Direct fabrication of polyimide waveguide grating by synchrotron radiation

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Abstract
Synchrotron radiation induces a change in the refractive index of a fluorinated polyimide by an order of 10−2, which is about ten times larger than the change it induces in silica glass irradiated by ultraviolet light, presumably due to fluorine detachment and subsequent volume compaction. We have fabricated a 0.51-μm-period grating structure in an embedded waveguide through a 15-μm-thick overcladding by using an x-ray mask with a spatially modulated pattern. The grating is fabricated at a dose of 160 A s and shows a reflectivity of 60% and a full width at half maximum as narrow as 0.25 nm at around a wavelength of 1.55 μm.