A new beam-patterns switchable MLWA is presented in this letter. The MLWA fed by two feeding terminals on different sides radiates out the single main beam. Through controlling the SPDT switch, the MLWA is fed by different feeding terminals combination, the beam-patterns change from single-beam mode to dualbeam mode. When the MLWA is fed by two feeding terminals on different sides, the scanning angle region of the single main beam is about 32°. When the MLWA is in dual-beam mode, the right beam steers from 53°to 35°; meanwhile the left beam scans from 130°to 148°. This new configuration MLWA can be useful for collision avoidance or automobile radar system. 2. A.A. Oliner, Leakage from various waveguides in millimeter wave circuits, Radio Sci 6 (1987), 866 -872. 3. C.
The dispersion characteristics of superstructure fiber gratings written in multimode fibers and side-polished multimode fibers are investigated at different bending curvatures. The experimental results show that the group time delay in multimode superstructure fiber gratings can be tuned more easily than that of superstructure gratings in single-mode fiber. This method can provide tunable dispersion of superstructure fiber gratings by controlling the bending curvatures for application in dispersion compensators, fiber sensors, or suitable optical filters of optical communication systems.
A fiber sensor based on a polyaniline (PANI) film that is coated on the surface of an etched superstructure fiber grating to detect volatile solvent vapors is experimentally demonstrated. This sensing mechanism is based on the interaction of the testing gas with the polyaniline coating film, which changes the film index, resulting in a shift in the Bragg wavelength. The sensitivity of this sensor to ammonia (NH 3 ) gas is about 0.073 pm ppm −1 , which depends on the optical characteristics of the fiber grating, the diameter of the fiber cladding and the constituents of the sensing film. Methanol concentrations can also be measured using this sensing scheme. The sensitivity of this sensor must be improved to provide a simple, reliable, repeatable and non-destructive method for sensing various chemical gases.
In this article we have demonstrated that a 2 ϫ 2 ports fused fiber-grating-coupler can be implemented by combining the technique of fabricating a fused-fiber coupler as well as that of writing a fiber Bragg grating for applying in an all-fiber optical filter. The grating Figure 4 Optimization of measurement range and 1/maximum resonant frequency (1/GHz) against accumulated CD (ps/nm) Figure 5 Optimization of the sensitivity (GHz) and 1/maximum resonant frequency (1/GHz) against accumulated CD (ps/nm)
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