## 1 Introduction  
In recent years, optical fiber sensors made of silicon-based optical fibers or polymer optical fibers have been commonly utilized for numerous types of physical detection [1; 2; 3; 4; 5; 6; 7; 8; 9; 10; 11; 12] because a fiber sensor has many features that are better than conventional electronic sensors. Fiber optic sensors can be used for large-scale distributed monitoring, and also have anti-electromagnetic interference, high sensitivity, light weight, good adaptability in shape, and electrical isolation. Fiber-optic sensors can increase or decrease the number of sensors according to system requirements. They are easy to install and can be static or dynamic.  
With the development of fiber Bragg grating (FBG), the applications of fiber grating sensors have gradually increased. Not only silica optical fiber sensors but also polymer optical fibers (POF) sensors are widely used in different sensing applications. Several fiber sensor designs based on FBG have been reported for various applications, such as liquid level monitoring [13], transverse force sensing [14], concentration measurement [15], biomedical measurement [16; 17], pressure [18; 19; 20], displacement [21; 22], temperature [23; 24], and ground vibration [25]. An FBG is a type of distributed Bragg reflector constructed in a short segment of optical fiber that reflects particular wavelengths of light and transmits all others. The center wavelength \(\lambda_{B}\) of the reflected spectral band is defined by the Bragg condition [26]:  
\[\lambda_{B}=2n_{eff}\Lambda, \tag{1}\]where \(\lambda_{B}\) is the Bragg wavelength of FBG, \(n_{\mathit{eff}}\) is the effective refraction index of the fiber core, and \(\Lambda\) is the period of the index modulation. Both \(n_{\mathit{eff}}\) and \(\Lambda\) depend on temperature and strain, and consequently the Bragg wavelength is sensitive to both strain and temperature. By measuring the wavelength change accurately, the physical properties can be measured. The shift of a Bragg wavelength due to the change in temperature (\(\Delta T\)) and the change in applied strain (\(\Delta\varepsilon\)) can be expressed as [27]:  
\[\frac{\Delta\lambda_{B}}{\lambda_{B}}=\Big{(}\alpha_{f}+\xi_{f}\Big{)}\Delta T +(1-p_{e})\Delta\varepsilon, \tag{2}\]  
where \(\alpha_{f}\) is the thermal expansion coefficient, \(\xi_{f}\) is the thermo-optic coefficient, and \(p_{e}\) is the strain-optic coefficient of the optical fiber. In general, when the temperature of FBG is increased or decreased by 1 \({}^{\circ}\)C, it will cause the FBG reflection central wavelength to shift about by 0.0115-0.012 nm. In this study, the effect of stress on the wavelength shift of FBG is much greater than that of temperature, so the effect of temperature is neglected.  
Recently, several FBG-based tilt sensors with different configurations for one- or two-dimensional (1D or 2D) measurements have been reported [28; 29; 30; 31]. Tilt angle measurement is very important for many applications, such as the fields of aviation and civil engineering. In this paper, we develop a novel fiber tilt sensor for public construction monitoring. It has the advantages of simple structure and low cost. Furthermore, the FBG tilt sensor can embed a fiber optic communication module to achieve real-time sensing and monitoring.