We propose and demonstrate an interferometric sensor based on visibility modulation. In the interferometric sensor, a section of
polarization maintain (PM) fiber is spliced into one arm as the sensing head. Due to the interference between the two beams in the two
arms, respectively, an interferometric fringe can be obtained. The birefringence of the PM fiber splits the beam in the sensing arm,
yielding a visibility envelop in the interferometric fringe. Strain applied on the PM fiber can be demodulated by measuring the
visibility change in a given wavelength. Experimental result shows that the sensor can achieve resolution of up to 28 nano-strain. This
demodulation scheme is immunity to the wavelength shift and power fluctuation of OSA, thus improving the accuracy of the sensor.
This type of sensor can be improved by using a wavelength-swept laser or a mode-locked fiber laser.
Laser scanners are critical components in material processing systems, such as welding, cutting, and drilling. To achieve high-accuracy processing, the laser spot size should be small and uniform in the entire objective flat field. However, traditional static focusing method using F-theta objective lens is limited by the narrow flat field. To overcome these limitations, a dynamic focusing unit consisting of two lenses is presented in this paper. The dual-lens system has a movable plano-concave lens and a fixed convex lens. As the location of the movable optical elements is changed, the focal length is shifted to keep a small focus spot in a broad flat processing filed. The optical parameters of the two elements are theoretical analyzed. The spot size is calculated to obtain the relationship between the moving length of first lens and the shift focus length of the system. Also, the Zemax model of the optical system is built up to verify the theoretical design and optimize the optical parameter. The proposed lenses are manufactured and a test system is built up to investigate their performances. The experimental results show the spot size is smaller than 450um in all the 500*500mm~2 filed with CO<sub>2</sub> laser. Compared with the other dynamic focusing units, this design has fewer lenses and no focusing spot in the optical path. In addition, the focal length minimal changes with the shit of incident laser beam.
This paper proposed a solution about low cost multi-channels Gallium Arsenide (GaAs) absorption-based fiber optic
temperature sensing system, which can get specific channel temperature information at pre-set time slots by combining
time division multiplexing technology and fiber optic multiplexing module. Established an seven channels fiber optic
temperature sensing system using only one spectrum analysis unit and achieved -/+ 1°C temperature resolution, 2Hz
measuring frequency at temperature range from 0°C to 150°C.