Design, fabrication, and characterization of dual-wavelength inhibited-coupling guiding hollow-core fibers

Abstract

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.