Ridge-waveguide sidewall-grating distributed feedback structures fabricated by x-ray lithography

Abstract

A novel distributed feedback structure has been developed in which the grating is patterned onto the sidewalls of a ridge waveguide. Such a laser structure results in simplified processing in that the grating fabrication is independent of both the materials growth and the guide formation. The ridge waveguide is first formed by wet-chemical etching. Then, a poly(methylmethacrylate) grating (Λ=230 nm) is patterned onto this ridge waveguide using x-ray lithography. A Ti/Al etch mask is lifted-off to serve as a mask for subsequent reactive-ion etching. Gratings with long-range spatial-phase coherence and negligible distortion, characteristics which are necessary for accurate control of the wavelength and bandwidth, are obtained using a holographically generated x-ray mask.