Abstract
This paper presents a numerical study of high birefringence induced by four types (Type 1–4) of different sizes of elliptical air holes in photonic crystal fibers (PCFs). The numerical simulation is carried out by using the finite element method. The statistical correlations between the birefringence and the various parameters are obtained. Based on our results, the birefringence is found to be largely dependent on the variation of the normalized frequency, size ratio, effective area of the circular and elliptical air holes, and the ring number of cladding. Two of our suggested structures, Type 1 and Type 3, can considerably enhance the birefringence in PCFs leading to values as high as7.697×10−3and8.002×10−3, respectively, which are much higher than that obtained by a conventional step-index fiber.
Highlights
Photonic crystal fibers (PCFs) guide the electromagnetic field by an arrangement of air holes that run down the entire fiber length
Symmetry in PCFs implies the existence of doubly degenerate pairs of modes, that share the same propagation constant (β) and free-space wavelength (λ), so they must be degenerate
A number of recent studies indicate that PCFs with a preferred direction in their geometry could exhibit birefringence of about an order of magnitude higher than that obtained with conventional techniques [8,9,10]
Summary
Photonic crystal fibers (PCFs) guide the electromagnetic field by an arrangement of air holes that run down the entire fiber length. For any fiber with rotational symmetry of order higher than two, a mode that has a preferred direction must be one of a pair of degenerate modes. The observation of birefringence must be a result of asymmetry in the structure These perturbations couple the modes that propagate at slightly different phase velocities, with the consequence that the polarization of light becomes unpredictable after a short propagation. To overcome this drawback, it is highly desirable to generate a large birefringence with a low scattering loss and at the same time to avoid significant perturbations in the cladding modes to cope with recent challenges and demands in fiber optic polarization control. A number of recent studies indicate that PCFs with a preferred direction in their geometry could exhibit birefringence of about an order of magnitude higher than that obtained with conventional techniques [8,9,10]
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