We report a three-dimensional (3D) SERS substrate with different numbers of silver nanoparticle (Ag NP) layers using multilayer graphene oxide (GO) as a spacer. The SERS performance of the 3D nanostructure was investigated and it was found that the SERS effect increased as the number of Ag NP layers increased, and showed almost no change for more than four layers. We found that the SERS performance of the 3D nanostructures can be mainly attributed to the topmost hot spots which are closely related to the Ag NP layers in the 3D nanostructure. Furthermore, we explored 3D nanostructures with different Ag NP layers using the finite difference time domain method (FDTD). The 3D SERS substrates also exhibit excellent detection capability. The limit of detection (LOD) was calculated down to 10⁻¹⁵ M for R6G and 10⁻¹² M for CV. In addition, the reproducibility of the 3D SERS substrate was attributed obviously to the increasing number of Ag NP layers. Based on these promising results, the highly sensitive detection of molecules such as malachite green was demonstrated for food safety inspection.

We proposed a high sensitivity and a high resolution surface plasmon resonance sensor composed of graphene–WS₂ hybrid nanostructure and Au–Ag bimetallic-layers film.

The fiber-optic cascaded Fabry-Perot (FP) cavity structure is a significant interferometric sensor configuration, offering superior spectral resolution compared to Mach-Zehnder type sensors. In response to the comb-spectrum characteristics of fiber-optic cascaded FP sensors, we propose a novel optical vernier processing method. This method calculates the peak positions of individual resonance peaks without the need to track the drift of envelope modulation curve peaks, as required by traditional optical vernier scale methods. Utilizing this approach, we have significantly enhanced the sensitivity of cascaded FP cavity sensors. The strain and temperature sensing tests achieved sensitivities of 4.76 pm/μϵ and 271.61 pm/°C, respectively, representing an increase of over 20 times compared to a single-stage cascaded FP cavity. More importantly, the Figure of Merit (FOM) for the cascaded FP cavity sensors can be improved by more than two orders of magnitude under the same sensitivity amplification factor, compared to traditional optical vernier technologies based on envelope curve recognition. This also effectively avoids potential errors that may arise during the fitting process of the envelope modulation curve. These advantages endow the cascaded FP cavity sensors with significant potential for application in the field of high-performance fiber-optic sensing.

Wavelength-tunable dissipative solitons and amplifier similaritons have been obtained by inserting all-fiber Mach–Zehnder interferometer (MZI) filters with different free spectral ranges (FSRs) in a Yb-doped mode-locked fiber laser. The MZI filter is fabricated by splicing one segment of seven-core fiber (SCF) between two segments of single-mode fibers. The bandwidth of the filter depends on the FSR of the modulated interference curve and consequently depends on the tapered fiber diameter. Inserting MZI filters with bandwidths in a fiber laser and applying a tensile strain on the tapered SCF, both wavelength-tunable dissipative solitons and amplifier similaritons have been obtained.

The optical vernier method is a widely implemented technique for significantly enhancing the sensitivity of interferometric optical sensors. Traditional method requires two physical interferometer arms (sensor and reference arms) to track the envelope modulation curve peaks/dips of the fitted curves of the combined interference spectrum. The key limitations of this method are: 1) the introduction of physical reference arm, which increases the complexity and cost of the sensor system; 2) decreased quality (Q) factor due to relatively large full width at half maximum (FWHM) of the fitted envelope curve, which decreases the measurement accuracy. In this article, a novel virtual optical vernier method is proposed to achieve sensor sensitivity enhancement by peak position recognition method without introduction of physical reference arm. The application of this method across different fiber-optic sensor types has been demonstrated, including fiber cascaded Fabry-Pérot (FP) cavity sensors and tapered seven-core fiber (TSCF) sensors, with different types of interference spectra. Experimental results show that by employing the proposed envelope-free vernier method, a sensitivity enhancement of over 1000 times can be achieved. This approach offers the significant advantage of elevating sensitivity without compromising spectral resolution, thereby effectively enhancing the sensor's figure of merit (FOM) and solidifying its position as a high-performance sensing solution.