Design and analysis of coupling elements between optical fibres and optical free space

摘要

Nowadays optical fibres are significant appliances in telecommunications. They offer advantages, such as a high transmission capacity and minor cable attenuation. Furthermore no crosstalk occurs by using optical fibres. The insensibility to electrical and magnetical interferences is another big benefit for using fibres. Also important to mention is that there is no interference radiation, compared to other systems. Optical fibres do not emit sparks after a possible cable break; therefore they can be installed in explosion-prone environments. One of the major disadvantages of optical fibres is that they are more expensive than normal copper cables. The handling during the transfer is more difficult and after a cable break, the whole optical fibre cable has to be replaced. Another considerable part of using optical cables is the challenge to couple light into it. There are several possible proceedings for coupling, which are introduced in this paper. The main goal of every coupling method is to reduce the losses, which appear at the junctions between every single medium (free space and fibre). These losses can be minored at a specific level. As already proven, the usage of light emitting diodes (LEDs) is not highly recommended. The incoherent light, emitted by LED can be responsible for higher coupling losses. The better way is to use a laser. The usage of optical tapers can increase the numeric aperture - even more light rays are coupled in opposition to a simple fibre cross section. This technique is also demonstrated in this paper. To evaluate different possible coupling methods, software tools can be utilized. Complex test set-ups are not necessary. At the end, some different tools are introduced.