High-Capacity Multi-Core Fibers for Space-Division Multiplexing

The transmission capacity of the present optical fiber communication systems based on timedivision multiplexing (TDM) and wavelength-division multiplexing (WDM) using single-mode fibers (SMFs) is reaching its limit of around 100 Tbit/s per fiber due to the fiber nonlinearities, fiber fuse phenomenon and the optical amplifier bandwidth. To meet the ever increasing global data traffic growth and to overcome the looming capacity crunch, a new multiplexing technology using new optical fibers is urgently needed. Space-division multiplexing (SDM) is a promising scheme to overcome the capacity limit of the present SMF-based systems. Among the proposed SDM schemes, the one based on uncoupled multi-core fibers (MCFs) having multiple cores in a mutual cladding has proven effective in substantially increasing the transmission capacity per fiber with least system complexity as demonstrated in several state-of-the-art high-capacity transmission experiments beyond Pbit/s. In order to increase the transmission capacity of MCFs, the total number of cores needs to be increased while keeping the inter-core crosstalk (XT) among neighboring cores low as it degrades the optical signal-to-noise ratio (OSNR) of data signals, limiting the usable modulation formats (i.e., spectral efficiency, hence transmission capacity) and the transmission distance. One of the most powerful and practical XT reduction techniques in an MCF is a trench-assisted (TA) structure, where each core is surrounded by a trench and such MCFs are called trench-assisted MCFs (TAMCFs). The traditional approach for TA-MCFs design has relied on numerical simulations, which make deriving relationships between XT and fiber structural parameters difficult and non-intuitive. As it is important to be able to understand the effects of various fiber structural parameters on XT performance in designing high-count, low-XT TA-MCFs, an analytical model for XT estimation and XT properties analysis in TA-MCFs has been greatly needed. In this thesis, a novel analytical model for designing low-XT and high-count homogeneous TAMCFs is described where all the cores have the same refractive index profiles. Based on the model,