Novel phase masks with overlapping regions to fabricate fiber Bragg gratings for filtering sky emission lines

We analyze aperiodic fiber Bragg gratings (FBGs) fabricated using an aperiodic phase mask, involving partial overlaps of distinct mask regions. Multichannel aperiodic FBG filters are promising candidates for suppressing hydroxyl (OH) emission lines in ground-based near-infrared astronomical observations. However, the fabrication of such multichannel aperiodic FBGs demands high repeatability. We explore the design of phase masks with repeatable FBG inscriptions. Previously, we have explored a phase mask (1st generation) designed and fabricated with partial overlapping regions using logical OR operation. Continuing this effort, we investigate three distinct phase mask designs capable of generating FBGs corresponding to five OH lines. The first mask features five discrete regions, each producing a specific FBG channel, while the other two masks incorporate numerically obtained overlap regions using logical OR and XOR operations. We present here the performances of the fabricated masks by comparing the Bragg wavelengths and the reflectivities of the inscribed FBGs.