JPH0573705B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for manufacturing a gradient index flat lens.

[Summary of the invention]

The present invention provides a method for manufacturing a gradient index flat lens, in which a dopant made of metal is deposited on a transparent dielectric material with a flat surface so that the surface becomes approximately spherical, and this deposited layer is used as a diffusion source to heat or heat the dielectric material. By diffusing dopants into a transparent dielectric material by applying an electric field, this method provides a simpler manufacturing method than conventional methods.

[Conventional technology]

Conventional lenses formed on transparent substrates such as LiNbO ₃ include geodesic lenses in which the surface layer of the substrate is partially processed into a concave shape, and Luneburg lenses in which convex projections are formed in the surface layer. (Luneburg lens), or a gradient index lens in which ions having a large contribution to the refractive index are diffused into a substrate are known.

The present invention relates to a method of manufacturing a gradient index lens among the above.

Conventionally, in order to manufacture a micro-diameter gradient index flat plate microlens, as shown in FIG. is formed by a sputtering method or the like. Next, a circular opening 3 is formed in a part of this ion diffusion prevention mask 2 using photolithography. Next, the circular opening 3 is brought into contact with high-temperature nitrate or sulfate containing ions such as Tl ⁺ , Cs ⁺ , and Ag ⁺ that make a large contribution to the refractive index, and the monovalent ions that make a small contribution to the refractive index in the glass substrate are brought into contact with the ions. The Na ⁺ ions and K ⁺ ions are exchanged with the ions that make a large contribution to the refractive index through the circular opening 3 to form a gradient index lens 4 as a hemispherical diffusion region.

In some cases, in order to promote ion exchange, an electric field is applied using a salt containing ions that greatly contribute to the refractive index as an anode.

[Problem that the invention seeks to solve]

However, in the above-mentioned conventional method for manufacturing a gradient index flat plate microlens, steps such as forming an ion diffusion prevention mask on a substrate and forming circular openings therein are required, which increases the number of steps. was. Furthermore, since it was necessary to use high-temperature molten salt for diffusion, etc., there were also safety problems.

The present invention has been made in view of the problems of the conventional methods, and it can be applied not only to glass substrates but also to dielectric substrates such as LiNbO ₃ and LiTaO ₃ .
The object of the present invention is to provide a method that can form a gradient index lens using simple steps and a dry process.

[Means for solving problems]

The above problem is solved by the present invention as follows. That is, in the present invention, a deposited layer of a dopant made of metal is formed on a transparent dielectric material with a flat surface so that the surface is approximately spherical, and the transparent dielectric layer is used as a diffusion source by applying heat or an electric field. A substantially hemispherical gradient index lens portion is formed by diffusing the dopant into the dielectric.

〔Example〕

Embodiments of the present invention will be described below with reference to FIGS. 1 to 3.

Example 1 First, as shown in Figure 1, the thickness is 0.5 to 1 mm.
A LiNbO ₃ substrate 11 with one side optically polished is prepared. Then, as shown in FIGS. 1 and 2, a metal mask 12 made of chrome or the like having a circular opening 13 is placed on this substrate 11.

The circular opening 13 of the metal mask 12 is composed of a conical surface 13a that is open toward the top and a relatively small conical surface 13b that is open toward the substrate 11 side. The metal mask 12 is approximately 1/10 to 1/1/2 of the minimum diameter (substantially the opening diameter) of the circular opening 13.
It is spaced apart from the substrate 11 by about twice as much.

In this state, Ti (titanium) is deposited on the surface of the LiNbO ₃ substrate 11 by sputtering, and the circular opening 1 is
3, a deposited layer 14 having an approximately spherical surface (that is, its surface is approximately spherical) is formed.

Next, the metal mask 12 is removed, and then,
Ti is diffused into the LiNbO ₃ substrate 11 by heat treatment at a temperature of about 1000° C. for 5 to 20 hours in an Ar gas atmosphere.

Subsequently, by performing thermal diffusion for another 1 to 5 hours while flowing O ₂ gas to compensate for oxygen vacancies in the crystal, as shown in Figure 3, the refractive index formed by the almost hemispherical gradient index lens portion is changed. A distributed microlens 15 was formed in the substrate 11.

The lens 15 obtained in this example has the maximum refractive index at the center of the lens, and the refractive index is approximately parabolic in the depth direction and radial direction from the center of the lens, as in the example shown in FIG. It had a refractive index distribution that decreased in a shape. Numerical aperture NA of the obtained lens 15
(a/f: a is lens radius, f is focal length) is 0.1
~0.2, and the lens diameter was 50 μφ to 500 μφ.

In the case of Ti diffusion, it is known that out-diffusion of Li ₂ O from the LiNbO ₃ substrate occurs. On the other hand, it is also well known that when performing Ti diffusion, this out-diffusion of Li ₂ O can be suppressed by flowing a gas with a humidity of about 86%.

Although Ar and O ₂ gas are used in this example, thermal diffusion can also be performed using only O ₂ gas. or
A LiTaO ₃ substrate may be used instead of the LiNbO ₃ substrate.

As for how to use the lens manufactured in this way, light may be incident on the substrate 11 perpendicularly, or may be incident parallel to the substrate 11.

Example 2 Using BK-7 glass with a thickness of 1 to 3 mm, a deposited layer with a spherical surface was deposited on the substrate by vapor deposition using the same method as in Example 1, using Ag instead of Ti. Formed. Next, heat treatment was performed at 500° C. for 2 to 10 hours to diffuse Ag into the glass substrate to form a gradient index lens.

The NA of the obtained lens was 0.1 to 0.2, and the lens diameter was 50 μφ to 500 μφ.

As another example, after forming a deposited layer of Ag on the surface of the substrate, aluminum is uniformly vapor-deposited on the surface opposite to this surface, and then the aluminum is deposited uniformly on the surface opposite to this layer, and the temperature range of 250 to 550°C is 2 to 500℃.
A DC voltage of 300 V/mm (the surface with the Ag deposited layer is used as an anode) was applied to diffuse Ag.

The lens diameter of the obtained lens is 100μφ ~ 1mmφ
The NA was 0.1 to 0.2.

In this example, Ag was used as a dopant, but Cu or Tl may also be used as a dopant.

In each of the examples described above, one lens is formed on the substrate, but it is also easy to form the same type of lenses in an array (one-dimensional or two-dimensional) on the substrate.

〔Effect of the invention〕

According to the present invention, the steps of forming an ion diffusion prevention mask on a dielectric substrate and forming circular openings therein are not necessary, so the number of steps is reduced and the process becomes very simple. Furthermore, since there is no need to use a high-temperature molten salt, the operation can be simplified and stability can be improved.

Furthermore, since the dopant deposition layer was formed on a transparent dielectric material with a flat surface so that the surface was approximately spherical, there was no need for troublesome high-temperature treatment to adjust the dopant distribution in the transparent dielectric material after the dopant was diffused. Through a simple diffusion process without heat treatment,
It is possible to form a substantially hemispherical gradient index lens portion with a good refractive index distribution and optically small aberrations.

[Brief explanation of drawings]

FIG. 1 is a longitudinal cross-sectional view showing a method for manufacturing a gradient index flat plate microlens according to an embodiment of the present invention;
FIG. 2 is a plan view of a mask, FIG. 3 is a longitudinal sectional view of a gradient index flat plate microlens, and FIG. 4 is a longitudinal sectional view showing a conventional manufacturing method. In addition, in the symbols used in the drawings, 11...
LiNbO ₃ substrate, 12...metal mask, 14...deposited layer, 15...gradient index lens.

Claims (1)

[Claims] 1. A stacked layer of a dopant made of metal is formed on a transparent dielectric material with a flat surface so that the surface is approximately spherical, and the stacked layer is used as a diffusion source by applying heat or an electric field to A method for manufacturing a gradient index flat lens, characterized in that a substantially hemispherical gradient index lens portion is formed by diffusing the dopant into a transparent dielectric. 2 LiNbO ₃ or LiTaO ₃ as the transparent dielectric material
2. The method of manufacturing a gradient index flat lens according to claim 1, wherein Ti is used as the dopant. 3. The method of manufacturing a gradient index flat lens according to claim 1, wherein glass is used as the transparent dielectric and Ag, Cu, or Tl is used as the dopant.