Microfluidic directional emission control of an azimuthally polarized radial fibre laser

Lasers with cylindrically symmetric polarization states are predominantly based on whispering-gallery modes 1 , 2 , 3 , 4 , 5 , 6 , 7 , characterized by high angular momentum and dominated by azimuthal emission. Here, a zero-angular-momentum laser with purely radial emission is demonstrated. An axially invariant, cylindrical photonic-bandgap fibre cavity 8 filled with a microfluidic gain medium plug is axially pumped, resulting in a unique radiating field pattern characterized by cylindrical symmetry and a fixed polarization pointed in the azimuthal direction. Encircling the fibre core is an array of electrically contacted and independently addressable liquid-crystal microchannels embedded in the fibre cladding. These channels modulate the polarized wavefront emanating from the fibre core, leading to a laser with a dynamically controlled intensity distribution spanning the full azimuthal angular range. This new capability, implemented monolithically within a single fibre, presents opportunities ranging from flexible multidirectional displays to minimally invasive directed light delivery systems for medical applications. Researchers realize a zero-angular-momentum radial-emission laser by filling a cylindrical photonic crystal fibre cavity with a microfluidic gain medium. Control of the electromagnetic fields is provided by electrically contacted and independently addressable liquid-crystal microchannels in the fibre.