Showing papers on "Photonic-crystal fiber published in 2016"

Topological protection of photonic mid-gap cavity modes

Abstract: Defect modes in two-dimensional periodic photonic structures have found use in a highly diverse set of optical devices. For example, photonic crystal cavities confine optical modes to subwavelength volumes and can be used for Purcell enhancement of nonlinearity, lasing, and cavity quantum electrodynamics. Photonic crystal fiber defect cores allow for supercontinuum generation and endlessly-single-mode fibers with large cores. However, these modes are notoriously fragile: small changes in the structure can lead to significant detuning of resonance frequency and mode volume. Here, we show that a photonic topological crystalline insulator structure can be used to topologically protect the resonance frequency to be in the middle of the band gap, and therefore minimize the mode volume of a two-dimensional photonic defect mode. We experimentally demonstrate this in a femtosecond-laser-written waveguide array, a geometry akin to a photonic crystal fiber. The topological defect modes are determined by a topological invariant that protects zero-dimensional states (defect modes) embedded in a two-dimensional environment; a novel form of topological protection that has not been previously demonstrated.

Negative Curvature Hollow-Core Optical Fiber

Abstract: The background, optical properties, and applications of low-loss negative curvature hollow-core fiber are reviewed. Data on spectral attenuation are collated and extended.

Broadband robustly single-mode hollow-core PCF by resonant filtering of higher-order modes.

Abstract: We report a hollow-core photonic crystal fiber that is engineered so as to strongly suppress higher-order modes, i.e., to provide robust LP01 single-mode guidance in all the wavelength ranges where the fiber guides with low loss. Encircling the core is a single ring of nontouching glass elements whose modes are tailored to ensure resonant phase-matched coupling to higher-order core modes. We show that the resulting modal filtering effect depends on only one dimensionless shape parameter, akin to the well-known d/Λ parameter for endlessly single-mode solid-core PCF. Fabricated fibers show higher-order mode losses some ∼100 higher than for the LP01 mode, with LP01 losses 110 THz bandwidth.

Highly sensitive multi-core flat fiber surface plasmon resonance refractive index sensor.

Abstract: A simple multi-core flat fiber (MCFF) based surface plasmon resonance (SPR) sensor operating in telecommunication wavelengths is proposed for refractive index sensing. Chemically stable gold (Au) and titanium dioxide (TiO2) layers are used outside the fiber structure to realize a simple detection mechanism. The modeled sensor shows average wavelength interrogation sensitivity of 9,600 nm/RIU (Refractive Index Unit) and maximum sensitivity of 23,000 nm/RIU in the sensing range of 1.46-1.485 and 1.47-1.475, respectively. Moreover, the refractive index resolution of 4.35 × 10−6 is demonstrated. Additionally, proposed sensor had shown the maximum amplitude interrogation sensitivity of 820 RIU−1, with the sensor resolution of 1.22 × 10−5 RIU. To the best of our knowledge, the proposed sensor achieved the highest wavelength interrogation sensitivity among the reported fiber based SPR sensors. Finally we anticipate that, this novel and highly sensitive MCFF SPR sensor will find the potential applications in real time remote sensing and monitoring, ultimately enabling inexpensive and accurate chemical and biochemical analytes detection.

Mid-infrared supercontinuum generation spanning 2.0 to 15.1 μm in a chalcogenide step-index fiber.

Abstract: We experimentally demonstrate mid-infrared (MIR) supercontinuum (SC) generation spanning ∼2.0 to 15.1 μm in a 3 cm-long chalcogenide step-index fiber. The pump source is generated by the difference frequency generation with a pulse width of ∼170 fs, a repetition rate of ∼1000 Hz, and a wavelength range tunable from 2.4 to 11 μm. To the best of our knowledge, this is the broadest MIR SC generation observed so far in optical fibers. It facilitates fiber-based applications in sensing, medical, and biological imaging areas.

Visible supercontinuum generation in a graded index multimode fiber pumped at 1064 nm.

Abstract: We observe efficient supercontinuum generation that extends into the visible spectral range by pumping a low differential mode group delay graded index multimode fiber in the normal dispersion regime. For a 28.5 m long fiber, the generated spectrum spans more than two octaves, starting from below 450 nm and extending beyond 2400 nm. The main nonlinear mechanisms contributing to the visible spectrum generation are attributed to multipath four-wave mixing processes and periodic spatio-temporal breathing dynamics. Moreover, by exploiting the highly multimodal nature of this system, we demonstrate versatile generation of visible spectral peaks in shorter fiber spans by altering the launching conditions. A nonlinearly induced mode cleanup was also observed at the pump wavelength. Our results could pave the way for high brightness, high power, and compact, multi-octave continuum sources.

Hollow-core fibers for high power pulse delivery

Abstract: We investigate hollow-core fibers for fiber delivery of high power ultrashort laser pulses. We use numerical techniques to design an anti-resonant hollow-core fiber having one layer of non-touching tubes to determine which structures offer the best optical properties for the delivery of high power picosecond pulses. A novel fiber with 7 tubes and a core of 30µm was fabricated and it is here described and characterized, showing remarkable low loss, low bend loss, and good mode quality. Its optical properties are compared to both a 10µm and a 18µm core diameter photonic band gap hollow-core fiber. The three fibers are characterized experimentally for the delivery of 22 picosecond pulses at 1032nm. We demonstrate flexible, diffraction limited beam delivery with output average powers in excess of 70W.

Hybrid Optical Fibers – An Innovative Platform for In-Fiber Photonic Devices

Abstract: The field of hybrid optical fibers is one of the most active research areas in current fiber optics and has the vision of integrating sophisticated materials inside fibers, which are not traditionally used in fiber optics. Novel in-fiber devices with unique properties have been developed, opening up new directions for fiber optics in fields of critical interest in modern research, such as biophotonics, environmental science, optoelectronics, metamaterials, remote sensing, medicine, or quantum optics. Here the recent progress in the field of hybrid optical fibers is reviewed from an application perspective, focusing on fiber-integrated devices enabled by including novel materials inside polymer and glass fibers. The topics discussed range from nanowire-based plasmonics and hyperlenses, to integrated semiconductor devices such as optoelectronic detectors, and intense light generation unlocked by highly nonlinear hybrid waveguides.

Copper-Graphene-Based Photonic Crystal Fiber Plasmonic Biosensor

Abstract: We propose a photonic crystal fiber surface plasmon resonance biosensor where the plasmonic metal layer and the sensing layer are placed outside the fiber structure, which makes the sensor configuration practically simpler and the sensing process more straightforward. Considering the long-term stability of the plasmonic performance, copper (Cu) is used as the plasmonic material, and graphene is used to prevent Cu oxidation and enhance sensing performance. Numerical investigation of guiding properties and sensing performance is performed by using a finite-element method. The proposed sensor shows average wavelength interrogation sensitivity of 2000 nm/refractive index unit (RIU) over the analyte refractive indices ranging from 1.33 to 1.37, which leads to a sensor resolution of $5\times 10^{-5}\ \text{RIU}$ . Due to the simple structure and promising results, the proposed sensor could be a potential candidate for detecting biomolecules, organic chemicals, and other analytes.

Optomechanical sensing of liquids outside standard fibers using forward stimulated Brillouin scattering

Abstract: The analysis of chemical species is one of the most fundamental and long-standing challenges in fiber-optic sensors research. Existing sensor architectures require a spatial overlap between light and the substance being tested and rely either on structural modifications of standard fibers or on specialty photonic crystal fibers. In this work, we report an optomechanical fiber sensor that addresses liquids outside the cladding of standard, 8/125 μm single-mode fibers with no structural intervention. Measurements are based on forward stimulated Brillouin scattering by radial, guided acoustic modes of the fiber structure. The acoustic modes are stimulated by an optical pump pulse and probed by an optical signal wave, both confined to the core. The acoustic vibrations induce a nonreciprocal phase delay to the signal wave, which is monitored in a Sagnac interferometer loop configuration. The measured resonance frequencies and excitation strengths of individual modes agree with the predictions of a corresponding quantitative analysis. The acoustic reflectivity at the outer cladding boundary and the acoustic impedance of the surrounding medium are extracted from cavity lifetime measurements of multiple modes. The acoustic impedances of deionized water and ethanol are measured with better than 1% accuracy. The measurements successfully distinguish between aqueous solutions with 0, 4%, 8%, and 12% concentrations of dissolved salt. The new fiber-sensing paradigm might be used in the monitoring of industrial processes involving ionic solutions.

Distributed shape sensing using Brillouin scattering in multi-core fibers

Abstract: A theoretical and experimental study on the response of Brillouin scattering in multi-core optical fibers (MCF) under different curving conditions is presented. Results demonstrate that the Brillouin frequency shift of the off-center cores in MCF is highly bending-dependent, showing a linear dependence on the fiber curvature. This feature is here exploited to develop a new kind of distributed optical fiber sensor, which provides measurements of a distributed profile mapping the longitudinal fiber shape. Using conventional Brillouin optical time-domain analysis with differential pulse-width pairs, fully distributed shape sensing along a 1 km-long MCF is practically demonstrated. Experimental results show a very good agreement with the theoretically expected behavior deduced from the dependence of the Brillouin frequency on the strain induced by the fiber bending over a given core. The analysis and results presented in this paper constitute the first demonstration of distributed bending sensing, providing the cornerstone to further develop it into a fully distributed three-dimensional shape sensor.

Cavity-based mid-IR fiber gas laser pumped by a diode laser

Abstract: Mid-infrared (IR) lasers are currently an area of rapid development, with several competing technologies. In traditional gas lasers, the effective interaction length is limited and the system as a whole is bulky and inflexible, limiting their applications. Standard gain fibers cannot be used in the mid-IR because the glass forming the fiber core is not transparent at these longer wavelengths. In this Letter, we report the demonstration of a mid-IR fiber gas laser using feedback in an optical cavity. The laser uses acetylene gas in a high-performance silica hollow-core fiber as the gain medium, and lases either continuous wave or synchronously pumped when pumped by telecom-wavelength diode lasers. We have demonstrated lasing on a number of transitions in the spectral band of 3.1–3.2 μm. The system could be extended to other selected molecular species to generate output in the spectral band up to 5 μm, and it has excellent potential for power scaling.

Fabrication and characterization of polycarbonate microstructured polymer optical fibers for high-temperature-resistant fiber Bragg grating strain sensors

Abstract: Here we present the fabrication of a solid-core microstructured polymer optical fiber (mPOF) made of polycarbonate (PC), and report the first experimental demonstration of a fiber Bragg grating (FBG) written in a PC optical fiber. The PC used in this work has a glass transition temperature of 145°C. We also characterize the mPOF optically and mechanically, and further test the sensitivity of the PC FBG to strain and temperature. We demonstrate that the PC FBG can bear temperatures as high as 125°C without malfunctioning. In contrast, polymethyl methacrylate-based FBG technology is generally limited to temperatures below 90°C.

Design and optimization of photonic crystal fiber for liquid sensing applications

Abstract: This paper proposes a hexagonal photonic crystal fiber (H-PCF) structure with high relative sensitivity for liquid sensing; in which both core and cladding are microstructures. Numerical investigation is carried out by employing the full vectorial finite element method (FEM). The analysis has been done in four stages of the proposed structure. The investigation shows that the proposed structure achieves higher relative sensitivity by increasing the diameter of the innermost ring air holes in the cladding. Moreover, placing a single channel instead of using a group of tiny channels increases the relative sensitivity effectively. Investigating the effects of different parameters, the optimized structure shows significantly higher relative sensitivity with a low confinement loss.

High sensitivity refractive index sensor based on splicing points tapered SMF-PCF-SMF structure Mach-Zehnder mode interferometer

Abstract: The paper proposed and studied a Mach-Zehnder mode interferometric refractive index sensor, which is based on splicing points tapered SMF-PCF-SMF (SMF, single-mode fiber; PCF, photonic crystal fiber) structure. For the reason that the effective refractive index of photonic crystal fiber cladding high-order modes near fiber core are more sensitive to surrounding refractive index changes, the refractive index measurement sensitivity of splicing points tapered SMF-PCF-SMF Mach-Zehnder mode interferometer can be enhanced further through tapering the splicing points. Relations between refractive index measurement sensitivity and photonic crystal fiber length and taper waist diameter are studied through numerical simulations and experiments. Simulation and experimental results show that sensitivity will be increased with the increase of photonic crystal fiber length and the decrease of taper waist diameter. In the refractive range of 1.3333–1.3737, splicing points tapered SMF-PCF-SMF Mach-Zehnder mode interferometer with PCF length of 4 cm and taper waist diameter of 60.4 μm has refractive index measurement sensitivity of 260.8 nm/RIU, compared with sensitivity of 224.2 nm/RIU of direct splicing SMF-PCF-SMF Mach-Zehnder mode interferometer with PCF length of 4 cm, the sensitivity increased by 16.3%. The research shows that the sensing structure is with good linearity and repeatability.

Ultrasensitive vector bending sensor based on multicore optical fiber.

Abstract: In this Letter, we demonstrate a compellingly simple directional bending sensor based on multicore optical fibers (MCF). The device operates in reflection mode and consists of a short segment of a three-core MCF that is fusion spliced at the distal end of a standard single mode optical fiber. The asymmetry of our MCF along with the high sensitivity of the supermodes of the MCF make the small bending on the MCF induce drastic changes in the supermodes, their excitation, and, consequently, on the reflected spectrum. Our MCF bending sensor was found to be highly sensitive (4094 pm/deg) to small bending angles. Moreover, it is capable of distinguishing multiple bending orientations.

Single mode step-index polymer optical fiber for humidity insensitive high temperature fiber Bragg grating sensors

Abstract: We have fabricated the first single-mode step-index and humidity insensitive polymer optical fiber operating in the 850 nm wavelength ranges. The step-index preform is fabricated using injection molding, which is an efficient method for cost effective, flexible and fast preparation of the fiber preform. The fabricated single-mode step-index (SI) polymer optical fiber (POF) has a 4.8µm core made from TOPAS grade 5013S-04 with a glass transition temperature of 134°C and a 150 µm cladding made from ZEONEX grade 480R with a glass transition temperature of 138°C. The key advantages of the proposed SIPOF are low water absorption, high operating temperature and chemical inertness to acids and bases and many polar solvents as compared to the conventional poly-methyl-methacrylate (PMMA) and polystyrene based POFs. In addition, the fiber Bragg grating writing time is short compared to microstructured POFs.

A New Type Circular Photonic Crystal Fiber for Orbital Angular Momentum Mode Transmission

Abstract: We proposed a new circular photonic crystal fiber (C-PCF), which can support 14 orbital angular momentum (OAM) modes transmission, with the good features of wide bandwidth, low confinement loss, and all OAM modes at the same size. At 1.55 μm, the designed C-PCF has a very low confinement loss of 3.434 × 10 -9 dB/m for HE41 mode and a relatively low nonlinear coefficient of 3.979 W -1 km -1 for EH 31 mode. The common bandwidth for the four orders of OAM modes is as large as 560 nm (about 1.25 μm-1.81 μm), which does cover all bands of optical fiber communication. Flat dispersion (a total dispersion variation of <;46.38 ps nm -1 km -1 over a 750-nm bandwidth from 1.25 μm to 2 μm for TE 01 mode) is another feature. With all these good features, the proposed C-PCF could be a well-promising OAM fiber for mode division multiplexing in high capacity fiber communication systems.

Hybrid photonic crystal fiber in chemical sensing.

Abstract: In this article, a hybrid photonic crystal fiber has been proposed for chemical sensing. A FEM has been applied for numerical investigation of some propagation characteristics of the PCF at a wider wavelength from 0.7 to 1.7 µm. The geometrical parameters altered to determine the optimized values. The proposed PCF contains three rings of circular holes in the cladding where the core is formulated with microstructure elliptical holes. The simulation result reveals that our proposed PCF exhibits high sensitivity and low confinement loss for benzene, ethanol and water than the prior PCFs. We have also shown that our proposed PCF shows high birefringence for benzene 1.544 × 10−3, for ethanol 1.513 × 10−3 and for water 1.474 × 10−3 at λ = 1.33 µm. The proposed PCF is simple with three rings which can be used for the sensing applications of industrially valuable lower indexed chemicals.

Coherent mid-infrared supercontinuum generation in all-solid chalcogenide microstructured fibers with all-normal dispersion.

Abstract: We report the coherent mid-infrared supercontinuum generation in an all-solid chalcogenide microstructured fiber with all-normal dispersion. The chalcogenide microstructured fiber is a four-hole structure with core material of AsSe2 and air holes that are replaced by As2S5 glass rods. Coherent mid-infrared supercontinuum light extended to 3.3 μm is generated in a 2 cm long chalcogenide microstructured fiber pumped by a 2.7 μm laser.

High-order random Raman lasing in a PM fiber with ultimate efficiency and narrow bandwidth.

Abstract: Random Raman lasers attract now a great deal of attention as they operate in non-active turbid or transparent scattering media. In the last case, single mode fibers with feedback via Rayleigh backscattering generate a high-quality unidirectional laser beam. However, such fiber lasers have rather poor spectral and polarization properties, worsening with increasing power and Stokes order. Here we demonstrate a linearly-polarized cascaded random Raman lasing in a polarization-maintaining fiber. The quantum efficiency of converting the pump (1.05 μm) into the output radiation is almost independent of the Stokes order, amounting to 79%, 83%, and 77% for the 1(st) (1.11 μm), 2(nd) (1.17 μm) and 3(rd) (1.23 μm) order, respectively, at the polarization extinction ratio >22 dB for all orders. The laser bandwidth grows with increasing order, but it is almost independent of power in the 1-10 W range, amounting to ~1, ~2 and ~3 nm for orders 1-3, respectively. So, the random Raman laser exhibits no degradation of output characteristics with increasing Stokes order. A theory adequately describing the unique laser features has been developed. Thus, a full picture of the cascaded random Raman lasing in fibers is shown.

High-Spatial-Multiplicity Multicore Fibers for Future Dense Space-Division-Multiplexing Systems

Abstract: Multicore fibers and few-mode fibers have potential application in realizing dense-space-division multiplexing systems. However, there are some tradeoff requirements for designing the fibers. In this paper, the tradeoff requirements such as spatial channel count, crosstalk, differential mode delay, and cladding diameter are discussed. Further, the design concept and transmission characteristics of high-core-count single-mode multicore fibers are discussed. A heterogeneous multicore fiber with 30 cores and quasi-single-mode multi-core fibers with 31 cores are developed.

Design and numerical analysis of microstructured-core octagonal photonic crystal fiber for sensing applications

Abstract: This paper presents an octagonal photonic crystal fiber (O-PCF) for liquid sensing, in which both core and cladding are microstructured. Some propagation characteristics of proposed structure have been investigated by using the full vectorial finite element method (FEM). Confinement loss and sensitivity are examined and compared with varying number of rings, core diameter, diameter of air holes in cladding ring and pitch. It is found that sensitivity is increased for the increment pitch value, air filling ratio, core diameter, inner ring diameter as well as number of rings. At the same time confinement loss is significantly decreased. It is also found that the increment of pitch by keeping the same air filling ratio increases the sensitivity and loss. Investigating the effects of different parameters, an O-PCF structure is designed which has a significantly higher relative sensitivity and lower confinement loss.

3D printed low-loss THz waveguide based on Kagome photonic crystal structure

Abstract: A low-loss hollow core terahertz waveguide based on Kagome photonic crystal structure has been designed and fabricated by 3D printing. The 3D printed waveguide has been characterized by using THz time-domain spectroscopy. The results demonstrate that the obtained waveguide features average power propagation loss of 0.02 cm-1 for 0.2-1.0 THz (the minimum is about 0.002 cm-1 at 0.75 THz). More interesting, it could be simply mechanically spliced without any additional alignment, while maintaining the excellent performance. The 3D printing technique will be a promising solution to fabricate Kagome THz waveguide with well controllable characteristics and low cost.

Highly Sensitive Plasmonic Photonic Crystal Temperature Sensor Filled With Liquid Crystal

Abstract: A novel highly sensitive surface plasmon resonance-based liquid crystal (LC) photonic crystal fiber (PCF) temperature sensor is presented and studied. Through this letter, the coupling characteristics between the core guided mode inside the PCF core infiltrated with nematic LC and surface plasmon mode on the surface of nano gold wire are studied in detail. The structural geometrical parameters of the proposed design, such as number of metal rods, core diameter, and metal rod diameter are optimized to achieve highly temperature sensitivity. The suggested sensor of compact device length of 20 $\mu \text{m}$ proved to surpass the recent sensors with high sensitivity of 10 nm/°C. The results are calculated using a full-vectorial finite-element method with irregular meshing capabilities and perfectly matched layer boundary conditions.

Simultaneous measurement of temperature and refractive index using focused ion beam milled Fabry-Perot cavities in optical fiber micro-tips.

Abstract: Optical fiber micro-tips are promising devices for sensing applications in small volume and difficult to access locations, such as biological and biomedical settings. The tapered fiber tips are prepared by dynamic chemical etching, reducing the size from 125 μm to just a few μm. Focused ion beam milling is then used to create cavity structures on the tapered fiber tips. Two different Fabry-Perot micro-cavities have been prepared and characterized: a solid silica cavity created by milling two thin slots and a gap cavity. A third multi-cavity structure is fabricated by combining the concepts of solid silica cavity and gap cavity. This micro-tip structure is analyzed using a fast Fourier transform method to demultiplex the signals of each cavity. Simultaneous measurement of temperature and external refractive index is then demonstrated, presenting sensitivities of - 15.8 pm/K and −1316 nm/RIU, respectively.

Gigahertz frequency comb offset stabilization based on supercontinuum generation in silicon nitride waveguides.

Abstract: Silicon nitride (Si3N4) waveguides represent a novel photonic platform that is ideally suited for energy efficient and ultrabroadband nonlinear interactions from the visible to the mid-infrared. Chip-based supercontinuum generation in Si3N4 offers a path towards a fully-integrated and highly compact comb source for sensing and time-and-frequency metrology applications. We demonstrate the first successful frequency comb offset stabilization that utilizes a Si3N4 waveguide for octave-spanning supercontinuum generation and achieve the lowest integrated residual phase noise of any diode-pumped gigahertz laser comb to date. In addition, we perform a direct comparison to a standard silica photonic crystal fiber (PCF) using the same ultrafast solid-state laser oscillator operating at 1 µm. We identify the minimal role of Raman scattering in Si3N4 as a key benefit that allows to overcome the fundamental limitations of silica fibers set by Raman-induced self-frequency shift.

Highly sensitive D-shaped photonic crystal fiber biological sensors based on surface plasmon resonance

Abstract: A D-shaped photonic crystal fiber (D-PCF) with square-lattice and nanoscale gold film is proposed and analyzed by the finite element method. Based on the strong surface plasmon resonance effect between fiber core modes and surface plasmon polariton modes, the designed D-PCF is sensitive to the refractive index variation of analyte and can be found application in biological sensors. The structure parameters of the proposed D-PCF are investigated in order to optimize the sensing performance. The sensitivity can reach to 12,450 nm/RIU as refractive index of analyte ranging from 1.345 to 1.410. The simulation results also show that the sensing performance has high linearity which is necessary in application.

Proposal of a gas sensor with high sensitivity, birefringence and nonlinearity for air pollution monitoring

Abstract: Flammable or poisonous gasses in the air are capable of destroying a geographical area of causing a fire, fulmination, and venomous exposure. This paper presents a micro-cored photonic crystal fiber based gas sensor for detecting colorless or toxic gasses and monitoring air pollution by measuring gas condensate components in production facilities. The numerical investigation of the proposed PCF takes place using the finite element method (FEM). The geometrical parameters of proposed PCF are varied to optimize and observe the dependence of guiding properties on them. According to simulated results, the high relative sensitivity of 53.07% is obtained at 1.33 μm wavelength for optimum parameters. In addition, high birefringence of the order 6.9 × 10− 3; lower confinement loss of 3.21 × 10− 6 dB/m is also gained at the same wavelength. Moreover, nonlinear coefficient, effective area, splice loss, V parameters and beat length are reported briefly.