I Single-mode vs multi-mode fiber coupling

[iVenky]

Hi,

Is coupling light from a laser into a single-mode fiber (transverse electric) more difficult than coupling to a multi-mode fiber?
If so, is it due to the geometry? Does the laser light have multiple modes to begin with or it can be designed to have just one mode?

Thanks

 

[Andy Resnick]

Hi,

Is coupling light from a laser into a single-mode fiber (transverse electric) more difficult than coupling to a multi-mode fiber?
If so, is it due to the geometry? Does the laser light have multiple modes to begin with or it can be designed to have just one mode?

It's been a while since I've thought about this, but IIRC, coupling to a multimode fiber is substantially easier because the geometry is more 'forgiving': larger acceptance angle, for example. The laser output is likely single-mode, but that's the free-space lasing mode, not the same as the fiber mode.