Realization of low back-reflection, wideband fiber bandpass filters using phase-shifted long-period gratings

In conclusion, we have reported for the first time, to our knowledge, two new wideband fiber bandpass filters (tens of nanometres width) with low back-reflection and insertion losses. The spectral shape of the two phase-shifted photoinduced long-period gratings proposed is radically different, with a flattened bandpass peak for the doubly phase-shifted one.