Optimal Positioning of the Nested Elements in Negative Curvature Hollow-core Fibers

A new negative curvature hollow-core fiber layout with optimally positioned nested elements is presented. Confinement losses of 0.003 dB/km at 1.55 μm are achieved, corresponding to two orders of magnitude improvement compared to conventional designs

Re-thinking the design of low-loss hollow-core fibers via optimal positioning of the nested elements

Nested negative curvature hollow-core fibers (NCFs) represent state-of-art optical guidance in the near-infrared (near-IR) region. In this Letter, we propose a unique design approach for these types of fibers in order to further improve optical transmission via the optimal positioning of the nested elements. The nested elements in the proposed design are located at the center of the cladding tubes and are supported by bar-type structures. The topological optimization for the nested elements results in improved light guidance by two orders of magnitude with confinement losses as low as 0.003 dB/km within the targeted wavelength range of 1450 nm to 1600 nm. This bar-supported design features strong single-mode operation and low bending sensitivity in a wide range of bending radii

Low-loss nested-compound negative curvature hollow-core fiber for mid-IR transmission

A new negative curvature hollow-core fiber with a compound cladding structure is proposed. Compared to conventional nested structures, the proposed design features one order of magnitude improvement in confinement losses as low as 0.03 dB

Designing Optical Negative Curvature Fibers with Rotated Elliptical Cladding Elements

We propose a unique design of negative curvature optical fibers utilizing rotational elliptical cladding structures. The silica-based fibers were numerically characterized using a finite element method-based electromagnetic solver. Different topologies consisting of rotational cladding elements with different tube thicknesses and core diameters were studied. The investigation focused on confinement losses, birefringence, and higher-order mode extinction based on varying tube sizes and rotational angles. Results showed up to 20% improvement in confinement losses for rotated structures, with minimum losses of 4.47*10-4 dB/m at 1.5 µm wavelength. The designed fibers possess polarization-dependent characteristics, and higher-order mode extinction analysis showed dominant single-mode transmission

Low-loss nested-compound negative curvature hollow-core fiber for mid-IR transmission

A new negative curvature hollow-core fiber with a compound cladding structure is proposed. Compared to conventional nested structures, the proposed design features one order of magnitude improvement in confinement losses as low as 0.03 dB

Nested compound negative curvature hollow-core fiber for single-mode operation in the infrared region

In this study, a novel tubular hollow-core fiber design with extended cladding structures aiming low transmission losses and dominant single-mode guidance in the infrared region is proposed. The fiber parameters are optimized to achieve low-loss operation at the target wavelength of 2μm, at which the emission spectrum of thulium-doped fiber lasers are centered. The confinement loss of the fundamental mode is found to be less than 0.02 dB/km in the near- and mid-infrared region, which makes the proposed design a strong alternative for conventional step-index silica optical fibers. Strong suppression of the higher order modes, and low bending sensitivity are also observed in the proposed design. The proposed fiber shows promising results to achieve low-loss transmission in the infrared spectrum

Investigation of 3D Printing Compatible THz Chemical Sensing Platform Using Negative Curvature Fibers with Elliptical Cladding Elements

In this study, a 3D printing compatible THz chemical sensing platform using negative curvature fibers was numerically investigated. Since the negative curvature design of the fiber allows spectral sensitivity based on the refractive index of the fiber core area, high sensitivities for liquid chemical sensing are observed. The fibers with elliptical tube cladding elements made of UV epoxy resin were designed using a finite element based electromagnetic solver to optimize the confinement and material losses, as well as to control polarization-based sensing by asymmetrical placement of tubes. By analyzing both confinement and material losses for different cladding structures, high sensitivities (\u3e98%) for the detection of ethanol and benzene at an operational frequency of 1 THz are achieved. In order to calculate sensitivity values, the power fraction between the core and cladding areas were computed, and dispersion coefficients were also analyzed in the designed fibers. Using a UV resin-based 3D printer, the designs with a core diameter of 3 mm and tube thicknesses of 0.1 mm were fabricated, and the feasibility of using 3D printing was investigated using image analysis. Overall, the optimized negative curvature fiber design with elliptical cladding elements allowed improved sensitivities for chemical sensing applications. The use of 3D printing technology offers potential for cost-effective and efficient fabrication of THz chemical sensing platforms

Enhancing polarization maintenance and spectral filtering in negative curvature hollow-core fibers

A new design of polarization-maintaining and spectral filtering negative curvature hollow-core fiber tailored for the telecommunication bands in the near-infrared region is presented. The optical fiber, consisting of a six-tube silica structure, incorporates vertically nested tubes anchored radially by a pole structure. By contrast, standard nested tubes in the horizontal direction form the asymmetric fiber structure, which encounters birefringence. This unique fiber design not only preserves the polarization states of light but also exhibits frequency selective transmission exclusively in the vertical direction due to the pole structure. Through fiber design optimization, a transmission loss below 0.1 dB/km for spectrally filtered wavelengths is achieved, with birefringence on the order of 10−5 within the wavelength range of 1.45 µm to 1.60 µm. These results demonstrate significant improvements in terms of birefringence, distinct loss separation between horizontally and vertically polarized states, and a reduced number of spectrally filtered wavelengths compared to previously reported findings. The proposed fiber design holds untapped potential for applications requiring selective transmissions with specific polarization

Supercontinuum Generation from a Thulium Ultrafast Fiber Laser in a High NA Silica Fiber

A broadband supercontinuum is generated from a thulium ultrafast soliton fiber laser in a high numerical aperture silica fiber with low nJ seed pulse energies. Amplification of a thulium based ultrafast soliton ring fiber laser in two customized thulium doped fiber amplifiers provides pulses varying in energy between 1.8 nJ and 13.5 nJ. Coupling these seed pulses into a high numerical aperture silica fiber UHNA 7 of varying length, a systematic study of the impact of pulse energy, pulse duration and nonlinear fiber length is conducted. Based on the normal dispersion, self-phase modulation dominates for lower pump power values and results in a symmetric spectral broadening process. For higher pulse energies, four-wave mixing and Raman scattering contribute to a strong red-shift of the spectrum beyond 2.3~\mu \text{m}. For a fiber length of 20 m of UHNA 7, a broadband supercontinuum spanning from 1.7~\mu \text{m} to 2.33~\mu \text{m} is generated with a 20 dB spectral bandwidth of 502 nm with an output pulse energy of 4.4 nJ, corresponding to an output power of 92 mW. This represents a low seed energy threshold for efficient flat supercontinuum generation at infrared wavelengths