Orbital angular momentum states in helically twisted PCF

31.10.2012, 14:58

Newsletter 5

Spiral twisting offers novel opportunities for controlling the loss, dispersion, and polarization state of light in optical fibres with noncircular guiding cores. In a recent paper we reported an effect that appears in continuously twisted "endlessly single-mode" photonic crystal fibre. The samples were fabricated by mounting one end of a length of fibre at the centre of a motorized rotation stage, the other being rigidly fixed. A permanent twist was produced by rotating the stage while scanning a focused CO2 laser beam (at a power level sufficient to soften the glass) along the fibre. Guided by the helical lattice of narrow interstitial glass strands, cladding light is forced to follow a spiral path. This diverts a fraction of the axial momentum flow into the azimuthal direction, leading to the formation of discrete orbital angular momentum states at wavelengths that scale linearly with the twist rate. Core-guided light phase-matches topologically to these leaky states, causing a series of dips in the transmitted spectrum. Twisted photonic crystal?fibre has potential applications in, for example, band-rejection filters and dispersion control.


Contact: gordon.wong(at)mpl.mpg(dot)de
Group: Russell Division
Reference: G. K. L. Wong et al., Science 337, 446–449 (2012).