Three-grating monolithic phase-mask for the single-order writing of large-period gratings

An optimized achromatic high-efficiency monolithic phase mask is presented whose principle was demonstrated and described in reference [1]. The mask comprises three submicron period diffraction gratings at a single substrate side that create a purely single spatial frequency interferogram of large period. The optical scheme is that of an integrated Mach-Zehnder interferometer where all light circulation functions are performed by diffraction gratings. The paper describes the operation principle of the phase mask, the fabrication process, and its utilization in a write-on-the-fly scheme for the writing of a long, 2 μm-period grating.