Tailoring the transmission characteristics of polymer long-period waveguide gratings by UV irradiation

We propose a simple technique of realizing complicated yet controllable transmission spectra from a uniform polymer long-period waveguide grating. The technique is based on varying the waveguide parameters along the grating by exposing the grating to a controlled distribution of ultraviolet (UV) irradiation. To demonstrate the idea, we produce transmission spectra that mimic those of a phase-shifted grating and a chirped grating by using a step-wise and a linear 248-nm UV distribution, respectively. The experimental results agree well with the simulation results. The UV process allows real-time monitoring of the change in the transmission spectrum. Furthermore, the resultant spectrum can be tuned thermally over the entire C+L-band with a temperature control of only ∼20°C. The proposed technique provides an effective means of achieving widely tunable complicated filter characteristics.