Characterization of Chromatic Dispersion and Refractive Index of Polymer Optical Fibers

Modeling the Impact of Dye Concentration on Polymer Optical Properties via the Complex Refractive Index: A Pathway to Optical Engineering

This work investigates the potential to rely on the complex refractive index to correlate the chemical composition of polymers with their optical properties, including transmittance, reflectance and absorbance. The optical properties of polycarbonate slabs with various controlled concentrations of two dyes were initially measured and analyzed. The reflection and transmission measurements obtained were used to determine the corresponding complex refractive index over a wide range of wavelengths. Comparing it with that of a clear material provided the spectral deviation of the complex refractive index induced by the dye concentrations and resulted in assigning a spectral efficiency to both of them. A modification function of the complex refractive index was established based on this spectral efficiency, which acts as a spectral fingerprint related to each dye. Finally, two samples doped with the two dyes mixed were studied to assess the model's capabilities. On the one hand, based on the measured transmittance, the dye concentrations were determined within a deviation below 8% in comparison with the values provided by the manufacturer. On the other hand, when the dye concentrations were known, the model reproduced the optical properties with good accuracy beyond the limitations of the experimental setup. The model's effectiveness in correlating the chemical composition of polymer with its optical properties through the complex refractive index makes it a valuable asset in analyzing and formulating plastics with intended optical properties.

Transmission characteristics of femtosecond laser pulses in a polymer waveguide

Femtosecond lasers have been widely employed in scientific and industrial applications, including the study of material properties, fabrication of structures on the sub-micrometer scale, surgical and medical treatment, etc. In these applications, the ultrafast laser is implemented either in free space or via an optical fiber-based channel. To investigate the light-matter interaction on a chip-based dimension, laser pulses with extremely high peak power need to be injected into an integrated optical waveguide. This requires the waveguide to be transparent and linear at this power, but also capable of providing a highly efficient and reliable interface for fiber-chip coupling. Contrary to the common belief that polymer materials may suffer from stability issues, we show that a polymer waveguide fabricated under simple and low-cost technology using only commercial materials can indeed transmit femtosecond laser pulses with similar characteristics as low-power continuous-wave laser. The coupling efficiency with a lensed fiber is ∼76% per facet. The pulse broadening effect in the polymer waveguide is also well fitted by the material and waveguide dispersion without nonlinear behavior. This study paves the way for developing a low-cost, highly efficient, polymer-based waveguide platform for the investigation of ultrafast phenomena on a chip.

Mode Coupling and Steady-State Distribution in Multimode Step-Index Organic Glass-Clad PMMA Fibers

Mode coupling and power diffusion in multimode step-index (SI) organic glass-clad (OGC) PMMA fiber is examined in this study using the power flow equation (PFE). Using our previously proposed approach we determine the coupling coefficient D for this fiber. When compared to standard multimode SI PMMA fibers, the multimode SI OGC PMMA fiber has similar mode coupling strength. As a result, the fiber length required to achieve the steady-state distribution (SSD) in SI OGC PMMA fibers is similar to that required in standard SI PMMA fibers. We have confirmed that optical fibers with a plastic core show more intense mode coupling than those with a glass core, regardless of the cladding material. These findings could be valuable in communication and sensory systems that use multimode SI OGC PMMA fiber. In this work, we have demonstrated a successful employment of our previously proposed method for determination of the coupling coefficient D in multimode SI OGC PMMA fiber. This method has already been successfully employed in the previous research of mode coupling in multimode SI glass optical fibers, SI PMMA fibers and SI plastic-clad silica optical fibers.

Optimization of Preparation Conditions for Side-Emitting Polymer Optical Fibers Using Response Surface Methodology

Polymer optical fibers (POFs) were used for preparing side-emitting polymer optical fibers (SPOFs), which were processed with acetone and n-hexane combined in selected proportions by a solvent treatment method. The effects of the volume ratio of acetone to n-hexane and treatment time on response variable factors were investigated. The center composite design (CCD) based response surface methodology (RSM), a quadratic model, and a two-factor interaction model were developed to relate the preparation variables of illumination intensity, breaking strength, and rigidity. According to analysis of variance (ANOVA), the factors affecting the optimization of each response factor were determined. The predicted values after process optimization were found to be highly similar to the experimental values. The optimal conditions for the preparation of SPOF were as follows: the volume ratio of acetone to hexane was 1.703, and the treatment time was 2.716 s. The three response variables of SPOF prepared under the optimal conditions were: illumination intensity 19.339 mV, breaking strength 5.707 N, and rigidity 572.013 N·mm2.

Ultrapermeable Organic Solvent Nanofiltration Membranes with Precisely Tailored Support Layers Fabricated Using Thin-Film Liftoff

Thin-film composite (TFC) membranes are favored for precise molecular sieving in liquid-phase separations; they possess high permeability due to the minimal thickness of the active layer and the high porosity of the support layer. However, current TFC membrane fabrication techniques are limited by the available materials for the selective layer and do not demonstrate the level of structural control needed to substantially advance organic solvent nanofiltration (OSN) membrane technology. In this work, we employ the newly developed thin-film lift-off (T-FLO) technique to fabricate polybenzimidazole (PBI) TFC membranes with porous support layers uniquely tailored to OSN. The drop-cast dense PBI selective layers endow the membranes with an almost complete rejection of common small dye molecules. The polymeric support layer is optimized by a combinatorial approach using four different monomers that alter the cross-linking density and polymer chain flexibility of the final composite. These two properties substantially affect the porogen holding capacity of the reticular polymer network, leading to the formation of different macropore structures. With a 150 nm thick PBI selective layer and fine-tuning of the support layer, the resulting membrane achieves stable and superior permeance of 14.0, 11.7, 16.4, 11.4, 17.1, and 19.7 L m^-2 h^-1 bar^-1 for water, ethanol, methanol, isopropanol, tetrahydrofuran (THF), and acetonitrile, respectively.

Anti-Resonant Hollow Core Fibers with Modified Shape of the Core for the Better Optical Performance in the Visible Spectral Region-A Numerical Study

In this paper, we present numerical studies of several different structures of anti-resonant, hollow core optical fibers. The cladding of these fibers is based on the Kagomé lattice concept, with some of the core-surrounding lattice cells removed. This modification, by creating additional, glass-free regions around the core, results in a significant improvement of some important optical fiber parameters, such as confinement loss (CL), bending loss (BL), and dispersion parameter (D). According to the conducted simulations (with fused silica glass being the structure's material), CL were reduced from ~0.36 dB/m to ~0.16 dB/m (at 760 nm wavelength) in case of the structure with removed cells, and did not exceed the value of 1 dB/m across the 700⁻850 nm wavelength range. Additionally, proposed structure exhibits a remarkably low value of D-from 1.5 to 2.5 ps/(nm × km) at the 700⁻800 nm wavelength range, while the BL were estimated to be below 0.25 dB/m for bending radius of ~1.5 cm. CL and D were simulated, additionally, for structures made of acrylic glass polymethylmethacrylate, (PMMA), with similarly good results-DPMMA ∊ [2, 4] ps/(nm × km) and CLPMMA ≈ 0.13 dB/m (down from 0.41 dB/m), for the same spectral regions (700⁻800 nm bandwidth for D, and 760 nm wavelength for CL).