Optical Fiber 101: Understanding Single Mode Fiber (Part 1 of 2)

[@Bacharus]

Fine! Incredibly good work! Thank you for taking the time to create this presentation. There is a desire to translate everything into Russian. You told everything in great detail.

[@thorlabs]

Thank you for your suggestion and your kind feedback!

[@lidarman2]

Excellent. I Look forward to part two--especially the coupling to in a mismatch fiber core diameter.

[@thorlabs]

Thank you! Part 2 will premiere November 3rd.

[@שירבני-ח7ח]

Thnak you! These lectures are really informative! Do we also know what we will get at the output of a SM fiber for an incoherent light input? And do the un-gaussian components are returned to the inital part of the fiber?

[@thorlabs]

Thank you for your comment! If an incoherent light source is coupled into an SM fiber, the output will be gaussian. This is because only the gaussian “portion” of the input beam will be coupled into and guided by the SM fiber. The rest of the input beam will not be coupled into the fiber. The coupling efficiency will be very low, and the SM fiber effectively acts as a gaussian “filter.” For more information, part 2 of this webinar series goes into these concepts in-depth ( kzbin.info/www/bejne/fqetlouXoMhrgcU ).

[@BibhatsuKuiri]

informative. thank you

[@thorlabs]

We're glad you found it useful!

[@pendalink]

Super cool, thanks

[@pendalink]

... do you guys bend the fiber around a 1" post for the attenuation test? lol

[@thorlabs]

@@pendalink Thanks! When testing the attenuation of multimode fibers, you can use a mode scrambler, such as a mandrel wrap, to remove any cladding modes and ensure the light is traveling through the fiber with a mode distribution close to equilibrium. This prevents erroneous attenuation measurements due to lossy cladding modes propagating through the fiber and being measured. The radius of the mandrel is chosen based on the NA of the fiber (and sometimes other design characteristics) so that the loosely guided cladding modes are stripped out but the modes propagating in the core are left intact. This is especially necessary when light is launched into the fiber using an overfilled launch condition. This mode scrambling technique is not necessary, however, if the launch into the fiber is sufficiently well controlled so that light is launched in at something close to the equilibrium mode distribution without any cladding modes being coupled in. However, even in this case, it can’t hurt to use a mandrel wrap or other mode scrambler as a backup in case the launch is not as optimal as intended. Mandrel wraps can also be used when testing single mode fiber. In this case, there is no concern about the modal distribution of light within the core; however, the concern about cladding modes still applies.

[@rift3353]

44:53

[@arashrohani7071]

Just a quick comment that LP01 doesn't have a cutoff. Optical fiber is not like metallic waveguide that has an absolute cutoff.

[@thorlabs]

Hi Arash, LP01 eventually "cuts off" and/or ceases to be guided in the fiber at wavelengths longer than the bend edge.

[@arashrohani7071]

Thanks for the reply. I understand the concept of bend edge but that is not the same mechanism as actual cutoff for higher order modes. Solving the characteristic equation for a fiber shows that for V number from 0 to 2.405 we will have single mode operation. So basically V can go to zero. After the bend edge the transmission drops dramatically making the fiber practically useless for higher wavelengths but I don't think that is an actual cutoff in the sense that higher order modes cutoff.

[@thorlabs]

@@arashrohani7071 Our Tech Support Team would be happy to discuss this with you further! You can contact them at [e-mail].