Singlemoded THz guidance in bendable TOPAS suspended-core fiber directly drawn from a 3D printer.

Terahertz (THz) technology has witnessed a significant growth in a wide range of applications, including spectroscopy, bio-medical sensing, astronomical and space detection, THz tomography, and non-invasive imaging. Current THz microstructured fibers show a complex fabrication process and their flexibility is severely restricted by the relatively large cross-sections, which turn them into rigid rods. In this paper, we demonstrate a simple and novel method to fabricate low-cost THz microstructured fibers. A cyclic olefin copolymer (TOPAS) suspended-core fiber guiding in the THz is extruded from a structured 3D printer nozzle and directly drawn in a single step process. Spectrograms of broadband THz pulses propagated through different lengths of fiber clearly indicate guidance in the fiber core. Cladding mode stripping allow for the identification of the single mode in the spectrograms and the determination of the average propagation loss (~ 0.11 dB/mm) in the 0.5-1 THz frequency range. This work points towards single step manufacturing of microstructured fibers using a wide variety of materials and geometries using a 3D printer platform.

Suspended-Core Microstructured Polymer Optical Fibers and Potential Applications in Sensing.

The study of the fabrication, material selection, and properties of microstructured polymer optical fibers (MPOFs) has long attracted great interest. This ever-increasing interest is due to their wide range of applications, mainly in sensing, including temperature, pressure, chemical, and biological species. This manuscript reviews the manufacturing of MPOFs, including the most recent single-step process involving extrusion from a modified 3D printer. MPOFs sensing applications are then discussed, with a stress on the benefit of using polymers.

Mid-IR Hollow-core microstructured fiber drawn from a 3D printed PETG preform.

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.

A Review of Microfiber-Based Temperature Sensors.

Optical microfiber-based temperature sensors have been proposed for many applications in a variety of industrial uses, including biomedical, geological, automotive, and defense applications. This increasing demand for these micrometric devices is attributed to their large dynamic range, high sensitivity, fast-response, compactness and robustness. Additionally, they can perform in-situ measurements remotely and in harsh environments. This paper presents an overview of optical microfibers, with a focus on their applications in temperature sensing. This review broadly divides microfiber-based temperature sensors into two categories: resonant and non-resonant microfiber sensors. While the former includes microfiber loop, knot and coil resonators, the latter comprises sensors based on functionally coated/doped microfibers, microfiber couplers, optical gratings and interferometers. In the conclusions, a summary of reported performances is presented.

Novel method for manufacturing optical fiber: extrusion and drawing of microstructured polymer optical fibers from a 3D printer.

Microstructured polymer optical fibers (MPOFs) have long attracted great interest due to their wide range of applications in biological and chemical sensing. In this manuscript, we demonstrate a novel technique of manufacturing MPOF via a single-step procedure by means of a 3D printer. A suspended-core polymer optical fiber has been extruded and directly drawn from a micro-structured 3D printer nozzle by using an acrylonitrile butadiene styrene (ABS) polymer. Near-field imaging at the fiber facet performed at the wavelength λ~1550 nm clearly indicates guidance in the fiber core. The propagation loss has been experimentally demonstrated to be better than α = 1.1 dB/cm. This work points toward direct MPOFs manufacturing of varieties of materials and structures of optical fibers from 3D printers using a single manufacturing step.

All-fiber fused directional coupler for highly efficient spatial mode conversion.

We model and demonstrate a simple mode selective all-fiber coupler capable of exciting specific higher order modes in two- and few-mode fibres with high efficiency and purity. The coupler is based on inter-modally phase-matching the propagation constants in each arm of the asymmetric fused coupler, formed by dissimilar fibres. At a specific coupler diameter, the launched fundamental LP(01) mode is coupled into the higher order mode (LP(11), LP(21), LP(02)) in the other arm, over a broadband wave-length range around 1550 nm. Unlike other techniques, the demonstrated coupler is composed of a multimode fiber that is weakly fused with a phase matched conventional single mode telecom fiber (SMF-28). The beating between the supermodes at the coupler waist produces a periodic power transfer between the two arms, and therefore, by monitoring the beating while tapering, it is possible to obtain optimum selection for the desired mode. High coupling efficiencies in excess of 90% for all the higher order modes were recorded over 100 nm spectral range, while insertion losses remain as low as 0.5 dB. Coupling efficiency can be further enhanced by performing slow tapering at high temperature, in order to precisely control the coupler cross-section geometry.

Nonlinear microfiber loop resonators for resonantly enhanced third harmonic generation.

We model and demonstrate resonantly enhanced third harmonic generation in microfiber loop resonators, in which the large pump field intensity is exploited to improve the conversion on resonance. Silica microfibers were fabricated with waist diameters near 0.76 µm to ensure intermodal phase matching. When pumped with λ=1.55 µm 4 ns pulses at 100 W peak power, the conversion efficiency is 3×10(-6) over an estimated interaction length of ∼1 mm near the waist. The resonator is then formed by manually translating and twisting the microfiber ends to produce loop diameters down to 6 mm and resonant enhancements up to 7.7 dB for the same pump parameters.

A self-coupling multi-port microcoil resonator.

A new type of self-coupling multi-port microcoil resonator using a microfiber coupler is presented. The microresonators, a simple combination of a microfiber coupler and microcoil resonator, were fabricated by coiling a four port microfiber coupler around a low index support rod to induce optical resonance via coupling between adjacent turns. Light propagates along the coil whilst the beating between the supermodes of the coupler is still present, giving an increased extinction ratio and an output spectrum strongly dependent on the microfiber coupler diameter. The multiport microcoil resonator was embedded in a low refractive index polymer to improve its robustness and the polarization dependence was further analyzed.