Suspended-core Fiber Research Articles

All-optical fiber filter based on an FBG inscribed in a silica/silicone composite fiber.

An all-optical tunable filter based on a fiber Bragg grating (FBG) inscribed in a self-heated silica/silicone composite fiber is demonstrated. A thin silicone film is coated inside the suspended core fiber), which acts as the silicone cladding. A periodic refractive index modulation is inscribed in the silicone cladding by UV irradiation. Silicone is an organic material whose optical properties are different than silica, which leads to interesting applications. The high thermo-optic properties are studied and applied here. A 1550 nm pump laser is utilized to heat the silicone grating where a wavelength shift is observed for the gratings when subjected to different pump powers. Experimental results indicate a wavelength tuning coefficient of -0.128nm/mW with a response time of 0.5 s to obtain a wavelength shift of 1 nm under periodic pump light. The new design of this miniature all-optical filter is cost-effective and can potentially be adhered in optical fiber sensing and communication systems.

Singlemoded THz guidance in bendable TOPAS suspended-core fiber directly drawn from a 3D printer

Terahertz (THz) technology has witnessed a significant growth in a wide range of applications, including spectroscopy, bio-medical sensing, astronomical and space detection, THz tomography, and non-invasive imaging. Current THz microstructured fibers show a complex fabrication process and their flexibility is severely restricted by the relatively large cross-sections, which turn them into rigid rods. In this paper, we demonstrate a simple and novel method to fabricate low-cost THz microstructured fibers. A cyclic olefin copolymer (TOPAS) suspended-core fiber guiding in the THz is extruded from a structured 3D printer nozzle and directly drawn in a single step process. Spectrograms of broadband THz pulses propagated through different lengths of fiber clearly indicate guidance in the fiber core. Cladding mode stripping allow for the identification of the single mode in the spectrograms and the determination of the average propagation loss (~ 0.11 dB/mm) in the 0.5–1 THz frequency range. This work points towards single step manufacturing of microstructured fibers using a wide variety of materials and geometries using a 3D printer platform.

Arsenic Sulfide Suspended-core Fiber Simulation with Three Parabolic Air Holes for Supercontinuum Generation

Highly nonlinear suspended-core fibers (SCFs) with tunable dispersion have attracted much attention in the fields of Raman amplification, optical frequency combs, broadband and flat supercontinuum generation (SCG). To address the limitation of applications due to its fragile suspension arms, this study proposes the design of a fiber structure with three parabolic air holes. Numerical simulations are performed to optimize an arsenic sulfide SCF in terms of dispersion management and SCG in the wavelength range from 0.6 µm to 11.6 µm. Results show that the proposed SCF has dual zero-dispersion wavelengths (ZDWs) that can be shifted by adjusting the parabolic coefficient of the air-hole and the equivalent diameter of the suspended core. By means of structural optimization, an SCF with 1 μm equivalent diameter and a parabolic coefficient of 0.18 μm−1 is proposed. The first ZDW of the SCF is blue-shifted to 1.541 μm, which makes it possible to use a commercial light source with a cheaper price, more mature technology and smaller volume as the pump source. SCG is studied by solving the generalized nonlinear Schrödinger equation using the split-step Fourier method, and a 0.6–5.0 μm supercontinuum spectrum is obtained at a pump source peak power of 40 kW.

Supercontinuum generation in all-normal dispersion suspended core fiber infiltrated with water

Octave spanning all-normal dispersion supercontinuum generation (SCG) was experimentally demonstrated in a solid, suspended-core fiber (SCF) infiltrated with water. Replacement of air with water in the cladding air-holes leads to a dramatic modification of the dispersion profile of the fiber, significantly flattening the characteristic over the visible and much of the near-infrared wavelength range at normal values. In such a fiber infiltrated with water, all-normal dispersion supercontinuum was generated with the spectral coverage from 435 nm to 1330 nm using femtosecond pumping with the output peak power of 150 kW and 800 nm central wavelength. The SCF without water infiltration – air in the cladding region – had a zero-dispersion wavelength at 760 nm and enabled the generation of the anomalous dispersion dynamics-based SCG in the wavelength range from 450 nm to 1250 nm. We also numerically calculated the coherence of simulated supercontinuum pulses with one-photon-per-mode noise seeds and point out that the all-normal dispersion SCG in suspended-core fiber infiltrated with water has the potential for high temporal coherence, while the fiber without water infiltration shows gradual decoherence of generated supercontinuum pulses with increasing pump power, over similar peak power range.

Supercontinuum generation in all-normal dispersion suspended core fiber infiltrated with water

Octave spanning all-normal dispersion supercontinuum generation (SCG) was experimentally demonstrated in a solid, suspended-core fiber (SCF) infiltrated with water. Replacement of air with water in the cladding air-holes leads to a dramatic modification of the dispersion profile of the fiber, significantly flattening the characteristic over the visible and much of the near-infrared wavelength range at normal values. In such a fiber infiltrated with water, all-normal dispersion supercontinuum was generated with the spectral coverage from 435 nm to 1330 nm using femtosecond pumping with the output peak power of 150 kW and 800 nm central wavelength. The SCF without water infiltration – air in the cladding region – had a zero-dispersion wavelength at 760 nm and enabled the generation of the anomalous dispersion dynamics-based SCG in the wavelength range from 450 nm to 1250 nm. We also numerically calculated the coherence of simulated supercontinuum pulses with one-photon-per-mode noise seeds and point out that the all-normal dispersion SCG in suspended-core fiber infiltrated with water has the potential for high temporal coherence, while the fiber without water infiltration shows gradual decoherence of generated supercontinuum pulses with increasing pump power, over similar peak power range.

Simulation Study of Mid-infrared Supercontinuum Generation at Normal Dispersion Regime in Chalcogenide Suspended-core Fiber Infiltrated with Water

We report simulation results of supercontinuum generation in the suspended-core optical fibers made of chalcogenide (As2S3) infiltrated with water at mid-infrared wavelength range. Applying water-hole instead of the air-hole in fibers allows improving the dispersion characteristics, hence, contributing to supercontinuum generations. As a result, the broadband supercontinuum generation ranging from 1177 nm to 2629 nm was achieved in a 10 cm fiber by utilizing very low input pulse energy of 0.01 nJ and pulse duration of 100 fs at 1920 nm wavelength.

Numerical simulation of dispersion and nonlinear characteristics of microstructured silica fibres with a thin suspended core in a wide range of their parameters

Dispersion and nonlinear characteristics of microstructured silica fibres with a thin suspended core surrounded by three, four or six air holes have been studied theoretically in the wavelength range 1 – 2 μm. It has been shown that, owing to strong fundamental mode confinement near the core, the Kerr nonlinearity coefficient can exceed the nonlinearity coefficient of standard telecom fibre SMF28e by two orders of magnitude. The large waveguide contribution allows for effective group velocity dispersion management. Estimates are presented that demonstrate the feasibility of using suspended core fibre exhibiting Kerr nonlinearity for generating non-classical light: a state with squeezed quantum fluctuations in one of the quadrature components of a cw laser signal at a wavelength near 1.55 μm.

Broadly tunable photon-pair generation in a suspended-core fiber

Nowadays fiber biphoton sources are nearly as popular as crystal-based ones. They offer a single spatial mode and easy integrability into optical networks. However, fiber sources lack the broad tunability of crystals, which do not require a tunable pump. Here, we report a broadly tunable biphoton source based on a suspended core fiber. This is achieved by introducing pressurized gas into the fibers hollow channels, changing the step index. The mechanism circumvents the need for a tunable pump laser, making this a broadly tunable fiber biphoton source with a convenient tuning mechanism, comparable to crystals. We report a continuous shift of 0.30THz/bar of the sidebands, using up to 25bar of argon.

A theoretical study on the supercontinuum generation in a novel suspended liquid core photonic crystal fiber

We theoretically propose a novel liquid filled suspended core photonic crystal fiber as a new class of microstructure optical fiber for ultrabroad supercontinuum generation. We emphasize the advantage of liquid infiltration in enhancing the fiber nonlinearity. To further enhance the nonlinearity of the liquid-infiltrated fibers, we introduce a suspended liquid core photonic crystal fiber which significantly elevates the fiber nonlinearity through reduced effective area. A comparative study on the continuum generated in conventional microstructured optical fiber (without suspension effect) and the suspended core microstructured optical fiber is performed. A broad continuum is numerically demonstrated through the suspended core fiber, which is substantially broader than the fiber without suspension effect. Thus, we propose a new means to enhance the nonlinearity beyond the intrinsic material dependence. The underlined suspended liquid core photonic crystal fiber can be a new class of fibers for next generation of broadband laser sources.

Refractive Index Sensor Based on Fiber Bragg Grating in Hollow Suspended-Core Fiber

A fiber Bragg grating (FBG) has been fabricated in a hollow suspended-core fiber (HSCF). The HSCF is suitable for refractive index sensor because its core is exposed in the large air hole, which can be used as a microfluidic channel. The refractive index sensitivity of the grating is 8.9 nm/RIU in the range from 1.41 to 1.44. The strain and temperature sensitivities of the HSCF-FBG are 0.8648 pm/με and 9.089 pm/°C, respectively, which are similar to the traditional single-mode fiber FBGs. Remarkably, the bending characteristic of HSCF-FBG has a great dependence on the bending direction and the maximum bending sensitivity is 84.11 pm/m-1. Therefore, the proposed HSCF-FBG can be also utilized as a bending sensor with direction recognition.

Design and fabrication of all-normal dispersion nanohole suspended-core fibers

Suspended-core fibers (SCFs) with a submicron diameter hole in the core offer interesting new possibilities in dispersion management, light confinement, and nonlinear applications. We discuss the geometric demands and options of fused silica-based nanohole SCFs suitable for all-normal dispersion (ANDi) and compare them to the possibilities provided by photonic crystal fibers (PCFs). We show that nanohole SCFs extend the options PCFs provide, enabling ANDi further into the near infrared. In addition, fabrication conditions are evaluated, a reliable fabrication scheme is outlined, and ANDi nanohole SCFs are demonstrated.

Evaluation of Nanoplasmonic Optical Fiber Sensors Based on D-Type and Suspended Core Fibers with Metallic Nanowires

The introduction of metallic nanostructures in optical fibers has revolutionized the field of plasmonic sensors since they produce sharper and fine-tuned resonances resulting in higher sensitivities and resolutions. This article evaluates the performance of three different plasmonic optical fiber sensors based on D-type and suspended core fibers with metallic nanowires. It addresses how their different materials, geometry of the components, and their relative position can influence the coupling between the localized plasmonic modes and the guided optical mode. It also evaluates how that affects the spatial distributions of optical power of the different modes and consequently their overlap and coupling, which ultimately impacts the sensor performance. In this work, we use numerical simulations based on finite element methods to validate the importance of tailoring the features of the guided optical mode to promote an enhanced coupling with the localized modes. The results in terms of sensitivity and resolution demonstrate the advantages of using suspended core fibers with metallic nanowires.

Fiber optic surface plasmon resonance sensor based on a silver-coated large-core suspended-core fiber.

A fiber optic surface plasmon resonance (SPR) sensor based on a silver-coated large-core suspended-core fiber was proposed. A dynamic chemical liquid phase deposition method was adopted to fabricate a set of proposed sensors with different silver layer thicknesses. A stable fully spiced all-fiber sensing system was established to evaluate the performance of the fabricated sensors. The results show that the proposed sensor with a thicker silver layer exhibits higher sensitivity and figure of merit. The performance of the proposed sensor is comparable to those of the conventional solid-core fiber and hollow fiber SPR sensors and much higher than that of the metal nanoparticle functionalized suspended-core fiber sensors.

Mid-Infrared Gas Detection Using a Chalcogenide Suspended-Core Fiber

A fast-response mid-infrared gas sensor based on a chalcogenide suspended-core fiber with microchannels fabricated by a tightly focused femtosecond laser pulse was demonstrated. Chalcogenide four-hole suspended-core fiber was fabricated by extrusion and exhibited the lowest transmission loss of 1 dB/m at 4.7 μm. The 50-μm-diameter solid core in the suspended-core fiber was protected by an outside solid jacket to avoid other environmental factors, such as dust and liquid pollution and touch damage. To increase gas filling rate, we introduced microchannels on the side of the suspended-core fiber by femtosecond laser writing to allow gases to enter into the fiber and fully interact with the core. The distribution, shape, and size of the channels could be controlled by laser writing technology. The engineered technique showed the advantage of increased minor loss in the suspended-core fiber. Methane gas sensing utilizing evanescent wave in the core was carried out in the prepared suspended-core fiber with several hundred microchannels. The methane sensitivity was 100 ppm, and the response time was estimated to be less than 20 s.

Highly sensitive fiber-optic accelerometer using a micro suspended-core fiber.

A compact fiber-optic accelerometer was proposed and demonstrated experimentally based on Fabry-Perot interference (FPI). The device consists of a suspended-core fiber embedded in a hollow-core fiber, forming an enclosed cavity structure. A short section of multi-mode fiber (MMF) was spliced on the leading-in single-mode fiber (SMF), which worked as a micro lens to focus the light to decrease the transmission loss. A well-defined interference spectrum was achieved by a low-fitness FP interferometer formed by both the end-face of lead-in fiber and the end-face of suspended-core fiber. Thanks to the outstretched FP cavity by suspended-core fiber, the sensor is highly sensitive to vibration along the fiber axis. Moreover, a one-dimensional mechanical transducer was used to improve the frequency band of the sensor. By the side-band filtering technology, the vibration was detected and analyzed by a simple intensity interrogation technology.

Mid-infrared two-octave spanning supercontinuum generation in a Ge–Se–Te glass suspended core fiber

We report on both the fabrication and the application of a Ge–Se–Te glass-based suspended core fiber for mid-infrared supercontinuum generation. A two-octave spanning mid-infrared light source (from 3.25 to 13 µm) is experimentally demonstrated by pumping the chalcogenide fiber with sub-100 fs pulses at 8.6 µm. Numerical simulations of nonlinear pulse propagation as well as fiber properties are also provided and support experimental measurements.

Stability of Grating-Based Optical Fiber Sensors at High Temperature

We present a comparison of four different grating-based optical fiber high-temperature sensors. Three of the sensors are commercially available, and include a heat treated, twisted (chiral) pure-silica microstructured optical fiber, a femtosecond laser written Bragg grating in a depressed cladding single mode fiber, and a regenerated fiber Bragg grating. We compare these to an in-house fabricated femtosecond laser ablation grating in a pure-silica microstructured optical fiber. We have tested the sensors in increments of 100 °C up to 1100 °C for the duration of at least 24 hours each. All four sensors were shown to be operational up to 900 °C, however, the two sensors based on pure-silica microstructured fiber displayed higher stability in the reflected sensor wavelength, compared to the other sensors at the temperatures of 700 °C and higher. We further investigated the high-temperature stability of silica suspended-core fibers with femtosecond laser inscribed ablation gratings, which show improved stability up to 1050 °C, following thermal annealing. This investigation can be used as a guide for selecting fiber types, packaging, and grating types for high-temperature sensing applications.

Precision fabrication of a four-hole Ge15Sb15Se70 chalcogenide suspended-core fiber for generation of a 15–12 µm ultrabroad mid-infrared supercontinuum

We reported the fabrication of a high-precision, long-length (>10 cm), four-hole, and As-free Ge15Sb15Se70 chalcogenide (ChG) suspended-core fiber (SCF) preform based on the computerized numerical control (CNC) precision mechanical drilling method. Four holes of the preform were highly symmetrical and have a depth of 103 mm. A fiber with a core diameter of 7 µm, cladding diameter of 300 µm, and regular air hole structure was drawn by using inflating methods through accurately controlling the inflation pressure. Theoretical simulation of the zero-dispersion wavelength (ZDW) of this fiber was located at approximately 3.3 µm. Under pumping at 3.5 µm with an average power of 23 mW, the fiber with length of 14 cm generates a mid-infrared (MIR) supercontinuum (SC) that spans from 1.5–12 µm within a 30 dB dynamics range.

Effects of pressurization and surface tension on drawing Ge-Sb-Se chalcogenide glass suspended-core fiber

Drawing chalcogenide glass microstructured optical fibers efficiently requires a good understanding of the different drawing conditions beforehand, due to the high cost of the chalcogenide glass materials. A simulation based on Stokes’ model that includes pressurization and glass surface tension is validated with respect to drawing a Ge$_{28}$28Sb$_{12}$12Se$_{60}$60 chalcogenide glass single hole capillary, as well as microstructured optical fiber with three holes, with different pressurizations. Suspended-core Ge$_{28}$28Sb$_{12}$12Se$_{60}$60 fibers with bridges just hundreds of nanometer wide are drawn using parameters predicted by the simulations. These fibers should be suitable for applications such as generating mid-infrared (MIR) supercontinuum based on chalcogenide glasses.

Mid-infrared supercontinuum generation from 2 to 14 μm in arsenic- and antimony-free chalcogenide glass fibers

We demonstrate the fabrication of arsenic-and antimony-free chalcogenide glasses compatible with glass fiber processing. Optical fibers with distinct index profiles are presented and characterized, namely, single-material fibers with or without a suspended core and standard step-index fibers with varying core diameter. In addition, we evidence their potential for nonlinear photonic devices in the mid-infrared spectral region by means of super-continuum generation experiments in the femtosecond regime. Spectral broadenings extend on several octaves in the mid-infrared from 2 to 14 μm.