Long-period gratings in wavelength-scale microfibers

We report the fabrication of long-period gratings (LPGs) in wavelength-scale microfibers with diameters from 1.5to3 μm. The LPGs were fabricated by use of a femtosecond IR laser to periodically modify the surface of the fibers. These LPGs have grating periods of a few tens of micrometers, much smaller than those in conventional optical fibers. A compact 10-period LPG with a device length of only ~150 μm demonstrated a strong resonant dip of >20 dB around 1330 nm. These microfiber LPGs would be useful in-fiber components for microfiber-based devices, circuits, and sensors.