FI80347B - Method for manufacturing an optical adapter, in particular a multi-form adapter - Google Patents

Description

80347

The present invention relates to a method for manufacturing an optical adapter, in particular a multimode adapter, according to the preamble of claim 1.

Multimode adapters can be used e.g. between ion-exchanged waveguides and fibers to reduce coupling loss.

Because ion-exchanged glass waveguides are low attenuation and inexpensive to manufacture, they are increasingly used as passive components in integrated optics. The use of several single and multiple waveguides made by ion exchange technology in telecommunication and sensor applications has been demonstrated.

Recently, attention has been paid to the coupling between diverse ion-exchanged components and optical fibers. Usually, attempts have been made to limit the switching attenuations by optimizing the shape of the waveguide, i.e. by using waveguides manufactured by a two-phase, electrically controlled ion exchange technique. In the second stage of this ion exchange, the refractive index near the surface of the glass is reduced and a rather round waveguide is obtained. Another option for reducing coupling attenuation is to shape the refractive index profile of the coupling end of the coupling fiber (tail fiber) to be connected to the ion-exchanged component or to attach a separate adapter substrate provided with a glass substrate in which the refractive index profile changes between the fiber and the ion-exchanged.

Finnish patent application 872816 discloses a method for manufacturing a single-shape shape field transducer in which a geometrically variable core is obtained in the production of a blank by making a blank from two component 80807 quartz substrate tubes and an MCVD core fiber attached to its inner surface.

In addition, the prior art has been discussed in the following publications: tl] Okuda E, Tanaka I, Yamasaki T: Planar gradient index glass Waveguide and its application to a 4-port branched circuit and star coupler, Appl. Opt. 23, 1745 (1984).

[2] Honkanen S: Ion exchange process for fabrication of integrated optical Waveguide structures into glass substrates (1988).

A disadvantage of the prior art is that difficult-to-handle salt melts have to be used in the two-step ion exchange.

The object of the present invention is to obviate the disadvantages of the technique described above and to provide a completely new type of method for manufacturing an optical adapter, in particular a multiform adapter.

The invention is based on the application of an optical fiber, a quartz plate and a deformable region of a fiber to a substantially planar surface of a quartz substrate by heat treatment locally so that the quartz substrate softens at the most deformable part of the fiber. the cross-sectional surface is formed substantially in a semicircular shape.

More specifically, the method according to the invention is characterized by what is set forth in the characterizing part of claim 1.

The invention provides considerable advantages.

3 80347

The advantages of the method according to the invention are its straightforwardness, speed and low manufacturing costs.

In addition, the method of manufacturing the multimode adapter according to the invention causes the cross-section of the core to change from round to semicircular in a few centimeters. The attenuation of the multimode adapters thus prepared is very low, and the components in question are compatible with waveguides manufactured by single-phase ion exchange technology. Said single-stage dry silver ion exchange has considerable advantages over the molten salt ion exchange technique.

The invention will now be examined in more detail with the aid of application examples according to the accompanying drawings.

Figures 1a to 1a show the calculated core cross-sections of the deformable end of a multimode adapter made by the method according to the invention at different stages of the process.

Figures 2a to 2c show the actual cross-sections of a multimode adapter made by the method according to the invention at different points of the adapter.

Figure 3 shows a cross section of an ion-exchanged waveguide.

Figure 4 shows one multimode adapter made by the method according to the invention.

The method according to the invention makes it possible to produce components in which the end of the tail fiber 2 is deformed into a semicircular shape by utilizing the surface tension of molten quartz. The deformed part of the tail fiber 2 attached to the quartz substrate is called a multimode adapter. The multimode adapter can also be used as a stand-alone component separate from the tail fiber, as a matching element between the fiber and the ion-exchanged light channel. By the method, the cross-sectional geometry of the core 4 4 80347 can be changed from circularly symmetrical to semicircular. The manufacturing method of the multiform adapter is based on the heat treatment of the tail fiber 2 placed on the surface of the quartz glass 1 according to Figures 1a. In the process, one end of a diversified standard quartz fiber 2 (e.g., a fiber made by the MCVD method) is placed on a quartz glass substrate 1 and fused thereto. The melting takes place locally in the longitudinal direction of the fiber so that the highest temperature is applied to the deformable end of the fiber 2. The temperature gradient is chosen so that at a distance of 10 to 30 mm from the tip of the fiber 2, the cross-sectional geometry remains unchanged. When the temperature is high enough (approx. 2000 ° C) and the quartz glass softens, the surface area of the structure tends to be minimized. This forces the surface to be smooth. As a result, the tip portion of the fiber 2 (geometric disturbance on the surface of the flat glass) melts inside the substrate material 1. After the tip portion of the fiber 2 has sunk into the substrate 1, the surface tension is minimized and no force is moved further deeper into the glass substrate 1. As the heater, for example, a hydrogen burner can be used, in which case the flame can be applied to the substrate 1 from below.

We have used a simple model for the defermentation of the core 4 during melting. The model is based on the following assumptions: 1) As the fiber 2 melts, it spreads against the surface of the substrate 1 so that the width (2ac ^) of the fiber 2 is about half the circumferential length of the original undeformed fiber 2 (see Figures 1a to 1e). This assumption is in good agreement with the experiments we performed.

2) The thickness of the glass between the surface of the substrate tube and the core 4 is equal to the thickness of the shell of the flattened core 4.

It follows from the first assumption that the flattened nucleus is an ellipse with a major axis half of 5 80347 aco β rco frV2 (1) and a minor axis half of ^ co = rco2 // iT (2)

The equation of the flattened core at this stage is thus Y '= ± bc od-x / aCo> 2> * (3)

Based on the second assumption, the equation of the deformed core is: y “± bcl (1_ (x / acl) 2> * + y '(4) where ac and bc ^ are the diameters of the flattened fiber in the same way as equations (1) and (2).

Manufacturing experiments were performed using Heraus quartz tubes and a glass lathe equipped with a hydrogen burner. The outer diameters of quartz tubes are typically between 12 and 25 mm and the corresponding inner diameters are between 9 and 19 mm. The fiber 2 was placed inside the tube 1 and the tube 1 was heated from the outside. The typical diameter of the fibers 2 is about 125 μm. The curvature of the inner surface of the quartz tubes 1 does not substantially change the above consideration, since the diameter of the tube 1 is very much larger than the diameter of the fiber, as can be seen from the dimensions given above. In practice, for a planar approximation, it is sufficient that the ratio of the inner diameter of the quartz tube to the diameter of the fiber is greater than 100. Manufacturing tests have also been performed on a planar substrate surface.

Figures 2a to 2c show the change in the cross-sectional geometry of the core as a function of location at different points in the multimode adapter. The distances are measured along the axis of the fiber. The length of the deformed area is about 12 mm. In Fig. 2a, the distance z from the undeformed region is 0 mm, in Fig. 2b 6 mm and in Fig. 2c 12 mm, respectively. These figures can be compared with the theoretically calculated cross-sections of Figure 1. The cross-sectional area of the deformed core (Fig. 2c) can also be compared to the typical cross-sectional area of an ion-exchanged waveguide shown in Fig. 3. The cross-sections are very similar in geometry.

Figure 4 shows the finished end product. The deformed core 4 is inside the substrate 1 and the undeformed core 4 'is completely on the surface of the substrate. The multimode adapter 5 can also be used as an independent component separate from the tail fiber 2 '. In this case, the multimode adapter 5 acts as a matching element between the ion-exchanged light channel and the fiber.

The proposed method for fabricating a diversified, cross-sectional adapter component offers a new opportunity to reduce the coupling attenuation of a multifunctional fiber and an ion-exchanged waveguide.

This manufacturing method can also be applied to single-mode waveguides. Adapter components can be used to reduce coupling attenuation, e.g., between waveguides fabricated on a LiNbCO 3 substrate and optical fibers.

Claims (3)

A method of producing an optical adapter, in particular a multiform adapter, characterized in that - an optical fiber (2) having a light-conducting core (4) is applied to a substantially pane surface of a quartz substrate (1), area of the quartz substrate (1) and the fiber (2) to be deformed is treated locally with heat in such a way that the quartz substrate (1) melts at the location of the fiber (2) to be deformed most, the fiber (2) at the here, substantially decreases to the level of the surface of the quartz substrate during deformation, whereby the cross-sectional area of the most deformed site of the core (4) of the fiber (2) becomes substantially semicircular. 2. A method according to claim 1, characterized in that the quartz substrate (1) and the fiber (2) are treated with heat in such a region that the axial length of the at least partially deformed fiber becomes about 10-30 mm. 3. A method according to claim 1 or 2, characterized in that as a quartz substrate (1) a quartz tube is used, whose inner diameter is considerably, at least 100 times, larger than the diameter of the fiber (2). il