Abstract
We demonstrate an integrated programmable photonic filter structure
capable of producing bandpass filters with both tunable passband bandwidth
and center frequency. Such filters could provide dynamic pre-filtering of
very wide bandwidth analog microwave signals, essential to the next generation
RF-front ends. The photonic filter is constructed from an array of uncoupled
identical filter stages, each reconfigurable as a zero or a pole using an
asymmetrical Mach-Zenhder Interferometer (MZI) structure with feedback. Integrated
on a standard InP–InGaAsP material platform, semiconductor optical amplifiers
(SOAs) and current injected phase modulators (PMs) are used to rapidly adjust
the individual pole and zero locations, thereby reconfiguring the overall
filter function. In this paper, we demonstrate cascaded filter structures
with up to four filter stages, capable of producing a variety of higher order
filters. Demonstrated filters have a free spectral range (FSR) of 23.5 or
47 GHz. A center frequency tunability over 28 GHz is demonstrated for a 2nd
order bandpass filter, and a passband tunability of 1.9–5.4 GHz with
stopband rejection ${>}32$ dB using 3rd and 4th order filters. Finally, the linearity of our
active filters is investigated; a preliminary spurious-free dynamic range
(SFDR) of 86.3 dB$*$Hz$^{2/3}$ is obtained. However, we believe this number can be improved significantly
by optimizing the design.
© 2011 IEEE
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