Double-pass microwave photonic sensing system based on low-coherence interferometry.

In this Letter, we propose and experimentally demonstrate, to the best of our knowledge, a novel high-performance microwave photonic sensing system employing a reflective double-pass spectrum-slicing sensing scheme, based on low-coherence interferometry in combination with a dispersive medium. The setup is implemented by configuring a double-pass spectrum slicing sensing scheme, which significantly increases the output power level of a low-coherence optical source by approximately 12 dB to compensate for the optical loss of the system. Moreover, since the light passes through the same optical path twice, the conversion efficiency between the applied optical path difference and the dependent radiofrequency (RF) resonance shift is doubled compared to the conventional approaches. It is also possible to realize a very high resolution thanks to the broad bandwidth of the semiconductor optical amplifier (SOA) spectrum. In addition, this SOA-based scheme enables the future realization of a fully integrated sensing system. As an application example, a highly sensitive displacement sensor was investigated, and the experimental results presented a highly linear relationship between the applied OPDs and the RF frequency shifts. The proposed sensing system successfully achieved a high conversion slope of 5.56 GHz/mm and a nearly constant resolution of approximately 124 μm using a Gaussian power density spectrum.