Spiral Planar-Waveguide Bragg Gratings

摘要

A photonic integrated circuit is designed containing a long grating with spiral geometry. Waveguide width and index modulation are studied as methods to form the grating structure. Both methods require an initial mask step for waveguide formation. In the case of width modulation the grating is formed in the same step as the waveguide, whereas a second mask step is required for index modulation. Thus width modulation removes the alignment tolerances associated with a two step process. The spiral geometry enables a long grating (～1 m) to be realized in a small area (1 cm~2). The ability to form the grating in such a small area enables the use of current lithography mask / projection equipment. Thus, the requirements for mechanical/optical precision in a customized long fiber Bragg grating fabrication system is transferred to the precision of commercial lithography mask fabrication and projection equipment.