JPS6289910A - Geodesic lens and its production - Google Patents

Abstract

PURPOSE:To correct aberrations by adjusting partially the quantity of ultraviolet rays or light irradiated to a thin film consisting of an arsenic sulfide if the shape of a recess is deviated from a design and aberrations occur in a geodesic lens. CONSTITUTION:If the center of the recess is deeper than the design, the refractive index of an optical waveguide 7 consisting of an arsenic sulfide provided on the recess is raised gradually in the direction vertical to the propagation direction of a guided light according as going away from the optical axis, but is uniform in the propagation direction of the incident guided light. Consequently, since the part along the optical axis in the waveguide in the recess has the lowest equivalent refractive index if the depth of the recess 3 is deeper than the design and the optical path length of the beam propagated is most deviated from the design value, the propagation speed of the beam passing the optical axis is high to cancel the phase difference due to the extension of the optical path length, thus obtaining the geodesic lens having no aberrations.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a geodesic lens having a function of focusing planar guided light in a plane, and a method for manufacturing the same.

(Prior Art) In general, coherent optical processing technology is characterized by being capable of parallel processing and being fast, and is therefore suitable for application to signal processing devices such as correlation. In order to realize this signal processing device fi1, a Ti plate such as an optical glass or an optical crystal is used, a layer with a refractive index lower than that of the substrate is provided on the surface, and energy is concentrated on this high refractive index, n, and propagated. The wavefront and energy propagation direction of planar waveguide light are 1
Recently, optical circuits that perform fflJ# have been actively researched.The planar lens used in such a planar optical circuit has an imaging function and a 7-layer conversion function, and has a heavy responsibility of controlling the planar optical circuit. 0 As such planar lenses, there are known lenses such as Geodeci, Cleanse, Lunepul lens, Grating lens, Planar 7 Lenell lens, etc. Since this portion is used as a lens portion, it is possible to create a lens with a large diameter, a short focal length, and a small F number by processing the recess into a desired shape. Further, it has the advantage that there is no chromatic aberration, and the focal length does not depend on the order of the waveguide mode. Conventionally, a recess is provided on a dielectric substrate,
An example of a geodesic lens that forms an optical waveguide in this recess is published in the magazine ``IEE Transaction Fist on Hybrid and Manufacturing Technology (IEEE Tll
, ANSACTIONS ONCOMPONENTS.

HYBRIDS, AND MANUFACTURIN
GTECHNOLOGY)J, VOL CHMT-
5, No. 2, June 1982, pages 205-209.

FIGS. 3(a) and 3(b) are a plan view and an analytical view showing the structure of this conventional geodefault lens. This geodesic lens is made by cutting a depression 3 on the surface of a lithium niobate substrate 1 using a diamond cutting tool, polishing the cut portion, and then applying a titanium film to the entire surface of the lithium niobate substrate 1, including the depression. , the optical waveguide @8 and the geodesic lens part 4 are formed by thermally diffusing this titanium g.
According to Fell's principle, the light beam 5 propagates along the geodetic axis of the curved surface where it is the shortest, so the optical path length changes depending on the position of the lens through which the incident guided wave light 5 passes. Is 5 a fruit and vegetable effect? 0 (Problem to be solved by the invention) In order to realize an aberration-free lens, the aperture must be several ax @ the depth at the center must be 1 In the case of a lens with a diameter of 1 to 5 μm, it is necessary to process the shape of the recess with a depth of 1 to 5 μm.Therefore, geodesic lenses have the disadvantage that if the shape of the recess deviates even slightly from the design, aberrations will occur. 0 The purpose of the present invention is to eliminate such drawbacks of conventional geodesic lenses, and to create a lens that is free from aberrations even if the shape of the depression cannot be processed as designed. What geodesic lenses can you get and how to make them? It is about sharing.

(Problem 'T: Means for Solving) The 4aX of the first invention is a geodecisive or cleansing device in which an upper part of a dielectric substrate is formed and an optical waveguide is provided on the surface of the dielectric substrate including this four parts. , the refractive index distribution of the optical waveguide provided in the recess is gradually changed as it moves away from the optical axis in a direction perpendicular to the propagation direction of the guided light, and is uniform in the direction of the propagation force of the guided light? Features.

The second structure of the present invention is a method for manufacturing a geodesic lens in which a recess is provided on the surface of a dielectric substrate and an optical i-wavepath is formed in the recess, the refractive index being higher than that of the visiting body substrate No. 811 and A photosensitive material whose refractive index increases upon irradiation with an electron beam or light is provided on the surface of the dielectric substrate, which corresponds to the recess, so that the film thickness is the same, thereby forming the optical waveguide. , the electron beam or light irradiation source to the recessed portion is
The effect of the present invention is to gradually increase vC/A as it moves away from the optical axis in a direction perpendicular to the propagation direction of the guided light, and to be controlled so that it becomes uniform in the propagation direction of the guided light. Due to the structure, the optical waveguide in the hollow part has the following refraction 4/f5, which is 0, that is, the hollow If the center of the recess becomes more compact than designed, the refractive index distribution will gradually become worse as it moves away from the original axis in the direction perpendicular to the propagation direction of the guided light, and the center of the recess will become shallower than designed. In this case, aberrations can be corrected by creating a refractive index distribution that gradually decreases as it moves away from the optical axis in a direction perpendicular to the propagation direction of the four-wave light.

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

FIGS. 1(a) and 1(b) are a plan view and a sectional view showing an embodiment of the present invention. This Geodex Cleanse has a depression 3 on the surface of the lithium niobate substrate 10. A geodesic lens portion 4 is provided, and an optical waveguide 2 made of arsenic sulfide with a uniform refractive index is provided on the surface of the substrate 1 other than the recess 3, and an optical waveguide 2 made of arsenic sulfide with a uniform refractive index is provided on the surface of the substrate l. An optical waveguide 7 made of arsenic is provided. If the center of the sulfide atom optical waveguide 7 provided above this depression is deeper than designed, the refractive index will gradually decrease as it moves away from the optical axis in the direction perpendicular to the propagation direction of the guided light. The refractive index has a uniform distribution in the propagation direction of the incident guided light.

Therefore, in the case where the depth of the recess 3 becomes deeper than the design and the optical path length of the beam propagating through the source deviates from the design value by the longest, in the non-example, the waveguide inside the recess aligns with the optical axis. This part has the smallest equivalent refractive index, so the propagation speed of the beam passing through the optical axis is fast, and by increasing the optical path length, all phase differences can be eliminated, making it possible to create a geodesic lens with no aberrations0 Konohara 8! According to , if the center of the depression is shallower than designed, the waveguide in the depression will adopt a refractive index distribution that gradually decreases as it moves away from the optical axis in a direction perpendicular to the propagation direction of the guided light. Aberrations can be corrected by

Figure 2 +a) to +C) are cross-sectional views showing the manufacturing method of Geodex Cleansing in the order of steps to realize the structure of the non-example, and Figure 2(d) is A-A in Figure 2(C). 'This is a cross-sectional view.

First, in FIG. 2(a), a depression 3 is cut on the surface of the lyticum niobate substrate 10 using a diamond cutting tool, and after this cutting, the entire row 90 is polished.Next, as shown in FIG. ! , arsenic sulfide is vaporized on the surface of a techniobate substrate 1 to form an optical waveguide 2 of arsenic sulfide with a constant film thickness.
form 7. Next, the transmittance at the ultraviolet edge is shown in Figure 2 (+J
As shown in Figure 5, the incident guided light is uniform in the propagation direction, and as shown in Figure 2 [
As shown in d), the sulfurization film provided above the recess is passed through the exposure mask 10, which has a distribution that is minimum at the optical axis portion and increases as the distance from the original axis increases, perpendicular to the propagation direction of the incident guided wave light. The arsenic optical waveguide 7 is irradiated with ultraviolet light 11. The geodeck thus shown in Figure 1.

You can complete Kremme.

(Effects of the Invention) According to the structure of the present invention, when the shape of the recess deviates from the key design and aberrations occur in the geodesic lens, the irradiation period of ultraviolet rays or light irradiated to the N film of arsenic sulfide can be reduced. By making partial adjustments, the aberration can be corrected.

Specifically, the aperture and focal length of this embodiment are 3.21nllL and 3.21nllL, respectively. When forming a depression for Qurrn's geodesic lens, and the deviation from the shape design was greatest at the center of the depression, and the center was 20μm deeper than the design, the film thickness was uniform at 0.4μm, and the film thickness was 0.4μm and arsenic gold sulfide. Is it provided in the hollow part and has the above-mentioned transmittance distribution? 5. Apply ultraviolet rays with a wavelength of 400 nm through the waiting exposure mask at the maximum irradiation point. sJZ Wei2 irradiation.

By irradiating the ultraviolet edge in this way, the refractive index of arsenic sulfide along the optical axis remains 2.46 for the TE mode of the He-Ne laser beam, and the refractive index of arsenic sulfide in the portion farthest from the optical axis remains 2.46. The value becomes 2.48 at the end portion of , which cancels out the deviation in optical path length due to the deviation in the shape of the recess, making it possible to reduce aberrations.

As described above, according to the present invention, it is possible to realize a geodex lens with low aberrations without being affected by the machining process of the depressions.

[Brief explanation of drawings]

The construction drawings ta) and tbl are a plan view and a sectional view showing an example of the geodex lens according to the present invention, and FIGS. Method? The cross-sectional views shown in the order of steps, FIG. 3 (fan, tb), are a plan view and a cross-sectional view of a conventional geodesic lens. 1...Lithium Niobait plate, 2.7...
... Arsenic sulfide optical waveguide, 3... Hollow part,
4...Geodesic lens section, 5...
Incoming guided wave light, 6...Focusing point of incident guided wave light, 8.
...Optical waveguide, 10...Exposure mask,
11... Ultraviolet rays. Agent Patent Attorney Uchihara: Do, 1'\n Liang l Figure

Claims (2)

[Claims] (1) In a geodesic lens in which a recess is formed on the surface of a dielectric substrate and an optical waveguide is provided on the surface of the dielectric substrate including the recess, the refractive index distribution of the optical waveguide provided in the recess is A geodesic lens characterized in that the waveguide light is gradually changed according to the distance from the optical axis in a direction perpendicular to the propagation direction of the guided light, and is made uniform in the propagation direction of the guided light. (2) In a method for manufacturing a geodesic lens in which a recess is provided on the surface of a dielectric substrate and an optical waveguide is formed in the recess, the refractive index is higher than that of the dielectric substrate, and the refractive index is lowered by electron beam or light irradiation. The optical waveguide is formed by providing an increasing amount of photosensitive material on the surface of the dielectric substrate including the recess so that the film thickness is uniform, and the amount of electron beam or light irradiated to the recess is set to A method for manufacturing a geodesic lens, characterized in that the waveguide light is controlled to gradually change in a direction perpendicular to the propagation direction according to the distance from the optical axis, and to be uniform in the propagation direction of the guided light.