Optical waveguide encapsulation

(54) NAME Enclosure for optical waveguide (56) PUBLICATIONS TO BE CALLED: - - - (57) SUMMARY:

The present invention relates to an enclosure for optical waveguides, to facilitate deflection of light signals. The optical waveguide comprises an optical medium, preferably of polyimide. According to the invention, an encapsulating material consists of an index-matching medium for the waveguide's light-conducting core. The light-conducting core has a greater refractive index than the refractive index of the encapsulating material and the encapsulating material is made of an elastic material.

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The numbers in brackets indicate international identification code, INID code. Letters in clamps indicate international document code.

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Technical area

The present invention relates to an optical waveguide enclosure for facilitating deflection of light signals, wherein the optical waveguide consists of an optical medium, preferably of polyimide.

The prior art

In today's fiber-optic communication area, and especially in the telecommunications field, it is desirable to be able to divert light signals to control the traffic on the optical fiber. The deflection of the light signals on the fiber is done today with a permanently fixed deflection device. The fiber consists of a light-conducting core and a covering sheath. Furthermore, the sheath has been peeled off or the fiber bent to make the light signal accessible to the deflection device. It has the task of capturing the light signal from the core through its evanescence field.

U.S. Patent No. 3,982,123 describes two ways of deflecting a light signal from an optical fiber without interrupting the fiber. The inventive idea of ​​the patent is to go in and look at the traffic contained in the fiber, where deflection can take place anywhere without disturbing the traffic. This is done by attaching a deflection device, which in this case is a material with a built-in photodetector, to a light-conducting core or to the fiber so that deflection of light signals can take place. The optical fiber consists of the core with low optical losses and the sheath with a lower refractive index than the core.

A first way described in the patent is to remove all or almost all sheath material on the fiber. Then, the detector is attached to the light-conducting core, whose peeled area must be at least 3 times the wavelength of the optical fiber.

Another way to deflect light signals is to bend the optical fiber without removing the sheath material. Thereby can

470 The 147 light signals go out through the mantle and are captured by the detector. In both cases, the deflection is permanent.

Another US patent US 4,784,452 discloses a method in which deflection occurs with a deflection device on an optical fiber. This fiber consists of a light-conducting core and at least one sheath material. The deflection device, a probe, is an optical fiber, of the same type as the fiber from which the deflection is made. This probe has a free end with a light-conducting core. To deflect light signals from the fiber, it must be peeled off so that the core is exposed. Here the probe is used, the free end of which is placed on the peeled part of the fiber. To get the best possible deflection, the angle between the probe and the fiber axis must be adjusted. A coupling medium encloses the area at the probe and the scaled portion of the fiber, and conducts light signals from the scaled portion of the fiber to the probe. The coupling medium, which is a solid and hard material, fixes the probe in relation to the fiber.

Through various experiments it has been found that the light-conducting core can be made of polyimide. In the article “Dependence of Precursor Chemistry and Curing Conditions on Optical Loss Characteristics of Polyimide Waveguides by CP Chien and KK Chakravorty at Boeing Aerospace and Electronics, Seattle, USA, SPIE vol 1323, Optical Thin Films III, New developments (1990), shows that Polyimide is a good material for the core of the optical fiber. Polyimide has good thermal stability and a dielectric number of 3.5, which is compatible with other IC materials. It is good for light transmission such as for optoelectric circuits in the frequency range of the size GHz. The advantage of the polyimide is that in the production of cores they can be packed tightly next to each other. Further data on the polyimide is that it has a refractive index of 1.6 (1.58-1.62) and optical losses in the nucleus of about 1 dB / cm at UV exposure.

Experiments have been made with a silicone elastomer as an index-matching medium for the light-conducting core. In the article Index

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Matching Elastomers for Fiber Optics by Robert. W. Filas, BH Johnson and CP Wong at AT&amp;T Bell laboratories, NJ, USA in the journal IEEE, Proc. Electron. COMPON. Cont., 39th, 486-9, shows that silicone elastomer is a good material for indexing the core. Reflection of copolymer as a function of diphenyl content and temperature is obtained by measuring the reflection strength of a single-mode waveguide, whose core is encapsulated by an elastomer. It is possible to obtain the same refractive index on a silicone rubber material as on the core. One way to use the silicone rubber is as an interface between different components. Another way is to use it as protection against, for example, moisture and dust.

Today, air is used as the refractive medium for the light-conducting core of the light-waveguide. The air has a significantly lower refractive index than the polyimide. The air has 1 as the refractive index, the polyimide has 1.6 as the refractive index and the silicone rubber has 1.5 as the refractive index.

A disadvantage of the previous solutions is that deflection of light signals from optical fibers takes place with permanently attached devices. This means that the deflection of light signals from the fiber takes place at a specific location where the sheath has been peeled off. The previous solutions have several additional disadvantages. One of these disadvantages is that the light deflection can only take place on waveguides in the form of fibers, where the sheath must be peeled off at the place where the deflection is to take place. The deflector must be attached to the optical fiber at the location where the sheath has been peeled off. Deflection in permanent branches results in losses that are too large.

Disclosure of the Invention

The object of the present invention is to provide an optical waveguide which allows deflection of light signals in a simplified manner, without the disadvantages of previous solutions.

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The idea of ​​the invention is to encapsulate the optical guide with an encapsulating material, a sheath, which is elastic. Because the encapsulating material is elastic, a deflection device, a probe, can be pressed down against a light-conducting core. As a result, the probe can absorb light from the evanescence field that exists around the core and thus deflection has been made without having to peel off some of the sheath material on it.

The invention relates to a choice of material in order to obtain an intended physical property of the waveguide in a simple manner. The new thing is that the waveguide sheath is replaced by the encapsulating material, which is elastic, for example silicone rubber.

The optical waveguide is in one case a light waveguide and in the other case an optical fiber. The two optical waveguides differ from each other in that the light waveguide is adhered to a substrate, comprising a thin layer, a light-conducting core and an encapsulating material, while the optical fiber consists of a light-conducting core and the encapsulating material.

According to a first alternative, the encapsulating material is used as a comprehensive protection over the light-conducting core and over the components connected to the light-waveguide. The light waveguide and components are attached to the substrate. The encapsulating material is elastic and additionally optically transparent, which has three distinct functions. The first function is as encapsulating material, which covers the core to obtain an index-matching medium that does not output the light signals from the core. The second function is as a light-conducting layer between the end of the light-waveguide and a component that emits or receives the light signals, for example a laser diode. It is used as a coupling material to direct the light signals to / from the laser diode from / to the core. The numerical aperture of the light is controlled by the refractive index of the encapsulation material. The encapsulating material is outside the laser diode window. The third function is that the encapsulating material, when there are several components on the substrate, such as connectors, is used to protect the components and the core from external influence.

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According to a second alternative, the optical fiber jacket is constituted by the encapsulating material, which is located around the light-conducting core.

The advantage of the invention is that it is possible to deflect the light signals without having to permanently attach the deflection device to a certain location on the optical waveguide. Another advantage is that it is possible to deflect light from the light waveguide when it is stuck to the substrate. Deflection from light waveguides on substrates has not previously been done. Thus, it is easy to divert light signals from such a system. Further advantages are that the deflection can be carried out temporarily if desired, and that the elastic enclosure protects against external environmental effects such as dust, air and humidity at the deflection of light.

Further objects and advantages of the invention will become apparent from the preferred embodiments described below and with reference to the accompanying drawings.

Figure Description

Figures 1-3 show a first embodiment and figure 4 shows a second embodiment.

Figure 1 shows a light waveguide on a silicon wafer seen from above. Figure 2 shows part of an enlarged cross section AA of the light waveguide on the silicon wafer.

Figure 3 shows part of an enlarged cross-section BB of the light waveguide on silicon wafer.

Figure 4 shows a section of the optical fiber.

Preferred embodiment

The figures shown are not scalable but only show the parts which are essential for describing the idea of ​​the invention.

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A first embodiment is shown in Figures 1-3. Figure 1 shows a device 20 consisting of a substrate 21, a connector 25, a light waveguide 23 and an optical component 24 that emits or receives light.

Figure 2 is a sectional AA of the device 20 of Figure 1 at the optical component 24. On the substrate 21 is a very thin layer 40 which is to act as a refractive medium for a light-conducting core 30. Between one end of the core 30 and the component 24 there is a very narrow gap 31. The connector 25 connects directly to the other end of the core 30. On top of component 24 and core 30 is an elastic encapsulating material 32.

Figure 3 is an enlargement of the light waveguide 23 at the section BB of Figure 1. Figure 3 shows the light waveguide, which consists of the light-conducting core 30, and the thin layer 40 on the substrate 21 and the encapsulating material 32. The encapsulating material has a lower refractive index than the core 30. The layer 40 lies on the substrate 21 and on top of the layer 40 lies the core 30. The encapsulating material 32 covers everything that lies on the substrate 21.

The substrate 21 shown in Figure 1 is a silicon wafer which is usually made of semiconductor. On the disc, it is possible to lay several light waveguides 23, components 24 and connectors 25. The substrate 21 can also be made of a circuit board material, a glass material or any other material, only the substrate 21 has a lower refractive index than the core 30. It is important that the damping becomes as small as possible in the core 30.

In Figures 2 and 3, the light waveguide 23 is made up of three different parts, the thin layer 40 which is on the substrate 21, the core 30 and the encapsulating material 32. The layer 40 is silica if the substrate 21 is silicon. It must be of a lower refractive index than the core 30 in order for it not to emit light from it. The light-conducting core 30 is patterned in the form of thin threads and has a single mode width of 5-10 µm. and for multimode 40-100 µm. To apply to the core 30, a photo-patternable polyimide which is used

470 147 can be of two different types, probimide 412 and probimide 348. They are wetted on the substrate 21. Wet etching is an inexpensive and easy manufacturing technology to produce light-conducting cores 30. This method can also be used when the substrate 21 is large, such as eg a whole circuit board. Other substances which can also be used for the core 30 are acrylate, polymethacrylate and polystyrene. There are also non-photo-patternable polyimides where the structure can be crosslinked. If single mode is selected, it becomes a little more difficult to get the correct refractive index, since the encapsulation material must be more well defined than for multimode.

The optical components 24 consist of, for example, a laser diode or an LED. When the substrate 21 is of silicon, the thin layer 40, silica, is first applied to obtain the proper refractive index. The core 30 is made of the polyimide material and is wetted on the silica. Gold electrodes are then applied to the location where the laser diode is mounted, to contact current to the laser diode. The laser diode, 0.2 x 0.3 mm, is soldered to the substrate 21 which is about 5 x 5 mm. The laser emitting portion of the laser diode, the window, is 1.5 x 1 / xm, where the laser diode directs light to the light waveguide. Another component is the connector 25 of Figure 1, which is a simple connector. Ti 'll end adds encapsulation material such as silicone rubber on.

One area that gets very hot is the laser diode. This is because it gives off so much heat. One way to dissipate heat is to use a small diamond disc as a heat conveyor. With this action, the encapsulation material does not become so hot that the material degrades and degrades. In Figure 2, the encapsulating material 32 is of silicone rubber, which is a type of elastomer. The encapsulating material 32 is for deflecting light signals from the light-conducting core 30. Because it is elastic, a light-conducting probe can be pressed down against the core 30. The silicone rubber is optically conductive. One method of applying the encapsulating material 32 to the substrate 21 with the components 24 and 25 is then it is still malleable and then cures, whereby the silicone rubber becomes elastic. Because the silicone rubber can also

470 147 control monkeys turn one, the waveguiding properties, it is good as a refractive medium. By using the silicone rubber, a protective layer is obtained over the components 24, 25 and the light-conducting core 30 and this layer simultaneously has good optical properties. In addition, the rubber is elastic and can absorb thermal stresses. The encapsulating material 32 is used in three places on the substrate 21: first, as the encapsulating material 32 to the core 30. Second, to encapsulate the components 24 and 25. Third, as the index-matching medium between the core 30 and the optical component 24. The numerical aperture is controlled by the index-matching medium by the refractive index.

There are several different ways of applying the encapsulating material 32. One of these methods is by printing a small strand much like when sacking over the substrate 21. Another way is by spinning technique. The spin technology assumes that the encapsulating material 32 is applied to the center of the substrate 21. Subsequently, the substrate 21 is rotated in a spinning machine and with centrifugal forces, the encapsulating material 32 is spread on the entire substrate 21 in a simple and good manner. The result of this technique is that the encapsulating material 32 is evenly and thinly distributed on the substrate 21.

The above-described device 20 is utilized for a method of deflecting a light signal with a light-conducting probe directly onto the optical waveguide. By passing the probe down through the encapsulating material 32, which is elastic, it is possible to get so close to the light-conducting core 30 that the evanescence field around the core 30 can be absorbed. Thus, almost no losses are achieved in the core 30. It is important not to get too far down with the probe, because then the deformation of the enclosure can be permanent. If the probe is not pushed down far enough into the encapsulation material 32, it cannot take up the evanescence field. The distance between the probe and the core 30 must be of the correct order of magnitude less than µm. To obtain the same distance at each deflection, a measuring instrument can read that the correct distance is obtained.

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The method concerns the following:

In a first step, the fiber end of the light-guiding probe is brought down toward the encapsulated optical guide. In a second step, the fiber end of the probe is pressed into the encapsulating material 32 during an elastic deformation thereof, so far as the elastic properties of the material are allowed or the remaining deformation, the set, does not remain. In a final step, the fiber end of the probe is angled toward the optical guide 23 so that a portion of the light signal is absorbed into the probe. The angle is for the probe to deflect a certain light signal. If the angle is changed, another light signal is obtained.

It should be noted that the fiber end of the light-conducting probe is as wide as the optical waveguide, to obtain the best possible deflection. Furthermore, the probe must be made of the same material as the light-conducting core or a material with equal or greater refractive index. The probe may also be made of a plastic fiber.

The method also makes it possible to have the light-conducting probe permanently attached to the optical waveguide if desired. After the deflection has occurred, the probe is removed and no remaining deformations remain. When deflecting the light waveguide, no further action is needed to make the deflection possible.

A second embodiment of the device is shown in Figure 4. In Figure 4, an optical fiber 1, consisting of a light-conducting core and an encapsulating material 3, is shown which is elastic. The core 2, which is constituted, for example, of polyimide, has a higher refractive index than the encapsulating material 3. Encapsulation of the core 2 is made of the elastic material, which is preferably silicone rubber. Because the material is elastic, a deflection device, probe, can be inserted into the encapsulating material 3 and when the probe reaches the evanescence field, deflection can take place. The deflection device is removable if desired. The optical fiber 1 exists between different telephone stations or, for example, between different computers.

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These can be large distances and sometimes someone wants to go in and investigate the traffic that is there. Here it is shown that the fiber 1 is not attached to any substrate but is exposed.

The same method of light deflection can be used for optical fibers 1 previously described regarding the light waveguide 23. Prior to the first step of the method of the fiber 1, it must be laid on a hard surface for deflection to occur. Since the optical fiber 1 is too flexible, it is not possible to insert a probe on it but it is on a hard surface.

It is quite expensive to encapsulate laser diodes with current technology using a metal capsule. One of the advantages of encapsulating the components on the substrate is that this is relatively inexpensive. Another advantage of using the encapsulating material with elastic properties is that it is possible to depress a probe and deflect light signals. Another advantage is that it is inexpensive and easy to manufacture optical waveguides according to the above embodiments. The method allows to temporarily deflect light signals from optical waveguides. Another advantage of using the encapsulating material is that it can absorb the movements that the optical components give off when they become hot.

The invention is, of course, not limited to the embodiments described above and shown in the drawings, but can be modified within the scope of the appended claims.

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