As disposable products, waveguide-based biochips offer a wide of possibilities, but relatively high manufacturing costs often make their use uneconomical. The most important cost factor is the structuring of the chip, which enables effective coupling of the laser light. A novel coupler makes it possible to couple light into chips without structuring.

Planar thin film waveguides have become indispensable tools in various fields such as telecommunication technology, biosensors and material characterization. In biosensor technology, for example, they can be used to efficiently excite dye molecules and to follow changes in the surface coating extremely precisely. A decisive point in the use of waveguide-based biochips is the coupling of the laser beam into the waveguide. Due to the low layer thickness and the high refractive index, coupling via the end surface of the waveguide or prism coupling is not feasible. The only practical method to date is light coupling via so-called grating couplers, i.e. gratings with periods in the sub-micrometer range that are structured in the waveguide using an etching process. This grating is responsible for a large part of the costs used to manufacture the chip. Since biochips are generally disposables, a cost reduction is very interesting here.

Figure: Function principle of evanescence field microscopy: The light of a laser is coupled into a microscope slide via a grating structure. The evanescent field stimulates optical transitions in molecules located on the surface of this carrier. (Source: Fricke-Begemann)




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