JP2000011401A - Optical disk device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make a laser beam shorter in wavelength and an optical system higher in aperture and to enable stable and sure focus control by executing focus control by a focus error signal obtd. by synthesizing first and second focus signals varying in a signal level change with respect to a change in a defocus quantity. SOLUTION: The focus error signal TFE is formed by the second focus error signal FE2 of high sensitivity in a small range of the defocus quantity and the signal TFE is formed by correcting the signal level of the first signal FE1 in a wide focus controllable range on the outer region of the focus controllable range of the second signal FE2 at the time of synthesizing the focus error signal TFE in a synthesizing circuit 56. The signal TFE of the high sensitivity and the wide focus controllable range is thus formed by the second signal FE2 of the high sensitivity and the first signal FE1 of the wide focus controllable range in the synthesizing circuit 56. Then, the focus control is executed with the signal TFE.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical disk device and can be applied to, for example, a mastering device and an optical disk device for accessing a rewritable optical disk. According to the present invention, the focus is controlled by a focus error signal obtained by combining first and second focus error signals having different signal level changes with respect to a change in the defocus amount, thereby shortening the wavelength of a laser beam and increasing the optical system. Even if the numerical aperture is increased, stable and reliable focus control can be performed.

[0002]

2. Description of the Related Art Conventionally, in an optical disk device such as a compact disk player, by performing focus control in addition to tracking control, data recorded on a compact disk can be reliably reproduced.

FIG. 5 is a schematic diagram showing a focus control system based on an astigmatism method applied to this type of optical disc apparatus. The focus control system 1 focuses a laser beam emitted from a laser diode (not shown) on an information recording surface of a compact disc by an objective lens 2 and receives the returned light by the objective lens 2. The focus control system 1 converts the return light into substantially parallel light by the objective lens 2 and then converts the light into convergent light by the relay lens 4 via a predetermined optical system.

The focus control system 1 gives astigmatism to light emitted from the relay lens 4 by the multi-lens 6, and receives light by the light receiving element 7. As described above, when the return light is received by the light receiving element, the focus control system 1 operates when the laser beam is held in focus on the information recording surface.
The distance and the like from the multi-lens 6 to the light receiving element 7 are set such that the return light forms a substantially circular beam spot on the light receiving surface of the light receiving element 7. Accordingly, when the focus position of the laser beam is displaced before and after the information recording surface, the focus control system 1 changes the spot shape of the return light formed on the light receiving surface of the light receiving element 7 in the direction of the displacement and the magnitude of the displacement. The shape is changed to an elliptical shape according to the degree.

As shown in FIG. 6, the light receiving element 7 has a light receiving surface divided into four minute light receiving surfaces A, B, C, and D by dividing lines LH and LV that are substantially orthogonal to each other at the center. A, B, C, and D light receiving results can be respectively output. The focus control system 1 uses the dividing line LH
When the optical axis of the return light crosses the light-receiving surface at the intersection of LV and LV, and the spot shape of the return light formed on the light-receiving surface changes to an elliptical shape, the major axis direction of the elliptical shape is divided by a dividing line. The light receiving element 7 is arranged so as to be inclined approximately 45 degrees with respect to LH and LV.

Accordingly, when the laser beam is kept in focus on the information recording surface, the focus control system 1
As shown by reference numeral B1, a circular beam spot is formed with the intersection of the dividing lines LH and LV substantially at the center,
Return light is received by the minute light receiving surfaces A, B, C, and D with the same amount of light. Also, when the laser beam is held in focus on the back side of the information recording surface, the beam spot shape becomes an ellipse whose long axis is in the -45 ° direction, as indicated by reference numeral B2 (divided). The inclination of the line LH is 0 °), and when the small light receiving surfaces A, B, C, and D are viewed as a set in the diagonal direction, the other set is compared with the one set of the small light reception surfaces A and C. The amount of return light incident on the minute light receiving surfaces B and D is reduced. Further, when the laser beam is held in focus on the near side of the information recording surface, as shown by reference numeral B3, this beam spot shape becomes an elliptical shape having a + 45 ° direction as a major axis, and thereby the information recording surface is formed. Contrary to when the in-focus state is maintained on the back side of
And D, the amount of return light incident on one set of minute light receiving surfaces A and C is reduced.

The arithmetic circuit 8 receives the light receiving results of the minute light receiving surfaces A, B, C, and D from the light receiving element 7 and performs a current-voltage conversion process on the light receiving results. Furthermore, the current-voltage conversion result is represented by the sign of each light receiving surface, and

[0008]

(Equation 1)

The arithmetic processing of [1] is executed. Thus, as shown in FIG. 7, when the focus position of the laser beam changes with respect to the information recording surface according to the above-described behavior of the beam spot shape on the light receiving surface, the arithmetic circuit 8 sets 0 according to the change. A focus error signal FE whose signal level changes around the level is generated.

Here, the focus error signal FE is
As described above, when the optical system is assembled with high accuracy, the laser beam is at the 0 level when the laser beam is held in focus on the information recording surface, and an offset occurs due to a variation in the optical system. Accordingly, the focus control system 1 drives the actuator 10 having the voice coil motor configuration to displace the objective lens 2 by the driving circuit 9 so that the signal level of the focus error signal FE becomes a predetermined signal level. A servo loop is formed to keep the laser beam in focus on the information recording surface.

The focus error signal FE generated in this way and provided for focus control is a beam spot formed on the light receiving surface of the light receiving element 7 when the focus position of the laser beam is far away from the information recording surface. Since the light beam protrudes from the light receiving surface in the long axis direction, the signal level changes in accordance with the focus error amount in a predetermined range AR1 centered on the 0 level, and the signal level changes with respect to the focus error amount outside this range AR1. Is this range AR1
The opposite is true. Thereby, the focus error signal FE
Changes the signal level due to the so-called S-shaped characteristic,
In the focus control system 1, focus control is performed in a range AR1 (hereinafter, referred to as a focus controllable range) in which a signal level changes according to a focus error amount.

[0012]

In the focused state, the size (diameter) d of the beam spot of the laser beam formed on the information recording surface is given by the following equation.

[0013]

(Equation 2)

[0014] The smaller the wavelength of the laser beam and the larger the numerical aperture NA of the objective lens 2, the smaller it becomes. If the size d of the beam spot is reduced, the optical disk device can improve the recording density accordingly. Incidentally, in the case of a DVD-RAM, the wavelength λ is 650 [nm], and the numerical aperture NA is specified as 0.6.

However, the depth of focus fd of the objective lens 2 determined by the maximum value of the wavefront aberration (λ / 4) is given by the following equation.

[0016]

(Equation 3)

In the case of shortening the wavelength λ of the laser beam and increasing the numerical aperture NA of the objective lens 2 for high-density recording, the value sharply decreases.

That is, in the case of the above-mentioned DVD-RAM,
The depth of focus fd is about 1.8 [μm], for example, when the wavelength λ is 410 [nm] and the numerical aperture N of the objective lens is N.
When A becomes 0.95, the depth of focus fd becomes about 0.45
[Μm], which is a quarter of the value in the DVD-RAM.
Decreases to

Thus, in the DVD-RAM, a focus control system can be configured so that the focus control error can be reliably set to a small value of 1.8 [μm] or less corresponding to the depth of focus fd. On the other hand, in an optical disc device in which the laser beam has a shorter wavelength and the optical system has a higher numerical aperture, it is necessary to further reduce the error in the focus control. That is, in the above-described example, it is necessary to suppress the error of the focus control to a quarter or less of the DVD-RAM.

In this case, in the focus control system, the change in the signal level of the focus error signal FE with respect to the change in the defocus amount is increased.
It is necessary to increase the detection sensitivity of the defocus amount. Such an increase in the sensitivity of the focus error signal FE is achieved by switching the imaging magnification of the optical system to enlarge the image of the beam spot formed on the light receiving element 7, and by reducing the astigmatism by the multi-lens 6. By giving
Can be realized.

However, in this case, the focus controllable range AR1 is reduced accordingly, and it becomes difficult to perform stable and reliable focus control in the optical disc apparatus. That is, in the optical disk device, the focus servo is hardly locked, and the focus servo is easily released. This phenomenon has a greater effect when the numerical aperture NA of the optical system is increased than when the wavelength λ of the laser beam is shortened according to equation (2).
Is set to 0.6 or more.

The present invention has been made in view of the above points, and proposes an optical disk apparatus that can perform stable and reliable focus control even when a laser beam has a short wavelength and an optical system has a high numerical aperture. It is assumed that.

[0023]

According to the present invention, in order to solve the above-mentioned problems, at least a first and a second focus error signal whose signal level changes according to a defocus amount of a laser beam are synthesized. In this manner, the focus error signal is generated, and the first and second focus error signals are signals having different signal level changes with respect to a change in the defocus amount.

The first and second focus error signals, which have different signal levels with respect to a change in the defocus amount, have different focus controllable ranges. Therefore, if the focus error signal is generated by combining the first and second focus error signals, the change in the signal level with respect to the change in the defocus amount is high, and the large focus on the low sensitivity side is obtained. A focus error signal can be generated based on the controllable range, thereby enabling stable and reliable focus control even when the wavelength of the laser beam is shortened and the numerical aperture of the optical system is increased.

[0025]

Embodiments of the present invention will be described below in detail with reference to the drawings.

FIG. 2 is a block diagram showing a mastering device according to an embodiment of the present invention. In the optical disk manufacturing process, a master disk is exposed by the mastering device 20 to create a mother disk, and an optical disk is created using the mother disk.

Here, the master disk 21 is formed, for example, by applying a photoresist on the surface of a glass substrate, and is driven to rotate by a spindle motor 22 under predetermined conditions.
The spindle motor 22 drives and rotates the disk master 21 under the control of the spindle servo circuit 23, and outputs an FG signal whose signal level rises every predetermined angular rotation from a built-in rotary encoder. The spindle servo circuit 23 drives the spindle motor 22 to rotate so that the frequency of the FG signal becomes the frequency instructed by the central processing unit (CPU) 24. The master 21 is driven to rotate under the conditions of constant angular velocity, constant linear velocity, zone CAV, and the like.

The encoder 25 includes, for example, user data D1 to be recorded on the master disk 21 from a data storage.
After adding an error correction code to the user data D1, an interleave process is performed. Further, the encoder 25 adds data such as a header and a subcode to the interleaved data and outputs the data. The modulation circuit 26 modulates the output data of the encoder 25 by a modulation method suitable for recording on an optical disk and outputs the modulated data.

An automatic light amount control circuit (APC) 27 switches the signal level of a drive signal SD for driving the optical head 28 in accordance with the output data of the modulation circuit 26, thereby controlling the light amount of the laser beam applied to the master disk 21. Switching is performed according to the output data of the modulation circuit 26. At this time, the automatic light amount control circuit 27 detects the light amount of the laser beam based on the monitor signal SM output from the optical head 28, and the light amount of this laser beam is
The signal level of the drive signal SD is changed so that the reference light amount REFP is specified.

While the optical head 28 is sequentially displaced from the inner peripheral side to the outer peripheral side of the disc master 21 by a predetermined driving mechanism, the light amount of the laser beam irradiated on the disc master 21 is raised by the drive signal SD, whereby the disc is raised. The master 21 is exposed. At this time, the optical head 28 detects the amount of the laser beam by the built-in light receiving element, and outputs the detection result as a monitor signal SM. Also, output signals A1 to D1 and A2 to D2 of predetermined light receiving elements are output to the focus servo circuit 29, and the focus servo circuit 29
The focus position of the laser beam is changed by the drive signal SA output from the controller.

The focus servo circuit 29 outputs output signals A1 to D1 and A2 to D2 output from the optical head 28.
A focus error signal is generated, and the drive signal SA is output so that the signal level of the focus error signal becomes the reference voltage REFF output from the central processing unit 24.

The central processing unit 24 is a controller for controlling the operation of the mastering device 20, and outputs various control signals to the spindle servo circuit 23, the focus servo circuit 29 and the like.

FIG. 1 is a schematic diagram showing the configuration of the optical head 28 and the focus servo circuit 29. Optical head 28
, The laser 30 is a krypton laser, and emits a laser beam having a wavelength of 413 [nm].

The beam expander 31 receives a laser beam from the laser 30 via the right-angle prism 32, and expands and outputs the light beam of the laser beam. The light modulator 33 is configured by an electroacoustic optical element, modulates the amount of the laser beam according to the drive signal SD, and outputs the modulated light. The collimator lens 34 is connected to the optical modulator 33
The output laser beam is converted into a parallel light beam and guided to a relay lens 35. The relay lens 35 gives the laser beam an aberration so as to cancel a spherical aberration of an objective lens 36 described later and emits the laser beam.

The half-wave plate 37 converts the ordinary ray component and the extraordinary ray component of the laser beam transmitted through the inside into a 1/2.
An optical path difference for two wavelengths is generated and emitted. Further, the half-wave plate 37 is configured to be rotatable around the optical axis, and the rotation allows the ratio between the ordinary ray component and the extraordinary ray component to be varied.
Is adapted to adjust the amount of light incident on the light receiving element 38 that generates the monitor signal SM.

The polarizing beam splitter 39 receives the laser beam emitted from the half-wave plate 37, reflects a part of the laser beam in accordance with the plane of polarization of the laser beam, and forms a lens 40.
Out. The lens 40 condenses the laser beam on the light receiving surface of the light receiving element 38, and the light receiving element 38 changes the signal level according to the light amount of the laser beam applied to the master disk 21 based on the result of receiving the laser beam. The monitor signal SM is output.

Further, the polarization beam splitter 39 has a function of 1 /
Of the laser beam emitted from the two-wavelength plate 37,
The remaining components are transmitted and emitted, and the half-wave plate 41 converts the laser beam emitted from the polarization beam splitter 39 into linearly polarized light in a predetermined direction and emits it.

The objective lens 36 includes the half-wave plate 41
The laser beam that has passed through is focused on the disk master 21, and the return light obtained from the disk master 21 is received and emitted to the half-wave plate 41.

Here, as shown in FIG.
Is constituted by a two-group lens in which a pair of aspheric lenses 36A and 36B are integrally held by a lens holder 36C, thereby forming an optical system with a high numerical aperture and condensing a laser beam. . In this embodiment, the numerical aperture NA of the objective lens 36 is set to 0.95.

Further, the objective lens 36 is attached to the holder 3 by an electromagnetic actuator 36D having a voice coil motor structure.
6C is configured to be movable along the optical axis, so that the electromagnetic actuator 36D can be driven to perform focus control. The objective lens 36
Has a working distance WD from the lens tip to the information recording surface of about 100 [μm] corresponding to the numerical aperture NA.
It has been made to be set to.

Thus, the laser beam irradiated on the master disc 21 by the objective lens 36 exposes the photoresist on the master disc 21 and is partially reflected and received by the objective lens 36 as return light. . In the optical head 28, the polarization plane of the return light is converted by the half-wave plate 41 in a direction orthogonal to the laser beam, and is reflected by the polarization beam splitter 39 when tracing the optical path of the laser beam in reverse. Is separated from the laser beam.

The half-wave plate 44 transmits and emits the return light separated by the polarization beam splitter 39, and at this time, generates an optical path difference of 1/2 wavelength between the ordinary ray component and the extraordinary ray component. . The half-wave plate 44 is configured to be rotatable about the optical axis, and the rotation allows the ratio between the ordinary ray component and the extraordinary ray component to be variable.
Accordingly, the optical head 28 can adjust the incident light amount ratio of the return light that enters the light receiving element 45 that outputs the light receiving results A1 to D1 and the light receiving element 46 that outputs the light receiving results A2 to D2.

The polarizing beam splitter 48 is formed by forming a vapor deposition film on one slope of a parallelogram prism or a slope of a right-angled triangle prism and then bonding these slopes, and is emitted from the half-wave plate 44. The return light is split into two light beams according to the plane of polarization, and the two light beams are emitted almost in parallel.

The relay lenses 49 and 50 convert the luminous flux emitted from the polarizing beam splitter 48 into convergent light and emit the convergent light, respectively. The multi-lenses 51 and 52 apply astigmatism to the light emitted from the relay lenses 49 and 50 respectively. And emit. The light receiving elements 45 and 46 receive the light emitted from the multi-lenses 51 and 52, respectively, and
Inject 1 to D1, A2 to D2.

Here, the relay lens 49 and the multi-lens 5
1. The light receiving element 45 includes the relay lens 4, the multi lens 6, and the light receiving element 7 described above with reference to FIG. 5 except that the imaging magnification by the relay lens 49 and the amount of astigmatism given by the multi lens 51 are different. It has the same configuration.
Thus, the optical head 28 receives the light-receiving results A1, B1,.
C1 and D1 are output.

The relay lens 50 and the multi-lens 5
2. Similarly, the light receiving element 46 includes the relay lens 4, the multi lens 6, and the light receiving element described above with reference to FIG. 5 except that the imaging magnification by the relay lens 50 and the amount of astigmatism given by the multi lens 52 are different. It has the same configuration as the element 7. As a result, the optical head 28 receives the light-receiving results A1, B whose signal level changes according to the focus position of the laser beam.
1, C1, D1 and A2, B2, C2, D2 are detected in two systems.

The two optical systems including the relay lenses 49 and 50, the multi-lenses 51 and 52, and the light receiving elements 45 and 46 provide light receiving results A1, B1, C1, D1 and D1 with respect to a change in the focusing position of the laser beam. A2, B2, C
2, formed so that changes in D2 are different. Specifically, the relay lenses 49 and 50 are formed of convex lenses having different focal lengths, and the imaging magnifications of the light receiving elements 45 and 46 are set to be different, and / or the curvatures of the lens surfaces of the multi-lenses 51 and 52 are different. And the amount of astigmatism given to the return light is set to be different.

Thus, the optical head 28 can generate two focus error signals having different signal level changes (ie, different sensitivities) with respect to a change in the defocus amount. In this embodiment, the relay lens 49, the multi-lens 51, and the light receiving element 45
While the focus error signal is set to be generated with the same detection sensitivity as the focus control system in the DVD-RAM, the relay lens 50 and the multi-lens 5
2. The light receiving element 46 is set so that a focus error signal can be generated with a sensitivity four times higher than the focus control system in the DVD-RAM.

In the focus servo circuit 29, the arithmetic circuit 55 determines the light receiving results A1, B1, C of these two systems.
After performing the current-voltage conversion processing on each of D1, A1 and A2, B2, C2, and D2, the calculation processing of the equation (1) is performed. As a result, as shown in FIG. First and second focus error signals FE1 and FE2 having different controllable ranges are generated (FIG. 4A).

The synthesizing circuit 56 synthesizes the first and second focus error signals FE1 and FE2 to generate a focus error signal TFE (FIG. 4B), and the drive circuit 57 outputs the focus error signal TFE. The actuator 36D is driven such that the signal level becomes the signal level REFF instructed by the central processing unit 24.

Thus, the focus error signal TF
In synthesizing E, the synthesizing circuit 56 generates a focus error signal TFE based on the second focus error signal FE2 having high sensitivity in a small range of the defocus amount, and controls the focus of the second focus error signal FE2. In a region outside the possible range, the first focus error signal F having a wide focus controllable range is provided.
The signal level of E1 is corrected and the focus error signal TF
Generate E.

At this time, the synthesizing circuit 56 amplifies the first and second focus error signals FE1 and FE2 by an amplifying circuit having a focus gain set to 4: 1 and thereafter, based on a result of comparison with a predetermined reference level. By selecting the amplified first and second focus error signals FE1 and FE2 and generating the focus error signal TFE, the first focus error signal is added to the characteristics of the focus controllable range of the second focus error signal FE2. Signal F
The focus error signal T
Generate FE.

Thus, the synthesizing circuit 56 generates a focus error signal TFE with high sensitivity and a wide focus controllable range by using the focus error signal FE2 with high sensitivity and the focus error signal FE1 with a wide focus controllable range. .

In the above configuration, the mastering device 2
0 (FIG. 2), a laser beam is emitted from the optical head 28 in a state where the disk master 21 is rotationally driven, and the light amount of the laser beam is started in accordance with the user data D1 input to the encoder 25. The disc master 21 is sequentially exposed, and user data D1 is recorded on the disc master 21.

In this laser beam irradiation, the mastering device 20 (FIG. 1) modulates the short-wavelength laser beam emitted from the laser 30 in the optical modulator 33, thereby increasing the light amount according to the user data D1. Generate a beam. Mastering device 2
Numeral 0 focuses the modulated laser beam on the disk master 21 by the objective lens 36 having a two-lens configuration set to a high numerical aperture, thereby exposing the disk master 21 sequentially.

At this time, the mastering device 20 receives the return light reflected by the master disk 21 by irradiating the laser beam with the objective lens 36, and separates this return light into two light beams by the polarization beam splitter 48. Further, one of the two light beams thus separated is guided to the first optical system for generating a focus error signal by the relay lens 49, the multi-lens 51, and the light receiving element 45, and the remaining light beam is transmitted to the first optical system. It is led to an optical system for generating a focus error signal by the relay lens 50, the multi-lens 52, and the light receiving element 46, which have higher detection sensitivity than the system.

Further, the light receiving result A of each light receiving element 45, 46
1 to D1 and A2 to D2 are input to the arithmetic circuit 55, and the arithmetic processing of the equation (1) is executed here.
A first focus error signal FE1 having a low detection sensitivity and a wide focus controllable range corresponding thereto and a focus error signal FE2 having a high detection sensitivity and a correspondingly narrow focus controllable range are generated.

The mastering device 20 selects the focus error signal FE2 having a high detection sensitivity near the just focus requiring high accuracy and a correspondingly narrow focus controllable range, and conversely, it is so high. The first focus error signal FE1 having a low detection sensitivity in a portion separated from the just focus which does not require accuracy and having a correspondingly wide focus controllable range.
Is selected, and a focus error signal TFE is generated by a characteristic obtained by connecting the first and second focus error signals FE1 and FE2, and the signal level of the focus error signal TFE becomes a predetermined signal level REFF. The objective lens 36 is moved.

As a result, the mastering device 20 can execute the focus control with less error by the focus error signal FE2 with high sensitivity while securing a wide focus controllable range by the focus error signal FE1. Thus, even if the wavelength of the laser beam is shortened and the numerical aperture of the optical system is increased, focus control can be performed stably and reliably.

In particular, in the mastering device 20, it is necessary to precisely control the focus by generating a mother disk for mass production of optical disks, and thus the focus error signals FE1 and FE2 having different sensitivities.
If focus control is performed using a focus error signal TFE obtained by combining the above, focus control can be reliably performed even on a mass-produced optical disc. Also, accidents such as collision of the objective lens with the master disk can be prevented.

According to the above configuration, the focus is controlled by the focus error signal TFE obtained by combining the focus error signals FE1 and FE2 having different sensitivities, thereby shortening the wavelength of the laser beam and increasing the numerical aperture of the optical system. Also, focus control can be performed stably and reliably.

In the above-described embodiment, a case has been described in which focus control is performed using a focus error signal TFE obtained by combining two focus error signals having different sensitivities. However, the present invention is not limited to this, and the focus control is performed as necessary.
Focus control may be performed by a focus error signal obtained by combining more than two types of focus error signals.

In the above-described embodiment, the case where the focus error signal is detected by giving astigmatism to the return light has been described. However, the present invention is not limited to this, and various methods such as the Foucault method are used. It can be widely applied when detecting a focus error signal.

In the above-described embodiment, the case where the return light is separated into two light beams to generate two focus error signals having different sensitivities and then combine them is described. However, the present invention is not limited to this. Alternatively, a focus error signal may be generated by combining two focus error signals having different sensitivities from one optical system. That is, in this case, in the optical system described above with reference to FIG. 5, an optical image corresponding to the first and second focus error signals may be formed on the light receiving surface of the light receiving element 7 in a superimposed manner. Can be realized by interposing. Alternatively, optical images having different imaging magnifications and astigmatism may be formed on the right half and the left half of the light receiving surface described above with reference to FIG. 6, for example.

In the above embodiment, the wavelength 4
Although a case in which a laser beam of 13 [nm] is focused on an optical disc by an objective lens having a numerical aperture of 0.95 has been described, the present invention is not limited to this. The present invention can be widely applied to the case where the laser beam is condensed, and is particularly effective when the laser beam is condensed by an optical system having a numerical aperture of 0.6 or more. It should be noted that the present invention can be applied to an optical disk device having a numerical aperture of the same level as the conventional one in addition to the optical disk device having such a high numerical aperture, and the focus controllable range can be expanded more than before. In this way, accidents such as collision of the optical head with the optical disk can be prevented.

In the above-described embodiment, the case where the laser beam is focused by the two-group objective lens has been described. However, the present invention is not limited to this, and the laser beam is focused by the single objective lens. In this case, the present invention can be widely applied to a case where a laser beam is condensed by an optical system having a mirror configuration instead of a convex lens.

Further, in the above-described embodiment, the case where the present invention is applied to a mastering apparatus to expose a master disc is described. However, the present invention is not limited to this, and the present invention is not limited to this. It can be widely applied to optical disk devices using recording media such as. In particular, the present invention can be applied to near-field recording / reproduction in which the depth of focus becomes extremely small and focus control becomes much more difficult than in the past, thereby making it possible to reliably access an optical disk.

[0068]

As described above, according to the present invention, the focus control is performed by the focus error signal obtained by synthesizing the first and second focus error signals having different signal level changes with respect to the change in the defocus amount. Focus control can be performed stably and reliably even if the wavelength of the beam is shortened and the numerical aperture of the optical system is increased.

[Brief description of the drawings]

FIG. 1 is a schematic diagram illustrating an optical head and a focus servo circuit of a mastering device according to an embodiment of the present invention.

FIG. 2 is a block diagram showing a mastering device using the optical head and the focus servo circuit of FIG. 1;

FIG. 3 is a sectional view showing an objective lens of the optical head of FIG. 1;

FIG. 4 is a characteristic curve diagram for explaining the operation of the focus servo circuit of FIG. 1;

FIG. 5 is a block diagram showing a conventional focus control system.

FIG. 6 is a plan view showing a light receiving surface of the light receiving element.

FIG. 7 is a characteristic curve diagram showing characteristics of a focus error signal.

[Explanation of symbols]

2, 36 ... objective lens, 4, 49, 50 ... relay lens, 6, 51, 52 ... multi-lens, 7, 38, 4
5, 46: light receiving element, 8, 55: arithmetic circuit, 9, 5
7: drive circuit, 56: synthesis circuit, 20: mastering device, 28: optical head, 29: focus servo circuit

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Koichiro Kijima 6-7-35 Kita-Shinagawa, Shinagawa-ku, Tokyo Inside Sony Corporation (72) Inventor Kenji Yamamoto 6-35-35 Kita-Shinagawa, Shinagawa-ku, Tokyo Inside Sony Corporation (72) Inventor Shimada Maeda 6-7-35 Kita-Shinagawa, Shinagawa-ku, Tokyo Sony Inside (72) Inventor Kiyoshi Osato 6-7-35 Kita-Shinagawa, Shinagawa-ku, Tokyo Soni -In-house (72) Inventor Toshio Watanabe 6-35, Kita-Shinagawa, Shinagawa-ku, Tokyo Sony Corporation F-term (reference) 5D118 AA13 BA01 CA11 CC12 CD02 CF06 DA03 DA17 DA20 DB12 DC03 EA02

Claims (5)

[Claims] 1. An optical system for converging a laser beam emitted from a predetermined light source on an optical disk and receiving return light of the laser beam obtained from the optical disk, and based on the return light received by the optical system. A focus error signal generating means for generating a focus error signal whose signal level changes in accordance with the defocus amount of the laser beam; and the optical system controls the laser beam so that the focus error signal has a predetermined signal level. A drive unit for displacing the focusing position, wherein the focus error signal generation unit synthesizes at least a first and a second focus error signal whose signal level changes according to a defocus amount of the laser beam. The focus error signal is generated, and the first and second formats are generated. Suera signal, the optical disk apparatus characterized by signal level change with respect to change of the defocus amount are different signals. 2. The optical disk device according to claim 1, wherein a numerical aperture of the optical system is set to 0.6 or more. 3. The focus error signal generation means, a light separation means for separating the return light into first and second light fluxes, and a first focus error signal generation means for generating the first focus error signal from the first light flux. Signal generating means, a second signal generating means for generating the second focus error signal from the second light flux, and a signal synthesizing means for synthesizing the first and second focus error signals. The optical disk device according to claim 1, wherein: 4. The focus error signal generation means: a signal generation means for receiving the return light by one light receiving element to generate the focus error signal, and corresponding to the first and second focus error signals. The optical disk device according to claim 1, further comprising: an optical element that forms an optical image by the return light on a light receiving surface of the light receiving element. 5. The optical disk device according to claim 4, wherein said optical element is a hologram element.