A fiber-optic temperature sensor based on the harmonic Vernier effect (HVE) was proposed, which consists of a sensing Sagnac interferometer (SSI) and a reference Sagnac interferometer (RSI) in parallel. Different order HVEs are generated by controlling the length of the panda fiber in the SSI to be about an integer multiple of that in the RSI. The sensitivity and detuning of different order HVEs compared with the normal Vernier effect (NVE) are investigated, and the results show that the HVEs have almost the same temperature sensitivity as the NVE when they have the same magnification factor, while their detunings are much larger than that of the NVE, and the higher the order of the HVE, the larger the detuning. As we all know that the larger the detuning, the easier the magnification factor is to be controlled, that is, the easier the sensor is to be prepared, so from the point of view, the sensors based on the HVEs are better than those based on the NVE. This conclusion is also suitable for other fiber-optic sensors based on Vernier effect.

This paper presents a high-sensitivity temperature and humidity synchronous measurement sensor based on virtual Vernier demodulation, designed to overcome the limitations of traditional sensors in high-sensitivity and synchronous measurements. By combining a dual-cavity parallel structure with the Virtual Vernier effect (VVE), two interferometers were designed, with one using a temperature-sensitive material (polydimethylsiloxane, PDMS) and the other using a humidity-sensitive material (polyvinyl alcohol, PVA) for temperature and humidity measurement, respectively. Based on actual interference spectra, a modulation function was used to generate the virtual reference interferometer spectrum, which was then superimposed with the sensing interferometer’s spectrum to form a virtual Vernier envelope. By monitoring the displacement of the envelope, precise measurements of temperature and humidity changes were achieved. Experimental results showed a temperature sensitivity of 5.61 nm/°C and 7.62 nm/°C, a humidity sensitivity of 0 nm/%RH and −3.07 nm/%RH, and average errors of 0.64% and 1.10% for temperature and humidity, respectively, demonstrating the feasibility of the method. The introduction of the virtual interferometer effectively reduces environmental interference with the measurement results and avoids the material loss and errors associated with traditional reference interferometers. More importantly, the VVE enables dynamic adjustment of the envelope magnification, thereby enhancing the sensor’s flexibility and overcoming the structural limitations of traditional interferometers. This sensor provides efficient and reliable technological support for future environmental monitoring and climate change research.

Hierarchical NiO-SnO₂ nanoflowers were prepared via a one-step hydrothermal method. The morphology, structure and components of the hierarchical NiO-SnO₂ nanoflowers were examined via scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray powder diffraction (XRD) and X-ray photoelectron spectroscopy (XPS), respectively. The ethanol gas-sensing performance was systematically analyzed between pure hierarchical SnO₂ nanoflowers and the hierarchical NiO-SnO₂ nanoflowers. The results indicated that the hierarchical NiO-SnO₂ nanoflowers showed better gas-sensing properties than the pure hierarchical SnO₂ nanoflowers at 164 °C. The enhanced gas-sensing performance was ascribed to the formation of p-n heterojunctions between p-type NiO and n-type SnO₂. Additionally, NiO has a catalytic role. Therefore, hierarchical NiO-SnO₂ nanoflowers could be a potential gas-sensing material for the fabrication of high-quality ethanol gas sensors.

This paper proposes a temperature-salt synchronous sensitisation detection technique based on data signal processing (DSP). The method first employs spectral analysis to decouple the independent interference spectra of each cavity from the combined interference spectrum of the parallel dual-cavity system. Subsequently, a virtual interferogram corresponding to each independent interferogram is constructed, and the two are superimposed to generate their respective vernier effect spectra. Finally, based on the relationship between the envelope peaks (or troughs) of the two vernier spectra and variations in temperature and salinity, a sensitivity matrix equation is established, thereby achieving highly sensitive simultaneous detection of temperature and salinity parameters. Experimental results indicate that within the temperature range of 21°C to 28°C, the temperature sensitivities of the dual-vernier spectrum are -2.0544 nm/°C and -4.9609 nm/°C, respectively, representing 8.08 times and 5.83 times the sensitivity of a single independent cavity. Within a salinity range of 20‰ to 50‰, the salinity sensitivities of the dual-vernier spectra were 1.4248 nm/‰ and 0, respectively, representing 7.98 times and 0 times the sensitivity of a single independent cavity. This method, requiring no physical interferometer and relying solely on algorithms, not only achieves simultaneous measurement of both temperature and salinity parameters but also realizes sensitivity amplification. This method offers simplicity of implementation, high sensitivity, and low cost, demonstrating promising application prospects in the field of high-sensitivity marine sensing.

This paper presents a high-sensitivity multi-point seawater temperature detection system based on the virtual Vernier effect, achieved through multiplexed Fabry–Perot (FP) cavities combined with optical frequency-modulated continuous wave (FMCW) interferometry. To address the nonlinear frequency scanning issue inherent in FMCW systems, this paper implemented a software compensation method. This approach enables accurate positioning of multiple FP sub-sensors and effective demodulation of the sensing interference spectrum (SIS) for each FP interferometer (FPI). Through digital signal processing (DSP) algorithms and spectral demodulation, each sub-FP sensor generates an artificial reference spectrum (ARS). The virtual Vernier effect is then achieved by means of a computational process that combines the SIS intensity with the corresponding ARS intensity. This eliminates the need for physical reference arrays with carefully detuned spatial frequencies, as is required in traditional Vernier effect implementations. The sensitivity amplification can be dynamically adjusted with the modulation function parameters. Experimental results demonstrate that an optical fiber link of 82.3 m was achieved with a high spatial resolution of 23.9 $\mathsf{\mu }\mathrm{m}$. Within the temperature range of ${30 }^{\circ }\mathrm{C}$ to ${70 }^{\circ }\mathrm{C}$, the temperature sensitivities of the three enhanced EIS reached −275.56 $\mathrm{pm}{/}^{\circ }\mathrm{C}$, −269.78 $\mathrm{pm}{/}^{\circ }\mathrm{C}$, and −280.67 $\mathrm{pm}{/}^{\circ }\mathrm{C}$, respectively, representing amplification factors of 3.32, 4.93, and 6.13 compared to a single SIS. The presented approach not only enables effective multiplexing and spatial localization of multiple fiber sensors but also successfully amplifies weak signal detection. This breakthrough provides crucial technical support for implementing quasi-distributed optical sensitization sensing in marine environments, opening new possibilities for high-precision oceanographic monitoring.