JP3046394B2 - Optical head and optical information recording device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION This invention relates to an optical information recording apparatus using an optical heads.

[0002]

2. Description of the Related Art In an optical disk device, information is optically recorded on a surface of an optical disk along a spiral or concentric track, and a reflected light is detected by irradiating a light beam (generally, a laser beam). And play the recorded information. As a write-once optical disk device that allows users to record information on an optical disk using a laser, a document file system was initially commercialized, and was later used for peripheral storage devices of computers that required higher reliability. Products have been put to practical use. In addition, a rewritable optical disk device capable of erasing recorded information and rewriting the information has been put to practical use. Further, the development of an optical card memory device or an optical tape memory device in which the same technology is applied to a card-shaped or tape-shaped recording medium has been advanced.

In the case of an optical disk, for example, a recording mark having a size of about 1 μm is formed on a recording row having a track pitch of about 1.6 μm by a laser beam having a light spot diameter of about 1.2 μm. It is formed.
As a method of forming a recording mark, various methods of causing local destruction, deformation, or change in optical properties of a recording film have been proposed and put into practical use.

In this type of optical information recording apparatus, it is important to accurately track a recording row with a laser beam. For this reason, a track guide groove is provided in advance on an optical disc, and a tracking error signal obtained from diffracted light by this is provided. Tracking control systems that control the position of a laser beam based on the laser beam are widely used. However, this tracking control method is used when the reflected light from the disk is guided to the photodetector when the objective lens deviates from the optical axis following eccentricity or when the disk is warped or inclined. Since the optical axis shifts, an offset corresponding to the shift of the optical axis occurs in the tracking error signal, and normal tracking cannot be performed. That is, the light spot follows a position slightly deviated from the regular track. In such a state, of course, good recording / reproducing cannot be performed, and the reliability of the apparatus is significantly reduced.

As a countermeasure, a technique has been developed in which a mirror surface area is provided in a part of a track and a tracking error signal is corrected by a signal detected there. Specifically, by not forming a guide groove, a pit, a mark, or the like near the region to be a mirror surface region, the track guide groove is made discontinuous in the mirror surface region. For example, in the standard specification of a write-once optical disc having a diameter of 130 mm, such a region is provided in each sector at the time of preformatting.

FIG. 9 is a diagram schematically showing a pit arrangement around a mirror surface area in such an optical disk.
It has a track guide groove 801, a discontinuous portion 802 of the track guide groove 801, a pre-pit 803, and a mirror surface area 804. In this example, the positions of the sectors on adjacent tracks are set to be in the same radial direction, and the mirror area 804 is also in the same radial direction in each track. The track guide grooves 801 and the pre-pits 803 are formed as irregularities on the disk surface at the time of manufacturing the substrate. Pre-pit 80
3, a sector mark indicating the head of the sector, a clock synchronization signal, address information, and the like are recorded. On the track corresponding to the discontinuous portion of the track guide groove 801,
The mirror surface area 804 is left without forming a prepit.

FIG. 10 is a diagram showing the detection characteristics of a tracking error signal in a conventional optical disk device. The horizontal axis represents the tracking error amount, that is, the deviation amount between the track center and the center of the focused laser beam spot, and the vertical axis represents the tracking error amount. Signal. The track pitch is 1.6 μ in this example.
m. The tracking error signal when there is no optical axis shift of the objective lens, the warpage or the tilt of the disk, and the like is 901, and is 0 when the tracking error amount is 0. Therefore, when the feedback control is performed so that the tracking error signal becomes 0, the operating point becomes 90 in the figure.
2 and good tracking characteristics can be obtained.

On the other hand, the optical axis decentering of the objective lens,
Alternatively, the tracking error signal in the case where the disk is warped or tilted is as indicated by 903. If feedback control is performed using the tracking error 903 as it is, the operating point becomes 904, and good tracking characteristics cannot be obtained. Therefore, it is necessary to obtain the offset amount 905 of the tracking error signal 903, correct the amount, and perform feedback control.
If the optical axis of the objective lens is displaced, or the disk is warped or tilted, an offset also occurs in the tracking error signal detected in the mirror surface area due to the optical axis displacement. This offset has a simple functional relationship approximately or approximately in proportion to the offset amount 905 in the area where the track guide groove is located. Therefore, it is possible to correct the offset of the area where the track guide groove is present to some extent based on the tracking error signal obtained in the mirror area.

[0009] However, in order to further improve the reliability of the apparatus or to further increase the recording density, more accurate tracking performance than before is required. In the correction of the tracking error signal using the mirror surface area used in the above-mentioned conventional technology, the detection area of the offset of the tracking error signal is dispersed on the disk, so that it is difficult to realize quicker and more accurate tracking. It is. Also, in the track count when the optical head is moved in the radial direction for access, the mirror surface area often causes a miscount. This is a major obstacle when trying to improve access speed.

[0010]

As described above, in the prior art in which the offset of the tracking error signal is obtained by using the mirror surface area provided on the optical recording medium to perform offset compensation, the detection area of the offset It is difficult to achieve quick and precise tracking due to the distribution on the top, and the presence of a mirror surface area causes a miscount in the track count when the optical head is moved in the radial direction for access. There is a problem that it becomes a major obstacle in increasing the speed.

[0011] The present invention has been made in view of such circumstances, and an object without specially providing a space for the offset compensation on the recording medium, the detected and offset compensation offset of the tracking error signal It is an object of the present invention to provide an optical information recording apparatus capable of performing tracking control and access control more precisely than before.

[0012]

In order to solve the above-mentioned problems, an optical information recording apparatus according to the present invention comprises: a light beam generating means for generating two coaxial light beams having different beam diameters and optical characteristics; An objective lens for converging and irradiating a light beam from the light beam generating means onto an optical recording medium, and an objective lens 2 reflected by the optical recording medium and passing through the objective lens.
Light beam separating means for separating two light beams by utilizing a difference in optical characteristics, and first and second means for detecting two light beams separated by the light beam separating means, respectively.
And the first and second split type light detecting means.
A first method for generating a differential signal from the output of the light detecting means;
And second differential signal generation means, and the first and second differential signal generation means.
2 of the differential signals from the differential signal generating means.
The differential signal corresponding to the larger light beam is
Compensated by the differential signal corresponding to the other light beam
Using the corrective means and the differential signal corrected by the corrective means.
The light beam to follow a track on an optical recording medium
Tracking means for causing

[0013]

The two light beams generated by the light beam generating means have, for example, different polarization states as their optical properties. The light beam generating means for generating two light beams having different beam diameters and polarization states includes (1) a polarization separation optical element for separating light beams having two polarization states, an aperture for limiting the beam diameter, and Or (2) a beam splitter for splitting the light beam, a polarizer for selecting the polarization state of the split light beam, and a split light beam Or (3) a polarizing beam splitter for splitting the light beam according to polarization, and an aperture for limiting the beam diameter of at least one of the two, and a reflecting mirror for returning the two separated light beams to the beam splitter. A wave plate for changing the polarization state of each light beam, an aperture for limiting the beam diameter of at least one of the separated light paths, and the two separated light beams Constituted by the reflecting mirror back to over beam splitter.

The optical properties of the two light beams generated by the light beam generating means may be different in wavelength. Such a light beam generating means is composed of two laser light sources oscillating at different wavelengths, and these two light sources. It is constituted by means for combining the respective optical paths from the laser light source into one.

[0016]

When a light beam having a large beam diameter is focused and irradiated on an optical information recording medium by an objective lens, a spot size on the recording medium becomes small. Therefore, a tracking error can be detected with high sensitivity from the reflected light. Can be. on the other hand,
Conversely, a light beam with a small beam diameter has a large spot size on the recording medium and a low resolution, so that the detection sensitivity of the tracking error signal due to the reflected light is significantly reduced, but the objective lens shifts and the recording medium warps. The optical axis shift of the light beam due to the inclination or the inclination occurs similarly to the light beam having the larger beam diameter.

Accordingly, by generating a differential signal with respect to the output of the split-type light detecting means for the reflected light of the light beam having the smaller beam diameter, the offset due to the optical axis deviation of the light beam is detected, and the beam diameter is increased. The offset of the tracking error signal is always compensated by correcting the tracking error signal obtained by generating a differential signal with respect to the output of the split type light detecting means with respect to the reflected light of the light beam.

Further, if to perform such offset compensation, since the discontinuous regions of the track guide grooves for offset compensation is not required, track count errors in the access operation is also greatly reduced .

[0019]

Embodiments of the present invention will be described below with reference to the drawings. (First Embodiment) FIGS. 1 and 2 are a perspective view and a plan view schematically showing the structure of an optical head according to a first embodiment of the present invention. This optical head includes a semiconductor laser 101,
Collimator lens 102, polarizing beam splitter 10
3, reflection prisms 104 and 105, half mirror 10
6. Aperture 107, half mirror 108, rising mirror 109 and objective lens 110, cylindrical lens 111, condenser lens 112, polarization beam splitters 113 and 4.
It is composed of split photodetectors 114 and 115.

A linearly polarized light beam is emitted from the semiconductor laser 101, is converted into parallel light by a collimator lens 102, and then becomes 45 ° with respect to the polarization direction of the incident light beam.
The light is split into two types of polarization components by the polarization beam splitter 103 arranged so as to be in the direction of the angle. The light beams of the respective polarization components are guided to the half mirror 106 by the reflecting prisms 104 and 105 and are coaxially combined. At this time, the beam diameter of one light beam reflected by the reflection prism 105 is limited by the opening 107.

As described above, the semiconductor laser 101 and the collimator lens 102 and the polarization beam splitter 10
3. Reflecting prisms 104 and 105, half mirror 106
And a beam diameter control unit 117 composed of the aperture 107 generates two coaxial linearly polarized light beams having different polarization directions and beam diameters. The two coaxial light beams thus obtained pass through a half mirror 108, are then raised in a direction perpendicular to the plane of FIG.
8 is focused.

After passing through the objective lens 110, a part of the reflected light from the optical disk 118 is guided by the half mirror 108 to the signal detection system 116. In the signal detection system 116, the reflected lights corresponding to the respective polarization components are separated via the cylindrical lens 111, the condenser lens 112, and the polarization beam splitter 113, and then the photodetectors 114 and 1 are separated.
15 detected. That is, the photodetector 114 detects reflected light corresponding to the light beam having the larger beam diameter, and the photodetector 115 detects reflected light corresponding to the light beam having the smaller beam diameter. Cylindrical lens 111
Is provided to generate astigmatism for focus error detection.

Next, the operation of the optical head will be described. FIG. 3 is a cross-sectional view of a beam showing a polarization state of the light beam raised by the rising mirror 109. Reference numeral 201 denotes a polarization component of one of the polarization components that has sequentially passed through the polarization beam splitter 103, the reflection prism 104, and the half mirror 106. The light beam 202 is a light beam of a polarization component orthogonal to the light beam and sequentially passing through the polarization beam splitter 103, the reflection prism 105, the aperture plate 107, and the half mirror 106.

FIG. 4 is a diagram schematically showing a state in which the light beams of the respective polarization components condensed by the objective lens 110 are condensed. As shown in FIG. 4, since the light beam 201 has an intensity distribution spread over the entire aperture of the objective lens 110, the numerical aperture (NA) of the objective lens 110 is the same as the light beam irradiated by a normal optical head. And a small light spot close to the diffraction limit determined by the light wavelength
18 on the recording surface 119.

On the other hand, the beam diameter of the other light beam 202 is limited by the aperture 107 inserted in the optical path, and the numerical aperture is equivalently reduced.
Forms a light spot having a diameter larger than that of the light beam 201 on the recording surface 119. Therefore, since the resolution of the light beam 202 with respect to the recording surface 119 of the optical disk 118 is extremely low, it is possible to make the reflected light hardly contain a component corresponding to the tracking error signal, as described later. However, since the optical axis shift of the light beam 202 due to the shift of the objective lens 110 or the inclination of the optical disk 118 occurs in the same manner as the light beam 201, the same as in the tracking error signal detection system based on the reflected light of the light beam 202 It is possible to detect an offset component with a circuit configuration.

The wavelength of the light beam 202 (the same applies to the light beam 201 in this case) is λ, the aperture radius of the objective lens 110 is a, the focal length of the objective lens 110 is f, and the optical disk 11
Assuming that the track pitch on 8 is p, the tracking error signal contained in the reflected light of the light beam 202 becomes almost zero when the condition represented by the following equation (1) is satisfied. Therefore, it is desirable to set a under this condition. However, since a signal is also reduced due to a decrease in the amount of light, a value slightly larger than the right side may be set in some cases. a ≦ f · λ / (2p) (1)

FIG . 5 is a block diagram of the optical information recording apparatus according to the present invention.
O is a block diagram for showing an over Kashingu control and the tracking control system configuration. In FIG. 5, the photodetector 1
Numerals 14 and 115 denote quadrant photodetectors, whose outputs are supplied to a focus error detection circuit 401, a tracking error detection circuit 404 and an offset detection circuit 405.

The focus error is detected by an astigmatism method. That is, the focus error detection circuit 40
1 is for each output of the two photodetectors 114 and 115,
The focus error is detected by adding the outputs of the diagonal elements of the four divided photodetectors and taking the difference between the two addition values, and further, the focus error detected by each of the photodetectors 114 and 115. By adding the signals, a final focus error signal is generated. This focus error signal is phase-compensated and power-amplified by a focusing servo circuit 402 and then supplied to a focusing actuator 403. The focusing actuator 403 moves the objective lens 110 of FIG. 1 in the optical axis direction, and is controlled so that the light spot is always correctly focused on the recording surface of the optical disk 118.

On the other hand, the tracking error is detected by a push-pull method. That is, the tracking error detection circuit 404 adds the outputs of the left and right elements in the direction corresponding to the track guide groove on the optical disk 118 among the four divided photodetectors of the photodetector 114, and performs both addition. The tracking error is detected by taking the difference between the values. The tracking error signal detected as a differential signal in this manner includes an offset due to the shift of the objective lens 110 and the tilt of the optical disk 118 as described above, so that the tracking error signal is accurately proportional to the tracking error. Not.

The offset detection circuit 405 includes the photodetector 1
The above-described offset component is detected by performing the same addition and subtraction processing as that of the tracking error detection circuit 404 on the outputs of the fifteen divided photodetectors. Photodetector 1
The beam diameter of the light beam corresponding to the reflected light detected at 15 is small, and the light spot diameter on the optical disk 118 is large. Therefore, the offset signal output as a differential signal from the offset detection circuit 405 contains only a very small tracking error signal component.
An offset component caused by a shift of 0, an inclination of the optical disk 118, and the like is largely included.

The offset compensating circuit 406 amplifies the output of the offset detecting circuit 405 by a constant coefficient in order to cancel the offset included in the output of the tracking error detecting circuit 404, and after passing through a filter having an integral characteristic, By subtracting from the output of the tracking error detection circuit 404, an accurate tracking error signal not including an offset is generated. This tracking error signal is supplied to a tracking servo circuit 407, and after phase compensation and power amplification, is supplied to a tracking actuator 408. The tracking actuator 408 is controlled by the output of the tracking servo circuit 407 to move the objective lens 110 in the radial direction of the optical disc 118 so that the light spot always correctly tracks the recording sequence.

(Second Embodiment) FIG. 6 is a perspective view showing a configuration of a main part of an optical head according to a second embodiment of the present invention. In particular, FIG. The structure of a beam diameter control unit 507 for changing the beam diameter of the light beam is schematically shown. In FIG. 6, the light emitted from the semiconductor laser 101 is
The light beam that has become the parallel light in 2 is split by the half mirror 501 into two light beams. As for one of the separated light beams, only a linearly polarized light component in one direction is selected by the polarizer 502 and is reflected by the reflecting mirror 503. As for the other separated light beam, only the linear polarization component in the direction orthogonal to the linear polarization component selected by the polarizer 502 is selected by the polarizer 504, and the beam diameter is limited by the aperture 505.
The light is reflected by the reflecting mirror 506. The respective light beams reflected by the reflecting mirrors 503 and 506 are recombined by the half mirror 501 and go upward in the figure. The optical system after this is the same as in FIGS.

In the configuration of this embodiment, each light beam passes through the polarizer twice, so that sufficient performance can be obtained even if a relatively inexpensive polarizing film having a small extinction ratio is used. Further, it is easy to integrate the polarizer with a half mirror, a reflecting mirror, or both, and in such a configuration, effects such as reduction in the number of parts, miniaturization, and cost reduction can be obtained. (Third embodiment)

FIG. 7 is a perspective view showing a configuration of a main part of an optical head according to a third embodiment of the present invention. In particular, if the beam diameters of two kinds of polarized light beams irradiated on an optical disc are different. The structure of a beam diameter control unit 607 for tightening is schematically shown. In FIG. 7, a light beam emitted from a semiconductor laser 101 and converted into parallel light by a collimator lens 102 is split by a polarizing beam splitter 601 into two linearly polarized light beams having different polarization directions. One of the separated light beams is converted into circularly polarized light by the 波長 wavelength plate 602, and then reflected by the reflecting mirror 603.
The light is converted into linearly polarized light by the wave plate 602. By the two passes, the polarization direction of one light beam is rotated by 90 °. The other separated light beam is a quarter-wave plate 604.
Similarly, the polarization direction is rotated by 90 ° by the reflection mirror 605, but the beam diameter is limited by the opening 606 provided in the middle of the optical path. The two light beams are half mirror 60
1, but the polarization directions are 90 ° each.
Since it has been converted, it goes upward in the figure. The optical system after this is the same as in FIG. In the configuration of this embodiment, it is easy to integrate the quarter-wave plate with the polarizing beam splitter and / or the reflecting mirror, as in the second embodiment. Effects such as reduction, size reduction, and price reduction can be obtained. (Fourth embodiment)

FIG. 8 is a plan view showing a configuration of a main part of an optical head according to a fourth embodiment of the present invention, in which two light beams have different wavelengths. In FIG. 8, a short-wavelength light beam emitted from a first semiconductor laser 701 is collimated by a collimator lens 702. on the other hand,
The long-wavelength laser light emitted from the second semiconductor laser 703 is collimated by the collimator lens 704. These light beams are combined by the reflecting prism 705 and the dichroic mirror 706. The beam diameter of one light beam is limited by the aperture 707 to obtain a greater effect, but the aperture 707 can be omitted if an inexpensive device is to be provided. The combined two coaxial light beams pass through a half mirror 708, are raised in a direction perpendicular to the plane of the drawing by a rising mirror 709, and are focused on the recording surface of the optical disk by an objective lens.

After the reflected light from the optical disk passes through the same objective lens, a part of the reflected light is guided to the signal detection system 710 by the half mirror 708. The signal detection system 710 includes a cylindrical lens 711, a condenser lens 712, a dichroic mirror 713, and a four-segment type photodetector 714, 715. The photodetectors 714, 715 correspond to the wavelength components of short wavelength and long wavelength, respectively. The detected signal is detected. The cylindrical lens 711 generates astigmatism for detecting a focus error.

The operation of the present embodiment is the same as that described above, but two detection systems are constituted not by the difference in polarization component but by the difference in wavelength. Since the resolution of each of the detection diameters of these two systems is determined by the numerical aperture and the wavelength, the wavelength to be used and the aperture radius can be set in accordance with the equation (1) as in the first embodiment.

The present invention is not limited to the above-described embodiment, but can be implemented in various modifications as follows. In the embodiment, an infinite optical system, that is, an optical system in which a light beam is once collimated and then condensed on an optical disk by an objective lens is used. However, a finite optical system, that is, a light beam emitted from a laser and diverging is directly transmitted to the optical disk. The present invention can be applied to a case where an optical system that converges light on the top is used.

In the embodiment, the astigmatism method is used for focus error detection. However, it goes without saying that methods such as the Foucault method, the critical angle method, the knife edge method, and the beam size method may be used.

In the embodiment, the polarization of the light beam incident on the beam diameter control unit for making the diameters of the light beams having two different polarization states different is linearly polarized light, but may be circularly polarized light. This can be realized by a method such as converting linearly polarized light using a 波長 wavelength plate. The shape of the optical recording medium is not limited to a disk shape, but may be a card shape.

[0041]

According to the present invention, it is possible to perform offset compensation by detecting an offset of a tracking error signal caused by an optical axis shift of an objective lens or a warp or tilt of a disk by a simple optical system. Tracking control and access control can be performed more precisely than before.

Moreover, since it is not necessary to provide a mirror area for offset compensation on a recording medium such as an optical disk,
The substantial reduction in track count error significantly reduces the substantial access time and expands the application of the device.

[Brief description of the drawings]

FIG. 1 is a perspective view showing a configuration of an optical head according to a first embodiment of the present invention.

FIG. 2 is a plan view of the optical head of the embodiment.

FIG. 3 is a beam cross-sectional view showing a polarization state of a light beam set up by a setting mirror in the embodiment.

FIG. 4 is a diagram schematically showing a state of condensing light beams of respective polarization components condensed by an objective lens in the same embodiment.

FIG. 5 is a block diagram showing a configuration of a focusing control circuit and a tracking control circuit in the optical information recording apparatus according to one embodiment of the present invention.

FIG. 6 is a plan view showing a main part configuration of an optical head according to a second embodiment of the present invention.

FIG. 7 is a plan view showing a main configuration of an optical head according to a third embodiment of the present invention.

FIG. 8 is a plan view showing a main configuration of an optical head according to a fourth embodiment of the present invention.

FIG. 9 is a plan view schematically showing a pit arrangement around a mirror surface region in a conventional disk having a mirror surface region.

FIG. 10 is a diagram showing detection characteristics of a tracking error signal in a conventional optical disk device.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 101 ... Semiconductor laser 102 ... Collimator lens 103 ... Polarization beam splitter 104 ... Reflection prism 105 ... Reflection prism 106 ... Half mirror 107 ... Aperture 108 ... Half mirror 109 ... Rising mirror 110 ... Objective lens 111 ... Cylindrical lens 112 ... Condenser lens Reference numeral 113: polarization beam splitter 114: four-segmented photodetector 115: four-segmented photodetector 116: signal detection system 117: beam diameter control unit 118: optical discs 201, 202: light beam 404: tracking error detection circuit 405: offset Detection circuit 406 ... Offset compensation circuit 407 ... Tracking servo circuit 408 ... Tracking actuator

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) G11B 7/09 G11B 7/095 G11B 7/135 G11B 7/14

Claims (1)

(57) [Claims] 1. A light beam generating means for generating two coaxial light beams having different beam diameters and optical characteristics, and a light beam from the light beam generating means for converging and irradiating an optical recording medium with the light beam. An objective lens, and a light beam separating unit that separates two light beams reflected by the optical recording medium and passing through the objective lens using the difference in the optical characteristics, and separated by the light beam separating unit. First and second split-type light detecting means for detecting the two light beams respectively, and first and second split-light detecting means for respectively generating a differential signal from the output of the first and second split-type light detecting means. A differential signal generating means, and a differential signal corresponding to a light beam having a larger beam diameter among the differential signals from the first and second differential signal generating means is converted into a light beam having a smaller beam diameter. versus And a tracking means for causing the light beam to follow a track on the optical recording medium using the differential signal corrected by the correction means. Optical information recording device.