JPS6113563B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a lens formed in a thin film optical waveguide.

When a light beam is incident on a thin-film optical waveguide and propagated, if it is necessary to condense the light at one end, a portion that acts as a lens must be formed within the optical waveguide. The part that has such a lens effect can be made to have a lens effect by, for example, protruding or recessing a part of the thin film optical waveguide into a spherical shape. In this case, the spherical part can be made into a unispherical surface. This results in extremely large aberrations. Therefore, as a method for removing aberrations in this case, Japanese Patent Laid-Open No. 50-57255, Applied Optics
Vol. 13, No. 9, pp 2105-2108 proposes changing the film thickness or refractive index of the concave portions (or convex portions) from the center to the outer periphery. However, controlling the film thickness and refractive index by changing them from the center to the outer periphery so as to correct aberrations is extremely difficult in terms of manufacturing and has the disadvantage of being expensive.

SUMMARY OF THE INVENTION An object of the present invention is to eliminate the above-mentioned drawbacks, to provide a thin film optical waveguide lens that has a simple structure, can be manufactured at low cost, and has extremely small aberrations.

The thin-film optical waveguide lens of the present invention is a lens in which a concave portion or a convex portion is formed in a part of a thin-film optical waveguide, and provides a refraction effect on a light beam propagating within the thin-film optical waveguide, and the lens has a flat surface with the concave portion or convex portion. It is characterized in that the thickness of the intermediate thin film that propagates the light flux is the same in the concave portions or the convex portions, and the shape of the intermediate thin film in the concave portions or convex portions is formed into a spherical shape having two or more different surfaces of curvature.

The present invention will be described in detail below with reference to the drawings.

FIG. 1 is a cross-sectional view showing the configuration of an example of the thin film optical waveguide lens of the present invention.
It is composed of three layers of thin films 2, 3 and 4, with the intermediate thin film 3 being at least light-transmissive and having a refractive index greater than the refractive index of the thin films 2 and 4 on both sides. Therefore, the light beam incident on the intermediate thin film 3 undergoes multiple reflections at the interface between the two thin films and propagates. In this example, the lens 5 is formed by forming a spherical concave portion in the thin film optical waveguide 1 without changing its thickness. This lens 5 has a large radius of curvature R at the deep part and a small radius of curvature R' at the periphery, and the centers of curvature O and O' are placed on a perpendicular line to the center of the concave part.

2A and 2B show an enlarged plan view and a sectional view of the thin film optical waveguide lens of this embodiment shown in FIG. Figures and cross-sections are shown. As is clear from FIG. 3B, the conventional thin film optical waveguide lens is composed of a single spherical surface, so its shape has a radius of curvature R and a center of curvature O.
It is determined by two parameters: the angle θ formed by the radius line drawn from the center of the lens and the edge of the lens. Therefore, focal length f and numerical aperture NA
is uniquely determined, but spherical aberration cannot be freely controlled.

On the other hand, since the thin film optical waveguide lens of this example has two spherical surfaces, the parameters that determine its shape are as shown in Figure 2B.
As is clear from the above, it is determined by at least four parameters: the radius of curvature R and angle β regarding the first spherical surface, and the semi-radius of curvature R' and angle α regarding the second spherical surface. Therefore, spherical aberration can be controlled to some extent. here,
In this embodiment, as shown in FIG. 2A, the focal length f of the incident light 6 is expressed by the following equation.

f/R'=- _sinαsinφ1 /sin ( _2φ2 ×ΔB) However, R', α, _φ1 , _φ2 , and ΔB are as shown in FIGS. 2A and B.

As is clear from the above equation, R′, α, φ ₂ , Δ
If B, that is, R', α, β, and γ (γ is the angle formed by the semi-meridian drawn from the center of curvature O' of the second spherical surface to the lens center and the boundary with the first spherical surface, respectively), Even if _φ1 changes, the change in f can be made small, and therefore a thin film optical waveguide lens with small spherical aberration can be obtained.

The spherical surfaces of the lens of the present invention may be arranged such that the deep part has a small radius of curvature and the periphery has a large radius of curvature (R<R'), or another spherical surface may be added. In addition, in order to prevent light loss due to light leakage, optical mode conversion, reflection in the opposite direction, etc. when propagating the luminous flux at the boundaries from a flat part to a spherical surface or from one spherical surface to another spherical surface, these boundaries must be made gentle. It is preferable to use a continuous curved surface, a chamfered plane for approximation, or a curved surface.

4A and 4B show the results of calculations of spherical aberration by a large computer, and FIG. 4B shows the spherical aberration of a conventional thin film optical waveguide lens constructed with a single spherical surface. In addition, FIG. 4A shows the conditions for minimizing the maximum longitudinal aberration when designing a thin-film optical waveguide lens with aberration correction according to the present invention, with peripheral rays passing through the paraxial focus. This figure represents the spherical aberration of the thin film optical waveguide lens according to the present invention, which was obtained by determining the values of the radius of curvature, etc. of two spherical surfaces. As is clear from the figure, the spherical aberration in the lens of the present invention is much smaller than that in the conventional lens. That is, according to the present invention, as is clear from the above, by appropriately setting R′α, β, and γ in FIGS. 2A and B, negative spherical aberration can be obtained.
It was found that a thin film optical waveguide lens in which spherical aberration was well corrected as a whole could be obtained.

Note that as the number of curved surfaces having different radii of curvature increases, the aberration becomes better, but in this case, the surface becomes closer to an aspheric surface, making manufacturing more troublesome. Furthermore, even if the number of curved surfaces is increased, the effect of increasing the number of curved surfaces will be reduced. Therefore, how many curved surfaces with different radii of curvature should be used to construct a spherical lens was determined based on manufacturing issues and effects, but in practice it is best to use two or three curved surfaces. It is preferable to configure the following.

As described above, since the thin film optical waveguide lens according to the present invention has a spherical shape having two or more curved surfaces with different radii of curvature, its spherical aberration can be made smaller than that of a lens consisting of a single curved surface. Further, it has the advantage that the structure is simpler and can be manufactured at a lower cost than in the case where the film thickness and refractive index are changed from the center to the outer periphery.

Note that the present invention is not limited to the above-mentioned examples, and can be modified or modified in many ways.
For example, the centers of curvature of different surfaces of curvature do not necessarily have to lie on a perpendicular line to one curved surface.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing the structure of an example of the thin film optical waveguide lens of the present invention, FIGS. 2A and B are enlarged plan views and sectional views of the thin film optical waveguide lens shown in FIG. 1, and FIGS. 3A and B 4A and 4B are graphs showing a comparison of spherical aberration between the thin film optical waveguide lens of the present invention and a conventional thin film optical waveguide lens. It is. 1... Thin film optical waveguide, 2, 3, 4... Thin film, 5
...Lens, 6...Incoming light.

Claims (1)

[Claims] 1. In a lens in which a concave portion or a convex portion is formed in a part of a thin film optical waveguide, and a refracting effect is applied to a light beam propagating within the thin film optical waveguide, an intermediate thin film in which the light beam propagates between the concave portion or convex portion and a flat portion. 1. A thin film optical waveguide lens, characterized in that the thickness of the intermediate thin film is the same, and the shape of the intermediate thin film in the concave portion or convex portion is formed into a spherical shape having two or more different surfaces of curvature.