JP2001235317A - Apparatus for measuring radius of curvature of optical spherical surface - Google Patents

Abstract

PROBLEM TO BE SOLVED: To measure the radius of curvature of an optical spherical surface with accuracy of a submicron order and by means of a compact and simple device constitution by employing the idea of techniques for measuring steps in a plane while using a variable wavelength laser as a light source, and adopting a cat's-eye technique. SOLUTION: This apparatus comprises a source 1 of variable wavelength laser beams, a half prism 20, a collimator lens 6, a second reference lens 5R causing the laser beam to impinge on the reference surface 5a (concave spherical surface) of the first reference lens 5F of a reference lens portion 5 at approximately right angles so that the laser beam exits the reference surface 5a at approximately right angles, a reflector 7 having a reflecting plane at the focal position of the second reference lens 5R, a light intensity detecting means 9 for detecting the intensity of light interference occurring between the laser beam LA normally reflected by the reflecting plane and the laser beam LB coming from the source 1 and reflected at a position 5b where it re-impinges on the reference surface 5a at right angles, a Fourier transform means 10 for measuring the frequency n of variation in light intensity through a Fourier transform, and a radius-of-curvature calculating means 11 for calculating the radius of curvature R of the reference surface 5a on the basis of the frequency n.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical spherical radius of curvature measuring device for measuring the radius of curvature of an optical spherical surface with high accuracy. More specifically, the present invention relates to a variable wavelength light source having coherence as a measuring light source, a lens surface and the like. The present invention relates to an optical spherical curvature radius measuring device for measuring the radius of curvature of an optical spherical surface with extremely high precision using an interference technique.

[0002]

2. Description of the Related Art In recent years, it has become increasingly necessary to measure the shape of a curved surface of an object with an interferometer device with high accuracy, and reference is made in accordance with the curved surface shape of the object. It is necessary to measure the reference surface of the reference lens used for the measurement with high accuracy and simply.

[0003] It is difficult to measure the radius of curvature of the lens surface of such a reference lens with high accuracy on the order of submicrons, and it has been a conventional method to use a high-precision length measuring device. Inevitably increases the size and complexity of the device.

SUMMARY OF THE INVENTION The present invention has been made in view of such circumstances, and provides a compact and simple optical radius of curvature measuring apparatus capable of measuring the radius of curvature of an optical spherical surface with high accuracy on the order of submicrons. It is intended for.

[0005]

According to the present invention, there is provided an optical spherical curvature measuring apparatus for measuring the radius of curvature of a concave optical spherical surface of a subject, comprising: a light source capable of changing the wavelength of output light with time; The light beam incident along the optical axis such that a part of the light beam from the light source is vertically reflected by the optical spherical surface and the remaining light is vertically emitted from the optical spherical surface. A convergent lens that causes the subject to enter the subject at a predetermined angle, and a reflecting surface disposed perpendicular to the optical axis of the optical system at a focal position of an optical system including the convergent lens and the subject, Light intensity detecting means for detecting a change in the intensity of light interference generated between the light vertically reflected by the optical spherical surface and the light reflected by the reflecting surface and re-entered perpendicularly to the optical spherical surface; and The circumference of the light intensity change detected by the light intensity detection means Fourier transform means for measuring the number n, and curvature radius calculation means for determining the radius of curvature R of the optical spherical surface based on the measured frequency n of the change in light intensity, the reference wavelength λ of the output light, and the change width Δλ of this wavelength. It is characterized by having.

Further, it is preferable that the curvature radius calculating means obtains the curvature radius R using the following equation (2). R = 1 / {2 (1 / n) × (Δλ / λ ² )} (2) Preferably, the light source is a laser light source. Further, the method of the present invention is particularly effective when the optical spherical surface of the subject is a reference surface of a reference lens used in an interferometer.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An optical spherical radius of curvature measuring apparatus according to one embodiment of the present invention will be described below with reference to the drawings. FIG. 1 shows an optical spherical radius of curvature measuring apparatus according to the present embodiment. In the present embodiment,
Reference surface of a reference lens used for an interferometer device with an optical spherical surface
(Concave surface) will be described as an example.

This optical spherical radius of curvature measuring apparatus is a wavelength tunable laser light source 1 capable of changing the wavelength of output light with time.
A half prism 20 that reflects the laser light from the light source 1 to the side, a collimator lens 6, and a laser light that reflects the laser light from the reference surface 5 a of the first reference lens 5 F (the concave spherical surface; A second reference lens 5R for causing the laser light to enter the reference surface 5a substantially perpendicularly so that the laser light is emitted perpendicularly from the concentric surface; and a reference lens portion at the focal position of the reference lens portion 5. and the reflector 7 having arranged reflecting planes so as to be perpendicular with respect to the fifth optical axis, the laser beam L _a, which is regularly reflected by the reflecting plane, perpendicular to the laser beam L _a is the reference surface 5a and light intensity detecting means 9 for detecting the intensity change of light interference occurs between the _(only part of the optical path in the drawing) the laser beam L _B from the light source 1 is reflected at a position 5b re-entering, this Detected by light intensity detecting means 9 Fourier transform means 10 for measuring the frequency n of the light intensity change by Fourier transform, and the reference surface 5a based on the measured frequency n of the light intensity change, the reference wavelength λ of the output light, and the change width Δλ of this wavelength. It comprises a radius-of-curvature calculation means 11 for obtaining a radius of curvature R.

The tunable laser light source 1 comprises tunable means such as a combination of a laser diode and an AOM. Further, both surfaces of the first reference lens 5F are substantially concentric spherical surfaces, and their center positions coincide with the reflection points of the reflector 7. In addition, since both surfaces of the first reference lens 5F are substantially concentric spherical surfaces, they coincide with the focal position of the second reference lens 5R.

In the present embodiment, the optical fiber 21 and the objective lenses 22A, 22B, and 22C are disposed between the wavelength tunable laser light source 1 and the half prism 20, but the wavelength tunable laser light source 1 When the distance from the prism 20 is short, the optical fiber 21 is unnecessary. Note that an imaging lens 23 is disposed between the half prism 20 and the light intensity detecting means 9.

The light intensity detecting means 9 may be any one which can read out the temporal change of the light intensity at a high speed, and may be, for example, a CCD imaging camera. Further, the Fourier transform means 10 and the curvature radius calculating means 11
Is generally configured as software in a computer.

The radius of curvature R is obtained by the above-mentioned radius of curvature calculation means 11 using the following equation (3). R = 1 / {2 (1 / n) × (Δλ / λ ² )} (3)

By the way, it has conventionally been difficult to easily measure the radius of curvature of the reference surface of the interferometer reference lens in accordance with the curved surface shape of the subject with high accuracy on the order of submicrons. In view of such circumstances, the present inventor, as a result of trial and error, can measure easily and with high accuracy by applying a method of measuring a step of a plane using a tunable laser as a light source to a radius of curvature of an optical spherical surface. Was found.

That is, a method of measuring a step on a plane using a wavelength-variable laser as a light source is to irradiate a beam from a wavelength-variable laser light source to a surface to be measured having a step to generate a step. The interference light generated by the two reflected light beams from the two planes is set so that it can be detected, and then the wavelength of the beam can be scanned by Δλ from the reference wavelength λ. (Fast Fourier Transform) and a step is obtained based on this frequency.

The value of the step measured using the wavelength tunable laser as described above has extremely high accuracy, and the configuration of the apparatus is extremely simple. Therefore, the present invention, which is inspired by the technique of measuring the level difference of a plane using a wavelength tunable laser as the light source, can also have a highly accurate and simple device configuration.

The operation of the above embodiment will be described below.
You. Laser light from the tunable laser light source 1 is collimated
The light is collimated by the lens 6 and is collimated by the second reference lens 5R.
From the reference surface 5a of the first reference lens 5F.
It is emitted directly and is specularly reflected on the reflection plane of the reflector 7,
Thereafter, the position is shifted to the position 5b of the reference surface 5a of the first reference lens 5F.
Re-enter vertically. On the other hand, the second reference lens 5R
The laser beam refracted by the reference lens of the first reference lens 5F
The light is also perpendicularly incident on the position 5b of the surface 5a, and a part thereof
At the position 5b. This makes the position 5b transparent.
Laser light L_AAnd the ray reflected at the position 5b
The light L _BWill go in the same direction,
Since both are laser beams from the same light source 1, they are mutually
have a finger in the pie. In the above description, the position of the reference plane 5a is
Although only the light that interferes with the device 5b is mentioned,
The phenomenon occurs in the entire area of the reference plane 5a.
You. The arrangement of such optical surfaces is based on the well-known cat's eye technology.
It is an application of

[0017] generating the interference light of two laser beams L _A, L _B, as is apparent from FIG. 1, the distance between the reflection point on the reference surface 5a and the reflection plane of the first reference lens 5F r
Has an optical path difference that is twice as large. Moreover, the reflection point position on the reflective plane coincides with the focal position of the second reference lens 5R, and the two laser beams L _A, L _B is to be perpendicularly incident on the both surfaces of the first reference lens 5F , The distance r is equal to the radius of curvature R of the reference surface 5a.

By the way, the above two laser beams L _A and L _B
It has been described above that the optical path difference of may be considered to be equivalent to the optical path difference in the above-described planar step measurement. That is, in the method of performing step measurement plane by using a tunable laser in the light source, measured the frequency of the light intensity change n, the laser light L _A, a reference wavelength of L _B lambda, the change width of the wavelength Is Δλ, the step is 1 / {2 (1 / n) × (Δλ / λ
² )}, the distance r is also 1 / {2 (1
/ N) × (Δλ / λ ² )}.

That is, for example, the reference wavelength λ of the wavelength tunable laser is 660 nm, and the variation width Δλ of this wavelength is 10n.
When the distance r is small, the intensity change of the interference light becomes a low frequency as shown in FIG. 2A when the distance r is small, and is shown in FIG. 2B when the distance r is large. The frequency becomes as high as this, and the change in the frequency is proportional to the change in the distance r.

More specifically, assuming that a wavelength variable laser scans the wave number (2π / λ) from k1 to k2 and captures an image for each Δk, the interference fringe intensity change I (x, y,
k) is generally I (x, y, k) = I ₀ (x, y) {1 + γcos [kL (x, y)]}.

Here, L (x, y) indicates the optical path difference 2r, I ₀ (x, y) indicates the interference fringe intensity distribution, and γ indicates the interference fringe modulation. If the interference fringe change at a certain pixel at this time is n times, (k2-k1) = 2πn, and since k = 2π / λ, L (x, y) = 2πn / (k2-k1) = nλ1λ2 / (λ1-λ2).

That is, the optical path difference can be measured by determining the frequency n when scanning the wavelength. To determine this frequency n, a Fourier transform is required.
Here, the frequency n can be easily obtained by the Fourier transform means 10 (computer) using a well-known Fourier transform equation such as the following equation (4).

[0023]

(Equation 1)

The distance r thus obtained is the radius of curvature R, which is the final solution, and these calculations are performed by the curvature radius calculating means 11 as described above. In addition,
The optical spherical radius of curvature measurement apparatus of the present invention can be applied not only to the radius of curvature of the lens surface of the reference lens but also to various other optical spherical surfaces.

The subject having an optical spherical surface includes:
It is not necessary that the surface opposite to the optical spherical surface be a concentric spherical surface with respect to the optical spherical surface. In short, it is sufficient if the incoming and outgoing rays are perpendicular to the optical spherical surface.

[0026]

As described above, according to the optical spherical radius of curvature measuring apparatus of the present invention, the technique of measuring the level difference of a plane using a tunable laser as a light source is inspired, and the technique of cat's eye is applied. To measure the radius of curvature of the optical sphere, so that it is highly accurate on the order of submicrons,
Moreover, the radius of curvature of the optical spherical surface can be measured with a compact and simple device configuration.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing an optical spherical curvature radius measuring apparatus according to an embodiment of the present invention.

FIG. 2 is a diagram showing a graph used to explain the operation of the embodiment device of FIG. 1;

[Explanation of symbols]

 Reference Signs List 1 wavelength variable laser light source 5 reference lens unit 5F first reference lens 5R second reference lens 5a reference surface 6 collimator lens 7 reflector 9 light intensity detection means 10 Fourier transform means 11 curvature radius calculation means 20 half prism 21 optical fiber

 ──────────────────────────────────────────────────続 き Continuing on the front page F term (reference) 2F064 AA09 BB04 CC04 DD08 EE09 FF02 FF08 GG02 GG22 HH03 HH05 HH08 JJ01 JJ15 2F065 AA46 BB22 CC22 DD03 FF51 GG06 GG25 JJ03 JJ26 LL00 LL86 Q028

Claims (4)

[Claims] An apparatus for measuring a radius of curvature of a concave optical spherical surface of a subject, comprising: a light source capable of changing a wavelength of output light with time; A converging lens that causes the light beam incident along the optical axis to enter the subject at a predetermined angle so that the light is reflected vertically by the spherical surface and the remaining light is emitted perpendicularly from the optical spherical surface. A reflecting surface disposed perpendicular to an optical axis of the optical system at a focal position of an optical system including the converging lens and the subject; light vertically reflected by the optical spherical surface; Light intensity detecting means for detecting a change in the intensity of light interference generated between the light reflected by the surface and perpendicularly re-entering the optical spherical surface; and a frequency n of the light intensity change detected by the light intensity detecting means. Fourier transform means for measuring the A radius of curvature calculating means for calculating a radius of curvature R of the optical spherical surface based on a frequency n of light intensity change, a reference wavelength λ of the output light, and a width of change Δλ of the wavelength. measuring device. 2. The optical spherical radius of curvature measuring apparatus according to claim 1, wherein the radius of curvature calculating means obtains the radius of curvature R using the following equation (1). R = 1 / {2 (1 / n) × (Δλ / λ ² )} (1) 3. An optical spherical curvature radius measuring apparatus according to claim 1, wherein said light source is a laser light source. 4. The optical spherical curvature radius measuring apparatus according to claim 1, wherein the optical spherical surface of the subject is a reference surface of a reference lens used for an interferometer.