We have designed and studied the fabrication limitations for a new type of optical waveguide filter based on the concept of a "Segmented Waveguide Array Grating" (SWAG, see refs. 1,2). The idea is to make an optical waveguide consisting of a large number of segments which differ from each other by their precise length and by a precise change in one of their transverse dimensions. The transitions between different segments are abrupt in the transverse dimension on the scale of one tenth the wavelength of light in the medium and are positioned with nanometer precision along the propagation axis of light. Reflections from a given subset of these transitions add up coherently and can give a grating-like reflection spectrum. By precisely positioning the segment transitions and by setting the variable transverse dimension at precise values one can design a large variety of filtering functions. As an example we have designed a filtering function that has a nearly rectangular profile, something that would be very useful in applications of WDM optical communications. The light scattering losses at segment transitions can be minimized by choosing average transverse dimensions such that the waveguide operates near the diffraction minimum. The lithography step of simple planar SWAG devices has been carried out by means of electron beam direct writing. The waveguide materials used were 6-micron thick silica/germania layers (index 1.454) spaced from a silicon substrate by a 14-micron thick pure silica layer. Trapped electron phenomena in the silica layer were eliminated by depositing metal layers on top of the silica in order to stop electrons traversing the photoresist. SWAG patterns with sharp features were obtained and are expected to give the expected spectral filtering functions.

Date Published: 8 September 2006
PDF: 10 pages
Proc. SPIE 6343, Photonics North 2006, 63431F (8 September 2006); doi: 10.1117/12.707739

Published in SPIE Proceedings Vol. 6343:
Photonics North 2006
Pierre Mathieu, Editor(s)