Single mode fiber question

Jem · Post by **Jem** » Mon Jun 23, 2008 11:17 am

Hi all

As some here will know I have an unhealthy interest in using fiber optic cable for holography, so far i've been using 6um ex-telecom fiber to experiment with.

I would now like to get a bit more 'scientific' and use some 'correct' fiber. I have a Coherent Compass 315m 100mw laser, what fiber size should I be using in order to keep the beam single mode? also what size microscope objective should I be using to launch the beam into the fiber?

Thanks in advance for your help.

Cheers

Jem

Colin Kaminski · Post by **Colin Kaminski** » Mon Jun 23, 2008 3:01 pm

Single mode fiber is really designed to keep a single mode over miles of twists and turns. Everyone I ask in the know says if we keep the runs short and the bends wide it makes no difference. I have a customer who sold fiber optics and when I asked him about a few feet of single mode fiber he laughed at me.

Jem · Post by **Jem** » Mon Jun 23, 2008 6:21 pm

Colin Kaminski wrote:Single mode fiber is really designed to keep a single mode over miles of twists and turns. Everyone I ask in the know says if we keep the runs short and the bends wide it makes no difference. I have a customer who sold fiber optics and when I asked him about a few feet of single mode fiber he laughed at me.

Thanks for the reply Colin, I find this hard to believe though.

If it is true, does that mean I can use some thick fiber (which is easy to launch into)? will polarisation be maintained? Call me Mr Sceptical if you wish but I can't see that the beam will be preserved however short the run. In a way I do hope you are right though, it will make things much easier.

I know John Klayer(I think - sorry john if iv'e got your surname wrong

) has done some good experiments and had success making holograms with allsorts of fibers, but something inside me says that it must be better to use the correct fiber

Anyone else care to chip in ???

Jem

John Klayer · Post by **John Klayer** » Tue Jun 24, 2008 12:55 am

Yes, I've made some decent two beam transmission holograms using a 1 mm multimode fiber and even fiber bundles for the reference beam. Good luck using a single mode fiber. If I was trying it, I'd use a space filter movement and use the focal length calculated for a pinhole the same diameter as the fiber core. Thor Labs sells short lengths.