JP5095539B2 - Aberration measurement error correction method - Google Patents

Description

  The present invention relates to alignment of a test lens in aberration measurement in which coma aberration, spherical aberration, and the like of a lens used in various optical devices such as a digital camera, an optical sensor, and an optical pickup are obtained by transmission wavefront measurement using an interferometer. The present invention relates to an aberration measurement error correction method for correcting a measurement error caused by an error.

2. Description of the Related Art Conventionally, a technique for measuring coma aberration, spherical aberration, and the like of a test lens by transmission wavefront measurement using an interferometer has been widely used for performance inspection of the test lens.
In such transmitted wavefront measurement, it is necessary to install the lens to be measured with high accuracy with respect to the measurement optical axis of the interferometer, and methods for that purpose have also been proposed (see Patent Documents 1 and 2 below).

  The technique described in the following Patent Document 1 is proposed by the applicant of the present application, and by observing an optical mark based on the intensity distribution of reflected light of the measurement light beam from the surface of the test lens, The deviation between the optical axis and the optical axis of the reference spherical reflector (in this specification, such a reference spherical reflector is also treated as one of the null optical elements) is automatically adjusted.

  The method described in Patent Document 2 below determines the installation alignment of the test lens based on the Seidel aberration amount obtained by developing the transmitted wavefront aberration of the test lens obtained by the transmitted wavefront measurement using a Zernike polynomial. Automatic adjustment is made.

JP 2007-78593 A Japanese Patent No. 2951366

  In recent years, there is an increasing demand for aspherical lenses having a large numerical aperture (NA). In such a high NA aspherical lens, a minute aberration that has not been considered as a problem is regarded as a problem.

  Also, when measuring aberrations of high NA aspherical lenses, the measurement errors caused by the alignment errors of the aspherical lenses have a great adverse effect on the measurement results. There is a demand for high precision.

  However, the higher the accuracy of alignment adjustment, the longer the time required for the adjustment and the longer the measurement time. In addition, due to the problem of mechanical accuracy on the adjustment mechanism side such as an adjustment stage, it is expected that it will become more difficult in the future to perform alignment adjustment as requested as the required level of measurement accuracy increases.

  The present invention has been made in view of such circumstances, and corrects a measurement error caused by an alignment error of the test lens in the measurement of the aberration of the test lens based on a transmitted wavefront measurement using an interferometer. An object of the present invention is to provide an aberration measurement error correction method that can be used.

The aberration measurement error correction method according to the present invention performs transmission wavefront measurement on a test lens using an interferometer provided with a null optical element, and based on an interference fringe image obtained by the transmission wavefront measurement, the test lens A method of correcting a measurement error caused by an alignment error of the test lens in an aberration measurement for measuring a predetermined aberration of
A correspondence specifying step for obtaining a correspondence between the amount of occurrence of the alignment error and the amount of occurrence of the predetermined aberration by computer simulation;
An installation error actual measurement step for measuring an actual generation amount of the alignment error;
An aberration generation prediction amount calculation step for obtaining a generation prediction amount of the predetermined aberration predicted to be generated due to the actual generation amount based on the correspondence and the actual generation amount;
An error correction step of correcting the measurement error based on the predicted generation amount is performed in this order.

In the aberration measurement error correction method according to the present invention, the predetermined aberration is coma aberration,
The alignment error may be a tilt error of the test lens with respect to the measurement optical axis.

In this case, the test lens has a projecting surface installed so as to be perpendicular to the optical axis of the test lens,
The inclination of the protruding surface with respect to the measurement optical axis of the interferometer is measured, and the actual generation amount of the inclination error can be obtained based on the measurement result.

The predetermined aberration is spherical aberration,
The alignment error may be an installation position error of the lens to be measured with respect to the null optical element in the measurement optical axis direction.

  In this case, based on the interference fringe image obtained by the transmitted wavefront measurement with respect to the subject, the defocus amount of the subject lens is measured, and based on the measurement result, the actual amount of error of the installation position Can be obtained.

  In the present invention, the null optical element refers to a null mirror (reflecting surface is aspherical) having a reflecting surface capable of retroreflecting a transmitted wavefront from a test lens, a reference spherical reflecting mirror (reflecting surface is spherical), etc. And a transmission type optical element such as a null lens for converting a transmission wavefront from a lens to be examined into a predetermined wavefront such as a spherical wave.

  According to the aberration measurement error correction method of the present invention, the following effects can be obtained by providing the above-described configuration.

  That is, the correspondence between the amount of occurrence of the alignment error of the lens to be examined and the amount of occurrence of the predetermined aberration is obtained in advance by computer simulation, so that the predetermined amount of occurrence of the alignment error (determined by measurement) is determined from the predetermined amount. The predicted amount of occurrence of aberration can be calculated, and the measurement error of aberration can be corrected based on the predetermined amount of predicted occurrence of aberration.

  Therefore, even if an alignment error occurs when the lens to be tested is installed in the interferometer, the measurement can be performed as it is, so that the time required for alignment adjustment can be shortened, and transmission wavefront measurement can be performed efficiently. It becomes possible to carry out. In addition, since an aberration measurement error caused by the alignment error can be corrected after the measurement, a highly accurate measurement result can be obtained.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a schematic configuration diagram of a lightwave interference measurement apparatus used for an aberration measurement error correction method according to an embodiment of the present invention, and FIG. 2 is a block diagram showing a schematic configuration of an analysis control apparatus shown in FIG. 3 is a schematic diagram showing the shape of the lens to be examined ((A) is a front view, (B) is a plan view), and FIG. 4 is a schematic diagram showing the shape of a protruding surface pedestal of the lens mounting jig. It is.

  The optical interference measuring apparatus shown in FIG. 1 constitutes a Fizeau interferometer, and includes an interferometer main body 20 and a subject positioning unit 30. The interferometer body 20 includes a light source 21 having a long coherence distance, such as a laser light source, a beam diameter expanding lens 22, a beam splitter 23, a collimator lens 24, an imaging lens 25, and an imaging means 26 having a light detection surface. ing. The interferometer body 20 includes an analysis control device 27 composed of a computer and the like for performing image processing, various arithmetic processes, and drive control of various adjustment units on the image captured by the imaging unit 26, an interference fringe image, and the like. Is provided, and an input device 29 for performing various inputs to the analysis control device 27. The reference plate 4 shown in FIG. 1 is usually included in the interferometer main body 20, but will be described in the subject positioning unit 30 for convenience of explanation in this specification.

  On the other hand, the object positioning unit 30 has a reference spherical surface, a test lens 1, a correction plate 6, and a reference spherical surface in the direction of travel of the measurement light beam from the interferometer body 20 (upward in FIG. 1). The reference spherical reflector 7 as the null optical element and the shutter device 8 are supported in this order, and the alignment of each part is adjusted.

  That is, the reference plate 4 is supported by the manual biaxial tilt stage 11 and rotated around the X axis (axis extending in the left-right direction in FIG. 1) and the Y axis (axis extending perpendicular to the paper surface in FIG. 1). The angle (tilt) is adjusted manually. Although not shown, the reference plate 4 is provided with a fringe scan adapter for finely moving the reference plate 4 in the optical axis direction when performing the fringe scan measurement.

  The lens 1 to be tested is supported by an electric biaxial tilt stage 13 via a lens mounting jig 5 and the rotation angle (tilt) about the X and Y axes is automatically adjusted. Yes. Further, the correction plate 6, the reference spherical reflecting mirror 7, and the shutter device 8 are sequentially supported by a manual biaxial tilt stage 12, an electric Y axis stage 14, an electric X axis stage 15, and an electric Z axis stage 16.

  The correction plate 6 is a transparent plate (usually a glass plate) provided so as to correspond to the protective layer of the optical recording medium, and is arranged for the purpose of aligning the actual recording / reproducing state and optical conditions of the optical recording medium. The rotation angle (tilt) about the X and Y axes is manually adjusted by the manual biaxial tilt stage 11 so as to be parallel to the reference plane of the reference plate 4. It is like that. On the other hand, the reference spherical reflecting mirror 7 is moved in each direction of the Y axis, the X axis, and the Z axis (axis extending in the vertical direction in FIG. 1) by the electric Y axis stage 14, the electric X axis stage 15 and the electric Z axis stage 16. The movement can be adjusted in parallel, and the alignment is automatically adjusted accordingly.

  Further, although not shown, this optical interference measuring apparatus includes a sample stage moving mechanism for automatically performing loading / unloading operations of the lens 1 to be examined. This sample stage moving mechanism is the same as that described in the above-mentioned Patent Document 1 and Japanese Patent Application No. 2006-223668 (see Japanese Patent Application Laid-Open No. 2008-46051, hereinafter referred to as “Prior Application 1”). The detailed description thereof is omitted.

  In this embodiment, the test lens 1 is mounted as an optical pickup lens on an apparatus for recording / reproducing an optical recording medium such as CD, DVD (including AOD), BD (Blu-ray Disc), etc. As shown, it consists of a lens part 2 and a flange part 3. The lens unit 2 is a biconvex lens having an aspherical shape or a spherical shape, and a surface having a strong curvature is arranged on the light source side of the optical recording medium recording / reproducing apparatus. Further, the flange lower surface 3A disposed on the light source side of the flange portion 3 constitutes an overhanging surface and is set to be perpendicular to the optical axis of the lens 1 to be measured with high accuracy.

  The shape of the lens 1 to be tested and its application are not limited to those of the above-described embodiment, and for example, a diffractive optical surface can be provided. In the present embodiment, it is assumed that the test lens 1 converts an incident plane wave into a spherical wave and outputs the spherical wave. However, when an aspheric wave is output from the test lens 1, Instead of the reference spherical reflecting mirror 7, a null optical element (null mirror) having an aspheric reflecting surface is arranged.

  When viewed from the interferometer main body 20, the shape of the projecting surface cradle of the lens mounting jig 5 is such that, as shown in FIG. 4, the transmitted wavefront measurement of the lens portion 2 of the lens 1 to be tested is performed at the center thereof. The center window 5A, four overhanging surface reflection light windows 5B located outside the center window 5A, and four correction plate reflection light windows 5C located outside the overhanging surface reflection light window 5B. A window portion and four projecting surface receiving regions 5D projecting into corresponding regions of the flange lower surface 3A are provided.

  As shown in FIG. 2, the analysis control device 27 includes a storage unit such as a CPU and a hard disk mounted in the analysis control device 27 and a tilt error calculation unit configured by a program stored in the storage unit. 31, an aberration error generation prediction amount calculation unit 32, an installation position error calculation unit 33, an aberration analysis unit 34, a correspondence relationship storage unit 35, and an aberration measurement error correction unit 36.

  The inclination error calculation unit 31 is based on the interference fringe image of the flange lower surface 3A of the lens 1 to be tested (details will be described later), and the inclination of the flange lower surface 3A with respect to the measurement optical axis L (see FIG. 1) of the interferometer body 20. And the actual generation amount of the tilt error of the lens 1 to be examined is obtained based on the measurement result.

  The aberration analysis unit 34 is configured to perform predetermined aberrations (spherical aberration and coma aberration) of the test lens 1 based on an interference fringe image obtained by transmission wavefront measurement with respect to the lens unit 2 of the test lens 1 (described in detail later). ) (Including a measurement error due to the alignment error of the lens 1) and a defocus amount (also referred to as focal shift or power) of the lens 1 to be measured.

  The installation position error calculation unit 33 calculates an actual generation amount of the installation position error in the measurement optical axis L direction of the lens 1 to be measured with respect to the reference spherical reflecting mirror 7 based on the defocus amount obtained by the aberration analysis unit 34. It is what you want.

  The correspondence relationship storage unit 35 determines the alignment error of the lens 1 to be measured (the error of the installation position of the lens 1 to be measured in the direction of the measurement optical axis L relative to the reference spherical reflecting mirror 7 and the measurement optical axis L) obtained by computer simulation. The correspondence relationship established between the amount of occurrence of tilt error of the lens 1 to be examined and the amount of occurrence of predetermined aberrations (spherical aberration and coma aberration) is stored.

  The aberration error generation prediction amount calculation unit 32 stores the actual generation amount of the tilt error of the test lens 1 with respect to the measurement optical axis L, which is obtained by the tilt error calculation unit 31, and is stored in the correspondence storage unit 35. Based on the correspondence between the amount of tilt error generated by the test lens 1 relative to the measurement optical axis L and the amount of coma aberration generated (hereinafter referred to as “first correspondence”), it is caused by the tilt error of the test lens 1. And the actual generation amount of the installation position error in the measurement optical axis L direction of the lens 1 to be measured with respect to the reference spherical reflector 7, which is calculated by the installation position error calculation unit 33. The correspondence relationship between the amount of error in the installation position of the lens 1 to be measured in the direction of the measurement optical axis L with respect to the reference spherical reflector 7 and the amount of spherical aberration (hereinafter referred to as “second”). Is called "correspondence of Based on bets, and requests generation predictor of the spherical aberration due to the error of the installation position of the lens 1.

  Hereinafter, an implementation procedure of the aberration measurement error correction method according to the embodiment of the present invention will be described. The aberration measurement error correction method of the present embodiment is applied when the transmitted wavefront measurement of the test lens 1 is performed using the above-described optical interference measuring apparatus.

  When the transmitted wavefront measurement is performed, alignment adjustment of the reference plate 4, the correction plate 6, the reference spherical reflecting mirror 7, and the test lens 1 is performed. For these alignment adjustments, for example, the technique disclosed in the above-mentioned prior application specification 1 can be applied, but detailed description thereof is omitted here.

  The aberration measurement error correction method of the present embodiment is the alignment error of the test lens 1 that has not been adjusted by such alignment adjustment (the tilt error of the test lens 1 with respect to the measurement optical axis L and the target spherical reflector 7). The measurement error relating to the spherical aberration and the coma aberration of the lens 1 to be detected, which is caused by the error of the installation position of the test lens 1 in the measurement optical axis L direction), is corrected according to the following procedure.

  <1> First, by computer simulation, the first correspondence relationship (correspondence relationship between the amount of tilt error and the amount of coma aberration with respect to the measurement optical axis L) and the second correspondence relationship are described. (Corresponding relationship between the amount of error in the installation position of the lens 1 to be measured with respect to the reference spherical reflecting mirror 7 in the measurement optical axis L direction and the amount of spherical aberration) is determined (corresponding relationship specifying step).

  FIGS. 5 and 6 show examples of the first and second correspondences, respectively. FIG. 5 is a diagram showing an example of a correspondence relationship between the amount of tilt error (tilt angle) of the lens 1 to be measured with respect to the measurement optical axis L and the amount of Seidel third-order coma aberration. FIG. It is a figure which shows an example of the correspondence of the amount of generation | occurrence | production (measurement optical-axis direction position) of the installation position of the to-be-tested lens 1 in the axis | shaft L direction, and the generation amount of Seidel's third-order spherical aberration. Note that the tilt angle in FIG. 5 indicates the tilt angle in the maximum tilt direction of the test lens 1, and the position in the measurement optical axis direction in FIG. 6 indicates the measurement optical axis L of the test lens 1 with respect to the reference spherical reflector 7. The separation distance (the direction away from the reference spherical reflector 7) of the test lens 1 from the proper installation position in the direction (position where the focal position of the test lens 1 matches the center of the reference spherical reflector 7) is shown in FIG. The graph shows the negative direction on the horizontal axis).

  The first and second correspondence relationships obtained by computer simulation are stored in the correspondence relationship storage unit 35. The computer simulation may be configured to be executed by the analysis control device 27, but may be performed using another computer simulation system. When a plurality of types of lenses with different designs are to be measured, computer simulation is performed for each type, and the corresponding relationship is stored in the corresponding relationship storage unit 35.

  <2> Subsequently, using the optical interference measuring apparatus shown in FIG. 1, the actual amount of tilt error of the test lens 1 with respect to the measurement optical axis L and the measurement optical axis of the test lens 1 with respect to the reference spherical reflector 7 The actual amount of installation position error in the L direction is measured (installation error actual measurement step).

  First, the actual amount of tilt error (hereinafter referred to as “tilt error value”) of the test lens 1 with respect to the measurement optical axis L is measured by the following procedure.

  (A) The optical path between the correction plate 6 and the reference spherical reflecting mirror 7 and the lens 1 to be examined is closed by the shutter device 8 shown in FIG. The shutter device 8 is for preventing the measurement light beam from entering the correction plate 6 and the reference spherical reflecting mirror 7, and preventing the reflected light from entering the image pickup means 26. A drive unit 8B that rotates the plate 8A in a plane orthogonal to the optical axis of the reference spherical reflecting mirror 7, and opens and closes the optical path of the measurement light beam by inserting and removing the light shielding plate 8A in and out of the optical path of the measurement light beam. Is configured to do.

  (B) While maintaining the state in which the optical path is closed by the shutter device 8, the measurement lens 1 is irradiated with the measurement light beam, and the above-described interference fringe image of the flange lower surface 3A of the test lens 1, that is, the target An interference fringe image (hereinafter referred to as an “interference fringe image of the protruding surface”) carrying the tilt information of the flange lower surface 3A, which is formed by the interference between the reflected light from the flange lower surface 3A of the test lens 1 and the reference light, is obtained. In addition, when obtaining the interference fringe image of the overhanging surface, a masking process is appropriately performed in order to shield an image related to a region other than the flange lower surface 3A (see the above-mentioned prior application specification 1).

  (C) Based on the obtained interference fringe image of the overhanging surface, the inclination angle of the flange lower surface 3A with respect to the measurement optical axis L is calculated, and this is obtained as the inclination error value. Note that this processing is executed in the inclination error calculation unit 31 shown in FIG.

  Next, the actual generation amount of the installation position error in the measurement optical axis L direction of the test lens 1 with respect to the reference spherical reflecting mirror 7 (hereinafter referred to as “installation position error value”) is measured by the following procedure.

  (A ′) The shutter device 8 opens the optical path between the correction plate 6 and the reference spherical reflecting mirror 7 and the lens 1 to be examined.

  (B ′) In this state where the optical path is open, the interference fringe image obtained by the transmission wavefront measurement with respect to the lens portion 2 of the lens 1 to be tested, that is, the reference spherical reflector that is transmitted through the lens portion 2 of the lens 1 to be tested. 7 is an interference fringe image (hereinafter referred to as “interference fringe image of the lens unit”) formed by the interference between the light retroreflected by the lens 7 and the light transmitted through the lens unit 2 again and the reference light and carrying the transmitted wavefront information of the lens unit 2. Called). In addition, when obtaining the interference fringe image of the lens unit, a masking process is appropriately performed in order to block an image related to a region other than the lens unit 2 (see the above-mentioned prior application specification 1).

  (C ′) Based on the obtained interference fringe image of the lens portion, the aberration analysis of the transmitted wavefront of the test lens 1 is performed, and the obtained wavefront aberration is developed by the Zernike polynomial, thereby defocusing the test lens 1 Find the amount. At this time, the third-order spherical aberration and the third-order coma aberration of the test lens 1 are also obtained based on the interference fringe image of the lens portion. Note that this processing is executed in the aberration analyzer 34 shown in FIG.

  (D ′) The installation position error value is calculated based on the obtained defocus amount. This process is executed by the installation position error calculator 33 shown in FIG.

  <3> Next, based on the above-described first and second correspondence relationships stored in the correspondence relationship storage unit 35, the obtained tilt error value, and the installation position error value, it is caused by these error values. The predicted generation amount of the third-order coma aberration and the third-order spherical aberration of the test lens 1 that is predicted to occur is calculated (aberration generation predicted amount calculation step). This process is executed by the aberration error generation prediction amount calculation unit 32 shown in FIG.

  Specifically, based on the first correspondence relationship shown in FIG. 5 and the tilt error value calculated by the tilt error calculation unit 31, the predicted generation amount of the third-order coma aberration of the lens 1 (hereinafter “coma aberration”). The third order of the lens 1 to be tested is calculated based on the second correspondence shown in FIG. 6 and the installation position error value calculated by the installation position error calculation unit 33. The error generation prediction amount of the spherical aberration (hereinafter referred to as “spherical aberration error generation prediction amount”) is obtained.

  <4> Next, the third-order coma aberration and the third-order spherical aberration of the test lens 1 obtained by the aberration analysis unit 34 based on the error occurrence prediction amount of the coma aberration and the error generation prediction amount of the spherical aberration. Each measurement error is corrected (error correction step). This process is executed in the aberration measurement error correction unit 36 shown in FIG.

  Specifically, the corrected coma measurement value is obtained by subtracting the coma aberration error occurrence prediction amount from the coma measurement value obtained by the aberration analysis unit 34, and is obtained by the aberration analysis unit 34. The corrected spherical aberration measurement value is obtained by subtracting the spherical aberration error generation prediction amount from the obtained spherical aberration measurement value.

  As mentioned above, although one Embodiment of this invention was described, this invention is not limited to this Embodiment, The thing of a various aspect can be made into Embodiment.

  For example, the present invention can be applied to transmitted wavefront measurement using a transmission-type null optical element (null lens) as disclosed in Japanese Patent Application Laid-Open No. 2008-89356.

  In the above embodiment, the optical interference measuring apparatus is a Fizeau interferometer. However, the present invention is also applicable to transmitted wavefront measurement using another type of interferometer such as a Michelson type. It is possible.

1 is a schematic diagram of an optical interference measuring apparatus used in an aberration measurement error correction method according to an embodiment. The block diagram which shows schematic structure of the analysis control apparatus shown in FIG. Schematic diagram showing the shape of the test lens ((A) is a front view, (B) is a plan view) Schematic showing the shape of the overhang surface cradle of the lens mounting jig The figure which shows an example of the correspondence of the inclination angle of a test lens, and a coma aberration The figure which shows an example of the correspondence of the measurement optical axis direction position of a test lens, and spherical aberration

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Test lens 2 Lens part 3 Flange part 3A Flange lower surface (projection surface)
4 Reference plate 5 Lens mounting jig 6 Correction plate 7 Reference spherical reflector (null optical element)
DESCRIPTION OF SYMBOLS 8 Shutter apparatus 8A Light-shielding plate 8B Drive part 5A Center window 5B Overhanging surface reflected light window 5C Correction plate reflected light window 5D Overhang surface receiving area 11 Manual biaxial tilt stage (for reference plate adjustment)
12 Manual 2-axis tilt stage (for correction plate adjustment)
DESCRIPTION OF SYMBOLS 13 Electric 2 axis tilt stage 14 Electric Y axis stage 15 Electric X axis stage 16 Electric Z axis stage 20 Interferometer body part 21 Light source 22 Beam diameter expansion lens 23 Beam splitter 24 Collimator lens 25 Imaging lens 26 Imaging means 27 Imaging control 27 Device 28 Monitor device 29 Input device 30 Subject positioning unit 31 Inclination error calculation unit 32 Aberration error generation prediction amount calculation unit 33 Installation position error calculation unit 34 Aberration analysis unit 35 Corresponding relationship storage unit 36 Aberration measurement error correction unit L Measurement optical axis

Claims (5)

In an aberration measurement in which a transmission wavefront measurement is performed on a test lens using an interferometer equipped with a null optical element, and a predetermined aberration of the test lens is measured based on an interference fringe image obtained by the transmission wavefront measurement. A method for correcting a measurement error caused by an alignment error of the test lens,
A correspondence specifying step for obtaining a correspondence between the amount of occurrence of the alignment error and the amount of occurrence of the predetermined aberration by computer simulation;
An installation error actual measurement step for measuring an actual generation amount of the alignment error;
An aberration generation prediction amount calculation step for obtaining a generation prediction amount of the predetermined aberration predicted to be generated due to the actual generation amount based on the correspondence and the actual generation amount;
An aberration measurement error correction method comprising: performing an error correction step of correcting the measurement error based on the predicted generation amount in this order. The predetermined aberration is coma,
The aberration measurement error correction method according to claim 1, wherein the alignment error is a tilt error of the lens to be measured with respect to the measurement optical axis. The test lens has a protruding surface installed so as to be perpendicular to the optical axis of the test lens,
3. The aberration measurement error correction method according to claim 2, wherein an inclination of the protruding surface with respect to a measurement optical axis of the interferometer is measured, and an actual generation amount of the inclination error is obtained based on the measurement result. The predetermined aberration is spherical aberration;
The aberration measurement error correction method according to claim 1, wherein the alignment error is an error in an installation position of the test lens in the measurement optical axis direction with respect to the null optical element. Based on the interference fringe image obtained by the transmitted wavefront measurement with respect to the subject, measure the defocus amount of the subject lens, and obtain the actual generation amount of the installation position error based on the measurement result. The aberration measurement error correction method according to claim 4.

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