Cut-off Wavelength Reference Fibre
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NPL supplies cut-off wavelength reference fibres, these are crucial to network designers and manufacturers who need to know the wavelength above which a fibre only supports one mode where no chromatic dispersion can occur. A “single-mode” optical fibre can support many modes (or paths) of propagation, but at wavelengths above the cut off wavelength it only supports one mode. It is also a guide to the fibres sensitivity to bend loss.
The reference fibre consists of a length of single-mode fibre, approximately 2.2 m in length, whose cut-off wavelength has been determined. The fibre cut-off wavelength measurement service uses the internationally recognised transmitted power reference test method.
The transmitted power through the fibre is recorded.
A single turn of 60 mm diameter is then made in the fibre and the measurement of transmitted power repeated.
The ratio R(λ) of these measurements is recorded.
The reference test method defines the cut-off wavelength as the point at which the ratio R(λ) drops below 0.1 dB.
Other lengths of fibre and different fibre types can be provided on request.
Retractable fibre holders for protecting fragile cleaved fibre ends can be provided.
Fibre cut-off plot
The graph above shows a typical plot of Ratio R(λ) as a function of wavelength for a fibre sample.
A copy of a typical Calibration Certificate is available to download.
| Measurement range | Typical uncertainties | |
| Fibre cut-off | 800 to 1600 nm | ± 2 nm |