JP2583894B2 - Optical information recording / reproducing device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical information recording / reproducing apparatus capable of erasing an offset of a position error information signal such as a focus error signal and a tracking error signal during recording.

[Problems to be Solved by the Related Art and the Invention] In recent years, by condensing a light beam and irradiating the optical recording medium, information is recorded on the recording medium at a high density, An optical information recording / reproducing apparatus capable of reading out (reproducing) recorded information written on a recording medium at a high speed by receiving the return light of the photodetector with a photodetector has attracted attention. .

In the device, in order to perform recording or reproduction at high density, it is necessary to keep a light beam focused and irradiated on a recording medium in a focus state and an on-track state. Therefore, the apparatus is usually provided with a focus control unit and a tracking (radial) control unit.
These control means detect the focus and radial displacement information included in the return light from the recording medium as a focus error signal and a tracking error signal, and based on these error signals, change the focus of the light beam to a focus state and a tracking error signal. The on-track state is maintained.

Various methods for detecting the focus error signal and the tracking error signal have been proposed. FIG. 9 shows a conventional example of an optical information recording / reproducing apparatus using a critical angle method as a focus error signal detection method.

As shown in this figure, the optical information recording / reproducing apparatus includes an optical pickup 20 disposed opposite to the surface of a disk-shaped recording medium (hereinafter, referred to as a disk) 6. The optical pickup 20 can be moved by a moving means (not shown) in a direction crossing a recording track of the disk 6 which is driven to rotate in a direction indicated by an arrow T, for example.

A laser diode 1 as a light source is housed in a housing of the optical pickup 20. For example, P-polarized diffused light emitted from the laser diode 1 is converted into a parallel light beam by a coupling lens 2. The parallel light beam is incident on the polarization beam splitter 3, transmits almost 100%, is circularly polarized by the λ / 4 plate 4, and is condensed and irradiated on the disk 6 by the objective lens 5. The light beam condensed and radiated on the disk 6 is radiated to the recording layer of the disk 6 in a spot-like state close to focus. The reflected light from the recording layer of the disk 6 is condensed by the objective lens 5 to be almost parallel light, and
/ 4 plate 4 makes S-polarized light whose polarization direction is 90 degrees different from the forward path.
The light enters the polarization beam splitter 3. The light reflected from the disk 6 is almost 100% reflected by the polarizing beam splitter 3, further reflected by the reflecting prism 7, and incident on the critical angle prism 8. The light beam reflected by the slope of the critical angle prism 8 is received by a photodetector 9 disposed at a position for receiving the diffracted light in the far field (far field). The photodetector 9 is formed by a light receiving element such as a four-division photodiode. Then, a difference signal AB is obtained from the respective outputs A and B of the light receiving elements 9A and 9B adjacent in the left-right direction in FIG. 9 by an arithmetic circuit 10 such as a differential amplifier. A focus error signal SFE is generated. On the other hand, a tracking error signal is generated by the difference signal between the light receiving elements adjacent in the direction perpendicular to the paper of FIG.

The focus error signal SFE is supplied to the phase compensation circuit 1
1. The voltage is applied to the focus coil 13a of the lens actuator 13 via the objective lens drive circuit 12. The objective lens 5 is moved in a direction perpendicular to the surface of the disk 6 by the lens actuator 13 based on the focus error signal SFE to perform focus control.

The tracking error signal is also applied to a tracking coil (not shown) of the lens actuator 13 via a phase compensation circuit (not shown) and an objective lens driving circuit, and the spot light condensed and irradiated by the objective lens 5 onto a predetermined track. It can be made to follow.

Further, a data signal can be obtained from the sum signal of the front light receiving element of the photodetector 9.

By the way, in an apparatus for recording or reproducing information due to a structural change or a pit that causes a change in reflectance of a recording medium as a recording form, an offset may occur in the focus error signal SFE in some cases. This may be caused by a displacement of a component of the optical pickup 21 such as the photodetector 9 or an offset generated in the signal processing circuit of the focus error signal SFE. If this offset is adjusted so that there is no displacement or offset of the signal processing circuit at the time of reproduction, the offset at the time of recording can also be eliminated.

Unlike this offset, there is an offset that does not occur during reproduction but occurs during recording.

That is, at the time of recording, the light beam is set to the light emission power having a large energy density in a pulsed manner according to the recording data, and the light beam is focused on the surface of the recording medium irradiated with the light emission power. As shown in FIG. 10, pits 21 and the like are formed. The pits 21 are not generated uniformly with respect to the entire beam spot 22 operated at a high speed on the recording medium, but are generated first from a portion where the irradiation energy is large. Therefore, as shown in FIG. 10, an unrecorded portion 23 and a recorded portion 24 are simultaneously present in the rotation direction (tangential direction) indicated by the arrow T in the beam spot 22 on the recording medium. Therefore, the unrecorded part
As a result of a diffraction effect due to a reflectance difference between the 23 and the recorded portion 24 and a phase difference, the light amount distribution in the tangential direction T of the far field pattern 25 of the reflected light from the recording medium becomes non-uniform. As a result, an offset occurs in the focus error signal SFE between the reproduction section and the recording section. FIG. 11 shows how the focus error signal SFE changes.

In the optical adjustment, the offset is set to 0 during reproduction, and according to a recording command pulse as shown in FIG.
It is assumed that the reproduction state R and the recording state W are switched. Immediately after switching from the reproduction state R to the recording state W, b) as shown in the figure, the focus error signal SFE includes the light amount in the tangential direction T of the far field pattern 25 of the reflected light from the recording medium as described above. Since the distribution becomes non-uniform, an offset OS occurs. The focus error signal SFE gradually converges toward the ground level GND while being swung due to the transient response of the servo system. In the drawing, TR indicates an excessive response section of the servo system. Immediately after the focus error signal SFE is switched from the reproduction state R to the recording state W,
Immediately after switching from the recording state W to the reproducing state R, the light beam hardly swings because of the unevenness of the light quantity distribution in the tangential direction T of the far-field pattern 25 of the reflected light.
Also, the fact that the degree of the non-uniformity varies depending on the defocus amount occurs only during recording.

As described above, in the conventional optical information recording / reproducing apparatus, since the focus error signal SFE is offset between the reproducing state R and the recording state W, it is difficult to perform the optimal focus control in both states.

When an offset occurs in the focus error signal SFE, the light spot 22 particularly expands at the time of recording, and the irradiation power is insufficient, so that data cannot be written in a normal state. For this reason, there arises a problem that the reliability of the optical information recording / reproducing device is reduced.

The offset is not limited to the focus error signal obtained by the critical angle method, but also occurs in a focus error signal by another method or a tracking error signal depending on the method.

To solve the above problems, the applicant of the present application
No. 216819 proposes a device capable of eliminating the offset.

In this device, as shown in FIG. 12 and FIG.
Instead of the reflecting prism 7 in the figure, a half prism
The disk 6 at the far field position is provided at a position where the light beam transmitted through the harp prism 36 is received.
Light amount distribution detecting means 31 for detecting a light amount distribution of the return light from the disk 6 in the tangential direction of the disk 6. The light amount distribution signal Sd detected by the light amount distribution detecting means 31 detects the positional error information of the focus error signal STE. An offset erasing unit 32 for erasing a signal offset is provided. The light amount distribution detecting means 31 includes, for example, a light receiving element 33C,
33D comprises a photodetector 33 arranged adjacently in the tangential direction, and an arithmetic circuit 34 for calculating the output C, D of each of the light receiving elements 33C, 33D or a difference signal CD. CD is output as the light quantity distribution signal Sd. The offset erasing means 32 outputs, for example, a difference signal SFE−Sd = (A−) between the focus error signal SFE and the light amount distribution signal Sd.
B) -A / C-D, and outputs the difference signal SFE-Sd as the focus error signal S'FE from which the offset has been eliminated.

Incidentally, a focus search for guiding the objective lens 5 into the focus servo pull-in range is performed, for example, in a fourteenth focus search.
It may be performed as shown in the figure. That is, the objective lens 5 is gradually moved closer to the disk 6 from a state too far (state 1) far away from the disk 6 as shown in FIG. After entering the focus servo pull-in range, the servo loop is closed to maintain the in-focus state (state 3) as shown in FIG. In this focus search, the normal focus error signal at the time of the open loop gradually increases, reaches a maximum value, decreases, reaches a minimum value, and then increases again, as shown in FIG. 15 (a). And then reach the focal point. When the disk 6 is further approached than the focal point, the focus error signal further increases, reaches a maximum value, and then gradually decreases.

Incidentally, the position adjustment of the light quantity distribution detecting light receiving elements 33C and 33D is performed in a focused state (state 3) as shown in FIG. 14 (c). At this time, even if there is a slight positional error such as eccentricity or inclination of the optical system, the light receiving elements 33C and 33D can output the difference signal CD-D.
= 0 is adjusted. However, the focus offset component δn (n =
1,2,3) = | C−D |, the difference signal between the light receiving elements 33C and 33D when the returning light from the disk 6 forms an image on the light receiving elements 33C and 33D as shown in state 2. CD = δ2 is
It is much larger than δ1 and δ3 in states 1 and 3. Therefore, at this time, the focus error signal at the time of the open loop is
Due to the influence of δ2, distortion occurs as shown in FIG. 15 (b). When focus servo pull-in is performed by determining the shape of the focus error signal at the time of the open loop, focus servo pull-in may fail due to the influence of this distortion. The distortion of the focus error signal waveform as shown in FIG. 15 (b) is caused by the position adjustment error δd of the light amount distribution detecting elements 33C and 33D as shown in FIG. 14 (b), other aberrations of the optical element, This can occur as long as the displacement does not disappear at all.

Thus, there is room for improvement in the invention proposed in Japanese Patent Application No. 61-216819. In addition, actual opening 60-70
Japanese Patent Application Laid-Open No. 924 discloses an offset correction for focus detection.
There is no description on switching to the two states of not operating.

[Object of the Invention] The present invention has been made in view of the above circumstances, and is capable of eliminating an offset of a positional displacement information signal at the time of recording and performing a force servo pull-in reliably. It is an object of the present invention to provide an optical information recording / reproducing device.

[Means for Solving the Problem] The optical information recording / reproducing apparatus according to the present invention, as shown in the conceptual diagram of FIG. 1, is configured to return light from the recording medium at the far field position in the tangential direction of the recording medium. A light amount distribution detecting means 31 for detecting a light amount distribution, and an offset erasing means 32 for erasing an offset of a positional deviation information signal such as a focus error signal SFE based on the light amount distribution signal Sd detected by the light amount distribution detecting means 31 are provided. ,
For example, a switching means 50 is provided for switching between two states, that is, a state in which the offset erasing means 32 is operated and a state in which the offset erasing means 32 is not operated, in accordance with the state of the focus servo pull-in.

[Operation] For example, a difference signal AB obtained by the arithmetic circuit 10 from the outputs A and B of the light receiving elements 9A and 9B of the photodetector 9,
In other words, the focus error signal SFE is superimposed with an offset due to non-uniform light amount distribution of the return light from the recording medium in the tangential direction.

The light amount distribution detecting means 31 is, for example, a light detector 33 in which light receiving elements 33C and 33D are arranged adjacent to each other in the tangential direction at a far field position, and a difference between respective outputs C and D of the light receiving elements 33C and 33D. An arithmetic circuit 34 for calculating the signal CD outputs a difference signal CD corresponding to an offset as a light amount distribution signal Sd.

The offset erasing means 32 is, for example, a difference signal SFE- between the focus error signal SFE and the light quantity distribution signal Sd.
The arithmetic circuit 35 calculates Sd = (AB)-(CD), and outputs the difference signal SFE-Sd as the focus error signal S'FE from which the offset has been eliminated.

The switching means 50 includes, for example, a switch S interposed between the arithmetic circuit 34 and the arithmetic circuit 35, and a switch drive circuit 51 for driving the switch S. Until the focus servo pull-in is completed, the switch S is kept open, (AB) becomes a focus error signal, and after the focus servo pull-in is completed, for example, the focus servo pull-in input to the switch driving circuit 51 is performed. In response to the completion signal, the switch S is closed, and (AB)-(CD) becomes the focus error signal.

Embodiment An embodiment of the present invention will be described below with reference to the drawings.

2 to 6 relate to the first embodiment of the present invention, FIG. 2 is an explanatory diagram showing the configuration of an optical information recording / reproducing apparatus, and FIG. 3 is a diagram explaining the operation of the present embodiment at the time of offset erasing. FIG. 4 is an explanatory diagram showing the configuration of the focus search system, FIG. 5 is a flowchart showing the operation of the focus search system, and FIG. 6 is a waveform diagram for explaining the operation of the focus search system. is there.

As shown in FIG. 2, the optical information recording / reproducing apparatus of the present embodiment includes an optical pickup 20 disposed on the surface of the disk 6. This optical pickup 20
Can be moved by a moving means (not shown) in a direction crossing a recording track on the disk 6 which is driven to rotate in a direction indicated by an arrow T, for example.

A laser diode 1 as a light source is housed in a housing of the optical pickup 20. For example, P-polarized diffused light emitted from the laser diode 1 is converted into a parallel light flux by a coupling lens 2. Has become. The parallel light beam is incident on the polarization beam splitter 3, transmits almost 100%, is circularly polarized by the λ / 4 plate 4, and is then condensed and irradiated on the disk 6 by the objective lens 5. . The light beam condensed and radiated on the disk 6 is radiated on the recording layer of the disk 6 in a spot-like and near-focus state. The luminous flux condensed and irradiated on the recording layer forms a concave portion or a hole called a pit because the light emission intensity of the laser diode 1 is set to be large during the light emission in the recording state.

The reflected light from the recording layer of the disk 6 is condensed by the objective lens 5 into almost parallel light, and
The light is converted into S-polarized light having a polarization direction different from that of the forward path by 90 degrees by the plate 4, and is incident on the polarization beam splitter 3. The reflected light from the disk 6 is almost 100% reflected by the polarizing beam splitter 3.

In this embodiment, the light beam reflected by the polarization beam splitter 3 is split into two by a half prism 36. One light beam reflected by the half prism 36 is incident on the critical angle prism 8, and the light beam reflected on the slope of the critical angle prism 8 is a light beam disposed at a position for receiving the far-field diffracted light. The light is received by the detector 9. This photodetector 9 is, for example, 4
It is formed of a light receiving element such as a divided photodiode. Then, the light receiving elements 9A, 9 adjacent in the left-right direction in FIG.
An arithmetic circuit 10 such as a differential amplifier is output from the respective outputs A and B of B.
As a result, a difference signal AB is obtained, and the focus error signal SFE is generated by the difference signal AB. Note that a tracking error signal is generated by a difference signal between light receiving elements adjacent in the direction perpendicular to the paper surface of FIG.

The critical angle prism 8 is arranged so that the light amount distribution of the reflected light from the disk 6 in the tangential direction changes according to the shift of the focal position of the light beam with respect to the disk 6. Therefore, the photodetector 9 detects the light quantity distribution of the reflected light of the critical prism 8 in the tangential direction by the two light receiving elements 9A and 9B. Therefore, the focus error signal SFE is superimposed with an offset due to non-uniform light amount distribution in the tangential direction of the reflected light from the disk 6.

On the other hand, the other light beam transmitted through the half prism 36 is received by a photodetector 33 disposed at a position for receiving the far-field diffracted light. The photodetector 33 is formed of a light receiving element such as a two-division or four-division photodiode or the like. And the light receiving elements 33C and 33D arranged adjacently in the tangential direction
Thereby, the light amount distribution of the reflected light from the disk 6 in the tangential direction is detected. Outputs C and D of the light receiving elements 33C and 33D are input to an arithmetic circuit 34 as light amount distribution detecting means.
The arithmetic circuit 34 calculates a difference signal CD between the outputs C and D of the light receiving elements 33C and 33D, and outputs the difference signal CD.
Output as d.

Further, in the present embodiment, an arithmetic circuit 35 is provided as an offset erasing means. The arithmetic circuit 35 calculates a difference signal SFE- between the focus error signal SFE and the light quantity distribution signal Sd.
Sd = (AB)-(CD) is calculated, and this is output as a focus error signal S'FE from which the offset has been eliminated.

In the present embodiment, a switch S whose opening and closing is controlled by a switch driving circuit 51 is interposed between the arithmetic circuit 34 and the arithmetic circuit 35. The switch drive circuit 51
In the focus search for guiding the objective lens 5 into the focus servo pull-in range, the switch S is kept open until the focus servo pull-in is completed. Thus, the switch S is closed. Therefore, until the focusing servo pull-in is completed, the arithmetic circuit 10
, The focus error signal SFE is output, and after the focus servo pull-in is completed, the focus error signal S′FE = SFE−Sd from which the offset has been eliminated is output.

The focus error signal S'FE is supplied to the phase compensation circuit 1
1. The voltage is applied to a focus coil 13a of a lens actuator 13 via an objective lens drive circuit 12. The objective lens 5 is moved in a direction perpendicular to the surface of the disk 6 by the lens actuator 13 based on the focus error signal S'FE to perform focus control.

The tracking error signal is applied to a tracking coil (not shown) of the lens actuator 13 via a phase compensation circuit (not shown) and an objective lens driving circuit so that the spot light condensed and irradiated by the objective lens 5 follows a predetermined track. It can be made to be.

Further, a data signal can be obtained from the sum signal of all the light receiving elements of the photodetector 9.

Next, the operation of the focus servo system at the time of offset erasing according to the present embodiment will be described with reference to FIG.

The optical adjustment is performed so that the offset becomes 0 during reproduction, and the reproduction state R and the recording state W are switched according to a recording command pulse as shown in FIG. Immediately after switching from the reproduction state R to the recording state W, as shown in FIG. 3B, the focus error signal SFE obtained by the photodetector 9 and the arithmetic circuit 10 includes the tangential direction of the reflected light from the disk 6. The offset occurs because the light amount distribution of the image becomes non-uniform.

On the other hand, the light amount distribution signal Sd obtained by the photodetector 33 and the arithmetic circuit 10 is a signal corresponding to the light amount distribution in the tangential direction of the reflected light from the disk 6, as shown in FIG.

Therefore, the focus error signal S′FE obtained by calculating the difference signal SFE−Sd between the focus error signal SFE and the light quantity distribution signal Sd by the arithmetic circuit 35 is, as shown in FIG. The offset caused by the unevenness of the light amount distribution of the reflected light in the tangential direction is eliminated.

By the way, in the present embodiment, the focus search system is configured as shown in FIG. 4, for example.

That is, the focus error signal S from the arithmetic circuit 35
FE (at the time of focus search, until the focus servo pull-in is completed, since the switch S is open, the offset is not erased), and a controller 55 for determining the shape of the focus error signal waveform is provided. A switch SW1 for opening and closing the focus servo loop is interposed between the arithmetic circuit 35 and the phase compensation circuit 11, and the phase compensation circuit 11 and the objective lens drive circuit 12
Between them, an adder 56 is interposed. The other input terminal of the adder 56 receives the output of the adder 59 for adding the outputs of the Miller integrating circuit 57 and the step voltage generating circuit 58. Incidentally, between the adder 56 and the adder 59,
Switches SW2 and SW3 are interposed between the adder 59 and the step voltage generation circuit 58, respectively. The controller 55 includes a switch driving circuit 51, a Miller integrating circuit 57,
And switches SW1, SW2, and SW3.

The operation of the focus search system will be described with reference to FIGS.

First, in step (hereinafter referred to as S) 1 in FIG.
As shown in FIG. 6 (g), when a command (L level) for orch focus ON (AFS ON) is given to the Miller integrating circuit 57 by the controller 55, the output of the Miller integrating circuit 57 named a drive signal is output. Is applied to the objective lens drive circuit 12 via the adder 59, the switch SW2, and the adder 56, and the objective lens 5 is moved to the farthest end of the actuator movable range (Lens Down). At this time, the switch SW2 is closed to apply the drive signal to the objective lens drive circuit 12 via the adder 56, and the switch SW1 is opened to open the servo loop. Further, the switch S is opened, and the offset Sd is not erased from the focus error signal SFE.

Along with the AFS ON, as shown in FIG. 6 (h), the search ON (SRCH ON also becomes L, and by this SRCH ON,
As shown in FIG. 6 (f), the output of the Miller integrating circuit 57 decreases at a constant slope. The output of the mirror integration circuit 57 causes the objective lens 5 to approach the disk 6 at a constant speed.

Next, in S2, as shown in FIGS. 6 (a) and (b),
Pass the point P1 of the focus error signal to the detection level l1
To produce a focus error signal level high (FES LV
Confirm that H) changes to L.

Further, at S3, as shown in FIG. 6 (a), when the focus error signal passes through the point P2, the TOO FAR detecting the detection level l2 becomes L as shown in FIG. 6 (c). At the same time, SRCH ON becomes H as shown in FIG. 6 (h), and the change of the drive signal is stopped as shown in FIG. 6 (f).

Next, in step S4, the switch SW3 is closed with the low level of DC ADD as shown in FIG. 6 (i) after receiving the signal H of SRCH ON as shown in FIG. 6 (i). The step voltage generated by the voltage generating circuit 58 is added to the drive signal via the adder 59, and the objective lens 5 is forcibly brought closer to the focal point.

As a result, the objective lens 5 is suddenly moved toward the focal point, and the focus error signal passes through the point P3 as shown in FIG. The passage of this P3 is S5,
As shown in FIG. 6D, it is confirmed that the focus error signal level low (FES LVL) for detecting the detection level 13 returns to L.

At S6, at the timing when the FES LVL becomes L, as shown in FIG.
N) goes low, which causes switch SW1 to close,
The servo loop is closed.

Next, in S7, as shown in FIG.
At a timing delayed by a predetermined time from ON low, DC ADD goes high.
The switch SW3 is opened, and the application of the step voltage of the step voltage generation circuit 58 is stopped. At the same time, as shown in FIG. 6 (g), AFS ON also returns to H, and the switch SW2
Is opened, the output of the Miller integration circuit 57 is also cut off, and the application of the drive signal is stopped, as shown in FIG. 6 (f).
Then, normal focus servo is performed.

As the focus servo pull-in completion signal sent to the switch drive circuit 51, the fall of the FSRV ON to L may be used, or the FSRV ON may be set to a normal at the fall of the FSRV ON to L. The vibrator may be triggered and the output delayed by a predetermined time by the mono-multi vibrator may be used. In addition, the fall of FES LVL, TOO F
The rise of AR may be used.

In the above search state, when the focus error signal does not pass through each level of P1, P2, and P3, if the predetermined grace time nms is not reached in S8, the determination is repeated, and the grace time is repeated. If nms has elapsed, in S9,
It returns to the initial state as a reset.

As described above, according to the present embodiment, it is possible to eliminate the offset of the focus error signal caused by the unevenness in the light amount direction in the tangential direction of the reflected light from the disk 6 at the time of recording. Optimal focussing points in the recording state W coincide with each other, and optimal focus control can be performed in both states.

Further, during the focus search, the switch S is kept open until the focus servo pull-in is completed, and the difference signal (A−B) between the light receiving elements 9A and 9B becomes a focus error signal. Light receiving element 33C, 33
It is possible to prevent the waveform of the focus error signal from being distorted due to the value of the difference signal (CD) of D and causing an unstable servo state. In addition, even if the assembly position error of the optical system or the position adjustment error of the light receiving elements 33C and 33D for detecting the light quantity distribution is about the same as the conventional one, that is, even if it does not disappear at all, it is possible to reliably perform the focus servo pull-in. .

Further, according to this embodiment, even if the diffraction pattern of the reflected light from the disk 6 at the far field position changes for each disk, for example, the diffraction patterns on the photodetector 9 and the photodetector 33 are the same. , The optimum focus control can always be performed.

Incidentally, the servo gain is switched between the preformat portion and the data portion of the disk 6 because the amount of incident light is switched. However, if the switching of the servo gain is incomplete, the offset of the focus error signal changes to change the focus. An error signal may be emitted. According to the present embodiment, since the offset is deleted, it is possible to eliminate the fluctuation of the focus error signal between the preformat section and the data section.

In this embodiment, the opening and closing of the switch S may be manually performed.

FIG. 7 is an explanatory view showing the configuration of an optical information recording / reproducing apparatus according to a second embodiment of the present invention.

This embodiment is an example in which the present invention is applied to a system using a knife edge method as a focus error signal detection system.

In the present embodiment, one light beam reflected by the half prism 36 is condensed by the condenser lens 37. In the vicinity of the focal position of the condenser lens 37, a wedge-shaped light shielding plate (knife edge) 38 is arranged.
The photodetector 9 is disposed at a position where the light beam that has received the diffracted light of the far field in the light beam partially shielded by the light detector 9 is disposed. Then, the arithmetic circuit 10 calculates a difference signal AB between the outputs A and B of the light receiving elements 9A and 9B of the photodetector 9 and uses the signal as a focus error signal SFE.

The other light beam transmitted through the half prism 36 is received by a photodetector 33 as a light amount distribution detecting means, as in the first embodiment.

The light receiving elements 9A and 9B of the light detector 9 and the light detector 33
The light receiving elements 33A and 33B are arranged such that the polarity of the focus error signal SFE and the polarity of the light amount distribution signal Sd match the light amount distribution of the reflected light from the disk 6 in the tangential direction.

Other configurations, operations and effects are the same as those of the first embodiment.

FIG. 8 is an explanatory diagram showing a configuration of an optical information recording / reproducing apparatus according to a third embodiment of the present invention.

This embodiment is an example in which the present invention is applied to a system using an astigmatism method as a focus error signal detection system.

In the present embodiment, the cylindrical lens 14 is arranged in the optical path of one light beam reflected by the half prism 36. A four-divided photodetector 42 is arranged at a position where the light beam converged to an astigmatism by the cylindrical lens 41 becomes a perfect circle in the focus state.
The focus error signal SFE is obtained by calculating the sum (A + C) and (B + D) of the outputs of the diagonal elements of the photodetector 42 and then calculating the difference signal (A + C)-(B + D) by the arithmetic circuit 10. Can be

On the other hand, in the optical path of the other light beam transmitted through the half prism 36, a cylindrical lens 43 is disposed. The luminous flux converged to an astigmatism by the cylindrical lens 43 is moved to a position where it becomes a perfect circle in the focus state.
A split photodetector 44 is arranged. Then, the sum of the outputs of the diagonal elements of the photodetector 44 (A '+ C'), (B '+
D ′), the difference signal (A ′ +
By calculating C ′) − (B ′ + D ′), a light amount distribution signal Sd can be obtained.

Incidentally, each light receiving element of the photodetector 42 and the photodetector 44,
The focus error signal SFE and the light quantity distribution signal Sd are arranged so that the polarities of the light quantity distribution signal Sd and the light quantity distribution of the reflected light from the disk 6 in the tangential direction match.

Other configurations, operations and effects are the same as those of the first embodiment.

The present invention is not limited to each of the above embodiments.
In the second embodiment, after calculating the difference signals AC and BD, the difference signals (AC)-(BD) are further calculated.
May be calculated, and this may be used as the focus error signal S′FE in which the offset has been eliminated. In this case, as the switching means for switching between the two states of the state where the offset erasing means is operated and the state where the offset erasing means is not operated, between each arithmetic circuit for calculating the differences AC and BD and the light receiving elements 33C and 33D. Each may be provided with a switch.

Further, a means for adjusting the gain of the focus error signal SFE and the light amount distribution signal Sd may be provided in order to surely eliminate the offset.

The present invention can be applied to a case where a focus error signal by a method other than the above-mentioned embodiment or an offset of a tracking error signal is deleted depending on the method.

The configuration and operation of the focus search system are not limited to those described in the first embodiment. For example, after moving the objective lens 5 to the nearest end of the movable range of the actuator, the objective lens 5 is gradually moved to the disk 6. , And may be guided into the focus servo pull-in range.

In addition, the present invention is not limited to a recording mode in which pits are formed, but may be applied to a system in which the reflectance or the transmittance is changed by phase transition or the like.

Further, the present invention can be applied not only to a disk driven by rotation but also to a case where writing is performed on a card-shaped recording medium.

[Effects of the Invention] As described above, according to the present invention, a light quantity distribution detecting means for detecting a tangential light quantity distribution of return light from a recording medium, and a light quantity distribution signal detected by the light quantity distribution detecting means Thus, since the offset erasing means for erasing the offset of the displacement information signal is provided, the offset of the displacement information signal at the time of recording can be erased, and the offset erasing means can be operated in two states: Since the switching means for switching to the state is provided, there is an effect that the force servo pull-in can be reliably performed.

[Brief description of the drawings]

FIG. 1 is a conceptual diagram of the present invention, FIGS. 2 to 6 relate to a first embodiment of the present invention, FIG. 2 is an explanatory diagram showing the configuration of an optical information recording / reproducing apparatus, and FIG. FIG. 4 is a waveform diagram for explaining the operation of the embodiment at the time of offset erasing, FIG. 4 is an explanatory diagram showing the configuration of the focus search system, FIG. 5 is a flowchart showing the operation of the focus search system, and FIG. FIG. 7 is an explanatory diagram showing a configuration of an optical information recording / reproducing apparatus according to a second embodiment of the present invention, and FIG. 8 is an optical information recording apparatus according to a third embodiment of the present invention. FIG. 9 to FIG. 11 relate to a conventional example, FIG. 9 is an explanatory view showing the configuration of an optical information recording / reproducing apparatus, and FIG. 10 is reflected light from a recording medium. FIG. 11 is a diagram showing the non-uniformity of the light quantity distribution of FIG. FIG. 12 is a conceptual diagram illustrating a means for erasing an offset, FIG. 13 is an explanatory diagram showing a configuration of an optical information recording / reproducing apparatus provided with a means for erasing an offset, and FIG. FIG. 15 is an explanatory diagram showing a change in an offset component during a focus search, and FIG. 15 is a waveform diagram showing a focus error signal waveform during a focus search. 5 Disc 9,33 Photodetector 10,34,35 Arithmetic circuit 20 Optical pickup 31 Light intensity distribution detecting means 32 Offset erasing means 36 Half prism 50 Switching means S: Switch 51: Switch drive circuit

Claims (2)

(57) [Claims] 1. A light amount distribution of return light from the recording medium at a far field position is changed in accordance with a position shift of a light beam with respect to a recording medium, and positional deviation information is obtained from the changed light amount distribution. In an optical information recording / reproducing apparatus for generating a signal, a light amount distribution detecting means for detecting a light amount distribution in a tangential direction of the recording medium of return light from the recording medium at a far field position, and the light amount distribution detecting means Offset offset erasing means for erasing the offset of the displacement information signal in accordance with the light quantity distribution signal provided, and switching means for switching the offset erasing means to a state in which the offset erasing means is operated and a state in which the offset erasing means is not operated. Optical information recording and reproducing device. 2. An optical information recording / reproducing apparatus according to claim 1, wherein said switching means can perform a switching operation in accordance with a state of a focus servo pull-in.