WO2009066599A1

WO2009066599A1 - Aberration measuring method and its device

Info

Publication number: WO2009066599A1
Application number: PCT/JP2008/070626
Authority: WO
Inventors: Kenji Amaya
Original assignee: Tokyo Institute Of Technology
Priority date: 2007-11-21
Filing date: 2008-11-06
Publication date: 2009-05-28
Also published as: JPWO2009066599A1; TW200935414A

Abstract

There is provided an aberration measuring method for evaluating the aberration of a light spot image detected by a photodetector and the light spot image, with an inexpensive instrument and at a high speed. In the method, based on a model observation signal and an observation signal acquired from a scan output signal of the photodetector receiving the light spot image, the aberration of an optical system for forming the light spot image is analyzed from data at at least two locations.

Description

Aberration measurement method and apparatus therefor

The present invention relates to an aberration measuring method for measuring an aberration of the optical system from a spot image detected by a photo detector, such as a photo detector or a CCD, in an optical pickup of an optical disk such as a CD or DVD and an imaging optical system. And the device. Background art

In recent years, the demand for optical disks such as CD and D V D for conserving content is expected to expand as the network speeds up, the start of digital terrestrial broadcasting, and the capacity of hard disks increase. In order to respond to the expansion of demand for optical disks, it is essential to increase the capacity of optical disks, and it is necessary to improve the recording density of optical disks. For this purpose, it is important to improve the quality of the optical pick-up, and it is necessary to speed up and improve the quality evaluation of the optical pick-up.

There are two methods for evaluating the quality of the optical pick-up, an electrical evaluation method and an optical evaluation method. In the electrical evaluation method, the electric signal obtained by reproducing the reference disk is measured and analyzed, and the error rate of the electric signal and the amount of jitter are mainly evaluated. However, with this evaluation method, it can not be specified whether the cause of the error is in the electric circuit, in the irradiation optical system, in the recording medium, or in the reproduction optical system.

In addition, optical evaluation methods include a method of measuring the intensity distribution of spot images and a wavefront aberration measurement method using an interferometer. These methods have a more detailed It has the advantage that it can be priced and if there is a problem it is easy to identify the cause. However, measurement can not be performed in a short time, the measuring device is expensive, and there are problems with being vulnerable to external disturbances.

In order to solve the above problems, a method of measuring the phase distribution of light by a simple method without using an expensive measuring device is disclosed in Japanese Patent Application Publication No. It is disclosed in the document 1). In this optical phase distribution measurement method, the light to be measured is input to an optical system whose optical characteristics are known, the complex amplitude of the light to be measured is expanded by the Zernike series, and the nonlinear minimum for determining the Zernike coefficient 2 By solving the multiplication problem, it is possible to measure the optical phase distribution.

Patent Document 1 discloses a method of measuring the phase distribution of light by a simple method without using an expensive measuring device, but measures the aberration of the laser light detected at the position of the photodiode. There is no disclosure of a specific method to Therefore, there was a problem in measuring the aberration of the return light at the position of the photo detector practically.

The present invention has been made under the circumstances as described above, and it is an object of the present invention to analyze the aberration of the spot image of the laser beam received by the photodiode and evaluate the spot image of the laser beam at low cost. Method and apparatus for aberration measurement that can be performed with various devices, and the measurement time can be shortened. Disclosure of the invention

The present invention relates to an apparatus for measuring an aberration of a spot image of light received by the light detection element, and the above object of the present invention is to project the spot image formed by the optical system to be measured onto the light detection element. Means, first moving means for relatively moving the spot image on the light detection element in a direction perpendicular to the optical axis, and A second moving means for moving the position of the spot image projected onto the light detection element relative to the light detection element in the optical axis direction; and an aberration based on an output signal from the light detection element. This is achieved by providing an aberration analysis means to analyze.

The second moving means controls the spot image and the position of the light detection element to at least two positions, and the first moving means generates an observation signal of the light intensity distribution formed by the spot image. The aberration analysis means analyzes the aberration of the optical system for forming the spot image based on the observation signal and the model observation signal, or the second movement means performs the spot image and When the position of the light detection element is controlled to at least two positions, the light detection element is disposed before and after the imaging point of the spot image, or the aberration analysis means And determining an observation signal and a model observation signal of the spot image based on the output signal, and analyzing the aberration of the spot image based on the observation signal and the model observation signal. Or by determining the model observation signal by convolution integration of the intensity distribution of the spot image and the sensitivity distribution of the light receiving window of the light detecting element, or In an optical system having an optical source and the light detection element and being an optical pickup for recording and reproducing data on an optical disc, a correction plate inserted at a mounting position of the optical disc on the optical pickup, and the optical pickup The laser beam from the laser beam is incident through the correction plate, and the received laser beam is reflected to the optical pickup, and a spot image of the laser beam is projected onto the light detection element, and the first moving means and The spot image is scanned by the second moving means, and an observation signal and a model observation signal are obtained from the output signal from the light detection element to obtain the spot. By kicking set and aberration analysis unit for analyzing aberrations of the image it is more effectively achieved. Further, the present invention relates to an aberration measuring method, and the above object of the present invention is to project a spot image formed by an optical system to be measured on a light detecting element, and to position the spot image on the light detecting element. And scan in the vertical direction to obtain the observation signal and the model observation signal, and then the spot image is relatively moved to another position in the optical axis direction to obtain the observation signal and the model observation signal. The above is achieved by analyzing the aberration of the spot image based on the observation signal and the model observation signal.

By calculating the model observation signal based on the intensity distribution of the spot image and the sensitivity distribution of the light receiving window of the light detection element, or the complex amplitude of the spot image of the laser light is expanded by a finite series. The intensity distribution of the spot image is given by the square of the absolute value of the complex amplitude, the observation signal and the model observation signal are discretized, and the discretized observation signal and the discretized model observation signal are discretized. By solving the non-linear least squares problem based on the above, it is more effectively achieved by analyzing the aberration of the spot image of the laser beam and evaluating the spot image of the laser beam. Brief description of the drawings

FIG. 1 is a block diagram showing a first embodiment of an aberration measuring apparatus according to the present invention.

FIG. 2 is a flowchart showing an operation example of aberration analysis of a spot image in an aberration analysis unit.

FIG. 3 is a schematic view of a spot image in a focused image and a defocused image of each coefficient.

FIG. 4 is a block diagram showing a second embodiment of the aberration measuring apparatus according to the present invention.

FIG. 5 is a block diagram showing a third embodiment of the aberration measuring apparatus according to the present invention. FIG.

FIG. 6 is a block diagram showing a fourth embodiment in which an XY stage is attached to a photo detector.

FIG. 7 is a block diagram showing a fifth embodiment of the aberration measuring apparatus according to the present invention.

FIG. 8 is a block diagram showing a sixth embodiment of the aberration measuring apparatus according to the present invention.

FIG. 9 is a configuration diagram for explaining an optical system aberration of the optical pickup before the objective lens module is attached.

FIG. 10 is a configuration diagram for explaining an optical system aberration of the optical pickup before the objective lens module is attached.

FIG. 11 is a configuration diagram showing a configuration example of focus scanning means for measuring the optical system aberration of the optical pickup before the objective lens module is attached. FIG. 12 is a configuration diagram showing a configuration example of a focus scanning means for measuring an optical system aberration of the optical pickup before the objective lens module is attached. FIG. 13 is a diagram for explaining optical system adjustment of a small camera. FIG. 14 is a block diagram showing an example of a configuration in which the present invention is applied to the adjustment of the optical system of a small camera.

FIG. 15 is a characteristic diagram of the numbers and coefficients of the force coefficients calculated by changing the position of the initial point by the F G S method.

FIG. 16 is a characteristic diagram showing an ideal window function.

FIG. 17 is a characteristic diagram for explaining the sensitivity distribution of the light receiving window. FIG. 18 is a characteristic diagram for explaining the sensitivity distribution of the light receiving window. FIG. 19 is a characteristic diagram for explaining the sensitivity distribution of the light receiving window. FIG. 20 is a characteristic diagram for explaining the sensitivity distribution of the light receiving window. Figure 21 shows the characteristics of an example window function using Gaussian distribution (α = 1 0) FIG.

FIG. 22 is a characteristic diagram showing an example of the inverse analysis result for the Gaussian distribution (H = 10).

FIG. 23 is a characteristic diagram showing an example of a window function using a Gaussian distribution (α = 50).

FIG. 24 is a characteristic diagram showing an example of the inverse analysis result for the Gaussian distribution (ひ = 50).

FIG. 25 is a diagram showing the values of the Zernike coefficients obtained by numerical simulation and the exact values of the Zernike coefficients.

Figures 26 (Α) and (Β) show the intensity distribution calculated by performing an inverse analysis from the correct solution of the intensity distribution of the observed signal of the photo detector and the results obtained by numerical simulation. FIG. BEST MODE FOR CARRYING OUT THE INVENTION

In the aberration measuring method and the aberration measuring apparatus according to the present invention, light (for example, a laser) to be detected by a light detection element such as an optical pickup, a photo detector of an imaging optical system, a CCD, or a CMOS device is generated. A spot image is generated on the light detection element, and the spot image is scanned relatively (XY (horizontal) direction: perpendicular to the optical axis) on the light detection element. The spot image of the light detection element is generated by adjustment in the Z (vertical) direction (optical axis direction), and the output signal of the light detection element is input to the aberration analysis unit. The aberration analysis unit measures the aberration of the optical system from the spot image and evaluates the light spot image based on the observation signal of the spot image and the model observation signal. The observation signal is acquired by relatively XY scanning the spot image of light on the light detection element, and this observation signal is acquired at at least two different focal positions, that is, at two focal positions adjusted in the Z direction. Do. The model observed signal is by assuming the aberration It is calculated by convolution of the calculated intensity distribution of the spot image and a function that models the sensitivity distribution of the light receiving window of the light detection element.

As described above, in the present invention, aberration analysis of an optical system that forms a spot image based on an observation signal acquired from an output signal of a light detection element that receives a spot image of light and a model observation signal is described. Is going. The model observation signal can be calculated based on the intensity distribution of the spot image and the sensitivity distribution of the light receiving window of the light detection element. Therefore, it is necessary to measure and evaluate the aberration of the optical system that forms the spot image using an inexpensive device. Can reduce the measurement time and evaluation time.

The details of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram showing a first embodiment of an aberration measuring apparatus according to the present invention, and shows an optical pickup 1 for performing time recording and reproduction on an optical disk such as a CD or DVD, and a spot image. X-Z moving unit 10 for scanning and adjusting focal position, and aberration analysis unit 9 for performing aberration analysis and evaluation of spot image of laser light, and CD or DVD was mounted. In order to measure the aberration of the optical pickup 1 in the state, a transparent correction plate 6 having optical characteristics corresponding to the CD or DVD is inserted at the CD or DVD mounting position of the optical pickup 1.

The optical pickup 1 comprises a laser diode 2 for irradiating a laser beam 8, a half mirror 3 for reflecting and transmitting the irradiated laser beam 8 A, an optical system 4 for condensing the laser beam 8 B, and a laser beam 8. A photo detector 5 is provided which receives the spot image of D, converts it into an electric signal, and outputs an output signal ES. The output signal E S from the photo detector 5 is input to the aberration analysis unit 9.

The XYZ moving unit 10 is a lens 1 1 that receives the laser beam 8 B transmitted through the optical system 4 of the optical pickup 1 and transmitted through the correction plate 6 to be collimated light; To move the flat mirror 12 reflecting the laser beam 8 C in the direction of entry, and the lens 11 or the mirror 12 in the X axis direction, the Y axis direction, and the Z axis direction, respectively. It consists of an XYZ stage 13 and a control unit 14 that controls the XYZ stage 13. The X axis, the Y axis, and the Z axis are coordinate axes of the orthogonal coordinate system, and an XY plane is taken parallel to the light receiving window where the photo detector 5 receives the laser light 8D. When moving the lens 1 1 and / or the mirror 1 2, only the lens 1 1 is moved to fix the mirror 1 2, or the lens 1 1 and the mirror 1 2 are moved. Can be moved collectively.

Here, the correction plate 6 to be inserted into the CD or D V D mounting position of the optical pickup 1 will be described. The substrates of D V D and C D use polycarbonate resin having a refractive index of about 1.55. Then, the laser light is condensed to one point through this substrate and the recording bit is read out. Therefore, the objective lens to be used is designed to have spherical aberration in advance so that it can be focused to one point through the substrate of a predetermined thickness in consideration of the thickness and refractive index of the disk substrate. The correction plate 6 is inserted for the purpose of correcting this spherical aberration. That is, by inserting a transparent plate having the same optical thickness as that of the substrate in order to simulate the substrate at the time of measurement, it is possible to simulate the state in which the optical pickup 1 reads out the focal point inside the disc of the normal DVD.

In such a configuration, the laser beam 8 A emitted from the laser diode 2 of the optical pickup 1 is reflected by the mirror 1, becomes a laser beam 8 B and passes through the optical system 4. The laser light 8 B transmitted through the optical system 4 is transmitted through the correction plate 6, passes through the lens 1 1, is reflected by the mirror 12, and the reflected laser light 8 C is output from the XYZ moving unit 10. The laser light 8 C travels in the direction opposite to that of the incident laser light 8 B, passes through the correction plate 6 and the optical system 4, and further passes through the half mirror 3 to become laser light 8 D. Ha The light is received by the auto detector 5. The photo detector 5 converts the received laser light 8 D into an electric signal, and inputs the output signal ES to the aberration analysis unit 9.

The aberration analysis unit 9 obtains an observation signal p (X, Y) ((X, Y) is a relative position of the spot image) based on the output signal ES from the photo detector 5. The observation signal p (X, Y) moves the lens 11 or Z and the mirror 12 in the XY direction by the XYZ stage 13. The spot image of the laser beam 8 D received by the photo detector 5 is XY (X) Horizontal) Acquired by scanning in the plane.

When analyzing the spot image of the laser beam 8D, the aberration analysis unit 9 further calculates a model observation signal P (X, Y). The model observation signal P (X, Y) is obtained from the intensity distribution s (x, y) of the spot image and the function W (x, y) that models the sensitivity distribution of the light receiving window of the photo detector 5. The following is calculated by convolution-integral number 1.

[Number 1]

The convolution integral of the above equation 1 can be an integral of the rectangular wave region when the function W (x, y) is constant. In addition, convolutional integration Fourier-transforms the function W (X, y) that models the sensitivity distribution of the photodiode 5 and the intensity distribution s (x, y) of the spot image, and reverses the product in frequency space It may be Fourier transformed.

When the above equation 1 is discretized, the following equation 2 is obtained.

[Number 2]

{P} = [W] {s} The matrix [W] of the above equation 2 discretizes the sensitivity distribution W (X, y) of the light receiving window of the photo detector 5, maps each component to the component of the matrix [W] in consideration of the relative position, Is configured.

The intensity distribution s of the spot image is given by the following equation 3, where f is the complex amplitude of the spot image of the laser beam 8D.

[Number 3]

s = I f I ^{2 In the} present invention, the complex amplitude f of the spot image of the laser beam 8 D is represented by the Nipoesernike series given by the following equation 4.

[Equation 4] f {r, e) ^ {K „) D„ {r, e) where K is the coefficient of Nyboesernike and D is the basis function of the two-poeze ernike, (r, Θ) Represents polar coordinates. When the above equation 4 is discretized, the following equation 5 is obtained.

[Number 5]

{f} = [D] {K} The equation obtained by discretizing equation 3 is equation 6 below. Substituting equation 5 into equation 6 results in equation 7 below.

[Number 6]

{s} = I {f} I ²

[Number 7]

{s} = I [D] {K} I ² The following number 8 is derived from the above number 7 and the above number 2

[Number 8]

{P} = [W] I [D] {K} I ² Nipoezernike coefficient Assuming that K, model observed signal {P} = [W] I [D] {Κ} I ² is calculated and observed signal {p Solve the nonlinear least-squares problem with the following number 9 as the objective function based on} and the model observation signal {P}.

[Number 9] mm

The spot image of the laser beam 8 D is analyzed by solving the nonlinear least squares problem of the above-mentioned 9 and determining the design variable K.

In order to solve the non-linear least-squares problem of the above equation 9 and to determine the design variable K, the observation signal p can be obtained by moving the lens 11 or Z and the mirror 12 in the Z direction by the XYZ stage 13. It is necessary to acquire (X, Y) for at least two different focal positions of the laser beam 8 and to improve the solution accuracy when analyzing the spot image of the laser beam 8 D The nonlinear least squares problem may be solved using Tikonov's method with the following number 10 as the objective function.

[Number 1 0]

W-[] | []} | ² + HIWI ² → ^min where W is a weight value. Note that the objective function of the nonlinear least squares problem using Tikonov's method is not limited to the number 10. Further, in the above description, the model observation signal is expanded in the two Poesernike series, but the present invention is not limited thereto, and general finite series expansion such as Fourier series expansion and Lagrange series expansion can be used.

FIG. 2 is a flow chart showing an example of the aberration analysis of the spot image of laser light 8 D in the aberration analysis unit 9.

First, the output signal ES from the photo detector 5 is input to the aberration analysis unit 9 (step S 1). The aberration analysis unit 9 obtains an observation signal P (X, Y) from the output signal ES when the spot image of the laser light 8 D is scanned in the XY plane of the photo detector 5 (step S 2). In the aberration analysis in the aberration analysis unit Si according to the present invention, it is necessary to acquire the observation signal P (x, y) with respect to two or more different focus positions in the Z direction. The reason is described below with reference to FIG.

FIG. 3 is a schematic view of a spot image in a focused image and a defocused image of each coefficient amn,) 3 mn. In the present invention, when aberration analysis is performed using only one spot image, the solution lacks uniqueness, and correct analysis can not be performed. If it is considered to use two or more spot images by giving up analysis on only one plane, using "focus plane + defocus plane" or positive and negative defocus planes solves this problem. can do. That is, the influence of the expansion coefficients a mn and / 3 mn of the complex amplitude distribution, which is an unknown quantity in the present invention, on the intensity distribution of the spots differs in characteristics depending on the coefficients a mn and β mn. Consider the case where m is an odd number as in the example of n = 3 and m = l (third coma) shown at the top of Fig.3. Focusing only on the focus plane, the sensitivity to the 3 mn focus plane, which is the coefficient of the real part, is the same, so this positive / negative can not be determined (eg, "ex. 1" in Fig. 3). On the other hand, if we focus on only one side of the defocus plane, it will be possible to discriminate between positive and negative, as in "ex. 2" in Fig. 3. However, this time it becomes impossible to determine whether it is the effect of the real part coefficient) 3 mn or the effect of the coefficient amn of the imaginary part (for example, "ex. 3" in Fig. 3). Also, when m is even as in the example of n = 2 and m = 2 (third-order astigmatism) shown in the lower part of Fig. 3, the effect on the spot image is compared to when m is an odd number. Therefore, the influence of am _n ,) 3 mn is opposite. Also in this case, for the same reason as m is odd, the effect of positive / negative, amn, and j3 mn values can not be distinguished if there is only one spot image. For this reason, it is impossible to analyze correctly with only one spot image. Therefore, in the present invention, the observation signal p (X, y) is acquired for two or more different focal positions in the Z direction. Although it is at least two or more, the spot image of two is optimal in terms of accuracy and processing speed.

The aberration analysis unit 9 next calculates a model observation signal P (X, Y) (step S 5). In the model observation, first, it is hypothesized that the Nipoezelnike coefficient {K}, which is an aberration assumption, is assumed (step S3), and then the intensity distribution {s} of the spot image is calculated according to the equation 7 (step S4). Calculate the model observation signal {P} by Eq. 8 (step S 5).

The aberration analysis unit 9 minimizes the difference between the observation signal {p} and the model observation signal {P} based on the obtained observation signal {p} and the model observation signal {p} (step S6). The objective function of the non-linear least squares problem used in performing this minimization is given by the above equation 9 or the above equation 10.

Next, it is judged whether the Nipoesernicke coefficient {K} which is a design variable of the nonlinear least squares problem has converged (step S 7). If it is determined that convergence has not occurred, the intensity distribution {s} of the spot image and the model observation signal {P} are calculated again based on the Nivosezernike coefficient {K} obtained by the minimization, and the observation signal { Based on p} and the obtained model observation signal {P} And / /, to do.

If it is determined in step S7 that the two Poeselnike coefficients {K}, which are design variables of the nonlinear least squares problem, have converged, the aberration distribution (the declination distribution) is easily determined from the determined two Boeselnike coefficients {K}. Can be calculated. The calculated aberration distribution is output (step S 8), and the aberration analysis process is completed. The aberration distribution can also be expressed as a Zernike coefficient, which is a commonly used aberration index, using a linear least squares problem.

Next, a second embodiment of the aberration measuring apparatus according to the present invention will be described with reference to FIG.

In the second embodiment, as in the first embodiment, an optical pickup 1 for recording and reproducing data on an optical disc such as a CD or a DVD, and scanning and adjustment of a spot image are also performed. And an aberration analysis unit 9 for performing aberration analysis and evaluation of a spot image of a laser beam, and the correction plate 6 is inserted at the CD or DVD mounting position of the optical pickup 1. There is. The configuration and operation of the optical pickup 1, the correction plate 6 and the aberration analysis unit in the present embodiment are the same as those in the first embodiment.

The XYZ moving unit 20 of the second embodiment transmits the optical system 4 of the optical pickup 1 and further receives the laser beam 8 B transmitted through the correction plate 6 and transmits the laser beam 8 B in the direction in which the laser beam 8 B has entered. It consists of a reference spherical surface 2 1 that reflects light 8 C, an XYZ stage 2 2 for moving the reference spherical surface 2 1 in the X and Y directions, and a control unit 2 3 that controls the XYZ stage 2 2 . The reference spherical surface 21 is a hemispherical concave mirror whose focal point is at the center of the hemisphere, and has the same function and effect as the lens 11 and the mirror 12 in the first embodiment.

In such a configuration, the laser beam 8 A emitted from the laser diode 2 of the optical pickup 1 is reflected by the half mirror 1 and the laser beam 8 B The laser light 8 B passes through the optical system 4 and the correction plate 6 and is received by the reference spherical surface 2 1. The laser beam 8B received by the reference spherical surface 21 is reflected by the reference spherical surface 21 to become a laser beam 8C, the laser beam 8C passes through the correction plate 6 and the optical system 4, and further passes through the half mirror 3. Then, it becomes laser light 8 D and is received by the photodetector 5. The output signal ES of the laser light 8 D received by the photo detector 5 is input to the aberration analysis unit 9.

After focusing and moving the reference spherical surface 2 1 in the Z direction with the XY Z stage 2 2, move the reference spherical surface 2 1 in the XY direction and a spot image of the laser beam 8 D received by the photo detector. The aberration analysis unit 9 acquires the observation signal p (X, Y) of the spot image of the laser light 8 D by scanning the light source with the focal position fixed. In addition, by moving the reference spherical surface 21 again in the Z direction by the XY Z stage 22 in order to carry out the aberration analysis, the observation signal p (X, X at at least two different focal positions of the laser light 8 is obtained. Get Y)

The calculation of the model observation signal P (X, Y) is performed in the same manner as in the first embodiment. Then, in the same procedure as shown in Fig. 2, the aberration of the spot image of the laser beam 8D is analyzed based on the observation signal {p} and the model observation signal {P}.

Next, a third embodiment of the aberration measuring apparatus according to the present invention will be described with reference to FIG.

The aberration measuring apparatus of the third embodiment comprises an optical pickup 1, a reference light source 30 for irradiating a reference laser beam 33 whose aberration is known, and an XY Z stage 3 1 for moving the reference light source 30 in the XY Z direction. And a correction plate 6 inserted at the CD or DV D mounting position of the optical pickup 1, and an aberration analysis unit 9. The reference light source 30 is installed so that the irradiated reference laser light 33 passes through the correction plate 6, the optical system 4 and the half mirror 1 and is received by the photo detector 5. Do. The configuration of the optical pickup 1 in the present embodiment is the same as in the first and second embodiments.

In the present embodiment, when performing the aberration measurement, the reference laser beam 33 is irradiated from the reference light source 30. The irradiated reference laser light 33 is transmitted through the correction plate 6, and further transmitted through the optical system 4 and the half mirror 1 of the optical pickup 1 and received by the photo detector 5. The reference laser beam 33 received by the photo detector 5 is converted into an electrical signal, and the output signal ES is input to the aberration analysis unit 9.

The observation signal p (X, Y) required to analyze the aberration in the aberration analysis unit 9 is moved by the reference light source 30 in the Z direction by the XYZ stage 31 and focused, and then the reference light source 3 By moving 0 in the X and Y directions, horizontal scanning is performed with the focal position of the spot image of the reference laser light 33 fixed, and light is received by the photo detector 5. Also, to perform aberration analysis, the reference light source 30 is moved again in the Z direction by the XY Z stage 31 and the observation signal p (X, Y) differs by at least two or more of the reference laser light 33. Acquire at the focus position.

The aberration analysis unit 9 acquires the model observation signal P (X, Y) in the same manner as in the first and second embodiments, and based on the observation signal {p} and the model observation signal {p}, FIG. Perform the aberration analysis in the same procedure as the flowchart. In order to derive an aberration caused by the optical system 4 or the like of the optical pickup 1 from the aberration obtained by the aberration analysis, the aberration of the reference laser beam 33 may be subtracted from the aberration obtained by the aberration analysis.

By the way, in the first embodiment, the lens 1 1 and the mirror 12 are moved in the XYZ directions by the XY Z stage 13. In the second embodiment, the reference spherical surface 21 is moved in the XY Z direction by the XY Z stage 20. In the third embodiment, the reference light source 30 is moved in the XY Z direction by the XY Z stage 31. It is done. Such an XYZ stage is a Y stage that can move only in the Y direction, and it is possible to move both the lens 11, the mirror 12, the reference spherical surface 21 and the reference light source 30 only in the Υ direction. By allowing the optical system 4 to move in the X direction and the Ζ direction by means of focus tracking correction (not shown), scanning of the spot image of the laser light in the Υ plane and the laser light You may move the focus position of the Also, in the manufacturing process of the optical pickup 1, before fixing the position of the photo detector 5, as shown in FIG. 6, the Χ stage 15 is attached to the photo detector 5 and the photo detector 5 is mounted. By moving in the Χ direction, Χ scanning of the spot image of the laser beam may be performed (fourth embodiment). In this case, the eyebrow stages (10, 20, 31) in the first to third embodiments can be moved only in the eyebrow direction. The focal position of the laser light is moved by moving both the reference sphere surface 2 1 and the reference light source 30 in the Z direction.

Next, a fifth embodiment of the aberration measuring apparatus according to the present invention will be described with reference to FIG.

The aberration measuring apparatus of this embodiment moves a measured optical pickup 1 for measuring an aberration, a reference optical pickup 41 with known optical characteristics such as aberration, and a reference optical pickup 41 in the XYZ directions. The analysis of the spot image of the laser beam 48 received by the XYZ stage 4 6, the control unit 4 7 that controls the XYZ stage 4 6, and the photo detector 5 of the measured light pickup 1 The aberration analysis unit 9 and the correction plate 6 inserted at the CD or DVD mounting position of the measured optical pickup 1 are provided. The configuration of the measured optical pickup 1 in the present embodiment is the same as that of the optical pickup 1 in the previous embodiment, and the same reference numerals are given to the respective constituent elements. A reference optical pickup 41 comprises a laser diode 42 that emits a reference laser beam 48 whose aberration is known, a half mirror 43 that reflects or transmits the reference laser beam 48, and an optical that collects the reference laser beam. The system comprises a system 4 4 and a photo detector 45 for receiving a reference laser beam 4 8.

When measuring the aberration of the measured optical pickup 1, the reference laser light 48 is irradiated from the laser diode 42 of the reference light pickup 41. The irradiated reference laser light 48 is reflected by the half mirror 43, passes through the optical system 4 4 and the correction plate 6, and enters the measured optical pickup 1. The reference laser light 4 8 is transmitted through the optical system 4 and the half mirror 1 of the light pickup 1 and is received by the photo detector 5. The photo detector 5 converts the received reference laser light 48 into an electrical signal ES, and the electrical signal ES is input to the aberration analysis unit 9.

Aberration analyzing unit 9, the observed signal p ^(X,; Y) for performing aberration analysis it is necessary to acquire. First, after the reference optical pickup 41 is moved in the Z direction by the XYZ stage 46 and focused, the reference laser light 4 received by the photo detector 5 is moved by moving the reference optical pickup 41 in the XY direction. The spot image of 8 is scanned with the focal position of the reference laser beam fixed, and the observation signal p (X, Y) is acquired. By moving the reference light pick-up 41 again in the Z direction by means of the XYZ stage 46 in order to carry out the aberration analysis, the observation signal p (for the focal position of at least two or more different reference laser lights 48) Get X, Y).

The aberration analysis unit 9 calculates the model observation signal P (X, Y) in the same manner as in the first embodiment, and the observation signal {p} and the model observation signal {P in the same procedure as the flowchart of FIG. Analyze the spot image of the reference laser beam 48 based on}. The aberration produced by the optical system 4 etc. of the measured optical pickup 1 can be determined from the aberration obtained by the above-mentioned aberration analysis. It is derived by subtracting the aberration of 1 reference laser light 4 8 and the aberration generated by the optical system 4 4 etc.

Next, a sixth embodiment of the aberration measuring apparatus according to the present invention will be described with reference to FIG.

The aberration measuring apparatus according to the sixth embodiment moves a measured light pickup 1 for measuring aberration, a reference optical pickup 41 with known optical characteristics such as aberration, and a reference optical pickup 41 in the XYZ directions. To analyze the aberration of the spot image of the laser beam 8 received by the XYZ stage 46, the control unit 47 that controls the XYZ stage 46, and the photo detector 45 of the reference light pickup 41. The aberration analysis unit 9 and the correction plate 6 inserted at the CD or DVD mounting position of the measured optical pickup 1 are provided. The configuration of the present embodiment is the same as that of the fifth embodiment except that the aberration analysis unit 9 receives the output signal ES of the photo detector 45 of the reference optical pickup 41. The corresponding components are denoted by the same reference numerals. In the present embodiment, when the aberration of the measured optical pickup 1 is measured, the laser light 8 is irradiated from the laser diode 2 of the measured light pick-up 1. The irradiated laser light 8 is reflected by the half mirror 13, passes through the optical system 4 and the correction plate 6, and enters the reference optical pickup 41. Further, the laser beam 8 passes through the optical system 4 4 of the reference optical pickup 4 1 and the half mirror 4 3 and is received by the photo detector 45. The photo detector 45 converts the received laser light 8 into an electrical signal, and inputs the output signal ES to the aberration analysis unit 9.

The aberration analysis unit 9 needs to acquire an observation signal p (X, Y) for performing the aberration analysis. First, after the reference optical pickup 4 1 is moved in the Z direction by the XYZ stage 46 and focused, the ray is received by the photo detector 5 by moving the reference optical pickup 41 in the XY direction. The spot image of the light 8 is scanned with the focal position of the laser light fixed, and the observation signal P (X, Y) is acquired. The observation signal p (X, Y) is acquired from the output signal ES of the laser diode 45. In order to perform aberration analysis, the reference optical pickup 41 is moved in the Z direction by the XYZ stage 46, and the observation signal p (X, Y) is acquired with respect to the focal position of at least two different laser beams 8. .

The aberration analysis unit 9 calculates the model observation signal in the same manner as in the first embodiment, and based on the observation signal {p} and the model observation signal {p} in the same procedure as the flowchart of FIG. The aberration of the spot image of the light 8 is analyzed. The aberration produced by the optical system 4 or the like of the measured optical pickup 1 can be derived by subtracting the aberration produced by the optical system 4 4 or the like of the reference optical pickup 4 1 from the aberration obtained by the above-described aberration solution.

Optical pickup 1 or measured optical pickup 1 and reference optical pickup 4 1 in the first to sixth examples, AS (astigmatism) In order to cancel out the influence of the generating optical element, an AS key cell optical element may be provided. The AS cancellation optical element corresponds, for example, to one in which the correction plate 6 is inclined. This is because when an inclined parallel plate is inserted into a light collecting or diverging ray, the optical distance in the inclined direction increases, and the optical distance in the direction orthogonal to the inclination is maintained, which causes astigmatism. In addition, although a laser diode is mentioned as an irradiation source of laser light, another laser generating element may be used.

The aberration measuring method using the aberration measuring apparatus shown in the first to sixth examples may be used as an optical pickup adjustment method for adjusting the aberration of the optical pickup to an optimum aberration. In addition, the aberration measurement method may be used to adjust the aberration of the optical pickup so as to be optimal in the manufacturing process of the optical pickup. In this case, the optical pickup may be composed of a collimator lens and an objective lens module. In that case, there is a need to inspect the optical system of the optical pickup before the objective lens module of the optical pickup is mounted. For example, as shown in FIG. 9, when the optical pickup 1 00 has a collimator lens 1 0 1 and a photo detector 1 0 2 and the objective lens module 1 1 0 is attached later, the optical pickup 1 In the manufacturing process of 0 0, it is required to inspect other optical systems before attaching the objective lens module 1 1 0. In such a case, as shown in FIG. 10, the collimated light from the focus scanning means 120 is directly irradiated to the optical pickup 100 before the objective lens module 110 is attached, and the photo detector 10 By generating a focal point on the top and XY scanning the focal point, it is possible to measure the aberration of the optical system of the optical pickup 100 before the objective lens module 110 is attached.

A specific configuration example of the focus scanning means 120 is as shown in FIGS. 11 and 12. In the example of FIG. 11 1, the focus scanning means 120 is an optical system 1 2. A laser light source 12 2 and a stage 1 2 3 for scanning the laser light source 1 2 2 are configured. The laser light emitted from the laser light source 12 2 is collimated by the optical system 1 2 1 and incident on the optical pickup 1 0 0 0, and the spot image collected through the collimator lens 1 0 1 is Measured in Fortune mode. XY scanning of the spot image on the photo detector 102 can be performed by moving the stage 1 2 3. Further, in the embodiment shown in FIG. 12, the focus scanning means 120A is an optical system, a laser light source 124 for irradiating a parallel laser beam, and a stage which can be tilted to scan the laser light source 124. It consists of 1 2 5 The parallel laser light emitted from the laser light source 124 is incident on the optical pickup 100, and the spot image collected through the collimating lens 101 is focused on the light source. Measured in T.12. XY scanning of the spot image on the photo detector 102 can be performed by driving the stage 125. For example, it can be realized by changing the angle by a galvanomier or the like. In addition, a small camera is mounted in the mobile phone, and the present invention can be applied to the adjustment request for such a small power camera. There is a demand for thinner, higher image quality, and higher resolution in the optical system of cameras for mobile phones, and there is a demand for aberration measurement for inspection and adjustment of lens tilt etc. during manufacturing.

As shown in FIG. 13, a laser beam 200 from a laser light source is condensed by an optical system 201, and the laser spot is projected on C C D 2 10 as a light detection element. Then, by analyzing the output signal of the CCD 210 obtained by scanning the spot with respect to one pixel 21 of the CCD 210 according to the method of the present invention described above, an optical system 2 0 can be obtained. Aberration of 1 can be identified. It should be noted that one pixel of CCD 210 is in the order of lm, the spot of the laser is also in the order of submicron to micron, and the output from one pixel of CCD 210 integrates a part of the projected spot. The amount will be the same. The amount of movement of the scan is on the order of microns.

FIG. 14 shows a configuration example of measuring the aberration of the optical system 201 by finely scanning the camera optical system to be measured with the focus scanning means 220 described in the present invention.

In order to confirm the effectiveness of the present invention, a demonstration example in which analysis of the aberration of the optical pickup is performed by numerical simulation will be shown. That is, the present invention is applied to the output data from the simulated photo detector for the assumed aberration, the aberration is identified, and the identified aberration is compared with the assumed aberration. The effectiveness of the present invention was verified. Measurement errors are also modeled and added to the simulated data. In the first to sixth embodiments, a plurality of hardware configurations for obtaining measurement data are shown. Since there is no difference in the errors included in the evening, it is verified by this simulation whether aberrations can be identified for all the examples.

The analysis conditions were as follows. The optical pickup is a DVD optical pickup, the wavelength of the laser diode is 650 nm, the numerical aperture NA is 0.6, and the size of the photodiode is 7500 nm 7 It is assumed that 5 0 0 [nm] (discretized into 1 2 5 points X 1 2 5 points). The analysis area covers 3 0 0 0 [nm] x 3 0 0 0 [nm] (discretized into 5 1 point X 5 1 point) that can cover approximately the primary ring when reconstructed. When the spot image of the laser light scans, scan is performed from the outside of this area. The laser diode used for analysis is ideal (G (u, ゆ) = 1), and the observation data shall be separated from the focus plane by 5 0 0 [nm] and 1 0 0 0 [nm] . The analysis aims to identify up to the 3rd-order spherical aberration, and makes the number of unknowns 18.

As a method to confirm that the numerical simulation is not multimodal, the BFGS method was used to calculate the coefficients by changing the position of the initial point. As a result, the characteristics as shown in FIG. 15 were obtained, and it could be shown that they were not multimodal. That is, the aberration can be stably identified as the only solution. The BFGS method is one of the non-linear optimization methods announced by Broyden, Fletcher, Goldfarb, and Shannon. It is also called the quasi-Newton method. Next, an ideal window function is shown in FIG. In this characteristic chart, the sensitivity of the central part is 100% and the sensitivity of the other parts is shown. The window function used here is a square pyramid with sides of 1 2 5 and height h = 1 2 5/2 x cut out at the position of height "1". The case of X = 4 in the above equation is shown in Figure 17 and the case of X = 16 is the sensitivity distribution of the light receiving window as shown in Figure 19, and reverse analysis was performed using these. Here, the respective analysis results are shown in FIG. 18 in the case of FIG. 17 and in FIG. 20 in the case of FIG. As above, It can be confirmed that the identification is stable even if the sensitivity distribution of the photodetection window of the photodiode is depressed at the periphery.

Also, in this simulation, a Gaussian distribution was used as the window function to block high frequency components. In this way, it is possible to think of the browsability when the high frequency component considered to be most important in scanning is cut off. The equation used for the Gaussian distribution this time is:

[Number 1 1]

1-α α ( ⁶ここ Here, Fig. 2 1 is a window function using a Gaussian distribution of α = 10, Fig. 2 3 is a window function using a Gaussian distribution at α = 5 0 Also, Fig. 22 shows the result of inverse analysis for the Gaussian distribution when = = 10, and Fig. 24 shows the result of inverse analysis for the Gaussian distribution when 0 = 50. Thus, according to the present invention, even in the case where the window function is dulled, identification can be stably performed.

The values of the Zernike coefficients obtained by analysis and the exact values of the Zernike coefficients are shown in FIG. Also, Fig. 26 (Α) shows the correct solution of the intensity distribution of the observed signal of the photodiode, and Fig. 26 (Β) is calculated by performing the inverse analysis from the results obtained by the numerical analysis. The intensity distribution is shown. These results show that the aberration measurement method according to the present invention can perform aberration analysis with sufficient accuracy.

As mentioned above, although the embodiment of the present invention was concretely explained, the present invention is not limited to this and can be suitably changed in the range which does not deviate from the meaning.

According to the present invention, the observation signal is output based on the output signal of the photo detector. The model observation signal is calculated on the basis of the intensity distribution of the spot image and the sensitivity distribution of the light receiving window of the photo detector, and the spot of the laser light received by the photo detector on the basis of the observation signal and the model observation signal. Since the analysis of the aberration of the projection image and the evaluation of the spot image of the laser light are performed, the analysis of the aberration of the spot image of the laser light and the evaluation of the spot image of the laser light can be performed using an inexpensive apparatus. And can reduce the measurement time.

The present invention is intended to perform aberration measurement, but can also be applied to measurement of optical evaluation amounts such as MTF (Modulation Transfer Function) _2⁄4 PSF (Point Spread Function), TF (Optical Transfer Function), and the like. In addition, the present invention is mainly applicable to the optical evaluation of optical pickups such as DVD, but it is further equivalent to one pixel of a CCD for an optical system composed of a lens such as a camera and a CCD. It can also be applied to analyze the aberration of the spot size. That is, if the light sensitivity to one pixel of the CCD is used as a window function, the aberration can be identified by the same method.

Patent Document 1: Japanese Patent Application Laid-Open No. 2 0 6-2 3 4 3 8 9

Claims

The scope of the claims

1. Projection means for projecting a spot image formed by the optical system to be measured onto the light detection element, and the spot image is relatively moved on the light detection element in the direction perpendicular to the optical axis. First moving means, second moving means for moving the position of the spot image projected on the light detecting element relative to the light detecting element in the optical axis direction, and the light from the light detecting element An aberration measurement apparatus comprising: an aberration analysis unit that analyzes an aberration based on an output signal.

2. The second moving means controls the spot image and the position of the light detecting element to at least two positions, and the first moving means forms a light intensity distribution formed by the spout image. The aberration measuring apparatus according to claim 1, wherein an observation signal is obtained, and the aberration analysis means analyzes an aberration of an optical system forming the spot image based on the observation signal and a model observation signal.

3. When the position of the spot image and the light detection element is controlled to at least two positions by the second moving unit, the light detection element is disposed before and after the imaging point of the spot image. The aberration measurement apparatus according to claim 2, wherein

4. The aberration analysis means determines an observation signal and a model observation signal of the spot image based on the output signal, and analyzes an aberration of the spot image based on the observation signal and the model observation signal. The aberration measurement device according to claim 1 which is configured as described above.

5. The model observation signal, the intensity distribution of the spot image and the light detection element The aberration measuring apparatus according to claim 2, which is obtained by convolution integral with the sensitivity distribution of the light receiving window of the child.

6. In an optical system having an optical pickup which has a laser light source and the light detection element in an optical system to be measured and which performs recording and reproduction on an optical disc, mounting of the optical disc of the optical pickup A correction plate inserted at a position, laser light from the light pickup is incident through the correction plate, and the received laser light is reflected to the light pickup, and a spot image of the laser light is the light The spot image is scanned by the first moving means and the second moving means, and an observation signal and a model observation signal are obtained from the output signal from the light detection element to obtain the spot image. The aberration measurement apparatus according to claim 2, further comprising: an aberration analysis unit that analyzes the aberration of the lens.

7. The second moving mechanism includes: a lens for converting the laser light into parallel light; a mirror for reflecting the transmitted laser light of the lens; a stage for moving the lens and the mirror in the horizontal direction and the vertical direction; 7. The aberration measuring apparatus according to claim 6, further comprising: a control unit that controls the stage.

8. A reference spherical mirror for receiving and reflecting the laser light, a stage for moving the reference spherical mirror in the horizontal direction and the vertical direction, and a control unit for controlling the stage. The aberration measurement device according to claim 6, which is configured.

9. An optical pickup having a light detection element in the optical system to be measured, and performing recording and reproduction of data on an optical disc, and the optical disc of the optical pickup. A correction plate inserted at the mounting position of the disk, a reference light source for irradiating a reference laser beam whose aberration is known, a stage for moving the reference light source horizontally and vertically, and a control unit for controlling the stage The aberration measuring apparatus according to claim 2, further comprising: an aberration analysis unit configured to obtain an observation signal and a model observation signal from an output signal from the light detection element and analyze the aberration of the spot image. .

An optical pickup having a laser light source and a light detection element in an optical system to be measured and performing data recording and reproduction on an optical disc, a correction plate inserted at a mounting position of the optical disc on the optical pickup, First moving means for receiving a laser beam from the optical pickup through the correction plate, reflecting the received laser beam to the optical pickup, and moving a focal position of a spot image of the laser beam; A second moving means for moving the light detection element horizontally, and an aberration analysis unit for analyzing an aberration of the spot image by obtaining an observation signal and a model observation signal from an output signal from the light detection element. The aberration measurement device according to claim 2 provided.

1 1. A light detection element for recording and reproducing data on an optical disk, an optical pickup to be measured for measuring aberration, a laser light source, and a reference optical pickup having known optical characteristics, A correction plate inserted into the mounting position of the optical disc, and laser light from the reference light pickup passes through the correction plate to be incident, and an observation signal and a model observation signal are obtained from an output signal from the light detection element. An aberration analysis unit that analyzes the aberration of the spot image, a stage that moves the reference light pickup in the horizontal direction and the vertical direction, and a control unit that controls the stage. The aberration measurement device according to Item.

1 2. A laser light source, an optical pickup to be measured for measuring aberration while recording and reproducing data on an optical disc, a reference optical pickup having an optical detection element and having known optical characteristics, A correction plate inserted into the mounting position of the optical disc, laser light from the optical pickup to be measured is incident through the correction plate, and an observation signal and a model observation signal are output from an output signal from the light detection element. An aberration analysis unit for performing analysis of the aberration of the spot image, a stage for moving the reference light pickup in the horizontal direction and the vertical direction, and a control unit for controlling the stage; The aberration measurement device according to item 2.

The spot image formed by the optical system to be measured is projected on a light detection element, and the spot image is scanned on the light detection element in the direction perpendicular to the optical axis to obtain an observation signal and a model observation signal. After that, the spot image is relatively moved to another position in the optical axis direction to obtain the observation signal and the model observation signal, and the spot is determined based on the observation signal and the model observation signal. An aberration measurement method comprising analyzing an aberration of an image.

14. The aberration measuring method according to claim 13, wherein the model observation signal is calculated based on the intensity distribution of the spot image and the sensitivity distribution of the light receiving window of the light detecting element.

The complex amplitude of the spot image of the laser light is expanded by a finite series, and the intensity distribution of the spot image is given by the square of the absolute value of the complex amplitude, and the observation signal and the model observation signal are Nonlinear least squares based on the discretized and discretized observation signal and the discretized model observed signal The method according to claim 13, wherein the analysis of the aberration of the spot image of the laser beam and the evaluation of the spot image of the laser beam are performed by solving the problem.