Post-irradiation resonance wavelength adjustment of long period grating based loss filters

We present a simple technique to precisely and continuously adjust the resonance wavelengths of long-period cladding-mode-coupled gratings without strongly affecting the coupling strength. The main principle of this method is based on the strong dependence of the propagation constants and hence the peak positions of the cladding modes on the cladding diameter. Therefore, one can shift the grating resonance wavelength by changing the cladding dimension. In our case, this has been achieved by etching the fiber in a HF acid solution.