Development of multi-mode rod-type hollow-core antiresonant fiber

With the increasing output power of lasers, the problem of poor beam quality in most of them also arises. Therefore, we design, simulate and fabricate a hollow-core antiresonant fiber that can reduce high-order modes loss. The fabricated fiber has a rod structure (710 μm outer diameter) to resist the influence of bending, and its cladding is composed of ten noncontact capillaries. The fiber has a 128 μm core inscribed circle diameter, an average 40 μm cladding capillary inner diameter, and a tube wall thickness of about 650 nm. The test results of this fiber show that the transmission loss at 1 μm and 1.5 μm is close to 0.1 dB/m and in 2.6-4 μm band is mostly below 0.5 dB/m (except molecular absorption peak). The beam quality test results of this fiber show that its M² is basically inversely proportional to the wavelength at 2.6-4 μm, and M² below 3 μm is about 2. By observing the output spot of this fiber at 1 μm and 1.5 μm wavelength with a CCD camera, we can intuitively see its multimode transmission characteristics.