AUTHORS:

Le H.V., Hong P.N.T., Nguyen H.T., Kasztelanic R., Buczyński R., Hoang V.T.

ABSTRACT:

Large core fibers typically offer high coupling efficiency with laser sources and standard single-mode fibers in supercontinuum generation systems. However, their large cores result in large effective mode areas, leading to low nonlinearity for spectral broadening. In this paper, we report the development of a large core fiber that exhibits high nonlinearity for broad-spanning supercontinuum (SC) generation. The fiber is made of transparent glass (lead-bismuth-gallate) having high nonlinearity. The nonlinear coefficient of the fiber is 36.5 W⁻¹ km⁻¹ at 1560 nm, which is three times higher than that of commercial nonlinear silica fibers. The linear properties of the fiber are numerically and experimentally verified, while the nonlinear propagation is thoroughly characterized numerically, taking into account the influence of relative intensity noise (RIN) and both X-/Y- polarization components. Numerical results demonstrate that the fiber allows the high-coherence normal-dispersion SC generation with a spectral bandwidth of 850 nm (from 1300 nm to 2150 nm) when being pumped by 100 fs laser pulses at 1560 nm with a peak power of 30 kW. Anomalous-dispersion SC generation with an octave spectral bandwidth (1150 nm–2450 nm) is obtained when using 1950 nm fs pulses with a pulse duration of 100 fs and a peak power of 20 kW. In addition, the coherence degradation due to the interaction between polarization components of the fundamental mode is numerically investigated for several pulse durations (100 fs – 200 fs). The results indicate that using short laser pulses (100 fs) enables wider bandwidth SC generation with high coherence in both normal and anomalous dispersion regimes. With a large core diameter, high nonlinearity, and high transparency, the investigated fiber is well-suited to develop a compact all-fiber supercontinuum source with broad spectral bandwidth and high output power. Such a system benefits numerous applications, including multi-photon microscopy and sub-ppm detection of nerve agent simulants.

Optics Communications, 2024, vol. 570, art. 130882, doi: 10.1016/j.optcom.2024.130882