The subway is a representative form of the rail transit, and its catenary suspension system is a very important aspect to
the safety of the whole system. The safety monitoring of the subway catenary suspension system is studied in this paper.
A demonstrate model is set up in the laboratory, and some fiber Bragg grating (FBG) sensors including strain sensors
and displacement sensors were utilized in the demonstrate system. It is shown that the used sensors could indicate the
safety information of the system effectively. Especially, the designed displacement sensor that is packaged by athermal
technique can abandon the influence of the environment temperature in a certain degree. Its engineering applicability is
We propose an ultrasensitive temperature sensor based on an in-line liquid-filled photonic crystal fiber (PCF) Mach-
Zehnder interferometer. It consists of a small piece of index-guiding PCF fully infiltrated by fluid and two standard
single-mode fibers offset spliced with the PCF. Two core modes of LP<sub>01</sub> mode and LP<sub>11</sub> mode are conveniently utilized
as optical arms to form an in-line Mach-Zehnder-type interferometer. Experimental and theoretical investigation of its
response to temperature confirms that and a high temperature sensitivity up to -0.244nm/(<sup>o</sup>C-mm) could be realized by
such a compact inline liquid-filled PCF Mach-Zehnder interferometer.
In this paper, we present a novel optical fiber fluorescent temperature sensor based on photonic crystal fiber(PCF) and its
theory of forward stimulated fluorescence emission in PCF. It is realized by liquid filling in hollow-core PCF, the liquid
is of higher temperature coefficient of refractive index than that of silicon, and is mixed with fluorescent material.
Stimulating light and fluorescence propagating in the fiber are in the same direction. Because the band gaps of PCF are
modulated by temperature, besides the sensitivity of fluorescence, the stimulating light passing through the photonic
crystal fiber is also sensitive to temperature. Experiment results and theory modulation show that when PCF length is
shorter than an optimum length, stimulating light in fiber will increase and fluorescence will decline gradually with the
increase of temperature.
A transmission ellipsometer with the configuration of modified Mach-Zehnder heterodyne interferometer is demonstrated. Two acousto-optical modulators are employed to generate a 20-kHz beat frequency. The scheme offers high resistance to environmental turbulence because of the interferometric components passing through the same path. A single layer of indium tin oxide on a glass substrate was measured, and an error up to several nanometers of the sample thickness is observed. The polarization mixing error is mainly due to the imperfection of polarizing beamsplitters (PBSs) and to the elliptical polarization and nonorthogonality of the light beams produced by the laser source and wave plates. The mechanism governing the error and its influence on measurement accuracy is analyzed with the Jones matrix method. In contrast with interferometric reflection ellipsometry using a Zeeman laser, the theoretical analysis indicates that only second-order error is introduced in this system. The elliptical polarization and nonorthogonality, occurring only before the light splitting, have little influence on measurement accuracy; the imperfection of PBSs is the major contributor to the polarization mixing error.