Confinement losses in microstructured optical fibers

Au-TiO2-Coated Spectroscopy-Based Human Teeth Disorder Detection Sensor: Design and Quantitative Analysis

Human tooth functionality is the most important for the human body to become fit and healthy. Due to the disease attacks in human teeth, parts may lead to different fatal diseases. A spectroscopy-based photonic crystal fiber (PCF) sensor was simulated and numerically analyzed for the detection of dental disorders in the human body. In this sensor structure, SF11 is used as the base material, gold (Au) is used as the plasmonic material, and TiO₂ is used within the gold and sensing analyte layer, and the sensing medium for the analysis of the teeth parts is the aqueous solution. The maximum optical parameter values for the human tooth parts enamel, dentine, and cementum in terms of wavelength sensitivity and confinement loss were obtained as 28,948.69 nm/RIU and 0.00015 dB/m for enamel, 33,684.99 nm/RIU and 0.00028 dB/m, and 38,396.56 nm/RIU and 0.00087 dB/m, respectively. The sensor is more precisely defined by these high responses. The PCF-based sensor for tooth disorder detection is a relatively recent development. Due to its design flexibility, robustness, and wide bandwidth, its application area has been spreading out. The offered sensor can be used in the biological sensing area to identify problems with human teeth.

High Sensitivity Surface Plasmon Resonance Sensor Based on a Ge-Doped Defect and D-Shaped Microstructured Optical Fiber

In this work a plasmonic sensor with a D-Shaped microstructured optical fiber (MOF) is proposed to detect a wide range of analyte refractive index (RI ;na) by doping the pure silica (SiO2) core with distinct concentrations of Germanium Dioxide (GeO2), causing the presentation of high spectral sensitivity. In this case, the fiber is shaped by polishing a coating of SiO2, on the region that will be doped with GeO2, in the polished area, a thin gold (Au) layer, which constitutes the plasmonic material, is introduced, followed by the analyte, in a way which the gold layer is deposited between the SiO2. and the analyte. The numerical results obtained in the study shows that the sensor can determine efficiently a range of 0.13 refractive index units (RIU), with a limit operation where na varies from 1.32 to 1.45. Within this application, the sensor has reached an average wavelength sensitivity (WS) of up to 11,650.63 nm/RIU. With this level of sensitivity, the D-Shaped format and wide range of na detection, the proposed fiber has great potential for sensing applications in several areas.

Hybrid topological guiding mechanisms for photonic crystal fibers

We create hybrid topological-photonic localisation of light by introducing concepts from the field of topological matter to that of photonic crystal fiber arrays. S-polarized obliquely propagating electromagnetic waves are guided by hexagonal, and square, lattice topological systems along an array of infinitely conducting fibers. The theory utilises perfectly periodic arrays that, in frequency space, have gapped Dirac cones producing band gaps demarcated by pronounced valleys locally imbued with a nonzero local topological quantity. These broken symmetry-induced stop-bands allow for localised guidance of electromagnetic edge-waves along the crystal fiber axis. Finite element simulations, complemented by asymptotic techniques, demonstrate the effectiveness of the proposed designs for localising energy in finite arrays in a robust manner.

Harnessing Deep-Hole Drilling to Fabricate Air-Structured Polymer Optical Fibres

The performance of a precisely controlled drilling technique is critical in the fabrication process of microstructured polymer optical fibres. For the creation of a holey preform, adequate drilling bits with large length-to-diameter ratios provide the ability of machining preforms with complex structures and large lengths in a relatively short time. In this work, we analysed different drilling bits and techniques that can be employed for the creation of such preforms, and key parameters characterising the quality of the drilled holes, such as surface rugosity, diameter deviation, coaxiality and cylindricity were measured. For this purpose, based on theoretical simulations, four rings of air holes arranged in a hexagonal pattern were drilled in the preforms with different drill bits, and the experimental results for the above mentioned parameters have been presented. Additionally, optical power distribution of the fabricated microstructured polymer optical fibres was theoretically calculated and experimentally measured.

Refractive index sensing characteristics in a D-shaped photonic quasi-crystal fiber sensor based on surface plasmon resonance

A D-shaped photonic quasi-crystal fiber (PQF) sensor based on surface plasmon resonance is proposed for refractive index (RI) sensing. The influences of the width of the gold film, the diameter of the air holes, and the thickness of the gold film on the sensing performance are analyzed. When the RI of a liquid analyte gradually increases from 1.415 to 1.427, the average sensitivity is calculated as 10,250 nm/RIU, and the maximum sensitivity is up to 34,000 nm/RIU, which realizes the high-sensitivity sensing in the near-infrared band. The D-shaped PQF sensor proposed has great application potential in the detection of biochemical analytes and provides a new way to improve the sensing performance.

Analysis and design of fibers for pure-quartic solitons

The recently discovered pure-quartic solitons, arising from the interaction of quartic dispersion and Kerr nonlinearity, open the door to unexplored soliton regimes and ultrafast laser science. Here, we report a general analysis of the dispersion and nonlinear properties necessary to observe pure-quartic solitons in optical platforms. We apply this analysis, in combination with numerical calculations, to the design of pure-quartic soliton supporting microstructured optical fibers. The designs presented here, which have realistic fabrication tolerances, support unperturbed pure-quartic soliton propagation providing access to an unmatched platform to study novel soliton physics.

Tellurite glass defect-core spiral photonic crystal fiber with low loss and large negative flattened dispersion over S + C + L + U wavelength bands

A defected-core spiral photonic crystal fiber is proposed to achieve very large negative flattened dispersion and small confinement loss. Simulation results reveal that the designed structure exhibits very large flattened dispersion over S+C+L+U wavelength bands and an average dispersion of about -720.7  ps nm(-1) km(-1) with an absolute dispersion variation of 12.7  ps nm(-1)  km(-1) over the wavelength ranging from 1.45 to 1.65 μm. The proposed fiber has five air-hole rings in the cladding leading to very small confinement loss of 0.00111  dB/km at the excitation wavelength of 1.55 μm. The tolerance of the fiber dispersion of ±2% changing in the structural parameters is investigated for practical conditions.

Air-structured optical fiber drawn from a 3D-printed preform

A structured optical fiber is drawn from a 3D-printed structured preform. Preforms containing a single ring of holes around the core are fabricated using filament made from a modified butadiene polymer. More broadly, 3D printers capable of processing soft glasses, silica, and other materials are likely to come on line in the not-so-distant future. 3D printing of optical preforms signals a new milestone in optical fiber manufacture.

Endlessly single-polarization single-mode holey fibers with low confinement loss

We present a novel structure for holey fibers (HFs) with endlessly single-polarization single-mode characteristics, which is realized by introducing four elliptical airholes arranged in a hexagonal matrix in the core region. The validation of the design is done by use of a full-vectorial finite element method. We exhibit one typical design that can deliver a single-polarization single-mode region of more than 2400 nm with a confinement loss level lower than 0.01 dB/km. We have also shown that the persevered polarization state possesses a wide wavelength band of flat dispersion behavior. As a consequence, such HFs are useful in high-speed communication systems or optical-fiber sensors since they are free of polarization mode dispersion and simultaneously immune to cross-talk effect.

Control of the properties of micro-structured waveguides in lithium niobate crystal

We study numerically depressed-index cladding, buried, micro-structured optical waveguides that can be formed in a lithium niobate crystal by femtosecond laser writing. We demonstrate to which extent the waveguiding properties can be controlled by the waveguide geometry at the relatively moderate induced refractive index contrasts that are typical of the direct femtosecond inscription.

Dispersion-stabilized highly-nonlinear fiber for wideband parametric mixer synthesis

Conventional highly-nonlinear fiber (HNLF) designs are optimized for high field-confinement but are also inherently susceptible to dispersion fluctuations. The design compromise prevents fiber-optical parametric mixers from possessing high power efficiency and extended operating bandwidth simultaneously. Using a new fiber waveguide design, we have fabricated and tested a new class of HNLF that possesses a significantly lower level of dispersion fluctuations while maintaining a high level of field-confinement comparable to that in conventional HNLFs. The fiber was used to demonstrate an all-fiber parametric oscillator operating in short-wavelength infrared (SWIR) band with a watt-level pump, for the first time.

Supercontinuum generation for coherent anti-Stokes Raman scattering microscopy with photonic crystal fibers

Photonic crystal fiber (PCF) designs with two zero-dispersion wavelengths (ZDWs) are experimentally investigated in order to suggest a novel PCF for coherent anti-Stokes Raman scattering (CARS) microscopy. From our investigation, we select the optimum PCF design and demonstrate a tailored spectrum with power concentrated around the relevant wavelengths for lipid imaging (648 nm and 1027 nm). This new PCF is characterized by varying the fiber length, the average power, and the pulse width of the fs pump pulses. It was found that the selected PCF design gave a significantly improved spectral distribution compared to an existing PCF for CARS microscopy. Furthermore, the PCF is designed in a twofold symmetric structure allowing for polarization maintaining propagation. Finally, the pulse propagation is investigated numerically showing good agreement with the measured spectrum. From the numerical analysis, the nonlinear effects responsible for the spectral broadening are explained to be soliton fission processes, dispersive waves, and stimulated Raman scattering.

Enhancement of chemical sensing capability in a photonic crystal fiber with a hollow high index ring defect at the center

A new type of index-guided photonic crystal fiber is proposed to enhance chemical sensing capability by introducing a hollow high index ring defect that consists of the central air hole surrounded by a high index GeO2 doped SiO2 glass ring. Optical properties of the fundamental guided mode were numerically analyzed using the full-vector finite element method varying the design parameters of both the defects in the center and the hexagonal air-silica lattice in the cladding. Enhanced evanescent wave interaction in the holey region and lower confinement loss by an order of magnitude were achieved simultaneously, which shows a high potential in hyper sensitive fiber-optic chemical sensing applications.

Structure fits the purpose: photonic crystal fibers for evanescent-field surface-enhanced Raman spectroscopy

We report numerical simulation and hyperspectral Raman imaging of three index-guiding solid-core photonic crystal fibers (PCFs) of different air-cladding microstructures to assess their respective potential for evanescent-field Raman spectroscopy, with an emphasis on achieving surface-enhanced Raman scattering (SERS) over the entire fiber length. Suspended-core PCF consisting of a silica core surrounded by three large air channels conjoined by a thin silica web is the most robust of the three SERS-active PCFs, with a demonstrated detection sensitivity of 1x10(-10) M R6G in an aqueous solution of only approximately 7.3 microL sampling volume.

Mode degeneration in bent photonic crystal fiber study by using the finite element method

The development of highly dispersive lower and higher order cladding modes and their degeneration with respect to the fundamental core mode in a bent photonic crystal fiber is rigorously studied by use of the full-vectorial finite element method. It is shown that changes in the bending radius can modify the modal properties of large-area photonic crystal fibers, important for a number of potential practical applications.

High birefringence photonic crystal fiber with a complex unit cell of asymmetric elliptical air hole cladding

High birefringence induced by elliptical air hole photonic crystal fibers (EHPCFs) is analyzed numerically using the finite-element method. Statistical correlations between the birefringence and the various parameters are obtained. We found that the complex elliptical air hole is better than that of a circular one to obtain high birefringence in photonic crystal fibers. Our suggested structures can considerably enhance the birefringence in EHPCFs and show that the birefringence can be as high as 1.1294 x 10(-2), which is higher than the birefringence obtained from conventional step-index fiber (5 x 10(-4)), circular air holes PCF (3.7 x 10(-3)), and elliptical hollow PCF (2.35 x 10(-3)).

Experimental and theoretical investigations of birefringent holey fibers with a triple defect

We have manufactured and characterized a birefringent holey fiber of a new construction. The birefringence in this fiber is induced by the highly elliptical shape of the core, which consists of a triple defect in a hexagonal structure. Using a hybrid edge-nodal finite-element method, we calculated the spectral dependence of phase and group modal birefringence for spatial modes E11 and E21 in idealized and in real fiber, whose geometry we determined by using a scanning-electron microscope. Results of our calculations show that technological imperfections significantly affect the fiber's birefringence. Normalized cutoff wavelengths for higher-order modes relative to the filling factor were also determined for the idealized structure. We observed a significant disagreement between theoretical and experimental values of cutoff wavelengths, which was attributed to high confinement losses near the cutoff condition. We also measured the spectral dependence of the phase and the group modal birefringence for spatial modes E11 and E21. The measured parameters showed good agreement with the results of modeling.

Finite-element analysis of birefringence and dispersion properties in actual and idealized holey-fiber structures

Using a full-vector finite-element method, we calculate birefringence and dispersion in index-guiding photonic crystal fibers, also called holey fibers. Through real-model simulations the polarization-dependent dispersion in actual fiber structures is numerically demonstrated, for the first time to our knowledge. Furthermore the transverse-electric-field vector distributions in the fabricated holey fibers are also clarified for the two linearly polarized fundamental modes.

Characterization of microstructured optical fibers for wideband dispersion compensation

Microstructured optical fibers (MOFs) with small hole-to-hole spacing and large airholes are designed to compensate the anomalous dispersion and the dispersion slope of single-mode fibers. The geometrical parameters that characterize triangular MOFs are chosen to optimize the fiber length and the compensation over a wide wavelength range. A proper design of the photonic crystal fiber geometry allows us to achieve dispersion values of approximately -1700 ps nm(-1) km(-1) at 1550 nm and to compensate the dispersion of standard fibers within +/- 0.5 ps nm(-1) km(-1) over a 100-nm range. The MOF dispersion properties have been studied by means of a numerical simulator for modal analysis based on the finite-element method.

Reduced microdeformation attenuation in large-mode-area photonic crystal fibers for visible applications

We consider large-mode-area photonic crystal fibers for visible applications in which microdeformation-induced attenuation becomes a potential problem when the effective area A(eff) is sufficiently large compared to lambda2. We argue that a slight increase in fiber diameter D can be used in screening the high-frequency components of the microdeformation spectrum mechanically, and we confirm this experimentally for both 15- and 20-microm core fibers. For typical bending radii (R approximately 16 cm) the operating bandwidth increases by approximately 3-400 nm to the low-wavelength side.

Improved large-mode-area endlessly single-mode photonic crystal fibers

We numerically study the possibilities for improved large-mode-area endlessly single-mode photonic crystal fibers for use in high-power delivery applications. By carefully choosing the optimal hole diameter, we find that a triangular core formed by three missing neighboring air holes considerably improves the mode area and loss properties compared with the case with a core formed by one missing air hole. In a realized fiber we demonstrate an enhancement of the mode area by approximately 30% without a corresponding increase in the attenuation.

Chromatic dispersion and losses of microstructured optical fibers

Using a rigorous and vector multipole method, we compute both losses and dispersion properties of microstructured optical fibers with finite cross sections. We restrict our study to triangular lattices of air-hole inclusions in a silica matrix, taking into account material dispersion. The fiber core is modeled by a missing inclusion. The influence of pitch, hole diameter, and number of hole rings on chromatic dispersion is described, and physical insights are given to explain the behavior observed. It is shown that flattened dispersion curves obtained for certain microstructured fiber configurations are unsuitable for applications because of the fibers' high losses and that they cannot be improved by a simple increase of the number of air-hole rings.

Resonance and scattering in microstructured optical fibers

We present an investigation into the mechanism for guidance of microstructured optical fibers consisting of high-refractive-index cylinders embedded in a low-index background. A new guidance regime is identified in which the fibers' confinement losses depend strongly on wavelength and the positions of the loss minima and maxima depend on the scattering properties of individual cylinders and only weakly on their position and number. We point out similarities between these results and those reported recently for two-dimensional antiresonant reflecting waveguides.

Cylinder gratings in conical incidence with applications to modes of air-cored photonic crystal fibers

We develop a formulation for cylinder gratings in conical incidence, using a multipole method. The theory, and its numerical implementation, is applied to two-dimensional photonic crystals consisting of a stack of one-dimensional gratings, each characterized by its plane wave scattering matrix. These matrices are used in combination with Bloch's theorem to determine the band structure of the photonic crystal from the solution of an eigenvalue problem. We show that the theory is well adapted to the difficult task of locating the complete band gaps needed to support air-guided modes in microstructured optical fibers, that is, optical fibers in which the confinement of light in a central air hole is achieved by photonic band-gap effects in a periodic cladding comprising a lattice of air holes in a glass matrix.

Modal cutoff in microstructured optical fibers

We analyze the nature of modal cutoff in microstructured optical fibers of finite cross section. In doing so, we reconcile the striking endlessly single-mode behavior with the fact that in such fibers all propagation constants are complex. We show that the second mode undergoes a strong change of behavior that is reflected in the losses, effective area, and multipolar structure. We establish the parameter subspace in which the fibers are single mode and an accurate value for the limit of the endlessly single-mode regime.