1. Modal profiles at the SPR wavelengths for different SF values
Enhancement of birefringence using metal-filled suspended core microstructured optical fibers
Rajat Kumar Basak1,2, Debashri Ghosh1
1. Fiber Optics & Photonics Division, CSIR-Central Glass and Ceramic Research Institute, Kolkata, WB, India
2. School of Material Science and Nanotechnology , Jadavpur University, Kolkata, WB, India
Figure 3. Cross sections of the metal-filled SC-MOF for min. and max. SF
Figure 2. Cross-sections of SC-MOFs in COMSOL GUI showing the min. and max. SF
2D modal analysis of metal-filled SC-MOFs carried out using the RF module of COMSOL Multiphysics (version 4.3b) in the frequency domain to analyze the enhancement of birefringence.
Structural Parameter: Λ = 2 µm, d/Λ = 0.95
SF Range: 0.95 ≤ SF ≤ 1.55
RI of silica calculated using Sellmeier’s eqn.
Metal used: Gold (Au)
RI of gold calculated using Lorentz-Drude Model
Parameters and Variables incorporated in ‘Global Definitions’ and ‘Model (Definitions)’
Material properties defined in ‘Materials’ section
Operational wavelength range: 0.6 µm µm
Effective indices simulated for the entire wavelength range using ‘Parametric Sweep’
Division of SC-MOF geometry into minute triangular elements using ‘Physics-controlled Mesh’
Introduction
Certain applications of MOF need small core size.
Instead of decreasing Λ, core size can be reduced by elongating and tapering the air holes in the first ring.
Computational Method
Figure 4. Physics-controlled Mesh applied to a plasmonic SC-MOF design
Results
Modal profiles at the SPR wavelengths for different SF values
Dispersion & Loss Curves
Figure 9. Dispersion curves of x and y-polarization
Birefringence Curves
Figure 11. Variation in birefringence with increase in SF
Conclusions
Numerical results show enhancement of modal birefringence with the increasing of SF values.
For SF = 1.55, it is increased by an order of magnitude as compared with the existing birefringent fibers.
These SC-MOFs have the potential of efficiently functioning as in-fiber polarizers for a particular wavelength range.
P. St. J. Russell, ‘Photonic crystal fibers’ J. Lightwave Technol., 24 (12), (2006).
D. Ghosh, S. Bose, S. Roy and S. K. Bhadra, ‘Design and fabrication of microstructured optical fibers with optimized core suspension for enhanced supercontinuum generation,’ J. Lightwave Technol., 33 (19), (2005).
References
Microstructured optical fiber (MOF) consists of a solid silica core surrounded by a hexagonal lattice of air holes. Geometrical parameters like hole diameter (d), pitch (Λ) and their ratio (d/Λ) controls the fiber properties. MOFs have carved out a niche in the field of both plasmonics and photonics in the last decade.
Effective indices of two orthogonal polarizations of the fundamental mode is noted and the variation in birefringence as a function of wavelength is studied.
Improvement in birefringence with the increase in SF is observed.
Figure 1. Schematic of the formation of the elongated and tapered air hole
Quantitative measure of the elongation and tapering is given by the parameter Suspension Factor, SF = OP2/OC.
MOFs thus developed are called suspended core MOFs (SC-MOFs).
Air holes in first ring Circle + Second order Bézier curve
Bézier Curve
Figure 5. SF = 1.35
(Incomplete Coupling)
Figure 6. SF = 1.35
(Complete Coupling)
Figure 7. SF = 1.55
Figure 8. SF = 1.55
Figure 10. Loss curves of x and y-polarization
For SF = 1.55, achieved birefringence value is at the wavelength of 1.50 μm.