This PDF file contains the front matter associated with SPIE Proceedings Volume 10681, including the Title Page, Copyright information, Table of Contents, and Conference Committee listing.

The realization of a new type of a photonic band gap (PBG) optical fiber based on the infiltration of an endlessly single mode microstructured optical fiber with 2-methyl 4-nitroaniline (MNA) is presented in this work. A commercially available microstructured optical fiber (LMA-10) with single mode operation over a large wavelength range was used for filling its capillaries with molten MNA. The all-solid MNA-silica PBG optical fiber was characterized over a broad range of wavelengths, from the absorption bandgap of the MNA (~450nm) to near infrared, using objective lens light coupling. The transmission spectra obtained revealed three wavelength regimes of particular interest: for short wavelengths (450nm to ~800nm) distinct bandgap guidance was observed, then for a band between 800nm and 1200nm, the composite optical fiber exhibited high losses, and finally for wavelengths longer than 1200nm a gradual increase of the transmitted throughput was measured. That particular guiding behavior is attributed to the high refractive index dispersivity of MNA. The photonic bandgaps amplitude measured for the first regime of light guidance is dependent upon the infiltration conditions and post-infiltration processing of the composite optical fiber. An increase in the strength of the formed bandgaps was observed after annealing the composite optical fiber at a temperature gradient from 110°C to 50°C with a pulling speed lower than 10mm/hr, for assisting crystallization of the infiltrated MNA.

The spectral UV properties of silica-based multi-mode and few-modes fibers will be shown using pulsed 355 nm lasers with pulse density levels close to damage threshold. A new experimental set-up with spectral analyses and parallel damaging will be introduced and discussed. Using pulsed UV-laser with good beam quality, low-mode fibers can be studied in respect to spectral losses in a wavelength region significantly below the wavelength of operation.

Hollow-core fibers (HCFs) which guide light by an antiresonant reflection from arrays of silica walls have been attracting much interest due to their extraordinary optical properties and potential interdisciplinary applications including highly efficient laser-matter interaction, ultra-short pulse delivery, pulse compression and low-loss mid-infrared transmission. There are several types of HCFs having either a photonic crystal cladding, Kagome lattice or a single cycle of capillaries surrounding the core. In the latter case the antiresonant guidance properties depend strongly on the core size and the shape of the core/cladding boundary. In this work, we focus on the capabilities of two HCF designs (negative curvature of the core/cladding boundary and nodeless capillary structure) to obtain a nearly single-mode guidance from the visible to the mid-infrared spectral regions. The first HCF (Sample A) was drawn from the stack comprising a cycle of eight touching capillaries having the wall thickness 1.5 µm which provided a negative curvature of the core/cladding boundary. The fiber was intentionally manufactured with the trapezoidal shape of the capillaries in order to minimize the interaction between the surface modes, trapped amidst the touching trapezoids, and the fundamental mode in a hollow core. The negative curvature of the boundary resulting in the octagonal shape of the core was achieved by putting an excess gas pressure inside the capillaries during the drawing process. The second HCF (Sample B) was produced from the stack comprising a cycle of six non-touching capillaries having the wall thickness 2.5 µm with a view to restrict the abovementioned interaction via breaking the surface modes coupling between the adjacent capillaries. As in the first case, the gas pressure was controlled carefully to keep all capillaries separately from each other. In both samples the core diameter was equal to 50 µm ensuring a relatively large effective mode area. Taking into account the periodic nature of HCFs transmission windows, we simulated and measured accurately transmission spectra and modal properties of the fibers. The simulations were performed using the finite element analysis. The transmission spectra were measured by passing light from the tungsten halogen lamp through the samples of 35 cm long and registering output signal applying three optical spectrometers covering the wavelength range 600-2500 nm. We observed a good agreement between the simulation and the experiment. The Sample A has transmission windows at the wavelengths 650, 750, 850-900, 950-1050, 1150-1300, 1450-1700, 2000-2300 nm and the Sample B – at the wavelengths 600, 650-700, 750-800, 850-950, 1000-1100, 1150-1350, 1450-1750, 1900-2400 nm. The mid-infrared window for the Sample B is larger and more pronounced in terms of relative transmission due to the larger wall thickness at the core/cladding boundary. Moreover, the Sample B is predicted to be practically single-mode in the considered spectral region, as the losses of the most competitive higher-order modes are estimated to be much above 1 dB/m. A similar regime for the Sample A is expected only when operating at the long-wavelength limit of the spectral region, due to the increase in the fundamental and higher-order modes refractive index difference.

The sol-gel based granulated silica method has several advantages for the production of active optical fibers. It offers a high degree of freedom regarding the usable dopants and co-dopants, the maximum possible dopant concentration and the homogeneity of the dopants. The freedom in controlling the co-dopant concentration enables the full control to tailor the refractive index of the core. Several ytterbium (Yb) doped, aluminum (Al) and phosphorus (P) co-doped double cladding silica fibers with varying Al and P co-dopants concentrations have been produced by the sol-gel based granulated silica method, in order to study the influence of the different co-dopants concentrations on the fibers performance. To do so, we fixed the Yb concentration to 0.3 at% in all the fibers, as well as the cores and claddings diameters to 10 and 125 micrometer respectively. The variation of the core-cladding refractive index steps due to the different Al and P co-dopants concentration have been confirmed by measuring the one dimensional and two dimensional refractive index profile of every fiber by two different measurement apparatus, resulting in core-cladding refractive index steps that correspond well with the fibers compositions. In addition, the effect of the different co-dopants concentration on the fibers performance have been investigated by measuring the upper state lifetimes and the lasing performance (slope efficiency) of the fibers. We observed different fluorescence lifetimes among the differently co-doped fibers, and different slope efficiencies that are well correlated with the corresponding lifetime of each fiber. One of the fibers featured 60% slope efficiency at 1030nm by pumping the fiber at 976nm by a fiber-pigtailed laser diode (LD).

Space division multiplexing (SDM) technique is proposed to overcome the bandwidth density drives of short-reach optical transmission systems by utilizing 8-core multicore fiber (MCF). Intercore crosstalk (XT) and higher order modulation format are the most challenging impairments of SDM based optical interconnect (OI) systems. To satisfy the exponential growth of the Internet traffic a frequency interleaving scheme is applied to short-reach MCF OI transmission systems. The negative effects of spectral overlap and intercore XT is reduced by shifting channel frequencies between adjacent cores. To exploit the full potential of SDM power efficient binary phase shift keying (BPSK) modulation format and digital signal processing such as multiple input multiple output (MIMO) equalization are used.

We report our latest investigations on 2D-layered materials integrated fiber optic configurations for chemical and labelfree biosensing applications. Due to the favorable combination of exceptionally high surface-to-volume ratio and excellent optical and biochemical properties, graphene oxide (GO) and black phosphorus (BP) were deposited on fiber grating device as the bio-photonic linking layer to provide the remarkable platform for light-matter interface and affinity binding interaction. We developed a novel in-situ layer-by-layer (i-LbL) deposition technique based on chemicalbonding associated with physical-adsorption for the deposition of 2D materials. This approach secured high-quality 2D materials deposition on cylindrical fiber with strong adhesion as well as a prospective thickness control. By taking advantage of i-LbL deposition, the unique optical tunable features and polarization-selective characteristics have been experimentally observed. Several 2D material integrated fiber optic sensors have been proposed for chemical and biochemical applications, such as GO-long period grating (GO-LPG) based Hemoglobin sensor, GO dual-peak LPG (GO-dLPG) based label-free immunosensor, and the first BP fiber optic chemical sensor based on BP-tilted fiber grating (BP-TFG). We believe that 2D material integrated fiber optic configurations open the path as highly sensitive biophotonic platform for food safety, environmental monitoring, clinical diagnostics and biomedical applications.

We demonstrate a long period grating (LPG) inscription in microstructured polymer optical fibers (mPOFs) using a single 248 nm UV laser pulse of 15 ns duration for every inscription point using a point by point technique with total length of 25 mm. The fabrication time indicates shortening for a single coupling point (15 ns against 42 s reported in literature). A grating with 20 dB transmission dip has been fabrication by using two UV pulses for each coupling point. The device has been fabricated in mPOF with a core that has been doped with benzyl dimethyl ketal (BDK) for photosensitivity increase. The strain and temperature responses of the fabricated gratings under different conditions have been characterized in order to assess the viability for sensing applications. Better performance was achieved with suitable post annealing process of the gratings.

Polymer optical fibre (POF) has been receiving increasing attention for sensing applications. The fundamental properties of POF such as PMMA deliver at least an order of magnitude in improvements over silica fibres, though practical difficulties create additional complexity. POF has the potential to deliver lower acoustic impedance, a reduced Young’s Modulus and a higher acoustic sensitivity within the megahertz region. In contrast, existing piezo-electric transducers have an inherent narrow acoustic bandwidth and a proportionality to size that causes difficulties for applications such as endoscopy within the biomedical domain. POF generally suffers high attenuation per kilometre at telecommunications wavelengths, limiting fibre lengths to mere centimetres. However, CYTOP, a graded index perfluorinated polymer, is a commercially certified product allowing the use of telecoms region technology and tens of meters of fibre without exceeding acceptable losses. With an effective refractive index between 1.32 and 1.33, it is fundamentally better placed for applications using water or a similar media for acoustic coupling. We demonstrate ultrasonic detection at 5,10 and 15 MHz using a TFBG within a CYTOP fibre in the telecoms region and the latest knowledge in POF handling and connectorisation. This first step in the use of CYTOP demonstrates the viability of the sensor and paves the way towards further advances towards its eventual application.

We present a novel method based on optical fibre tapering for fabrication of Surface Nanoscale Axial Photonics (SNAP) devices with parabolic profiles with an unprecedentedly large number of axial eigenmodes. Tapering of a commercial 125 μm single-mode optical fibre to a 30 μm diameter waist by laser brushing creates a SNAP bottle microresonator with parabolic radius variation in the centre of the tapered region. Ideal parabolic resonators should demonstrate equal spacing between resonances. Our spectral measurement of the parabolic profile shows spacing of ~6 GHz with 10% deviation over a bandwidth of 2.5 THz containing up to 400 axial eigenfrequencies. This new discovery for the creation of SNAP parabolic microresonator devices is important for fabrication of miniature delay lines, buffers and frequency comb generators. Characterisation of our exemplar microresonators is briefly explored, particularly for broadband frequency comb generators which require equidistant frequency spacing. Further investigations include scaling of the parabolic feature with tapering process parameters, repeatability testing, and the fabrication of more complex shapes.

In this paper we describe the results of laser damage threshold studies conducted on silica fibers with etched random anti-reflection surfaces on their end faces. This study includes damage threshold of Motheyed surfaces on witness sample and fibers. Initial work has shown very promising results with damage thresholds greater than 46J/cm² at 755nm on fibers.

Ever growing importance of optical fiber technology in the fields of data transfer, sensors, imaging or advanced light generation pushes the effort of integration of functional microoptical elements in the fiber based systems [1]. Here we present a femtosecond (fs) pulse based 3D laser lithography (3DLL) of free-form polymeric structures on tips of single mode optical fibers. Fabricated objects include both microoptical elements (for instance aspheric microlenses) and woodpile photonic crystals. Also, freeform 3D monoliths, combining several of these elements into one functional component, are integrated on the tip of the fiber [2, 3]. Methods allowing enhancement and large scale fabrication, such as advanced fiber holders or synchronization of linear stages and galvo-scanners, are discussed. In contrast to standard lithographic techniques, fs 3DLL can be employed for processing a wide array of materials, including otherwise non-processable (non-photosensitized) polymers. It is relevant to the most of the fields where microoptics are applied, as photoinitiators introduce additional short wavelength (<400 nm) absorption to the material, resulting in information loss, lower optical damage threshold, parasitic fluorescence and, therefore, should be avoided if possible. One material that could be structured in this fashion is hybrid organic-inorganic zirconium containing SZ2080 which displays many favourable qualities such optical transparency and low shrinkage [4]. Here we provide notes on peculiarities of 3DLL of a pure SZ2080. Experimental results show that compared to photosensitized counterpart photoinitiator-free polymer has comparable characteristics when it comes to fabrication throughput, optical properties (transmission spectra and surface roughness), mechanical strength (structure survival rate and adhesion to the substrate) as well as others. A physical phenomenon behind fs structuring of pure material such as interplay between multiphoton absorption and avalanche ionization [5] is highlighted. Optical resiliency of microoptical elements created with this technology is investigated and their feasibility in applications reliant on high light intensities is shown. The most resistant material was found to be non-photosensitized SZ2080 as microlenses produced out of such material can withstand peak intensities of 515 nm 300 fs 200 kHz laser in range of GW/cm^2 within minutes to hours [6]. Such results tie well with earlier findings showing that optical damage threshold of pure materials films are in fact higher than that of a photosensitized material [7]. Additionally, CW 405 nm laser operating at the intensity of 8.66 GW/cm^2 cannot damage microoptical elements produced out of SZ2080 in pure and photosensitized form even after tens of hours of continuous exposure. Further comparison with the optical resiliency of microoptical elements fabricated out of other lithographic materials such as Ormocer and SU8 are made. References: [1] Gissibl et al., Nat. Commun. 7, 11763 (2016). [2] Brasselet et al., Appl. Phys. Lett. 97, 211108 (2010). [3] Žukauskas et al., J. Laser Micro. Nanoen. 9, 68 (2014). [4] Ovsianikov et al., ACS Nano 2, 2257 (2008). [5] Buividas et al., Opt. Mater. Express 3, 1674 (2013). [6] Jonušauskas et al., Materials 10, 12 (2017). [7] Žukauskas et al., Opt. Mater. Express 4, 1601 (2014).

This paper presents a study focusing on a fabrication process to shape an optical fibre tip capable of producing a photonic nanojet. Photonic nanojet generated in the near field of a dielectric bead have been comprehensively studied. Contradicting the usual laws of optical geometry, this propagative, slightly diverging, light beam can have a Full Width at Half Maximum smaller than a half-wavelength, subsequently going beyond the diffraction limit. Thanks to these useful properties, the photonic nanojet is an ideal tool for near-field optical microscopy and subwavelength micromachining. Nevertheless, for a repeatable and industrial processes, one need to bypass the use of dielectric beads that are tedious to manipulate. A photonic jet can also be generated at the end of a shaped optical fiber tip. Optical fibres are commonly shaped by various methods revolving around thermoforming. Unfortunately, the thermoforming process has some limitations: controlling the curvature of the tip is hazardous and the effect on the diffusion of the dopant in the core and cladding is unknown. Nonetheless, other approaches to optical fibre shaping have been investigated by the scientific community. A promising method, further investigated in this work, is chemical etching with hydrofluoric acid. The process, often labelled as highly hazardous due to the nature of the chemical involved, offers a great way to carefully shape the tip of silica based-fibre. The optimisation of the fibre tip shape, in order to get the desired photonic jet, was made by 2D modelisation, by finite elements method. The wanted tip shape is then obtained by thermoforming, chemical etching and the combination of two methods. The thermoforming was done by electric arc. The isotropical etching was performed in a solution of 24 % HF. The characterisation of the fibre tips was carried out by the direct ablation of silica and photosensitive resin insulation using respectively 1064 nm and 514 nm lasers. The results were studied by optical microscopy and white light scanning interferometry. Insulated spots of 3.5 µm were measured on SU8. Ablated spots of 685 nm were observed on silica. These encouraging results prove that the combination of thermoforming and chemical etching can lead to highly accurate fibre tip shaping for Photonic NanoJet generation and thus open the way to enhanced sub-wavelength Material Laser Processing.

The new manufacturing method for fabrication of Surface Nanoscale Axial Photonics (SNAP) structures has been developed. We showed experimentally that the bent fiber can achieve the nanometer-scale variation in the effective fiber radius sufficient for fabrication of SNAP microresonators. The advantage of the demonstrated method is in its simplicity, robustness, and mechanical tunability of the fabricated devices.

The paper presents the results of design, manufacturing and characterization of an hybrid broad band in-line device using a nematic liquid crystal as an active medium which influences light propagating in a biconical optical fibre taper. A liquid crystal mixture denoted 6CHBT*and E7 is designed for electric, as well as temperature control of electromagnetic wave propagation in a broad wavelength range. The main reason of using the taper structure with a waist of 10± 0.5 μm and losses lower than 0.5 dB is possibility of using a liquid crystalline medium as cladding. Such approach enables effective control of its refractive index. Two kinds of initial liquid crustal molecules’ orientation (parallel and orthogonal) in relation to the light beam propagating in a taper were applied. Performance of a tuned cladding was studied at electric field of the range of 0V – 160V in the room temperature equal to 20°C. Influence of induced reorientation of liquid crystal molecules was measured at a broad wavelength range [500-1700 nm].

We provide a detailed explanation of the effect of coupling in helical microstructured optical fibers (MOFs) based on decomposition of core and cladding modes into multiple angular harmonics, each carrying integer orbital angular momentum and spin. The obtained results show that in twisted hexagonal MOFs, the fundamental mode characterized by spin σ may couple only to the cladding modes composed of harmonics carrying the total angular momentum J=6K+σ, where K is an integer number. Strongest couplings are observed to the cladding modes composed primarily of the harmonics with the same spin as the fundamental mode. However, there is also a second type of coupling to the modes composed primarily of the harmonics with opposite spin, which we identify for the first time in case of twisted MOFs. These couplings result in polarization dependent narrow maxima in loss characteristics of the fundamental modes. Furthermore, we explain how the harmonic of opposite spins influence the ellipticity angle distribution in the cladding modes.

We demonstrate narrow band spectral intensity switching in dual-core photonic crystal fibers made of highly nonlinear glass under femtosecond excitation. The fibers expressed dual-core asymmetry, thus the slow and fast fiber cores were unambiguously distinguished according to their dispersion profiles. The asymmetry effect on the dual-core propagation in anomalous dispersion region was studied both experimentally and numerically. The experimental study was carried out using femtosecond laser amplifier system providing tunable pulses in range of 1500 nm - 1800 nm. The obtained results unveiled, that it is possible to improve nonlinearly the coupling between the two waveguides by excitation of the fast fiber core. The results were obtained in regime of high-order soliton propagation and were verified numerically by the coupled generalized nonlinear Schrödinger equations model. The spectral analysis of the radiation transferred to the non-excited core revealed the role of effects such as third order dispersion, soliton compression and spectral dependence of the coupling efficiency. The simulation results provide reasonable agreement with the experimentally observed spectral evolutions in the both fiber cores. Under 1800 nm excitation, narrow band spectral intensity switching was registered with contrast of 23 dB at 10 mm fiber length by changing the excitation pulse energy in sub-nanojoule range.

A variety of optical components are fabricated by the so called “Heat and Pull” technique in which optical fibers are fused and tapered. A numerical model simulating the temporal and spatial material distribution in such components is presented and validated by comparison with experimental results.

Over the years, numerous models and tools have been developed to simulate the optical behavior of fused fiber-optic components. While these models are well established, their predictions depend on accurate knowledge of the component’s physical structure and its refractive index distribution. Unfortunately, no such generic simulation tools are readily available. The need of a high fidelity structural simulation tool for such components is further emphasized in complex systems, which are difficult to fabricate and are optically sensitive to small structural variation. In view of the above, we developed a novel numerical methodology based on Immersed Boundary (IB) Method specifically designed to simulate flows in the presence of complex geometries and moving boundaries. In the present formulation pressure and interface curvature are implicitly embedded into the system of incompressible Navier-Stokes equations as distributed Lagrange multipliers. The developed methodology is currently capable to simulate two phase flows in two dimensions and is also adapted to solve quasi-3D evolutions. For validation, the simulation output is compared to the cross-sectional material distribution of a real component fabricated at our lab. The developed model, as well as the experimental results and the comprehensive analysis predicting the structure of symmetric and non-symmetric optic fiber components are presented and discussed.

We demonstrate a simple and efficient technique that allows for a complete characterization of silica-based tapered optical fibers with sub-wavelength diameters ranging from 0.5 μm to 1.2 μm. The technique is based on Brillouin reflectometry using a single-ended heterodyne detection. It has a high precision sensitivity down to 1% owing to the strong dependence of the Brillouin spectrum on the taper diameter. We further investigate the tensile strain dependence of the Brillouin spectrum for an optical microfiber up to 5% of elongation. The results show strong dependences of several Brillouin resonances with different strain coefficients ranging from 290 MHz/% to 410 MHz/% with a specific nonlinear deviation at high strain. Those results therefore show that optical micro and nanofibers could find potential application for sensitive strain optical sensing.

The propagation of light pulses through the chirped Bragg structures with superimposed PT-symmetric complex potential (gain and loss) has been studied using the numerical methods. The reflective properties of such structures in the regime below PT-symmetry breaking threshold are discussed. It is shown, that due to the balanced amplification of different spectral components of a reflected pulse such structures can effectively transform the profile of a reflected pulse and at the same time amplify its amplitude.

Surface Plasmon resonance (SPR) optical fiber sensors can be used as a cost-effective and relatively simple-toimplement alternative to well established bulky prism configurations for in-situ high sensitivity biochemical and electrochemical measurements. The miniaturized size and remote operation ability offer them a multitude of opportunities for single-point sensing in hard-to-reach spaces, even possibly in vivo. Grating-assisted and polarization control are two key properties of fiber-optic SPR sensors to achieve unprecedented sensitivities and limits of detection. The biosensor configuration presented here utilizes a nano-scale metal-coated tilted fiber Bragg grating (TFBG) imprinted in a commercial single mode fiber core with no structural modifications. Such sensor provides an additional resonant mechanism of high-density narrow cladding mode spectral combs that overlap with the broader absorption of the surface Plasmon for high accuracy interrogation. In this talk, we briefly review the principle, characterization and implementation of plasmonic TFBG sensors, followed by our recent developments of the “surface” and “localized” affinity studies of the biomolecules for real life problems, the electrochemical actives of electroactive biofilms for clean energy resources, and ultra-highly sensitive gas detection.

Fiber-based evanescent wave spectroscopy in the mid-IR is a powerful tool for the remote chemical analysis of liquids and gases in real time. Design of a sensing element of the fiber sensor is important for optimization of its output characteristics. In addition to unclad chalcogenide fibers that were previously used as the sensing elements, we consider core-clad fibers consisting of a multimode core and a ring cladding with the refractive index greater than that one of the core. For numerical analysis, a theoretical approach based on electromagnetic theory of optical fibers has been used. Calculated transmittance of the sensing elements is compared with the measured output characteristics of a sensing element made of an unclad chalcogenide fiber, which was immersed into aqueous acetone solutions.

Solution doping of off-the-shelf plastic optical fibers (POFs) represents rather simple and cheap way for preparing custom cladding-doped POFs (CD-POFs) with short to medium lengths. CD-POFs are especially attractive for environmental sensing applications, but might be of interest for illumination task as well. In this work, the proposed doping technique is tested with three different commercial low-cost polymethyl methacrylate (PMMA) POFs; Eska CK-40 and Eska GK-40 from Mitsubishi Rayon and Raytela PGU-FB1000 from Toray. The aim of the work is to aid the selection of the most suitable fiber yielding highest optical quality of prepared CD-POFs. Firstly, the optimal doping times are determined for the individual fiber types using short fiber samples. Secondly, longer 10 m CD-POFs are prepared from all tested fibers using the optimized doping procedure. Finally, attenuation of pristine POFs and prepared CD-POFs is measured using optical time domain reflectometry in order to characterize the impacts of the doping on fiber optical properties. In addition, the importance of post-doping drying procedure for CD-POF optical performance is investigated as well. The results suggest that, although doping of all tested fibers is generally feasible, Eska CK-40 is the most suitable candidate with regard to the doping efficiency and fiber post-doping performance.

Smart textiles, also known as smart garments, smart clothing, or smart fabrics are revolutionizing our world because of their ability to sense, communicate, conduct energy, and transform providing a new sense reality to our daily lives. Over the past years our research group at Redondo Optics and support collaborators have been working on developing novel methods for embedding fiber optic sensors within high performance “Smart” textile synthetic materials used in the manufacturing of fabrics, ropes, and cables.

We present a novel fiber type with a trilobal, non-circular cross section. The fiber is designed for illumination purposes with a special shape in order to form a distinct asymmetrical radiation pattern, which can be used to concentrate light on particular locations in order to cure resins or polymers but can also find its applications for illumination purposes.

Optical fibers have been employed for several years in biomedicine and mainly used for light delivery and collection with high efficiency and selectivity. So far most of the research effort has been devoted to the optical configurations and the functions of the fibers rather than on the materials employed. Indeed, this aspect has been mainly considered to assure biocompatibility with tissues and non-toxic behavior limiting the choice mostly to silicate fibers. We report on the recent advances in engineering inorganic glass optical and hollow fibers fabricated with optical glasses which are also resorbable in body fluids. Suitable phosphate glass compositions were designed to combine resorbability and optical transparency. Glasses were fabricated by melt-quenching inside a chamber furnace under a flux of dried air and cast into preheated brass molds. The fibers were obtained by preform drawing, with the core rod fabricated by melt quenching whilst the cladding tube by rotational casting. Extrusion techniques were also applied to obtain more complex cross sections with increased functionalities. Glasses and fibers were characterized in their physical and optical properties. The materials showed high stability toward crystallization and a wide optical transmission window, ranging from the ultraviolet to the near infrared wavelength regions. Hollow fibers were employed to demonstrate multifunctional fiber probes, able to provide drug delivery and light excitation in the prospect of developing resorbable endoscopes for intravital monitoring and therapy, such as photodynamic therapy. Optimization of drug delivery was carried out using functionalization procedures on the surface of both bulk glasses and hollow fibers, aiming to modify the release kinetics: a silanization protocol was developed and successfully tested using different organic compounds. The modification of the surface roughness was monitored using atomic force microscopy, while surface energy changes verified using contact angle measurements. The possibility of performing drug excitation was assessed by guiding light through the capillary using optical beams produced by different wavelength sources covering the visible spectrum. Finally, mechanical characterization of the prepared optical fibers and hollow fibers was carried out to measure the elastic moduli, the tensile strength and the minimum radius of curvature attainable. The overall results allowed to demonstrate the reliability of the proposed optical fibers and hollow fibers for biomedical applications.

Integrating nanowires into microstructured fibers represent a promising pathway to include sophisticated functionalities into optical fibers which allowing to develop novel types of photonic devices with unprecedented properties. Beside solid materials such as plasmonic metals or soft glasses particular interesting is the combination of liquids and fibers, which allows to access new regimes for fiber optics. The first part of my presentation is related to ultrafast nonlinear light generation inside liquid core optical fibers. I will discusses our recent results on a new kind of optical soliton inside carbon-disulphide (CS2) filled liquid core fibers, which results from the hybrid nonlinear response functions of inorganic liquids, consisting of both instantaneous and noninstantaneous contributions. Using this fiber system we have measured octave-spanning mid-IR supercontinuum generation ranging from 1.1 µm towards more than 2.8 µm, showing clear indications of an improved shot-to-shot correlation, i.e., higher degree of coherence across the entire generated bandwidth at soliton numbers solely instantaneous systems deliver highly incoherent spectra, i.e., are modulatin instability driven. I will also discuss the unique temperature tuning potential of liquid core fibers, allowing to shift the central wavelength of dispersive waves by more than 100nm by locally changing the temperature within an interval of 20°C only. In the second part of the talk I will present our recent results on tracking single individual nanoobjects inside optofluidic optical fibers via elastic light scattering. The nanoobjects are located within an aqueous environment inside a well-selected channel of the microstructured optical fiber used. Light from the core mode which hits the freely diffusing nanoobject scatters off and can be detected transversely. Tracking of unlabeled dielectric particles as small as 20 nm as well as individual cowpea chlorotic mottle virus (CCMV) virions at rates of over 2 kHz for durations of tens of seconds has been achieved in nanobore optical fibers, whereas full 3D information about the nanoobject’s trajectory are retrieved in modified step index fibers. From the light scattering intensities and the diffusion constants we were able to determine key properties of the particles such as size or hydrodynamic radius.

ABSTRACT In this paper we investigate supercontinuum (SC) generation in several suspended-core soft-glass photonic crystal fibers (PCFs) pumped by an optical parametric oscillator (OPO) tunable around 1550 nm. The fibers were drawn from leadbismuth- gallium-cadmium-oxide glass (PBG81) featuring a wide transmission window from 0.5 μm till 2.7 μm and a high nonlinear refractive index up to 43×10^-20 m²/W. They have been specifically designed with a microscale suspended hexagonal core for efficient pumping around 1550 nm. This microstructure geometry also prevents from glass recrystallization and provides higher mechanical durability. We experimentally demonstrate two SC spectra spanning from 1.07 μm to 2.31 μm and 0.89 μm to 2.46 μm by pumping two PCFs in both normal and anomalous dispersion regimes at 1550 nm and 1580 nm, respectively. We further show a number of nonlinear phenomena such as spectral broadening due to self-phase modulation, soliton generation, and Raman soliton self-frequency shift in the fiber at the pumping wavelengths. We also numerically simulate the group velocity dispersion curves for these fibers from their scanning electron microscope (SEM) images.

This work presents a numerical study of a W-type index chalcogenide fiber design for Mid-Infrared (MIR) supercontinuum (SC) generation beyond 10μm. Our fiber design consists of a Ge₁₅Sb₁₅Se₇₀ glass core, a Ge₂₀Se₈₀ glass inner cladding and a Ge₂₀Sb₅Se₇₅ glass outer cladding. These chalcogenide materials have the advantages to broaden the spectrum to 12μm, due to their low material absorption. The optical mode distribution of the chalcogenide fiber is simulated by a finite element method based on edge elements. With a 6 μm core diameter and a 12 μm inner cladding diameter, the proposed fiber design exhibits flat anomalous dispersion in the wavelength range (4.3-6.5μm), with a peak of about 7ps/(nm.km). The position of the second zero-dispersion wavelength (ZDW) can be easily and precisely controlled by the inner cladding size and should be shifted to around 7μm for a 18 μm inner cladding diameter. This design is more suitable for a pump wavelength at 6.3μm which is in the anomalous dispersion regime between two ZDWs and can broaden the spectrum due to the soliton dynamics. Our fiber design modelling shows that the nonlinear parameter at 6.3μm is 0.1225W⁻¹ m⁻¹, when using a nonlinear refractive index nNL=3.44 ×10⁻¹⁸ m²W⁻¹, and the chromatic dispersion is D = 3.24ps/(nm.km). Compared to previously reported step-index fibers, the proposed W-type index chalcogenide structure ensures single mode propagation, which improves the nonlinearity, flattened dispersion profile and reduces the losses, due to a tight confinement of the mode within the core.

Publisher’s Note: This conference presentation, originally published on 23 May 2018, was withdrawn on 18 July 2019 per author request

Photonic crystal fiber (PCF) can provide both large mode area and low numerical aperture, meanwhile, offer heavy doping rate, good beam quality, and effective dispersion control. Coherent combining is an effective way to further elevate output power of a fiber laser. It is hence very beneficial to develop high-power fiber lasers using coherent combining through a multi-core PCF. In this work, by using multi-core PCF design and coherent combining technique, we studied theoretically and experimentally the multi-beam coherent combining in PCFs. We adopted a symmetrical structure to arrange multiple fiber cores, and have air holes surround them uniformly forming the cladding. Between these cores are solid glass filled. With an appropriate design of PCF structure, the coherent combining of multiple laser beams can bring higher output power up to kilowatts, while maintain good beam quality. Based on the evanescent-wave coupling theory, the modal coupling among seven cores and nineteen cores was studied. It is shown that the evanescent coupling is much stronger than the diffractive coupling if the cores are close enough. In the experiment, we fabricated rare-earth doped double-clad seven-core and nineteen-core PCFs using a stacking-capillary method. The near-field and far-field images were adopted to observe the mode coupling. Since all laser beams pass nearly the same optical length in one PCF, the phase matching can be easily realized. The theoretical and experimental results were compared, which shows that this kind of integrated multi-core PCFs can be very good candidates to achieve high-power coherent beam combining.

Three single-mode fibers have been drawn from each of four MCVD-made pure-silica-core F-doped-silica-cladding preforms, the drawing parameters (temperature, speed, and tension) being varied among the fibers in a controlled fashion. The initial optical loss spectra in the range 200-1700 nm as well as radiation-induced attenuation (RIA) spectra in the near-IR range under γ-irradiation to 82 kGy (7.6 Gy/s) are measured in the fibers. RIA is found to increase significantly with increasing the drawing temperature and to increase much less with increasing the speed and tension. The mechanism of the strong drawing temperature effect on RIA is argued to be associated with a rise in the fiber silica fictive temperature, which, in turn, enhances the concentration of strain-assisted radiation-induced self-trapped holes.

High-birefringence photonic crystal fiber (PCF) has many applications in fiber lasers, optical fiber communications and sensors, and is usually made by arranging asymmetrical air holes in its cross section. Though this design can obtain high birefringence in the fiber, it may lose the structural symmetry of mode field, and increase difficulty when connected to other fiber-optic devices. In this work, we propose a new design with a capability of having both high birefringence and good structural symmetry. Our design is based on a photonic quasi-crystal (PQC) fiber structure, in which air holes are arranged in an aperiodic order in the cladding. This kind of PQC fiber can introduce controllable birefringence into the fiber core and maintain certain symmetry of mode field. Using the full vector finite element method, we studied the mode field, birefringence, loss and nonlinear effect of the proposed PCF. It is shown that a birefringence coefficient of glt;1.5x10^-2 can be obtained at 1.55 μm.

The results on tilted fiber Bragg gratings (TFBGs) inscription using the method of transverse scanning of the fiber core by a femtosecond laser beam is reported in this paper. As an example, TFBGs consisting of unidirectional and bi-directional grating planes and having a tilt angle up to 9° are created. It is shown that different transverse mode groups of the fiber cladding can be excited with the created structures. The corresponding resonant dips reach the amplitude up to 30 dB that indicates the inscription method efficiency.

Optical transmission spectra of polysiloxane polymers used in fiber optics were investigated. Temperature dependences of the polymer absorption coefficients at pump and generation wavelengths of Yb-doped laser were measured by means of laser calorimetry. Thermal regime of the commercial fiber unit under laser generation conditions was investigated.

Supercontinuum (SC) sources offer very significant advantages for imaging and characterization of materials: full VIS-NIR spectrum availability, high spectral power density, reduced temporal coherence, among others. Certain applications require a very accurately customized emission spectrum, which in turn requires reliable tools to measure the dispersion spectra of the microstructured optical fiber of the SC source with very high spectral resolution and very short acquisition time. This measurement to be done ideally on the fly, while manufacturing the fiber, in order to fine tune the drawing variables to match the aimed dispersion profile in real time. In this work we present an interferometric method to measure chromatic dispersion using a pulsed FYLA SCT1000 supercontinuum. Very high-resolution dispersion measurement is obtained by optimization of the visibility of interferometric fringes, which is achieved by a fast synchronization of pulses overlapping.

FYLA SCT1000 Supercontinuum offers a very broadband emission with SPD close to 1 mW/nm, consisting of a train of white pulses of few ps timewidth, trigger output for synchronized measurements and very stable emission, with full spectrum average power stability < 0.5% and peak to peak stability < 1% in VIS region and < 0.6% in NIR region (stabilities refer to standard deviation over mean value). The sample to measure, which can be an optical fiber or any photonic device, is placed in one of the arms of a Michelson interferometer. Interferences obtained with different displacements give values of dispersion at different wavelengths. The standard way is to use a lamp or a SLED at each band [1,2]. This makes the measurement long and tedious. Lamps or SLEDs can be replaced by a single FYLA SCT1000 to obtain the dispersion curve in a fast and very robust way. Since the source is pulsed with a fixed rep rate, delay can be easily controlled to overlap properly light from arms of the interferometer. With a single source, the complete dispersion curve is obtained with resolution below 1 nm. In this work this synchronous interferometric method to measure dispersion is used to optimize the design and manufacture of microstructured optical fibers through an iterative protocol implemented in the fiber drawing process.

Mode division multiplexing (MDM) could bring a technological progress in the field of optical telecommunication by increasing the data transmission bandwidth. A key challenge for enabling MDM lies in manufacturing of efficient and cost-effective mode–selective fiber couplers. The fiber grating based mode selective coupling approach is a method that is currently being under research in this context. In this work a novel process for manufacturing of asymmetric evanescent field polished couplers is presented which enables grating assisted mode selective coupling. In addition, we discuss the optical setup developed for characterization of these couplers.

It is expected that opto-electronic printed wiring board (OE-PWB) will appear very soon. We study optical coupling schemes to multi-layer and multi-channel OE-OWB, and propose several optical coupling devices fabricated by using UV-curable resin. The “optical pin” is a vertical optical pillar, and that is one promising approach to achieve optical coupling with 90-deg path conversion between surface devices and optical wiring. Analysis using Optical Ray Tracing method shows that optical pin has potential to achieve higher optical coupling efficiency and larger positional tolerance. The optical pin can be fabricated by the Mask-Transfer Self-Written Waveguide (SWW) method using UV-curable resin. Next we propose optical coupling device with micro lens array. The advantage of using micro lens is that there will be no interaction between the beams crossings which means no crosstalk and noise will not occur. In addition, micro lens is flexible for fabrication. Starting fabrication of a single micro lens on tip of fiber, we succeeded in fabrication of micro lens array on patterned substrate.

Self-trapping of laser sub-pulses with basic and triple frequencies propagating in a medium with cubic nonlinear response under THG process is predicted. It appears due to cross- and self-modulation of laser pulses as well as due to SOD influence on interacting waves. Under certain conditions a sequence of sub-pulses or the single color sub-pulse with high intensity is appeared. If the sequence of the sub-pulses occurs they propagate separately each other. Observed sub-pulse formation can be used for generation of attosecond pulses at both frequencies with soliton or soliton-like shape.

Highly nonlinear optical 4-(4-dimethylaminostyryl)-1-methylpyridinium tosylate (DAST) crystals have been successfully grown in micron scale and have been fixed in polymerized mixture of isodecyl acrylate (IDA) and trimethylolpropane ethoxylate (1 EO/OH) methyl ether diacrylate (TMP). The formation of DAST crystals in polymerized thin film (2 μm) was proceeded by three steps. Firstly, an evaporation of methanol during spincoating initiated crystalization. Secondly, polymerization by UV exposure in vacuum condition fixed crystals in matrix. Thirdly, annealing process at 80 °C completed crystals growth. It was evidenced that the ratio of IDA:TMP monomers strongly influenced on DAST crystals size (from 10 microns to submicron scale) and hence influenced on properties. The absorption and luminescence spectra and the second-harmonic generation signal confirmed surface morphology of DAST crystals, which is responsible for second-order nonlinear properties. Thus created thin film with DAST crystals is promising candidate for nonlinear optical applications, in particular those employing the quasi-phase matching method.

The purpose of this study was researching the optical properties of Al-doped zinc oxide (ZnO) nanorods and nanotubes arrays by nanoimprint lithography. First, the substrate processed with nanoimprint lithography to form nanohole arrays. Based on the processed substrate we grown the Al-dope ZnO nanorods which incorporated Al(NO₃)₃·9H₂O as the Al source via the hydrothermal method. The zinc oxide nanorods were grown by hydrothermal method because it’s a simple and effective way for low temperature synthesis. The structure of Al-doped ZnO nanorods were affected by PH value of growing solution. Due to the Al source was aluminum nitrate, so we added the ammonia water to control the PH value of growing solution. Until grown the vertically oriented Al-dope ZnO nanorods that row orderly. The ZnO nanorods was transformed to nanotube via a chemical aqueous etching process with well-controlled reaction time. Therefore, the Aldoped ZnO nanorods and nanotubes arrays were obtained. Finally, the Al-doped ZnO nanorods and nanotubes arrays were characterized by field emission scanning electron microscopy (FESEM), Transmission electron microscopy (TEM), Energy Dispersive Spectrometer (EDS) and X-ray diffraction (XRD). The FESEM and TEM images showed the morphologies of Al dope ZnO nanorods were row orderly on the substrate which processed with nanoimprint lithography. The XRD and EDS analysis showed that the Al element could be successfully doped into the ZnO lattice.