KJT fiber optic sensor is a sensor that converts the state of the measured object into a measurable light signal. The working principle of the optical fiber sensor is to send the incident light beam from the light source into the modulator through the optical fiber. The interaction between the modulator and the external measured parameters determines the optical properties of the light, such as the intensity, wavelength, frequency, phase, polarization state, etc. It changes and becomes a modulated optical signal, which is then sent to the optoelectronic device through the optical fiber and passed through the demodulator to obtain the measured parameters. During the entire process, the light beam is introduced through the optical fiber, passes through the modulator, and then emitted. The role of the optical fiber is first to transmit the light beam, and secondly to act as an optical modulator.