Jianshe Li

High Sensitivity of Refractive Index Sensor Based on Analyte-Filled Photonic Crystal Fiber With Surface Plasmon Resonance

Two kinds of novel plasmonic high sensitivity of refractive index (RI) sensors based on analyte-filled photonic crystal fiber (AF-PCF) are proposed in this paper. The metallic gold and silver is used as the surface plasmon resonance activity metal. A full-vector finite-element method is applied to analyze and investigate the sensing and coupling characteristics of this designed AF-PCF with the gold or silver layer. Phase matching between the second surface plasmon polariton and fundamental modes can be met at different wavelengths as the analyte of the RI is increased from 1.40 to 1.42. The phase-matching wavelength of the designed AF-PCF with the gold layer is shifted to the longer wavelength direction compared with that with the silver layer, and the resonance strength is much stronger. The average sensitivities of 7040 and 7017 nm/RIU in the sensing are arranged from 1.40 to 1.42 with high linearity are achieved for the designed sensors with the gold and silver layers, respectively, which are almost the same. However, the figure of merit with the silver layer is much better than that with the gold layer.

A Novel Polarization Splitter Based on Dual-Core Photonic Crystal Fiber With a Liquid Crystal Modulation Core

A novel polarization splitter based on dual-core silica glass photonic crystal fiber with a liquid crystal modulation core is studied by the finite-element method. The mode birefringence is enlarged greatly with the infilling of nematic liquid crystal of E7. The simulation results demonstrate that the polarization splitter has an ultrabroad bandwidth of 250 nm, covering the E S C L optical communication bands, with the extinction ratio better than -20 dB. The separate length is 0.175 mm, and the extinction ratio is -80.7 dB at the communication wavelength of 1550 nm. The polarization splitter exhibits satisfactory splitter performance as the fabrication deviation reaches to 1%. The extinction ratio maintains better than -20 dB, at the C L optical communication bands, as the temperature increases from 15 °C to 50 °C.

Photonic Crystal Fiber Temperature Sensor Based on Coupling Between Liquid-Core Mode and Defect Mode

A high-sensitivity temperature sensor of compact photonic crystal fiber (PCF) based on the coupling between liquid-core mode and defect mode has been analyzed by the finite element method. The temperature sensitive materials with high refractive index (n = 1.65 at 25 °C), which support liquid-core modes, are filled into the central air hole of PCF. Six cores are formed by removing air holes in the second layer. The six cores work as defect modes and show high confinement losses. The liquid-core mode couples to defect mode as the phase matching condition is satisfied. The sensitivity and figure of merit reach -1.85 nm/°C, -0.072/°C and -1.95 nm/°C, -0.035/°C. The temperature sensor is competitive in the reported temperature sensors. The simple structure is easy to fabricate, and the structure can be further improved.

A Polarization Filter Based on Photonic Crystal Fiber with Asymmetry Around Gold-Coated Holes

We propose a modified design for a photonic crystal fiber (PCF) filter based on surface plasmon resonance(SPR). The air holes are arrayed in rectangular lattices, while the size and the pitches of holes around the gold-coated holes are different. That can separate the x-polarization and y-polarization of second-order surface plasmon polariton (SPP). The resonance strength of the surface plasmon mode and import of structural parameters of the PCF on the filter characteristics are studied through using the finite element method (FEM). Numerical simulations demonstrate that the thickness of the gold layer, the gold-coated or gold-filled, and the asymmetry around the gold-coated holes have a great effect on the filter characteristics. It is certain to obtain a resonance strength as high as 873 and 771.5 dB/cm at the communication wavelength of 1050 and 1310 nm in x-polarization by adjusting the size and the place of the gold-coated holes, while the loss is extremely low in y-polarization.

Numerical Analysis of Polarization Filter Characteristics of D-Shaped Photonic Crystal Fiber Based on Surface Plasmon Resonance

In this paper, a novel D-shaped photonic crystal fiber (D-PCF) based on surface plasmon resonance (SPR) is designed, and gold nanowire is used as the SPR active metal. A full-vector finite element method is applied to analyze the polarization filter characteristics. Phase matching between the second-order surface plasmon polariton (SPP) mode and the core-guided modes of x- and y-polarization can be met in two different wavelengths. By adjusting the diameters of the large air holes and the gold nanowire, this designed D-PCF can be used to the polarization filter in two communication bands. The loss of unwanted y-polarization mode can reach 244.9 and 292.8 dB/cm at the wavelength of 1.31 and 1.55 μm, respectively. With a length of 1 mm of the designed D-PCF, the bandwidths with the crosstalk better than 30 dB can reach to 88 and 150 nm, and the crosstalks are 208.4 and 249.5 dB the wavelength of 1.31 and 1.55 μm, respectively.

Polarization Splitter Based on d-Shaped Dual-Core Photonic Crystal Fibers with Gold Film

A novel polarization splitter based on d-shaped dual-core photonic crystal fiber with gold film is proposed and analyzed by the finite element method. The designed polarization splitter involves side-polishing of photonic crystal fiber and depositing of gold film. The numerical results reveal that the separate length is 0.782 mm and the extinction ratios are -151 and -55 dB for the x- and y-polarized modes at the communication wavelength of 1,550 nm. The bandwidths of the polarization splitter are 40 and 65 nm for the x- and y-polarized modes with extinction ratios better than -20 dB and insertion losses lower than 0.3 dB. This d-shaped dual-core photonic crystal fiber is competitive for polarization splitter.

Plasmonic Polarization Beam Splitter Based on Dual-Core Photonic Crystal Fiber

In this paper, two kinds of novel plasmonic polarization beam splitters based on dual-core photonic crystal fiber (DC-PCF) have been designed and analyzed through the full-vector finite element method. The metallic gold is used as the surface plasmon resonance (SPR) active metal. The coupling characteristics of the designed DC-PCF can be enhanced by the resonant coupling between the second-order surface plasmon polariton (SPP) mode and the core-guided modes. A gold layer in the designed DC-PCF is introduced to achieve an perfect splitting performance and an ultra-bandwidth compared to the designed DC-PCF with gold wire. Numerical results show the ultra-bandwidth of core A and B of the polarization beam splitter with gold layer can reach 210 and 220 nm, as the extinction ratio better than -20 dB, covering the E, S, C, and L optical communication bands. The extinction ratios of core A and B can reach to -84 and -46 dB at the wavelength of 1.55 μm, respectively, and the length of splitter is 0.542 mm.

High Sensitivity of Temperature Sensor Based on Ultracompact Photonics Crystal Fibers

A temperature sensor with high sensitivity based on ultracompact photonics crystal fibers is proposed and analyzed by the finite-element method. The temperature-sensitive materials are injected into one cladding air hole, which shows high confinement loss and works as a defect core. As the phase-matched condition is satisfied, the power in the transferring core couples to the defect core. The temperature sensitivity and figure of merit reach to 2.82 nm/°C, 0.105/°C and 1.99 nm/°C, 0.048/°C, for the y-polarized and x-polarized directions, respectively, which are one to two orders of magnitude better than other reported sensors. The performance characteristics can be further improved by optimizing the structure parameters and infilling materials.

Photonic Crystal Fiber Polarization Filter Based on Coupling Between Core Mode and SPP Mode

A polarization filter at the two communication windows of 1.31 and 1.55 μm based on photonic crystal fiber (PCF) coated by nanoscale gold film is proposed. The effects of geometrical parameters of the PCF on the performances of polarization filter are evaluated by finite element method (FEM). Numerical simulations reveal that the polarization filter possesses ultra-short length of 400 μm and high extinction ratios of 41 and −150 dB at the communication wavelengths of 1.31 and 1.55 μm respectively. The bandwidth of extinction ratio (ER) better than 20 dB is 58 nm at the communication window of 1.31 μm. Moreover, the bandwidth of ER better than −20 dB is 164 nm at the communication window of 1.55 μm.

Chaos weak signal detecting algorithm and its application in the ultrasonic Doppler bloodstream speed measuring

At the present time, the ultrasonic Doppler measuring means has been extensively used in the human bodys bloodstream speed measuring. The ultrasonic Doppler measuring means can achieve the measuring of liquid flux by detecting Doppler frequency shift of ultrasonic in the process of liquid spread. However, the detected sound wave is a weak signal that is flooded in the strong noise signal. The traditional measuring method depends on signal-to-noise ratio. Under the very low signal-to-noise ratio or the strong noise signal background, the signal frequency is not measured. This article studied on chaotic movement of Duffing oscillator and intermittent chaotic characteristic on chaotic oscillator of Duffing equation. In the light of the range of the bloodstream speed of human body and the principle of Doppler shift, the paper determines the frequency shift range. An oscillator array including many oscillators is designed according to it. The reflected ultrasonic frequency information can be ascertained accurately by the intermittent chaos quality of the oscillator. The signal-to-noise ratio of −26.5 dB is obtained by the result of the experiment. Compared with the tradition the frequency method compare, the dependence to signal-to-noise ratio is lowered consumedly. The measuring precision of the bloodstream speed is heightened.