Optical Fiber Temperature Sensor Using a Stabilized Transeverse Zeeman Laser and Reduction of Nonlinearity Caused by Crosstalk

Abstract

As a functional type fiber temperature sensor has a long sensing fiber for a range of measurands, the phase sensitivity is high for temperature change. An optical heterodyne interferometer has been used to measure small phase variation in the temperature sensor. However, the interferometer has suffered from external disturbance because the reference light has a different path from the measurement arm. This paper describes an optical fiber temperature sensor using heterodyne interferometory to enable free from external disturbance easily. The measurement arm is made loop to remove the reference arm. A stabilizied transverse Zeeman laser (STZL) is used to exclude the phase fluctuation due to the phase difference between the measurement path and the reference path. The STZL has the leak frequncy components. The leakage causes the periodic nonlinearity of the heterodyne interferometer and decreases the accuracy of the interferometer. The relation between the cross talk due to the leakage and the measured phase error is analyzed with considering initial phase difference between polarization components of the STZL beam. From the analyzed result it is found that the cross talk can be measured from amplitude modulation of beat signal. To reduce crosstalk term, the leakage is decreased by phase compensation method using a quarter-wavelength plate, and the cross talk term is cancelled by a new fringe distribution method.In the temperature sensor, the reduction of the non-linearity is confirmed experimentaly.

A subnanometre heterodyne interferometric system with improved phase sensitivity using a three-longitudinal-mode He-Ne laser

“…The cross talk error of the two-frequency system can be compensated in a similar way [8]. φ err of the two-mode system, which is also obtained from the amplitude variation of the heterodyne beat signal, is given by…”