JP2005083861A - Measurement method and system of optical pickup, and its regulating apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To accurately detect aberration of optical pickup or lens, without being affected by measurement errors caused by an optical interferometer detecting aberration. <P>SOLUTION: The measurement method has processes of: detecting the inclination quantity of the optical pickup from the light emitted from a light source and correcting the inclination; diffracting the light emitted from the lens, interfering the two diffraction lights with different orders and obtaining a sharing interference image; changing the phase of the diffraction lights; obtaining the phase of light intensity change at a plurality of measuring points on a specific line in the sharing interference image; approximating the phase ϕ by the function of the measurement position X, when the measurement position is X and the above phase is ϕ, and evaluating the aberration of the lens by the coefficient value of the function; rotating the optical pickup around a light axis of the light emitted from the lens; and detecting the measurement error quantity of the interference measurement and the aberration quantity such that the lens has, by redetecting the aberrations of the lens by the interference method at the rotated position. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an optical pickup that forms an optical spot by forming an image of light in an optical lens for recording and reproducing information on an optical disk type information recording apparatus (for example, a CD or a DVD) or a digital still camera (DSC). And a method and an apparatus for detecting the characteristics of a lens.

  In order to read information from an optical disk type high-density information storage medium and store information in the high-density information storage medium, an optical system capable of accurately irradiating light emitted from a light source to a target location is required. . Therefore, in particular, the objective lens of the optical pickup is not only required to have strict optical characteristics, but must be accurately fixed at a target location. 2. Description of the Related Art Conventionally, a measurement device using optical interference has been used as an optical property detection device for detecting aberration that is an optical property of an optical pickup or an objective lens in the optical pickup and adjusting its position. Among such optical interferometers, a diffraction interference method as shown in FIG. 6 has been proposed and implemented (see Patent Document 1). This diffraction interference method will be briefly described below with reference to FIG.

  In FIG. 6, the light emitted from the objective lens 102 in the optical pickup 101 is incident on the diffraction grating 103 to generate zero-order light and ± first-order light. Then, the 0th order light and the −1st order light are overlapped to generate interference fringes. This pattern is imaged on the CCD 105 by the imaging lens 105. The CCD 106 is connected to a signal processing and display device 107. On 106, an interference pattern as shown in FIG. 7 is obtained. Aberrations are detected by analyzing interference fringes formed in a region where 0th order light and + 1st order light and 0th order light and −1st order light overlap.

  FIG. 8 shows the types of aberration and the interference fringes generated thereby.

  8A is a fringe pattern due to defocus, FIG. 8B and FIG. 8C are fringe patterns due to coma, FIG. 8D is a fringe pattern due to astigmatism, and FIG. (E) shows a fringe pattern due to spherical aberration, and FIG. (F) shows a fringe pattern when the aberration is zero. Zero aberration is uniform in the interference region.

  In general, aberrations occur in a composite manner, resulting in a fringe pattern in which FIGS. 8A to 8F are mixed. Each aberration is extracted based on this pattern. A phase shift method is used for aberration extraction. In the phase shift method, the diffraction grating 103 is moved minutely in the direction of the arrow by the diffraction grating moving mechanism 108, thereby shifting the phases of the two wavefronts to interfere with each other, changing the fringe pattern, That is, the aberration is obtained by analyzing the phase distribution of the intensity change. Aberration is detected by analyzing the distribution of how the fringe pattern changes, that is, the phase distribution of the light intensity change, by the signal processor, but without using the phase data of the entire interference area, The phase data obtained by representing the position of a plurality of points on the minute as A, the phase at that position as φ, and representing φ as an approximate function of A is used. The optical system is adjusted based on the aberration detection result.

As described above, in the prior art, the optical characteristics of the objective lens are detected, evaluated and adjusted using optical interference.
JP 2000-329648 A

  However, the conventional optical characteristic detection method as described above has the following problems.

  In the conventional method, the light emitted from the objective lens of the optical pickup generates 0th order light and ± 1st order light by the diffraction grating, and the aberration is detected by analyzing the interference image of these lights. However, in this method, aberration measurement deviation occurs due to Fresnel loss that occurs when light enters the diffraction grating in the objective lens or the optical interferometer, and the detected value may have an error. Fresnel loss occurs in transmitted light and reflected light when light is incident obliquely on a transparent dielectric surface. As a result, the polarization characteristic of the light emitted from the diffraction grating changes, and as a result, a phase difference is generated in the intensity change of the interference fringes, and it is measured as if there is an aberration. When a high NA objective lens with a large numerical aperture (NA) of NA 0.8 or higher is used, the incident angle to the diffraction grating increases, and the aberration detection error increases.

  In particular, in recent years, information recording devices such as DVDs have become multifunctional and high-density recording, objective lenses have high NA, and high-precision detection of optical characteristics is required. It had the problem of having a big impact on

  SUMMARY OF THE INVENTION An object of the present invention is to provide a method and apparatus for measuring aberration of an optical pickup with high accuracy by detecting aberration measurement errors.

  In order to solve the above problems, the optical pickup measuring method of the present invention is a vector quantity having a magnitude and a direction in which the aberration as an optical characteristic is a magnitude and direction. Aberration is detected. At this time, the locus of aberration values draws a circle. The radius is the magnitude of the aberration of the optical component, and the amount of deviation from the origin of the rotation center position becomes an error in the measured value. An aberration measurement error is detected using this characteristic.

  Thereby, it is possible to detect the aberration of the optical component with high accuracy.

  As described above, according to the optical pickup measuring method of the present invention, the aberration of the optical pickup can be measured with high accuracy by detecting the aberration measurement error.

  Hereinafter, embodiments of the present invention will be described with reference to FIGS. 1 to 5.

  FIG. 1 shows an optical pickup measuring method and apparatus according to an embodiment of the present invention. In FIG. 1, the same components as those in FIG.

  In FIG. 1, reference numeral 1 denotes a mirror attached to a shaft or the like that serves as a position reference for the optical pickup. A θZ stage 2 rotates the optical component around the Z axis. Reference numeral 3 denotes a θX stage for adjusting the inclination of the optical pickup about the X axis, reference numeral 4 denotes a θY stage for adjusting the inclination of the optical pickup about the Y axis, and reference numeral 5 denotes a return light applied to the mirror 1. For example, a light source such as a laser for detecting the tilt of the optical pickup. Further, 6 is a half mirror that branches the light reflected by the mirror 1, 7 is a lens that collects the light branched by the half mirror, and 8 is an image pickup such as a CCD that captures the collected light. It is an element. Reference numeral 9 denotes a monitor that captures an image from the image sensor. 1, 5, 6, 7 and 8 are optical lever optical systems for detecting the inclination of the optical pickup.

  A method for detecting an aberration measurement error will be described below.

  First, the mirror 1 is installed on, for example, a shaft that serves as a position reference for the optical pickup. As a result, the mirror 1 moves with the optical pickup. The light emitted from the light source 5 is reflected by the mirror 1, and the reflected light is branched by the half mirror 6 and collected by the lens 7. The image sensor 8 is installed at the light condensing point to detect the condensing position. When the optical pickup is tilted in the θX direction, the condensing position is shifted in the X direction on the monitor 9.

  Similarly, the focusing position is shifted in the Y direction at θY. The inclination of the optical pickup is detected from the detected light position, and the position of the optical pickup in the θX and θY directions is adjusted by the stages 3 and 4 to a state where there is no inclination. The optical pickup is caused to emit light in a state where the inclination of the optical pickup is excluded. The light emitted from the optical pickup enters the optical interferometer and detects aberration which is an optical characteristic of the optical pickup. The optical pickup is rotated around the Z axis by a predetermined amount (for example, 45 °, 90 °, 135 °, etc. every 45 °) on the θZ stage. When the θZ stage 2 is rotated, the tilt generated by mechanical backlash or the like is again detected by the optical lever, and the tilt is removed using the θX and θY stages. As a result, the optical pickup can be measured in a fixed posture with respect to the optical interferometer.

  Again, the outgoing light from the optical pickup is measured with an optical interferometer, and the aberration of the optical pickup is detected. When this aberration is detected by the interferometer of the optical pickup and the rotation around the θZ axis is repeated, and the change in aberration when the optical pickup is rotated 360 ° is plotted on a graph, it rotates around a point as shown in FIG. To do.

  This principle is shown as follows. Wavefront aberration, which is an optical characteristic of a lens, is generally expressed using a Zernike polynomial. In this Zernike polynomial, the third-order aberration treated as a basic aberration is expressed by the following equation.

ρ (3ρ ² −2) cos (θ) (1)
ρ (3ρ ² −2) sin (θ) (2)
ρ ² cos (2θ) ..... Equation (3)
ρ ² sin (2θ) ..... Equation (4)
6ρ ⁴ -6ρ ² +1 Equation (5)
The above equation is a function on the unit circle (radius is 1) and has polar coordinate arguments (ρ, θ). Here, θ is the rotational direction in the XY plane of the aperture of the objective lens as shown in FIG. Equation (1) is coma aberration in the X direction component, Equation (2) is coma aberration in the Y direction component, Equation (3) is astigmatism in the X direction component, Equation (4) is astigmatism in the Y direction component, Expression (5) is a mathematical expression indicating spherical aberration.

  As shown in equations (1) and (2), coma is a vector amount having the magnitude and direction of aberration, and when the lens rotates θ, the amount of aberration also rotates θ. As shown in the equations (3) and (4), astigmatism is also a vector amount having the magnitude and direction of the aberration. When the lens rotates θ, the amount of aberration rotates 2θ. That is, the aberration amount is rotated by 360 ° by rotating the lens by 180 °. Further, as shown in the equation (5), the spherical aberration has only the magnitude of the aberration and has no direction. That is, the aberration does not depend on the rotation direction of the lens. When the lens is thus rotated in the circumferential direction, the astigmatism and coma aberration, which are measured values, are also rotated in the XY plane. The radius is the aberration amount (size) of the lens, and the rotation angle is determined by the rotation angle of the lens.

  At this time, the center of rotation is originally the origin of the coordinate system, but when an error occurs in the measurement value due to the high NA objective lens and the optical system in the optical interferometer, the center of rotation is not the origin as shown in FIG. . However, the generated error is an error caused by the optical system of the measuring device, and is not an aberration inherent in the optical pickup as the object to be detected. Therefore, the aberration value of the lens rotates as the lens rotates. By utilizing this, it is possible to extract only the aberrations inherent to the lens.

  At this time, the amount of deviation from the origin of the rotation center of the circle drawn by the aberration value is the error amount, and the rotation radius is the aberration amount of the optical pickup. Therefore, when the position of the lens is adjusted when the rotation center of the circle drawn by the aberration value is the origin (aberration = 0) in the measurement including an error, the adjustment is made so that the aberration value becomes this rotation center. For example, the aberration is adjusted to zero. The amount of error can be detected by rotating the optical pickup in this way. However, in practice, it is not necessary to rotate 360 °, and measurement at a minimum of two positions, for example, coma aberration as shown in FIG. 5, measurement at the measurement start position and two points rotated 180 ° from that position, astigmatism Then, if aberration is detected at two points rotated by 90 ° from the measurement at the measurement start position, the aberration amount and the error amount can be detected because the two diagonal aberrations are detected. .

If the aberration component measured at the measurement start position at this time is (X0, Y0) and the aberration component measured at the diagonal position is (X1, Y1), the measurement error component (Xerror, Yerror) is ,
Xerror = (X0 + X1) / 2
Yerror = (Y0 + Y1) / 2
The aberration amount Abe excluding the error is: Abe = √ {(X0−Xerror) ² + (Y0−Yerror) ² }
It becomes.

  As described above, according to the embodiment of the present invention, when measuring the aberration which is the optical characteristic of the optical pickup, the rotation of the circle drawn by the aberration value when the optical pickup aberration measurement and the rotation direction shift are performed. By obtaining the radius, high-accuracy measurement can be performed without errors. Further, when adjusting the position of the lens of the optical pickup or the like, it is possible to adjust with high accuracy by adjusting to the rotation center of the circle drawn by the aberration value.

  In the present embodiment, the object to be detected is described as an optical pickup. However, it goes without saying that a single lens may be used. In this embodiment, an interferometer that generates an error when measuring aberration is a diffraction interferometer. However, other interferometers such as a Mach-Zehnder interferometer and a Fizeau interferometer can also provide suitable results. It is done.

  The optical pickup measuring method and apparatus of the present invention and the adjusting device thereof are capable of high-accuracy measurement without errors by obtaining the rotational radius of a circle drawn by an aberration value when a lens or the like is moved in the rotational direction. It can be applied to optical characteristic inspection and position adjustment applications such as optical pickups and lenses mounted on DVDs.

Device configuration diagram of an embodiment of the present invention The figure which shows the change of the aberration with respect to rotation of the lens which concerns on embodiment of this invention. The figure which shows the relationship between the lens which concerns on embodiment of this invention, and the coordinate system of an aberration The figure which shows the relationship between the error which concerns on embodiment of this invention, a rotation center, and an aberration value The figure which shows calculation of an error amount from the two measurement points which concern on embodiment of this invention Schematic diagram of conventional diffraction interference method Diagram showing interference pattern Diagram showing interference fringes caused by each aberration

Explanation of symbols

1 mirror 2 θZ stage 3 θX stage 4 θY stage 5 light source 6 half mirror 7 lens 8 image sensor 9 monitor 101 optical pickup 102 objective lens 103 diffraction grating 104 detection lens 105 imaging lens 106 CCD
107 display device 108 moving mechanism

Claims (3)

(A) detecting a tilt amount of the optical pickup from the light emitted from the light source and correcting the tilt;
(B) diffracting the light emitted from the lens and interfering two diffracted lights of different orders to obtain a shearing interference image;
(C) changing the phase of the diffracted light;
(D) obtaining a phase of a light intensity change at a plurality of measurement points on a specific line segment in the sharing interference image;
(E) a step of approximating φ of the phase with a function of the measurement position X when the measurement point position is X and the phase is φ, and evaluating the aberration of the lens with a coefficient value of the function;
(F) rotating the optical pickup around the optical axis of the light emitted from the lens;
(G) An optical pickup measuring method comprising: detecting a lens measurement error amount and a lens aberration amount by detecting the lens aberration again by the interference method at the rotated position. . (A) means for detecting the amount of inclination of the optical pickup from the light emitted from the light source and correcting the inclination;
(B) means for diffracting the light emitted from the lens and interfering two diffracted lights of different orders to obtain a sharing interference image;
(C) means for changing the phase of the diffracted light;
(D) means for obtaining a phase of a light intensity change at a plurality of measuring points on a specific line segment in the sharing interference image;
(E) When the measurement point position is X and the phase is φ, the phase φ is approximated by a function of the measurement position X, and the lens aberration is evaluated by a coefficient value of the function;
(F) means for rotating the optical pickup around the optical axis of the light emitted from the lens;
(G) An optical pickup measuring apparatus comprising: a measurement error amount of interference measurement and a means for detecting the aberration amount of the lens by detecting the aberration of the lens again by the interference method at the rotated position. . (A) means for detecting the amount of inclination of the optical pickup by the light emitted from the light source and correcting the inclination;
(B) means for diffracting a plurality of lights emitted from the lens and interfering two diffracted lights of different orders to obtain a sharing interference image;
(C) means for changing the phase of the diffracted light;
(D) means for obtaining the phase of the light intensity change at a plurality of measurement points on the specific line segment in the sharing interference image;
(E) When the measurement point position is X and the phase is φ, the phase φ is approximated by a function of the measurement position X, and the lens aberration is evaluated by a coefficient value of the function;
(F) rotating the optical pickup around the optical axis of the light emitted from the lens;
(G) An optical pickup adjusting apparatus comprising: a means for detecting a measurement error amount of interference measurement and an aberration amount of the lens by detecting the aberration of the lens again by the interference method at the rotated position. .

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