Big Air Holes Research Articles

A square-lattice D-shaped photonic crystal fiber sensor based on SPR to detect analytes with large refractive indexes

With the booming of nanotechnology, surface plasmon resonance (SPR) technology has become one of the most active research hotspots in optical sensing. In this work, a square-lattice photonic crystal fiber (PCF) sensor based-SPR with indium tin oxide (ITO) coating is investigated to detect analytes with large refractive indexes (RIs) varying from 1.380 to 1.405. To confirm the dependence of sensing characteristics on the geometrical parameters, the finite element method (FEM) is applied to modeling and numerical simulation. The big air holes in cladding cause a birefringence effect, which is stronger with y-polarization mode. In this way, the maximum and average spectral sensitivity of 60,000 and 18,400 nm/RIU can be achieved with resolution in 10−6 order. Furthermore, this sensor which provides a high-sensitivity detection in large analyte RIs with near-infrared region (1500–2800 nm) shows excellent figure of merit (FOM), signal-to-noise ratio (SNR) and detection limit (DL). There will be more extensive space and prospect for progression in biochemical safety with DNA hybridization, blood glucose analysis and organic chemical samples detection involved.

Large mode area single mode photonic crystal fiber with ultra-low bending loss

A novel asymmetrical structure of Photonic Crystal Fibers (PCFs) has been proposed in this article. The first ring consists of three big air holes which can confine the propagating mode in the core region. The second ring consists of twelve doped rods with two different diameters which can decrease the difference of refractive index between the core and the cladding in order to provide the large mode area. The third ring consists of eleven air holes to help the higher-order-modes (HOMs) to leak out. The bending properties of proposed fiber are investigated by full vector finite element method with an anisotropic perfectly matched layer. The numerical results show that the effective mode area of the FM of the proposed fiber is as large as 595.02 μm2 with small bending radius of 10 cm at the wavelength of 1064nm. The bending loss of fundamental mode (FM) is 9.884×10−5dB/m, while large bending loss for the high-order mode (HOMs) is 14.685dB/m. Moreover, the loss ratio can reach 1.45×105which can realize the effective and stability single-mode operation. Therefore, the novel fiber has potential application in high-power fiber lasers.

Optical four-channel demultiplexer based on air-bridge structure and graphite-type ring resonators

A novel an optical four-channel demultiplexer based on a hexagonal lattice shape of embedded air holes in dielectric substrate (air-bridge type) is proposed. Demultiplexing for each channel is obtained by designing the graphite-type ring resonator which consists of small air hole defects in own unit cells. The physical parameters which govern the demultiplexer performance are investigated. It is observed that employing big air hole as a defect in the end of input waveguide enhanced the coupling efficiency between the rings and waveguides. By engineering the refractive index of substrate and size of air holes, the proposed demultiplexer is tuned. The demultiplexer has an average quality factor > 3000 and channel spacing $$\Delta \lambda \le 2\;{\text{nm}}$$ . We showed that big air hole defect in the end of input waveguide is an effective scheme for improving the transmission efficiency and cross talk between channels. The average transmission efficiency and cross talk value are above 98% and − 23 dB, respectively. The total size of proposed structure and its maximum delay time are 289 μm2 and 0.3 ps, respectively. Our demultiplexer has an easy fabrication structure, and it can find key applications for many cores CPU in an on-chip optical network and the dense wavelength demultiplexing in optical integrated circuits.

A Refractive Index Sensor Based on H-Shaped Photonic Crystal Fibers Coated with Ag-Graphene Layers.

An Ag-graphene layers-coated H-shaped photonic crystal fiber (PCF) surface plasmon resonance (SPR) sensor with a U-shaped grooves open structure for refractive index (RI) sensing is proposed and numerically simulated by the finite element method (FEM). The designed sensor could solve the problems of air-holes material coating and analyte filling in PCF. Two big air-holes in the x-axis produce a birefringence phenomenon leading to the confinement loss and sensitivity of x-polarized light being much stronger than y-polarized. Graphene is deposited on the layer of silver in the grooves; its high surface to volume ratio and rich π conjugation make it a suitable dielectric layer for sensing. The effect of structure parameters such as air-holes size, U-shaped grooves depth, thickness of the silver layer and number of graphene layers on the sensing performance of the proposed sensor are numerical simulated. A large analyte RI range from 1.33 to 1.41 is calculated and the highest wavelength sensitivity is 12,600 nm/RIU. In the linear RI sensing region of 1.33 to 1.36; the average wavelength sensitivity we obtained can reach 2770 nm/RIU with a resolution of 3.61 × 10−5 RIU. This work provides a reference for developing a high-sensitivity; multi-parameter measurement sensor potentially useful for water pollution monitoring and biosensing in the future.

Surface plasmon resonance induced tunable ultra-wideband polarization filters based on gold film coated photonic crystal fibers

Surface plasmon resonance induced tunable broadband polarization filters based on photonic crystal fibers (PCFs) were designed and investigated. The characteristics of the designed PCF were calculated by using the finite element method (FEM). The air holes in the PCFs which were arranged in hexagonal lattice were of the same size except one big air hole. The big air hole which was located on the right side of the fiber core was designed to be coated with gold film in the inner wall. Because of the arrangement of the big air hole, the surface plasmon resonance inspired on the surface of gold film was quite different for the two orthogonal polarized incident lights. As the edge of the big air hole approaching the adjacent air holes, the plasmon modes were influenced strongly by the adjacent air holes and as a results the cascaded resonances appeared. The index-matching liquid infilling in the big air hole was used to adjust the resonant wavelengths and strength. Numerical simulation results showed that the bandwidth of the polarization filter was 1200 nm covering the wavelengths from 1.0 μm to 2.2 μm with high extinction ratio (ER).

Spiral photonic crystal fiber structure for supporting orbital angular momentum modes

We propose a spiral photonic crystal fiber structure for supporting orbital angular momentum modes. The structure has 12 arms, arranged in a spiral shape in the cladding region, and a big air hole at the center of the structure. It can support 14 well-separated OAM modes with a mode index difference of 10−4. Our numerical results show a nonlinear coefficient of 2.78 W−1 Km−1 for the HE21 mode at 1550-nm wavelength. The fiber shows a dispersion difference over a 600 nm bandwidth for HE21 mode is 12.1 ps/km-nm, and the structure shows a low confinement loss. We have also calculated the effect of ellipticity on the mode’s effective index. Numerical results suggest that, this structure can be utilized in high-capacity communication systems for multiplexing fiber-based OAM.

In-Fiber M-Z Interferometer Based on Cascaded Long Period Gratings in Embedded-Core Fiber

A novel Mach-Zehnder interferometer (MZI) in an embedded-core hollow optical fiber (ECOF) was demonstrated, which was composed of a pair of long period gratings (LPGs). In order to form an in-fiber MZI in an ECOF, a high-frequency CO2 laser was used to fabricate two similar LPGs with their peak attenuation of approximate 3 dB. The responses of the MZI to the temperature, the axial strain, and the refractive index were measured and discussed. The temperature sensitivity of the MZI is about 48.8 pm/°C, and the sensitivity of the axial strain is 0.5 pm/ $\mu \varepsilon $ . The ECOF has a big air hole, which is easy to form a microfluidic channel. The sensitivity of the internal refractive index can be as high as 1437.4 nm/RIU in the refractive index range of 1.4248~1.4569. The proposed MZI has a high resolution and can be a potential candidate for sensing, especially for on-line microfluidics sensors.

A broadband core shift polarization filter based on photonic crystal fiber with a big gold-coated air hole

We propose a modified design for a Core shift photonic crystal fiber (PCF) polarization filter based on surface plasmon resonance. The Core shiftting is achieved by the air holes with different diameters around the gold-coated holes, which can separate the refractive index of the x-polarization and y-polarization second order surface plasmon polariton modes. The influences of structural parameters of the PCF on the filter characteristics are studied using the finite element method. Simulation results great changes have taken place in the results of numerical simulation by changing the thickness of the gold film and air hole diameter. We obtain a resonance wavelength with 1550 nm. The y-polarization mode is supressed significantly with the loss of 58,456.7 dB/m. With the length of the fiber is 300 μm, a extinction ratio is higher than 20 dB and a bandwidth achieve to 450 nm at the communication wavelength can be got. All these properties we achieved in the core shift PCF are important properties of PCF in broadband polarization filter in application. Our design can offer some guidance to the production of the polarization filter.

A design strategy of the circular photonic crystal fiber supporting good quality orbital angular momentum mode transmission

Based on 5 requirements which are essential for stable OAM mode transmission, we propose an OAM fiber family based on a structure of circular photonic crystal fiber (C-PCF). The proposed C-PCF in the family is made of pure silica, with a big round air hole at the center, several rings of air-hole array as the cladding, and a ring shaped silica area in between as the core where the OAM modes propagate. We also provide a design strategy with which the optimized C-PCF can be obtained with optimum number of high quality OAM modes (up to 42 OAM modes), large effective index separation for corresponding vector modes over a wide bandwidth, relative small and flat dispersion, and low nonlinear coefficient compared with a conventional single mode fiber. The designed fiber can be used in MDM communications and other OAM applications in fibers.

Design of a polarization filtering photonic crystal fiber with a big gold-coated air hole

The polarization characteristics of photonic crystal fiber (PCF) with nanoscale gold film is evaluated by using the finite element method. The cross-section structure of the PCF is composed of a hexagonal lattice of air holes in which an air hole is gold coated. The resonance strength and the impact of structural parameters of the PCF on the polarization filter characteristics are studied. By our structure, the loss of y-polarized mode is further larger than the loss of x-polarized mode at the wavelength 1.31 and 1.55 μm. The corresponding loss in y-polarized can reach a value of 136,253 and 167607 dB/m at the resonance wavelengths of 1.31 and 1.55 μm respectively. It can be used for carrying data/voice at the communication windows of 1.31 and 1.55 μm. Meanwhile, we can realize the filtering effect with a very short fiber.

Photonic crystal fibre polarization filter with round lattice based on surface plasmon resonance

A kind of photonic crystal fibre polarization filter with round lattice based on surface plasmon resonance is proposed. Complete coupling happens between core mode and second-order surface plasmon polariton (SPP) mode when the phase-matching condition is satisfied. We can adjust the resonance point and strength in two polarizations by changing the fibre birefringence and the thickness of gold film. Numerical simulation with the finite-element method shows that the resonance strength can reach 364.8 dB/cm in the y-polarized direction at the communication wavelength of 1550 nm, when the diameter of big air holes that lead to the birefringence is 2.0 m and the thickness of gold film is 26 nm. Moreover, when the fibre length is 800 m, the peak value of the crosstalk can reach 231.8 dB and the bandwidth of the crosstalk better than 20 dB can reach 130 nm. This makes it a promising candidate for polarization filter devices.

Fabrication and Characteristic of Polarization-Maintaining Photonic Crystal Fiber with Two Big Air Holes Structure

In this article, polarization-maintaining photonic crystal fibers with two big air holes, which are based on a kind of multi-component glass, are fabricated by the capillary-stacking and drawing method. The microstructure of the small air holes is found to be well kept through a scanning electron microscope, even with a diameter close to 0.6 μm. Numerical results show that the chromatic dispersion of the proposed fiber with a 125-μm-diameter approaches zero at 1,550 nm. Meanwhile, experimental results display that the beat length of the same photonic crystal fiber is 3.6961 mm at 1,550 nm, and the related polarization extinction ratio and polarization mode dispersion is 17.23889 dB and 2.58321 ps, respectively.

Characteristic analyses of high birefringence and two zero dispersion points photonic crystal fiber with octagonal lattices

Aiming to the requirements of high birefringence and multiple zero dispersion points of optic-fiber sensing and communication systems, a new type of photonic crystal fiber (PCF) is proposed. The cladding is arrayed by octagonal air holes, and two big elliptical air holes are added in inner cladding to increase the birefringence. Numeral results show that this type of PCF exhibits high birefringence with a level of 10-3 when wavelength ranges from 0.8-2 m, which fulfils the requirement of high birefringence, and two zero dispersion points are obtained after optimization. In addition, high nonlinear coefficient with a level of 10-2 m-1W-1 is obtained, which could be used in the case where the nonlinearity is highly required.

Characteristics Analysis of Photonic Crystal Fiber with Hexagonal and Octagonal Structure

Aiming at the requirements of high performance of optical communication systems, a new type of photonic crystal fiber (PCF) is proposed. This kind of PCF consists of hexagonal air holes in the inner cladding and octagonal air holes in the others layers. Two big elliptical air holes are embedded to enhance the birefringence. Numeral results show that this kind of PCF exhibits high birefringence with the level of 10-3 and high nonlinearity with the level of 10-2m-1w-1. In addition, two zero dispersion points are obtained after optimization, which will find application in dispersion compensation PCFs.

Analysis of birefringent and dispersive properties of photonic crystal fibers

Two types of high birefringence photonic crystal fiber (PCF) which import four or six big circular air holes near the elliptical-hole are proposed. Their birefringent and dispersive properties are analyzed by full-vector finite-element method (FEM). Numerical analysis demonstrates that importing the big circular hole near the center of elliptical-hole PCFs can achieve a high birefringence. When the ratio (d/Λ) of diameter to hole spacing is larger than 0.8, the proposed two types of PCF have a larger birefringence than that of sole elliptical air hole ones. When the ratio d/Λ is equal to 0.95, the birefringences of these two types PCF can be as high as 4.27×10(-3) and 5.09×10(-3) at the wavelength of 1.55 μm, respectively. Besides, PCF with the four big circular air holes has a large negative dispersion at the long wavelength in x-polarized mode, which indicates a potential in single-polarized mode dispersion compensation.

PCF-Based Fabry–Pérot Interferometric Sensor for Strain Measurement at High Temperatures

We report a simple and robust all-fiber in-line Fabry-Perot interferometer (FPI) with an air bubble cavity, which is fabricated by directly splicing a multimode photonic crystal fiber (MPCF) to a conventional single-mode fiber with a commercialized fusion splicer. The air microbubble inserted between the two fibers has two smooth glass-air interfaces separated by a distance L as two reflective mirrors of the FPI. Due to the big air holes in the cladding of MPCF and its large numerical aperture, this device has higher signal-to-noise ratio and fringe contrast than that of the FPI based on hollow-core photonic crystal fiber. Experimental results show that the FPI can be used to measure strain in the range of 0 ~ 1850 μe at high temperatures of up to 750°C. Therefore, such an FPI sensor may find important applications in the aeronautics or metallurgy areas.

새로운 구조의 큰 복 굴절을 가진 광자결정 광섬유의 제작에 관한 연구

Stack-and-draw 방법을 사용하여 새로운 구조의 높은 복굴절을 가진 광자 결정 광섬유(highly birefringent photonic crystal fiber, Hi-Bi PCF)를 제작하였다. 제작된 광섬유는 공기구멍으로 구성된 클래딩 외부에 큰 공기구멍을 추가함으로써 광섬유 인출 과정중에 코어와 공기층 클래딩 영역에 비대칭적인 압력이 인가되어 코어가 타원형으로 변형되어 복굴절이 유도된다. 제작된 Hi-Bi PCF의 복굴절은 1550 nm에서 <TEX>$2.29{\times}10^{-4}$</TEX>로 측정되었다. We fabricate highly birefringent photonic crystal fiber with new structure using a stack and draw method. Fabricated fiber has two big air holes, one at each side of the outside air cladding region, leading to core ellipticity during the drawing process. Birefringence of the fabricated Hi-Bi PCF is measured to be <TEX>$2.29{\times}10^{-4}$</TEX> (at 1550 nm).

Novel index-guided photonic crystal fiber surface-enhanced Raman scattering probe

We demonstrate a novel index-guided (IG) photonic crystal fiber (PCF) surface-enhanced Raman probe. Different from a regular PCF, the IGPCF has four big air holes inserted between the solid silica core and the photonic crystal cladding holes. The gold nanoparticles, serving as the surface enhanced Raman scattering (SERS) substrate, are either coated on the inner surface of the holes or mixed in the analyte solution in two separate experiments, respectively. The analyte solution enters the holes via the capillary effect. The excitation light propagating in the silica core interacts with the gold nanoparticles and the analyte through the evanescent wave which extends significantly into the four big holes when they are filled with liquid leading to a large interaction volume between the excitation light and the nanoparticles/analyte.

New nonlinear and dispersion flattened photonic crystal fiber with low confinement loss

A new nonlinear dispersion flattened photonic crystal fiber with low confinement loss is proposed. This fiber has threefold symmetry core. The doped region in the core and the big air-holes in the 1st ring can make high nonlinearity in the PCF. And the small air-holes in the 1st ring and the radial increasing diameters air-holes rings in cladding can be used to achieve the dispersion properties of the PCF. We can achieve the optimized optical properties by carefully selecting the PCFs structure parameters. A PCF with flattened dispersion is obtained. The dispersion is less than 0.8ps/(nmkm) and is larger than −0.7ps/(nmkm) from 1.515μm to 1.622μm. The nonlinear coefficient is about 12.6456W−1km−1, the fundamental mode area is about 10.2579μm2. The confinement loss is 0.30641dB/km. This work may be useful for effective design and fabrication of dispersion flattened photonic crystal fibers with high nonlinearities.

Design of a new type high birefringence photonic crystal fiber

A High birefringence microstructure fiber with four big elliptical air holes is investigated by using the finite-difference frequency-domain (FDFD) method. Based on the numerical simulations, the influence of the air-hole size and pitch upon the mode birefringence is analyzed. The work may be helpful for the design and fabrication of high birefringence PCFs.