CH666969A5 - METHOD FOR MANUFACTURING AN OPTICAL PHASE DELAY MEMBER. - Google Patents

Description

DESCRIPTION

The invention relates to a method for producing an optical phase delay element.

The transmission of messages by means of light waves is becoming increasingly important. Components are required for this - e.g. optical transmitters and receivers - which, like the electrical components, endeavor to be produced in the form of integrated circuits. To produce optical phase delay elements, components are required with which the light intensity (amplitude) can be modulated and / or the frequency (or also the transit time) can be shifted. This is e.g. achieved by applying 4 μm wide titanium strips to a substrate made of a lithium niobate single crystal and then diffusing into the substrate. The titanium is installed in the place of the niobium atoms and increases the refractive index of the substrate crystal, so that a light wave is guided in the channel formed by the diffused material. By applying an electric field, the state of polarization of the crystal and thus the speed of light propagation in this medium can be changed.

In a method which has become known in practice, a titanium layer is applied to a ground, polished and cleaned surface of a lithium niobate substrate in a sputtering system. Sputtering is the bombardment of a solid or a melt in a vacuum with particle beams, whereby the particles can either be individual atoms, ions or molecules (cf.Maissei & Glang, Handbook of Thin Film Technology, McGraw-Hill, 1970). The titanium surface is coated with a photoresist and this layer is masked according to the desired light channel structure and then exposed. After development, the unexposed areas of the titanium layer are etched away, so that only the desired titanium strip or strips remain on the substrate. These are then diffused into the substrate by heating. Along the optical channels formed in this way, electrical contacts must still be attached, via which the electrical field required for control can be applied.

The manufacturing method described above is complex and it is also difficult to subsequently apply the contacts parallel to the edges of the channel. The formation of a lithium dioxide layer during annealing causes a considerable dielectric loss when the optical channel is driven.

The invention has for its object to provide a simplified manufacturing process, which in particular avoids subsequent influencing of the light channel.

This object is achieved according to the invention by the method characterized in claim 1.

The invention is explained below using an exemplary embodiment.

The figure shows various stages A to E in the production of an optical phase delay element according to the invention.

In line A of the figure, a lithium niobate single crystal 1 is shown schematically, on the polished and cleaned surface of which an approximately 100 nm thick layer-shaped diffusion barrier 2 made of an oxygen-inert material, e.g. in the form of a platinum layer. This platinum layer is applied either by electron beam evaporation or by direct current or high-frequency sputtering. Line B shows a negative photoresist image 3 of the channel 4 to be formed, which is applied to the platinum layer. This negative image is produced in a known manner by masking, exposing and developing a negative photoresist applied to the surface of the substrate 1.

Then - see line C - the platinum layer is etched away by sputtering, so that the lithium niobate is exposed again at the location of a strip 6, along which titanium is to be diffused, as explained below.

An approximately 30 nm thick titanium layer 7 is now applied to the now partially covered with platinum and partially exposed surface of the substrate 1 by electron beam evaporation or by sputtering (line D).

The substrate is then heated in a diffusion furnace under an oxygen atmosphere. The titanium diffuses in the region of the strip 6 into the LiNbOs of the substrate 1 and forms a strip-shaped light channel 8, while the titanium layer is oxidized on its surface and thus forms a TiO layer 9. The light channel 8 is then laterally delimited by two parallel platinum strips 10 and 11 (row E).

The platinum strips 10, 11 already form the contacts required for applying an electrical field and thus for controlling the phase delay element. You then just have to be structured into one contact, whatever

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is also easily possible through the oxidized titanium layer, and can be connected to an electrical connection.

The manufacturing steps required to manufacture an optical phase delay element are reduced by the invention. The platinum strips 10 and 11 form contacts which are flush with the edge of the light channel 8. They adjust themselves. When tempering, no lithium oxide with a low dielectric constant forms as a passivation layer under the contact, the applied electric field can therefore work without dielectric losses at the light channel.

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1 sheet of drawings

Claims (7)

666 969 1. A method for producing an optical phase delay element, characterized by the following method steps: a layered oxygen-diffusion barrier (2) is applied to the surface of a substrate (1) made of a lithium niobate crystal (FIG. A), a strip-shaped structure (6) is etched out of this diffusion barrier (FIG. C), a titanium layer (7) is applied to the now partially covered and partially exposed substrate surface (FIG. D), By heating the substrate (1) in an oxygen atmosphere, the titanium layer (7) is diffused into the substrate on the one hand at the exposed substrate locations along the strip-like structure (6), whereby - the titanium layer - forms a strip-shaped light channel (8) and on the other hand on its surface oxidized (FIG. E), and finally the diffusion barrier is structured through the oxidized titanium layer (9) into at least one contact (10, 11) and connected to an electrical connection (FIG. E). 2. The method according to claim 1, characterized in that a platinum layer is applied as the oxygen-inert diffusion barrier (2). 2nd PATENT CLAIMS 3. The method according to claim 1 or 2, characterized in that the diffusion barrier is applied by electron beam vaporization. 4. The method according to claim 1 or 2, characterized in that the diffusion barrier is applied by direct current or high-frequency sputtering. 5. The method according to any one of the preceding claims, characterized in that the titanium layer is applied by electron beam evaporation or sputtering. 6. The method according to claim 5, characterized in that the titanium layer is heated after application in a diffusion furnace under an oxygen atmosphere. 7. Optical phase delay element, produced by the method according to claim 1, characterized in that the at least one contact (10, 11) consists of a layer-shaped oxygen-diffusion barrier (2) applied to the surface of the substrate (1), from which the light channel (8) corresponding strip (6) has been etched out.