Why do we aim for Single Mode waveguides?

[Fixar Frazze]

I trying to formulate a new project based on waveguides (~1 cm long) for sensing with the evanescent field. In all papers I've seen on similar topics they all aim for single mode (SM) waveguides, but I never understood the reason.

Is there a quick answer?

 

[Khashishi]

It totally depends on the application. If you use multimode fiber, then the different modes will have different optical path lengths through the fiber, and might cause some confusion with interference and stuff. Single mode is simple, just one optical path (or perhaps two polarizations)

 

[Fixar Frazze]

Yes, for fibers I can understand that the dispersion is something you want to manage over long distances, but for short waveguides I just don't see much of a point in making it SM. Maybe if you have a SM fiber as input and output with a waveguide in-between it is probably beneficial to have a SM waveguide in order to not loose to much power into other modes that don't fit into the output SMF. Ah and also if you have a grating coupler I fusee you want SM-operation in order to not spread the light in all directions...