A kind of single-polarization single-mode photonic crystal fiber

A kind of single-polarization and single-mode totally internal reflection photonic crystal fiber (SPSM TIR-PCF) is proposed in this paper. It is a PCF structure with elliptical air holes in the cladding and four large holes in the first ring. A full-vector plane wave expansion method is employed to analyze this PCF structure. The numerical results show that this PCF structure can realize an ultra-broad SPSM bandwidth of 540?nm with a confinement loss less than 0.1?dB?km^?1, the broadest bandwidth to the best of our knowledge. Moreover, the structure that we proposed can realize a high nonlinear coefficient.     

Ultra-bandwidth polarization splitter based on soft glass dual-core photonic crystal fiber

A novel ultra-bandwidth polarization splitter based on soft glass dual-core photonic crystal fiber (DC-PCF) is designed in this paper, which is analyzed through the finite element method (FEM). The coupling characteristics of the designed DC-PCF can be enhanced by a high refractive index As₂S₃ core. Numerical results show the ultra-bandwidths of the x- and y-polarization modes can reach to 86 nm and 60 nm as the extinction ratios better than −20 dB and −30 dB at the vicinity of the wavelength of 1.31 μm. The length of the designed soft glass DC-PCF is 52.29 mm and the extinction ratios of the x- and y-polarization modes are −85.57 dB and −56.81 dB at the wavelength of 1.31 μm, respectively. In addition, the designed splitter has a tolerance of ±10 nm in its all structure parameters, which make the design not sensitive to the perturbation during the fabrication process.     

A compact optical wavelength splitter in one-dimensional photonic crystal waveguides

A fundamental T-branch in one-dimensional photonic crystal waveguides based on the omnidirectional reflection is constructed. Numerical simulations of this T-branch indicate that without any structural optimization, four high reflectance peaks and three high transmittance peaks appear alternately within a wide enough frequency band. The T-branch with the unique transmission characteristics can be used as a wavelength splitter. Combining the fundamental T-branch with flexible bends of one-dimensional photonic crystal waveguides, we construct simple and compact wavelength splitters with arbitrary branching angles. Those wavelength splitters are expected to be applied to high density photonic integrated circuits.     

Design of a single-polarization single-mode photonic crystal fiber with a near-Gaussian mode field and wide bandwidth

Single-polarization single-mode (SPSM) fiber can efficiently eliminate polarization mode coupling, polarization mode dispersion, and polarization-dependent loss. Up to now, most single-polarization fibers have been designed based on form birefringence, which would result in a non-Gaussian field distribution and a small effective mode field area. In this paper, a novel structure of SPSM photonic crystal fibers based on the resonant coupling phenomena is proposed and analyzed by using a full-vector finite-element method with a second-order transparent boundary condition. From the numerical results it is confirmed that this fiber has a near-Gaussian mode field within the wavelength range from 1.46 to 2.2 μm, where only one polarized mode exists effectively, and the mode field area is about 79 μm(2) at the wavelength of 1.55 μm, matching that of the conventional single-mode fiber.     

Polarization beam splitter based on honeycomb-lattice photonic crystal ring resonators

A new polarization beam splitter is proposed based on a photonic crystal ring resonator (PCRR) composed of honeycomb-lattice cylindrical silicon rods in air. By shrinking the width of the bus waveguide and adjusting the radii of two nearest-neighbor center rods of the PCRR, an unpolarized beam can be separated well into TE and TM polarization states, respectively, at the backward and forward output ports. Simulation results obtained by the two-dimensional finite-difference time-domain technique show that the insertion losses are 3.58 dB and 3.08 dB, and the polarization extinction ratios are 21.42 dB and 28.53 dB for TE and TM polarization, respectively, at a 1566.7 nm center wavelength. The excess loss is less than 0.34 dB and its dimensions are roughly 43.2 μm × 27.52 μm. These findings offer potential practical applications in high-density photonic integrated circuits.     

Dispersion-compensating photonic crystal fiber with wavelength tunability based on a modified dual concentric core structure

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.     

High-birefringence dual-wavelength single-polarization photonic crystal fibre polarizing filter based on surface plasmon resonance

A dual communication band single-polarization photonic crystal fibre polarizing filter based on surface plasmon resonance is presented in this paper. Numerical simulation results demonstrate that the resonance strength of x- and y-polarized direction can reach 569.83 and 719.25?dB.cm^?1 simultaneously at the communication wavelength of 1.31 and 1.55?µm. By filling liquid analyte, the confinement loss of x- and y-polarized direction can simultaneously reach 831.7 and 580.53?dB.cm^?1 at the wavelength of 1.31 and 1.55?µm. Furthermore, when the fibre length L is equal to 700?µm, the peak value of the crosstalk can reach 493.86 and ?323.67?dB at the same time at the wavelength of 1.31 and 1.55?µm, and when the length of the fibre L is 400?µm, the bandwidths of the crosstalk better than 20?dB and less than ?20?dB are about 160 and 210?nm, respectively. These performances make it an ideal candidate for designing dual-band polarization filter equipment.     

Design of low-loss single-polarization single-mode photonic-crystal fiber based on polymer

A new structure for single-polarization single-mode photonic-crystal fiber is proposed and numerically analyzed by using a full vector finite element method with anisotropic perfectly matched layers. The cutoff wavelength of two linearly polarized states can be controlled artificially by varying the structure parameters of photonic crystal fiber. The confinement loss are also numerically calculated and optimized at 650 nm communication wavelength of polymer optical fiber. From the numerical results it is confirmed that the proposed fiber is low-loss single-polarization single-mode photonic-crystal fiber within the wavelength range from 0.63 to 0.73 µm, where only the slow-axis mode exists and the confinement loss is less than 0.05 dB m^?1.     

Three-dimensional power splitter based on self-imaging effect in multimode layer-by-layer photonic crystal waveguides

The self-imaging effect based on symmetrical interference in multimode layer-by-layer photonic crystal waveguides (PhCWs), is numerically studied with finite-difference time-domain simulations. With the properties of twofold images, a kind of three-dimensional (3D) PhCW-based power splitters with an ultracompact size using complete photonic bandgaps is proposed, calculated, and analyzed. The presented structure can be extended for the design of M×N power splitters for 3D photonic integrated circuits applications.     

Biological sensor based on a hollow-core photonic crystal fiber

A new class of hollow photonic crystal fibers (PCFs) that can be used as sensitive elements of chemical and biological sensors is presented. The spectral characteristics of a PCF change depending on the physical properties of a medium filling its periodic structure. The concentration of a solution of an organic compound influences the spectrum of radiation guided in the PCF. A method of measuring the response of the PCF-liquid system to changes in the concentration of a substance dissolved in the analyzed medium is developed.     

Design and development of a temperature-compensated fiber optic polarimetric pressure sensor based on photonic crystal fiber at 1550 nm

Use of photonic crystal fibers (PCFs) in the field of sensing is relatively new. We propose the application of a PCF for pressure sensing. The fiber analyzed is a polarization-maintaining PCF that has negligible sensitivity to temperature, making it an ideal candidate for pressure sensing in harsh environments. On the basis of theoretical and experimental analysis, PCF is proposed to be applied as a temperature-compensated pressure sensor. Detailed theoretical analysis and the experiment carried out are described to show the concept of the sensor.     

Design of bent photonic crystal fiber supporting a single polarization

In this work, it is shown that the differential loss between the TE- and TM-polarized fundamental modes in a highly birefringent photonic crystal fiber (PCF) can be enhanced by bending the fiber. As a result, a design approach for single-mode single-polarization operation has been developed and is discussed. A rigorous full-vectorial H-field-based finite element approach, which includes the conformal transformation and the perfectly matched layer, is used to determine the single-polarization properties of such a highly birefringent PCF by exploiting its differential bending losses.     

Design and modeling of a photonic crystal fiber gas sensor

We report the modeling results of an all-fiber gas detector that uses photonic crystal fiber (PCF). The relative sensitivity of the PCF as a function of the fiber parameters is calculated. Gas-diffusion dynamics that affect the sensor response time is investigated theoretically and experimentally. A practical PCF sensor aiming for high sensitivity gas detection is proposed.     

Surface plasmon resonance biosensor based on large size square-lattice photonic crystal fiber

A surface plasmon resonance biosensor based on large size square-lattice photonic crystal fiber has been designed and simulated by finite element method. The square-lattice airholes are first coated with a calcium fluoride layer to provide mode confinement, then a nanoscale gold layer is deposited to excite the plasmon mode, and finally, the sample is infiltrated into the holes. The numerical results reveal that the resonance properties are easily affected by many parameters. The refractive index resolution of corresponding sensor can reach 4.3 × 10^?6 RIU when the optimum parameters are set as the radius of curvature of the airhole r = 2 μm, the thickness of the core struts c = 200 nm, the auxiliary dielectric layer s = 1 μm, and the gold film d = 40 nm. In addition, the effective area and nonlinear coefficient are calculated.     

基于光纤光栅的波分复用系统设计

设计了两种基于光纤布拉格光栅的波分复用(WDM)系统,一种为基于光纤光栅的四路波分复用系统,另一种为结合光分插复用器(OADM)的四路波分复用系统。给出了基于Opti System的波分复用光传输系统仿真模型,对复用及解复用后的光信号进行仿真得出了光谱图,对传输性能及Q因子、误码率、眼图等参数进行分析。在第二种结构中光纤光栅作为色散补偿器、光反射器和滤波器使用,可以实现任一波长的上载和下路。两种波分复用系统眼图张开良好,误码率均低于10e-9。证明了波分复用系统的正确性和设计方案的可行性。     

High-stability erbium-doped photonic crystal fiber source

A single-pass backward configuration superfluorescent fiber source (SFS) based on erbium-doped photonic crystal fiber (EDPCF) with a high mean wavelength stability was proposed. The EDPCF was used to improve the intrinsic temperature dependence of the SFS. Using the optimal EDPCF length of 24.2 m and pump power of 204 mW, a 20.7 ppm mean wavelength stability of a prototype SFS was demonstrated with increased temperature from -40 °C to 60 °C. The mean wavelength had an ultra stability of 10.3 ppm with increased temperature from -20 °C to 60 °C.     

Design of a broadband highly dispersive pure silica photonic crystal fiber

A highly dispersive dual-concentric-core pure silica photonic crystal fiber is designed with a maximum chromatic dispersion value of about -9500 ps/(nm km) around the 1.56 microm wavelength region and a full width at half-maximum (FWHM) of 55 nm. The change in the dispersion-bandwidth product as a function of period is carefully studied by using the plane wave expansion method. The coupled mode theory matches well with the plane wave expansion method that was used to simulate the chromatic dispersion. This kind of a photonic crystal fiber structure is suitable for high-dispersion application in phased array antenna systems based on photonic crystal fiber arrays.     

Temperature sensor based on surface plasmon resonance within selectively coated photonic crystal fiber

We demonstrate a temperature sensor based on surface plasmon resonances supported by photonic crystal fibers (PCFs). Within the PCF, to enhance the sensitivity of the sensor, the air holes of the second layer are filled with a large thermo-optic coefficient liquid and some of those air holes are selectively coated with metal. Temperature variations will induce changes of coupling efficiencies between the fundamental core mode and the plasmonic mode, thus leading to different loss spectra that will be recorded. In this paper, variations of the dielectric constants of all components, including the metal, the filled liquid, and the fused silica, are considered. We conduct numerical calculations to analyze the mode profile and evaluate the power loss, demonstrating a temperature sensitivity as high as 720 pm/°C.