JP2005351876A - Astigmatic difference measuring method, spot diameter correction method and spot evaluation system of optical device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an astigmatic difference measuring method of an optical device which can correct astigmatism present on a condensing performance evaluation system itself, without the use any optical elements for astigmatism correction to contribute to reduction in the number of components and cost required for astigmatic difference measuring of the optical device. <P>SOLUTION: This astigmatism measuring method uses software-based data processing to correct astigmatism, without relying on any optical element for astigmatism correction, and then measures astigmatic difference of the optical device. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a method for measuring astigmatism of an optical device such as an optical pickup device, and in particular, the optical device includes correcting the astigmatism of a light collection performance evaluation device itself such as a spot evaluation device. The present invention relates to a method for measuring astigmatic difference.

  In recent years, data (information) is frequently written in an optical disk device such as a CD or MD using an optical pickup device, and it is expected that a large amount of data can be stored in the optical disk device. In order to increase the capacity, it is necessary to reduce the recording spot on the optical disk device medium and increase the recording density. For this reason, it is important to shorten the wavelength of the laser beam of the optical pickup device. However, the laser beam has astigmatism that appears at different light emitting point positions in the vertical and horizontal directions of the beam, and the beam was extremely elliptical, so the device was designed using an optical system to correct these. In general, the optical pickup device is optically evaluated in order to measure the correction amount.

  As described above, the light collecting performance of the optical pickup device is generally determined by spot evaluation. As an evaluation index of this spot evaluation, for example, a spot diameter, a focal depth, or spherical aberration, coma aberration, There are various aberrations such as astigmatism. And the spot evaluation regarding this evaluation index is performed by the spot evaluation apparatus. For example, an optical pickup evaluation system OPT-W series manufactured by Nissho Electronics Co., Ltd. that measures a condensing spot from an optical pickup unit using a microscope optical system is known.

  The basic configuration of the spot evaluation apparatus is the same as the basic configuration of the microscope because a microscope optical system is used. Therefore, each aberration such as spherical aberration, coma aberration, and astigmatism also exists in the spot evaluation apparatus itself, and these are factors that hinder accurate astigmatism measurement.

  For this reason, in order to accurately perform the spot evaluation of the optical pickup device using the spot evaluation device, each aberration existing in the spot evaluation device itself must be corrected. Of each aberration, spherical aberration can be corrected by changing the thickness of the cover glass of the spot evaluation device. Further, coma aberration can be corrected by tilting the cover glass.

  However, among the aberrations existing in the spot evaluation apparatus itself, astigmatism is difficult to correct mechanically (mechanically) because the basic configuration of the spot evaluation apparatus is the same as the basic configuration of the microscope. In order to correct this, conventionally, an optical element for correcting astigmatism (for example, oblique glass) had to be incorporated in the spot evaluation apparatus. Although astigmatism can be corrected by incorporating oblique glass in this way, new astigmatism will occur due to the incorporation of oblique glass, so it is necessary to correct the newly generated aberration, and the correction work Was complicated. Such a situation has led to an increase in the number of parts necessary for evaluating the light collecting performance of the optical pickup device, which in turn has led to an increase in astigmatism measurement cost.

  The present invention has been made in view of these points, and an object of the present invention is to correct astigmatism existing in the light collecting performance evaluation apparatus itself without using an optical element for correcting astigmatism. It is possible to provide an optical device astigmatism measurement method, a spot diameter correction method, and a spot evaluation device that can contribute to the reduction of the number of parts and the cost required for the astigmatism measurement of the optical device. . It is another object of the present invention to provide an optical device astigmatism measurement method, spot diameter correction method, and spot evaluation device that can prevent the correction operation from becoming complicated and can simplify the correction operation. .

  In order to solve the above-described problems, the present invention corrects astigmatism without using an astigmatism correction optical element by using software information processing, and astigmatic difference of the optical apparatus. Is measured.

  More specifically, the present invention provides the following.

(1) While correcting the astigmatic difference of the condensing performance evaluation device that evaluates the condensing performance of the optical device that is the device to be evaluated, the astigmatic difference of the optical device using the condensing performance evaluation device Is an astigmatic difference measurement method for an optical device that measures the astigmatism difference R (θ _n ) at one angle θ _n while rotating data acquired from the optical device with respect to a predetermined basic axis. Using the step, the angle θ _max when the astigmatic difference R (θ _n ) is maximum, and the maximum astigmatic difference R (θ _max ) at that time, the vector coefficient R in the same direction as the basic axis ₀ , a vector coefficient R _{45 in a} direction that forms an angle of 45 degrees with respect to the basic axis, and a fitting technique to calculate an arbitrary value from the vector coefficient R ₀ and the vector coefficient R ₄₅ . Calculate astigmatic difference R (θ) at angle θ A step of correcting the vector coefficient R ₀ and the vector coefficient R ₄₅ by measuring a reference optical device whose astigmatic difference is known in advance with the light collecting performance evaluation device, and a corrected vector Calculating an astigmatism difference of the optical device using coefficients R ₀ and R ₄₅ .

(2) While correcting the astigmatic difference of the condensing performance evaluation device that evaluates the condensing performance of the optical device that is the device to be evaluated, the astigmatic difference of the optical device using the condensing performance evaluation device Is an astigmatic difference measurement method for an optical device that measures the astigmatism difference R (θ _n ) at one angle θ _n while rotating data acquired from the optical device with respect to a predetermined basic axis. Using the step, the angle θ _max when the astigmatic difference R (θ _n ) is maximum, and the maximum astigmatic difference R (θ _max ) at that time, the vector coefficient R in the same direction as the basic axis ₀ , a vector coefficient R _{45 in a} direction that forms an angle of 45 degrees with respect to the basic axis, and a fitting technique to calculate an arbitrary value from the vector coefficient R ₀ and the vector coefficient R ₄₅ . Calculate astigmatic difference R (θ) at angle θ And calculating a correction coefficient α ₀ and a correction intercept β _{0 of the} vector coefficient R ₀ by measuring a reference optical device whose astigmatic difference is known in advance with the light collection performance evaluation device, The correction coefficient α ₄₅ and the correction intercept β _{45 of the} vector coefficient R ₄₅ are calculated, the vector coefficient R ₀ is corrected using the correction coefficient α ₀ and the correction intercept β _0, and the correction coefficient α ₄₅ above using the method of correcting the vector coefficient R ₄₅ by using the correction sections beta _45, the vector coefficients of the corrected R ₀ and R ₄₅ and, a step of calculating the astigmatism of the optical device, An astigmatic difference measuring method for an optical device, comprising:

According to the present invention, astigmatism difference R (θ _n ) at one angle θ _n (discrete value) is acquired while rotating the data acquired from the optical device with respect to a predetermined basic axis, and is necessary for orthogonal decomposition. a and calculates two and a vector coefficient R ₀ and R _45, with their vector coefficients calculated arbitrary angle theta astigmatism R in (continuous values) (theta), the reference astigmatism is known A correction coefficient and a correction intercept are calculated by measuring the optical device with a focusing performance evaluation device such as a spot evaluation device or an interferometer, and the two vector coefficients R ₀ and R ₄₅ are calculated using the correction coefficient and the correction intercept. Since the astigmatic difference of the optical device is calculated using the corrected two vector coefficients R ₀ and R ₄₅ , the astigmatism correction is performed in the middle of the focusing performance evaluation device for astigmatism correction. It is not necessary to incorporate the optical element .

  Therefore, the astigmatism existing in the light collecting performance evaluation apparatus itself can be corrected, which can contribute to the reduction in the number of parts and the cost required for evaluating the light collecting performance of the optical device.

  (3) The optical device is an optical pickup device, the light collecting performance evaluation device is a spot evaluation device, and the spot diameter acquired from the optical pickup device is calculated by the above astigmatism measurement method. A spot diameter correction method, wherein correction is performed based on a point difference.

  (4) A spot evaluation apparatus that corrects a spot diameter using the above-described spot diameter correction method.

  According to the present invention, since the spot diameter acquired from the optical pickup device is corrected based on the astigmatism calculated by the above-described astigmatism measurement method, astigmatism correction is performed in the middle of the spot evaluation device. It is possible to correct the spot diameter without incorporating the optical element.

  As described above, the astigmatic difference measuring method, the spot diameter correcting method, and the spot evaluating device of the optical device according to the present invention are configured to correct astigmatism using software information processing. Astigmatism can be corrected without using an optical element for correcting astigmatism, and as a result, it is possible to contribute to a reduction in the number of parts and cost required for astigmatism measurement. Further, the correction work can be prevented from becoming complicated, and the correction work can be simplified.

  The best mode for carrying out the present invention will be described below with reference to the drawings.

[Hardware configuration]
FIG. 1 is a diagram showing a hardware configuration for executing the astigmatism measurement method according to the embodiment of the present invention.

  In FIG. 1, an astigmatic difference measuring method according to an embodiment of the present invention includes a spot evaluation device 1 having a configuration similar to the basic configuration of a microscope, an optical pickup device 2 to be inspected, and a spot evaluation device 1. And the computer 3 connected to.

  The spot evaluation apparatus 1 is connected to a CCD camera 1a that photoelectrically converts a light beam transmitted by an optical element, an eyepiece 1b that condenses the light beam on a light receiving element in the CCD camera 1a, and a focus fine movement mechanism. And an objective lens 1c capable of finely adjusting the focus position.

  In the optical pickup device 2, the definition of the attitude with respect to the basic axis composed of the x-axis and the y-axis orthogonal thereto is determined. In addition, on the display of the computer 3 that displays the spot diameter of the light beam emitted from the optical pickup device 2, a basic axis composed of the x axis and the y axis orthogonal thereto is determined. These basic axes have a corresponding relationship. For example, when the optical pickup device 2 is rotated by an angle θ with respect to the basic axis, the spot diameter (data) displayed on the display of the computer 3 is also an angle with respect to the basic axis. It will rotate by θ.

[Astigmatic difference measurement method]
FIG. 2 is a flowchart showing the flow of the astigmatic difference measurement method according to the embodiment of the present invention.

  In FIG. 2, the astigmatic difference measurement method according to the embodiment of the present invention first measures the spot diameter of the light beam (step S21). More specifically, the spot diameter of the light beam emitted from the optical pickup device 2 is measured by the CCD camera 1a in the spot evaluation device 1, and stored in a memory (not shown) in the computer 3.

  Here, when the spot diameter is measured by the CCD camera 1a, when the spot diameter of the light beam is observed while defocusing the point image intensity distribution including astigmatism, a circle of minimum confusion is obtained in the middle of the astigmatic difference. The cross-sectional shape of the spot diameter becomes almost circular (see FIG. 3B), and when it deviates from that, the cross-sectional shape of the spot diameter becomes elliptical (see FIG. 3A or 3C). Further, depending on the characteristics of the optical pickup device 2, the ellipse may be inclined from the basic axis. For example, as shown in FIGS. 3D to 3F, the ellipse has an inclination of 45 degrees with respect to the basic axis. There is.

Next, an astigmatic difference (discrete value) is acquired (step S22). More specifically, a focus position where both axes (long axis and short axis) of the ellipse are minimum is detected from the spot diameter data captured in the computer 3 in step S21, and the two focus positions at that time are detected. Is calculated as the astigmatic difference R (θ _n ). Note that the inclination of the ellipse with respect to the basic axis at this time is defined as an angle θ _n .

In step S22, the astigmatic difference is acquired while rotating the data acquired from the optical pickup device 2 with respect to a predetermined basic axis. More specifically, as described above, when the optical pickup device 2 is rotated by the angle θ with respect to the basic axis, the spot diameter data is also rotated by the angle θ with respect to the basic axis, so the optical pickup device 2 is rotated. Astigmatism difference is acquired. For example, as shown in FIG. 4, when the rotation angle of the spot diameter data with respect to the basic axis is 0 degree (θ _n = 0), the astigmatism difference R (0) is calculated (FIG. 4 (a)), When the rotation angle of the spot diameter data with respect to the basic axis is 22.5 degrees (θ _n = 22.5), the astigmatism difference R (22.5) is calculated (FIG. 4B), and the spot axis data with respect to the basic axis is calculated. When the rotation angle of the spot diameter data is 45 degrees (θ _n = 45), the astigmatic difference R (45) is calculated (FIG. 4C). 4A to 4C, the amount of astigmatism varies depending on the rotation angle of the spot diameter data (R (0)> R (22.5)> R (45)), This is due to the characteristics of the optical pickup device 2.

  In order to appropriately perform the fitting described later, it is preferable to perform the process of step S22 for points of 3 points or more within a range of 0 to 45 degrees.

Next, the largest value among the plurality of astigmatic differences R (θ _n ) acquired in step S22 is defined as the maximum astigmatic difference R (θ _max ) (and the inclination of the ellipse with respect to the basic axis at that time) _Is defined as an angle θ _max ), and an orthogonal decomposition of the astigmatic difference R (θ _max ) is performed (step S23). More specifically, by substituting the maximum astigmatism amount R (θ _max ) and the angle θ _max into the following equation, the astigmatism difference 0 (vector coefficient R ₀ ) in the same direction as the basic axis and the basic axis Astigmatism difference 45 (vector coefficient R ₄₅ ) in a direction forming an angle of 45 degrees with respect to the angle is calculated.

  Next, an astigmatic difference (continuous value) is calculated (step S24). That is, using the fitting method, the astigmatism difference R (θ) at an arbitrary angle θ is calculated from the astigmatism difference 0 and the astigmatism difference 45 obtained by the equations (1) and (2). More specifically, the astigmatic difference at an arbitrary angle θ (continuous value) is calculated by a fitting method such as the least square method by substituting the astigmatic difference 0 and the astigmatic difference 45 into the following equation.

  A typical fitting method is the least square method, but the present invention is not limited to this. For example, any method suitable for a fitting method such as multiformal expansion or Chebyshev method may be used. It doesn't matter.

Next, a correction coefficient and a correction intercept are calculated (step S25). More specifically, by measuring a reference optical pickup device in which the astigmatic difference is known in advance with a spot evaluation device, the correction coefficient α ₀ and the corrected intercept β ₀ for the astigmatic difference 0 are calculated, and the astigmatism is calculated. A correction coefficient α ₄₅ and a correction intercept β ₄₅ for the difference 45 are calculated. Here, the spot evaluation device is adopted as the light collecting performance evaluation device, but an evaluation device such as an interferometer can also be adopted. In such a case, the correction coefficient and the correction intercept calculated in step S25 play a role as parameters between different evaluation devices such as the spot evaluation device and the interferometer.

  Next, the astigmatic difference 0 and the astigmatic difference 45 are corrected using the correction coefficient and correction intercept calculated in step S25 (step S26). More specifically, the astigmatic difference of the spot evaluation apparatus itself is removed by substituting the astigmatic difference 0 of the object to be measured and the astigmatic difference 45 of the object to be measured into the following equation.

  FIG. 5 shows how the astigmatic difference is corrected by step S26. The vertical axis is represented by astigmatic difference R (θ) × cos θ, and the horizontal axis is represented by astigmatic difference R (θ) × sin θ. In addition, the circles in FIG. 5 indicate the astigmatic difference (discrete value) before correction, and the thin line indicates the astigmatic difference (continuous value) calculated (fitted) in step S24, and the thick line Indicates the astigmatic difference corrected in step S26. According to FIG. 5, it can be seen that the amount of astigmatism (the distance between an arbitrary point on the broken line or the solid line and the origin) is reduced as a whole.

  Finally, the spot diameter is calculated again from the corrected astigmatic difference, and the spot diameter changed due to the machine difference of the spot evaluator and the astigmatic difference is corrected to be closer to the true value (step S27). An example in which the spot diameter is corrected in step S27 is shown in FIG.

  In FIG. 6A, the vertical axis indicates the spot diameter (μm) on the left, the maximum (relative) luminance on the right, and the horizontal axis indicates the amount of focus (μm). As parameters, the spot diameter in the X-axis direction is represented by a black rhombus, the spot diameter in the Y-axis direction is represented by a black square, and the maximum luminance of the light intensity distribution at each focus amount is represented by a white triangle. Approximate curves are drawn for each parameter.

  According to FIG. 6A, the spot diameter in the X-axis direction before correction is 0.8560 μm at the focus amount (0.1644 μm) at which the maximum luminance is the largest, and the focus amount (0.1644 μm) at which the maximum luminance is the largest. ), The spot diameter in the Y-axis direction before correction is 0.8100 μm. Here, the spot diameter at the focus amount at which the maximum luminance is maximized is considered because recording and reproduction are actually performed with the focus amount at which the maximum luminance is maximized.

  The astigmatic difference before correction is a distance in the horizontal axis direction between the minimum value m1 of the approximate curve of the spot diameter in the X-axis direction and the minimum value m2 of the approximate curve of the spot diameter in the Y-axis direction. 0.239 μm.

  On the other hand, based on the corrected astigmatism, the approximate curve of the spot diameter in the X-axis direction and the approximate curve of the spot diameter in the Y-axis direction in FIG. 6A are shifted in the horizontal axis direction. Specifically, the approximate curve of the spot diameter in the X-axis direction and the approximate curve of the spot diameter in the Y-axis direction are shifted by an equal amount in the horizontal axis direction so that the corrected astigmatism is obtained. In this example, since the astigmatic difference after correction is 0.089 μm, an approximate curve of the spot diameter in the X-axis direction is shown on the right side so that the distance between the minimum value m1 and the minimum value m2 is 0.089 μm. The approximate curve of the spot diameter in the Y-axis direction by 0.075 μm in the direction is shifted by 0.075 μm in the left direction in the figure.

  In this way, according to FIG. 6B shifted in the horizontal axis direction, the corrected spot diameter in the X-axis direction at the focus amount (0.1644 μm) at which the maximum luminance is the largest is 0.8557 μm, which is the maximum. The corrected spot diameter in the Y-axis direction at the focus amount (0.1644 μm) at which the luminance is greatest is 0.8075 μm.

  As described above, according to FIGS. 6A and 6B, the spot diameter in the X-axis direction is corrected from 0.8560 μm to 0.8557 μm, and the spot diameter in the Y-axis direction is from 0.8100 μm. It can be seen that the correction is made to 0.8075 μm.

  According to the astigmatic difference measuring method and the spot diameter correcting method as described above, it is possible to easily correct astigmatism without using an astigmatism correcting optical element.

[Other embodiments]
The astigmatic difference measurement method in the above-described embodiment is an example of a preferred embodiment of the present invention, but is not limited thereto, and various modifications can be made without departing from the scope of the present invention. For example, by using a laser diode as an optical device that is an evaluation target and using a near field measurement device as a light collecting performance evaluation device, the near field measurement device itself can be used without using an astigmatism correction optical element. It is possible to easily correct astigmatism. That is, the astigmatism measurement method in the present invention is not limited to the spot evaluation device for the optical pickup device, and can be applied to the light collection performance evaluation device for evaluating the light collection performance of other optical devices. Is possible.

  The astigmatism measurement method, the spot diameter correction method, and the spot evaluation apparatus according to the present invention are useful as a method and apparatus that can contribute to the number of parts and cost reduction necessary for the astigmatism measurement of an optical device.

It is a figure which shows the hardware constitutions which perform the astigmatic difference measuring method which concerns on embodiment of this invention. It is a flowchart which shows the flow of the astigmatic difference measuring method which concerns on embodiment of this invention. It is a figure for demonstrating the shape by the focus state of the spot in which an astigmatic difference exists. It is a figure for demonstrating the change of the focusing amount to the in-focus position of a basic axis with angle (theta). It is a figure which shows a fitting astigmatic difference and the astigmatic difference after correction | amendment. It is a figure which shows an example by which the spot diameter of a X-axis direction and a Y-axis direction is correct | amended.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Spot evaluation apparatus 2 Optical pick-up apparatus 3 Computer

Claims (4)

The astigmatic difference of the optical device is measured using the condensing performance evaluating device while correcting the astigmatic difference of the condensing performance evaluating device for evaluating the condensing performance of the optical device that is the device to be evaluated. An astigmatic difference measuring method for an optical device,
Obtaining astigmatic difference R (θ _n ) at one angle θ _n while rotating data acquired from the optical device with respect to a predetermined basic axis;
Using the angle θ _max when the astigmatic difference R (θ _n ) is maximum and the maximum astigmatic difference R (θ _max ) at that time, a vector coefficient R _{0 in the} same direction as the basic axis, Calculating a vector coefficient R _{45 in a} direction that makes an angle of 45 degrees with respect to the basic axis;
Calculating an astigmatism difference R (θ) at an arbitrary angle θ from the vector coefficient R ₀ and the vector coefficient R ₄₅ using a fitting method;
Correcting the vector coefficient R ₀ and the vector coefficient R ₄₅ by measuring a reference optical device in which the astigmatic difference is known in advance with the light collecting performance evaluation device;
By using the vector coefficient R ₀ and R ₄₅ after correction, astigmatism measuring method of an optical device comprising the steps of calculating, in that it consists of astigmatism of the optical device. The astigmatic difference of the optical device is measured using the condensing performance evaluating device while correcting the astigmatic difference of the condensing performance evaluating device for evaluating the condensing performance of the optical device that is the device to be evaluated. An astigmatic difference measuring method for an optical device,
Obtaining astigmatic difference R (θ _n ) at one angle θ _n while rotating data acquired from the optical device with respect to a predetermined basic axis;
Using the angle θ _max when the astigmatic difference R (θ _n ) is maximum and the maximum astigmatic difference R (θ _max ) at that time, a vector coefficient R _{0 in the} same direction as the basic axis, Calculating a vector coefficient R _{45 in a} direction that makes an angle of 45 degrees with respect to the basic axis;
Calculating an astigmatism difference R (θ) at an arbitrary angle θ from the vector coefficient R ₀ and the vector coefficient R ₄₅ using a fitting method;
By measuring the reference optical device that is known in advance astigmatism in the condensing performance evaluation device, and calculates a correction coefficient alpha ₀ and the correction section beta ₀ of the vector coefficient R _0, the vector coefficient R ₄₅ Calculating a correction coefficient α ₄₅ and a correction intercept β ₄₅ of
Correcting the vector coefficient R ₀ using the correction coefficient α ₀ and the correction intercept β _0, and correcting the vector coefficient R ₄₅ using the correction coefficient α ₄₅ and the correction intercept β ₄₅ ; ,
By using the vector coefficient R ₀ and R ₄₅ after correction, astigmatism measuring method of an optical device comprising the steps of calculating, in that it consists of astigmatism of the optical device.   The optical device is an optical pickup device, and the light collecting performance evaluation device is a spot evaluation device, and the spot diameter obtained from the optical pickup device is calculated by the astigmatism measurement method according to claim 1 or 2. A spot diameter correction method, wherein correction is performed based on the astigmatic difference.   A spot evaluation apparatus that corrects a spot diameter by using the spot diameter correction method according to claim 3.