Optical coherence tomography based on ultra technology is used for the assessment of subcutaneous tissue. Using high swept laser technology based on Fourier domain mode locking (FDML), the system operated in the 1300 nm wavelength range with axial scan rate of 150 kHz. Imaging at this wavelength range reduces optical scattering and improves imaging penetration depths in the tissues. The laser consists of a semiconductor amplifier as the gain medium, a tunable Fabry-Perot filter to change the wavelengthcand a long fiber ring cavity. The tuning range of laser is 102 nm. A balanced detector is used for spectra collection instead of the expensive CCD.
A Fabry–Perot (F-P) fiber acoustic sensor, which can work under high-temperature harsh environment with temperature self-compensation, is designed and prepared. A condenser was used to maintain the sensor to work in a stable temperature environment. Because of the special structure of the sensor and the function of the condenser, the cavity variation of the sensor caused by changes of external temperature from −10°C to 500°C would not exceed 8 nm. The experimental results show that the sensor has a good frequency response in a range of 1 to 5 kHz and the field experiment results show that it could be used for hydraulic decoking online monitoring by judging the acoustic frequency spectrum.
The vibration sensors with high sensitivity and wide frequency range have a large application demand for in the engineering project. Combining with the advantages of optical fiber sensor monitoring technique, in the paper, a kind of optical fiber Fabry-Perot (F-P) vibration sensor has been designed based on the differential-type structure of the double V-shaped cantilever a optical fiber F-P cavity. Through two different differential vibration of the cantilever beam, change the F-P cavity length, the realization of the vibration signal of large frequency range measurement the differential-type optical fiber F-P vibration sensor with large frequency range.