Optical fiber sensors (OFSs) are recognized as important devices for monitoring many physical parameters, such as bending, strain and torsion in mechanics [1], [2], [3], temperature, refractive index (RI) and magnetic field in the environment [4], [5], [6], [7]. Among them, strain and temperature are important indicators in industrial fields such as aerospace, health monitoring, and engineering. OFSs have become an alternative to traditional electrical sensors due to their inherent advantages, such as easy fabrication, survivability in challenging environments, and anti-electromagnetic interference.

The sensitivity of OFSs is usually associated with the material and fabrication methods. There are many ways to improve the sensitivity, including coating the surface with sensitive materials, singularity testing and Vernier effect (VE), etc [8], [9], [10], [11]. Coating sensitive materials requires complex manufacturing process, which increases the difficulty. And VE is achieved by special demodulation methods. It is obtained by the spectral superposition of two structures with regular but slightly different free spectral range (FSR). Fabry–Perot interferometer (FPI), fiber Sagnac structures and microfiber coupler structures [12], [13], [14], [15] all satisfy this property.

First, the interference of the FPI comes from two reflected beams, and the output spectrum shows a regular FSR spectrum due to the constant phase difference. So the FPIs have become the preferred choice to realize the VE. Second, in the Sagnac structures, two beams traveling clockwise and counterclockwise interfere, but the structures need longer birefringent fibers to accumulate phase difference and increase the volume. Third, for the microfiber coupler structures, the phase difference and power oscillation between x and y polarization contribute to the superposition of sine and cosine signals in the output port. But the weak waist region increases the brittleness of the sensor.

In this paper, a dual-parameter amplificated sensor is realized by VE, which consists of two discrete sensing units. The sensor is fabricated by simple and cost-effective techniques such as cleaving, splicing and gluing, which greatly simplifies the fabrication process. The correlation between the wavelength shift direction and FSR is verified theoretically and experimentally, which provides a strong insight for understanding VE. The temperature and strain sensitivities of the sensor are 188.38pm/°C and 201.18pm/με, with the magnification factors of 21.2 and 19.6, respectively. The separated FPI structures reduce the fabrication difficulty and become a competitive candidate for practical applications.