Abstract
Mid-infrared (mid-IR) optical fibers have long attracted great interest due to their wide range of applications in security, biology and chemical sensing. Traditionally, research was directed towards materials with low absorption in the mid-IR region, such as chalcogenides, which are difficult to manipulate and often contain highly toxic elements. In this paper, we demonstrate a Polyethylene Terephthalate Glycol (PETG) hollow-core fiber (HCF) with guiding properties in the mid-IR. Guiding is provided by the fiber geometry, as PETG exhibits a material attenuation 2 orders of magnitude larger than the HCF propagation loss. The structured plastic fiber preforms were fabricated using commercial 3D printing technology and then drawn using a conventional fiber drawing tower. The final PETG fiber outer diameter was 466 µm with a hollow-core diameter of 225 µm. Thermal imaging at the fiber facet performed within the wavelength range 3.5–5 µm clearly indicates air guidance in the fiber hollow-core.
Highlights
Since the invention of laser sources in the mid-IR range spectral region (2.5 to 25 μm), there has been a growing interest in the development of optical fibers transparent at these wavelengths for applications in chemical, biological and atmospheric sensing[1,2,3,4], where the unique molecular absorption associated to the excitation of specific fundamental vibrational and rotational modes allows for an accurate chemical fingerprinting[5]
An alternative approach relies on the use of hollow-core fibers (HCFs) such as photonic bandgap fibers and anti-resonant fibers, where light is confined within the hollow-core, greatly decreasing the influence of the material optical properties
While in the straight fiber most of the light is guided in the air-core (Fig. 4(b)), when the fiber is bent, an increasingly larger amount of light is coupled to the polymer cladding (Fig. 4(c))
Summary
Since the invention of laser sources in the mid-IR range spectral region (2.5 to 25 μm), there has been a growing interest in the development of optical fibers transparent at these wavelengths for applications in chemical, biological and atmospheric sensing[1,2,3,4], where the unique molecular absorption associated to the excitation of specific fundamental vibrational and rotational modes allows for an accurate chemical fingerprinting[5]. An alternative approach relies on the use of hollow-core fibers (HCFs) such as photonic bandgap fibers and anti-resonant fibers, where light is confined within the hollow-core, greatly decreasing the influence of the material optical properties. Such fibers have been already exploited for numerous applications in infrared spectroscopy such as laser surgery, gas sensing, label-free biological sensing, thermal imaging and infrared countermeasures[9,10,11,12,13]. Silica HCFs were manufactured using the stack and draw technique, where capillaries are manually assembled into a hexagonal structure prior to draw. The 3D geometry is generated repeating iteratively the process layer-by-layer
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