TITLE
Method for connecting a fibre optic cable to a light guide.
TECHNICAL FIELD The present invention relates to a method for connecting a fibre optic cable to a light guide on a substrate, and an arrangement manufactured in this way.
BACKGROUND ART
When connecting a fibre optic cable to a light guide on a substrate, such as for example a circuit board, a possible method is to attempt to align one end of the fibre cable to one end of the light guide by means of a mechanical device on the circuit board and also to attempt to have these two ends making as close contact with each other as possible, as there should be as small an air gap between them as possible.
Before this is carried out, the respective ends of the light guide and suitably also of the fibre optic cable, should be treated in some way, for example by polishing or grinding, after which the connection is made. Making the connection using a mechanical device has a number of disadvantages, including difficulties in aligning the fibre cable correctly to the light guide, and the fact that as, in principal, there will always be a space between the fibre cable and the light guide, the refractive index for air (if it is air that is the intervening material) will impair the connection. In addition, polishing or grinding the light guide and/or the fibre cable is a time-consuming and expensive task.
DISCLOSURE OF INVENTION
There is thus a need to be able to connect a fibre cable to a light guide without the disadvantages mentioned above. This need is fulfilled by the present invention, as it provides a method for connecting a fibre optic cable to a light guide on a substrate, according to which method one end of the fibre optic cable is first brought into contact with the substrate, after which the
light guide is arranged around the end of the fibre optic cable, in contact with the substrate.
The light guide is suitably placed against the end of the fibre optic cable in a condition in which the light guide still requires curing.
Alternatively, of course, conversely, the fibre optic cable can also be connected to the light guide on a substrate, one end of the fibre optic cable being brought into contact with the light guide in such a way that the light guide surrounds the end of the fibre optic cable.
Also in this case, the end of the fibre optic cable is suitably placed against the light guide in a condition in which the light guide still requires curing.
The end of the fibre optic cable is suitably, but not necessarily, polished before the connection is carried out.
By means of the invention, a connection is thus achieved without any air between the fibre and light guide, which minimises the impairment of the connection. In addition, if so required, the connecting end of the fibre optic cable can be arranged at such a distance from the end of the light guide that there is uniformity in the conductor.
BRIEF DESCRIPTION OF DRAWINGS The invention will be described in greater detail in the following with reference to the attached drawings, in which
Figure 1 shows a plane view from above of a circuit board with a light guide, and
Figures 2a-2d show various steps in a method according to the invention, and
Figures 3a-3c show various steps in an alternative method according to the invention, and
Figure 4 shows a plane view from above of the circuit board from Figure 1 , with a fibre cable connected to the light guide.
MODES FOR CARRYING OUT THE INVENTION Figure 1 shows a plane view from above of a substrate 100, in this case a circuit board which is suitably a so-called LTCC board. A light guide 110 is arranged on the substrate 100, and a fibre optic cable is to be connected to one end 115 of the light guide. At this stage of the invention, the light guide is in a non-cured condition, and has been arranged on the substrate 100 in a required pattern by means of one or more different methods which are already known. The methods for arranging the light guide 110 on the substrate 100 include, for example, offset printing, lithographic methods or screen printing using stencils.
Figure 2a shows the substrate 100 and the light guide 110 viewed along the line ll-ll in Figure 1. One end 125 of a fibre optic cable 120 is to be connected to one end 115 of the light guide 110, which is shown in Figure 2b.
As mentioned above, the light guide is in a non-cured condition, in other words in a condition in which the light guide can be processed with relative ease. Normally, the light guide 110 is arranged on the circuit board 100 in the form of a paste which comprises glass beads with a binding agent that normally comprises an oil. After the light guide has been laid in a required pattern, quantity and extent, the resulting arrangement can be cured, which however has not yet been carried out at the stage that is shown in Figures 2a and 2b.
As the light guide 110 has not yet been cured, the end 125 of the fibre optic cable 120 can be "pressed" into the light guide 110, after which the material in the light guide surrounds one end 125 of the fibre cable, which is shown in Figure 2c.
Figure 2d shows a variant of the invention; when the material in the light guide is applied onto the substrate, a particular part d at the edge 115 of the material can, if required, be given a shape that is not perpendicular but slopes downwards. It can then be important for the end 125 of the fibre cable to be arranged so that it comes within the sloping area d. In addition, a part d of the end 115 of the light guide can be non-uniform, in which case it can also be desirable to arrange the end 125 of the fibre cable within this distance .
After the steps that are shown in Figures 2a-2c, and if required also 2d, the light guide can be cured, which for example is carried out by the whole circuit board being subjected to a raised temperature. If the material in the light guide is a paste of the type mentioned above, the temperature rise is suitably applied in two steps: in a first step the arrangement/light guide is subjected to a temperature that is so high (in normal applications approximately 400 degrees Celsius) that the oil that constitutes the binding agent in the paste boils away. Thereafter the temperature is increased to a level (often approximately 800 degrees Celsius) at which the glass beads melt, after which the light guide cures with one end of the fibre cable enclosed in the light guide.
When the fibre cable is pressed down into the not yet cured light guide, there is a danger that the light guide can be deformed. In order to prevent this, there are many possible solutions that support the light guide in the pattern and design that is required. Examples of such solutions are some form of lateral support for the paste, which can be removed after curing, or alternatively can remain in place.
An alternative method according to the present invention is shown in Figures 3a-3c, with the same reference numbers as above.
In this variant of the invention, the fibre cable 120 is arranged on the substrate 100, after which the light guide 110 is arranged in such a way that it
surrounds one end 125 of the fibre cable 120, which is shown in Figures 3a- 3c. The methods for arranging the light guide 120 on the substrate 100 can be the same as have been described above, in other words, printing, for example offset printing, various lithographic methods or screen printing using stencils. When the light guide has been arranged in the required pattern and in association with the fibre cable, the light guide is cured in the same way as has been described above in association with Figures 2a-2c.
Figure 4 shows a resulting arrangement 400, with a light guide 110 arranged on a substrate 100. The arrangement 400 comprises, in addition, a fibre optic cable 120, and the light guide 110 encloses one end 125 of the fibre optic cable.
The invention is not restricted to the embodiments described above, but can be varied freely within the framework of the following patent claims.