Browsing by Author "Chen, Bowen"

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    Design, fabrication, and characterization of dual-wavelength inhibited-coupling guiding hollow-core fibers
    (2025) Chen, Bowen; Kühlthau, Tim; Kleem, Götz; Graf, Thomas; Abdou Ahmed, Marwan
    The present paper reports on the design, fabrication, and characterization of an 8-tube inhibited-coupling guiding hollow-core photonic crystal fiber (IC-HCPCF) capable of guiding both the beam emitted from an Yb:YAG laser at the fundamental wavelength of λ=1030nmand its second harmonic at λ=515nm. By controlling the strut thickness of the glass capillaries to approximately 362nm, the transmission of laser radiation at both wavelengths was possible with low losses. Optimizing the outer diameter of the glass capillaries mitigates the bending-induced increase of the confinement loss at the wavelength of 515nmwithout compromising the optical performance of the fiber at the wavelength of 1030nm. Experimental results confirm the near to diffraction-limited beam quality M2<1.15of the laser beams exiting the fiber at both operational wavelengths. Operating in the first transmission band at the wavelength of 1030nm, the calculated chromatic dispersion is 1.02ps/(nm∙km), despite a diameter of the hollow core of 40μm. At the wavelength of 515nmthis value amounts to 0.62ps/(nm∙km). The measured losses are 27.5±0.3dB/kmat the wavelength of 515nmand 25.7±0.7dB/kmat the wavelength of 1030nm, which is comparable to the loss of state-of-the-art IC-HCPCFs with tubular cladding structures. The measured bending-induced increase of the confinement losses confirms the potential of the proposed approach for flexible, low-loss guiding of ultrashort laser pulses at the two wavelengths using a single fiber. This gained flexibility can significantly enhance the options for wavelength selection in laser material processing applications.
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    Efficient delivery of sub-ps laser pulses with pulse energies exceeding 100 µJ at average powers of up to 95 W through a hollow-core fiber
    (2025) Kühlthau, Tim; Chen, Bowen; Graf, Thomas; Abdou Ahmed, Marwan
    We report on the efficient delivery of sub-picosecond laser pulses with high peak and high average powers through a home-made 7.5 m long tubular inhibited-coupling guiding hollow-core photonic-crystal fiber (IC-HCPCF). The experiments were performed using an ultrafast laser generating pulses with durations between 430 fs and 560 fs at a central wavelength of 1030 nm. Pulses with an energy of either 263 µJ or 150 µJ were coupled into the fiber at average powers of either 48 W or 95 W, respectively. In both cases, the transmittance through the fiber was measured to exceed 85% without detectable distortion of the temporal pulse shapes or damage to the fiber.
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    Influence of fabrication deviations on the polarization-maintaining behavior of inhibited-coupling guiding hollow-core fibers
    (2024) Chen, Bowen; Kühlthau, Tim; Röhrer, Christian; Graf, Thomas; Abdou Ahmed, Marwan
    Numerical simulations were conducted to analyze the influence of the design parameters of tubular inhibited-coupling guiding hollow-core photonic crystal fibers (IC-HCPCFs) on the bending-induced phase shift. The possibility to implement polarization-maintaining (PM) tubular IC-HCPCFs using a low-birefringence approach (with a modal birefringence parameter B<7×10-9) is discussed. Two different tubular IC-HCPCF designs with 7 and 8 glass capillaries are proposed for operation at a wavelength of 1030 nm. The numerical simulation predicts low guiding losses and a PM behavior sustaining a degree of linear polarization (DOLP) larger than 90% after 10 m of fiber with a bend radius larger than 0.2 m. This shows great potential for high-power beam delivery in an industrial environment. The influence that fabrication deviations have on the polarization-maintaining behavior was also investigated and indicates tight fabrication tolerances for both proposed fiber designs. Small deviations from the ideal symmetrical structure can lead to an enhancement of undesired modal birefringence. To ensure a DOLP larger than 90% at the exit of a 10 m-long fiber and for a bending radius > 0.2 m precise control of the drawing parameters during the fiber production is required, which is challenging but is considered to be technically feasible.