Hello guest: Log in or Register Sales & Support Tel: +44 (0)23 8076 9893 Contact us

Cut-off wavelength

The wavelength above which the fiber is single-mode; only at wavelengths above the cut-off will the fiber guide be single-mode. Cut-off wavelength is important because, in most cases, it determines your choice of fiber type. Just below cut-off a few modes may be guided, and multi-mode fiber operates far below the single-mode cut-off point. Cut-off is measurable from a plot of transmission with wavelength. At the cut-off wavelength there is a noticeable dip in transmission as the higher order modes are lost, followed by a slight increase in transmission as the fundamental mode field expands into the cladding slightly, where attenuation is less. 

 
 
 
 
 
 
 
 
 
 
 
 
 
 
The number in the fiber product code (i.e. HB450, SM600 etc.) is the ‘nominal’ cut-off wavelength.  If you need Single Mode operation, you should choose the fiber type with the closest cut-off wavelength range below the operating wavelength of your optical source.  For example, if you are using a helium-neon laser, at 632.8nm, then you need HB600, while a 1550nm diode laser would call for HB1500.

The following key facts should help:

The cut-off wavelength is the wavelength at which an optical fiber becomes single-mode

At wavelengths shorter than cut-off several optical modes may propagate - the fiber is multi-mode

As the cut-off wavelength is approached, progressively fewer modes may propagate until, at cut-off, only the fundamental mode may propagate - the fiber is then single-mode

At wavelengths longer then cut-off the guidance of the fundamental mode becomes progressively weaker, until eventually (usually at a wavelength several hundred nanometers above cut-off) the fiber ceases to guide - the fiber loses all optical function. This is often referred to as the bend edge

 

Register
Login

To access more information please register

Here at Fibercore we take your privacy seriously and will only use your personal information to administer your account and to provide the products and services you have requested from us. We will never sell personal data to 3rd parties. Click here for full details of our Privacy Policy.






  • I would like to subscribe to the Fibercore eNewsletter

    Fibercore will from time-to-time send you product and company news. You may unsubscribe at any point

    Register

How can we help you?

Here at Fibercore we take your privacy seriously and will only use your personal information to administer your account and to provide the products and services you have requested from us. We will never sell personal data to 3rd parties. Click here for full details of our Privacy Policy.
  • required fields* Submit