Design and Numerical Investigation of a Step-Modulated Circular Defect Core Photonic Crystal Fiber with Near-Zero Dispersion and Enhanced Nonlinear Response for Optical Communication
Ajay Sudhir Bale, B V Santhosh KrishnaIntroduction:
Photonic crystal fibers (PCFs) are known to provide exceptional flexibility in tailoring chromatic dispersion, modal confinement, and nonlinear optical characteristics by using modified fiber geometries. In this work, a step-modulated circular defect core photonic crystal fiber having a five-ring hexagonal lattice with alternating air-hole radii is analysed numerically. This structure consists of a solid circular silica core that is embedded within a microstructured silica cladding, and its successive rings employ air-hole radii r1 = 0.3Λ and r2 = 0.45Λ, with pitch Λ = 28 μm.
Methods:
The optical properties of this proposed fiber are analyzed over the wavelength range 1.2–1.8 μm by using a full-vector finite element method with perfectly matched layer boundary conditions. Wavelength-dependent silica refractive index is incorporated through the Sellmeier equation, which will account for material dispersion. Key performance parameters like effective refractive index, chromatic dispersion, confinement loss, effective mode area, and nonlinear coefficient are evaluated systematically.
Results:
The proposed fiber supports stable single-mode propagation with the imaginary component of the effective refractive index on the order of 10−14. Confinement loss is found to be ultra- -low throughout the investigated wavelength range, and the chromatic dispersion is confined within a near-zero interval of approximately −0.01 to +0.005 ps/nm·km. The nonlinear coefficient is found to be approximately 195 W−1·km−1 at shorter wavelengths, and this is due to enhanced modal confinement.
Discussion:
The alternating air-hole radii will regulate the waveguide dispersion and optical confinement. The wavelength-dependent effective mode area shows an inverse relationship with the nonlinear coefficient, which confirms that there is stronger nonlinear interaction at shorter wavelengths.
Conclusion:
The proposed step-modulated circular defect core photonic crystal fiber achieves a balanced combination of near-zero dispersion, low confinement loss, and enhanced nonlinear response over the 1.2–1.8 μm wavelength range, which demonstrates a strong potential for dispersion- managed optical communication and nonlinear photonic applications.