CO2-Laser Writing of Polymer Long-Period Waveguide Gratings

We propose a CO₂-laser writing technique for the fabrication of long-period waveguide gratings on polymer waveguides. This technique is based on introducing corrugation on the waveguide surface and a refractive-index modulation in the waveguide material by scanning a beam of CO₂-laser pulses along the waveguide. We demonstrate this technique by writing gratings on epoxy-clad benzocyclobutene channel waveguides. The rejection band of a typical fabricated grating has a contrast of ~12 dB and a 3-dB bandwidth of ~15 nm at the wavelength 1568 nm, which is the result of coupling from the core mode to the first cladding mode on the second diffraction order.