## 1 Introduction
The demodulation of the two transverse strains, longitudinal strain and temperature can be realized by using four equations. Scholars further confirmed that the polarization-maintaining fiber sensor can simultaneously measure the lateral, axial strain and temperature, and analyze the spectral response of bow tie-type and elliptical cladding-type fiber gratings under lateral load conditions [15; 16; 17]. [PERSON] et al. [18] investigated the lateral load sensitivity of different high birefringence (HiBi) FBG. The wavelength reflected by FBG in each polarization eigenmode can be measured independently using a customized demodulation system. The experimental results show that the lateral loading sensitivity of HiBi-FBG obtained by elliptic cladding fiber is the highest, at 0.23 \(\pm\) 0.02 nm/(N/mm). Although literature has reported on the measurement of lateral stress with polarization-maintaining fiber gratings, there is still a long way to go before practical use. As a matter of fact, it takes specific skills to deal with the induced polarization effect, and customized devices are strictly required, making them incompatible with conventional single-mode fiber systems. Furthermore, when measuring radial pressure with polarization-maintaining fibers, the angle between the lateral stress and the polarization axes will directly affect the pressure sensitivity [19]. In addition, due to the mismatch between polarization-maintaining fiber and non-polarization fiber, insertion loss and attenuation cannot be neglected. When the FBG is subjected to uniform lateral pressure, characteristics similar to those of PM fiber also appear [20; 21; 22]. [PERSON] and [PERSON] [23] calculated that the pressure sensitivities are 6.17 pm/N and \(-\)0.4332 pm/N in the x and y polarization directions, respectively, within a force range is 0-100 N in the case of plane strain. [PERSON] et al. [24] realized pressure measurement through the demodulation of fiber Bragg grating peak cracking caused by transverse stress differences in a single-mode fiber core bonded on the outer surface of the cylinder. The measurement sensitivity is estimated to be -27 pm/MPa, measured in the range of standard atmospheric pressure up to 100 MPa. [PERSON] et al. [22] used fiber Bragg grating cross-line sensor for strain measurement, with a sensitivity of 41 pm/\(\upmu\varepsilon\). [PERSON] et al. [25] conducted later load tests on polyimide coated and uncoated fibers, and obtained sensitivities of -0.06 nm/(N/mm) and -0.08 nm/(N/mm), respectively. [PERSON] et al. [26] used a roll-bearing pin to apply lateral load to FBG, and measured the wavelength differences of the Bragg peak to be 0.128 nm, 0.108 nm and 0.34 nm when the force was 2 N, 5 N and 20 N, respectively. In this paper, a transverse stress detection method based on spectral split sensing using a fiber Bragg grating is proposed, which is for monitoring spacecraft-small particle collisions. A FBG lateral stress sensing system was established and verified, and the lateral detection threshold was analyzed. Its pressure characteristics were experimentally studied in the range of 4.0-7.0 N and error analysis was carried out. The pressure sensitivity was 14.76 pm/N and 32.29 pm/N at the split point and right peak, respectively. This study provides a basis for the selection of lateral stress sensing systems.