitter 4 and the 174 wavelength plate 5 is removed, the loss of light will only occur in the half prism, and in this case, there is no quarter wavelength plate 5. The light is not circularly polarized and is projected onto the photodetector 8 in exactly the same way as in the above case, only the polarization plane does not change.

Next, to explain the basic principle of position detection of the objective lens 3, the spot size of the laser beam converted into a parallel beam by the collimating lens 2 is sufficiently larger than the inner diameter of the objective lens 3. only that will pass through the objective lens 3. The laser beam passing through the objective lens 3 is focused on the light reflecting surface 7 as incident light,
After being reflected on the light reflecting surface 7, the light passes through the objective lens 3 again and returns as reflected light. Furthermore, the laser beam that has not passed through the objective lens 3 cannot return again. Moreover, the spot size of the laser beam that is reflected by the light reflecting surface 7 and passes through the objective lens 3 again to become a parallel beam does not become larger than the inner diameter of the objective lens 3, so the position of the spot size of the laser beam By detecting this, the position of the objective lens 3 can be indirectly detected. That is, if we assume that the light reflecting surface 7 is always positioned on the back focal plane of the objective lens 3, the laser beam as reflected light will be reflected from the objective lens 3.
When the light is at the regular position, the light is irradiated onto the light amount detection area 8a of the photodetector 8, as shown in FIG. 2(A). Here, the size of the light amount detection area 8a is set equal to the spot size of the projected laser beam. and,
When the objective lens 3 deviates from its normal position, as shown in FIG.
, 8c. Therefore, these first and second positional deviation detection areas 8b, 8c
The position of the objective lens 3 can be detected by taking the difference between the respective optical detection signals obtained from the d signal.

Here, by calculating the sum of the light amount detection area 8a and the first and second positional deviation detection areas 8b and 8C, ff,
It is possible to read the information signal on the Ml storage medium 6. Furthermore, a light amount detection area 8a and first and second positional deviation detection areas 6b.

The light amount detection area 8C is bisected in the same direction as the arrangement direction of the light amount detection area 8C to form first and second light amount detection areas 8a'.

8a", the signal from the first light amount detection area Qa' on the first misalignment detection area 8b side is A, and the signal from the second light amount detection area 8a" on the second misregistration detection area 8C side is A. B
, if the signal from the first positional deviation detection area 8b is C1 and the signal from the second positional deviation detection area 8C is D, then (A+
By performing the calculation C)-(B+D), it can also be used as a detector for tracking error detection using diffracted light from a guide groove (tracking guide) on the information storage medium 6. Therefore, it does not matter how many minutes the light amount detection area 8a is left in the tank, so it can be used for other purposes.

In the above lens position detection means, the position of the objective lens 3 can be detected using a simple principle and structure, and the photodetector 8 that detects the position of the objective lens 3 is capable of detecting information, which is a basic function of the optical head. Since it is sufficient to make slight changes to the conventional photodetector that can read signals or tracking signals (change the size of the photodetector, the detection area, etc.), the manufacturing cost is low, and it is easy to use as a device. Reliability can be improved. In addition, since there is no need to modify the objective lens 3, even if the above-mentioned lens position detection means is added to a conventional optical head, the frequency characteristics with respect to the movement of the objective lens 3 will not be deteriorated. Since no mechanical changes are required to the lens 3, there is no change in the dimensions, weight, etc. of the lens itself or its surroundings, and therefore the overall height and thickness of the optical head can remain low (thin). There is also a small change in weight.

Note that, as shown in FIG. 3, a projection lens 9 may be placed before projecting light onto the photodetector 8. In this case, the light reflecting surface 7
Even if the laser beam reflected by the laser beam has a large diameter, it can be made into a small spot diameter on the photodetector 8. Therefore, since the photodetector 8 may be small, a low-cost and highly reliable photodetector can be used, and moreover,
The entire optical head can be made smaller.

Next, an embodiment of the optical head according to the present invention to which the above lens position detection means is applied will be described based on FIG. 4.

Reference numeral 11 in FIG. 4 is a semiconductor laser (light source), and this semiconductor laser 11 generates a diverging laser beam. In this case, the information is transferred to the light reflective layer of the information storage medium 12 (
When writing to the recording layer 13, a laser beam whose light intensity is modulated according to the information to be written is generated, and when reading information from the light reflection layer 13, a laser beam having a constant light intensity is generated. be done. The diverging laser beam generated from the semiconductor laser 11 is converted by the collimator lens 14 into a parallel beam having a diameter sufficiently larger than the diameter of an objective lens 15, which will be described later, and is guided to the deflection beam splitter 16. The laser beam guided to this polarized beam splitter 16 is reflected by this polarized beam splitter 16, passes through a 1/4 wavelength plate 17, and enters the objective lens 15.
The light is focused toward the light reflecting layer 13 of the information storage medium 12 by. Here, the objective lens 15 is moved in the axial direction by the axial voice coil 18, and in the direction perpendicular to the optical axis (radial direction) by the radial voice coil 19.
are movably supported by the objective lenses 15 and 15.
is positioned at a predetermined position, the beam waist of the focused laser beam emitted from the objective lens 15 is projected onto the surface of the light reflection layer 13, and a minimum beam spot is formed on the surface of the light reflection layer 13. Ru. In this state, the objective lens 15 is maintained in a focused state and a focused track state, as will be described later, and information can be written and read. When writing information, bits are formed on the tracking guide 20 on the light reflection layer 13 by a laser beam whose light intensity is modulated, and when reading information, a laser beam having a constant light intensity is used to form bits. The light intensity is modulated by the bits formed on the tracking guide 20 and reflected.

The diverging laser beam reflected from the light reflection layer 13 of the information storage medium 12 is converted into a parallel beam by the objective lens 15 when it is focused, passes through the quarter-wave plate 17 again, and is returned to the polarizing beam splitter 16. It will be done. By reciprocating through the quarter-wave plate 17, the plane of polarization of this laser beam is rotated by 90 degrees compared to when it is reflected by the polarizing beam splitter 16. It passes through a polarizing beam splitter 16. The laser beam passing through the deflection beam splitter 16 is divided into two systems (information detection/track deviation detection/position deviation detection system and defocus detection system) by a half mirror 21, and one of them (information detection/track deviation detection/position deviation detection system) (detection system) is irradiated onto the first photodetector 23 by the projection lens 22. This first photodetector 23 is provided with photodetection cells (light amount detection areas) 23a, 23b and photodetection cells (positional deviation detection areas>230, 23d,
These detection cells 23a, 23b.

Signals γ, δ, and ε are obtained from 23c and 23d, respectively.

ζ is output. For track deviation detection, (γ
Two types of signals are used: +ε) and (δ+ζ). Further, the signal detected by the first detector 23 includes information recorded on the information recording medium 12, and is sent to a signal processing device (not shown) and converted into digital data. In this case, a signal of (γ+δ+ε+ζ) is used. Furthermore, the photodetection cells 23C and 23d of the first photodetector 23
The signals ε and ζ from the radial voice coil drive circuit 2
4, and this radial voice coil drive circuit 24
The radial direction voice coil 19 is driven in accordance with the signal to maintain the objective lens 15 at a predetermined position. On the other hand, from the other (defocus detection system) laser beam divided by the half mirror 21, only the component that passes through the area separated from the optical axis is extracted by the light shielding plate 25, and after passing through the projection lens 26, the second The photodetector cells 27a and 27b of the photodetector 27 are irradiated. Signals α and β are output from the photodetection cells 27a and 27b of this second optical detector 27, and these signals α and β are given to the axial voice coil drive circuit 28, and the axial voice coil drive circuit 28 The coil drive circuit 28 drives the axial voice coil 18 in accordance with the signal to maintain the objective lens 15 in a focused state.

Next, a control circuit for operating the above optical system will be explained.

First, focusing I11 control will be explained. Signals α and β obtained from the respective photodetection cells 27a and 27b of the second photodetector 27 are transmitted to the photodetection cell 27a.

After being amplified by the preamplifiers 29 and 27b, the signals are subjected to subtraction processing and addition processing by the subtraction circuit 31 and the addition circuit 32, and then input to the CPLI 33. At initialization, the CPLI 33 supplies an initial pull-in signal to the axial voice coil drive circuit 28 via the switching circuit 34. As a result, the axial voice coil drive circuit 2
8 drives the axial voice coil 18 to move the objective lens 1
5 to the in-focus position. And CPtJ3
3, when the subtraction result of the subtraction circuit 31 becomes "±0", it is determined that the focus position is reached, and the switching circuit 34 is switched.
A signal corresponding to the defocus output from the subtraction circuit 31, that is, a signal obtained by taking the difference between the detection signals α and β from the photodetection cells 27a and 27b, is sent to the waveform shaping circuit 35.
and is supplied to the axial voice coil drive circuit 28 via the switching circuit 34. As a result, the axial voice coil drive circuit 28 moves the objective lens 15 in the axial direction by driving the axial voice coil 18 in accordance with the signal from the waveform shaping circuit 35, and performs normal force-twisting. Do the following.

Next, tracking control will be explained. Each photodetection cell 23a, 23b, 23C,
23 (photoelectric signals γ, δ obtained from l.

ε and ζ are photodetection cells 23a, 23b, and 23c.

After being amplified by preamplifiers 36, 37, 38, and 39 of 23d, the signals are subjected to subtraction processing and addition processing by a subtraction circuit 40 and an addition circuit 41, and then input to the CPU 33. CPLJ33
If normal tracking control is determined by
The CPLJ 33 switches the switching circuit 47 and supplies the signal from the waveform correction circuit 43 to which the signal from the subtraction circuit 40 is supplied to the radial voice coil drive circuit 24 .

Thereby, the radial voice coil drive circuit 24 drives the radial voice coil 19 according to the signal supplied from the waveform correction circuit 43 to move the objective lens 15 in the radial direction, thereby performing normal tracking. Let's do it. Further, the signals ε and ζ obtained from the photodetection cells 23c and 23d of the first photodetector 23 are amplified by the preamplifiers 38° and 39 of the photodetection cells 23C and 23d, and then subtracted by the subtraction circuit 44, and the switching It is supplied to circuit 42. C
If high-speed tracking is determined by PLI33,
The CPU 33 switches the switching circuit 42 and supplies the signal from the subtraction circuit 44 to the radial voice coil drive circuit 24 via the switching circuit 42. This results in
The radial voice coil drive circuit 24 drives the radial voice coil 19 in accordance with the signal supplied from the subtraction circuit 44 to move the objective lens 15 in the radial direction, thereby eliminating blurring of the objective lens 15. That is, when the objective lens 15 shifts from the normal position to the left in the figure, a portion of the laser beam is irradiated only on the photodetection cell 23c of the photodetection cells 23c and 23d. The signal ε from this photodetection cell 23c is supplied to a subtraction circuit 44 via a preamplifier 38. The subtraction result of the subtraction circuit 44 is supplied to the radial voice coil drive circuit 24 via the switching circuit 42.

The radial voice coil drive circuit 24 moves the objective lens 15 to the right, that is, to a home position, in response to the signal supplied from the subtraction circuit 44. Similarly, objective lens 1
5 deviates from the normal position to the right in the figure, the photodetection cell 2
Of the cells 3c and 23d, only the photodetection cell 23d is irradiated with a portion of the laser beam. The signal ζ from this photodetection cell 23d is supplied to a subtraction circuit 44 via a preamplifier 39.

The subtraction results of the subtraction circuits 4 and 4 are obtained by the switching circuit 42.
It is supplied to the radial voice coil drive circuit 24 via. The radial voice coil drive circuit 24 is a subtraction circuit 44
The objective lens 15 is moved to the left, that is, to a home position, in response to a signal supplied from the controller. Therefore, as described above, even if the objective lens 15 deviates from the fixed position during high-speed access, it is corrected, that is, it is fixed at the fixed position. As a result, when the high-speed access is completed and the contents of the corresponding track are to be read, the laser beam from the objective lens 15 can be immediately irradiated onto that track. As a result, when high-speed access is performed in the past, the time required to perform the reading (settling time) can be shortened compared to the case where the objective lens 15 is locked and then the track is read.

Note that, as in the above embodiment, when the semiconductor laser 11 is used, only one type of collimating lens 14 is required, but as shown in FIG. It is necessary to use collimating lenses 46 and 47 to widen the spot size of the collimated laser beam.

〔Effect of the invention〕

As explained above, according to the present invention, an optical head capable of reading at least information from an information storage medium using focused light includes a light source and a light beam emitted from the light source that is converted into a light beam of a predetermined spot size. a collimating means for converting; a collimator having an inner diameter smaller than the spot size of the light beam converted by the collimating means and movable at least in a direction orthogonal to the optical axis of the converted light beam; an objective lens for condensing a beam of light onto the information storage medium; and receiving a beam that is focused by the objective lens on the information storage medium, is reflected from the information storage medium, and has passed through the objective lens again. The photodetector includes a light amount detection area that detects the amount of light from the objective lens, and a light amount detection area that detects the amount of light that protrudes from the light amount detection area as the objective lens moves, and detects the amount of light that is emitted from the objective lens. Since it is configured with a positional deviation detection tilt area that detects the positional deviation of the lens, it is possible to move to tracking operation stably regardless of the shaking of the objective lens.
Moreover, it has excellent effects such as being able to be manufactured with a very simple structure at low cost and with high reliability.

[Brief explanation of the drawing]

The first factor is a schematic configuration diagram showing the lens position detection means applied to the optical head according to the present invention, FIG. 2 is an explanatory diagram of its operation, and FIG. FIG. 4 is a schematic configuration diagram showing a lens position detection means, FIG. 4 is a configuration diagram showing an embodiment of the optical head according to the present invention, and the fifth factor is a diagram showing a case where a gas laser is used instead of a semiconductor laser. be. 1... Light source (semiconductor laser), 2... Collimating lens, 3... Objective lens, 6... Information storage medium,
8... Photodetector, 8a... Light amount detection area (photo detection cell), 8b, 8G... Positional deviation detection area (photo detection cell), 9... Projection lens, 11... Light source ( semiconductor laser), 12... information storage medium, 14... collimating lens, 15... objective lens, 23... first photodetector, 23a, 23b... light amount detection area (photodetection cell ), 23G, 23d... positional deviation detection area (photodetection cell), 45... light source (gas laser), 46° 47... collimating lens. Applicant's Representative Patent Attorney Takehiko Suzue Figure 1 Figure 2 Prisoner 113 Figure 4

Claims (6)

[Claims] (1) An optical head capable of reading at least information from an information storage medium using focused light, which includes a light source, a collimator that converts a light beam emitted from the light source into a light beam of a predetermined spot size, and a collimator. The device has an inner diameter smaller than the spot size of the light beam converted by the means and is movable at least in a direction perpendicular to the optical axis of the converted light beam, and directs a part of the converted light beam onto the information storage medium. comprising an objective lens for condensing light, and a photodetector for receiving a beam that is focused on the information storage medium by the objective lens, reflected from the information storage medium, and passed through the objective lens again, The photodetector includes a light amount detection area that detects the amount of light from the objective lens, and a position shift area that detects the amount of light that protrudes from the light amount detection area as the objective lens moves to detect positional deviation of the objective lens. An optical head characterized in that it is configured by providing a detection area. (2) The optical head according to claim 1, characterized in that at least two photodetector displacement detection areas are provided. (3) The optical head according to claim 1, wherein the light amount detection area of the photodetector is divided into at least two parts. (4) The optical head according to claim 1, wherein the light amount detection area and the positional deviation detection area are used for reading information from an information storage medium, and the light amount detection area is used for detecting track deviation. (5) The optical head according to claim 1, wherein at least the light amount detection area has a size substantially equal to the spot size of the projected light beam. (6) The optical head according to claim 1, wherein the light amount detection area and the positional deviation detection area are adjacent to each other.