Spiral photonic-crystal fiber design is golden

Engineers at City University London (London, England) have demonstrated a photonic-crystal fiber (PCF) in which the air holes were laid out in a “golden spiral” (GS)–a pattern governed by a mathematical constant (approximately 1.61803) known by artists and architects since the Renaissance as the Golden Ratio. Such a hole design does not exhibit rotational symmetry, and thus has no degeneracy of modes. This property, along with a diffraction pattern of isotropic circular Bragg rings, enables for low-loss coupling of the fiber with other devices.

Arti Agrawal and colleagues used a vectorial finite-element method to compute a modal birefringence value of 0.015 at a wavelength of 1.55 µm. Such highly birefringent fibers can be used in high-speed optical communications, sensing, and polarized fiber lasers. The GS-PCF also exhibited highly tunable dispersion, which is dependent on the parameters of the spiral and the air holes, with multiple zero-dispersion wavelengths. Circular, identical air holes mean the fibers can be easily fabricated. The two-dimensional chiral nature of the GS-PCF may also hold promise for use in nonreciprocal optical dielectric devices at telecommunications wavelengths. Contact Aziz Rahman at [email protected].