A vector magnetic field sensor based on surface plasmon resonance (SPR) of a 15° tilted fiber Bragg grating (TFBG) and magnetic fluid is proposed and experimentally demonstrated. Both the orientation and the amplitude of the magnetic fields can be determined unambiguously via the wavelength and intensity monitoring of the SPR, which is essentially dominated by the arrayed Fe3O4 nanoparticles over the nanometric-film of fiber surface.
An ultra-thin silver-coated tilted fiber Bragg grating (TFBG) sensor with clear surface plasmon resonance (SPR) together with strong evanescent wave in transmission for "surface" and "bulk" surrounding refractive index (SRI) measurement is proposed and experimentally demonstrated. The thickness of the silver coating over the fiber surface is precisely controlled at 12~16 nm (much thinner than 40~50 nm for traditional SPR excitation). The transmission spectrum of the sensor provides a fine comb of narrowband resonances that overlap with the broader absorption of the surface plasmon and thus provide a unique tool to measure small shifts of the plasmon and identify the "surface" SRI changes with high accuracy. Meanwhile, the ultra-thin nanometric-coating permits part of high-order cladding modes to become leaky modes which have a large sensitivity to variations in the background solution for "bulk" SRI measurement. Experimental results show that above two resonances have an inverse amplitude responses to the SRI changing. Biological solutions (urine of rats with different concentration of Aquaporin) with different RI ranging from 1.3400 to 1.3408 were clearly discriminated in-situ by using the differential amplitude monitoring between “cut-off” cladding resonance and plasmonic resonance, with an amplitude variation sensitivity of ~8100 dB/RIU and a limit of detection of ~10-5 RIU.
A novel fiber-to-fiber tip-reflection sensing configuration for power-referenced refractometry with the capability to measure surrounding refractive index (SRI) as low as 1.33 is proposed and demonstrated. A short D-shaped fiber stub is parallel adjacent to another unshaped fiber containing a weakly tilted Bragg grating (TFBG). Light from the unshaped fiber can be effectively coupled into the adjacent D-shaped fiber through the TFBG which functions as a "bridge" between the core and cladding. Strong "comb" like cladding modes over a broad wavelength range have been recaptured in D-shaped fiber in reflection. These re-coupled cladding modes show different amounts of power as the SRI changes and the sensitivity is much higher than reported in-fiber sensing schemes, especially for low SRI measurement.
Broadband-trimming band-rejection filters based on chirped and tilted fiber Bragg gratings (CTFBG) are proposed and experimentally demonstrated. The flexible chirp-rate and wide tilt-angle provide the gratings with broadband filtering functions over a large range of bandwidth (from 10 nm to 150 nm), together with a low transmission loss (less than 1 dB) and a negligible back-reflection (lower than 20 dB). The slope profile of CTFBG in transmission can be easily tailored by adjusting the tilt angle, grating irradiation time and chirp rate-grating factor, and it is insensitive to polarization of launch condition. Furthermore, by coating the CTFBG with a suitable polymer (whose refractive index is close to that of the cladding glass), the cladding modes no longer form weakly discrete resonances and leave a smoothly varying attenuation spectrum for high-quality band rejection filters, edge filters and gain equalizers.
High sensitivity biological sample measurements have been achieved by using a 12o tilted fiber Bragg grating (TFBG). Human acute leukemia cells with different intracellular densities and refractive index (RI) ranging from 1.3342 to 1.3344 were clearly discriminated in-situ by using the differential transmission spectrum between two orthogonal polarizations for the last guided mode resonance before “cut-off”, with an amplitude variation sensitivity of 1.8×104 dB/RIU and a limit of detection of 2×10-5 RIU. The technique is inherently temperature-insensitive.
The polarimetric sensing characteristics of multi-mode-fiber based tilted fiber Bragg grating (MMF-TFBG) have been analyzed and experimentally demonstrated. The physical “enlarged” fiber core enables the tilted gratings to excite multi high-order core modes with significantly different polarization dependence and well-defined “comb” profiles which are spectrally separated at different wavelength. Orientation-recognized twist/rotation measurement (-90o to 90o) has been achieved with sensitivity of 0.075 dB/deg by using a cost-effective double-path power detection (power monitoring of two orthogonal-polarimetric odd core-modes, i.e. LP11 and LP12).
In this paper, we design a hand-shape image acquisition and processing system based on DSP for solving the problem of hand-shape recognition. Acquisition configuration was designed, and the key parts (encoder, decoder, memory chip etc.) are selected. And a new method for hand-shape recognition based on wavelet moment is presented to overcome some shortage in present method for hand shape recognition. Firstly, image processing including binary processing and segment of hand silhouette are used, and then translation and scale normalization algorithms is implemented on the palms and fingers image. After that the wavelet moment characteristics of image are extracted. At last, support vector is achieved by training 100 images data in images database, 10 testing images were selected randomly to verify validity and feasibility of algorithms. Experimental results indicate that the 10 testing images are all classified correctly. The new method of extracting hand shape wavelet moment as characteristic matrix is easy to realize with characteristic of high utility and accuracy, and solve the problem of translation, rotation and scaling during the image acquisition process without positioning aids.
Video sequence fusion has a high request on real-time. A new fusion method of infrared and visible video fusion is proposed, which has the characteristics of low computational complexity and noise suppression. Firstly the improved mixed frame difference method is used to achieve the separation of the infrared target areas and the background areas. Secondly the new fusion algorithm is proposed to fuse the target areas of the infrared and visible light sequence. By image smoothness operator , the source images are divided into two parts: the edge region and the smooth region. Different fusion strategies are adopted for the different regions, can highlight the image edges and texture details more accurately and remove redundant, as well as suppressing noise. Finally, the fused target areas are combined with the background area of the visible light sequence to form the final fused image, which can avoid the high background noise of infrared sequence. The experimental results show that the proposed method not only can suppress noise effectively ,but also can acquire good fusion effects as well as achieve the real time need.
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