Nonlinear dynamic of picosecond pulse propagation in atmospheric air-filled hollow core fibers

Abstract

Atmospheric air-filled hollow core (HC) fibers, representing the simplest yet reliable form of gas-filled hollow core fiber, show remarkable nonlinear properties and have several interesting applications such as pulse compression, frequency conversion and supercontinuum generation. Although the propagation of sub-picosecond and few hundred picosecond pulses are well-studied in air-filled fibers, the nonlinear response of air to pulses with a duration of a few picoseconds has interesting features that have not yet been explored fully. Here, we experimentally and theoretically study the nonlinear propagation of ~6 ps pulses in three different types of atmospheric air-filled HC fiber. With this pulse length, we were able to explore different nonlinear characteristics of air at different power levels. Using in-house-fabricated, state-of-the-art HC photonic bandgap, HC tubular and HC Kagomé fibers, we were able to associate the origin of the initial pulse broadening process in these fibers to rotational Raman scattering (RRS) at low power levels. Due to the broadband and low loss transmission window of the HC Kagomé fiber we used, we observed the transition from initial pulse broadening (by RRS) at lower powers, through long-range frequency conversion (2330 cm) with the help of vibrational Raman scattering, to broadband (~700 nm) supercontinuum generation at high power levels. To model such a wide range of nonlinear processes in a unified approach, we have implemented a semi-quantum model for air into the generalized nonlinear Schrodinger equation, which surpasses the limits of the common single damping oscillator model in this pulse length regime. The model has been validated by comparison with experimental results and provides a powerful tool for the design, modeling and optimization of nonlinear processes in air-filled HC fibers.

Spectral Broadening of Femtosecond UV Pulses in Air-filled Hollow-Core Photonic Crystal Fiber

“…The narrow spectral fringes separated by 2.7 THz in the experimental plot are caused by beating with light in the LP11 mode, accidentally excited by imperfect launching conditions (the group velocity walk-off between the LP01 and the LP11 mode is ~4.6 fs/cm at 400 nm, accumulating to 370 fs after 80 cm, i.e., the inverse of 2.7 THz). The best agreement between experiment and theory was obtained for fr,air = 0.75, μrot,N2 = 0.986 and μrot,O2 = 1, in agreement with the values reported in [19] and confirming that the rotational responses of N2 and O2 dominate in the Raman response of air. Of these, the S(8)-transition of N2 (period 439 fs, frequency shift 2.28 THz) and the S(11)-transition of O2 (period 463 fs, frequency shift 2.16 THz) are long enough to be impulsively excited by the 54-fs pump pulses.…”

“…For the experiments reported here (HC-PCF core diameter 22 µm, 54 fs, ~1 µJ pulses), the soliton order was low and the selfcompression length less than 1 m, resulting in a compact system. To model the dynamics of pulse compression, we performed numerical simulations based on the generalized nonlinear Schrödinger equation described in [19]:…”

Nonlinearity-Free Coherent Transmission in Hollow-Core Antiresonant Fiber

“…The optical channels centered at 1550 nm with a 100 GHz channel spacing. The effective nonlinear coefficient (γ) of the HC-ARF was assumed to be 0.01 W -1 km -1 [33]. The in-line EDFAs were assumed to have 30 dB gain and a 7 dB noise figure.…”

“…By contrast hollow-core fibers (HCF)s exhibit ~30% reduction of latency, a high damage threshold and more than three orders of magnitude lower nonlinear response than standard silica optical fiber. Such a combination of advantages over conventional solid-core silica fiber make them an exciting option to meet both the emerging capacity and latency needs in future optical networks [12,13].…”

Hollow Core Optical Fibers for Industrial Ultra Short Pulse Laser Beam Delivery Applications

“…Variations can also be introduced and the results can be compared to experimental results using low-power beams (see Figure 3). Typically, high-power pulses travelling along the fiber will often have enough energy to interact with the gas inside the hollow core, which will alter the pulse characteristiocs [13][14][15]. In order to reduce these effects, the fiber material can be filled with other gases or kept at a vacuum to significantly reduce any gas interaction.…”