PROCEEDINGS ARTICLE | March 12, 2008
Proc. SPIE. 6624, International Symposium on Photoelectronic Detection and Imaging 2007: Optoelectronic System Design, Manufacturing, and Testing
KEYWORDS: Reflectors, Thin films, Refractive index, Mirrors, Reflection, Dispersion, Reflectivity, Photonic crystals, Linear filtering, Structural design
A periodic multi-layer thin film stack, which behaves as one-dimensional photonic crystal, exhibits "superprism effect",
or high spatial dispersion, which can be used for wavelength multiplexing and demultiplexing. For application purposes,
thin-film stacks of multi-cavity Gires-Tournois structure are more suitable to design linear spatial shifts than periodic
multi-layer structures. Using the modified design procedure for all-pass filters, a mathematical model of the spatial
dispersion with normalized frequency is set up to simulate the designed spatial dispersion at given wavelength band. As a
simulated result, the all-pass polynomial coefficients, and reflectivity coefficients of reflectors are obtained. According to
the calculation based on resonate theory, the spatial dispersion of the designed structure is in accordance with the
required dispersion. Then, this structure is implemented in thin film stacks, with layers of different periodical numbers as
different reflectors and materials of high or low refractive index as cavity materials. Adjusting the cavity lengths also
performs optimization. In our design, a linear spatial shift of 25μm caused by dispersion is designed at 850nm and
1550nm, and implemented in thin film stacks. Comparisons are made between designs of different center wavelength,
different cavity lengths, and different number of cavities.
