Geometric Optimization and IPA-Induced Dispersion Tuning in Solid-Core Photonic Crystal Fibers

TL;DR

This paper addresses tuning dispersion and nonlinearity in solid-core photonic crystal fibers (PCFs) for nonlinear photonics and sensing, focusing on how core geometry and ambient refractive index influence dispersion. A hybrid numerical workflow combining Plane Wave Expansion (PWE), Finite-Difference Time-Domain (FDTD), and Finite-Difference Eigenmode (FDE) analyses is used to map how core diameter $d_c$, pitch $\Lambda$, and air-filling fraction $f$ affect the zero-dispersion wavelength $\lambda_0$, dispersion slope, $A_{\rm eff}$, and the nonlinear coefficient $\gamma$, including IPA contamination modeled by $n_{\text{IPA}}=1.377$. The key findings show that decreasing $d_c$ blue-shifts $\lambda_0$ from $791\,\text{nm}$ to $646\,\text{nm}$ while boosting $\gamma$ from $72$ to $124\,\text{W}^{-1}\text{km}^{-1}$ and reducing $A_{\rm eff}$ from $2.75$ to $1.6\,\mu\text{m}^2$, with a concomitant rise in confinement loss; hexagonal lattices offer some confinement advantages over circular counterparts. IPA contamination further red-shifts $\lambda_0$ and increases $L_c$, underscoring environmental robustness challenges and potential sensing opportunities. The results are validated against experimental data (e.g., Thorlabs NL-2.3-790-02) with deviations below $4\%$, supporting a design framework for robust, efficient PCFs in supercontinuum generation and chemical sensing.

Abstract

This study presents a numerical investigation of solid-core photonic crystal fibers with circular and hexagonal cladding geometries. The goal is to optimize optical parameters for nonlinear photonics and environmental sensing. Full-vectorial simulations using FDTD, PWE, and FDE are used to analyze the effects of core diameter, pitch, and air filling fraction on the zero-dispersion wavelength, nonlinear coefficient, effective mode area, and confinement loss. Reducing the core diameter from 2.4 to 1.4 microns tunes the zero-dispersion wavelength from 791 to 646 nanometers and increases the nonlinear coefficient by 72 percent, from 72 to 124 inverse watts per kilometer. The study also examines the effect of isopropyl alcohol infiltration, which causes a red-shift in dispersion and degrades confinement. These results offer a design framework that balances nonlinear efficiency and environmental robustness for supercontinuum generation and chemical sensing.

Figures (8)

• Figure 1: Schematic cross-sectional view of the proposed PCFs (a) circular air holes composed of PCF-1 and (b) hexagonal air holes composed of PCF-2. Structural parameters of (c) PCF-1 and (d) PCF-2, where $\Lambda$ is the pitch, $d_c$ is the core diameter, $2r$ is the diameter of the circular air holes, and $s$ is the diameter of hexagonal air holes.
• Figure 2: Dispersion behavior and ZDW for $d_c = 1.4 \mu m$ to $d_c = 2.2 \mu m$ with $0.2 \mu m$ increase compared to the base structure of PCF-1. Inset showing ZDW for different $d_c$ values.
• Figure 3: Attenuation $L_c$ behavior for $d_c = 1.4 \mu m$ to $d_c = 2.2 \mu m$ with $0.2 \mu m$ increase compared to the base structure of PCF-1. Inset showing $L_c$ of the ZDW region for different $d_c$ values.
• Figure 4: Group index $n_g$ behavior for $d_c = 1.4 \mu m$ to $d_c = 2.2 \mu m$ with $0.2 \mu m$ increase compared to the base structure of PCF-1.
• Figure 5: Variation of effective mode area $A_{\text{eff}}$ (left axis, red dashed line with circles) and nonlinear coefficient $\gamma$ (right axis, blue solid line with squares) as a function of core diameter $d_c$. The results show that reducing $d_c$ decreases $A_{\text{eff}}$ and correspondingly enhances $\gamma$, consistent with the inverse proportionality $\gamma \propto 1/A_{\text{eff}}$.