Broadband Microwave Frequency Measurement Using a Heterogeneous Multicore Fiber

We experimentally demonstrate a microwave frequency measurement scheme using a heterogeneous multicore fiber (MCF). Taking advantage of the inherently different differential group delays (DGDs) among four cores of the heterogeneous MCF, two individual 2-tap microwave filters with different free spectral ranges (FSRs) are constructed and the power ratio between their frequency responses is used as the amplitude comparison function (ACF). Since the DGD among the cores and the FSR of the filters are wavelength-dependent, by tuning the operational wavelength over a set of different values, we can obtain a set of different ACF traces. The collective information provided by these ACFs is then used to estimate the unknown frequency. Compared to many previous microwave frequency measurement approaches using dispersive elements, this scheme offers higher flexibility, tunability and compactness, along with higher measurement resolution (±71 MHz) over a broader radiofrequency range (0.5–40 GHz).