Comparison of supercontinuum spectrum generating by hollow core PCFs filled with nitrobenzene with different lattice types

Three types of hollow-core photonic crystal fibers (HC-PCFs) of optimized design with respect to both chromatic dispersion and loss were used to investigate supercontinuum generation (SCG). The optical properties of HC-PCFs filled with nitrobenzene (C6H5NO2) with the circular lattice (CL), square lattice (SL), and hexagonal lattice (HL) are analyzed to choose the optimal fiber. As a result, the three optimized structures: #CF1 (lattice constant (Λ) of 1.0 μm, filling factor (f1) of 0.65, and core diameter (Dc) of 1.285 µm), #SF2 (Λ = 1.0 μm, f1 = 0.7, and Dc = 1.23 µm), #HF3 (Λ = 1.0 μm, f1 = 0.45, and Dc = 1.505 µm) with flat and close to zero chromatic dispersion curve in the investigated wavelength region, have the values of chromatic dispersion − 10 ps.nm−1.km−1 at 1.15 μm, − 7.7 ps.nm−1.km−1 at 1.23 μm, and − 3.0 ps nm−1 km−1 at the 1.55 μm pump wavelength, respectively are intended for SCG in an all-normal dispersion regime. We demonstrate the possibility of coherent octave-wide SCG in the wavelength range of 0.72 ÷ 1.7 μm, 0.74 ÷ 1.77 μm, and 0.83 ÷ 2.36 μm with 90 fs pulses and 10 pJ of low energy in-coupled into the considered fibers core. The obtained results show that SCG with HL-PCFs has the highest efficiency, although all fibers are examined with the same input energy. Especially, the supercontinuum (SC) spectral bandwidth is independent of the type of lattice at the pump energy of 1.57 pJ, and this can be seen as a limitation between the pure self-phase modulation and other nonlinear processes contributing to SCG.