In this paper, the feasibility of multimode fiber as pressure sensor is explore by using the straight structure of the fiber itself. The elastic mechanical model and the basic equation of the straight structure of the fiber is established. ANSYS software is used for the analysis of stress and strain distribution and the results show that the stress and strain of load section fiber are linearly related. In the experimental process, the straight structure fiber is used as the test unit and the change of the optical power is measured and analyzed during the pressure loading. The experimental results show that the linear correlation coefficient R<sup>2</sup> of the pressure loading process from 0g to 400g is 0.9117 for the multi-mode fiber; and the linear correlation coefficient R<sup>2</sup> of the pressure unloading process from 400g to 0g is 0.7061. So it can be concluded that the straight structure multimode fiber can be used as a pressure sensor.
A high resolution fiber optic spectrometer system was set up, which consists of a tunable laser, a fiber optic power meter, GPIB-USB data acquisition cards, and a computer control platform. The wavelength absolute accuracy of the tunable laser (Santec TSL-550) is±2.5pm, and the wavelength setting resolution can be 0.1pm, which makes the system features high resolution. However, the resolution of the laboratory fiber optic spectrometer (YOKOGAWA AQ6317C) can only be set to 20pm. The extinction ratio (ER), free spectral range (FSR) and the trough position of the spectrum of the microfiber knot resonator (MKR) is measured with our system and AQ6317C fiber optic spectrometer. The experimental results of the two methods show that the ER and FSR are offset by 0.675dB and 0.003nm, respectively, and the standard deviations are 0.17% and 0.43%, respectively. From the results, and the stability of MKR is considered, we conclude that the resolution of our system can be better than 1nm due to the resolution of the TSL-550 light source, and the overall standard deviation is also smaller, therefore, the repeatability and stability of our testing system are better than the AQ6317C fiber optic spectrometer, which can better meet the actual measurement requirements.