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An exciting prospect for the sensing community is the potential of midinfrared fiber sensors. Taking advantage of the design flexibility of photonic crystal fiber and the high excitation loss of gold layers, a high-performance midinfrared D-shaped sensor based on the surface-plasmon-resonance effect was designed and numerically investigated by a mature finite-element tool. Numerical results showed that the designed fiber is especially suitable for sensing. In an operating wavelength ranging from 2.9 to 3.6 μm, maximal wavelength sensitivity of 11,500 nm/refractive index unit (RIU) and a maximal refractive index (RI) resolution of 8.7 × 10−6 RIU were obtained by the wavelength-interrogation method when analyte RI varied from 1.36 to 1.37. Maximal amplitude sensitivity of 230 RIU−1 was obtained by the amplitude-interrogation method with a high linearity of 0.99519 and an adequate figure of merit of 142. Additionally, the sensor had good fabrication tolerance. Our sensor is a promising candidate for environmental monitoring. [ABSTRACT FROM AUTHOR]

A metal-filled photonic crystal fiber (PCF) polarization filter based on surface plasmon resonance (SPR) is proposed and designed. The structure of the cross-section of a PCF is composed of a hexagonal lattice of air holes, in which an air hole is selectively filled with metal. We realize the polarization filter at the communication wavelengths of 1.31 and 1.55  $\mu$ m with optimized structural parameters. The losses of the X polarization mode are 25126.44 and 22444.54 dB/m, while the losses of the Y polarization mode are about 1375.81 and 358.62 dB/m at the resonance wavelengths 1.31 and 1.55  $\mu$ m, respectively. Therefore, the two light polarizations can be clearly separated. When the fiber length is 600  $\mu$ m, cross-talk is over 20 dB at the communication wavelengths, while the achieved bandwidth is 160 and 200 nm at 1.31 and 1.55  $\mu$ m, respectively. Furthermore, the distance between the resonance peaks of the two polarizations can reach 267 nm at 1.55  $\mu$ m, achieving a significantly higher value than previously reported. These results are of great significance for the development of a polarization filter applicable in targeted communication bands. [ABSTRACT FROM AUTHOR]

We present a 5-layer air-hole dispersion-compensating photonic crystal fiber (PCF) with a modified dual concentric core structure, based on central rod doping. The finite element method (FEM) was used to investigate the structure numerically. If the structural parameters remain unchanged, a high degree of linear correlation between the central rod refractive index and the operating wavelength can be achieved in the wavelength range of 1.5457-1.5857 μm, which suggests that the operating wavelength can be determined by the refractive index of the centre rod. A negative dispersion coefficient between -5765.2 ps/km/nm and -6115.8 ps/km/nm was obtained by calculation and within the bandwidth of 108 nm (1.515-1.623 μm) around 1.55 μm, a dispersion coefficient of -3000 ps/km/nm can be ensured for compensation. In addition, this proposed PCF also has the advantage of low confinement loss, between 0.00011 and 0.00012 dB/m, and ease of fabrication with existing technology. The proposed PCF has good prospects in dispersion-compensating applications. [ABSTRACT FROM AUTHOR]

A polarization beam splitter is an important component of modern optical system, especially a splitter that combines the structural flexibility of photonic crystal fiber and the optical modulation of functional material. Thus, this paper presents a compact dual-core photonic crystal fiber polarization beam splitter based on thin layer As2S3. The mature finite element method was utilized to simulate the performance of the proposed splitter. Numerical simulation results indicated that at 1.55 μm, when the fiber device length was 1.0 mm, the x- and y-polarized lights could be split out, the extinction ratio could reach −83.6 dB, of which the bandwidth for extinction ratio better than −20 dB was 280 nm. It also had a low insertion loss of 0.18 dB for the x-polarized light. In addition, it can be completely fabricated using existing processes. The proposed compact polarization beam splitter is a promising candidate that can be used in various optical fields. [ABSTRACT FROM AUTHOR]

Polarization filter is a very important optical device with extinction characteristics. Due to the design flexibility of photonic crystal fibers and the high excitation losses of the gold layer, the polarization filter based on the photonic crystal fiber and surface plasmonic resonance effect is widely studied. Considering these, we present a simple and high-performance polarization filter using the finite element method. Numerical simulations show that there is a large difference in energy between the two polarization directions by reasonable adjustment of the structural parameters, the confinement loss in the x-pol direction is less than that in the y-pol direction, which is suitable to realize a broadband polarization filter. When the fiber length is 2 mm, the extinction ratio peak can reach −478 dB, and the bandwidth with the extinction ratio better than −20 dB is 750 nm, which covers communication wavelengths of 1.31 μm and 1.55 μm (1.05–1.8 μm). It also has a low insertion loss of 0.11 dB at 1.31 μm and 0.04 dB at 1.55 μm. In addition, our design has high feasibility in fabrication and better tolerance. The proposed filter with compactness, high extinction ratio, broad bandwidth, and low insertion loss would play an important role in the sensing detection, bio-medical, and telecommunication field. [ABSTRACT FROM AUTHOR]

A hexagonal photonic crystal fiber (PCF) sensor with a dual optofluidic channel based on surface plasmon resonance (SPR) effect is proposed. The sensor characteristic is numerically explored by software integrated with the finite element method (FEM). The numerical results show that, when the analyte refractive index (RI) varies from 1.32 to 1.38, high linearity between resonance wavelength and analyte RI is obtained and the value of adjusted R2 is up to 0.9993. Simultaneously, the proposed sensor has maximum wavelength sensitivity (WS) of 5500 nm/RIU and maximum amplitude sensitivity (AS) of 150 RIU−1, with an RI resolution of 1.82 × 10−5 RIU. Besides, owing to a simple structure and good tolerance of the proposed sensor, it can be easily fabricated by means of existing technology. The proposed sensor suggests promising applications in oil detection, temperature measurement, water quality monitoring, bio-sensing, and food safety. [ABSTRACT FROM AUTHOR]

A plasmonic sensor based on a dual-side polished photonic crystal fiber operating in a telecommunication wavelength range is proposed and investigated numerically by the finite element method (FEM). We study the effects of structural parameters on the sensor's performance and analyze their tuning effects on loss spectra. As a result, two configurations are found when the analyte refractive index (RI) changes from 1.395 to 1.415. For configuration 1, an RI resolution of 9.39 × 10−6, an average wavelength sensitivity of 10,650 nm/RIU (the maximum wavelength sensitivity is 12,400 nm/RIU), an amplitude sensitivity of 252 RIU−1 and a linearity of 0.99692 are achieved. For configuration 2, the RI resolution, average wavelength sensitivity, amplitude sensitivity and linearity are 1.19 × 10−5, 8400 nm/RIU, 85 RIU−1 and 0.98246, respectively. The combination of both configurations can broaden the wavelength range for the sensing detection. Additionally, the sensor has a superior figure of merit (FOM) to a single-side polished design. The proposed sensor has a maximum wavelength sensitivity, amplitude sensitivity and RI resolution of the same order magnitude as that of existing sensors as well as higher linearity, which allows it to fulfill the requirements for modern sensing of being densely compact, amenable to integration, affordable and capable of remote sensing. [ABSTRACT FROM AUTHOR]