Characterisation of Optical Fibers Using Dual-Comb Swept-Wavelength Interferometry

Licentiate thesis, 2022

The growth in data traffic coupled with trends in internet use will result in a requirement for interfaces of the network to reach Tb/s data rate in the future. Considering this, novel transmission techniques that can increase the date rate with orders of magnitude must be considered. One such example is space-division multiplexing (SDM) fibers. Application of novel fibers and SDM components in communication systems is always coupled with limitations and distortions of the signal due to crosstalk, dispersion, differential mode group delay (DMGD) and other effects. They can be calculated, studied and partially mitigated if the transfer function of the fiber under test is known. Thus, it is essential to characterize the fiber's and other component's transfer matrix using fast and accurate measurement techniques. Moreover, these characterisation measurements can be used for building channel models, which can assist in simulations of the transmission and estimation of ultimate system performance.

In this thesis various techniques for SDM devices characterisation are described and a novel method based on dual-comb spectroscopy and swept-wavelength interferometry is proposed and evaluated. The presented technique, dual-comb swept-wavelength interferometry (DC-SWI), is studied in terms of capabilities, advantages and limitations with application on different devices under test. This experimental scheme is also used for characterisation of a coupled-core fiber, where the transfer function and DMGD values were extracted.

Furthermore, different channel models describing the properties of SDM fiber links are briefly reviewed and discussed.