Properties of Fiber Bragg Grating in CYTOP Fiber Response to Temperature, Humidity, and Strain Using Factorial Design

Optical properties of a fs laser-created sphere inside a CYTOP fiber by Mueller polarimetry

Optical elements embedded in an optical fiber can be used to shape and modulate the light transmitted within. We consistently observe, via Mueller polarimetry, that the optical properties of a femtosecond (fs) laser-created spherical cavity within a perfluorinated fiber exhibit predictable patterns. Specifically, linear birefringence is always induced at the periphery of the cavity, with its value showing a bell-shape distribution. The peak value of LB showed an increase correlating with the laser fluence and power, but its FWHM remains unchanged. Furthermore, it is important to highlight that when the cavity is disrupted, forming a channel to the fiber's surface, a negative LB is observed at the cavity's periphery, with a value reaching up to -0.4 rad. These optical phenomena may pique the interest of engineering and technical fields, potentially inspiring innovative approaches in optical fiber technology and its associated applications.

Engine Knock Sensor Based on Symmetrical Rhomboid Structure-Encapsulated Fiber Bragg Grating

Due to the improvement of environmental protection emission standards, new energy vehicles fueled by natural gas and hydrogen green clean energy have developed rapidly. However, knock is one of the most important parameters that must be monitored for the safe operation of natural gas and hydrogen engines, so higher requirements are put forward for the reliability and durability of knock sensors. At present, the common knock sensors are mainly electronic sensors based on magnetostrictive and piezoelectric principles, and the sensing signals are easily interfered by electromagnetic interference during use, which is not conducive to the accurate measurement and control of knock. In this paper, a new resonant knock sensor based on fiber Bragg grating (FBG) is proposed to meet the actual needs of knock monitoring, and the FBG sensor unit is encapsulated with symmetrical rhomboid structure. The natural frequency of rhomboid structure is simulated and analyzed by Ansys software. The natural frequency of rhomboid structure is measured by applying transient impact. The resonance frequency of sensor is analyzed by Matlab software. The theoretical analysis is consistent with the measured value, which verifies the feasibility of the new knock sensor. Compared with the traditional engine knock sensor, this resonant engine knock sensor based on FBG has more advantages in anti-electromagnetic interference and multi-point networking, which provides a new method for knock monitoring of new energy engines.