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• MFC signals with four switchable frequencies have been generated, which can be switched by simply rotating the PC. • By cascading a dual-loop structure, MFC signals with supermode noise suppression can be obtained. • By applying the longer length of the PMFs, the higher switchable central frequency of the MFC can be achieved. In this paper, we propose and experimentally demonstrate a flexibly frequency switchable active mode-locking optoelectronic oscillator (FSAML-OEO) in which a multi-passband microwave photonic filter (MPF) with two polarization-maintaining fibers (PMF) based Solc-Sagnac interferometer is used. Microwave frequency combs (MFCs) signals with four switchable central frequencies of 217 MHz, 453 MHz, 662 MHz and 1101 MHz are generated by controlling the polarization state of the Sagnac interferometer via rotating the polarization controller (PC). By cascading a dual-loop structure, MFCs signals with adjustable comb spacing of 1 MHz, 3 MHz, and 5 MHz are obtained with fundamental and harmonic FSAML-OEO, in which the supermode noise suppression ratios of the dominate modes and the super-modes are measured to be about 30 dB. [ABSTRACT FROM AUTHOR]

• A highly sensitive surface plasmon resonance (SPR) sensor based on seven-core photonic crystal fiber (SCPCF) is proposed. • The surface of SCPCF is covered with gold film as the sensing region for refractive index (RI) and temperature measurement. • Gold film covers SCPCF surface for RI sensing, with polydimethylsiloxane (PDMS) coating for temperature sensing on one part of the gold film. • The experiment results show that the RI sensitivity and temperature sensitivity of the proposed sensor reach 1644 nm/RIU and −2.59 nm/°C, respectively. A highly sensitive surface plasmon resonance (SPR) sensor based on seven-core photonic crystal fiber (SCPCF) is proposed and experimentally demonstrated for refractive index (RI) and temperature measurement. The dual-parameter sensor is fabricated by inserting an SCPCF between two multimode fibers (MMFs). The surface of SCPCF is covered with gold film as the sensing region. One part of the gold film is additionally coated with polydimethylsiloxane (PDMS) to enable temperature sensing, while the rest is used for RI sensing. The experiment results show that the RI sensitivity and temperature sensitivity of the proposed sensor reach 1644 nm/RIU and −2.59 nm/°C, respectively. Additionally, the SPR dual-parameter sensor based on SCPCF has good stability and repeatability, which has great application potential in the field of environmental monitoring, disease diagnosis, and biochemical sensing. [ABSTRACT FROM AUTHOR]