Combination of virtual optical vernier method and peak position recognition without envelope fitting: a general method for sensor sensitivity enhancement

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 paper, 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.