Image-rejection multi-band frequency down-conversion based on photonic sampling

An image-rejection multi-band frequency down-conversion scheme is proposed and demonstrated based on photonic sampling. In this scheme, two radio-frequency (RF) signal replicas with a quadrature phase difference are sampled by two ultra-short optical pulse trains in orthometric polarization via the linear electro-optic modulation in a dual-polarization dual-drive Mach-Zehnder modulator (DP-DDMZM). After being polarization demultiplexed, the two sampled optical pulses are separated from each other and detected by using two photodetectors (PDs), respectively. Hence, the RF signals in multiple frequency bands are simultaneously down-converted to the intermediate-frequency (IF) band. Finally, the two IF signals are combined by using an electrical 90° hybrid coupler to eliminate the image-frequency components. In the experiment, an ultra-short optical pulse train with a repetition frequency of 8 GHz is generated by employing an electrooptic modulation-based time lens with the chirp compensation, and is used to achieve photonic sampling. The experimental results indicate that image-rejection down-conversion is achieved for the input signal in the frequency range of 6 GHz to 27 GHz, where the image rejection ratio is larger than 58 dB.