Programmable Photonic Microwave Filters Monolithically Integrated in InP–InGaAsP

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 analogmicrowave 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 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 is obtained. However, we believe this number can be improved significantly by optimizing the design.