JPS60140204A - Light guide lens and its manufacture - Google Patents

Abstract

PURPOSE:To improve diffraction efficiency and to reduce the propagation loss of a light guide which has a higher refractive index than a substrate by forming a light guide layer which has curved grating areas at irregular intervals on the light guide, and forming a clad layer which has a lower refractive index than the light guide layer thereupon. CONSTITUTION:Variation in the refractive index of the substrate by an ion exchange method is utilized to form the light guide layer and diffraction gratings. Namely, irregular interval curved grating areas 30 having the higher refractive index than the substrate are formed at part of the surface of the substrate 30, and then the light guide layer 34 having the higher refractive index than the substrate is formed in the surface area of the substrate. Then, the clad layer 36 having the smaller refractive index than the light guide layer 34 is formed to obtain a light guide lens. Thus, the light guide lens applied with variation in the refractive index of the substrate by the ion exchange method has large variation in refractive index and the transmission loss of the light guide is small.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical field to which the invention pertains] The present invention relates to an optical waveguide lens using a diffraction grating and a method for manufacturing the same.

[Technical Background of the Invention] In recent years, information communication and information recording and reproducing using light have been attracting attention. Optical components responsible for transmitting such optical information include, for example, so-called non-contact devices that connect optical waveguides and optical fibers, or optically read and write information from optical information media such as compact discs. Various types of optical information input/output devices have been developed.

For example, as one of the optical information input/output devices,
There is a planar optical waveguide provided with a diffraction grating in the form of an unevenly spaced curved grating, as described in Japanese Patent No. 169107. That is, as shown in the cross-sectional view in FIG.
A cladding layer 14 is further provided on the cladding layer 2, and the cladding layer has a structure of a diffraction grating 16 consisting of a group of unevenly spaced curves formed by etching the cladding layer into a fine pattern. A guided wave 11 propagating through an optical waveguide layer 12 is diffracted by a diffraction grating 16, extracted as external light, and converged at a focal point 19.

[Problems with Background Art D] The optical waveguide lens described above has a so-called relief type diffraction grating formed by etching on the optical waveguide layer, and the scattering loss is large, and the propagation loss of the optical waveguide is also large. There is a problem.

However, since it is difficult to make the surface so flat that the surface wavelength can be ignored, there is a problem in that it is not possible to converge light onto a minute spot around the ium, for example. It also had the disadvantage of low diffraction efficiency.

Note that as a diffraction grating other than the relief type, there is a holographic grating. However, when forming holographic gratings, the light source laser wavelength must be shorter than the red wavelength, and wet processing is required during development, which impairs flatness. If the writing wavelength is different, the aberration will be large and it will not be possible to converge it to a minute spot.

There is also a method of directly writing nonuniformly spaced curved gratings on the optical waveguide layer by electron beam writing, but the area that can be written is very narrow and the change in refractive index is small, resulting in extremely low productivity and very low diffraction efficiency. low.

[Object of the Invention] The present invention provides an optical waveguide lens that solves all of the above problems and a method for manufacturing the same.

[Summary of the Invention] According to the present invention, there is provided a substrate, an optical waveguide formed on the substrate made of a material having a higher refractive index than the substrate, and an optical waveguide formed on the optical waveguide and made of a material having a refractive index higher than that of the optical waveguide layer. and a cladding layer made of a low-density material, the optical waveguide layer having unevenly spaced curved grating regions having a different refractive index than the optical waveguide layer. According to the lens of the present invention, the diffraction grating is not a relief type diffraction grating formed by etching buttering, but the surface of the optical waveguide layer is flat, which is a major feature in that scattering loss can be reduced. Therefore, an optical waveguide lens is provided which has less aberration caused by surface distortion (flatness) and has high diffraction efficiency.

Further, according to the present invention, a method for manufacturing the above-mentioned optical waveguide lenses is provided. According to this, the optical waveguide layer and the diffraction grating utilize the change in the refractive index of the substrate due to the ion exchange method, and the change in refractive index is large, the diffraction efficiency is increased, and the propagation loss of the optical waveguide can be reduced. . Further, the flatness of the substrate can be maintained at a high level, scattering loss can be kept low, and the laser beam can be focused on a minute spot.

[Embodiments of the Invention] The present invention will be described below with reference to drawings showing embodiments. First, as shown in Figure 2, for example, L
An optical substrate 20 made of iNb0a is prepared, and a photoresist film 22 is formed on the upper surface of the substrate, for example, with an area of 10 m+.
Minimum pitch 0゜7Jlll in the area of nX 10aun
, line width 0.35J1111. Number of pieces: 3000-10000
Photomask 2 having book unequal spacing curved grid areas 23
4, the photoresist film 22 is exposed to light. Next, the photoresist film is developed, and as shown in FIG. Cr-Au11126 is formed by vapor deposition. After that, Cr- on the photoresist film 22 is removed by lift-off method.
The Au film is removed, leaving a Cr-Al1 film with openings 25 in irregularly spaced curved grid regions on the substrate 20, as shown in FIG. , 210-300
For example, the substrate 20 is immersed in benzoic acid 28 at 250° C. for 10 to 20 minutes, and a portion of the Ll ions of the substrate 20 and a portion of the H ions of the benzoic acid are ion-exchanged through the openings of the Qr-Au film. A region 30 with a higher refractive index than the substrate on a part of the surface
form. After that, the Cr-Au II on the surface of the substrate was peeled off, and the substrate was immersed again in benzoic acid at 210 to 300°C for several minutes, and as shown in Figure 6, a light guide having a higher refractive index than the substrate was formed on the surface area of the substrate. The wave path layer 34 is formed to have a thickness of, for example, 1 μm. Next, remove the substrate from the benzoic acid and dry it.
As shown in FIG. 1, a material having a refractive index lower than that of the leading waveguide layer 34, such as SiO□, is deposited on the leading waveguide layer 34 to a thickness of several Jjll, and a cladding layer 36 is formed to form a leading waveguide lens. The optical waveguide lens formed as described above utilizes the refractive index change of the substrate by the ion exchange method, so the refractive index change is large and the propagation loss of the optical waveguide is low. In the case of a so-called volume hologram type diffraction grating that utilizes changes in the refractive index in the substrate and optical waveguide, not only the scattering loss is small but also the diffraction efficiency itself is extremely high. All (100%) of the light propagating inside is diffracted toward the substrate, and a three-dimensional convergent beam can be taken out of the substrate through the side surface of the substrate.

The above-mentioned optical waveguide lens is used, for example, in the following manner. That is, as shown in FIG. 8, a method is shown in which the radiation end face of the semiconductor laser 44 is directly coupled to the entrance end face 42 of the optical waveguide 40. The light emitted from the semiconductor laser is
A non-uniformly spaced curved diffraction grating 46 propagating through an optical waveguide and illustrated.
At this point, the light is 100% diffracted toward the substrate, taken out to the outside via the end face of the substrate, and converged. For example, a compact disc or a video disc is placed on the converging surface.

[Other Example 1] In the above-mentioned example, regions with a high refractive index in the shape of an unevenly spaced curved lattice were formed in advance on the substrate surface, and then an optical waveguide layer was formed. However, after forming an optical waveguide layer, Unequally spaced curved lattice-like regions having a higher refractive index than the optical waveguide layer may be formed in the optical waveguide layer.

That is, for example, a substrate made of LiNbOa is heated in benzoic acid at 210 to 300°C for 10 to 20 minutes to exchange ions between Li ions in the substrate and H ions in benzoic acid, causing refraction on the surface of the substrate. Forms an optical waveguide layer with a high efficiency.

Next, in the same manner as in the above embodiment, a photoresist is coated, exposed, and developed on the leading waveguide layer, and Cr and Au films are deposited, and by the lift-off method, unevenly spaced curved grating regions are formed on the optical waveguide layer. An Or-Au film having pores is formed. The substrate on which this cr-Au film was formed was further heated in benzoic acid at 210 to 300°C for several minutes to ion-exchange the Li ions in the optical waveguide layer with the H ions of benzoic acid. In this method, irregularly spaced curved grating regions having a refractive index higher than that of the optical waveguide layer are formed. After this, Cr-A
The U film is removed and a cladding layer is formed on the optical waveguide layer to form an optical waveguide lens.

In the above embodiments, L + N b Oa was used as the substrate, but LiTaOa may also be used, and benzoic acid was used as the ion exchange solution, but AQNOa.

It may also be a molten salt containing metal ions such as TI No.

Furthermore, as shown in FIGS. 9 and 10, a planar waveguide lens 52.56 may be further formed on the incident side of the leading waveguide to which the semiconductor laser 50.54 is coupled.

[Effects of the Invention] As explained above, according to the present invention, since the diffraction grating is not a relief type diffraction grating formed by etching patterning, the surface of the optical waveguide layer is flat, reducing scattering loss. There is a big characteristic that koto is punishment - honor. Therefore, it is possible to provide an optical waveguide lens with less lens aberration caused by surface distortion (flatness) and with high diffraction efficiency.

Further, according to the method for manufacturing a guiding waveguide lens of the present invention, the optical waveguide layer and the diffraction grating utilize the change in the refractive index of the substrate by the ion exchange method, and the change in refractive index is large, the diffraction efficiency is large, and the optical waveguide layer and the diffraction grating are The propagation loss of the wave path can be reduced. Furthermore, the flatness of the substrate can be maintained at a high level, scattering loss can be kept low, and the laser beam can be focused on a minute spot.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view showing a conventional optical waveguide lens, FIGS. 2 to 7 are diagrams showing the manufacturing process of an optical waveguide lens in an embodiment of the present invention, and FIG. 8 is a diagram showing the use of the optical waveguide lens of the present invention. Figures illustrating examples, FIGS. 9 and 10 are diagrams showing other embodiments. 20...Substrate, 22...Photoresist 24...Photomask, 26...
・0r-Au film, 28...benzoic acid, 30.
. . . High refractive index region, 34 . . . Optical waveguide layer 1, 36 . . . Clad layer. Representative Patent Attorney Kensuke Norichika (other names) Figure 1 Figure 2 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9

Claims (4)

[Claims] (1) A substrate, a leading waveguide formed on the substrate and made of a material with a higher refractive index than the substrate, and a cladding layer formed on the optical waveguide and made of a material with a lower refractive index than the optical waveguide layer. An optical waveguide lens, wherein the optical waveguide layer has unevenly spaced curved grating regions having a different refractive index than the optical waveguide layer. (2) The optical waveguide lens according to claim 1, wherein the unevenly spaced curved grating regions have a refractive index higher than the refractive index of the optical waveguide layer. (3) A step of forming a mask having irregularly spaced curved lattice-like openings on a substrate made of an optical material, and heating the substrate on which the mask is formed in an ion exchange solution to remove the material constituting the substrate. a step of ion-exchanging the ions of the solution with ions of the solution to selectively form a region having a higher refractive index than the substrate on the surface layer of the substrate; a step of removing the mask from the substrate; and a step of removing the mask from the substrate; The substrate from which has been removed is heated in an ion-exchange solution, and the ions of the substance constituting the substrate are ion-exchanged with the ions of the solution to form an optical waveguide layer on the surface layer of the substrate that has a higher refractive index than the substrate. A method for manufacturing an optical waveguide lens, comprising: a step of forming a cladding layer made of a material having a refractive index lower than that of the optical waveguide layer on the optical waveguide layer. (4) A substrate made of an optical material is heated with an ion-exchange solution, and ions of the substance constituting the substrate are ion-exchanged with ions of the solution to form an optical waveguide layer on the surface layer of the substrate that has a higher refractive index than the substrate. a step of forming a mask having irregularly spaced curved grid-like openings on the optical waveguide layer;
The substrate on which the mask is formed is heated in an ion-exchange solution to exchange ions of the substance constituting the optical waveguide layer with ions of the solution, thereby forming a guide waveguide layer with an impurity having a higher refractive index than the optical waveguide layer. a step of forming equally spaced curved regions, a step of removing a mask on the optical waveguide layer, and a cladding layer made of a material having a lower refractive index than the optical waveguide layer on the optical waveguide layer from which the mask has been removed. 1. A method for manufacturing an optical waveguide lens, comprising a step of forming an optical waveguide lens.