JPH0432446B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a pickup device used in optical information recording and reproducing devices such as optical digital audio disc players and video disc players.

The basic structural diagram of such a pick-up device is shown in the first figure.
As shown in the figure. 1 is a light source such as a semiconductor laser device; 2 is a collimator lens that makes the diverging beam emitted from the light source 1 substantially parallel; 3 is a polarizing beam splitter;
4 is a 1/4 wavelength plate, 5 is an objective lens, 6 is an optical reflection disk, 7 and 8 are cylindrical lenses whose axes are substantially perpendicular to each other, and 9 is a parting line between the cylindrical lenses 7 and 8. It is a four-part photodetector arranged at 45 degrees to the axis.

A beam emitted from a light source 1 is made into substantially parallel light by a collimator lens 2, passes through a beam splitter 3 and a quarter-wave plate 4, and then is focused onto a disk 6 by an objective lens 5. The beam modulated by the signal recorded on the disk 6 is reflected by the disk 6, passes through the objective lens 5 and the 1/4 wavelength plate 4, enters the beam splitter 3, and is reflected at the polarization plane of the beam splitter 3. After being reflected, the light passes through cylindrical lenses 7 and 8 and is irradiated onto a photodetector 9.
Since the cylindrical lenses 7 and 8 exhibit astigmatism, the shape of the beam spot on the photodetector 9 is as shown in FIG.

That is, when the disk 6 is located within the focal depth of the objective lens 5, the spot on the photodetector 9 becomes approximately circular as shown in FIG. 2b. On the other hand disk 6
is farther than the depth of focus of the objective lens 5, the second
As shown in Figure a, if the long axis is an elliptical circle along the axis 8a of the cylindrical lens 8, and if the disk 6 is closer than the focal depth of the objective lens 5, then Figure 2c
As shown in the figure, the long axis is the axis 7 of the cylindrical lens 7.
It becomes a circle along a. Therefore, the sum of the outputs of one pair of photodetectors 9a and 9d arranged diagonally among the four divided photodetectors 9 and the sum of the outputs of the other pair of photodetectors 9b and 9c. By detecting the difference, an S-shaped focus error signal F as shown in FIG. 3 can be obtained.

Beam focus point by objective lens 5 and disk 6
The distance (defocus amount) C from the signal recording surface is Cn,
When Cf, positive and negative peaks occur in the focus error signal F, which are caused by the cylindrical lens 7 or 8 on the photodetectors 9a, 9d or 9b, 9c, respectively, as shown in FIG. 4a and b. This corresponds to the case where a line image is formed. If this focus error signal F is supplied to an actuator (not shown) to move the objective lens 5 in the optical axis direction (vertical direction in FIG. 1), even if the disk 6 is deflected, the signal recording surface of the disk 6 can be moved. The beam can always be focused precisely. As a result, the photodetector 9
The recorded information can be reproduced by demodulating the RF signal S obtained from the sum of the outputs a to 9d.

In order to realize a focus servo device based on such a principle, each of the above-mentioned optical components must be installed so that the focus error signal F becomes zero when the signal recording surface of the disk 6 is located within the focal depth of the objective lens 5. Must be in place. However, the accuracy of each optical component or the accuracy of its installation is not perfect and there are variations, so the above conditions cannot be immediately satisfied just by arranging the optical components at the designed predetermined positions. Therefore, it is necessary to finely adjust the position of the optical component.

Conventionally, such fine adjustment was performed by a photodetector 9. That is, a first adjustment is first performed to finely move the photodetector 9 in two directions in a plane perpendicular to the optical axis, so that the positive and negative peak positions of the focus error signal F are symmetrical about the zero point.
With only this first adjustment, even if the signal recording surface of the disk 6 is located within the focal depth of the objective lens 5, the focus error signal F will not necessarily become zero at that time. When the signal recording surface of the disc 6 is located within the depth of focus of the objective lens 5, the position on the optical axis at which the cross-sectional shape of the beam becomes approximately a perfect circle is a predetermined position.
This is because there is only a point, and the photodetector 9 is not necessarily accurately placed at a position corresponding to that one predetermined point on the optical axis. Therefore, since the level of the RF signal S is maximum when the signal recording surface of the disk 6 is located within the focal depth of the objective lens 5, in the first adjustment stage, the focus error signal F of FIG. Position C shifted to the right or left from zero cross point O ₁ or
At _C2 , the level of the RF signal S becomes maximum. Therefore, a second adjustment for accurately arranging the photodetector 9 at a position where the cross-sectional shape of the beam becomes a perfect circle is performed by moving the photodetector 9 in the optical axis direction.

However, such adjustment requires an adjustment mechanism to move one optical component (photodetector 9) in three axial directions, which not only complicates the configuration but also causes adjustment in one direction to affect adjustment in the other direction. It was easy to apply, took time to adjust, and was difficult to adjust accurately.

The present invention was made in view of the above situation, and an object of the present invention is to provide an optical pickup device that is simple in construction and easy to adjust.

Embodiments of the present invention will be described below with reference to the drawings.
In the figures referred to below, parts corresponding to those in FIGS. 1 to 4 are designated by the same reference numerals, and detailed description thereof will be omitted.

In FIG. 5, 10 is a housing, which includes a light source 1, a holder 11 that supports a collimator lens 2, a beam splitter 3 to which a quarter wavelength plate 4 is fixed, an objective lens 5, cylindrical lenses 7 and 8, and a light detector. Each of the vessels 9 is housed in a predetermined position, and passages 12 and 13 are formed for the beam to pass through. The objective lens 5 is attached to the housing 10 via an actuator (not shown) that drives the objective lens 5 in the focus direction. A holder 11 having a substantially cylindrical outer shape has an inner wall 12a of a passage 12 having a substantially circular cross section through which the beam emitted from the light source 1 passes.
The inner wall 12a is used as a guide for sliding in the optical axis direction. A groove 11a perpendicular to the optical axis direction is formed approximately in the center of the holder 11, and two shafts (not shown) of an eccentric driver are inserted into the center hole 14 and through hole 15 formed in the housing 10, respectively. , rotate the eccentric driver clockwise or counterclockwise in the figure around the center hole 14 to open the groove 11.
Holder 1 with one shaft of the eccentric driver engaged with a
1 can be moved in the optical axis direction. 16 is a screw screwed into the housing 10, one end of which is rotatable from the outside of the housing 10, and the other end of which comes into contact with the holder 11 to fix the holder 11 in a predetermined position. ing. The beam splitter 3 is composed of a parallelepiped-shaped prism 31 and a triangular prism 32, whose bonding surface 33 is a polarizing plane, and the bonding surface 3 is a polarizing plane.
A surface 34 parallel to 3 is formed as a reflective surface. Therefore, after the beam emitted from the light source 1 passes through the collimator lens 2 fixed to the holder 11, it is reflected by the surfaces 34 and 33, and the beam becomes 1/4
The light is irradiated onto a disk 6 via a wavelength plate 4 and an objective lens 5. The beam reflected by the disk 6 passes through the objective lens 5, the quarter-wave plate 4, the surface 33, and the cylindrical lenses 7 and 8, and is irradiated onto the photodetector 9.

FIG. 6 schematically shows the principle of the holding mechanism for the cylindrical lens 7 in FIG. 5. The cylindrical lens 7 is a holder 17 having a substantially rectangular parallelepiped shape.
It is fixed approximately at the center of the A surface that forms a passage 13 through which a beam directed toward the photodetector 9 of the housing 10 passes, and is located along the axis 7a of the cylindrical lens 7.
At least one surface 10a forming an approximately 45 degree angle with
is a flat surface, and a groove 18 is formed on the surface 10a in a direction perpendicular to the optical axis. The holder 17 is in the groove 18.
The holder 17 is guided with its bottom plane and left and right planes in contact with the bottom plane and left and right planes of the groove 18, respectively, and the holder 17 is guided along the groove 18 in a plane perpendicular to the optical axis. It is slidable in a direction forming approximately 45 degrees with respect to 7a. A screw 19 is inserted into the through hole 20 of the housing 10 and screwed into the holder 17. Reference numeral 21 denotes a leaf spring fixed to the housing 10, which biases the holder 17 in the direction of pressing the bottom of the groove 18 and in the direction parallel to the surface 10a and away from the through hole 20 (not shown). But holder 1
7 is also biased in the optical axis direction by a leaf spring).
Therefore, by rotating the screw 19, the holder 17 (and therefore the cylindrical lens 7) is aligned with the axis 7a.
It can be moved in a 45 degree direction.

Although not shown, the cylindrical lens 8 has the same structure as the cylindrical lens 7, and is held in the housing 10 so as to be able to slide independently of the cylindrical lens 7.

FIG. 7 schematically shows the positional relationship between the cylindrical lenses 7, 8 and the photodetector 9. That is, when the two dividing lines of the photodetector 9 are set in the x-axis and y-axis directions, the axes 7a and 8a of the cylindrical lenses 7 and 8 are arranged at 45 degrees with respect to the x-axis and the y-axis, respectively. , the direction of the track (not shown) formed on the disk 6 is the y-axis direction,
The adjustment movement direction of the cylindrical lenses 7 and 8 is x
It is assumed to be in the axial direction.

FIG. 8 shows a circuit diagram for outputting an electric signal from the photodetector 9, and shows the photodetector 9a and 9.
The output difference of c is obtained by the subtracter 22, and the output difference of the photodetectors 9b and 9d is obtained by the subtracter 23, and these are added by the adder 24 to obtain the focus error signal F. can get. Since the adder 25 adds the outputs of the photodetectors 9a to 9d, it outputs a signal corresponding to the RF signal S of the signal recorded on the disk 6.

Next, a method for adjusting the optical pickup device according to the present invention will be described. First, perform the first adjustment.
That is, the optical axis (the center of the spot) of the beam incident on the photodetector 9 is adjusted to coincide with the center of the photodetector 9. For this purpose, a disk or a mirror provided opposite to the objective lens 5 is deflected sufficiently (at least to the extent that a line image as shown in FIG. 4 is formed on the photodetector 9), and a focus error signal F is generated. Observe with a synchronoscope, etc. Since the focus servo loop is open at this time, an S-shaped characteristic as shown in FIG. 3 is observed in response to the surface runout. Then, by rotating the screw 19, the cylindrical lens 7 is first moved in the x-axis direction in FIG. Then, the beam spot on the photodetector 9 moves in a direction perpendicular to the axis 7a (in the direction of the axis 8a of the cylindrical lens 8), and the positive peak (point) of the focus error signal F in FIG.
Since the peak at Cn increases or decreases, the screw 19 is fixed when this peak reaches its maximum.
The maximum peak at point Cn is shown in Figure 4a.
As shown in FIG. 2, a line image is formed only on the photodetectors 9a and 9d, but not on the photodetectors 9b and 9c.

Next, the screw 1 that the cylindrical lens 8 corresponds to
9 to move the cylindrical lens 8 in the x-axis direction in FIG. The moving direction of the cylindrical lens 8 does not need to be parallel to the moving direction of the cylindrical lens 7, as will be described later.
By making them parallel, the adjustment work can be done from the same direction, making the adjustment work easier. When the cylindrical lens 8 is moved, the beam spot on the photodetector 9 moves in a direction perpendicular to the axis 8a (in the direction of the axis 7a of the cylindrical lens 7), and the negative peak of the focus error signal F in FIG. Since the peak at point Cf increases or decreases, the screw 19 is fixed when this peak becomes the minimum (negative maximum). The peak at point Cf is at its minimum when the line image is on the photodetector 9, as shown in Figure 4b.
This is when images are formed only on photodetectors 9a and 9c, but not on photodetectors 9a and 9d.

With the above adjustment, the optical axis of the beam is aligned with the center of the photodetector 9 in two directions in the plane perpendicular to the optical axis (in the x and y planes), so the optical axis of the beam is aligned with the center of the photodetector 9. This means that they almost match.

What should be noted here is that when adjusting each of the cylindrical lenses 7 and 8, one adjustment has no effect on the other adjustment (even if the cylindrical lens 7 (or 8) is moved, there is no point).
The Cf (or Cn) peak does not change). To explain this further, in the first adjustment to match the center on the photodetector 9 with the optical axis of the beam irradiated onto the photodetector 9, the optical components are moved in two directions in a plane perpendicular to the optical axis. It is necessary to move in the axial direction, but adjustment in one direction affects adjustment in the other direction because when adjustment is made in one direction, the direction in which the spot on the photodetector 9 moves is the same as the adjustment in the other direction. This is a case where the time spot is not perpendicular to the moving direction. However, in the present invention, when the cylindrical lens 7 or 8 is moved, the direction in which the spot moves on the photodetector 9 is perpendicular to the axis 7a or 8a, respectively, and the axis 7a and the axis 8a are arranged at right angles. Therefore, the moving directions of the spots are also perpendicular to each other. That is, the cylindrical lenses 7 and 8 have a lens action (beam deflection action) only in a direction perpendicular to each axis 7a and 8a,
Since it does not have a lens action in the direction parallel to the axes 7a and 8a, except when the cylindrical lens 7 or 8 is moved in the direction of the respective axis 7a or 8a (in this case, the spot position does not change). ,
No matter which direction the spot moves in a plane perpendicular to the optical axis (both in the x-axis direction in this embodiment), the spot moves in a direction perpendicular to the axis 7a or 8a, respectively. For example, even if the cylindrical lens 7 or 8 is moved in a direction perpendicular to the axis 7a or 8a, the direction of movement of the spot will be in the direction perpendicular to the axis 7a or 8a, respectively.
The direction is perpendicular to . Therefore, strict control of the moving direction of the cylindrical lens 7 or 8 is not necessarily required. However, maintaining the axes 7a and 8a at approximately right angles is necessary to ensure the symmetry of the focus error signal F, as in the case of the prior art, so in order to ensure this, Holder 17 for cylindrical lenses 7 and 8
The bottom planes of the grooves 18 on which the grooves 18 slide can be formed to be the same plane. In this way, the holders 17 of the cylindrical lenses 7 and 8 will each slide on the same reference plane, so that the relative mounting error between the two can be further reduced.

After the first adjustment is completed, a second adjustment is performed. For the second adjustment, first loosen the screw 16, and then
This is done by inserting and rotating an eccentric driver into the lens and moving the holder 11 holding the collimator lens 2 in the optical axis direction. At this time, together with the focus error signal F, a signal S (RF
It does not have to be a signal as long as it can be determined that the disk 6 or mirror is located within the focal depth of the objective lens 5). When the level of the signal S is maximum (the disk 6 and mirror are within the focal depth of the objective lens 5), the focus error signal F
If it is negative, move the holder 11 away from the light source 1, and if it is positive, move it closer to it, so that the level of the signal S becomes maximum at the zero cross point O of the focus error signal F, and then Fix the screw 16.

The fact that the focus error signal F is negative even though the disk 6 is within the depth of focus means that the amount of light received by each of the photodetectors 9a to 9d should be equal, as shown in FIG. As shown in Figure 2a, the photodetectors 9b and 9c are better than the photodetectors 9a and 9c.
This means that more light is being received than 9d. Therefore, by moving the collimator lens 2 away from the light source 1 so that the beam emitted from the collimator lens 2 tends to diverge more, the amount of light received by the photodetectors 9a and 9d is increased, and the amount of light received by the photodetectors 9b and 9c is reduced. The amount of light received by each of the photodetectors 9a to 9d is made equal (the spot on the photodetector 9 becomes an optically perfect circle).

On the other hand, if the focus error signal F is positive even though the disk 6 is within the depth of focus, the amount of light received by each photodetector 9a to 9d can be made equal by adjusting in the opposite direction to the case described above. It is clear that it can be done.

In the present invention, the second adjustment is performed by changing the relative distance between the light source 1 and the collimator lens 2, the cylindrical lenses 7 and 8 and the photodetector 9
Compared to the conventional case of changing the relative distance between the two, the following effects are achieved.

First, there is little possibility that the first adjustment will be adversely affected. That is, cylindrical lenses 7, 8
As mentioned above, the photodetector 9 and the photodetector 9 must be arranged in a predetermined direction in a plane perpendicular to the optical axis (the dividing line of the photodetector 9 and the cylindrical lenses 7, 8
(need to be arranged so that the axes 7a, 8a of If you try to make adjustments for Considering this, together with the fact that one of the cylindrical lenses 7, 8 or the photodetector 9 must be movable in at least two axial directions, changes in the plane perpendicular to the optical axis are likely to occur. It is. Moreover, since the cylindrical lenses 7 and 8 and the photodetector 9 constitute an optical system that focuses the beam,
Even if this change is slight, it greatly affects the mounting accuracy. On the other hand, when changing the relative distance between the light source 1 and the collimator lens 2, the moving direction of each optical component is only in one axis direction even when considering the moving direction for the first adjustment. This makes it possible to reduce changes that occur in a plane perpendicular to the optical axis. Moreover, the light source 1 and the collimator lens 2 generally do not have such directionality in a plane perpendicular to the optical axis (when a semiconductor laser is used as the light source 1, the cross section of the emitted beam is not necessarily circular). However, compared to the dividing line of the photodetector 9 and the directionality of the axes 7a and 8a, it can be almost ignored), and the beam emitted from the light source 1 is made into a substantially parallel beam by the collimator lens 2. Therefore, even if movement occurs in a plane perpendicular to the optical axis when adjusting the optical axes of the light source 1 and the collimator lens 2, the optical axes of the cylindrical lenses 7 and 8 and the photodetector 9 The influence on the directionality in the vertical plane is extremely small.

Second, the installation error that ultimately remains after adjustment can be reduced. In other words, the state in which the beam emitted from the light source 1 enters the objective lens 5 in parallel is as follows.
This is an ideal state in which the objective lens 5 can be used with little aberration. In other words, it is ideal if the position where the beam is focused by the objective lens 5 is as close as possible to the position where the beam is focused when it is ideally incident parallel to the objective lens 5, as shown in FIG. close. The installation error regarding the relative position of the light source 1 and the collimator lens 2 in the optical axis direction is Δx ₁ , and the light source 1, collimator lens 2, beam splitter 3, quarter wavelength plate 4, objective lens 5
Let k ₁ (k ₁
=(f ₂ /f ₁ ) ² , where f ₁ is the focal length of the objective lens 5,
f ₂ is the focal length of the collimator lens 2), the distance L ₁ by which the beam focusing position by the objective lens 5 deviates from the ideal position is L ₁ =Δx ₁ /k ₁ . On the other hand, the installation error regarding the relative position of the cylindrical lenses 7, 8 and the photodetector 9 in the optical axis direction is Δx ₂ , and the objective lens 5, quarter wave plate 4, beam splitter 3, cylindrical lenses 7, 8, The vertical magnification of the reflective optical system composed of the photodetector 9 is
When k ₂ (k ₂ ≒ (f ₃ /f ₁ ) ² , where f ₃ is the average focal length of the cylindrical lenses 7 and 8), the position is set to form a perfect circular spot on the photodetector 9. The distance L ₂ by which the focal point of the power objective lens 5 deviates from the ideal position is L ₂ =Δx ₂ /k ₂ . Even if it is assumed that both mounting errors Δx ₁ and Δx ₂ are equal, the distance L ₁ is generally larger than the distance L ₂ . If the collimator lens 2 is moved away from the light source 1, the effective utilization rate of the beam diverging from the light source 1 will decrease, so the focal length _f2 of the collimator lens 2 cannot be made too large. In order to reduce the severity of mounting accuracy in the plane perpendicular to the optical axis of the cylindrical lenses 7 and 8, the average focal length of the cylindrical lenses 7 and 8 must be
This is because a larger f ₃ is advantageous. Therefore, if only one of the collimator lens 2 and the photodetector 9 is adjusted in the optical axis direction, the residual error with respect to the ideal state can be reduced by adjusting the collimator lens 2.

In order to adjust the beam so that it enters the objective lens 5 in parallel, the distance between the light source 1 and the collimator lens 2 must be adjusted while observing the parallel state of the beam with a monitor camera etc. before attaching the objective lens 5 to the housing 10. It is also possible to adjust the objective lens 5 and then attach the objective lens 5 to the housing 10, but this would complicate the adjustment process and increase costs, making it impractical as an adjustment method for optical pickup devices used in consumer equipment. It is true.

FIG. 9 shows the principle of a second embodiment for adjusting the distance between the light source 1 and the holder 11 of the collimator lens 2 in the optical axis direction. That is, case 1
A spring 26 is interposed between the step portion 10b of No. 0 and the holder 11, and is adapted to bias the holder 11 downward in the figure. Reference numeral 27 denotes an adjustment screw which is screwed into the housing 10 and whose one end presses the holder 11, and has a hole 28 in the center through which the beam passes. It is clear that by rotating the screw 27, the position of the holder 11 can be adjusted in the optical axis direction.

In the above embodiment, the position of the collimator lens 2 is adjusted in the optical axis direction with respect to the light source 1, but the light source 1 may be adjusted in the optical axis direction with respect to the collimator lens 2.

Further, in the above embodiment, two cylindrical lenses are used in order to improve the symmetry of the focus error signal, but the cylindrical lens 7 may be a plano-convex lens if the symmetry is sacrificed. In this case, it is preferable to adjust the cylindrical lens 8 as described above and to perform the first adjustment by adjusting the photodetector 9 in a direction perpendicular to the axis 8a of the cylindrical lens 8.

Furthermore, as an optical element that provides astigmatism, something other than a cylindrical lens, such as a wedge prism, may be used.

[Brief explanation of drawings]

Figure 1 is a schematic diagram of the optical pickup device, Figures 2 and 4 are front views showing the shape of the spot on the photodetector, Figure 3 is a characteristic diagram of the focus error signal, and Figure 5 is the main FIG. 6 is a partial sectional view showing the structure of the optical pickup device according to the invention; FIG. 6 is a principle diagram of the cylindrical lens holding structure according to the invention;
FIG. 7 is a schematic diagram showing the positional relationship between the cylindrical lens and the photodetector in a plane perpendicular to the optical axis;
FIG. 8 is a circuit diagram for extracting the output from the photodetector, and FIG. 9 is a principle diagram showing a second embodiment for adjusting the positions of the light source and the collimator lens in the optical axis direction. 1... Light source, 2... Collimator lens, 3... Beam splitter, 4... 1/4 wavelength plate, 5... Objective lens,
6...Disc, 7,8...Cylindrical lens,
9...Photodetector, 11, 17...Holder.

Claims (1)

[Claims] 1. An optical pickup device comprising a housing, a light source, a collimator lens, a beam splitter, an objective lens, an optical element consisting of a plurality of cylindrical lenses providing astigmatism, and a photodetector arranged in the housing. The cylindrical lenses are each independently movable in a plane perpendicular to the optical axis,
An optical pickup device characterized in that the photodetector can be moved and fixed at a predetermined position by adjustment, and a holder including the collimator lens can be moved in the optical axis direction.