Fabrication of 800-μm-bore hollow optical fibers based on completely non-fragile and flexible Ni-Ti tube for the infrared

Ni-Ti tube is used as a supporting tube for the infrared hollow fiber to obtain flexibility and strong mechanical strength. The loss of Hollow optical fiber is inversely proportional to the cube of the inner diameter. Considering this, it is expected that the large-diameter hollow optical fiber has a low loss. Even with a large inner diameter of 800 μm, the Ni-Ti tube with a wall thickness of 0.1 mm can be bent with a small force to a bending radius of 15 mm. Therefore, 800-μm-bore hollow optical fiber based on Ni-Ti tube was fabricated. In order to reduce roughness of inner surface of Ni-Ti tube which causes the additional transmission loss, an acrylic-silicon resin material is used as a buffer layer to the inner wall of Ni-Ti tube for a low-loss characteristic. For the dielectric inner-coating layer, cyclic olefin polymer (COP) is used to lower the transmission loss. The COP layer is formed by using liquid-phase coating method. The hollow fibers with optimized COP inner film thickness for CO2 laser light were fabricated and reasonable transmission losses was demonstrated.