Precise phase-controlled flexible grating delineated by weighted-dose electron beam lithography

This paper describes a precise phase-controlled grating delineation method for distributed-feedback (DFB) laser diodes (LDs). This method, called weighted-dose allocation variable-pitch electron-beam lithography (WAVE), enables us to fabricate gratings with different pitches while suppressing the stitching errors between the exposure fields, thus producing a precise pitch-controlled grating as well as a flexible grating with a continuously chirped structure. The small stitching error and the accuracy of the pitch and phase were evaluated by using a moire pattern microscope. The WAVE method is a powerful tool for fabricating sophisticated optical grating devices such as precise wavelength controlled LDs with specific characteristics for use in WDM network systems.