WP Leader: VTT
WP1: Development of measurement techniques for the characterisation of advanced optical fibres
The production of standard telecommunication fibres has generally moved outside Europe to countries with lower production costs and European manufacturers have therefore mostly focused on more specialised advanced optical fibres, where they can compete with quality and different product offerings.
In this work package new measurement technologies will be developed for the characterisation of dimensional and optical properties of advanced optical fibres.
Task 1.1: Dimensional characterisation of advanced optical fibres
The aim of this task is to design, build and test a measurement setup for measuring dimensional parameters (the thicknesses of different layers of the fibre and the concentricity of different layers) of advanced optical fibres. The target uncertainties for fibre layer thickness and concentricity are 0.5 µm and 1 µm respectively.
A variety of different fibres will be tested under laboratory conditions to determine the capabilities of the developed measurement setup. In addition, the setup will be tested in a fibre manufacturing process in a real industrial environment at Oplatek. Numerical simulations of the measurement configuration are needed in order to determine the dimensional parameters from the measurement data, and will be developed in this task.
Task 1.2: Dispersion of advanced optical fibres
The aim of this task is to develop non-destructive and novel methods to measure dispersion and group velocities in optical fibres. The target is to measure optical dispersion with a relative uncertainty of 1×10‑3 for dispersion slope and zero dispersion wavelength for 100 m of silica fibre.
Dispersion is one of the most critical parameters in new and existing fibre-optic devices and deployments, affecting the link distance attainable, the data rate and channel cross‑talk. Dispersion arises from the wavelength and propagation mode dependence of speed of light. The three main types of dispersion in single-mode fibres are the material, chromatic dispersion and variation of the waveguide properties with wavelength and polarisation. The material effect and waveguide dispersion add together to give a wavelength-dependent chromatic dispersion of the fibre.
In this task a new method will be developed using a tuneable pulsed light source and time stamping of pulses using White Rabbit (WR) hardware pioneered by CERN, typically achieving an accuracy of 55 ps rms. To detect the pulse without breaking the fibre, a small fraction of the photons launched onto the fibre can be leaked out through e.g. bending loss, the location of which can be accurately determined using opaque screening. These photons can be detected with a fast detector, followed by time stamping. Thus, an accurate characterisation of the dispersion of an unknown fibre can be achieved. This method can be used to non-destructively characterise already spooled fibres, by unwinding – and later re-winding – a sufficiently long stretch of fibre from the spool.
In addition, in this task a SEA TADPOLE type white-light spatial-spectral interferometer will be customised for characterising optical fibres. This allows retrieving spectral phase and relative spectral amplitude in space introduced by an optical fibre. The configuration can be used for measuring dispersion and group velocities of different modes in a broad spectral range, currently from 400 nm to 1050 nm. The dispersion measurement results obtained with the method developed in this task (A1.2.4) will be compared to those obtained with different methods in Task 4.1.
Task 1.3: High power optical characterisation
The aim of this task is to develop guidelines on measurement procedures for high power fibre optics. The first activity is to evaluate the reliability of transmission loss measurements in doubled-clad fibres at high average power (kW-level). The discrimination between the light guided in the pump core and that in the signal core will also be considered, since this parameter is often neglected in current specifications of high power fibres. The target accuracy for the relation between the core and the cladding light is ±5 %.
The second activity is to measure the heat load along active fibres during high power experiments using Optical Backscatter Reflectometry (OBR) to obtain valuable information about the heat load distribution. This is relevant for users to evaluate cooling requirements and design parameters. Pump combiners, which are a critical component in high power fibre systems, will be the focus of the third activity. Their performance and performance degradation under high power operation will be investigated, using commercially available as well as custom pump combiners.