National Physical Laboratory

Optical Communications & Data

NPL has extensive facilities for the characterisation and calibration for optical fibre, related test equipment and components and has recently developed a computer model for predicting the performance of communications systems. We also have a new capability in wavefront measurement and laser beam parameter characterisation which supports, for example, the demanding requirements of modern laser macro and micro machining as well as eye surgery and free space optical communications.

Research is under way in the application of adaptive optics to metrology and includes the development of a human eye simulator to support the assessment of eye hazard and the Artificial Optical Radiation Directive.

  • Adaptive optics allows the dynamic manipulation of light that has led to innovative solutions for imaging systems within mobile phone cameras, binoculars, CCTV, microscopy systems and optical storage.
  • NPL has developed a system to measures the attenuation and isolation between waveguides with the ability to vary the launch spot size and numerical aperture to fully explore the capability of these multimode waveguides.
  • Wavefront sensors are increasingly being used in many new fields ranging from medical applications such as laser eye surgery to industrial laser beam manipulation, to optimise machining and welding.
  • The Optical Time Domain Reflectometer (OTDR), both single and multimode, is one of the most versatile and widely used pieces of fibre optic test equipment.
  • The time taken for radiation to propagate down a single-mode fibre depends on the wavelength of the radiation.
  • 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.
  • The effective area of single-mode fibres is calculated using the Hankel transform after acquisition of the far-field scan data using the mode field diameter measurement facility.
  • Calibration of the cladding diameter of optical fibres. Fibres with diameters in the range 123 µm to 127 µm can be calibrated with a best measurement capability of ± 0.05 µm.
  • Calibration of the outer coating diameter of optical fibres. Fibres with diameters in the range 230 µm to 260 µm can be calibrated with a best measurement capability of ± 0.15 µm.
  • Facilities have been developed for the calibration of fibre optic power meters using standard wavelength laser diodes.
  • NPL calibration fibres and artefacts suitable for the calibration of fibre optic test instrumentation.
  • The mode field diameter is a measure of the radial intensity distribution of radiation propagating within a fibre.
  • Calibration of the numerical aperture of multimode fibre at 850 nm. Both multimode fibre types, 50/125 µm and 62.5/125 µm, can be measured.
  • NPL can supply a 10 metre length of specially designed optical fibre with a multi-step refractive index profile.
  • Calibration of the optical length (time of flight) of both single-mode and multimode optical fibres. Standard measurements are made at 1310 nm and 1550 nm for single-mode fibre and at 850 nm and 1300 nm for multimode fibre.
  • A wavelength calibration service has been established to support fibre optic communication systems.
  • Calibration of the attenuation of single-mode fibre from 1200 nm to 1650 nm in 5 nm steps.


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