At wavelengths shorter than cut-off several optical modes may propagate - the fiber is multi-mode.Īs 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.Īt wavelengths longer than 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.The cut-off wavelength is the wavelength at which an optical fiber becomes single-mode.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. 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. HB450, SM600 etc.) typically represents the ‘nominal’ cut-off wavelength.
When referring to Fibercore products, the number in the fiber product code (i.e. G.654 (04/97) Characteristics of a cut-off shifted single-mode optical fibre cable. G.654 (03/93) Characteristics of a 1550 nm wavelength loss-minimized single-mode optical fibre cable. At wavelengths just below the cut-off, a few modes may be guided, whilst multi-mode fiber operates far below the second order cut-off point. G.654 (11/88) Characteristics of a 1550 nm wavelength loss-minimized single-mode optical fibre cable. The light required for a photochemical reaction may come from many. Cut-off wavelength is important because, in most cases, it determines your choice of fiber type. The low wavelength cut-off for some common glass types are given in the table on the right. The second order mode cut-off wavelength (commonly shortened to cut-off) refers to the wavelength above which the fiber is single-mode only at wavelengths above the cut-off will the fiber guide be single-mode.