National Physical Laboratory

Cut-Off Wavelength

Calibration of the cut-off wavelength of an approximately 2.2 m length of single-mode fibre (22 m for cable cut-off wavelength measurements). UKAS accredited service.

The cut-off wavelength is the wavelength of single-mode fibre is the shortest wavelength for which only the fundamental mode propagates through the fibre. Measurement of this parameter is necessary to avoid degradation of modal noise of the optical signals carried by a single-mode fibre.

The fibre cut-off wavelength measurement service uses the internationally recognised transmitted power reference test method. Spectrally selected radiation is launched from a grating monochromator into a few metres of the fibre under test and the power transmitted recorded as a function of wavelength. A single turn of 60 mm diameter is made in the fibre to suppress the higher modes and the measurement of transmitted power is repeated. The ratio of these two measurements as a function of wavelength is then used to calculate the cut-off wavelength of the fibre. The international reference test method defines the cut-off wavelength at which the ratio drops below 0.1 dB.

The cable cut-off wavelength measurement service uses the transmitted power technique, with measurements performed on 22 m of primary coated, uncabled fibre which is constrained in loops of radius greater than 140 mm. In place of the single 60 mm diameter loop, an 80 mm diameter loop is incorporated at each end of the fibre.

A copy of a typical Calibration Certificate is available to download.

Wavelength Range Typical Uncertainties
Fibre cut-off 800 - 1600 nm ± 5 nm
Cable cut-off 900 - 1600 nm ± 10 nm


Customer Service tel: +44 20 8943 8637

Last Updated: 18 Aug 2015
Created: 26 Jul 2007


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