Aligning a laser with a single-mode fibre

[superiority]

Does anybody have any tips for doing this well? Frankly, I'm pretty terrible at it. I mean, once I get a small amount going through, I can do a little bit of optimisation by adjusting the angle of the fibre in one direction, and then adjusting the angle of the incident beam along the same plane to see if I can get better output, but at the moment I'm getting less than 2 nanowatts out the other end. This is down from about 15 nanowatts after I made some adjustments to the positions of some of the components, which is down from about 250 microwatts.

 

[Andy Resnick]

It's not clear what type of laser you are using, but when we did free-space connecting of a DPSS laser to a single-mode fiber, we needed a fair amount of positioning equipment to get (at best) 25% of the light in.

It's similar to spatial filtering- you focus the beam down with a lens (for fiber launching we tried a variety of ball lenses, grin lenses, aspheres- you should match the NA of the lens with the acceptance angle of the fiber) and align the (clean!) fiber end to the focused spot. There are 5 degrees of freedom to control- x,y,z, altitude, and azimuth. There are several companies that make pre-aligned mounting kits (we tried OZ Optics and OFR), but the coupling efficiency wasn't much better than our home-brewed setup.