In this paper, a fiber Bragg grating (FBG) demodulation system based on high-birefringence fiber loop mirror (Hi-Bi FLM) is proposed and demonstrated. The approximate linear edge of the transmittance of the Hi-Bi FLM, which is a sinusoidal function of wavelength, is used to interrogate the sensing FBGs. The relationship between the wavelength period of the transmittance of the Hi-Bi FLM and the length of Hi-Bi fiber is studied and the results shows that the linear range of Hi-Bi FLM is in Inverse proportion to the length of the Hi-Bi fiber. To get wider linear range, the length of the Hi-Bi fiber must be shorter and it is limited by the fiber fusing technic. Two sections of Hi-Bi fiber is orthogonal fused and its effect is equal to one segment of fiber whose length is equal to the difference of that of the two section of fibers. Using this method, a Hi-Bi FLM with a wide linear range of 20nm is made and used to demodulate FBG sensing signal. The demodulator has advantages of all-fiber design, low price and high speed.
In this paper, a novel density sensor based on high-birefringence fiber loop mirror is proposed and studied. The high-birefringence fiber is pasted to a ring shaped rubber gasbag and placed in the liquid. Fasten the gasbag to the bottom of the container. When the density of liquid is changed, the liquid level keeps the same. The change of the pressure outside the gasbag leads to the variation of the volume of the air in the gasbag. Eventually, the strain of high-birefringence fiber varies with the variation of the volume of the air and the transmittance of high-birefringence fiber loop mirror shifts with the density change. The experimental result indicates that the shifts of wavelengths are in good linear relationship with the density of liquid. The experiment shows that the sensitivity is 8.024nm/(kg/m3). The novel density sensor has the advantages such as high sensitivity, polarization independent, low cost and good repeatability.
In this paper, a pressure sensor based on high-birefringence fiber loop mirror (HiBi-FLM) is proposed and demonstrated. The high-birefringence fiber is pasted to an inflated, elastic, ring shaped rubber gasbag and served as a sensitive probe. When outside pressure changes, the volume of the gas in the ring rubber gasbag changes and it makes the strength of the high-birefringence fiber variety. The relationship between shift of the resonant wavelength (peak wavelength) and pressure is discussed and experimentally researched. Experimental results show that the sensitivity is 1.63×10-3nm/Pa. The sensor has many advantages such as high sensitivity, polarization independent, easy manufacture, low cost.