KR100790689B1 - Method of testing lense using shack-hartmann wavefront sensor - Google Patents

Abstract

The present invention relates to a method for inspecting a lens using a Shark-Hartman wavefront sensor, comprising: a plurality of microlenses for transmitting a portion of an incident wavefront and an image sensor for detecting a plurality of images formed by the respective microlenses An inspection method of a lens using a Shark-Hartman wavefront sensor, comprising: calculating a wavefront passing through the inspection lens from design data of the inspection lens; Calculating a position at which the plurality of images formed when the calculated transmission wavefront is transmitted to the plurality of microlenses is detected by the image sensor and setting the first spot as a first spot, wherein each of the plurality of microlenses is provided with a corresponding plurality of images; 1 spot formed; Measuring a plurality of second spots at which the plurality of images formed when the wavefront passing through the inspection object lens is transmitted to the plurality of micro lenses is a position detected by the image sensor; For each of the plurality of second spots, matching a first spot at a closest position, and determining that the second spot is formed by a micro lens forming the corresponding first spot; And calculating a displacement difference between each of the plurality of second spots and a first spot corresponding to each of the plurality of second spots, and the wavefront calculated from the wavefront and the design data of the wavefront passing through the lens to be inspected from the displacement difference. A method of inspecting a lens using a Shark-Heartmann wavefront sensor, comprising calculating an error wavefront that is a difference from and.

Lens, wavefront, shark-heartmann wavefront sensor

Description

How to inspect a lens using the shark-hartmann wavefront sensor {METHOD OF TESTING LENSE USING SHACK-HARTMANN WAVEFRONT SENSOR}

1 is a conceptual diagram illustrating the measurement of the transmission wavefront passing through the lens using the Shark-Hartman wavefront sensor.

2 and 3 are plan views of a portion of the image sensor of the Shark-Hartman wavefront sensor.

Figure 4 is a flow chart showing a wavefront measuring method using a wavefront sensor according to the present invention.

5 is an exemplary view showing a first spot and a second spot of an image sensor of the Shark-Hartman wavefront sensor according to the present invention.

<Explanation of symbols for the main parts of the drawings>

10: inspection target lens 20: Shark-Heartman wavefront sensor

21: micro lens 22: image sensor

31, 32: wavefront 41, 42: spot

The present invention relates to a method of inspecting a lens, and more particularly, to a method of inspecting a lens using a Shark-Heartmann wavefront sensor.

According to the development direction of various electronic and mechanical products that are becoming smaller, there is a need for an optical system that can perform various functions while being slim, and the importance of aspherical lenses as an optical element that can meet such slimming and multifunctionalization needs is increasing. It is increasing.

Aspherical lens manufacturing methods include a polishing method and an injection method. As for the polishing processing method, the aspherical lens is manufactured by using a polishing machine, and the production cost is higher than that of the injection method and is not suitable for mass production. In addition, the injection method has the advantage that it is possible to manufacture aspheric lenses of various shapes that were difficult to provide in the polishing processing method.

As such, when the aspherical lens is manufactured by the injection method, it is possible to supply a large amount of aspherical lenses having various shapes that were difficult to provide by the polishing method at a low price, but in order to secure the performance stably, various deformations such as shape shrinkage that occur during the injection process The elements must be controlled effectively, which requires an effective measurement system that can evaluate the optical performance of aspherical lenses.

In general, a method of evaluating optical performance of a lens is performed by measuring a wavefront passing through the lens using a wavefront sensor, and as a wavefront sensor, a Shack-Hartmann wavefront sensor is frequently used as a wavefront sensor. have.

1 is a conceptual diagram illustrating the measurement of the transmission wavefront passing through the lens using the Shark-Hartman wavefront sensor.

As shown in FIG. 1, the Shark-Heartmann wavefront sensor 20 includes a plurality of micro lenses 21 and an image sensor 22. When the wavefront passes through the lens 10 to be inspected, the transmitted wavefront is incident on the plurality of micro lenses 21 of the Shark-Hartman wavefront sensor 20, and the plurality of micro lenses 21 The image is formed on the image sensor 22. The object to be inspected 10 is detected by detecting the position of the image formed on the image sensor 21 and measuring the degree of deviation from the point where the image is detected as a reference, and calculating the wavefront transmitted through the object to be inspected using the image. You can see the error of the degree. The point where the image is formed on the image sensor 22 is called spots 41 and 42 and is generated as many as the number of micro lenses 21.

The spot 41 in which the undistorted wavefront 31 is transmitted through the plurality of microlenses 21 in the Shark-Heartmann wavefront sensor 20 is referred to as a reference spot. In FIG. It becomes the point formed in (22).

In general, the wavefront transmitted through the lens 10 to be inspected has a distorted wavefront 32, and the spot 42 and the reference formed by the distorted wavefront 32 are transmitted through the plurality of micro lenses 21. The inspected lens 10 is inspected by analyzing the error of the inspected lens 10 from the calculated wavefront by calculating the wavefront from the displacement difference Δx, Δy, and Δx of the spot 41.

2 and 3 are plan views of a part of the image sensor of the Shark-Hartman wavefront sensor.

2 and 3, the image sensor 22 is divided into nine regions and displayed. The division is imaginary and indicates an area where a spot formed by each of the plurality of micro lenses 21 is formed. In the upper left square of each region, the serial numbers of the microlenses 21 corresponding to the region are described. The entire area of the image sensor 22 may be divided by the number of the plurality of micro lenses 21, and FIG. 2 shows only nine areas for description.

X denoted in each of the areas indicates a reference spot formed by the microlens 21 corresponding to the area. In addition, (circle) shown in each said area shows the actual spot at the time when the wave front which penetrated the inspection object lens 10 entered into the micro lens 21 corresponding to the said area | region. Ideally, the reference spot may be defined as the midpoint of each region of the image sensor 22, but even if an ideal wavefront without wavefront distortion is input due to factors such as alignment error of the measurement system, the reference spot may be It may not be formed at an intermediate point of each region of the image sensor 22. Therefore, in practice, the ideal wavefront is input and the measured position is used as the reference spot. The number written together with the reference spot and the actual spot is the serial number of the micro lens 21 forming the reference spot and the actual spot.

As described above, the inspection object is obtained by calculating the displacement difference (Δx, Δy) between the actual spot and the reference spot by the microlens 21 and calculating the transmission wavefront of the lens 10 to be inspected from the displacement difference. The optical performance of the lens 10 is examined.

2, when the wavefront passing through the inspection lens 10 is not severely deviated from the spherical wavefront so that the slope change of the wavefront is not severe, the image sensor 22 may be Spots formed by the microlenses 21 corresponding to the respective areas are formed, so that the displacement difference can be easily obtained. Accordingly, the wavefront passing through the lens 10 to be inspected can be easily measured.

However, as in the case of FIG. 3, when the wave front is inclined so that the spot formed by the microlenses is formed in another area instead of the corresponding area, the image sensor 22 only detects the position of the formed spot. It is not known which microlens formed the spot. Therefore, it is difficult to accurately measure the displacement difference between the reference spot and the actual spot, and therefore, the measurement of the wavefront is inaccurate and thus it is difficult to check the degree of error of the lens.

That is, as shown in FIG. 3, each spot is formed when the spot formed in the region 2 is caused by the microlens 8, the spot is not formed as in the region 9, or when two spots are formed as in the region 6. Although the point of can be measured, it is impossible to accurately measure the wavefront because it is unknown which microlens the spot is formed by.

The present invention has been made to solve the above-mentioned problems of the prior art, and an object thereof is to provide a method for accurately measuring the wavefront of the lens.

In order to achieve the above technical problem, the present invention, the Shark-Hartmann wavefront comprising a plurality of micro lenses each transmitting a partial region of the incident wavefront and an image sensor for detecting a plurality of images formed by each of the microlenses A method of inspecting a lens using a sensor, the method comprising: calculating a wavefront passing through the inspected lens from design data of an inspected lens; Calculating a position of a plurality of images detected in an area of the image sensor corresponding to each of the plurality of micro lenses when the calculated transmission wavefront passes through the plurality of micro lenses, and setting the first spot as a first spot; Measuring a plurality of second spots which are positions of images detected by the image sensor when the wavefront passing through the lens to be inspected passes through the plurality of micro lenses; For each of the plurality of second spots, matching a first spot at a closest position, and determining that the second spot is formed by a micro lens forming the corresponding first spot; And calculating a displacement difference between each of the plurality of second spots and a first spot corresponding to each of the plurality of second spots, and the wavefront calculated from the wavefront and the design data of the wavefront passing through the lens to be inspected from the displacement difference. A method of inspecting a lens using a Shark-Heartmann wavefront sensor, comprising calculating an error wavefront that is a difference from and.

The calculating of the wavefront passing through the lens to be inspected may include calculating an optical path difference passing through the lens to be examined from design data of the lens to be inspected; And calculating a wavefront passing through the lens to be inspected from the optical path difference, using the Shark-Hartmann wavefront sensor.

The calculating of the error wavefront may include developing the error wavefront into a Zernike coefficient and a Zernike polynomial; Calculating a coefficient of the Journich polynomial from the displacement difference; And calculating the error wavefront by substituting the calculated coefficient into the wavefront developed by the low-knee coefficient and the low-nickel polynomial, and inspecting the lens using the shark-hartmann wavefront sensor. .

Hereinafter, embodiments of the present invention will be described in more detail with reference to the accompanying drawings. Identical components use the same symbols.

4 is a flowchart showing a wavefront measuring method using a Shark-Heartmann wavefront sensor according to the present invention.

Referring to FIG. 4, the wavefront measuring method according to an embodiment of the present invention starts by setting a reference spot formed by a wavefront without distortion (S100).

The Shack-Hartmann wavefront sensor 20 used in the embodiment of the present invention is formed by a plurality of microlenses 21 and respective microlenses 21 which respectively transmit a portion of the incident wavefront. And an image sensor 22 for detecting a plurality of images.

The position of the plurality of images formed on the image sensor 22 when the wavefront without distortion is transmitted to the plurality of micro lenses 21 is called a reference spot, and the reference spot may be preset according to the Shark-Heartmann wavefront sensor. Can be. Each of the plurality of micro lenses 21 forms one reference spot and corresponds to the reference spot.

In an ideal case, the reference spot is located at the center of the area of the image sensor 22 corresponding to the plurality of micro lenses 21, respectively. However, since the reference spot may deviate from the center point due to alignment error, wavefront error, etc. of the shark-heartmann wavefront sensor 20 itself, the reference spot is distorted in the shark-heartmann wavefront sensor 20. It may be to measure directly through the wavefront without this.

If the reference spot is preset, step S100 may be omitted.

The transmission wavefront passing through the lens to be inspected is theoretically calculated from the design data of the lens to be inspected (S200).

Calculating the wavefront passing through the inspection object lens 10 calculates the optical path difference passing through the inspection object lens 10 from the design data of the inspection object lens 10, and from the optical path difference. The wavefront passing through the lens 10 to be inspected may be calculated.

The aspherical lens may express the aspherical surface of the lens as a formula. The aspherical equation is expressed by the base curvature c of the lens, the conic constant K, the aspheric deformation coefficient A, and the distance r from the lens center.

When the aspherical surface equation as shown in Equation 1 and design data such as the refractive index and the incident beam of the inspection target lens 10 are defined, an optical path may be tracked for each point of the inspection lens 10, and the inspection The optical path difference between the optical path at each point of the target lens 10 and the chief lay passing through the principal point of the lens may be known. Since the optical path difference represents a difference between the reference wavefront and the transmission wavefront of the lens 10 to be inspected, the transmission wavefront can be calculated therefrom.

Equation 1 is known as a Schulz equation, and the aspherical equation may be defined in another manner such as a spline equation in addition to Equation 1.

The calculated transmission wavefront enters the microlens 21 of the Shark-Hartman wavefront sensor 20 and calculates a first spot that is a position of an image formed in the image sensor 22 (S300).

In the Shark-Heartmann wavefront sensor 20, Δx _i and Δy _i (i is the serial number of the microlens), which are the displacement difference between the reference spot and the first spot, have the following relation with the calculated transmission wavefront. .

In Equation 1, f _l represents the focal length of the microlens 21 of the Shark-Hartmann wavefront sensor 20, and A _i represents the aperture of the microlens 21.

Substituting the transmitted wave front, calculated in the step S200 above in equation (2), the reference spots and the first and the displacement car Δx _i, Δy _i calculation of the spot, the displacement difference Δx _i, Δy _i, and adds the reference spot By this, the position of the first spot can be calculated. For example, if the reference spot is (x _i , y _i ) and the first spot is (x _1i , y _1i ), the following relation holds.

(x _1i , y _1i ) = (x _i + Δx _i , y _i + Δy _i )

Next, the wavefront is transmitted through the inspection lens (S400), and the wavefront passing through the inspection lens 10 is incident on the Shark-Hartman wavefront sensor 20 and formed on the image sensor 22. The second spot is measured (S500).

When the wavefront passing through the inspection object lens 10 is incident on the Shark-Hartmann wavefront sensor 20, the wavefront is transmitted through each microlens 21 of the Shark-Hartman wavefront sensor 20 and the microlens A plurality of second spots corresponding to each of 21 are formed in the image sensor 22.

However, it is unknown which of the microlenses 21 is formed of the plurality of second spots. In order to accurately measure the wavefront of the lens 10 to be inspected, it is important to accurately determine the microlenses 21 that form each of the second spots, and the present invention provides a method of forming a second spot from the measured second spots. A method of determining the microlens 21 is provided below.

After the second spot is measured, a micro lens in which each of the plurality of second spots is formed is determined (S600).

In general, since the shape of the manufactured lens does not greatly deviate from the designed lens shape, the position of the second spot formed by each micro lens 21 from the wavefront transmitted by the lens 10 to be inspected is determined by the corresponding micro lens ( It is formed in the vicinity of the first spot calculated by 21). Thus, for each of the plurality of second spots, it may be determined that the first spot in the closest position is matched, and the second spot is formed by the microlens 21 in which the corresponding first spot is formed.

For each microlens 21, the displacement difference between the second spot and the first spot is obtained (S700).

When the second spot corresponding to each micro lens 21 is determined, the displacement difference between the second spot and the first spot by each micro lens 21 can be obtained.

For example, _assuming that the first spot is (x _1i , y _1i ) and the second spot is (x _2i , y _2i ), the displacement difference Δx _i 'and Δy _i ' from the first spot with the second spot Is calculated as follows.

Δx _i '= x _2i -x _1i , Δy _i ' = y _2i -y _1i

Accordingly, the displacement difference is a displacement of a spot (first spot) formed by a wavefront passing through an ideal lens manufactured as designed and a wavefront (second spot) formed by a wavefront transmitted through the lens 10 to be inspected. It becomes a car.

When the displacement difference between the second spot and the first spot by each microlens 21 is calculated, an error wavefront that is a difference between the wavefront passing through the inspection object lens and the wavefront calculated from the design data is calculated from the displacement difference. (S800).

As described above, since the displacement difference is a displacement difference between a spot formed by a wavefront passing through an ideal lens manufactured according to a design and a wavefront passing through a lens to be inspected, a mathematical expression that is a relation between the displacement difference and the wavefront Equation 2 can be used to calculate the error wavefront due to the displacement difference.

The error wavefront means a difference between the wavefront of the ideal lens manufactured according to the design and the wavefront of the inspection target lens. Thus, the error wavefront may be analyzed to determine whether the inspection object lens 10 is defective. do. In addition, by adding an ideal wavefront by design data to the error wavefront, the difference between the wavefront passing through the inspection object lens 10 and the spherical wavefront can also be easily identified.

Computing the error wavefront from the displacement difference (S800) by developing the error wavefront with a Zernike coefficient and Zernike polynomial, and calculating the coefficient of the Zernike polynomial from the displacement difference Subsequently, the error wavefront may be calculated by substituting the calculated coefficient into the wavefront developed by the low-knee coefficient and the low-knee polynomial.

When the error wavefront is called W (x, y) and the Zurnik polynomial is Z _i (x, y), the error wavefront can be developed as a low-knick polynomial as in Equation 2.

W (x, y) = ∑c _n Z _n (x, y) (c _n is the low-k polynomial coefficient, n is the order of the low-k polynomial)

By differentially formulating Equation 3 with respect to x and y, a displacement difference due to the error wavefront can be obtained. The difference in displacement by the partial derivative and the difference in displacement between the reference spot and the second spot is calculated by using the Least Square Method. Substituting the low-knick polynomial coefficient into Equation 3, the wavefront passing through the inspection object lens 10 may be calculated.

The order of the Gernick polynomial may vary depending on a calculation method, and since the Gernick polynomial is a known polynomial, a detailed description thereof will be omitted.

In addition, conventionally, the image sensor was divided into regions corresponding to each microlens, and the wavefront was calculated as the spot formed in the region was formed by the corresponding microlens. Such a conventional method was able to measure when the aspherical degree of the wavefront, which means the degree of the wavefront deviated from the spherical wavefront, was not large, but when the aspherical degree of the wavefront was large, measurement was impossible or the accuracy was low. In contrast, the present invention can determine the wavefront by accurately determining the spot formed by each micro-lens, so that the wavefront can be measured more accurately than in the prior art.

5 is an exemplary view showing a spot on an image sensor of the Shark-Hartman wavefront sensor according to the present invention.

Referring to FIG. 5, an area corresponding to each micro lens of the micro lens 21 is included in the image sensor 22, and a number written in a rectangle in each area of the micro lens 21 corresponds to the area of the micro lens 21. Serial number.

The first spot calculated based on the design data of the lens 10 to be inspected is represented by x, and the second spot measured from the wavefront passing through the lens 10 to be inspected is represented by o. The numbers described by x and o indicate the serial numbers of the microlenses 21 corresponding to the respective spots.

Comparing FIG. 5 with FIG. 3, since the actual spots measured by the measurement are formed in the position adjacent to the reference spot calculated from the design data, the degree of distortion of the wavefront can be more accurately known by comparing the actual spots with the adjacent reference spots. do. For example, the first spot calculated by the microlens 8 and the measured second spot closest to the reference spot are determined. The smallest magnitudes of the displacement differences Δx and Δy with the first spot may be determined as the second spot by the microlens 8.

When the second spot is determined for each micro lens, the displacement difference can be easily obtained from the reference spot and the second spot, and the wavefront can be measured using the displacement difference as described above.

The present invention is not limited by the above-described embodiment and the accompanying drawings, but by the appended claims. Therefore, it will be apparent to those skilled in the art that various forms of substitution, modification, and alteration are possible without departing from the technical spirit of the present invention described in the claims, and the appended claims. Will belong to the technical spirit described in.

As described above, according to the present invention, it is possible to measure including aspherical transmission wavefronts that are large enough not to be measured by the conventional wavefront sensor, so that various types of lenses can be inspected.

In addition, by accurately grasping the spot formed by each microlens of the Shark-Hartmann wavefront sensor and calculating the wavefront, it is possible to more accurately measure and analyze the difference between the characteristics of the lens design and the characteristics of the lens through the measurement. It works.

Claims (3)

In the inspection method of a lens using a Shark-Hartman wavefront sensor comprising a plurality of microlenses each transmitting a partial region of the incident wavefront and an image sensor for detecting a plurality of images formed by each of the microlenses, Calculating a wavefront passing through the inspection lens from design data of the inspection lens; Calculating a position of a plurality of images detected in an area of the image sensor corresponding to each of the plurality of micro lenses when the calculated transmission wavefront passes through the plurality of micro lenses, and setting the first spot as a first spot; Measuring a plurality of second spots which are positions of images detected by the image sensor when the wavefront passing through the lens to be inspected passes through the plurality of micro lenses; For each of the plurality of second spots, matching a first spot at a closest position, and determining that the second spot is formed by a micro lens forming the corresponding first spot; And Calculate a displacement difference between each of the plurality of second spots and a first spot corresponding to each of the plurality of second spots, the wavefront transmitted from the displacement difference through the lens to be inspected, and the wavefront calculated from the design data; Compute error wavefront that is the difference of Method for inspecting the lens using the Shark-Heartman wavefront sensor comprising a. The method of claim 1, wherein the step of calculating the wavefront passing through the lens to be examined, Calculating an optical path difference passing through the inspection lens from the design data of the inspection lens; And Calculating a wavefront passing through the inspection object lens from the optical path difference Method for inspecting the lens using the Shark-Heartman wavefront sensor, characterized in that it comprises a. The method of claim 1, wherein the calculating of the error wavefront comprises: Developing the error wavefront with a Zernike coefficient and a Zernike polynomial; Calculating a coefficient of the Journich polynomial from the displacement difference; And Calculating the error wavefront by substituting the calculated coefficient into the wavefront developed by the low-knee coefficient and the low-knee polynomial; Method for inspecting the lens using the Shark-Heartman wavefront sensor, characterized in that it comprises a.

Images