The invention relates to joining plastic components into a microfluidic cartridge. The invention also concerns the production process of these stoppers by individual moulding, whereby the simultaneous feeding of the two types of granulate and the respective additives is done and the mould is closed by compression and then heated for a time for polymerisation. A wall mounting element is also included. The modulator element serves to modulate output radiation of the high efficiencyhigh power optical source to produce a modulated high frequency optical signal which may be transmitted through the air. The lower portion of the mold may be moved in space and time while receiving the flow of composite material to deposit a predetermined quantity of molten composite material thereon conforming to mold cavities of the lower and an upper portion of the mold.