High-Resolution Interrogation Scheme by Mapping FFT of MSM Optical Spectrum to RF Spectrum

A high-resolution temperature sensor based on MMF-SMF-MMF (MSM) utilizing the mapping from Fast Fourier transform (FFT) of MSM spectrum to RF spectrum is proposed and experimentally demonstrated. The MSM is the sensing element and consists of a single mode fiber (SMF) sandwiched between two short multimode fibers (MMFs). The MSM-based microwave photonic filter (MPF) down-converts the optical spectrum to the RF domain based on the mapping from Fourier transform of MSM spectrum to microwave photonic response. Temperature is extracted from the amplitude variations of the frequency response. Experiments shows that the amplitude variation of response has a quadratic relationship with temperature at 332.3MHz and 594.3MHz due to the differential temperature sensitive coupling coefficient between cladding modes and the core mode of SMF. Compared with the optical spectrum analyzer (OSA) interrogation scheme, the proposed scheme increases temperature resolution by two orders. The interrogation scheme is also suitable for a variety of multimode interferometer with high precision requirement.