Demonstration and performance evaluation of reconfigurable multiband microwave filters using a programmable photonic integrated circuit

A programmable silicon photonic multiband microwave filter with tunable bandwidths has been demonstrated. The filter has been successfully used to set up a radio-over-fiber link operating in the X-band as a proof of concept. For this purpose, we have investigated the programmable photonic integrated circuit comprising 14 tunable balanced Mach–Zehnder interferometers designed into a square mesh architecture and fabricated using CMOS-compatible silicon photonic technology. The photonic chip was electrically packaged for its reconfigurable operations using an external 16-channel programmable power supply by tuning the thermo-optic phase shifters integrated into both the arms of Mach–Zehnder interferometers. The operating temperature of the packaged chip is stabilized within ±0.002°C using a PID controller to avoid any interference of ambient temperature fluctuations. The mesh architecture is programmed into three different microring resonators (MRRs) operating independently in all-pass configurations for three free spectral ranges (23.25 GHz, 11.75 GHz, and 8.75 GHz, respectively). The multiband microwave photonic filter characteristics have been experimentally obtained using a fiber-coupled off-chip laser source (operating at λ ∼1550 nm ), a modulator (bandwidth ∼40 GHz ), and a photodetector (bandwidth ∼50 GHz ). Thus, we have demonstrated microwave filters with two, three, and four bands within the modulator bandwidth used in the experiments. Among these, the two-band filter realized for the X- and Ka-bands was thoroughly investigated in the experiments to understand the MRR coupling condition ( Q -factor) effect on the realized filter bandwidth and its tuning range, link gain, and rejection. The bandwidth of both the filter bands was tuned over the extensive range of 1.6–8.1 GHz by controlling the MRR Q -factor and the resonance spacing from the carrier. At the same time, the bandwidth tuning range of the three-band filter realized for the C-, Ku-, and Ka-band (2–6 GHz) and the four-band filter realized for the C-, Ku-, K-, and Ka-band (3–5 GHz) in our experiments was limited by the finesse of the ring resonator. Finally, the microwave filter response at the X-band is used for evaluating a radio-over-fiber receiver link as a proof of concept for its potential 5G/6G applications. With an optimized set of operating parameters of the programmable microwave filter, we could achieve a bit error rate as low as ∼10 −20 for a fiber-optic link length of 400 m (at 100 Mbps).