Long-period gratings in polymer ridge waveguides

We report the design and fabrication of long-period waveguide gratings (LPWGs) in benzocyclobutene (BCB) ridge waveguides. We apply an accurate perturbation theory to analyze the LPWGs. In particular, the phase-matching condition, the coupling coefficients, the temperature dependence of the resonance wavelength, the bandwidth, and the polarization dependence of the resonance wavelength are discussed. Several LPWGs in BCB ridge waveguides are fabricated by a UV-writing technique using a KrF excimer laser. The transmission spectra of the gratings are measured and discussed. An LPWG with a polarization-insensitive resonance wavelength at a specific temperature is demonstrated. Experimental results agree well with the theory. Our results are useful for the design of LPWG-based devices for various applications.