JPH0555041B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a technique for integrally forming optical elements such as optical waveguides and microlenses within a substrate by ion exchange.

[Conventional technology]

The surface of a glass substrate with a flat surface is covered with a mask material having openings in a planar pattern of desired optical elements such as optical waveguides and lenses, and the substrate glass such as Tl, Cs, Li, Ag, etc. is passed through the openings of this mask material. Composition means that ions that change the refractive index of the substrate with different ionic radii are internally diffused through exchange with ions in the glass, and an optical element with a refractive index distribution based on the concentration distribution of the diffused ions is integrated within the substrate. There are known methods of forming

[Problem that the invention seeks to solve]

In the above-mentioned conventional method, the mask material provided with the opening is placed only on the side of the substrate where the optical element is to be provided, and the back side is either entirely exposed or covered entirely with the mask material.

As a result, ions with a different ionic radius from the ions of the substrate material composition enter only the mask opening on the substrate surface side, causing expansion or contraction distortion between them and the surrounding ions in a plane parallel to the substrate surface. On the back side, the above-mentioned external ions penetrate uniformly over the entire surface of the substrate, or do not penetrate at all, so there is no distortion as described above. Therefore, in the part where the ion penetration area is different on both surfaces, there is a gap between the front side and the back side of the substrate. This causes a distortion difference.

Then, there is a problem that the stress caused by the strain difference between the front and back surfaces causes deformation such as warping in the substrate, deteriorating the optical characteristics of the device. In the case of optical waveguides, there is also a problem in that adjacent waveguide ends are no longer aligned in a straight line, making it difficult to connect them to optical fibers.

[Means to solve problems]

The surface (back surface) opposite to the surface on which the optical element is to be formed (front surface) of the substrate is also covered with a mask material that also has openings with almost the same pattern as the front surface side, and ion exchange is performed simultaneously on the front surface through this opening. I decided to do this.

[Effect]

Since strain occurs in approximately the same area on both the front and back sides of the substrate, the strains on both sides cancel each other out, eliminating the generation of local stress between them as in the past, and preventing warpage of the substrate during ion exchange treatment. This can prevent deformation such as

〔Example〕

The present invention will be described in detail below based on embodiments shown in the drawings.

As shown in FIG. 1, a flat transparent glass substrate 1
Both surfaces 1A and 1B of are coated with ion permeation prevention mask materials 2A and 2B, respectively.

The mask materials 2A and 2B are respectively provided with openings 3A and 3B in a planar pattern of a desired optical element (in the illustrated example, a microlens array), and the shapes and positions of the openings 3A and 3B of both mask materials are made almost the same. .

The mask materials 2A and 2B are obtained by, for example, depositing a metallic titanium film using a high-frequency sputtering method, and then forming a predetermined pattern of openings using a well-known photolithography technique. At this time, the photoresists provided on the front and back surfaces may be exposed simultaneously using a double-sided exposure machine and then etched with hot phosphoric acid or the like, or exposure and etching may be performed on one side at a time.

Next, as shown in FIG. 2, the substrate 1 with patterned opening masks on both sides is immersed for a certain period of time in a molten salt 5, such as thallium nitrate (TlNO ₃ ), containing ions to be diffused into the glass substrate. do.

As a result, ions 6 in the molten salt 5, for example Tl
The ions diffuse into the substrate through exchange with ions in the glass substrate 1 through the mask openings 2A and 2B, and the concentration distribution of the intruding ions 6 occurs in a region with a substantially semicircular cross section centered around the mask openings 2A and 2B. A refractive index gradient portion 7 based on , that is, a desired optical element is formed.

At this time, since the ionic radius of the invading ions 6 is different from that of the ions constituting the substrate glass 1, distortion occurs between the portion 7 and the peripheral substrate portion.

However, according to the above method, ions are diffused with almost symmetrical concentration gradients and penetration regions on both the front and back surfaces, so the above-mentioned strain is canceled out between the two surfaces, and stress is generated due to the strain difference between the two surfaces. is significantly reduced compared to the conventional method, and deformation such as warping of the substrate does not occur after the ion exchange treatment.

In the illustrated example, the mask openings 3A and 3B are circular for manufacturing a microlens array, but
Needless to say, the mask openings 3A and 3B may have any shape, and can be applied to the manufacture of various flat optical elements such as optical waveguides.

〔Effect of the invention〕

According to the present invention, it is possible to prevent uneven expansion between the front and back surfaces of the substrate during ion exchange treatment, warping and other deformations caused by contraction force, and it is possible to stably manufacture optical elements with excellent optical properties. It became.

[Brief explanation of the drawing]

The figures show an embodiment of the present invention. Figure 1 is a cross-sectional view and a plan view showing a state in which masks with the same opening pattern are applied to both sides of the substrate, and Figure 2 shows the process of ion exchange treatment of the substrate. FIG. 1...Substrate, 2A, 2B...Mask material, 3A,
3B... Opening, 5... Molten salt, 6... Ion, 7
...Optical element.

Claims (1)

[Scope of Claims] 1. One side of the substrate is coated with a mask material provided with openings in a predetermined pattern, and ions that can change the optical properties of the substrate are exchanged and diffused into the substrate through the openings. In the method of integrally forming an optical element on one side of the substrate, the back side of the substrate is also covered with a mask material having almost the same opening pattern as the front side, and ions are diffused through the openings simultaneously with the front side. An optical element using ion exchange, which is characterized by canceling out bias in changes in physical properties other than optical properties that occur in the substrate due to ion exchange, and removing the substrate layer including the optical element formed on the back side after the ion exchange treatment. manufacturing method.