Fabrication of long-period fiber gratings with no harmonics

We have shown that the extraneous resonances seen in fibers with long-period gratings are caused by higher-order harmonics of the grating's fundamental spatial frequency, and can be eliminated. Our fabrication technique uses a variable writing speed computed using the measured nonlinearity of the glass fiber to UV light. This fabrication technique can be extended to writing arbitrary index profiles for a wide variety of fiberoptic devices, enabling fabrication of chirped and apodized long-period gratings that are free from extraneous resonances.