Waveguide for plastic welding, arrangement for plastic welding, a welding method as well as a manufacturing method of a waveguide

A positive waveguide for plastic welding, comprising:

• an entry end defining an entry face for laser light,
• an exit end defining an exit face for laser light as well as
• a first and a second inner face which are arranged between the entry end and the exit end, which are arranged opposite to each other and by means of which laser light can be reflected, wherein
• a first distance between the entry end and the exit end defines a length of the waveguide and a second distance between the first and the second inner face defines the thickness of the waveguide, and
• the first inner face comprises a continuously curved concave shape which is part of a first spiral, especially a first natural spiral, so that a radius of the first spiral from a point of origin of the first spiral to the first inner face varies continuously along the waveguide.

A positive waveguide for plastic welding, comprising:

• an entry end defining an entry face for laser light,
• an exit end defining an exit face for laser light as well as
• a first and a second inner face which are arranged between the entry end and the exit end, which are arranged opposite to each other and by means of which laser light can be reflected, wherein
• a first distance between the entry end and the exit end defines a length of the waveguide and a second distance between the first and the second inner face defines the thickness of the waveguide, and
• the first inner face comprises a continuously curved concave shape which is part of a first curve.