KR20020004818A - Method for adjusting astigmatism of an optical pickup unit and a system thereof - Google Patents

Abstract

An optical pickup unit having a high light condensing property necessary for recording and reproducing a high density recorded recording medium is manufactured.

At least an astigmatism adjusting method of an optical pickup unit including, as a component, an optical system for condensing the laser diode 11 and the light beam generated by the laser diode 11 on the recording medium 14, and As an apparatus, the cross-sectional shape of a light beam is accommodated as an image by an image processing apparatus, the roundness is measured from the relationship between the long diameter and the short diameter of the accommodated image, and is close to a true origin. The astigmatism is adjusted by changing the incident angle of the light beam to the optical system by making the position the optimum position and moving the laser diode 11 in a plane perpendicular to the traveling direction of the light beam.

Description

Method and apparatus for adjusting astigmatism of optical pickup unit {METHOD FOR ADJUSTING ASTIGMATISM OF AN OPTICAL PICKUP UNIT AND A SYSTEM THEREOF}

The astigmatism of an optical pickup unit comprising at least a laser diode, a collimator lens having the light beam from the laser diode as parallel light, and an objective lens for focusing the light beam from the collimator lens on the recording medium. It relates to a method and a device for adjusting a point.

The optical pickup unit is a place that can be referred to as the heart of an optical product such as a compact disc (CD) player that performs an optical signal detection.

As shown in FIG. 1, the components of the optical pickup unit are roughly divided into three parts: the laser diode 11, the collimator lens 12, and the objective lens 13. As shown in FIG. Here, the collimator lens 12 enters between the laser diode 11 and the objective lens 13, parallel light is incident on the objective lens 13, and is condensed on the disk recording medium 14.

By the way, in the above-described CD player or the like, by appropriately selecting the component parts of the optical pickup unit, the light condensing characteristic required for the conventional player can be sufficiently obtained, and it is not necessary to adjust the astigmatism.

However, with the emergence of rewritable DVDs such as DVD-RW, there has been a need to detect finer signals. The preformatting of a DVD-RW disc arises from a combination of wobble and land prefit (LPP), wobble is used to control rotation of the disc, and LPP is used to obtain recording address information. The optical pickup detects these two signals by a radial push-pull method, generates a recording clock, and maintains high-precision recording and reproduction characteristics.

By the way, these two signals have a small level difference between the wobble and the LPP in relation to the amount of returned light from adjacent tracks in the DVD-RW disc after recording, making it difficult to detect the LPP signal. For this reason, in order to secure the LPP detection margin, it is possible to suppress the leakage noise from the radial push-pull signal to the focus error signal as much as possible to stabilize the servo, that is, optically speaking, optical path aberrations such as coma and astigmatism It is required to condense the light beam with the lowest power on the disk surface.

As in the related art, even if each component of the optical pickup unit is properly selected, sufficient condensing characteristics cannot be obtained in this manner, and it has been necessary to adjust the optical path aberration so that the optical path aberration is reduced as much as possible in the manufacturing process of the optical pickup unit.

Conventionally, there have been evaluators used by designers to evaluate optical path aberrations, but it has been difficult to use them in manufacturing processes, such as high cost, large size, and large measurement time. In the conventional evaluator for evaluating a single laser diode, the manufacturing process requires that the plurality of laser diodes be adjusted to performance within a certain range. Therefore, it was necessary to prepare separately for a manufacturing process.

That is, in order to adjust, it is necessary to repeat adjustment and measurement, and furthermore, there is a time limit in performing this in a production process, and the evaluator does not have such a function.

This invention is made | formed in view of the said situation, and by moving a laser diode in the plane perpendicular | vertical with respect to the advancing direction of a light beam, by changing the incident angle of the light beam to the said collimator lens and the said objective lens, and adjusting astigmatism It is an object of the present invention to provide a method for adjusting astigmatism of an optical pickup unit capable of manufacturing an optical pickup unit having a high light condensation property necessary for recording and reproducing a high density recorded recording medium such as a land pre-fit.

Moreover, by providing the image processing apparatus which accommodates the light beam spot image condensed on a recording medium, and the moving means which can move the laser diode mounted so that it can move in the plane perpendicular | vertical with respect to the advancing direction of the said light beam, It is also an object of the present invention to provide an astigmatism adjusting device of an optical pickup unit which is inexpensively compact without wasting time for adjustment.

1 is a diagram illustrating an optical system of an optical pickup unit.

2 is a graph showing the relationship between aberration and incident angle.

3 is a view showing an appearance structure of an optical pickup unit.

4 is a diagram showing the light intensity distribution in the light beam spot image.

5 is a diagram showing a spot image of a light beam before astigmatism adjustment.

It is a figure which shows the spot image of the light beam after astigmatism adjustment.

It is a figure quoted for demonstrating the astigmatism adjustment method of the optical pickup unit of this invention, and is a figure which shows the brightness characteristic of a short diameter direction and a long diameter direction.

FIG. 8 is a diagram cited for explaining the astigmatism adjusting method of the optical pickup unit of the present invention, and is a diagram showing luminance characteristics in the case of coma aberration.

9 is a graph created based on the measurement result of the light intensity distribution on the light beam spot.

FIG. 10 is a diagram cited for explaining the astigmatism adjusting method of the optical pickup unit of the present invention, and specifically, a diagram showing the flow of the rough adjustment procedure.

Fig. 11 is a drawing for explaining the astigmatism adjusting method of the pickup unit of the present invention, and specifically, it is a diagram showing the flow of a detailed adjustment procedure.

<Explanation of symbols for the main parts of the drawings>

11: laser diode (LD), 12: collimator lens, 13: objective lens, 14: disk, 110: body, 111: LD holder, 112: leaf spring.

In order to solve the above problems, the invention described in claim 1 includes at least a laser diode, a collimator lens having the light beam from the laser diode as parallel light, and an objective lens for condensing the light beam from the collimator lens on a recording medium. A method for adjusting astigmatism of an optical pickup unit that is a component, wherein the laser diode is moved in a plane perpendicular to the advancing direction of the light beam to change the incident angle of the light beam to the collimator lens and the objective lens, We decided to adjust aberration.

By moving the laser diode in a plane perpendicular to the traveling direction of the light beam, the incident angle of the light beam is changed to adjust astigmatism, so that the light condensing characteristics required for recording and reproducing high density recorded recording media such as land pre-fits are high. An optical pickup unit can be manufactured. In addition, the servo can be stabilized, and a highly reliable recording and reproducing apparatus is obtained.

The invention according to claim 2 is characterized in that the astigmatism adjusting method of the optical pickup unit according to claim 1 includes image processing means for accommodating a light beam spot image focused on the recording medium, and the roundness on the light beam spot image. The measurement was performed, and the position used as the roundness was adjusted as the optimum position.

An image processing means for accommodating the beam spot image focused on the recording medium, and measuring the roundness on the light beam spot to move the laser diode in a plane perpendicular to the traveling direction of the light beam as an optimal position at a position close to the origin. By adjusting the angle of incidence of the light beam to the optical system, the astigmatism can be adjusted, and the burden of the adjuster is reduced without wasting time for the adjustment.

According to the invention of claim 3, in the astigmatism adjustment method of the optical pickup unit according to claim 2, the luminance level at which the 0th order light and the primary light ring on the spot of the light beam can be separated is selected and accommodated in the image processing means. The roundness was measured.

Thereby, the adjustment work can be facilitated.

In the invention described in claim 4, in the astigmatism adjustment method of the optical pickup unit according to any one of claims 1 to 3, the astigmatism adjustment is performed after coma aberration adjustment.

Thereby, adjustment can be performed correctly, without being influenced by the bias of the light intensity distribution on a light beam spot.

The invention according to claim 5 comprises an optical pickup unit comprising at least a laser diode, a collimator lens for converting the light beam from the laser diode into parallel light, and an objective lens for condensing the light beam from the collimator lens on a recording medium. An apparatus for adjusting astigmatism of light, comprising: an image processing apparatus for receiving a light beam spot image focused on the recording medium, and a movement for moving a laser diode mounted to be movable in a plane perpendicular to a traveling direction of the light beam It was assumed that a means was provided.

With the above configuration, it is possible to provide an astigmatism adjusting device of an optical pickup unit which is inexpensively compact without wasting time for adjustment. In addition, the servo can be stabilized, and a highly reliable recording and reproducing apparatus can be obtained.

In the optical pickup unit comprising the collimator lens 12 shown in Fig. 1, a laser diode (hereinafter referred to simply as LD) 11, and an objective lens 13 for condensing a light beam on the recording medium 14, LD ( It is noted that the amount of astigmatism is determined by the angles θ and θ ′ at which the light beam generated and output by 11) is incident on the collimator lens 12 and the objective lens 13. 2 is a graph showing the amount of aberration when the LD 11 is moved in an arbitrary direction on a plane perpendicular to the advancing direction of the light beam to change the incident angle of the light beam to the lens.

In the present invention, the light beam is changed by changing the incidence angle of the light beam to the collimator lens 12 and the objective lens 13 by moving the LD 11 in an arbitrary direction on a plane perpendicular to the traveling direction of the light beam. The astigmatism is adjusted so that the astigmatism does not occur.

The light beam passes through the collimator lens 12 and the objective lens 13, but when the LD 11 is moved, the angle of incidence is different for two lenses. Obtained. For this reason, the amount of movement of the LD 11 is minimum, and the structure can be adjusted most efficiently. And the moving mechanism of LD11 is shown in FIG.

3 is a part of the structure of the optical pickup unit used in the present invention, 11 is LD, 110 is the body of the optical pickup unit, 111 is the LD holder, 112 is the leaf spring. 112a is a protrusion in which the leaf spring 112 protrudes in the z direction, and does not enter the inside of the LD holder 111, but applies a force in the z direction to the surface of the LD holder 111. The LD holder 111 is supported to be strongly pressed by the body 110 by this force, and is mounted on the xy plane (surface perpendicular to the light beam traveling direction) shown in FIG.

The LD 11 can be caught and moved by an apparatus (not shown) that holds the LD holder 111.

As is apparent from Fig. 2, the coma aberration and the spherical aberration hardly change while the astigmatism varies greatly with the change of the incident angle. Although the amount of coma aberration is determined by the inclination of the objective lens with respect to the disk 14, the LD 11 is moved in an arbitrary direction on a plane perpendicular to the traveling direction of the light beam, and the incident angle of the light beam to the lens is adjusted. By changing the astigmatism by changing, the positional relationship between the disk 14 and the objective lens 13 does not change, and thus little influence on coma aberration. The spherical aberration is caused by the spherical shape of the lens. Similarly, the spherical aberration hardly changes when the astigmatism is improved by changing the incident angle of the light beam to the lens. For this reason, astigmatism can be adjusted without affecting coma aberration, spherical aberration, or the like.

In the optical pickup unit shown in FIG. 1, the astigmatism is changed as shown in FIG. 2 in accordance with the angle at which the light beam is incident on the collimator lens 12 and the objective lens 13. Astigmatism changes depending on the nonuniformity of the individual optical products to be configured, the mounting nonuniformity at the time of assembly, and the like. Therefore, the incident angle of the light beam where the astigmatism becomes zero is not defined as one, and it is very difficult to adjust a large amount in the manufacturing process. Thus, in practice, the shape of the light beam spot focused on the disk as the recording medium is measured and adjusted.

As the shape of the spot on the light beam is closer to the circle, the astigmatism becomes smaller and the ellipse becomes larger when the astigmatism is large.

According to the optical pick-up unit astigmatism adjusting device of the present invention, in the optical pick-up unit shown in Fig. 1, a microscope objective lens is provided at a position located on the light-converging surface of the disk 14 as a recording medium, and the light on the light beam spot An image processing apparatus (not shown) is installed to receive the intensity distribution in a computer through a microscope.

By this image processing apparatus, astigmatism can be measured by measuring the roundness of the light intensity distribution on the light beam spot.

Fig. 4A is a diagram showing the light intensity distribution on the light beam spot taking the luminance level along the z axis, and the x and y axes extend in the short and long directions on the light beam spot. . 4B is a cross section parallel to the xy plane at a certain luminance level, that is, a light beam spot image. For the measurement of roundness, for example, it is considered to obtain the ratio of biaxial, long diameter y, and short diameter x orthogonal to the center point on the light beam spot as shown in Fig. 4 (b) by the following equation.

Roundness = y / x

Here, when y = x, i.e., roundness = 1, the light beam spot image is round, and there is no astigmatism.

In the present invention, the LD 11 is moved in the xy plane shown in Fig. 3A in the plane perpendicular to the traveling direction of the light beam so that the roundness is "1". The movement of the LD 11 is carried by holding the LD holder 111 as described above. When the position where the roundness becomes "1" is found, the LD holder 111 is fixed to the body 110 with an adhesive agent.

In general, since the state without astigmatism is considered to be good, the light beam spot image is adjusted so as to be a circle, but may be approximately a circle as long as it can satisfy the precision required for the optical pickup unit. In addition, although the roundness was measured from the relationship between the long diameter and the short diameter, other methods may be used.

By the way, when the roundness on a light spot is measured by the image processing apparatus as mentioned above, in the best focus state, the shape of a light beam cannot be observed.

5 and 6 are micrographs showing the cross-sectional shape of the light beam. As shown in the photograph, the light spot image includes a primary light ring around the zeroth light, a primary light ring around the zeroth light, and a secondary ring outside thereof. It extends to the Nth ring. For astigmatism adjustment, the roundness of the zeroth order light is measured.

5 and 6 are photomicrographs each showing the shape of an optical spot before astigmatism adjustment and after astigmatism adjustment. (b) shows the best focus, (a) shows the state in which the objective lens is defocused in the direction away from the disk, and (c) shows the state in which the objective lens is defocused in the direction close to the disk.

In the best focus state of FIGS. 5 (b) and 6 (b), it is not possible to observe the difference of the 0th order optical shape before and after the astigmatism adjustment. On the other hand, in the focus state, before the astigmatism adjustment, as shown in Fig. 5 (a) and (c), the shape of the zero-order light becomes an ellipse, and the difference between the long and short diameters can be reliably observed.

For example, if the roundness on the light beam spot shown in Fig. 5A is measured to be in the state shown in Fig. 6A, the astigmatism can be easily and accurately eliminated.

Therefore, the degree of defocus is set so that the roundness of the shape of the light beam is most easily measured to such an extent that the defocus is not completely defocused.

7 is a light intensity distribution of a cross section parallel to the yz plane (longer diameter direction) and the xz plane (shorter diameter direction) orthogonal to the center point on the light beam spot shown in FIG. 4 (a), the vertical axis representing the luminance level and the horizontal axis representing the light beam The spot phase diameter (the outer circumferential side as the 0 position is directed in the − direction and the + direction from the center on the light beam spot). In FIG. 7, light intensity distribution in three states is shown, c is a best focus state, a and a 'are the states of a defocus amount of 0.5 micrometer, and b and b' are the states of a defocus amount of 1.5 micrometers.

And a and b are light intensity distribution of the cross section (short diameter direction) parallel to the xz plane shown in FIG.4 (a), and a 'and b' are parallel to the yz plane shown in FIG.4 (a). It is a light intensity distribution of a cross section (long diameter direction).

Since c is the best focus state, the light spot image becomes a circle, and the luminance characteristics measured from the short diameter direction and the long diameter direction are superimposed. For this reason, in a best focus, roundness cannot be measured and it is not suitable for the measurement of astigmatism.

Light intensity distributions a and a 'with a defocus amount of 0.5 µm show a slight difference between the long and short diameters of the 0th order light depending on the luminance level. The light intensity distributions b and b 'with a defocus amount of 1.5 µm also show differences in the long and short diameters of the 0th order light depending on the luminance level, and the difference is larger than that in the case of the defocus amount of 0.5 µm. As described above, since the light intensity distribution varies depending on the defocus amount, it is necessary to set the defocus amount capable of reliably measuring the difference between the long and short diameters, that is, the roundness.

It is also necessary to set the luminance level when accommodating the light intensity distribution on the light beam spot. First, as shown in the characteristic a, a ', b, b' of FIG. 7, since the difference of a long diameter and a short diameter differs by a luminance level, you should measure the luminance which can reliably measure roundness. Further, at the luminance level at which the image of the primary optical ring appears, the boundary line between the zeroth order light and the primary light ring is not recognized, and it is difficult to accurately measure the roundness of only the zeroth order light. It is necessary to set a luminance level that can accommodate only zero-order light.

In addition, in the roundness measurement of zero-order light, coma aberration is an effect of the primary light ring. When the objective lens 13 is not parallel to the recording medium 14 which is the light converging surface of the light beam, coma aberration occurs, and the luminance distribution of the primary optical ring is not uniform. Similarly, there is a part where the luminance becomes extremely large. In this case, too, only the 0th order light cannot be taken out and it is difficult to accurately measure the roundness.

When evaluating the shape, intensity, etc. of the light beam, it is common to measure at the intensity peak 1 / e ² (near 13%). Figure shows a light intensity peak in the level of 1 / e ² to 7 by the dashed line. When looking at the light intensity distributions a and a 'with a defocus amount of 0.5 µm, a slight difference in the long and short diameter directions of the 0th order light is seen, but the roundness cannot be accurately measured. In the light intensity distributions b and b 'having a defocus amount of 1.5 µm, since there is no boundary between the primary light and the 0th light at the level of 1 / e ^{2 which} is the intensity peak, only the 0th light cannot be separated out.

In addition, the 25% level of the intensity peak is indicated by a dashed-dotted line. When looking at the light intensity distributions b and b 'with a defocus amount of 1.5 µm at a level of 25% of the intensity peak, the difference in the long and short diameter directions of the 0th order light can be reliably observed, and is not affected by the primary light ring. This is the level where only 0th order light can be taken out.

FIG. 9 shows the light intensity distributions of b and b 'in FIG. According to this, the luminance level that accommodates the light beam spot image is optimally 20 to 40%.

Therefore, in the present invention, by accepting the light intensity distribution on the light beam spot at a luminance level of 20 to 40% of the intensity peak and at a defocus amount of 1.5 μm, the primary light ring is not affected and thus complete defocusing. The roundness can be easily and accurately measured by measuring the difference between the long diameter and the short diameter without entering a state.

Next, the flow at the time of actually performing astigmatism adjustment of an optical pickup unit is demonstrated using this invention. The adjustment of the optical pickup unit of the present invention is carried out in the backward path until the light beam is emitted from the LD 11 and reaches the disk 14 serving as the recording medium, and then reflected on the recording surface of the disk. Adjustment in the return path until reaching a photodetector (photodetector) which is not shown in figure is performed.

The astigmatism adjustment method of the optical pick-up unit of the present invention is performed at the time of adjustment in the outward path (step S1), as shown in FIG. First, coarse aberration is adjusted before astigmatism adjustment (steps S12 and S13), in which rough adjustment of the inclination of the disk 14, which is the recording medium of the objective lens 13, is performed (step S11) and then adjusted in the order of coma aberration and astigmatism (steps S12 and S13). The adjustment is made to make the coma aberration to zero as much as possible in order to minimize the influence on the 0th order light of the primary optical ring. After that, the adjustment is made in the return path, and the adjustment process of the optical pickup unit is completed.

11 illustrates the adjustment procedure of coma aberration (step S12) and the adjustment procedure of astigmatism (step S13) in detail.

In the adjustment of the coma aberration, the focus is first focused on the position where the center luminance is maximized while looking at the light spot image of the image processing apparatus (step S121). Next, the deviation (coma aberration) of the intensity distribution is measured (step S122), and if there is coma aberration (step S123), the inclination of the objective lens 13 is adjusted (step S124), and the flow returns to step S121.

In step S123, if coma aberration is OK level (zero or near zero), it will continue to adjust astigmatism. In the adjustment of the astigmatism (step S13), first, the focus is achieved while looking at the light spot image of the image processing apparatus (step S131). Next, 1.5 µm defocus is performed to measure roundness (astigmatism) (steps S132 and S133). And when astigmatism is recognized (step S134), LD11 is moved and it returns to step S131. Repeat steps S131 to S134 until the astigmatism disappears.

As described above, the present invention moves the laser diode, which is a component of the optical pickup unit, in a plane perpendicular to the traveling direction of the light beam, thereby adjusting the astigmatism by changing the incident angle of the light beam with respect to the optical system, which is the component. As a result, an optical pickup unit having a high light condensing property required for recording and reproducing a high density recorded recording medium such as land prefit can be manufactured.

In addition, the spot image of the light beam is accommodated by the image processing apparatus, the roundness is measured from the relationship between the long and short diameters of the received spot image, and the laser diode is placed in the optical beam with the adjustment device as the optimal position. Since the astigmatism is adjusted by changing the angle of incidence of the light beam to the optical system by moving in a plane perpendicular to the advancing direction, it is possible to provide an astigmatism adjusting device of the optical pickup unit which is inexpensively compact without wasting time for adjustment. can do.

According to the invention of claim 1, the laser diode is moved in a plane perpendicular to the advancing direction of the light beam, thereby changing the incident angle of the light beam to adjust astigmatism, thereby recording a high density recorded recording medium such as land pre-fit. It is possible to manufacture an optical pickup unit having a high light condensation property necessary for regeneration. In addition, since the servo can be stabilized, a highly reliable recording and reproducing apparatus is obtained.

According to the invention of claim 2, there is provided an image processing means for accommodating a light beam spot image focused on a recording medium, the roundness of the light beam spot being measured, and the laser diode being a light beam with a position close to the epicenter as the optimal position. By moving in the plane perpendicular to the advancing direction, the angle of incidence of the light beam to the optical system can be changed to adjust the astigmatism, so that the burden of the adjuster is reduced without wasting time for the adjustment.

According to invention of Claim 3, adjustment operation can be made easy by selecting the brightness | luminance level which can separate | separate 0th order light and 1st order light on a light beam spot, and accommodate it in an image processing means, and measure roundness.

According to the invention of claim 4, by adjusting the coma aberration and then adjusting the astigmatism, the adjustment can be performed accurately without being affected by the bias of the light intensity distribution on the light beam spot.

According to the invention of claim 5, there is provided an image processing apparatus for accommodating a light beam spot image focused on a recording medium, and a movement for moving a laser diode mounted to be movable in a plane perpendicular to the traveling direction of the light beam. By providing means, it is possible to provide an astigmatism adjusting device of an optical pickup unit which is inexpensively compact without wasting time for adjustment.

Claims (5)

Astigmatism of an optical pick-up unit comprising at least a laser diode, a collimator lens for making the light beam from the laser diode into parallel light, and an objective lens for condensing the light beam from the collimator lens on a recording medium. Iii) as an adjustment method, By moving the laser diode in a plane perpendicular to the advancing direction of the light beam, the astigmatism of the optical pickup unit is adjusted by changing the incident angle of the light beam to the collimator lens and the objective lens to adjust astigmatism. Adjustment method. The method of claim 1, An image processing means for accommodating a light beam spot image focused on the recording medium, The astigmatism adjustment method of the optical pickup unit characterized by measuring the roundness on the said light beam spot and adjusting the position used as an optimal position to an optimal position. The method of claim 2, A method for adjusting astigmatism of an optical pickup unit, characterized by selecting a luminance level at which the 0th order light and the primary light ring on the spot of the light beam are separable, and accommodating the image processing means to measure the roundness. The method according to any one of claims 1 to 3, The astigmatism adjustment method of the optical pickup unit, characterized in that the astigmatism adjustment is performed after the coma aberration adjustment. An astigmatism adjusting device for an optical pickup unit comprising at least a laser diode, a collimator lens for making the light beam from the laser diode into parallel light, and an objective lens for condensing the light beam from the collimator lens on a recording medium. , An image processing apparatus accommodating a light beam spot image focused on the recording medium; Moving means for moving a laser diode mounted to be movable in a plane perpendicular to the traveling direction of the light beam An astigmatism adjusting device of the optical pickup unit, comprising: a.