RIDGE-WAVE-GUIDE SIDEWALL-GRATING DISTRIBUTED-FEEDBACK STRUCTURES FABRICATED BY X-RAY-LITHOGRAPHY

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 f abrication is independent of both the materials growth and the guide f ormation. The ridge waveguide is first formed by wet-chemical etching. Then, a poly(methylmethacrylate) grating (LAMBDA = 230 nm) is pattern ed onto this ridge waveguide using x-ray lithography. A Ti/Al etch mas k is lifted-off to serve as a mask for subsequent reactive-ion etching . Gratings with long-range spatial-phase coherence and negligible dist ortion, characteristics which are necessary for accurate control of th e wavelength and bandwidth, are obtained using a holographically gener ated x-ray mask.