Birefringence of guided modes in photonic wires: Gaussian-mode analysis

Optical fibers with subwavelength core sizes are shown to offer interesting possibilities for mode birefringence engineering. The Gaussian-mode approximation applied to the analysis of fiber birefringence reveals the existence of a physical limit of form birefringence in an optical fiber, controlled by the trade-off between diffraction and step-index confinement of electromagnetic field in a noncircular waveguiding channel. For fused silica waveguides, a maximum mode birefringence can be achieved in the case of subwavelength core sizes.