KR100780185B1 - Lens wavefront measuring device using diffractive optical element - Google Patents

Abstract

A lens wavefront measuring apparatus capable of measuring wavefront by non-axis irradiation using a diffractive optical element is provided.

Lens wavefront measuring device according to the invention, the light source; A first collimating lens disposed in front of the light source and configured to transmit light beams emitted from the light source and convert the light beam into parallel light beams; A diffraction optical element disposed between the first collimating lens and the test lens; A second collimating lens disposed in front of the test lens and converting the light passing through the test lens into two or more parallel rays; And a measuring sensor disposed in front of the second collimating lens and irradiating two or more parallel rays formed through the second collimating lens to interfere with each other.

According to the present invention, it is possible to accurately measure the wavefront for the lens assembly as well as the lens assembly in the imaging optical system such as a camera through the wavefront measurement by the stock-axis irradiation, it is possible to analyze the homogeneity and uniformity of the image through the lens Get the effect.

Description

Wavefront Measuring Device of Diffractive Optical Element {Wavefront Measuring Device of Lens using a Diffractive Optical Element}

1 is a configuration diagram schematically showing a conventional wavefront measuring apparatus.

2 is a configuration diagram schematically showing another conventional wavefront measuring apparatus.

3 is a schematic configuration diagram of a lens wavefront measuring apparatus according to a first exemplary embodiment of the present invention.

4 is a schematic diagram showing spots obtained on the surface of a measuring sensor using the lens wavefront measuring apparatus.

Figure 5 is a schematic diagram showing the wavefront analysis principle of the lens wavefront measuring apparatus according to the present invention when using the Shark-Hartman sensor as a measuring sensor.

6 is a schematic configuration diagram of a lens wavefront measuring apparatus according to a second exemplary embodiment of the present invention.

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

110: light source 115: test lens

120 diffraction optical element 130 first collimating lens

135: second collimating lens 140: measuring sensor

150: space filter

The present invention relates to a lens wavefront measuring apparatus, and more particularly, to a lens wavefront measuring apparatus capable of measuring wavefronts by non-axis irradiation using a diffractive optical element.

As the demands of mobile phone users are diversified, the functions of the mobile phone are not limited to just calls, but the functions are gradually being expanded by taking pictures, watching videos, playing games, etc. Recently, mobile phones equipped with camera modules for taking pictures Products are becoming commonplace.

The camera module is being changed to the center of the high pixel, and at the same time, the implementation of various additional functions such as auto focusing (AF) and optical zoom (OPTICAL ZOOM).

In addition, in order to realize lightweight, miniaturized and high-definition products in addition to the mechanical components, the development of a lens to improve resolution while the lens size is getting smaller is required. For this purpose, high precision shape accuracy is required when manufacturing the lens. It is becoming.

Accordingly, wavefront measuring apparatuses using holograms and interferometers for accurately measuring the shape of lenses have been developed one after another, and most interferometers and wavefront aberration meters for measuring lens wavefronts are based on optical axis irradiation.

1 is a schematic configuration diagram of a conventional wavefront measuring device, as shown in the conventional wavefront measuring device is converted to parallel light while the collimated light (3) irradiated through the light source 1 passes through the collimating lens (2) The converted parallel light passes through the collimated lens 4 and passes through another collimating lens 5 arranged at a predetermined distance, and is then irradiated to the sensor 6 installed perpendicular to the optical axis.

In this case, the interval between the center point positions of the point image formed on the sensor 6 has the same value if there is no wavefront distortion at all, and if there is wavefront distortion, the distance between the center point positions is not constant. Here, the wavefront measurement extracts the center point of each point image, extracts the movement amount of each center point with respect to the reference position, and extracts slope information of the wavefront.

However, in the conventional wavefront measuring apparatus as described above, since the edge portion of the image irradiated by parallel light in the imaging optical system is generated by the light irradiated to the maximum range of the field of view of the lens to be inspected, the image characteristic only by on-axis irradiation. There is no limit to the analysis. Therefore, the conventional method has been pointed out the problem that the wavefront measurement analysis by stock irradiation is inevitable.

On the other hand, in the conventional wavefront measuring apparatus as shown in FIG. 2, it is possible to perform a stock-axis irradiation on the lens by tilting the lens at a predetermined angle with respect to the optical axis, but in this case, the wavefront is only in one direction of the lens. Since it can be measured, there is a disadvantage that the difference in the wavefront in both directions of the lens to be examined can not be compared.

In addition, since it is not possible to know exactly where the test lens is set on the optical axis, various wavefront aberrations are measured according to the degree of tilt of the test lens, and the accuracy of the measurement is high because many lenses cannot be adjusted to have the same tilt. As a result, the problem of taking a long time for measurement has been raised.

The present invention has been proposed to solve the above problems, and an object of the present invention is to provide a lens wavefront measuring apparatus using a diffractive optical element to enable wavefront measurement by non-axis irradiation.

According to the present invention for achieving the above object,

Light source; A first collimating lens disposed in front of the light source and configured to transmit light beams emitted from the light source and convert the light beam into parallel light beams; A diffraction optical element disposed between the first collimating lens and the test lens; A second collimating lens disposed in front of the test lens and converting the light passing through the test lens into two or more parallel rays; And a measurement sensor disposed in front of the second collimating lens, wherein two or more parallel rays formed through the second collimating lens are interfering with and irradiated with each other. Is provided.

In the lens wavefront measuring device of the present invention,

Preferably, the first collimating lens has a positive refractive power, and may be disposed at a position separated by a focal length of the first collimating lens from the light source.

More preferably, the light beams passing through the diffractive optical element and the test lens may have a phase difference of an order of -1, 0, +1.

In addition, the second collimating lens may have a positive refractive power, and may be disposed at a position away from the lens by a distance obtained by adding a focal length of the lens to the second collimating lens.

In addition, the second collimating lens may be formed by bonding two or more lenses of different materials.

On the other hand, the measuring sensor may be a Shark-Hartmann lens.

In another aspect of the invention,

Light source; A first collimating lens disposed in front of the light source and configured to transmit light beams emitted from the light source and convert the light beam into parallel light beams; A diffraction optical element disposed between the first collimating lens and the test lens; A spatial filter disposed in front of the lens to be examined; A second collimating lens disposed in front of the spatial filter and configured to transmit light beams passing through the spatial filter to two or more parallel beams; And a measurement sensor disposed in front of the second collimating lens and irradiated with two or more parallel rays formed through the second collimating lens to cause interference with each other. Is provided.

In the lens wavefront measuring device according to another aspect of the present invention,

Preferably, the first collimating lens has a positive refractive power, and may be disposed at a position separated by a focal length of the first collimating lens from the light source.

In addition, the light ray passing through the diffractive optical element and the test lens may have a phase difference of an order of -1, 0, and +1.

More preferably, the spatial filter may be disposed at a position where the light beam passing through the test lens is focused.

In addition, the spatial filter may block light of -1 order or less.

In addition, the spatial filter may block light rays of +1 order or more.

Preferably, the second collimating lens has a positive refractive power, and may be disposed at a position apart from the lens by a distance obtained by adding a focal length of the lens to the second collimating lens.

In addition, the second collimating lens may be formed by bonding two or more lenses of different materials.

On the other hand, the measuring sensor may be a Shark-Heartman lens.

Hereinafter, a first embodiment of a lens wavefront measuring apparatus using a diffractive optical element according to the present invention will be described with reference to FIGS. 3 to 5.

3 is a schematic configuration diagram of a lens wavefront measuring apparatus according to a first exemplary embodiment of the present invention, and FIG. 4 is a schematic view showing spots obtained on a measurement sensor surface using the lens wavefront measuring apparatus.

As shown in FIG. 3, the apparatus for measuring a wavefront of a lens according to the first exemplary embodiment includes a light source 110, a first collimating lens 130, and a diffractive optical element along an optical axis. 120, the second collimating lens 135, and the measurement sensor 140 are sequentially arranged.

The light source 110 is for irradiating light rays for measuring the wavefront of the lens 115 to be measured, and generally uses white light or a laser.

The first collimating lens 130 is disposed in front of the light source 110, and transmits the light emitted from the light source 110 to convert into a collimating beam.

In this case, the first collimating lens 130 is disposed at a position separated by a focal length of the first collimating lens 130 from the light source 110 in order to convert the light beam emitted from the light source 110 into parallel light. It is desirable to have positive refractive power.

The diffraction optical element 120 is disposed between the first collimating lens 130 and the test lens 115, and the diffraction optical element 120 has an order of -1, 0, and +1. Accordingly, the light rays passing through the diffraction optical element 120 and the lens under test 115 form a phase difference between orders of -1, 0, and +1.

At this time, the distance between the first collimating lens 130 and the diffractive optical element 120 is not particularly limited.

In general, a diffraction optical element is a device that generates a periodic change in the phase or / and amplitude of an emission wave by causing phase modulation by using a constant pattern on the surface of a flat and transparent glass plate or by regularly changing the optical thickness. . In such a diffractive optical element, the diffraction angle of each order becomes large when its lattice spacing decreases.

Therefore, the present invention can control the angle of the stockpile to be measured by adjusting the grating spacing of the diffractive optical element 120.

Although the diffraction optical element 120 of the present embodiment has been described as having orders of -1, 0, and +1, the lens wavefront measuring apparatus of the present invention is not limited thereto, and has an order of -1 or less or an order of +1 or more. It is also possible to use the diffractive optical element 120. That is, the lens wavefront measuring apparatus of the present invention may be configured such that the parallel light transmitted through the first collimating lens 130 has a phase difference of various orders while passing through the diffractive optical element 120.

In addition, it is also possible to design the diffractive optical element 120 so as not to generate a zero order. In this case, the symmetry of the inspected lens 115 along the optical axis can be evaluated.

On the other hand, as the light rays having the phase difference of various orders pass through the inspected lens 115 and the optical axis is symmetrically ordered, a spot distribution appears as shown in FIG. 4. At this time, the interval of the spot can be changed according to the interval of the diffractive optical element (120).

The second collimating lens 135 is disposed in front of the lens 115.

By the second collimating lens 135, the light rays focused through the diffractive optical element 120 and the inspected lens 115 and according to the order of the diffractive optical element 120 are converted into two or more parallel rays. . That is, the light beam passing through the lens 115 may be irradiated in parallel to the measurement sensor 140 by passing through the second collimating lens 135.

In this case, the second collimating lens 135 has a focal length of the lens 115 and a focal length of the second collimating lens 135 in order to convert the light beam passing through the lens 115 into parallel rays. It is preferably disposed at a position away from the lens 115 by the distance plus, and has a positive refractive power.

On the other hand, the second collimating lens 135 is preferably formed by bonding two or more lenses of different materials, in order to minimize the aberration of the second collimating lens 135.

The measuring sensor 140 is disposed in front of the second collimating lens 135, and generally uses a CCD or Shark-Hartmann sensor.

Two or more parallel rays formed through the second collimating lens 135 are irradiated to the measuring sensor 140 by interfering with each other. That is, two or more parallel rays reaching the surface of the measuring sensor 140 may interfere with each other to generate an interference pattern, thereby measuring the performance of the lens 115.

In this case, when light rays of the same order cause interference, the relative performance of the left and right sides of the lens 115 may be compared.

5 is a schematic diagram showing the wavefront analysis principle of the lens wavefront measuring apparatus according to the present invention when using the Shark-Hartman sensor as the measuring sensor 140.

As shown in FIG. 5, the wavefront formed through the lens 115 is divided into a reference wavefront 112 and a measurement wavefront 114, and the reference wavefront 112 and the measurement wavefront 114 are paired. By passing through the micro lens 142, spots are obtained on the sensor surface 144, respectively.

The reference wavefront 112 and the measurement wavefront 114 are formed through the same lens 115.

At this time, the parallel light transmitted through the lens 115 to form the wavefront is set such that the incident angles are symmetrical with respect to the center of the lens 115 to be incident.

Here, the incident angle adjustment of the parallel light is performed by the diffraction optical element 120 disposed in front of the lens 115.

As described above, when the parallel light passes through the lens 115 at the same angle of incidence, the spots formed at the center of each pixel constituting the sensor surface 144 coincide with each other. Check whether aberration occurs.

That is, it is possible to relatively evaluate whether the aberration of the inspected lens 115 is generated by changing the spot position by the reference wavefront 112 and the spot position by the measurement wavefront 114.

In this case, when the difference between the spot position by the reference wavefront 112 and the spot position by the measurement wavefront 114 is connected, the analyzed wavefront 40 may be represented by a linearized solid line. Reference numeral 40 denotes a difference in spherical aberration between the fields constituting the interferometer formed by the wavefront transmitted through the lens 115.

As such, when using the Shark-Heartmann sensor as the measurement sensor 140 of the lens wavefront measuring apparatus according to the present invention, by measuring the wavefront of the other spot using one spot as a reference (example) For example, using the -1 order as a reference to measure the wavefront of the +1 order), it can be relatively evaluated how much the same aberration is generated by the lens 115 to the optical axis.

Hereinafter, a second embodiment of a lens wavefront measuring apparatus using the diffractive optical element 120 according to the present invention will be described with reference to FIG. 6.

6 is a schematic configuration diagram of a lens wavefront measuring apparatus according to a first embodiment of the present invention.

In the lens wavefront measuring apparatus according to the present exemplary embodiment, a spatial filter 150 disposed between the lens 115 and the second collimating lens 135 is additionally provided. Since it is the same as the configuration of the lens wavefront measuring apparatus according to the same, the same reference numerals are given to the same configuration and description thereof will be omitted.

The spatial filter 150 is disposed in front of the lens 115 to serve to block light rays other than the order required for the measurement.

The light rays passing through the spatial filter 150 pass through the second collimating lens 135 and are converted into two or more parallel rays.

In this case, the spatial filter 150 is preferably disposed at the position where the light beam passing through the lens 115 is focused, in order to facilitate the blocking of light rays other than the order required for the measurement.

FIG. 6 (a) illustrates the case where the light of -1 order is blocked using the spatial filter 150, and FIG. 6 (b) illustrates the lens wavefront when the light of the +1 order is blocked using the spatial filter 150. It is a schematic block diagram of a measuring apparatus.

When the beam of -1 order is blocked using the spatial filter 150, the performance of the lens 115 can be evaluated through the interference result between the light of the zero order and the light of the +1 order.

On the other hand, when the spatial filter 150 blocks the light of +1 order, the performance of the expression of the test lens 115 in the opposite direction can be evaluated through the interference result between the light of the 0 order and the light of the -1 order. have.

As mentioned above, although this invention was demonstrated in detail using the preferable Example, the scope of the present invention is not limited to a specific Example and should be interpreted by the attached Claim. In addition, those skilled in the art should understand that many modifications and variations are possible without departing from the scope of the present invention.

The lens wavefront measuring apparatus of the present invention as described above can accurately measure the wavefront of the lens assembly as well as the lens assembly in the imaging optical system such as a camera through the measurement of the wavefront by non-axis irradiation, homogeneity and uniformity of the image through the lens It has the effect that analysis is possible.

In addition, the eccentricity of the optical system can be measured through the degree of symmetry, and the relative performance of the left and right lenses can be compared through the interference result of light rays having the same order.

In addition, by measuring the wavefront of the other spot using one spot as a reference, it is possible to relatively evaluate how much the same aberration is generated by the inspected lens with respect to the optical axis.

Claims (15)

Light source; A first collimating lens disposed in front of the light source and configured to transmit light beams emitted from the light source and convert the light beam into parallel light beams; A diffraction optical element disposed between the first collimating lens and the test lens; A second collimating lens disposed in front of the test lens and converting the light passing through the test lens into two or more parallel rays; And A measurement sensor disposed in front of the second collimating lens and irradiated with two or more parallel rays formed through the second collimating lens to interfere with each other; Lens wavefront measuring device using a diffractive optical element comprising. The method of claim 1, The first collimating lens has a positive refractive power, and the lens wavefront measuring apparatus using a diffractive optical element, characterized in that disposed in the position away from the light source by the focal length of the first collimating lens. The method of claim 1, And a light ray passing through the diffractive optical element and the test lens has a phase difference of an order of -1, 0, and +1. The method of claim 1, The second collimating lens has a positive refractive power and is disposed at a position away from the lens by a distance obtained by adding a focal length of the lens to the second collimating lens and a diffractive optical element. Lens wavefront measuring device. The method of claim 1, The second collimating lens is a lens wavefront measuring device using a diffractive optical element, characterized in that made by bonding two or more lenses of different materials. The method of claim 1, The measuring sensor is a Shark-Hartmann lens, characterized in that the wavefront measuring device using a diffractive optical element. Light source; A first collimating lens disposed in front of the light source and configured to transmit light beams emitted from the light source and convert the light beam into parallel light beams; A diffraction optical element disposed between the first collimating lens and the test lens; A spatial filter disposed in front of the lens to be examined; A second collimating lens disposed in front of the spatial filter and configured to transmit light beams passing through the spatial filter to two or more parallel beams; And A measurement sensor disposed in front of the second collimating lens and irradiated with two or more parallel rays formed through the second collimating lens to interfere with each other; Lens wavefront measuring device using a diffractive optical element comprising. The method of claim 7, wherein The first collimating lens has a positive refractive power, and the lens wavefront measuring apparatus using a diffractive optical element, characterized in that disposed in the position away from the light source by the focal length of the first collimating lens. The method of claim 7, wherein And a light ray passing through the diffractive optical element and the test lens has a phase difference of an order of -1, 0, and +1. The method of claim 7, wherein The spatial filter is a lens wavefront measuring device using a diffractive optical element, characterized in that disposed in the position where the light beam passing through the lens to be focused. The method of claim 7, wherein The spatial filter is a wavefront measuring device using a diffractive optical element, characterized in that for blocking the light of less than -1 order. The method of claim 7, wherein The spatial filter is a wavefront measuring device using a diffractive optical element, characterized in that for blocking more than +1 order of light. The method of claim 7, wherein The second collimating lens has a positive refractive power and is disposed at a position away from the lens by a distance obtained by adding a focal length of the lens to the second collimating lens and a diffractive optical element. Lens wavefront measuring device. The method of claim 7, wherein The second collimating lens is a lens wavefront measuring device using a diffractive optical element, characterized in that made by bonding two or more lenses of different materials. The method of claim 7, wherein The measuring sensor is a lens wavefront measuring device using a diffraction optical element, characterized in that the Shark-Hartman lens.

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