JP2001147174A - Interference measuring apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a measuring apparatus capable of measuring geometric information and optical information on eccentricity or the like of a combination lens or the like including an aspherical surface, in a non-destructive, contactless manner after the assembly of a lens system or the like. SOLUTION: Eccentricity of the i-surface of a tested object 1 placed in an optical path of an interferometer is obtained from the interference fringe of the optical path including the i-surface obtained by passing luminous flux through the tested object 1, and data on eccentricity obtained by calculation.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an interferometer and, more particularly, to a method for irradiating light to a test object and obtaining geometrical or optical information of the test object from the obtained interference fringes. It concerns the device and the measured object.

[0002]

BACKGROUND OF THE INVENTION The present invention relates to lenses used for various optical products such as cameras, digital cameras, microscopes, endoscopes, bar code readers, optical disk pickups, and the like, optical elements such as reflecting mirrors, combined lenses, and combined mirrors. Etc. relates to measurement, inspection, and evaluation of optical systems.

As a non-contact, non-destructive inspection method for an optical system composed of a combination lens, an assembling eccentricity measuring machine as shown in FIG. 10 has been proposed for the purpose of measuring the eccentricity of a lens (OPTRONICS (1995)). No. 3, p.
120-121).

[0004] The eccentricity measuring machine will be briefly described. Laser light from a semiconductor laser 201 as a light source is sequentially transmitted to a center of curvature of each surface of a lens 203 to be measured via a measuring optical system 202 and a beam splitter 204. Projecting
The spot image due to the reflected light is captured by the CCD 207,
The eccentricity is measured by performing image processing in the arithmetic processing unit 210 and detecting the position. At this time, in order not to rotate the lens 203 to be measured, a reference axis setting optical system 206 using an image rotator 205 is provided on the extension of the optical axis of the measuring optical system 202 divided by the beam splitter 204. Is rotated, the spot image of the luminous flux reciprocating in the reference axis setting optical system 206 is
207 rotates on the image plane. The center of rotation serves as a reference for the eccentricity, and the spot image rotating on the image plane is moved along the rotation locus.
By capturing images at points and determining these positions, determining the reference position of rotation from this, and determining the shake amount of the spherical image of each surface of the lens 203 to be measured with respect to this reference position,
Assembled eccentricity data is required.

[0005]

However, FIG.
However, the assembled eccentricity measuring instrument as shown in (1) has disadvantages such as that the accuracy is slightly poor, and that the eccentricity of each lens of the lens system including the aspherical surface cannot be determined by this measuring instrument alone.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems of the prior art, and an object of the present invention is to provide, for example, geometric information of a combination lens including an aspherical surface, for example, eccentricity after assembly of a lens system. It is intended to provide a measuring instrument capable of non-destructive, non-contact measurement. It is another object of the present invention to provide a measuring instrument capable of measuring optical information such as a refractive index.

[0007]

According to the present invention, there is provided an interferometer for achieving the above object, comprising: an interference fringe in an optical path including an i-plane obtained by passing a light beam through a test object placed in an interferometer optical path; The eccentricity of the i-plane of the test object is obtained from the data on the eccentricity obtained by the calculation.

According to the present invention, the interference pattern of the optical path including the i-plane obtained by passing the light beam through the test object placed in the optical path of the interferometer and the data relating to the eccentricity obtained by calculation are used. i
Since the eccentricity of the surface is obtained, highly accurate interference measurement can be performed. This interferometer is excellent in that it can accurately measure any one or more of geometric information or optical information such as a surface shape, a surface interval, and eccentricity of an optical system.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the interferometer of the present invention and a measuring method using the same will be described.

FIG. 1 is a diagram showing the configuration of an example of an interferometer according to the present invention, and shows eccentricity for measuring the eccentricity of each lens surface of a combined lens system 1 including an aspherical lens. It is an example of the measuring device 2.

The light emitted from the low coherence light source 3 is converted into a substantially parallel light beam by the lens 4 and enters the beam splitter 5. One light flux l split by the beam splitter 5 is
The light enters the reference mirror 6, is reflected and enters the beam splitter 5. The reference mirror 6 can move in the x direction in the figure. Another light beam m reflected downward by the beam splitter 5
Enters the lens system 1 to be measured via the lenses 7 and 8 and the variable aperture stop 9. At this time, by changing the position of at least one of the lenses 7 and 8, the light beam is made to enter the approximate spherical center of the surface i of the lens system 1 to be measured now.

The light beam reflected by the surface i is transmitted through a variable aperture stop 9
The light flux l is passed through the lenses 8 and 7 by the beam splitter 5.
And is incident on the image sensor 10.

The information from the image sensor 10 is transmitted to the electronic circuit 1
1, a personal computer 12 and a display 13 for processing.

The air-converted length of the light beam ₁ measured from the center of the beam splitter 5 is L _l , and the air-converted length of the light beam m measured from the center of the beam splitter 5 is L _m . When calculating L _m in the example of FIG. 1, a lens 8, 7, a, is multiplied by the group index n _g of each material to b each center thickness t sums, further, the sum of the air gap the may be the L _m in addition.

Assuming that the coherence length of the light from the light source 3 is S, S is measured by the full width at half maximum. When L ₁ −2S ≦ L _m ≦ L ₁ + 2S (1), the two light beams interfere with each other. , Interference fringes are formed on the image sensor 10.

Then, the reference mirror 6 is moved in the x direction,
By satisfying the expression (1), the reflected light from the surface i
The interference fringes can be received by the image sensor 10. Soshi
And L _m= L_lAt this time, the intensity of the interference fringes reaches a peak. This
From which surface the light is reflected from the position of the reference mirror 6
Can be known. And the interference fringe intensity of each surface
Knowing the position of the reference mirror 6 where
It is also possible to know the surface spacing of the optical system such as
Wear.

The signal of the image pickup device 10 is processed by the electronic circuit 11 and taken into the personal computer 12. The wavefront aberration of the wavefront at this time is defined as W _i ⁰ . 0 of the wavefront aberration W _i ⁰ is,
It represents the azimuth of the lens system 1 around the z-axis, and is a superscript and does not represent a power.

Next, the test lens system 1 is rotated by 180 degrees about the z-axis (substantially equal to the optical axis), and the interference fringes are similarly captured, and the wavefront aberration is set to _Wi ¹⁸⁰ .

ΔW _i = (W _i ⁰ −W _i ¹⁸⁰ ) / 2 (2) defines ΔW _i .

The eccentricity of the surface i around the z-axis can be determined by the
Including ε_i, Δ_iDefined by ε _iIs the inclination of the aspheric axis
In the angle, the x component is ε_xi, Y component_yihave. δ_iIs a non-sphere
The shift (translation) of the plane axis gives the X component δ_xi, Y component δ_yi
have. FIG._yi, Ε_yiThe definition was given.

The surface of the lens system 1 to be measured is, for example, a flat surface, a spherical surface, or an axisymmetric aspheric surface, but is not limited thereto.

First, consider the case where i = 1. ΔW ₁ is
The wavefront aberration caused by the eccentricity of the surface 1 with respect to the z-axis (in this example, coincides with the rotation axis of the lens system 1 to be measured) is shown. If ε ₁ = 0, δ ₁ = 0 for surface 1
If so, ΔW ₁ = 0.

[0023] Therefore, a simulation of the wavefront aberration by ray tracing program such as, by comparison with [Delta] W _1, can be obtained in the epsilon ₁ and [delta] ₁ surface 1.

For example, specifically, in a simulation
Ε of k-item Zernike aberration obtained _x1, Δ_x1, Ε_y1, Δ
_y1変 化 Z_k/ ∂ε_x1, ∂Z_k/ ∂δ_x1, ∂Z_k/ ∂ε_y1, ∂
Z_k/ ∂δ_y1 Then, ΔW_1k= ∂Z_k/ ∂ε_x1× ε_x1+ ∂Z_k/ ∂δ_x1× δ_x1 + ∂Z_k/ ∂ε_y1× ε_y1+ ∂Z_k/ ∂δ_y1× δ_y1... (3) Where ΔW_1kIs ΔW₁To Zernike aberrations
Represents the components of k items when expanded.

That is, It is.

Here, in many cases, k can be selected from 9, 16, 25, and 37.

Z _k represents a component of the Z term of the Zernike aberration. See, for example, Table 1 for the definition of each term of Zernike aberration. Table 1 Term FRINGE Zernike Polynomial 1 1 2 Rcos (A) 3 Rsin (A) 4 2R ² -1 5 R ² cos (2A) 6 R ² sin (2A) 7 (3R ³ -2R) cos (A) 8 ( ^{3R 3 -2R) sin (A)} 9 6R 4- 6R 2 +1 10 R 3 cos (3A) 11 R 3 sin (3A) 12 (4R 4 -3R 2) cos (2A) 13 (4R 4 -3R 2 ) sin (2A) 14 (10R ⁵ -12R ³ + 3R) cos (A) 15 (10R ⁵ -12R ³ + 3R) sin (A) 16 20R ⁶ -30R ⁴ + 12R ² -1 17 R ⁴ cos (4A ) 18 R ⁴ sin (4A) 19 (5R ⁵ -4R ³ ) cos (3A) 20 (5R ⁵ -4R ³ ) sin (3A) 21 (15R ⁶ -20R ⁴ + 6R ² ) cos (2A) 22 (15R ^{6 -20R 4 + 6R 2) sin} (2A) 23 (35R 7 -60R 5 + 30R 3 -4R) cos (A) 24 (35R 7 -60R 5 + 30R 3 -4R) sin (A) 25 70R 8 - 140R ⁶ + 90R ⁴ -20R ² +1 26 R ⁵ cos (5A) 27 R ⁵ sin (5A) 28 (6R ⁶ -5R ⁴ ) cos (4A) 29 (6R ⁶ -5R ⁴ ) sin (4A) 30 ( 21R ⁷ -30R ⁵ + 10R ³ ) cos (3A) 31 (21R ⁷ -30R ⁵ + 10R ³ ) sin (3A) 32 (56R ⁸ -105R ⁶ + 60R ⁴ -10R ² ) cos (2A) 33 (56R ⁸ -105R ⁶ + 60R ⁴ -10R ² ) sin (2A) 34 (126R ⁹ -280R ⁷ + 210R ⁵ -60R ³ + 5R) cos (A) 35 (126R ⁹ -280R ⁷ + 210R ⁵ -60R ³ + 5R) sin (A) 36 252R ¹⁰ -630R ⁸ + 560R ⁶ -210R ⁴ + 30R ² -1 37 924R ¹² -2772R ¹⁰ + 3150R ⁸ -1680R ⁶ + 420R ⁴ -42R ² +1 .

Therefore, by solving a total of four equations (3) for the four k's as simultaneous equations, ε _x1 , ε _y1 ,
δ _x1 and δ _y1 are obtained.

If k> 4 or more, ε ₁ and δ ₁ can be obtained with better accuracy by using the least squares method or the like.

As a method for selecting k, t of Zernike aberration
It is preferable to select an ilt term and a comma term, and k = 2, 3,..., tilt term k = 7, 8,.

Next, the eccentricities ε ₂ and δ ₂ of the surface 2 are obtained. When the azimuths of the lens system 1 around the z axis are 0 ° and 180 °, when the light beam is incident on the spherical center of the surface 2, the wavefront aberration of the light beam passing through the surface 1 and reflected by the surface 2 is reduced. W ₁₂ ⁰ ,
Expressed as W ₁₂ ¹⁸⁰ .

At this time, the eccentricity of the second surface is considered to be 0, and the eccentricity of the first surface is determined by using a known value, for example, ε ₁ and δ ₁ obtained by solving equation (3). W ₁₂ ⁰ and W ₁₂ ¹⁸⁰ are obtained by the simulation of.

ΔW ₁₂ = (W ₁₂ ⁰ −W ₁₂ ¹⁸⁰ ) / 2 (5), and ΔW ₂ ^* ΔW ₂ ^* = ΔW ₂ −ΔW ₁₂ (6) is obtained by the following equation. . Note that ΔW ₂ is obtained by setting i = 2 in the equation (2).

Next, To the Zernike function ΔW _2k . ΔW _2k is obtained by multiplying the basis function of the k-item Zernike function by a coefficient.

ΔW _2k = ∂Z _k / ∂ε _x2 × ε _x2 + ∂Z _k / ∂δ _x2 × δ _x2 + ∂Z _k / ∂ε _y2 × ε _y2 + ∂Z _k / ∂δ _y2 × δ _y2 ·・ ・ (8) holds.

Here, ∂Z _k / ∂ε _x2 is the rate of increase of Z _k when ε _x2 changes. The same applies to the definitions of other differential quantities.

The four differential amounts of the equation (8) are obtained by simulation or the like. Similarly to the case of obtaining the eccentricity of the first surface, ε ₂ and δ ₂ are obtained by solving equation (7) by simultaneously setting four or more k's. k = 2, 3, 7, 8
It is advisable to choose k to include.

Similarly, the eccentricities ε _i and δ _i of the i-plane can be obtained as follows.

W _{i-1, i} ⁰ : Simulation of wavefront aberration of a light beam incident on a spherical center of the i-plane at an azimuth angle of 0 °, passing through the 1st to i-1 planes, and reflected by the i-plane. value. At this time, the eccentricity of the 1st to i-1th planes is assumed to be known and is considered at the time of simulation.

W _{i-1, i} ¹⁸⁰ : A luminous flux is incident on the spherical center of the i-plane at an azimuth of 180 °, passes through the 1st to i-1 planes, and
Simulation value of wavefront aberration of the light beam reflected by the surface. At this time, the eccentricity of the 1st to i-1th planes is assumed to be known and is considered at the time of simulation.

ΔW _{i−1, i} = (W _{i−1, i} ⁰ −W _{i−1, i} ¹⁸⁰ ) / 2 (9) ΔW _i ^* = ΔW _i −ΔW _{i−1, i.}・ (10) ΔW _ik represents a component of k items when ΔW _i ^* is expanded to Zernike aberration.

ΔW _ik = ∂Z _k / ∂ε _xi × ε _xi + ∂Z _k / ∂δ _xi × δ _xi + ∂Z _k / ∂ε _yi × ε _yi + ∂Z _k / ∂δ _yi × δ _yi · (12) ∂Z _k / ∂ε _xi : the rate of increase of Z _k when ε _xi changes,
It is determined by simulation or the like.

∂Z _k / ∂δ _xi : When δ _xi changes, Z _k
Is calculated by simulation or the like.

∂Z _k / ∂ε _yi : Z _k when ε _yi changes
Is calculated by simulation or the like.

∂Z _k / ∂δ _yi : Z _k when δ _yi changes
Is calculated by simulation or the like.

As in the case of one surface and two surfaces, four or more k
By solving equations (12) simultaneously, ε _i ,
δ _i is obtained. It is preferable to select k so as to include k = 2, 3, 7, and 8.

[Second Embodiment] This embodiment can also be applied to a case where the test object is a rotationally asymmetric surface. Although this embodiment is also described with reference to FIG. 1, the test lens system 1 does not rotate around the z-axis, and therefore is superior to the example of FIG. 1 in that the test object is easily held. And the folding method is different from the case described above.

The definitions of characters and expressions are as described above. First, the eccentricity of the first surface is determined.

[0049] Here, W _1k is a component when the expansion of W ₁ ⁰ to Zernike aberrations.

Ε ₁ and δ ₁ are obtained by the equation (3).

Next, how to determine the eccentricity of the i-plane will be described. When the azimuth angle is 0 °, the value of the wavefront aberration generated from the first surface to the i-th surface when the light beam is incident toward the spherical center of the i-th surface is W _{i−1, i}
Expressed as ⁰ .

W _{i−1, i} ⁰ is obtained by simulation in consideration of the known eccentricity of the first to i−1 planes. At this time, the eccentricity of the first surface is left as 0. The light beam is considered to be reflected on the i-th surface. Then, ΔW _i ⁰ = W _i ⁰ −W _{i-1, i} ⁰ (14) is set. If the i-th surface is not eccentric, ΔW _i ⁰
Becomes 0. Expand ΔW _i ⁰ into Zernike coefficients, Then, the next derivative is obtained by simulation.

[0053] ^{_{∂ΔW ik 0 / ∂ε xi, ∂ΔW}} ik 0 / ∂
δ _xi , ∂ΔW _ik ⁰ / ∂ε _yi , ∂ΔW _ik ⁰ / ∂δ _yi, and ε _xi , δ _xi , ε _yi , δ _yi are used as unknowns to solve the following simultaneous equations.

[0054] _{^{ΔW ik 0 = ∂ΔW ik 0 /}} ∂ε xi × ε xi + ∂ΔW ik 0 / ∂δ xi × δ xi + ∂ΔW ik 0 / ∂ε yi × ε yi + ∂ΔW ik 0 / ∂δ _yi × _δyi (16) Here, four or more different values of k are required. Similarly, in the case of the first surface, it is preferable to select four of k = 2, 3, 7, and 8.

Ε _xi , ε _yi , δ _xi , δ _yi can be obtained by solving equation (16) by simultaneously setting four or more than four k's, or by the method of least squares.

It should be noted that, as is common to all the embodiments, when the i-plane is a spherical surface, ε and δ become ε = δ /
Since they are linked by the relationship of R _i , it is only necessary to solve equations (12) or (16) by simultaneously setting two or two or more k. Here, R _i is the radius of curvature of the i-plane.

Compared to the first embodiment, in this example, since there is no relative position change due to the rotation of the lens to be inspected and the eccentricity measuring machine, the influence of deformation of the object to be inspected is small, and a more accurate measurement is possible. Can be.

[Third Embodiment] A third embodiment of the present invention will be described. The configuration of the measuring instrument is the same as, for example, FIG. 1 or the second embodiment.

First, the eccentricity of the first surface is determined. [Delta] W ₁ (or, W ₁ ⁰⁾ to match the wavefront aberration calculated in simulation, epsilon _1, selects the [delta] _1. Using ε ₁ and δ ₁ as variables, ΔW ₁ (or,
W ₁ ⁰⁾ to repeat the simulation so wavefronts match, epsilon _1, determines a [delta] _1.

Next, the eccentricity ε of the i-th surface_i, Δ_iHow to find
To explain, the eccentricity ε up to the i-1 plane _j, Ε_jIs known
(J = 1, 2,..., I−1), ε_i, Δ_iThe variable
And the observed ΔW₁(Or W₁ ⁰) To simulate
Adjust the wavefront aberration obtained in the section. Ε when combined_i,
δ_iIs the eccentricity of the i-plane. At this time, the i-1 plane
Since the eccentricity of each surface at has already been set,
Use that value when

By repeating this process, the eccentricity of all surfaces is obtained. FIG. 3 shows a flowchart applicable to the above procedure. That is, in step ST1, the interference fringes of the lens system 1 to be measured including the i-plane are measured. On the other hand, in step ST2, the interference fringes on the i-th surface are simulated using the eccentricity data from the first surface to the i-1th surface with ε _i and δ _i as variables. In step ST3, the interference fringes measured in step ST1 are compared with the interference fringes obtained in the simulation in step ST2, and when both the interference fringes match, ε _i and δ _i at that time are regarded as the eccentricity of the i-plane. (Step ST5).
If the two interference fringes do not match in step ST3, the process returns to step ST2 to perform simulation by changing ε _i and δ _i, and continues until both interference fringes match in step ST3.
After calculating the eccentricity of the specific i-plane in steps ST1 to ST4, it is verified whether or not the eccentricity of all the planes has been calculated in step ST5, and the steps ST1 to ST5 are continued until completion.

When ε _j and δ _j are obtained by simulation, they are obtained by the methods of the first and second embodiments (that is,
Ε _i , δ _i were obtained by solving simultaneous equations using differential quantities such as ∂ΔW _ik ⁰ / ∂ε _xi, etc.), and ε _i , δ _i were slightly reduced. The wavefront may be simulated while being changed, and ε _i and δ _i may be determined so as to reproduce the observed wavefront.

Alternatively, _j ε _i , δ _i (i = 1, 2,..., J) are simultaneously optimized so that the wavefront obtained by the simulation matches ΔW _j (or W _j ⁰ ). You may.

FIG. 4 is a view showing an example in which a free-form surface prism 51 is placed in the optical path of a Mach-Zehnder interferometer 50 as a test object. Reference numerals 52, 53, 54 and 55 are mirrors, and use the laser 16 as a light source. Other symbols are the same as those in FIG. Mach-Zehnder interferometer 50
Let W _T be the transmitted wavefront obtained in. Free-form surface prism 5
Simulation of the transmitted wavefront is performed using the eccentricity of each surface (lateral deviation and inclination error of each surface from the design value) as a variable,
By approaching W _T , the eccentricity of each surface can be obtained.

In the case where the i-plane is a spherical surface, the degree of freedom of eccentricity is two per plane as described above, so one of ε _i and δ _i may be obtained.

Although the four analysis methods have been described above, they may be used in combination. That is, for example, the i-th plane is obtained by the method of the first embodiment, the i + 1-th plane to the j-th plane is obtained by the method of the second embodiment, and the j + 1-th plane to the n-th plane is obtained by the third embodiment. The method may be used. Further, the method of the fourth embodiment may be used in combination.

If the eccentricity of some surfaces is known by some method, the method of the present invention may be applied only to the surface of which eccentricity is unknown.

As can be said in common with the embodiments described above, a laser light source may be used as the light source 3. This is because interference fringes on different surfaces of the test lens system 1 may be seen at the same time and may not be an obstacle.

If the coherence length of the light source 3 is long, the reference mirror 6 may be a fixed mirror. Because the coherence length is long, interference fringes can be seen even when the reference mirror 6 is fixed.

When the light source 3 is a semiconductor laser, a cylindrical member 14 may be provided between the light source 3 and the lens 4 or after the lens 4 to correct astigmatism, as shown in FIG.

Instead of moving at least one of the lenses 7 and 8, it may be replaced with a variable focus lens and the incident light may be made incident on the spherical center of each surface. As the varifocal lens, a lens using liquid crystal, a lens using a spatial modulator, or the like can be used. Since there is no mechanically movable part, there is a merit that accuracy is improved.

When a low coherence light source is used as the light source 3, specifically, a light source such as an SLD (super luminescent diode), an LED, a halogen lamp, or the like combined with a band-limiting filter may be used.

Hereinafter, the configuration of the measuring instrument will be described.

FIG. 5 is a diagram showing the configuration of an eccentricity measuring device 15 using a Fizeau interferometer according to an example of the present invention. Light emitted from the laser 16 is expanded by the beam expander 17 and enters the beam splitter 5.

The light beam directed downward by the beam splitter 5 is partially reflected by the reference surface 18 and travels upward as reference light. The light beam having passed through the reference surface 18 enters the image rotator 19, and enters the lens system 1 via the lens 7. The light beam reflected by the i-plane of the test lens system 1 travels in the opposite optical path, interferes with the reference light when passing through the beam splitter 5, and forms an interference fringe on the image sensor 10 through the lens 20.

The wavefront is obtained from the interference fringes by using the phase shift method, and ε _i and δ _i are obtained therefrom by using the above-described method. The difference is that the rotator 19 is rotated, and accurate measurement can be performed because the lens system 1 is not rotated. Alternatively, the image rotator 19 may be removed, and the analysis method of the second or fourth embodiment may be used.

As can be said in common with the examples described above, instead of moving the lenses 7 and 8, the lens system 1 to be inspected is moved back and forth in the z direction, and the spherical center or approximate spherical center of each surface is moved. May be made to enter light. A variable focus lens 21 may be used as 8 in FIG. 4 and 7 in FIG.

FIG. 6 shows still another example of the measuring instrument of the present invention, in which a variable focus lens using a spatial light modulator 21 is used instead of moving one of the lenses 7 and 8 having the structure of FIG. The eccentricity measuring machine 23 was used.

The spatial light modulator 21 is, for example, as shown in a plan view of FIG. 7, in which elements capable of transmitting or not transmitting light are arranged in a matrix and is controlled by the personal computer 12. And, as shown in FIG.
By forming a concentric black and white pattern such as a Fresnel zone plate, it can function as a lens. If the pitch of the black-and-white pattern is made fine, it acts as a lens with high power, and if the pitch of the pattern is made coarse, it acts as a lens with low power. A liquid crystal lens or the like may be used as the varifocal lens.

Since there are fewer movable parts than in the example of FIG. 1, there is a merit that measurement accuracy is improved. When a light source having a long coherence length, such as a laser, is used as the light source 3, the reference mirror 6 can be further fixed, thereby improving the accuracy. In addition, the test lens system 1 may or may not be rotated around the z-axis.

When the lens is not rotated, distortion of the lens system to be inspected can be reduced and accurate measurement can be performed.

In the embodiments of FIGS. 5 and 6, to determine the eccentricity of each surface from the interference fringes, one of the methods of the first to fourth embodiments of the present invention, or a combination of two or more of them. do it.

Also, as can be said in common with the embodiments described above, the incident light to the lens system 1 to be inspected is always incident on the spherical center of each surface if interference fringes on each surface can be observed. It is not necessary. This is because ε _i and δ _i can be obtained by simulation or the like if the path of the light ray is known. The varifocal lens 21 may be provided on the side of the reference optical path l. Alternatively, it may be provided on both the optical paths l and m.

FIG. 8 shows a measuring instrument according to another embodiment of the present invention.
It is an example of an aspherical surface measuring device 70. The non-contact length measuring device using low coherence interference shown in the first embodiment is incorporated in the Fizeau interferometer so that the distance between the measured aspheric surface 71 and the reference spherical surface 73 can be measured coaxially. This length measuring optical system may be replaced with another length measuring system (for example, a glass scale, a magne scale, etc.).

In the figure, reference numeral 74 denotes a solid-state image sensor having a large number of pixels. The light emitted from the laser 16 is expanded by the beam expander 17, reflected by the half mirror 75, passes through the lens 76 and the reference spherical surface 73, and passes through the sample lens 72.
Is incident on the aspheric surface 71 to be measured. The luminous flux reflected by the measured aspheric surface 71 is divided into a lens 76, half mirrors 75 and 77,
The light passes through the imaging lens 20 and interferes with the light beam reflected by the reference spherical surface 73 to form an interference fringe on the solid-state imaging device 74.

The phase is obtained from the interference fringes by the personal computer 78 using the phase shift method, and the result is displayed on the display 79.

The light source 3 is used for the length measuring optical system. As the light source 3, an SLD, LED, halogen lamp or the like having a short coherence length is used. A light beam from a light source 3 passes through a lens 4 and is split into two by a beam splitter 5, one of which is incident on a reference mirror 6 as reference light, is reflected, and is reflected by an image pickup device 10
Incident on.

The light traveling to the left in the figure by the beam splitter 5 passes through the lens 7, the half mirrors 77 and 75, the lens 76, the reference spherical surface 73 as the measuring light, is reflected by the aspheric surface 71 to be measured, and passes through the opposite optical path. As described above, the light is reflected by the beam splitter 5 and interferes with the reference light to form an interference fringe on the image sensor 10.

From the measured aspheric surface 71 to the beam splitter 5
The optical path length L _m to the center of the optical path length from the reference mirror 6 to the center of the beam splitter 5 and L _l, the interference fringes are observed on the imaging device 10 when satisfying the formula (1), L _m = At L ₁ , the intensity of the interference fringes peaks.

Therefore, by moving the position of the reference mirror 6 to know the position where the interference fringe peaks, the reference spherical surface 7 is obtained.
The distance between 3 and the aspheric surface 71 to be measured can be known. Then, since the distance between the measuring device 70 and the measured aspheric surface 71 is known, the absolute shape of the measured aspheric surface 71 can be obtained.

That is, since the measurement can be performed up to the second order term of the wavefront, the absolute shape of the measured aspheric surface 71 can be measured. This is an advantage of this embodiment as compared with a normal Fizeau interferometer.

When measuring an aspherical surface, distortion may occur in the interference fringes, and the correspondence between the phase obtained from the interference fringes and the aspherical shape may be lost. In this case, the personal computer 78 may correct the distortion. In order to make this correction, it is only necessary to know the distortion generated by performing ray tracing, and to deform the shape of the interference fringe in order to correct the distortion.

Since an image obtained by the image pickup device 10 can roughly see interference fringes, when a solid-state image pickup device 74 and a device such as a digital camera that cannot see moving images are used as the electronic circuit 11, the image pickup device 10 Is preferably used as a finder.

To perform the phase shift, a part of the optical system may be moved by using a piezoelectric element or the like to change the optical path length. However, when a digital camera is used, as shown in FIG. A plurality of digital cameras 80, 81, and 82 may be used to sequentially shoot images. By doing so, 1
Data transfer time can be saved as compared with the case where one digital camera is used.

By moving the position of the sample lens 72 back and forth with respect to the measuring device 70, the interference fringes on the lower surface of the aspheric surface 71 to be measured can be seen, and the method of the first and second embodiments can be seen. Thus, the eccentricity of each surface of the sample lens 72 can be obtained.

By using the length measuring optical path as in the first embodiment, the surface interval of the sample lens 72 can be measured.

As can be said to be common to all measuring apparatuses using interference of the present invention, it is preferable to use solid-state imaging devices 10, 74, etc., which capture interference fringes, having a large number of pixels.
This is because if the aspherical lens is in the object to be measured, the pitch of the interference fringes becomes extremely fine, and the solid-state imaging device with a small number of pixels cannot correctly capture the interference fringes.

Specifically, 250,000 pixels or more, preferably 3
It is preferable to use a solid-state imaging device having 80,000 pixels or more, or 500,000 pixels or more. It is also possible to use a solid-state image sensor for a high-definition television camera or the number of solid-state images for a digital camera. In these, since the number of pixels exceeds 700,000 to 1,000,000, good measurement can be performed. A high-definition camera or a digital camera itself may be used by combining the electronic circuit and the solid-state imaging device. When the interference fringes are taken into a personal computer, the number of pixels to be sampled is preferably 250,000 pixels or more, preferably 500,000 to 1,000,000 pixels. In addition,
Here, a television such as a BS digital television and a terrestrial digital television, which can obtain a higher-precision image than the NTSC and PAL systems, is called a high-vision television.

[0099] the number of pixels of the solid-state imaging device 10,74 is N _x ×
Let _Ny . N _x is the number of pixels in the horizontal direction, N _y is the number of pixels in the vertical direction. Consider a case where an aspheric surface is measured using an interferometer. When considered within the range of the luminous flux at the time of measurement, the best-fit reference spherical surface or the best-fit reference aspheric surface is used as the reference surface of the measured aspheric surface, and the maximum deviation from the reference surface is Δ. Expressed as _M. the wavelength of light used for lambda, and the refractive index of the object in the n [lambda lambda, when observing the wavefront of the light beam reflected by the test _{surface, Δ M <2 · λ /} 2 · N x / 2 · to become _{·· (17) Δ M <2} · λ / 2 · N y / 2 ··· (18). This is because if the number of interference fringes is large, the solid-state imaging devices 10 and 74 cannot capture an image.

[0100] In the case of transmission wavefront, the delta _M wavefront (reference wavefront) as a reference, is representative of the difference between the maximum of the wave front of the wave front passing through the test object. Equations (17) and (18) allow for some margin.

As the reference surface, a reference aspherical surface made by grinding metal or glass, or a spherical surface made by polishing can be used.

Further, the interval between the finest interference fringes (the interval between bright fringes next to the bright fringes) on the imaging surface of the solid-state imaging devices 10 and 74 is P _F , and the larger one pixel of the solid-state imaging devices 10 and 74 is larger. Assuming that _Px (horizontal direction) and _Py (vertical direction), it is desirable that P _F ≦ 2P _x (19) P _F ≦ 2P _y (20) Equations (19) and (2)
If 0) is not satisfied, interference fringes cannot be resolved by the solid-state imaging device, moiré fringes occur, and accurate measurement cannot be performed.

As can be said in common with the present invention, in the examples of FIGS. 1, 5, 6, 8, and 9, interference fringes on each surface of the optical system are observed. Can be obtained to obtain the surface shape and the eccentricity of the surface.

Further, in the examples shown in FIGS. 1, 6, 8, and 9, since a length measuring function is also provided, a surface interval can be measured. Further, when the surface interval t is known, _ng can be obtained by dividing the optical path length d between the two surfaces by t. If the interference fringes are analyzed using the thus obtained surface spacing to determine the eccentricity of the surface or the shape of the surface, the accuracy may be further improved. d and _ng are one of optical information. t, eccentricity, surface shape, and the like are pieces of geometric information.

The test object is not limited to the surface of an optical element such as a lens surface, but may be the surface of a solid-state image sensor or a film surface of a film camera, a pressure plate, each surface of a liquid crystal display, a thin film, a metal, a synthetic resin, or the like. It can be used to measure the inclination of a glass surface, the boundary surface of animal tissue, etc., surface position, surface spacing, refractive index, and the like.

The above-described interferometer of the present invention and a method for obtaining geometric or optical information of a test object from interference fringes obtained therefrom, an apparatus therefor, and a measured object are as follows, for example. Can be configured.

[1] A method or an apparatus or a measured object in which light is incident on the object and geometrical or optical information of the object is obtained from the obtained interference fringes.

[2] A method, apparatus, or measured object in which light is incident on the object and at least one of the eccentricity, the surface shape, and the surface interval of the object is obtained from the obtained interference fringes.
[3] A method or a device that irradiates light to a test object and determines eccentricity of the test object from the obtained interference fringes, or a measured object.

[4] A method or an apparatus for determining the eccentricity of the test object from the interference pattern obtained by irradiating light to the test object placed in the optical path of the interferometer and the calculated eccentricity, or What was measured.

[5] A method or apparatus for determining the eccentricity of the test object from the interference fringes of the obtained surface and the data relating to the eccentricity calculated by passing a light beam through the test object placed in the optical path of the interferometer Or the measured object.

[6] From the interference fringe of the optical path including the i-plane obtained by passing the light beam through the test object placed in the interferometer optical path and the data on the eccentricity calculated, the i-plane of the test object is determined. A method or device for determining eccentricity or a measured object.

[7] From the interference fringes of the optical path including the i-plane obtained by passing the light beam through the test object placed in the interferometer optical path, the eccentricity of the known plane, and the data on the eccentricity obtained by calculation. A method or apparatus for determining the eccentricity of the i-plane of a test object or a measured object.

[8] Interference fringes in the optical path including the i-plane obtained by passing a light beam through the test object placed in the interferometer optical path, eccentricity up to the known i-1 plane, and eccentricity calculated A method or apparatus for determining the eccentricity of the i-plane of the test object from the data relating to the test object or the measured object.

[0114]

[9] A method or apparatus for passing a light beam through an object placed in the optical path of the interferometer and obtaining the eccentricity of the i-plane of the object from the obtained interference fringes including the i-plane and the differential data relating to the eccentricity; What was measured.

[10] The luminous flux is passed through the test object placed in the optical path of the interferometer, and the eccentricity of the i-plane of the test object is obtained from the obtained information on the interference fringe including the i-plane and the simulation on the wavefront. Method or device or measured object.

[11] Formulas (4), (7), (11),
(13) A method or apparatus for determining the eccentricity according to any one of the above (5) to (10), which uses any one of (13) and (15), or a measured object.

[12] Equations (3), (12) and (16)
11. A method, apparatus, or measured object for determining the eccentricity according to any one of the above items 5 to 10, which uses any one of the above.

[13] A method, apparatus, or measured object for determining the eccentricity of a test object from a transmitted wavefront of the test object placed in the optical path of the interferometer and a simulation related to the wavefront.

[14] The method or apparatus according to any one of [1] to [13], wherein a part of the test object is axisymmetric, or a measured object.

[15] The method, apparatus or measured object according to any one of the above items 1 to 13, characterized in that the light beam passes near the optical axis of the test optical system.

[16] The method or apparatus according to any one of [1] to [13], or an object measured, wherein the test optical system is a combination lens.

[17] The method or apparatus according to any one of [1] to [13], or a measured object, wherein the test optical system includes an aspherical surface.

[18] A method for obtaining at least one of the eccentricity, the surface shape, and the surface interval of any one of the above items 1 to 17 wherein at least a part of the interferometer or the object moves during measurement. Or a device or measured object.

[19] The eccentricity or the eccentricity of the test object according to any one of the items 1 to 18, wherein the test object and the interferometer or a part of the interferometer do not relatively rotate during measurement. A method or apparatus for determining at least one of a surface shape and a surface interval or a measured object.

[20] Any one of the above items 1 to 19, wherein the test object and at least a part of the interferometer relatively rotate during measurement.
The method or apparatus for determining at least one of the eccentricity or the surface shape or the surface interval of the test object in the item, or the measured object.

[21] A method, apparatus, or measured object for obtaining geometric or optical information of the test object according to any one of the above items 1 to 20, which has an image rotator.

[22] A method, apparatus, or measured object for obtaining geometric or optical information of the object according to any one of the above items 1 to 20, using a low coherence light source.

[23] The above 1 using a variable focus lens
23. A method or apparatus for determining geometrical or optical information of a test object according to any one of to 22 or a measured object.

[24] A method, apparatus, or measured object for obtaining geometric or optical information of a test object according to any one of the above items 1 to 22, using a spatial light modulator.

[25] The above 1 using a digital camera
23. A method or apparatus for determining geometrical or optical information of a test object according to any one of to 22 or a measured object.

[26] A method, apparatus, or measured object for obtaining geometric or optical information of a test object according to any one of the above items 1 to 22, using a high-vision solid-state imaging device.

[27] A method or apparatus for obtaining geometric or optical information of the test object according to any one of the above items 1 to 22 using a solid-state imaging device having 500,000 or more pixels or a measured object. .

[28] The geometric or optical information of the test object according to any one of the above items 1 to 20, using a solid-state imaging device having 50 or more pixels satisfying the formulas (17) and (18). Method or device for measuring or measured object.

[29] The geometrical or optical information of the test object according to any one of the above items 1 to 20, using a solid-state imaging device having 50 or more pixels satisfying the equations (19) and (20). Method or device for measuring or measured object.

[30] A method or apparatus for determining geometric or optical information of a test object according to any one of the above items 1 to 29, wherein the distortion of the interference fringes is corrected by calculation. Thing.

[31] The method or apparatus for obtaining geometric or optical information of a test object or the measured object according to any one of the above items 1 to 30, which includes a system for measuring the length.

[32] The method or apparatus for determining the shape of a test object or the measured object according to any one of the above items 1 to 27, characterized by including an optical system for length measurement.

[33] The object of any one of the above items 1 to 27, wherein the optical system for measuring the length and the optical system for measuring the shape at least partially share the same optical element. A method or device for determining the shape or a measured object.

[34] Any one of the above items 1 to 27, wherein the optical system for measuring the position of the test object at the time of measurement and the optical system for measuring the shape share at least one optical surface. The method or apparatus for determining the shape of the test object or the measured object.

[35] A method or apparatus for measuring the eccentricity of a test object from a transmitted wavefront or a reflected wavefront of an eccentric optical system or a free-form surface optical system placed in an optical path of an interferometer and a simulation of the wavefront, or a measured object. .

[36] The eccentricity or surface shape of the test object according to any one of the above items 1 to 17, wherein the data of the surface distance of the test object obtained by the measurement is used in the analysis of interference fringes. Or a method or apparatus for determining any one or more of the surface intervals or a measured object.

[0142]

As described above, according to the present invention,
Highly accurate interferometry can be obtained. The interferometer according to the present invention is excellent in that it can accurately measure any one or more of geometric information or optical information such as a surface shape, a surface interval, and eccentricity of an optical system.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of an example of an interference measuring apparatus according to the present invention.

FIG. 2 is a diagram showing definitions of δ _yi and ε _yi .

FIG. 3 is a flowchart for determining the eccentricity of a surface according to a third embodiment of the present invention.

FIG. 4 is a diagram showing a configuration in which an interferometer according to the present invention is configured by a Mach-Zehnder interferometer and a free-form surface prism is used as a test object.

FIG. 5 is a diagram showing a configuration of an eccentricity measuring machine using a Fizeau interferometer of the present invention.

FIG. 6 is a diagram showing a configuration of still another interferometer of the present invention.

FIG. 7 is a plan view of a spatial light modulator used as a variable focus lens in the interferometer of FIG. 6;

FIG. 8 is a diagram showing a configuration of an aspherical surface measuring device according to another embodiment of the present invention.

FIG. 9 is a diagram illustrating a configuration obtained by adding a configuration for a phase shift method to the configuration of FIG. 8;

FIG. 10 is a diagram showing a configuration of a conventional assembled eccentricity measuring machine.

[Explanation of symbols]

 a, b, c, d, e: Lens 1: Test lens system (combination lens system) 2: Decentering measurement device 3: Coherence light source 4: Lens 5: Beam splitter 6: Reference mirror 7, 8, Lens 9: Opening Variable aperture 10 ... Solid-state imaging device 11 ... Information processing electronic circuit 12 ... PC 13 ... Display 14 ... Cylindrical 15 ... Eccentricity measuring machine 16 ... Laser 17 ... Beam expander 18 ... Reference plane 19 ... Image rotator 20 ... Shooting lens 21 ... Spatial light Modulator 50 ... Mach-Zehnder interferometer 51 ... Prism to be tested (free-form surface prism) 52,53,54,55 ... Mirror 70 ... Aspherical measuring machine 71 ... Aspherical to be measured 72 ... Sample lens 73 ... Reference spherical surface 74 ... Solid-state imaging device 75: half mirror 76: lens 77: half mirror 78: personal computer 79: disk Leh 80, 81, 82 ... digital camera

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2F064 AA06 AA09 BB04 BB05 EE04 EE05 FF01 FF03 FF05 FF07 GG12 GG13 GG22 GG41 GG47 HH03 HH08 JJ01 2F065 AA07 AA31 AA45 AA53 BB05 CC21 GG02 GG04 GG02 GG05 GG05 LL10 LL12 LL21 LL30 LL46 LL47 NN08 PP05 PP13 QQ13 QQ17 QQ18 QQ25 QQ27 2G086 FF04

Claims (3)

[Claims] 1. An eccentricity of an i-plane of an object based on interference fringes of an optical path including an i-plane obtained by passing a light beam through an object placed in an interferometer optical path and data on eccentricity obtained by calculation. An interferometer that is characterized by obtaining 2. The number of pixels satisfying the equations (17) and (18) is 5
2. The interferometer according to claim 1, wherein a solid-state imaging device having zero or more pixels is used. Δ _M <2 · λ / 2 · N _x / 2 (17) Δ _M <2 · λ / 2 · N _y / 2 (18) where N _x is the horizontal direction of the solid-state imaging device. Number of pixels, N _y
The number of pixels in the vertical direction of the solid-state imaging device, delta _M is the maximum amount of deviation from the reference plane of the surface to be measured, the wavelength of lambda is used light, is nλ is the refractive index of the object in lambda. 3. The interferometer according to claim 1, further comprising an optical system for measuring a length.