Direct fabrication of polyimide waveguide grating by synchrotron radiation

Synchrotron radiation induces a change in the refractive index of a fluorin ated 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, pres umably due to fluorine detachment and subsequent volume compaction. We have fabricated a 0.51-mu m-period grating structure in an embedded waveguide t hrough a 15-mu m-thick overcladding by using an x- ray mask with a spatiall y modulated pattern. The grating is fabricated at a dose of 160 A s and sho ws a reflectivity of 60% and a full width at half maximum as narrow as 0.25 nm at around a wavelength of 1.55 mu m. (C) 1998 American Institute of Phy sics. [S0003-6951(98)03849-2].