JPS615201A - Forming method of optical element - Google Patents

Abstract

PURPOSE:To form an optical element equivalent to an optical element having non-plane and aspherical functional surfaces easily with a high precision by forming both faces of optical materials into plane or spherical surfaces and giving a refractive index distribution to these surface layers and polishing them into plane or spherical surfaces. CONSTITUTION:For example, both faces of optical materials are formed into plane or spherical surfaces, and the refractive index distribution where the refractive index value accords with the depth is given to surfaces layers of optical materials by ion exchange or the like. Both faces of optical materials are polished into plane or spherical surface to form functional surfaces as optical faces. An ion exchange layer different by the length from the optical axis is formed on surface layers of the optical element obtained in this manner.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field] The present invention relates to a method for manufacturing an optical element, and particularly to a method for manufacturing an optical element having a non-uniform distribution of refractive index.

[Prior art]

In general, optical elements used in optical systems, such as lenses, prisms, or reflectors, have a flat or spherical surface that transmits or reflects light (hereinafter sometimes referred to as a "functional surface"). There is. As the optical material constituting such an optical element, one having a substantially uniform refractive index is used. Therefore, in order to impart desired optical performance to an optical element, the refractive index of the optical material must be adjusted.

The radius of curvature of the functional surfaces and the positional relationship between the functional surfaces are appropriately set. However, these optical elements have various optical aberrations, and it may be difficult to obtain desired optical performance in an optical system.

Therefore, recently, in order to obtain an optical element from which specific optical aberrations have been removed, functional surfaces have been formed into non-planar and aspherical shapes. However, creating this type of optical element is significantly more difficult than creating an optical element having only a flat or spherical functional surface. In other words, while the know-how for forming flat or spherical optical surfaces has been established over a long history and can achieve precision on the order of less than the wavelength of light, the technology for forming aspherical optical surfaces is Regarding grinding of optical materials, direct pressing, etc., which are the pre-processes for the final process of forming optical surfaces. Although it is possible to form an aspherical surface with a certain degree of accuracy, it is currently established that controlling the desired shape in the final process of forming an optical surface can achieve precision on the order of less than the wavelength of light. I can't say that.

Therefore, at present, optical elements having non-planar and aspherical functional surfaces are only produced that do not require strict precision or have extremely limited shapes. A specific example of such an optical element is a Schmidt plate.

On the other hand, there is a so-called selfoc lens as an optical element that provides an optical material with a refractive index distribution and thereby obtains an optical effect. This provides a refractive index distribution in a direction perpendicular to the direction in which light travels, thereby achieving a light focusing effect. Furthermore, an optical element in which the light transmitting surface of the cell 7 lens is formed into a spherical surface has already been proposed (Micr
o OpticsNews, Mol, 1+
A3 r Oct, 1,983. pl, 26-)
. According to these optical elements, even if the light transmitting surface is a flat or spherical surface, the optical performance is equivalent to that of a non-planar and aspheric optical element formed using a bibacterial material with a uniform refractive index distribution. can return.

However, since effective tiJj refractive index distribution can generally only be applied from the surface of the optical material to a relatively shallow area (approximately 1-=-2 tm), it is not effective for optical elements with small apertures. However, in the case of an optical element with a large l'' diameter, the effect is significantly 1-. ．． <It becomes small.

Therefore, the above-mentioned Selfoc lens is only used with an aperture that is as small as the aperture. To easily and highly accurately produce an optical element having optical performance equivalent to that of an optical element having a non-planar and aspherical functional surface of arbitrary size, which is produced using a material with uniform distribution. With the goal.

[Summary of the invention]

According to the present invention, the above-mentioned object is to form at least two or one of the corresponding parts of the optical element (optical part) into a flat or spherical surface to form the light transmitting surface or the original reflective surface of the optical element, Next, the above-mentioned plane or spherical surface of the optical material is provided with a refractive index distribution having a refractive index value depending on the depth, and then the above-mentioned plane or spherical surface is polished to form an optical surface.

[Embodiments of the invention]

Embodiments of the production method of the present invention will be described below with reference to the drawings.

FIGS. 1(&) and 1(b) are schematic cross-sectional views showing a first embodiment of the method for producing an optical element of the present invention.

First, as shown in FIG. 1(a), both surfaces of an optical material are formed into spherical surfaces. Functional surfaces of the optical element are formed on both surfaces. Glass is used as the optical material, and the spherical surface can be formed by grinding with, for example, a diamond cutting tool. In this process, both spherical surfaces have not yet been formed into optical surfaces, but the surface accuracy is, for example, 1.
It can be on the order of μm. After this process, both spheres have 0
．． Surface roughness and microcracks of about 5 to 1.0 μm are present.

Next, ion exchange of the surface layer of the optical material is performed.

This ion exchange is performed, for example, as shown in FIG. That is, salts 12 such as potassium nitrate are stored in an ion exchange tank 10, and the ion exchange tank 10 is heated from around it with a heater 14 to melt the salts 12. Optical material 16 is immersed in molten salt 12 in ion exchange tank 10 .

At this time, the optical material 16 is placed on the support 18. By holding it for an appropriate period of time, the ions contained in the surface layer of the optical material 16 and the ions in the molten salt 12 are ion-exchanged, thereby changing the refractive index of the surface layer of the optical material 16.゜It is an optical material, but the lath has Ns, +K +Cs.

It contains ions such as L++TI, and the salts used for ion exchange are KNO3.
, AgNO3, TlNO3, K2SO3, TI2so4
For example, when melted, ions are produced. When these ions are included in an optical material, the refractive index generally becomes Na(K(Cs(Ag(TI)).

Therefore, the Na of the optical material containing Na is T1
When ions are exchanged with K, the refractive index of the optical material increases. When Ag of an optical material containing Ag is ion-exchanged with K, the refractive index of the optical material decreases.

The dotted lines in FIG. 1 (,) are equirefractive index lines showing the refractive index distribution of the surface layer whose refractive index has been changed by ion exchange as described above. As shown in the figure, the refractive index varies depending on the depth from the surface. Incidentally, the depth at which the refractive index can be changed in this manner is sufficiently possible to be about 1 to 2 m from the surface.

Next, both spherical surfaces of the optical material in Fig. 1 (b) are ground and polished to form an optical surface and a functional surface is formed.
) An optical element as shown in K is obtained. As shown in the figure, ion exchange layers that differ depending on the distance from the optical axis are formed on the surface layer of the obtained optical element. Therefore, this optical element has optical performance equivalent to that of an aspheric lens made of a uniform optical material throughout, ie, a lens as shown in FIG.

The aspherical effect of the optical element thus obtained will be specifically explained.

In Fig. 1 (,), Sl is the left-hand spherical surface before giving the refractive index distribution, and the radius of curvature R1 of this spherical surface is 301I
I11, and the effective diameter of this spherical surface is 30 positive.

It is also assumed that the refractive index distribution is given as expressed by the following equation.

Δn (A = 0.1 exp (6,908・ρ) (here, ρ is the depth from the surface, and Δn is the refractive index difference with the uniform refractive index part) Figure 1 ( As shown in b), by grinding and polishing, the left spherical surface is turned into a functional surface S2 with a radius of curvature R2 of 33.72676 m.
Suppose we form it as . By processing the surface S1 into the surface S2, the amount δ8 by which Jay becomes thinner in the optical axis direction is as follows.

δ engineering=a4,22ci7e J欝2677τF-(30
-J "7F" When this is expressed numerically at several points, it becomes as follows.

The optical path length change OPD at the y position is as follows.

If this is expressed numerically at several points, it will look like this:

Thus, although the functional surface s2 of the optical element is a spherical surface, the same effect can be obtained as if the functional surface s2 of the optical element were made of a material with a uniform refractive index and was made non-planar and aspherical. When such an optical element is made of an optical material with a uniform refractive index (n=1.5) distribution, the deviation from the surface S2 in the direction parallel to the optical axis as shown in FIG. Ken δ can be expressed as follows.

OPD = δX (n-1) = 0.5X δ・°・δ=2X
OPD When this is expressed numerically for several points of y, it becomes as follows.

As shown in FIG. 3, consider a spherical surface connecting the point at y=0 and the point at y;15, and define this as the reference spherical surface S3. The radius of curvature R3 of the reference spherical surface S3 is 33.9694881
m. The displacement position δ8 of the equivalent aspherical surface in the optical axis direction with respect to the reference spherical surface s3 is as follows.

δ, = 33.9694881-J Positive 6948η Ear F- (3172676-OI Katanai 7F: Me δ) When this is expressed numerically for several points, it becomes as follows.

In the manufacturing process of the optical element as described above, FIG. 1 (IL
) to the shape shown in Figure 1(b), microcracks in the grinding process are removed, and even if the surface roughness is about 1 μm at the end of the grinding process as described above, the ion exchange layer The depth is about 1~21111)
Since the surface roughness is sufficiently larger than the above-mentioned surface roughness of 1 μm, there is almost no influence on the optical path length of the obtained optical element, and there is no problem in terms of optical performance.

FIGS. 4(a) and 4(b) are schematic cross-sectional views showing a second embodiment of the optical element manufacturing method of the present invention. This embodiment differs from the first embodiment only in the shape of the optical element. That is, as shown in FIG. 4(11), an optical material made of parallel flat glass is subjected to ion exchange treatment to obtain an optical element with both functional surfaces having concave spherical surfaces as shown in FIG. 4(b).

FIGS. 5(a) and 5(b) are schematic cross-sectional views showing a third embodiment of the optical element manufacturing method of the present invention. This embodiment also differs from the first embodiment only in the shape of the optical element. That is, first, an optical material is formed into a biconvex spherical shape as shown in FIG. 5(a) by grinding, etc., and this is subjected to ion exchange treatment, so that one functional surface is flat as shown in FIG. 5(b). In addition, an optical element is obtained in which the other functional surface is a convex spherical surface.

Although glass was used as the optical material in the above embodiments, other materials such as plastic or crystal may be used in the present invention.

Furthermore, in the above examples, grinding is performed in the flat or spherical surface forming process before the ion exchange treatment, but
In the present invention, the surface formed by Direct Soles may be used as is.

Incidentally, an optical surface may be formed in the flat or spherical surface forming step before the ion exchange treatment, and since this allows the surface to be formed with optical precision, the amount of aspheric surface in the final product can be extremely accurate. be able to.

In addition, in the above embodiments, an ion exchange method was used as a means to change the refractive index of the optical material, but in the present invention, other methods such as electric field transfer method, single molecule stuffing method, phase separation method, CVD method, plasma CVD method, Other refractive index changing means such as the VkD method, diffusion copolymerization method, and photochemical method can be used.

Further, in the above embodiments, a lens is exemplified as an optical element, but other examples of the optical element produced by the present invention include a prism, a mannon mirror, and the like.

〔Effect of the invention〕

According to the method of the present invention as described above, uniform refraction can be achieved by combining an extremely easy and accurate plane or spherical processing step with a step of changing the refractive index of the surface layer of the optical material in processing the surface shape of an optical element. It is possible to easily obtain an optical element of any size that has high-precision optical performance equivalent to that of an optical element having an aspherical functional surface made of an optical material having an index distribution.

[Brief explanation of the drawing]

1(a) and (b) are cross-sectional views showing the steps of the method of the present invention, FIG. 2 is a cross-sectional view of the ion exchange step, and FIG. 3 is a cross-sectional view of the optical element obtained by the method of the present invention. FIG. 3 is a cross-sectional view of an aspheric lens with equivalent optical performance. Figure 4 (,)
and (b), and FIGS. 5(a) and 5(b) are cross-sectional views showing the steps of the method of the present invention. Figure 1 (0) y Figure 3 Figure 4 <a) Figure 4 (b) Figure 5 (0) Figure 5 (b)

Claims (1)

[Claims] (1) Form at least one of the corresponding parts of the optical material that is to form the semi-transmissive surface or the light-reflecting surface of the optical element into a flat or spherical surface, and then add a depth to the flat or spherical surface of the optical material. A method for producing an optical element, characterized in that a refractive index distribution having a corresponding refractive index value is provided, and then the flat or spherical surface is polished to form an optical surface.