JP2518288B2 - Optical beam spot observation device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention will be described in the following order.

A Industrial Field of Use B Outline of the Invention C Conventional Technology D Problems to be Solved by the Invention E Means for Solving Problems F Action G Example G-1 First Example (Fig. 1- Fig. 5) G-2 Second embodiment (Fig. 6) G-3 Third embodiment (Fig. 7) H Effect of the invention A. Industrial field of application The present invention uses a light beam through an objective lens. The present invention relates to an optical beam spot observation device used for observing a beam spot formed by a light beam emitted from an optical pickup that is incident on an optical recording medium to read information.

B Outline of the Invention The present invention is applied to the observation of a beam spot formed by an optical beam emitted from an optical pickup which reads an information recorded on the optical recording medium by making the light beam incident on the optical recording medium through an objective lens. In a light beam spot observation apparatus used, a light beam from an optical pickup that has passed through an observation objective lens arranged facing the objective lens of the optical pickup is split into at least first and second split light beams by a beam splitter. Then, the first split light beam is guided to an observation unit used for observing the beam spot, and the beam spot of the second split light beam is guided to the image pickup means, and is observed based on the image pickup output signal obtained from the image pickup means. A signal that changes depending on the focus state of the first split light beam at the By driving the focus control means for the objective lens of the optical pickup according to the signal, the observation section observes the spot formed by the optical beam from the optical pickup, and the light beam from the optical pickup is always in the proper focus state. It is designed so that it can be performed under the influence of being placed.

C. Related Art An optical disc player for reproducing recorded information from an optical disc as an optical recording medium is equipped with an optical pickup that constitutes an optical system for reading recorded information from an annular recording track formed on the optical disc. To be

Such an optical pickup is, for example, as shown in a simplified manner in FIG. 8, assembled so as to form one optical system block 1 as a whole, and a radial direction of the optical disc D on which an annular recording track is formed. It is allowed to move along (the direction indicated by the arrow R). Then, the laser light beam emitted from the laser diode 2 which is the light beam generation source arranged in the optical system block 1 is incident on the polarization beam splitter 3 and passes through the analyzer surface 3a thereof, and then on the collimator lens 4. Incident. The laser light beam incident on the collimator lens 4 is collimated by the collimator lens 4, then passes through the quarter-wave plate 5, enters the objective lens 6, and is converged by the objective lens 6. It is made incident on D. Then, the laser light beam incident on the optical disc D is reflected in the state of being modulated by the recording track formed on the optical disc D to be a reflected laser light beam.

The reflected laser light beam from the disk D returns via the objective lens 6, is converted into a parallel light flux, and passes through the quarter-wave plate 5. In this way, the disc D passes through the quarter-wave plate 5
The reflected laser light beam which is incident on the disk D, is reflected by the disk D, and passes through the quarter-wave plate 5 again,
The polarization direction of the laser light beam incident on the disk D after passing through is rotated by π / 2.

The reflected laser light beam, which has been rotated by π / 2 in the polarization direction, enters the collimator lens 4, is focused into a beam by the collimator lens 4, and then enters the polarization beam splitter 3 to generate a polarization beam splitter. At 3, the light is reflected by the analyzer surface 3a and guided to the photodetector 8 through the light receiving lens 7. Then, a detection output signal for the reflected laser light beam is obtained from the photodetector 8, and a reproduction information signal, a focus control signal, a tracking control signal, and the like are formed in the signal processing unit based on the detection output signal. To be done.

The above-mentioned objective lens 6 has a focus control coil forming a focus control means for moving the objective lens 6 to move toward and away from the optical disc D along the optical axis direction according to the focus control signal. 9
And the objective lens 6 according to the tracking control signal,
A tracking control coil 10 forming a tracking control means for moving the optical disc D in the radial direction, which should be the direction orthogonal to the optical axis, is provided.

In the optical pickup configured as described above, the optical axis of the laser light beam that is made incident on the optical disc D from the laser diode 2 through the objective lens 6 is made orthogonal to the recording surface of the optical disc D in the adjustment stage. It is necessary to observe the shape, position, etc. of the beam spot to be formed on the optical disc D by the laser light beam for adjustment for adjustment or other adjustment. In such observation, for example, the laser light beam focused by the objective lens 6 of the optical pickup is made incident on the beam spot observation device, so that the laser light beam from the objective lens of the optical pickup device is incident on the observation surface of the beam spot observation device. This is performed so that a beam spot by the laser light beam is formed.

D Problems to be Solved by the Invention As described above, when the beam spot formed on the observation surface is observed by the laser light beam emitted from the optical pickup, the objective lens 6 of the optical pickup has its optical axis. Since the objective lens 6 is held in a free state for observation, the position of the objective lens 6 is, for example, in the direction along the optical axis of the objective lens 6 because it is held so as to be movable in the direction along and the direction orthogonal thereto. Reciprocating displacement may change the focus state of the laser light beam on the observation surface, and accordingly, the beam spot formed on the observation surface may fluctuate, making observation impossible. Therefore, in the related art, for example, by supplying a predetermined constant current to the focus control coil 9 provided for the objective lens 6 of the optical pickup, the position of the objective lens 6 in the direction along the optical axis thereof. Under a fixed state, the laser light beam focused by the objective lens 6 forms a beam spot on the observation surface of the beam spot observation device, and the beam spot is observed or the focus is focused. By supplying a predetermined lamp current to the control coil 9, the objective lens 6 is continuously moved in the direction along the optical axis thereof, and the laser light beam focused by the objective lens is observed by the beam spot observation device. Observe the laser beam from the objective lens 6 by forming a beam spot on the surface. When the correct focus state in the above method for performing the observation of the beam spot obtained on the observation plane is taken.

However, the beam spot obtained on the observation surface is observed under the condition that a predetermined constant current or a predetermined lamp current is supplied to the focus control coil 9 provided for the objective lens 6 of the optical pickup in this way. In the case where the optical pickup is performed, the situation in which the position of the objective lens 6 is changed easily due to the influence of external disturbance such as vibration that acts on the optical pickup easily occurs.
There is a disadvantage in that it is difficult to stably perform accurate observation of the beam spot formed by the laser light beam from the objective lens 6.

In view of such a point, the present invention is capable of observing a beam spot formed in an observing section by a light beam emitted through an objective lens in an optical pickup so that the light beam from the optical pickup is always kept in a proper focus state. It is an object of the present invention to provide an optical beam spot observation device that can be accurately and stably performed.

E Means for Solving the Problems In order to achieve the above-mentioned object, a light beam spot observation apparatus according to the present invention includes a light beam generation source, an objective lens for focusing a light beam from the light beam generation source, and an objective. At least first and second light beams from the observation objective lens arranged facing the objective lens in the optical pickup including the focus control means for the lens and the objective lens of the optical pickup that has passed through the observation objective lens.
In addition to the beam splitter for splitting into the split light beam and the observing section for making the first split light beam incident and observing the beam spot, the second split light beam is made to enter and A focus state detection unit that includes an image pickup unit that picks up an image of the beam spot, forms a detection output signal according to the focus state of the first split light beam in the observation unit based on the image pickup output signal obtained from the image pickup unit, and the focus state detection unit And a focus control unit that drives a focus control unit of the optical pickup according to a detection output signal obtained from the unit.

F Action In the light beam spot observation apparatus according to the present invention as described above, the light beam emitted from the optical pickup through the objective lens is guided to the beam splitter through the observation objective lens, and the first and second beam splitters are used. It is split into split light beams. Then, the first split light beam from the beam splitter is guided to the observation unit, and the beam spot formed by the first split light beam is observed in the observation unit. Further, the second split light beam from the beam splitter is guided to the image pickup unit of the focus state detection unit, and the focus state detection unit picks up an image of the beam spot formed by the second split light beam by the image pickup unit. At the same time, a detection output signal corresponding to the focus state of the first split light beam in the observation unit is formed based on the imaging output signal obtained thereby. Then, the focus control unit drives the focus control unit of the optical pickup according to the detection output signal obtained from the focus state detection unit, thereby adjusting the position of the objective lens of the optical pickup in the direction along the optical axis. Then, the first split light beam forms a beam spot under an appropriate focus state in the observation section.

By doing so, the observation of the beam spot formed by the first split light beam in the observation unit ensures that the first split light beam is always appropriate in the observation unit even when disturbance acts on the optical pickup. It is performed while maintaining the focus state. Therefore, the beam spot formed by the light beam emitted from the optical pickup through the objective lens can be observed accurately and stably.

G Example G-1 First Example (FIGS. 1 to 5) FIG. 1 schematically shows an example of a light beam spot observation apparatus according to the present invention. This example is summarized to form one optical system block 1 shown in FIG. 8 and described above, and includes a laser diode 2, an objective lens 6, a focus control coil 9 and a tracking control coil 10. It is used for observing a beam spot formed by a laser light beam emitted from the provided optical pickup through the objective lens 6.

In the example shown in FIG. 1, an observation objective lens 20 is arranged so as to face the objective lens 6 of the optical pickup forming the optical system block 1. In the observation objective lens 20, a laser light beam emitted from a laser diode 2 (not shown) which is a beam generation source incorporated in the optical pickup and emitted from the optical pickup through the objective lens 6 is focused by the objective lens 6. ,
After the focal point is formed, it is incident in a divergent state, and the observation objective lens 20 has, for example, a magnification of about 60 times and focuses the laser light beam from the optical pickup incident in a divergent state.

The focused laser light beam B ₀ from the observation objective lens 20 is made incident on a beam splitter 21 arranged behind the observation objective lens 20. The beam splitter 21 is formed of, for example, a half mirror, and divides the laser light beam B ₀ from the observation objective lens 20 into first and second split light beams B ₁ and B ₂ , The light beam B ₁ is guided to the observation section 51 side, and the second split light beam B ₂ is guided to the focus state detection section 52 side.

The observation section 51 is configured to include an eyepiece lens 22, a neutral density filter 23, and an observation camera 24. The eyepiece lens 22 has, for example, a magnification of about 5 times, and makes the first split light beam B ₁ from the beam splitter 21 which is incident in a divergent state after forming a focus point, into a focused state and reduces the beam. Optical filter 23
It is incident on the observation camera 24 via. The observation camera 24
For example, an image sensor (CCD image sensor) using a charge-coupled device (charge coupled device, CCD) is used, and the beam of the first split light beam B ₁ incident from the eyepiece lens 22 through the neutral density filter 23. Spot
It is formed on the imaging surface 24a of the CCD image sensor. Then, the beam spot of the first split light beam B ₁ formed on the imaging surface 24a is imaged by the CCD image sensor. The eyepiece lens 22 and the observation camera 24 are used for the eyepiece lens when the objective lens 6 of the optical pickup takes the reference position.
The first split light beam B ₁ focused by 22 is set so as to form a focus point on the image pickup surface 24a of the CCD image sensor in the observation camera 24, that is, a proper focus state on the image pickup surface 24a. To be done.

Then, the image pickup output signal Si obtained by the CCD image sensor obtained from the observation camera 24 is displayed on the image display unit 24D.
The image display section 24D observes the beam spot formed by the first split light beam B ₁ on the imaging surface 24a of the CCD image sensor. In other words, the laser light beam emitted from the optical pickup through the objective lens 6 is observed by the beam spot formed by the laser light beam B ₀ obtained by being focused by the objective lens 6. Note that the neutral density filter 23 has a relatively high intensity of the first split light beam B _{1 that} is focused by the eyepiece lens 22 and is incident on the observation camera 24, so that the intensity should be appropriately reduced. For example, it is configured by providing two to three filters that reduce the strength to 1/100.

On the other hand, from the beam splitter 21 to the focus state detection unit 52
The second split light beam B ₂ guided to the side is incident on a beam splitter 25 similar to the beam splitter 21.
The beam splitter 25 is also formed by a half mirror, for example, and further divides the second split light beam B ₂ into third and fourth beams.
Of the second divided light beams B ₃ and B ₄ , and the third divided light beam B ₃ is made incident on the first detection camera 28 through the neutral density filter 26, and the fourth divided light beam B ₄ is reduced. Optical filter 27
It is incident on the second detection camera 29 through. Similarly to the observation camera 24, each of the first and second detection cameras 28 and 29 uses, for example, a CCD image sensor. Then, in the first detection camera 28, the observation objective lens
A beam spot of the third split light beam B ₃ which is focused by 20 and enters from the beam splitter 25 through the neutral density filter 26 is formed on the imaging surface 28a of the CCD image sensor, and the beam spot is also formed by the CCD. The image is taken by the image sensor. At that time, the first detection camera 28 has the CCD image sensor whose imaging surface 28a is located at the reference position of the objective lens 6 of the optical pickup. It is set so that the light beam B ₃ is located in front of the position F _{1 at} which the focal point should be formed by a predetermined distance A. Further, in the second detection camera 29, the beam spot of the _fourth split light beam B ₄ which is focused by the observation objective lens 20 and enters from the beam splitter 25 through the neutral density filter 27 is a CCD.
Formed on the imaging surface 29a of the image sensor,
The beam spot is imaged by the CCD image sensor. At that time, the second detection camera 29 has a fourth division focused by the observation objective lens 20 with the image pickup surface 29a of the CCD image sensor thereof positioned at the reference position of the objective lens 6 of the optical pickup. It is set so that the light beam B ₄ is located at a position rearward by a predetermined distance A ′ by the position F _{2 at} which the focal point should be formed.

The above-mentioned predetermined distance A is selected as follows, for example. First, with the objective lens 6 of the optical pickup placed at the reference position, the first detection camera 28
The image pickup surface 28a of the CCD image sensor is the third split light beam.
B ₃ is placed in the position F ₁ where the focal point should be formed. At that time, in the first detection camera 28, the CC
D The beam spot formed on the image pickup surface 28a of the CCD image sensor is imaged by the third split light beam B ₃ which is in the proper focus state on the image pickup surface 28a of the image sensor, and the image obtained from the CCD image sensor at that time The neutral density filter 26 is adjusted so that the peak level of the output signal becomes a predetermined white clip level. Therefore, at this time, the imaging output signal SV ₁ obtained from the CCD image sensor of the first detection camera 28 is accompanied by the vertical synchronization signal Vs and the pedestal level Vp as a reference, as shown in FIG. 2, for example. The peak level matches the white clip level Lw. Then the first
Of the first detection camera 28 when the peak level of the image pickup output signal SV ₁ becomes 1/2 of the white clip level Lw by advancing the detection camera 28 of FIG.
Is fixed, and the position of the image pickup surface 28a of the CCD image sensor at that time is separated from the position F ₁ by a distance A. In such a state, the imaging output signal SV ₁ obtained from the CCD image sensor of the first detection camera 28 is, for example, the third
As shown in the figure, the peak level is made equal to 1/2 of the white clip level Lw, that is, 1 / 2Lw.

The above-mentioned predetermined distance A'is selected as follows, for example. First, with the objective lens 6 of the optical pickup placed at the reference position, the second detection camera
29, the imaging surface 29a of the CCD image sensor is placed at a position F ₂ where the fourth split light beam B ₄ should form the focal point. At that time, in the second detection camera 29, the CCD is generated by the fourth split light beam B ₄ which is in the proper focus state on the imaging surface 29a of the CCD image sensor.
The beam spot formed on the imaging surface 29a of the image sensor is imaged, and the neutral density filter 27 is adjusted so that the peak level of the imaging output signal obtained from the CCD image sensor at that time becomes a predetermined white clip level. To be done. Therefore, at this time, the imaging output signal SV ₂ obtained from the CCD image sensor of the second detection camera 29 is accompanied by the vertical synchronization signal Vs as shown in FIG.
The peak level is matched with the white clip level Lw with reference to the pedestal level Vp. Next, the second detection camera 29 is retracted in the direction away from the neutral density filter 27, and when the peak level of the imaging output signal SV ₂ becomes 1/2 of the white clip level Lw, the second detection camera 29 Is fixed, and the position of the imaging surface 29a of the CCD image sensor at that time is separated from the position F ₂ by a distance A '. In such a state, the CCD of the second detection camera 29
The image pickup output signal SV ₂ obtained from the image sensor has its peak level matched with 1/2 of the white clip level Lw, that is, 1 / 2Lw, as shown in FIG. 4, for example.

As described above, the imaging output obtained from the CCD image sensor of the first detection camera 28 positioned so that the imaging surface 28a of the CCD image sensor is located at the position ahead of the position F ₁ by the distance A. The signal SV ₁ is supplied to the peak hold circuit 32 after passing through the pedestal clamp circuit 30, and the imaging output signal SV ₁ is supplied from the peak hold circuit 32.
A signal S _1p having a level corresponding to the peak level of the CCD image sensor is obtained, while the imaging surface 29a of the CCD image sensor is positioned so as to be located at a position that is behind the position F ₂ by a distance A ′. The imaging output signal SV ₂ obtained from the CCD image sensor of the detection camera 29 of is passed through the pedestal clamp circuit 31 and then supplied to the peak hold circuit 33,
A signal S _2p having a level corresponding to the peak level of the imaging output signal SV ₂ is obtained from the peak hold circuit 33. These signals S _1p and S _2p are respectively amplified by the amplifier circuit 34 and
35 are supplied to the subtraction circuit 36 through a signal S level level from signal S _2p of _1p is subtracted from the subtraction circuit 36, an output signal corresponding to the level difference between the signal S _1p and the signal S _2p Sf is obtained.

The signals S _1p and S _2p obtained from the above-mentioned peak hold circuits 32 and 33, respectively, are focused by the eyepiece lens 22 when the objective lens 6 of the optical pickup is at the reference position, and therefore in the observation section 51. First split light beam
When B ₁ forms a beam spot on the image pickup surface 24a of the CCD image sensor in the observation camera 24 with a proper focus state for it, both take level 1 / 2Lw, and as a result, it is obtained from the subtraction circuit 36. The level of the output signal Sf is set to zero. Further, when the objective lens 6 of the optical pickup moves in a direction away from the observation objective lens 20 from the reference position, the first split light beam B ₁ focused by the eyepiece lens 22 in the observation unit 51 is accordingly , When forming a beam spot on the imaging surface 24a of the CCD image sensor in the observation camera 24 in an over-focused state, the signal S _1p takes a level higher than level 1 / 2Lw, and the signal S _2p is A level smaller than level 1 / 2Lw is taken, and as a result, the output signal Sf obtained from the subtraction circuit 36 has a positive level. Furthermore, when the objective lens 6 of the optical pickup moves from the reference position in the direction in which the objective lens 6 approaches the observation objective lens 20, accordingly, in the observation section 51, the eyepiece 22
The first split light beam B ₁ focused by
When a beam spot is formed on the image pickup surface 24a of the CCD image sensor in 24 with an under-focus state corresponding to it, the signal S _1p takes a level smaller than level 1 / 2Lw, and the signal S _2p has a level 1 / Taking a level greater than 2Lw, the result is that the output signal Sf obtained from the subtraction circuit 36 has a negative level.

Therefore, as shown in FIG. 5, the output signal Sf obtained from the subtraction circuit 36 is the first split light beam B ₁ in the observation unit 51 with respect to the imaging surface 24a of the CCD image sensor in the observation camera 24. Depending on the proper focus state, over-focus state or under-focus state, the level becomes zero, positive or negative, and the CCD of the observation camera 24 for the _first split light beam B ₁
The focus error signal represents the focus state of the image sensor 24a of the image sensor.

The output signal Sf obtained from the subtraction circuit 36 in the focus state detection unit 52 is supplied to the focus control drive circuit 38 via the phase compensation circuit 37, and the focus control drive circuit 38 outputs the output signal Sf. Drive signal according to
With SF, the focus control coil 9 provided for the objective lens 6 of the optical pickup is driven, and the objective lens 6 is controlled to be maintained at the reference position. By controlling the objective lens 6 of the optical pickup as described above, the first split light beam B ₁
However, the imaging surface 2 of the CCD image sensor in the observation camera 24
While maintaining the proper focus state for 4a, CCD
A beam spot formed on the imaging surface 24a of the image sensor is observed.

G-2 Second Embodiment (FIG. 6) FIG. 6 shows a second embodiment of the light beam spot observation apparatus according to the present invention.

Also in this example, as shown in FIG. 8, the optical pickups are combined to form one optical system block 1,
It is used for observing the beam spot formed by the laser light beam emitted through the objective lens 6. Then, in FIG. 6, parts corresponding to the respective parts shown in FIG.
The same reference numerals as those in FIG. 1 are attached and shown, and the duplicated description thereof is omitted.

In such an example shown in FIG. 6, although the illustration of the first split light beam B ₁ from the beam splitter 21 is omitted, the observation is provided in the same manner as in the case of the example shown in FIG. The observation camera 24 in the observation section 51 is guided by the section 51.
The second split light beam B ₂ from the beam splitter 21 is guided to the focus state detection unit 52, and in the beam splitter 41 including a half mirror, the two split light beams B ₃ ′ and B ₃ ′ and B It is divided into ₄ '. Then, the divided light beam B ₃ ′ passes through the neutral density filter 44a and the half mirror 42, enters the detection camera 40, and
The split light beam B ₄ ′ is passed through the neutral density filter 44b to the prism 4
After entering 3 and performing total reflection twice in the prism 43,
The light enters the half mirror 42, is further reflected by the half mirror 42, and enters the detection camera 40. As described above, since the split light beam B ₄ ′ passes through the prism 43, the optical path length from the beam splitter 21 to the detection camera 40 is determined by the split light beam B ₃ ′ from the beam splitter 21 to the detection camera. It is longer than the optical path length reaching 40.

The detection camera 40 uses, for example, a CCD image sensor, a beam spot of the split light beam B ₃ ′ that is focused by the observation objective lens 20, enters through the beam splitter 41, and also the observation objective lens. Beam spots of the split light beam B ₄ ′ which are focused by 20 and are reflected by the beam splitter 41 to enter are formed at different positions on the imaging surface 40 a of the CCD image sensor,
Both of these beam spots are imaged by a CCD image sensor. At that time, in the detection camera 40, the image pickup surface 40a of the CCD image sensor is located at the position F _{1 at} which the split light beam B ₃ ′ should form the focusing point while the objective lens 6 of the optical pickup is located at the reference position. It is set so as to be located at a position ahead of a predetermined distance B and at a position where the split light beam B ₄ ′ is behind a position F ₂ ′ at which a focal point should be formed by a predetermined distance B ′. It When the objective lens 6 of the optical pickup takes the reference position, the predetermined distances B and B ′ are determined by the divided light beams B ₃ ′ on the image pickup surface 40a of the CCD image sensor of the detection camera 40. The beam spot formed and the beam spot formed by the divided light beam B ₄ ′ are set to have the same luminance.

The imaging output signal SV ₃ obtained from the CCD image sensor of the detection camera 40 is supplied to the sampling and holding circuit 46 after passing through the pedestal clamp circuit 45. From the sampling and holding circuit 46, the imaging surface 4 of the CCD image sensor in the detection camera 40 in the imaging output signal SV ₃
The peak level portion corresponding to the beam spot formed by the split light beam B ₃ ′ on 0a and the detection camera 40
The peak level portion corresponding to the beam spot formed by the divided light beam B ₄ ′ on the image pickup surface 40a of the CCD image sensor is sampled and held separately to obtain the signal Ssa and the signal Ssb. To be Then, these signals Ssa and Ssb are supplied to the subtraction circuit 47, the level of the signal Ssb is subtracted from the level of the signal Ssa, and the output signal Sf corresponding to the level difference between the signal Ssa and the signal Ssb from the subtraction circuit 47. ′
Is obtained.

The signals Ssa and Ssb obtained from the sampling and holding circuit 46 described above are output when the objective lens 6 of the optical pickup takes the reference position, and accordingly, in the observing section 51,
Of the divided light beams B ₁ of the CCD image sensor in the observation camera 24 form a beam spot with an appropriate focus state on the imaging surface 24a of the CCD image sensor, take the same level as each other, and as a result, are obtained from the subtraction circuit 47. The level of the output signal Sf 'is set to zero. Further, when the objective lens 6 of the optical pickup moves in a direction away from the observation objective lens 20 from the reference position, therefore, in the observation unit 51, the first split light beam B ₁ is emitted from the observation camera 24.
When a beam spot is formed on the image pickup surface 24a of the CCD image sensor in the overfocus state, the level of the signal Ssa is made higher than the level of the signal Ssb, and as a result, the output signal obtained from the subtraction circuit 47 is obtained. Sf 'will have a positive level. Further, when the objective lens 6 of the optical pickup moves from the reference position in the direction closer to the observation objective lens 20, therefore, in the observation unit 51, the first split light beam B ₁ is emitted from the observation camera.
When a beam spot is formed on the image pickup surface 24a of the CCD image sensor in 24 with an under-focus state corresponding to it, the level of the signal Ssa is made smaller than the level of the signal Ssb, and as a result, the output obtained from the subtraction circuit 47 The signal Sf 'will have a negative level.

Therefore, the output signal Sf ′ obtained from the subtraction circuit 47 is
In the observation section 51, the first split light beam B ₁ is observed by the observation camera 24.
Depending on whether the image pickup surface 24a of the CCD image sensor is in the proper focus state, the over-focus state or the under-focus state, the level becomes zero, positive or negative, and the first split light beam B ₁ The focus error signal represents the focus state of the CCD image sensor of the observation camera 24 with respect to the imaging surface 24a.

The output signal Sf ′ obtained from the subtraction circuit 47 in the focus state detection unit 52 is supplied to the focus control drive circuit 38 via the phase compensation circuit 37, and the focus control drive circuit 38 outputs the output signal. The focus control coil 9 provided for the objective lens 6 of the optical pickup is driven by the drive signal SF corresponding to Sf ', and the objective lens 6 is controlled to be kept at the reference position. By controlling the objective lens 6 of such an optical pickup, the first split light beam B ₁ in the observation section 51 maintains the proper focus state with respect to the imaging surface 24a of the CCD image sensor in the observation camera 24. At first, a beam spot formed on the image pickup surface 24a of the CCD image sensor is observed.

G-3 Third Embodiment (FIG. 7) FIG. 7 shows a third embodiment of the light beam spot observation apparatus according to the present invention.

Also in this example, as shown in FIG. 8, the optical pickups are combined to form one optical system block 1,
It is used for observing the beam spot formed by the laser light beam emitted through the objective lens 6. In FIG. 7 as well, portions corresponding to the respective portions shown in FIG. 1 are denoted by the same reference numerals as those in FIG. 1, and duplicate description thereof will be omitted.

In such an example shown in FIG. 7, although the illustration of the first split light beam B ₁ from the beam splitter 21 is omitted, the observation is provided in the same manner as in the example shown in FIG. The observation camera 24 in the observation section 51 is guided by the section 51.
In addition, the second split light beam B ₂ from the beam splitter 21 is guided to the focus state detection unit 52, and is made incident on the detection camera 49 through the neutral density filter 48.

The detection camera 49 also uses, for example, a CCD image sensor, and the beam spot of the first split light beam B ₁ focused by the observation objective lens 20 is formed on the imaging surface 49a of the CCD image sensor. The spot is imaged by the CCD image sensor. At that time, the detection camera 49
Is the first with the image pickup surface 49a of the CCD image sensor at the reference position of the objective lens 6 of the optical pickup.
It is set so that the divided light beam B _{1 of} is divided by a predetermined distance C ahead of the position F _{0 at} which the focal point should be formed.

Then, the imaging output signal SV ₄ obtained from the CCD image sensor of the detection camera 49 is the pedestal clamp circuit 3
After passing 0 ', it is supplied to the peak hold circuit 32',
A signal S _4p having a level corresponding to the peak level of the imaging output signal SV ₄ is obtained from the peak hold circuit 32 '. This signal S _4p is supplied to the level comparison circuit 50 via the amplification circuit 34 ′, and the reference voltage V from the reference voltage generator 50R is supplied.
Compared with r. The reference voltage Vr is set to have a level corresponding to the level of the signal S _4p obtained at the output side of the amplification circuit 34 ′ when the objective lens 6 of the optical pickup takes the reference position, and the level comparison circuit 50 From the signal S
Comparison output signal according to the level difference between _4p and reference voltage Vr
Sf ″ is obtained.

This comparison output signal Sf ″ indicates that when the objective lens 6 of the optical pickup takes the reference position, the first split light beam B ₁ focused by the eyepiece lens 22 in the observing section 51 is observed in the observing camera 24. When the beam spot is formed on the image pickup surface 24a of the CCD image sensor with a proper focus state for it, the level is set to zero, and the objective lens 6 of the optical pickup is separated from the observation objective lens 20 from the reference position. Therefore, in the observation unit 51, the first split light beam B ₁ focused by the eyepiece lens 22 is focused on the image pickup surface 24a of the CCD image sensor in the observation camera 24 and overfocused on it. When a beam spot is formed depending on the state, it takes a positive level, and the objective lens 6 of the optical pickup is at the reference position. More observation objective lens
When moving in the direction close to 20, therefore, in the observation unit 51, the first split light beam B ₁ focused by the eyepiece lens 22 is focused on the imaging surface 24a of the CCD image sensor in the observation camera 24 against it. When forming a beam spot in the underfocus state, it takes a negative level. Therefore, the comparison output signal Sf ″ obtained from the level comparison circuit 50 becomes a focus error signal representing the focus state of the first divided light beam B _{1 on} the imaging surface 24a of the CCD image sensor in the observation camera 24.

Then, the comparison output signal Sf ″ obtained from the level comparison circuit 50 in the focus state detection unit 52 is supplied to the focus control drive circuit 38 via the phase compensation circuit 37, and the focus control drive circuit 38 Comparison output signal S
The focus control coil 9 provided for the objective lens 6 of the optical pickup is driven by the drive signal SF corresponding to f ″, and the objective lens 6 is controlled to be kept at the reference position. By controlling the objective lens 6, the observation unit 51
The beam spot formed on the imaging surface 24a of the CCD image sensor is observed while the first split light beam B ₁ maintains the proper focus state with respect to the imaging surface 24a of the CCD image sensor in the observation camera 24.

H Effect of the Invention As is clear from the above description, according to the light beam spot observation device of the present invention, when observing the beam spot formed in the observation part by the light beam emitted through the objective lens in the optical pickup, The light beam from the pickup is placed in a proper focus state when forming a beam spot in the observation section, and the proper focus state is maintained even when disturbance acts on the optical pickup, for example. Therefore, the accurate measurement of the beam spot formed by the light beam from the optical pickup can be stably performed.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic configuration diagram showing an example of a beam spot observation apparatus according to the present invention, and FIGS. 2, 3, 4, and 5 are shown in FIG. FIG. 6 is a signal waveform diagram used for explaining the operation of the example, FIG. 6 is a schematic configuration diagram showing a main part of another example of the light beam spot observation apparatus according to the present invention, and FIG. 7 is a light beam spot observation according to the present invention. FIG. 8 is a schematic configuration diagram showing a main part of still another example of the apparatus, and FIG. 8 is a schematic configuration diagram showing an optical pickup. In the figure, 1 is an optical system block, 2 is a laser diode, and 6
Is an objective lens, 9 is a focus control coil, 20 is an observation objective lens, 21, 25 and 41 are beam splitters, 22 is an eyepiece lens, 24 is an observation camera, 28 and 29 are first and second detection cameras, 37 is a phase compensation circuit, 38 is a drive circuit for focus control, 40 and 49 are detection cameras, 51 is an observation unit, and 52 is a focus state detection unit.

Claims (1)

(57) [Claims] 1. An optical pickup comprising a light beam generation source, an objective lens for focusing a light beam from the light beam generation source, and focus control means for the objective lens. An objective lens for observation, a beam splitter that splits the light beam from the objective lens of the optical pickup that has passed through the objective lens for observation into at least first and second split light beams, and the first split light beam Of the beam spot of the second divided light beam, and an image pickup means for picking up an image of the beam spot of the second divided light beam. Based on an image pickup output signal obtained from the image pickup means, A focus state detection unit that forms a detection output signal according to the focus state of one split light beam; A light beam spot observation apparatus comprising: a focus control unit that drives a focus control unit of the optical pickup according to a detection output signal obtained from the optical beam spot observation unit.