WO2006104193A1

WO2006104193A1 - Method for adjusting astigmatism

Info

Publication number: WO2006104193A1
Application number: PCT/JP2006/306464
Authority: WO
Inventors: Hiroshi Hosoyamada; Shinichi Fujinoki
Original assignee: Pioneer Corporation
Priority date: 2005-03-29
Filing date: 2006-03-29
Publication date: 2006-10-05
Also published as: JPWO2006104193A1

Abstract

The second electrode (107d) of an abberation correcting element (107) is arranged with total eight electrode patterns of patterns (1, 3, 5, 7) in ring band shape. Astigmatism is corrected depending on a voltage being applied to each pattern. When astigmatism is adjusted, it is decomposed into astigmatism components in first direction group and second direction group. For each decomposed component, a voltage applied to each pattern is determined as a displacement with respect to a reference voltage. Two orthogonal axes defining respective direction groups are respectively associated with total four patterns of two types being bordered by them, and the applying voltage is determined such that respective displacements have an equal absolute value and different signs. Final voltage applied to each pattern is calculated by mutually adding, for each pattern, the displacements obtained for respective direction groups.

Description

Specification

Astigmatism adjustment method

Technical field

The present invention relates to a technical field of an astigmatism adjustment method in a manufacturing process of an optical pickup device used for recording and reproducing information on an optical information recording medium, for example.

Background art

One example of this type of adjustment method is disclosed in Non-Patent Document 1, for example (hereinafter referred to as “conventional technology”). According to the conventional technology, it is possible to adjust astigmatism within a desired range by adjusting the image height by adjusting the tilt angle of the rising mirror that guides the emitted light from the light source to the objective lens. Has been.

[0003] Non-Patent Document 1: Shinichi Nagahara, 4 others, "DVD—R / RW (R5) pickup development", [online], [searched on February 1, 2005], Internet URL: http: 〃 www.pioneer.co.jp/crdl/rd /pdf/13-l-7.pdf>

Disclosure of the invention

Problems to be solved by the invention

[0004] When adjusting astigmatism, it is necessary to adjust the position of the objective lens each time the tilt angle of the rising mirror is adjusted, and the time required to determine the optimum image height is relatively long. The manufacturing process of the pickup device tends to be inefficient. In addition, due to the demand for improving the recording speed, the NA (Numerical Aperture) of the optical system tends to increase as a whole, and the allowable range of the tilt angle of the rising mirror tends to be reduced accordingly. is there. In this case, since it is necessary to adjust the astigmatism within an allowable range, the tact time required for the adjustment is likely to be further deteriorated. In other words, the conventional technique has a technical problem that it is difficult to efficiently adjust astigmatism in the manufacturing process of the optical pickup device.

The present invention has been made in view of the above-described problems, and provides an astigmatism adjustment method capable of efficiently adjusting astigmatism in an optical pickup device manufacturing process. Is an issue.

Means for solving the problem

[0006] Adjustment method for astigmatism>

In order to solve the above problems, an astigmatism adjustment method of the present invention includes a light source, an objective lens for condensing the emitted light emitted from the light source force on a recording medium, and an optical path of the emitted light. G) a pair of electrodes facing each other and a liquid crystal layer sandwiched between the pair of electrodes, and (ii) one of the pair of electrodes is arranged in a circumferential direction. (Iii) each of the plurality of partial electrodes is electrically independent of other partial electrodes adjacent to each other, and (iv) the liquid crystal layer includes And an astigmatism correction means for correcting astigmatism generated in the optical system including the objective lens by a phase difference applied to the emitted light according to an applied voltage between the pair of electrodes. A method of adjusting the astigmatism in the manufacturing process of the optical pickup device, The specific step of identifying the astigmatism to be corrected based on the condensing state of the emitted light through the objective lens, and the astigmatism to be corrected are determined on the one electrode. (I) a first direction group consisting of a first axis and a second axis orthogonal to each other, and (i) a first direction group rotated by 45 degrees and orthogonal to each other. An astigmatism conversion step corresponding to each of the second direction group consisting of the third axis and the fourth axis, and an astigmatism corresponding to the first direction group. From the first determination step of determining the applied voltage to the partial electrode associated with the first direction group and the astigmatism corresponding to the second direction group, the first of the plurality of partial electrodes. A second determining step for determining the applied voltage to the partial electrode associated with the two-direction group; and the first From Mukogun and applied voltage against the respective corresponding Tagged partial electrodes in the second direction group comprises a third determining extent E of determining the applied voltage of the plurality of partial electrodes, respectively.

In the astigmatism adjustment method of the present invention, the optical pickup device includes a light source, an objective lens, and astigmatism correction means.

[0008] The light source is a concept that includes means capable of emitting light according to the type of the recording medium. For example, if the recording medium is a DVD, a laser beam having a wavelength of about 635 to 670 nm. LD (Laser Diode) that emits light may be used. Further, this laser beam may be a laser beam having a wavelength of about 780 to 810 nm when the recording medium is a CD (Compact Disc). Alternatively, when the recording medium is a BRD (Blue Ray Disc), a laser beam having a wavelength of about 400 to 410 nm may be used. For example, the emitted light emitted from the light source is condensed on the recording medium via the objective lens in actual use.

[0009] It should be noted that, on the optical path of the outgoing light, as long as the outgoing light is finally collected on the recording medium via the objective lens, it depends on the configuration, application, or required performance of the optical pickup device. For example, various optical elements such as a grating collimator lens or various optical systems such as a lens may be interposed.

On the other hand, astigmatism occurs in an optical system including an objective lens. This astigmatism is corrected by astigmatism correction means.

[0011] The pair of electrodes in the astigmatism correction means is formed as a transparent conductive film made of, for example, ITO (Indium Tin Oxide) on a substrate made of, for example, a glass-based material. It has permeability. A liquid crystal layer is sandwiched between the pair of electrodes, and the orientation of the liquid crystal molecules constituting the liquid crystal layer changes and the refractive index changes according to the voltage applied between the electrodes. As the refractive index changes, a phase difference is given to the transmitted light, so that astigmatism of the optical system can be corrected.

[0012] Note that “sandwiched between a pair of electrodes” does not necessarily mean that each electrode and the liquid crystal layer are in direct contact with each other. For example, alignment that aligns liquid crystal molecules in a predetermined direction. The liquid crystal layer may be sandwiched through a film or a protective film.

[0013] One of the pair of electrodes has a plurality of partial electrodes. Here, the partial electrode is an individual electrode pattern patterned by photolithography, for example. The partial electrodes are arranged in the circumferential direction to form a ring zone shape. However, the other electrode may be formed with a partial electrode other than the ring-shaped partial electrode. For example, partial electrodes relating to correction of other aberrations generated in the optical system such as coma and spherical aberration may be appropriately formed. Alternatively, a partial electrode that defines the reference of potential in one of the electrodes may be formed.

[0014] The plurality of partial electrodes arranged 1J in the annular shape are electrically connected to other partial electrodes adjacent to each other. Independent. In addition, as long as the potential is independent of the partial electrodes adjacent in the circumferential direction, the partial electrodes may have a common potential. The partial electrode having the annular shape functions as an electrode for correcting astigmatism as a whole (hereinafter, referred to as “astigmatism correction electrode” as appropriate). The number and size of the partial electrodes in this astigmatism correction electrode may be freely determined as long as astigmatism can be corrected. For example, these may be appropriately determined in advance experimentally, empirically, or by simulation.

[0015] It should be noted that the other electrode opposed to the one electrode is not affected by the function of the astigmatism correction electrode, for example, other aberrations caused by the optical system, for example, coma convergence. In addition, a partial electrode for correcting spherical aberration may be appropriately formed. In this case, coma and spherical aberration can be suitably corrected by the astigmatism correction means, which is preferable.

[0016] The astigmatism correction unit operates by applying a voltage between the pair of electrodes. At this time, if the applied voltage is uniform between the pair of electrodes, the liquid crystal molecules in the liquid crystal layer are simply aligned uniformly. The applied voltages of the individual partial electrodes in the astigmatism correction electrode In the case of changing, in the liquid crystal layer, the refractive indexes of the respective portions corresponding to the individual partial electrodes change with each other according to the applied voltage of each of the partial electrodes. Therefore, the phase of the light transmitted through the liquid crystal layer is advanced or delayed depending on the voltage applied to each of the partial electrodes, and the wavefront of the light transmitted through the astigmatism correcting means is corrected. That is, depending on the voltage applied to this partial electrode, for example, astigmatism can be made zero or set to a predetermined value.

[0017] In particular, according to the action of such astigmatism correction means, astigmatism can be corrected without changing the image height by adjusting the tilt angle of the rising mirror as in the prior art. Therefore, the dependence on NA is small, which is advantageous in terms of improving the yield of the optical pickup device.

[0018] However, the tact time required for adjusting astigmatism can vary greatly depending on how the applied voltage of each of the partial electrodes constituting the astigmatism correction electrode is determined. That is, the applied voltage of each of the plurality of partial electrodes needs to be determined efficiently. Therefore, the present invention The astigmatism adjustment method includes the following steps, whereby the applied voltage of each partial electrode can be determined efficiently and astigmatism can be adjusted efficiently.

In other words, according to the astigmatism adjustment method of the present invention, astigmatism to be corrected based on the state of light collected through the objective lens by the operation related to the specific process during the operation. Is identified.

[0020] Here, "astigmatism to be corrected" refers to astigmatism that has been known or can be estimated astigmatism occurring in an optical system including an objective lens or astigmatism. Refers to aberration, for example, astigmatism in a state where no correction is made by the astigmatism correction means. Alternatively, it may be astigmatism with some correction made by the astigmatism correction means.

[0021] Such astigmatism to be corrected is specified based on, for example, a beam profile file of outgoing light through the objective lens. The beam profile is literally a profile (characteristic) of the emitted light, and represents, for example, a beam spot shape and a beam spot diameter. For example, the direction and magnitude of astigmatism to be corrected are specified from the change in the beam profile when the distance between the objective lens and the light source is changed by adjusting the position of the objective lens.

[0022] When the astigmatism to be corrected is specified, the specified astigmatism is converted into an aberration corresponding to each of the first direction group and the second direction group by an operation related to the aberration conversion step. .

Here, the first direction group is defined based on the control direction of astigmatism in one of the electrodes described above (that is, the electrode on which the astigmatism correction electrode is formed). A group consisting of a first axis and a second axis that are orthogonal to each other. The second direction group is a third direction orthogonal to each other obtained by rotating the first direction group, for example, by 45 degrees in the same plane. A group consisting of an axis and a fourth axis.

[0024] Since astigmatism is an aberration caused by the difference in focal length between two orthogonal sections including the optical axis, for example, the first direction group, that is, the first axis and the second axis. If the directions match, it can be expressed simply as the aberration of the first direction group. However, astigmatism occurs at various angles depending on the optical system through which the light beam passes. It is difficult to express only by the aberration of the direction group. So, with this first direction group and 45 degree inclination A defined second direction group is defined.

[0025] When two types of direction groups, the first direction group and the second direction group, are defined, astigmatism can be expressed as a vector sum of these two direction groups. In other words, the aberration conversion process refers to the astigmatism to be corrected by the components of the first direction group (that is, the astigmatism corresponding to the first direction group) and the component of the second direction group (that is, the second direction group). In other words, astigmatism corresponding to (1).

[0026] When the astigmatism to be corrected is converted into astigmatism corresponding to the first and second direction groups, the first determination step and the second determination step are executed.

[0027] In the first determination step, an applied voltage to a partial electrode associated with the first direction group among the plurality of partial electrodes is determined from astigmatism corresponding to the first direction group. Here, the partial electrode associated with the first direction group is at least one partial electrode set in advance as one that can suitably correct the astigmatism of the first direction group among the plurality of partial electrodes. Point to. In view of the nature of astigmatism, the partial electrodes associated with the first direction group are composed of at least a plurality of partial electrode groups, and each partial electrode group includes at least one partial electrode. Is preferred. Such partial electrodes may be appropriately set in advance experimentally, empirically, or by simulation.

[0028] The applied voltage to the partial electrode associated with the first direction group may be calculated each time according to some algorithm that associates the value of astigmatism with the applied voltage, for example, and the astigmatism is preliminarily determined. The control amount associated with the aberration value may be referred to from some storage means.

[0029] In the second determination step, an applied voltage to a partial electrode associated with the second direction group among the plurality of partial electrodes is determined from astigmatism corresponding to the second direction group. Here, the partial electrode associated with the second direction group refers to at least one partial electrode set in advance as one that can suitably correct the astigmatism of the second direction group among the plurality of partial electrodes. Point to. In view of the nature of astigmatism, the partial electrode associated with the second direction group is composed of at least a plurality of partial electrode groups, and each partial electrode group includes at least one partial electrode. Is preferred. Such partial electrodes may be appropriately set in advance experimentally, empirically, or by simulation. [0030] The applied voltage to the partial electrodes associated with the second direction group may be calculated each time, for example, according to some algorithm that associates the value of astigmatism with the applied voltage, and is previously astigmatized. The control amount associated with the aberration value may be referred to from some storage means.

[0031] Preferably, each of the plurality of electrodes belongs to both the first direction group and the second direction group. However, since the corresponding astigmatism differs between the first direction group and the second direction group, in this case, preferably, two types (including values and positive / negative concepts) are applied to each of the partial electrodes. The voltage will be determined.

When the applied voltages of the partial electrodes associated with the respective direction groups are determined in this manner, the applied voltages of the plurality of partial electrodes are determined by the third determining step. At this time, the partial electrodes associated with the first direction group and also the partial electrodes associated with the second direction group are determined in the first determination step and the second determination step. The final applied voltage is determined based on each applied voltage. For example, for a certain partial electrode, if the applied voltage is determined to be 3V in the first determination step and 5V in the second determination step, respectively, the average applied voltage of 4V may be the applied voltage of the partial electrode. Yo!

[0033] Thus, according to the astigmatism adjustment method of the present invention, the applied voltage of each of the plurality of partial electrodes arranged in a ring shape is divided into two direction groups, a first direction group and a second direction group. Can be easily determined based on the voltages applied to the partial electrodes associated with the first direction group and the second direction group, respectively, determined according to the astigmatism corresponding to. At this time, the process of converting astigmatism into astigmatism in each of the first direction group and the second direction group and the process of determining the applied voltage are numerical calculation processes, which are necessary in the manufacturing process of the optical pickup device. The mechanical adjustment becomes only the position adjustment of the objective lens in a specific process for specifying astigmatism to be corrected based on the beam profile. Therefore, the tact time required for the adjustment to set the astigmatism to a desired value (for example, zero) is obviously shortened compared to the conventional technique. That is, it becomes possible to adjust astigmatism efficiently.

In one aspect of the astigmatism adjustment method of the present invention, the astigmatism adjustment method is associated with the first direction group. The partial electrode belongs to one of a first partial electrode group defined by the first axis and a second partial electrode group defined by the second axis, and the first determining step includes the first determining step. The applied voltages to the partial electrodes belonging to the first and second partial electrode groups are determined as displacements having the same absolute value and different signs with respect to a predetermined reference voltage, respectively, and the partial electrodes associated with the second direction group Belongs to one of a third partial electrode group defined by the third axis and a fourth partial electrode group defined by the fourth axis, and the second determining step includes the third and fourth parts The applied voltages to the partial electrodes belonging to the respective electrode groups are determined as displacements having the same absolute value and different signs with respect to the reference voltage, and the third determining step is the same as the first and second determining steps. Each of the above determined Position you added to each said reference voltage for the plurality of partial electrodes respectively.

[0035] According to this aspect, the partial electrode associated with the first direction group is either one of the first partial electrode group and the second partial electrode group defined by the first axis and the second axis, respectively. Belonging to. Note that these electrode groups may be defined in any manner by each axis. The number of partial electrodes belonging to each electrode group is not limited at all, but preferably the same number. Preferably, all of the plurality of partial electrodes are partial electrodes associated with the first direction group. In this case, the plurality of partial electrodes provided in a ring shape belong to the first partial electrode group or the second partial electrode group.

[0036] Here, as long as the partial electrodes belonging to the first and second partial electrode groups are partial electrodes capable of correcting the astigmatism of the first direction group according to the applied voltage, It may have any correspondence with the axis. Such a correspondence relationship may be appropriately determined in advance, experimentally, empirically, or based on simulation, together with the quantity and arrangement of the partial electrodes. For example, if the boundary between the partial electrodes coincides with the first axis or the second axis, the partial electrodes belonging to the first and second partial electrode groups have the first axis and the second axis. Partial electrodes may be sandwiched between them.

[0037] In the first determination step, the voltage applied to the partial electrodes belonging to each of these partial electrode groups is determined. At this time, the applied voltage is determined as a displacement with respect to a predetermined reference voltage. The displacement with respect to the reference voltage is defined by dividing the reference voltage into a plurality of equal parts, for example. It may be expressed in predetermined step units. For example, when the reference voltage is 5 V, a voltage of about 20 mV expressed in 8-bit 256 gradations may be set as the step.

[0038] The applied voltages of the partial electrodes belonging to the first and second partial electrode groups are determined as displacements relative to the reference voltage as described above. At this time, these displacements are mutually absolute values (displacement amounts). Are equal and have different signs (inverted). That is, when the applied voltage of the partial electrode belonging to the first partial electrode group is controlled to be larger than the reference voltage (corresponding to the positive displacement), the partial electrode belonging to the second partial electrode group The applied voltage is controlled to be smaller than the reference voltage (corresponding to negative displacement).

Note that the absolute value of the displacement is a value determined based on the correlation between the magnitude of astigmatism and the phase difference given in the liquid crystal layer. Such correlation is given in advance experimentally, empirically, or by simulation.

[0040] On the other hand, the sign of the applied voltage of the partial electrode belonging to the first partial electrode group and the applied voltage of the partial electrode belonging to the second partial electrode group depends on the setting of the i-th axis and the second axis. In other words, the astigmatism of the first direction group and the partial electrodes belonging to the first partial electrode group and the second partial electrode group in advance, respectively, are not determined uniquely. The correspondence with the sign of the applied voltage can be set freely.

It should be noted that the applied voltage determined here is typically a force that is an applied voltage for completely canceling astigmatism in the first direction group, that is, approximately zero, with a predetermined amount of aberration. It may be an applied voltage that gives a phase difference that remains, that is, the aberration has a predetermined value.

On the other hand, the partial electrodes corresponding to the second direction group belong to either the third partial electrode group or the fourth partial electrode group defined by the third axis and the fourth axis, respectively. Note that these electrode groups may be defined in any way by each axis. The number of partial electrodes belonging to each electrode group is not limited at all, but preferably the same number. Preferably, all of the plurality of partial electrodes are partial electrodes associated with the second direction group. In this case, the plurality of partial electrodes provided in a ring shape belong to the third partial electrode group or the fourth partial electrode group.

[0043] Here, as long as the partial electrodes belonging to the third and fourth partial electrode groups are partial electrodes capable of correcting the astigmatism of the second direction group according to the applied voltage, of It may have any correspondence with the axis. Such a correspondence relationship may be appropriately determined in advance, experimentally, empirically, or based on simulation, together with the quantity and arrangement of the partial electrodes. For example, if the boundary between the partial electrodes coincides with the third axis or the fourth axis, the partial electrodes belonging to the third and fourth partial electrode groups are the third and fourth axes. It may be a partial electrode that sandwiches each.

In the second determination step, the applied voltage of the partial electrodes belonging to each of these partial electrode groups is determined. At this time, the applied voltage is determined as a displacement with respect to a predetermined reference voltage. The displacement with respect to the reference voltage may be expressed in a predetermined step unit defined by dividing the reference voltage into a plurality of equal parts, for example. For example, when the reference voltage is 5 V, a voltage of about 20 mV expressed in 8-bit 256 gradations may be set as the step.

[0045] The applied voltages of the partial electrodes belonging to the third and fourth partial electrode groups are determined as displacements relative to the reference voltage as described above. At this time, these displacements are mutually absolute values (displacement amounts). Are equal and have different signs (inverted). That is, when the applied voltage of the partial electrode belonging to the third partial electrode group is controlled so as to be larger than the reference voltage (corresponding to the positive displacement), the partial electrode belonging to the fourth partial electrode group The applied voltage is controlled to be smaller than the reference voltage (corresponding to negative displacement).

[0047] On the other hand, the sign of the applied voltage of the partial electrode belonging to the third partial electrode group and the applied voltage of the partial electrode belonging to the fourth partial electrode group depends on how the third axis and the fourth axis are set. In other words, the astigmatism of the second direction group and the partial electrodes belonging to the third partial electrode group and the fourth partial electrode group in advance, respectively, are not determined uniquely. The correspondence with the sign of the applied voltage can be set freely.

It should be noted that the applied voltage determined here is typically a force that is an applied voltage for completely canceling astigmatism in the second direction group, that is, approximately zero, with a predetermined amount of aberration. It may be an applied voltage that gives a phase difference that remains, that is, the aberration has a predetermined value. When the applied voltage of the partial electrode belonging to each partial electrode group is determined as a displacement from the reference voltage in this way, this displacement is added to the reference voltage for each of the plurality of partial electrodes. As a result, the final displacement from the reference voltage is determined for each of the plurality of partial electrodes. The applied voltage of each of the plurality of partial electrodes is determined according to this final displacement. In actual use of the optical pickup device, the astigmatism is corrected to a desired value, typically zero, by setting the applied voltage of each of the plurality of partial electrodes to the value determined in the third determination step. The

[0050] According to this aspect, since the applied voltage of each of the plurality of partial electrodes as described above is determined as a displacement with respect to the reference voltage, the applied voltage can be determined relatively easily. That is, it becomes possible to adjust astigmatism efficiently.

[0051] In another aspect of the astigmatism adjustment method of the present invention, the plurality of partial electrodes have boundaries between the first, second, third, and third adjacent to the partial electrodes adjacent to each other. It consists of eight partial electrodes defined by four axes, and (i) the first and second partial electrode groups consist of four parts of the eight partial electrodes that sandwich the first and second axes, respectively. (Ii) The third and fourth partial electrode groups are composed of four partial electrodes that sandwich the third and fourth axes, respectively, among the eight partial electrodes.

According to this aspect, the astigmatism correction electrode is divided into a total of eight partial electrodes along the first axis, the second axis, the third axis, and the fourth axis. All of these eight partial electrodes are partial electrodes associated with the first direction group and partial electrodes associated with the second direction group.

Of these eight partial electrodes, four partial electrodes sandwiching the first axis are the first partial electrode group, and four partial electrodes sandwiching the second axis are the second partial electrodes. The four partial electrodes sandwiching the third axis are the third partial electrode group, and the four partial electrodes sandwiching the fourth axis are the fourth partial electrode group. In this case, each partial electrode group is determined quickly and efficiently, and two of the four partial electrodes constituting each partial electrode group are arranged facing each other. Astigmatism can be finely corrected. In other words, astigmatism can be corrected accurately and efficiently.

[0054] In another aspect of the astigmatism adjustment method of the present invention, each of the determined applied voltages is determined. Is further stored in a predetermined type of storage means mounted on the optical pickup device.

[0055] According to this aspect, since the determined applied voltage of each partial electrode is stored in the storage means, only adjustment is performed in the manufacturing process, and no adjustment is necessary during actual use of the optical pickup device. . Therefore, it is possible to adjust astigmatism more efficiently.

It should be noted that the storage means described here may have any form as long as it is mounted on the optical pickup device and can be read out during operation of the optical pickup device. A non-volatile memory such as an EEPROM (Electrically Erasable Programmable Read Only Memory) may be used. In this case, the information on the applied voltage may be stored together with the specific information of the optical pick-up device, component information, serial number, and the like.

[0057] As described above, the astigmatism correction method of the present invention includes the specifying step, the aberration converting step, the first determining step, the second determining step, and the third determining step, so that astigmatism is efficiently performed. It is possible to adjust the aberration.

[0058] These effects and other advantages of the present invention will become apparent from the embodiments described below.

Brief Description of Drawings

FIG. 1 is a schematic configuration diagram of an optical pickup device according to an embodiment of the present invention.

2 is a schematic diagram of an aberration correction element in the optical pickup device of FIG. 1.

FIG. 3 is a plan view of a first electrode and a second electrode in the aberration correction element of FIG. 2.

FIG. 4 is a conceptual diagram of a first direction group and a second direction group according to an embodiment of the present invention.

FIG. 5 is an exemplary diagram of component decomposition of astigmatism according to an example of the present invention.

FIG. 6 is a table showing a design example of an applied voltage of an electrode pattern according to an example of the present invention. Explanation of symbols

[0060] 100: Optical pickup device, 107: Aberration correction element, 107d: Second electrode, 113---EEPROM.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, the best mode for carrying out the present invention will be described in each embodiment in order with reference to the drawings. <Configuration and operation of optical pickup device>

First, the configuration of the optical pickup device according to the embodiment of the present invention will be described with reference to FIG. FIG. 1 is a schematic configuration diagram of the optical pickup device 100.

In FIG. 1, an optical pickup device 100 includes a light source 101, a light source 102, a dichroic mirror 103, a half mirror 104, a collimator lens 105, a rising mirror 106, an aberration correction element 107, a λ / 4 plate 108, The apparatus includes an objective lens 109, a multi-lens 110, and a detector 111, and condenses light emitted from the light source 101 or 102 on the recording medium 200 to record and reproduce information.

The light source 101 is an LD (Laser Diode) configured to be able to emit laser light having a wavelength of 650 nm, and is an example of a light source according to the present invention that functions as a light source for DVD. The light source 102 is an LD configured to emit laser light having a wavelength of 780 nm, and is another example of the light source according to the present invention that functions as a light source for CD. In addition, a grating that diffracts the emitted light and a λ / 2 plate that converts the emitted light from p-polarized light to s-polarized light are disposed behind each light source, but the illustration is omitted.

Laser light emitted from the light sources 101 and 102 (solid line in FIG. 1) is incident on the dichroic mirror 103. The dichroic mirror 103 has a dichroic characteristic that reflects only light of a specific wavelength. In this embodiment, the dichroic mirror 103 is configured to reflect only the emitted light of the light source 102, that is, the laser beam for CD. Yes. Therefore, the optical path of the emitted light from the light sources 101 and 102 is made common through the dichroic mirror 103.

The half mirror 104 is a kind of PBS (Polarized Beam Splitter) and has a configuration in which the reflectance varies depending on the polarization direction of incident light. Light emitted from each light source is s-polarized light when it reaches the half mirror 104, is reflected by the half mirror 104, and enters the collimator lens 105. The collimator lens 130 is a lens that converts diffused light into parallel light.

The light that has passed through the collimator lens 105 is reflected by the rising mirror 106 and reaches the aberration correction element 107. The rising mirror 106 is a mirror disposed for converting the optical path of incident light. [0067] The aberration correction element 107 is an element for correcting various aberrations generated in the optical pickup device 100. The aberration correction element 107 is driven by a control unit (not shown) in FIG. It functions as an example of such “astigmatism correction means”. The details of the aberration correction element and the control unit will be described later.

The light that has passed through the aberration correction element 107 enters the λ 4 plate 108, is converted into circularly polarized light, and then enters the objective lens 109. The objective lens 140 is a lens that collects incident light on the recording medium 200.

[0069] Each laser beam condensed on the recording medium 200 is reflected and reflected at the condensing position, and is incident on the objective lens 109 again as return light (dotted line in FIG. 1). The return light is further converted into ρ-polarized light by the λ / 4 plate 108, and enters the half mirror 104 through the aberration correction element 107, the rising mirror 106 and the collimator lens 105 in order. Here, since the return light is ρ-polarized light, it passes through the half mirror 104 without being reflected and enters the multi-lens 110.

In the multi-lens 110, astigmatism or the like for obtaining a focus error signal necessary for recording / reproducing information is given to the return light, and the return light is received by the detector 111.

Next, details of the aberration correction element 107 will be described with reference to FIG. Where Figure 2

FIG. 6 is a schematic diagram of an aberration correction element 107. In the figure, the same parts as those in FIG. 1 are denoted by the same reference numerals and the description thereof is omitted.

In FIG. 2, the aberration correction element 107 includes a first substrate 107a, a first electrode 107b, a liquid crystal layer 107c, a second electrode 107d, and a second substrate 107e.

[0073] The first substrate 107a is a plate-like member made of a glass-based material, and has a first electrode 10 on the surface.

7b is formed. The first electrode 107b is a transparent conductive film obtained by patterning ITO.

[0074] The second substrate 107e is a plate-like member made of a glass-based material like the first substrate 107a, and the second electrode 107d as an example of "one electrode" according to the present invention is formed on the surface. Yes. Similar to the first electrode 107b, the second electrode 107d is a transparent conductive film in which the patterning process is applied to ITO. Further, the first electrode 107b and the second electrode 107d are arranged to face each other so as to be orthogonal to the direction of the illustrated light beam. [0075] The liquid crystal layer 107c is a layer containing liquid crystal molecules (not shown) sandwiched between the first electrode 107b and the second electrode 107d, and the alignment of the liquid crystal molecules according to the applied voltage between the two electrodes. As the refractive index changes, the refractive index changes.

The operation of the aberration correction element 107 is controlled by the control unit 112. The control unit 112 is a control unit including a CPU (Central Processing Unit) (not shown) and the like, and can control the applied voltage of each electrode pattern described later in each of the first electrode 107b and the second electrode 107d. It is configured.

The EEPROM 113 is a rewritable nonvolatile semiconductor memory, and an optical pickup device

100 serial numbers and parts information are stored. The EEPROM 113 stores voltage data to be applied to each of the electrode patterns described above. When the aberration correction element 107 is operated, the control unit 112 reads the information on the applied voltage from the EEPROM 113 and determines the voltage. Is applied.

Next, details of each electrode will be described with reference to FIG. FIG. 3 is a plan view of the first electrode 107b and the second electrode 107d. In the figure, the same parts as those in FIG. 2 are denoted by the same reference numerals and the description thereof is omitted.

In FIG. 3, FIG. 3 (a) represents the first electrode 107b, and FIG. 3 (b) represents the second electrode 107d.

[0080] The first electrode 107b includes a plurality of electrode patterns 107bl, 107b2, 107b3, 107b4, and 107b5. The configuration and arrangement of these patterns are set so that spherical aberration generated in the optical pickup device 100 is corrected, and among these, the electrode patterns 107b 1 and 107b3 are also used for correcting coma aberration. . The electrode pattern 107b2 is a pattern that serves as a reference for the potential of the first electrode 107b. Since the relevance of the astigmatism adjustment method according to the present invention and correction of the coma aberration and spherical aberration is small, detailed description is omitted for the sake of simplification.

[0081] The second electrode 107d has a plurality of electrode patterns 107dl (hereinafter referred to as pattern 1), 107d2 (hereinafter referred to as pattern 2), 107d3 (hereinafter referred to as pattern 3), 107d4 (hereinafter referred to as pattern 4), 107d5 (hereinafter referred to as pattern). 5), 107d6 (hereinafter referred to as pattern 6) and 107d7 (hereinafter referred to as pattern 7), and is an example of “one electrode” according to the present invention. Of these, Pattern 2 and Pattern 6 are the previous ones. Together with the electrode patterns 107bl and 107b3 in the first electrode 107b described above, it is used to correct coma aberration. Pattern 4 is a pattern that serves as a reference for the potential of the second electrode 107d.

Pattern 1, pattern 3, pattern 5 and pattern 7 are examples of “a plurality of partial electrodes having an annular shape” according to the present invention, and function as astigmatism correction electrodes. As shown in the figure, these patterns are evenly arranged in the circumferential direction, and are independent in potential from adjacent patterns.

In the aberration correction element 107, a reference voltage V (for example, 5V) is applied between the pattern 4 (electrode pattern 107d4) and the electrode pattern 107b2. Do not correct any aberrations

0

In this case, the potentials of the entire electrode 107b and the entire electrode 107d are controlled to be equal to the potentials of the electrode patterns 107b2 and 4 respectively. When correcting astigmatism, the applied voltage of pattern 1, pattern 3, pattern 5 and pattern 7 at electrode 10 7d is changed with respect to pattern 4, thereby changing the refractive index of the liquid crystal layer and transmitting light. Is given a phase difference. As described above, the applied voltages of patterns 1, 3, 5 and 7 are stored in EEPROM 113, and this applied voltage is astigmatism described below in the manufacturing process of optical pickup device 100. This is determined by performing the adjustment method. <Astigmatism adjustment method>

When astigmatism adjustment is performed, first, astigmatism to be corrected is specified. Astigmatism is specified, for example, by measuring the profile of the laser beam emitted from the light source 101 every time the position of the objective lens 109 is adjusted, and analyzing the profile using a known beam profile measurement technique or the like. . This process is an example of a specific process according to the present invention.

When astigmatism is specified, this astigmatism is decomposed into components of a predetermined direction group defined on the second electrode 107d. This step is an example of an aberration converting step according to the present invention.

[0085] Here, the concept of the direction group will be described with reference to FIG. FIG. 4 is a conceptual diagram of the first direction group and the second direction group.

As shown in FIG. 4, FIG. 4 (a) shows the first direction group, and FIG. 4 (b) shows the second direction group. still In order to prevent complication of the drawings, patterns 1, 3, 5 and 7 are simply represented as 1, 3, 5 and 7 in the respective drawings.

In FIG. 4 (a), the first direction group is defined by two axes orthogonal to each other, ie, the first axis and the second axis shown in the figure. The first axis defines the boundary between pattern 3 and pattern 5 in the second electrode 107d, and the second axis similarly defines the boundary between pattern 1 and pattern 7.

In FIG. 4B, the second direction group is defined by two axes orthogonal to each other, ie, the third axis and the fourth axis shown in the figure. The third axis defines the boundary between pattern 1 and pattern 3 in the second electrode 107d, and the fourth axis similarly defines the boundary between pattern 5 and pattern 7. It should be noted that the relationship between each of the first direction group and the second direction group and each electrode pattern is not limited to that shown in the figure, and may be set freely. The identified astigmatism is decomposed into vectors in the first direction group and the second direction group.

Here, with reference to FIG. 5, the identified astigmatism and the components of each direction group will be described. FIG. 5 is an exemplary diagram of astigmatism component decomposition.

In FIG. 5, the astigmatism to be corrected generated in the optical pickup device 100 is 0 · 17 λ (λ is the wavelength of the emitted light) in the direction of 30 degrees. When it is decomposed into components of the first and second direction groups, respectively, 0.085 and 0.147 λ are obtained. Here, a negative sign indicates that the phase is delayed.

When the astigmatism is decomposed into components of each direction group in this way, the applied voltage of each pattern is determined for each direction group. At this time, the applied voltage is the displacement with respect to the reference voltage V.

0

Determined. For example, when the reference voltage is V force V and the displacement is controlled by gradation with 8 bits.

0

In this case, the unit (step) of the displacement is about 20mV. The applied voltage of each pattern for each direction group is determined as an increase / decrease value of the number of steps. For example, the refractive index change of the liquid crystal layer 107c when the applied voltage is increased (or decreased) by one step, that is, the correctable aberration, is experimentally, empirically, or simulated in advance. Get it.

[0092] When correcting astigmatism in each direction group, due to the nature of astigmatism, if the phase of the wavefront corresponding to one of the two axes that define each direction group is corrected in the advance direction, be sure to Versus the other The corresponding wavefront phase needs to be corrected in the lag direction. Control that realizes such correction is called seesaw control.

In this embodiment, the four axes that define each direction group define the boundaries of eight electrode patterns (that is, patterns 1, 3, 5, and 7). These eight electrode patterns are all examples of the partial electrodes associated with the first direction group and the partial electrodes associated with the second direction group according to the present invention.

[0094] When correcting astigmatism corresponding to the first direction group, the pattern as an example of the first partial electrode group according to the present invention sandwiching the first axis (that is, defined by the first axis) 3 and 5, and patterns 1 and 7 as an example of the second partial electrode group according to the present invention sandwiching the second axis (that is, defined by the second axis) are treated as a pair, respectively. Executed. Further, when correcting astigmatism corresponding to the second direction group, patterns 1 and 3 as an example of the third partial electrode group according to the present invention sandwiching the third axis (that is, defined by the third axis). And the patterns 5 and 7 as an example of the fourth partial electrode group according to the present invention sandwiching the fourth axis (that is, defined by the fourth axis) are treated as a pair, and the seesaw control is executed. .

[0095] In FIG. 4, the arrow lines (that is, each axis) defining each direction group coincide with the boundaries of the patterns 1, 3, 5, and 7, and each partial electrode group is relatively clear. However, the positional relationship between each axis that defines each direction group and each pattern is not limited to this. That is, each pattern may rotate freely with respect to each axis.

Here, with reference to FIG. 6, an example of the applied voltage of each pattern determined for each direction group is shown. FIG. 6 is a table showing a design example of the applied voltage.

In FIG. 6, in order to correct astigmatism in the first direction group, the applied voltage of pattern 1 and pattern 7 is “V−0.85 V”, and the applied voltage of pattern 3 and pattern 5 is “V. + 0.8

0 0

5V "is determined. In addition, in order to correct astigmatism in the second direction group, the applied voltage of pattern 1 and pattern 3 is `` V-1.47V '', and the applied voltage of pattern 5 and pattern 7 is `` V

0

+ 1. 47V ". This process includes the first determination process and the second determination process according to the present invention.

0

It is an example of each fixed process.

When the applied voltage of each electrode pattern for correcting astigmatism in each direction group is determined in this manner, the applied voltage of each pattern is finally determined. In addition, this process It is an example of the 3rd determination process which concerns on invention.

[0099] Here, referring to FIG. 6, the final applied voltage of each electrode pattern will be described. The applied voltage of each pattern is easily determined by adding the displacements relative to the reference voltage determined for each of the first direction group and the second direction group. For example, for pattern 1, the displacement force S “_0.85V” required to correct the astigmatism in the first direction group is the same as that required to correct the astigmatism in the second direction group. Since the displacement is “1.1.4 7V”, the displacement with respect to the final reference voltage V is “_2.32V”. Therefore

0

The applied voltage of pattern 1 is “V-2.32V”. The same applies to other electrode patterns

0

The applied voltage is determined. The applied voltage determined for each of these electrode patterns is stored in the EEPROM 113 (that is, an example of the “storage process” according to the present invention). For example, at this time, the EEPROM 113 stores the voltage in hexadecimal.

[0100] As described above, according to the astigmatism adjustment method according to the present embodiment, astigmatism generated in the optical pick-up device 100 is included in the components of the first direction group and the second direction group. By decomposing each, and determining the voltage to be applied to each electrode pattern for each direction group as a displacement with respect to the reference voltage, finally, the applied voltage of each pattern can be easily determined. At this time, the mechanical adjustment only requires the adjustment of the position of the objective lens when specifying astigmatism, and these applied voltages are determined as numerical calculation processing when the astigmatism is specified. can do. Therefore, the tact time required for adjusting astigmatism in the manufacturing process of the optical pickup device is obviously shortened. In other words, astigmatism can be adjusted efficiently.

[0101] Note that the number of electrode patterns on the second electrode 107d used for correcting astigmatism need not be eight as described above. For example, it may be divided into more patterns. In this case, the number of patterns corresponding to each axis in each direction group increases accordingly, and astigmatism can be corrected more finely finally.

[0102] The present invention is not limited to the above-described embodiments, but can be modified as appropriate without departing from the gist or concept of the invention which can be read, and is not accompanied by such changes. Aberration adjustment methods are also included in the technical scope of the present invention. Industrial applicability

The astigmatism adjustment method according to the present invention can be used for an astigmatism adjustment method in a manufacturing process of an optical pickup device used for recording and reproducing information on an optical information recording medium, for example.

Claims

The scope of the claims

[1] a light source;

An objective lens for condensing the emitted light emitted from the light source on a recording medium; and (i) a pair of electrodes disposed on the optical path of the emitted light and facing each other, and between the pair of electrodes And (ii) one electrode of the pair of electrodes includes a plurality of partial electrodes that form a ring shape by being arranged in a circumferential direction, and (m) the plurality of the partial portions. Each of the electrodes is independent in potential with respect to other partial electrodes adjacent to each other. (Iv) In the liquid crystal layer, the position applied to the emitted light according to the applied voltage between the pair of electrodes. Astigmatism correction means for correcting astigmatism generated in the optical system including the objective lens due to the phase difference;

A method for adjusting the astigmatism in a manufacturing process of an optical pickup device comprising:

A specifying step of specifying the astigmatism to be corrected based on a state of convergence of the emitted light through the objective lens;

The astigmatism to be corrected is defined on the basis of the control direction of the astigmatism across the one electrode, and a first direction group consisting of a first axis and a second axis orthogonal to each other, and

(ii) an aberration conversion step of converting the first direction group into astigmatism corresponding to each of the second direction group consisting of the third axis and the fourth axis orthogonal to each other rotated by 45 degrees;

A first determination step of determining the applied voltage to a partial electrode associated with the first direction group among the plurality of partial electrodes from astigmatism corresponding to the first direction group; and the second direction. A second determination step of determining the applied voltage to a partial electrode associated with the second direction group among the plurality of partial electrodes from astigmatism corresponding to the group; the first direction group and the first direction group; And a third determination step of determining an applied voltage of each of the plurality of partial electrodes from an applied voltage to each of the partial electrodes respectively associated with the two direction groups.

[2] The partial electrode associated with the first direction group belongs to one of the first partial electrode group defined by the first axis and the second partial electrode group defined by the second axis. , In the first determining step, applied voltages to the partial electrodes belonging to the first and second partial electrode groups are determined as displacements having mutually equal absolute values and different signs with respect to a predetermined reference voltage,

The partial electrode associated with the second direction group belongs to one of a third partial electrode group defined by the third axis and a fourth partial electrode group defined by the fourth axis,

In the second determining step, the applied voltages to the partial electrodes belonging to the third and fourth partial electrode groups are determined as displacements having the same absolute value and different signs with respect to the reference voltage,

In the third determination step, the displacement determined in each of the first and second determination steps is added to the reference voltage for each of the plurality of partial electrodes.

The method for adjusting astigmatism according to claim 1, wherein:

[3] The plurality of partial electrodes include eight partial electrodes whose boundaries with the other partial electrodes adjacent to each other are defined by the first, second, third, and fourth axes. The first and second partial electrode groups consist of four partial electrodes that sandwich the first and second axes, respectively, of the eight partial electrodes, and (ii) the third and fourth partial electrode groups Is composed of four partial electrodes that sandwich the third and fourth axes, respectively, of the eight partial electrodes.

The method for adjusting astigmatism according to claim 1, wherein:

[4] The method further includes a storing step of storing each determined applied voltage in a predetermined type of storing means mounted on the optical pickup device.

The method for adjusting astigmatism according to claim 1, wherein: