JPH01193623A - Interference measuring apparatus - Google Patents

Abstract

PURPOSE:To enable highly accurate measurement of interference by a compact and low-cost optical system and a high quality interference pattern, by a method wherein an image of a pupil of lens surface to be inspected is taken out of an optical path of an interferometer and further, an expanded image thereof is formed. CONSTITUTION:An imaging lens 9A is arranged after a beam splitter 11 for converging a luminous flux to form a real image of the pupil of a lens 8 to be tested at a position P. An imaging lens 9B is arranged behind the lens to expand real image of the pupil of the lens 8 obtained with the lens 9A to form an image on an imaging surface 10. A cubic prism type beam splitter 11 is arranged as luminous flux converging element and in this case, a lens 9 is designed in abberation considering the refractive index and thickness of the splitter 11. Thus, an image is taken with the lens system 9A once outside an interferometer and formed to remove a larger size of the apparatus. A commercial high magnifying power lens with a short operation range can be used as lens B thereby realizing a reduction in the length of the optical path and a lower cost.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an interference measuring device, a so-called interferometer, for measuring the optical performance of an optical component such as a lens from the distortion of its transmitted wavefront. The present invention relates to an interference measuring device useful for measuring the optical characteristics of a minute lens having a diameter of one square inch or less.

[Prior art] For evaluating the optical performance of optical components such as lenses and mirrors,
Interference measurement technology has been developed for a long time, and various interference measurement devices and interferometers are commercially available and widely used.

FIG. 2 shows an example of such a conventional interference measurement device. In the figure, 1 is a HeNe laser light source, 2 is a beam expander, and the laser beam that has become a parallel beam from the beam expander 2 is sent to beam splitters 3, 4 and mirrors 5, 6.
The beam enters a Matsuha-Zehnder interferometer consisting of

An objective lens 7 and a test lens 8 are placed in one optical path,
Both lenses are arranged so that the light beam after passing through the test lens 8 becomes a substantially parallel light beam again. An imaging lens 9 is placed after the beam splitter 4, and forms an image of the pupil plane of the test lens 8 on an imaging plane 10. At this time, by aligning the direction of the light flux passing through the other optical path with the direction of the light flux after passing through the test lens 8, the test lens 8
The interference pattern of the transmitted wavefront is obtained.

FIG. 3 shows an example of the resulting interference pattern.

If the test lens has good optical properties, a straight interference pattern with equal intervals as shown in (a) will be obtained, but if the lens has aberrations, it will be distorted according to the amount of aberration, as shown in (b). An interference pattern is obtained. Therefore, by inputting the interference pattern obtained in this way using, for example, a CCD camera,
By converting the image (A/I) and performing appropriate computer processing, it is possible to quantify the aberration level of the lens under test.

[Problems to be solved by the invention However, conventional interferometers/! 11 is configured so that the pupil plane of the test lens 8 is directly imaged onto the imaging plane by one lens system 9. If an attempt was made to enlarge the lens (lens) to an appropriate size and form an image on the imaging plane, the disadvantage was that the imaging optical system would become long.

For example, if the pupil diameter of the test lens 8 is 50μ and an attempt is made to form this image on the imaging element of a CCD camera with a size of 5IIIlφ, the magnification of the imaging lens will be 100 times. Since the beam splitter 4 exists between the test lens 8 and the imaging lens 9, it is impossible to place them too close together.For example, if the distance between both lenses is 20 mm, the imaging lens 9 and the imaging lens The distance of the image plane is approximately 20smxlOO=2
m, resulting in an extremely long imaging distance, which has the drawback of increasing the size of the device.

Furthermore, the most readily available high-magnification imaging lenses are objective lenses for microscopes, but these have short working distances of only a few millimeters, and require space to insert a beam splitter between them and the test lens. Therefore, there was a drawback in that a high-magnification imaging lens with an extremely long working distance had to be specially designed and prepared.

On the other hand, there is a differential interference microscope that can perform interference measurements on such tiny lenses, but the interference pattern obtained with this device represents the differential phase of the wavefront transmitted through the lens, etc. In order to obtain the actual transmitted wavefront aberration from the interference pattern, the wavefront phase must be integrated according to the differential direction.The calculation becomes complicated.Errors tend to accumulate during integration (hard to improve accuracy, interference fringes There were drawbacks such as it was difficult to intuitively understand the amount of aberration from the bending.

[Means for solving the problem] At least two or more lens systems are provided after the beam merging element, and the first lens system forms a real image of the test object at a position in front of the second lens system. However, the second lens system is configured to form an enlarged image of the real image behind the second lens system.

[Operation] The first imaging lens system takes out the image of the object outside the interferometer optical path and forms it, and the second imaging lens forms an enlarged image, so the second lens can be used as a microscope. A high magnification lens with a short working distance can be used as the key objective lens, and the optical path length can be shortened and the cost of the device can be reduced.

[Implementation example] An embodiment of the present invention will be described below with reference to FIG.

Figure 1 is also based on a Matsuha-Zehnder type interferometer, and the arrangement and functions of the optical components at 1.2, 3, 5, and 8.7°8 in the figure are the same as those of the conventional example in Figure 2. It can be the same.

The difference between FIG. 1 and FIG. 2 lies in the imaging optical system.

A first imaging lens 9A is arranged after the beam splitter 11 that merges the light beams. This first imaging lens 9A converts the real image of the pupil of the test lens 8 into the first imaging lens 9A.
Make it at the position indicated by P behind the. First imaging lens 9A
The magnification does not need to be particularly high even when measuring a minute lens. Furthermore, a second imaging lens 9B is arranged behind this, and the real image of the pupil of the test lens 8 obtained by the first imaging lens 9A is magnified and formed on the imaging plane 10. In addition, a cube prism type beam splitter is arranged as the beam merging element 11, and the first imaging lens 9A is designed to have aberrations taking into account the refractive index and thickness of the beam splitter, and the pupil image is It is designed to be able to obtain the P position with extremely low aberrations.

In addition, aberration reduction design when a prism of a specific thickness, that is, a plane parallel plate, is inserted into the optical path (in this case, the surface configuration of the first imaging lens system is adjusted so as to satisfy the sine condition,
optimizing aspherical coefficients, etc.) is easy and will not be discussed here.

The advantages of the above device will be described below.

The features of the device of the present invention are as follows: First, the image of the pupil plane of the test lens is
First, the first imaging lens 9A takes the light out of the interferometer optical path, and the second imaging lens 9B forms an enlarged image, and the light beam combining element 11 is made into a prism type beam splitter. This makes it easy to design the first imaging lens with low aberrations.

Generally, the distance of the object to the pupil position of the imaging lens is a1
When the image distance is b, the magnification is expressed as b/a. If the diameter of the test lens is small, it is necessary to increase the imaging magnification b/a, but in the interference optical system, the value of a is small because the beam convergence element r is inserted between the test lens and the imaging lens. Therefore, if the magnification is increased, the value of b becomes extremely large (and the size of the device becomes large).In the device of the present invention, this constraint condition is met when the image is captured by the first lens system 9A. By taking it out and forming it once outside the interferometer, it can be removed and a high magnification lens with a short working distance, such as a commercially available microscope objective lens, can be placed as the second lens 9B. Therefore, this makes it possible to shorten the optical path length and lower the cost.

Furthermore, if the lens to be tested is an extremely small lens with a diameter of several tens of μm or less, the aberration of the imaging lens deteriorates the image of the interference pattern. When the beam merging element is composed of a parallel plate beam splitter 4 arranged at an angle as shown in FIG. 2, the light rays (represented by dotted lines in FIG. Since astigmatism and coma aberration are imparted to the aberration (which is caused by the aberration), it is extremely difficult to design an imaging lens to reduce these aberration components. However, in the present invention, as shown in FIG. 1, since a prism-type beam splitter 11 is used as a beam merging element, both surfaces of the prism can be arranged perpendicularly to the optical axis. Only spherical aberration is imparted to the light rays (represented by dotted lines in FIG. 1) involved in the imaging of .

Therefore, it is easy to design a lens for correcting this spherical aberration for the first imaging lens, and a good interference pattern can be obtained.

As described above, the present invention enables interference measurement of microlenses with lens diameters of several hundred microns and tens of microns, which was previously difficult to measure, using a compact, low-cost optical system and high-quality interference patterns. Can be achieved with high precision.

Although the above example describes the measurement of a minute lens, it is possible to measure the refractive index distribution of a waveguide cross section by measuring the transmitted wavefront of a waveguide slice sample as a test object. It can be applied to the evaluation of micro optical elements. In such a case, the objective lens 7 in FIG.

Furthermore, the light source may be a semiconductor laser or other light source.

In addition, although the explanation of the embodiment was based on a Matsuha-Zehnder type interferometer, other interference J! It may be used for other purposes.

[Effects of the invention] According to the present invention, interference measurement of extremely small lenses with lens diameters of several hundred μm or tens of μm, which has been difficult to measure up until now, can now be performed using a compact, low-cost optical system and high quality. High accuracy can be achieved with a unique interference pattern.

[Brief explanation of the drawing]

Fig. 1 is a plan view showing an embodiment of the present invention, Fig. 2 is a plan view showing a conventional interference measurement device, and Figs. 3 (a) and (b) are front views showing examples of interference patterns. be. 1... Laser light source 2... Beam expander 3... Luminous flux splitting element (beam splitter) 4... Luminous flux combining element (beam splitter) 5.6. ...Mirror 7...Objective lens 8...Test lens 9A...1st
Imaging lens 9B...Second imaging lens 10
...Imaging surface 11...Prism type beam splitter 1.1:l1ri, 1 Fig. 1

Claims (1)

[Claims] The light flux emitted from the light source is divided into two optical paths, a translucent subject is placed in one of the optical paths, and the other light flux is directed in the same direction as the light flux transmitted through the subject via a light flux merging element. In the interference measurement apparatus, at least two or more imaging lens systems are arranged behind the light beam merging element, and the first lens system converts the real image of the subject into a second image. a prism that forms an image at a position in front of a lens system, and forms an enlarged image of the real image behind the lens system by a second lens system, and has at least one pair of substantially parallel surfaces as the light beam merging element. An interference measurement device characterized by using a type beam splitter.