Suspended Core Research Articles

Fiber tip Michelson interferometer for temperature sensing based on polymer-filled suspended core fiber

A low-cost fiber tip temperature sensor is proposed and experimentally demonstrated. It is based on the Michelson interferometer (MI) structure which is partially filled with polymer-UV glue in the suspended core fiber (SCF). Due to the greater thermal properties of UV glue compared with the silica optical fiber, the length of the inner cavity in the MI structure is susceptible to temperature modulation, resulting in the interference wavelength drift. Experimental results show that the sensor achieves a sensitivity of −164 pm/°C in the temperature range of 25–60 °C, and the sensor offers good wavelength and power stability at room temperature. In addition, the sensor has advantages such as robust, small size, and low cost, especially the reflective tip structure is more suitable for remote sensing in practical applications.

Determination of the antibiotic minocycline by integrated optofluidic microstructured polymer optical fiber chemiluminescence

An in-fiber optofluidic chemiluminescence (CL) device is reported based on a low-cost microstructured polymer optical fiber (mPOF). The mPOF is composed of a central hole for liquid delivery and a suspended core for optical coupling. Due to the lower processing temperature of mPOF, the difficulty of constructing microfluidic channels is greatly reduced. In addition, the large core diameter of mPOF is more conducive to optical coupling. The microholes are opened on the surface of the mPOF by partial melting to complete the construction of the microfluidic channel. Simultaneously, the response of the CL reaction is detected on-line by the optoelectronic device. Minocycline (MC) was employed as the analyte for on-line optofluidic CL detection. The results show that the device detects aqueous minocycline from 0.0001 to 0.1 g/L with a linear response between 0.001 and 0.01 g/L. The limit of detection is 0.0001 g/L. Moreover, the ability of the device to detect minocycline in blood serum is investigated. The relative deviation from the linear calibration value is within 3.2%. Furthermore, the low-cost in-fiber optofluidic CL device may be integrated with other devices and offers potential in drug safety and medical detection.

Behavior of the Fused Quartz Suspended Core Acoustic Waveguide Sensor in Gamma Radiation

Previously, a fused-quartz acoustic waveguide named the suspended core waveguide with tight-field confinement in a small diameter was developed and its sensing potential in harsh environment was demonstrated with the fabricated periodic acoustic fiber Bragg grating. In this paper, the acoustic sensor was exposed to around 70 Gy/h gamma radiation at room temperature for 3550 h at Oak Ridge National Laboratory. For comparisons, a thermocouple and two optical fiber Bragg gratings were tested under the same conditions. The central frequency reading of the acoustic sensor was found to encounter a relatively fast decrease of 0.5 kHz in the first 800 hours. The reading then became stable, centering at 478.5 kHz with a fluctuation of ±0.2 kHz, and responded to small environmental temperature variations less than 1.2 °C. The major effect to the fluctuation was concluded to be radiation-induced material compaction and expansion. For optical fiber Bragg gratings, the same one-directional fast change of readings in the first 500 hours were observed as well. Although the optical gratings were able to track temperature changes, they also showed continuous drifts. The survivability and consistency of the acoustic sensor under long-term gamma radiation could lead to new sensing methods in nuclear applications.

In-fiber optofluidic online SERS detection of trace uremia toxin.

In this Letter, we propose a microstructured in-fiber optofluidic surface-enhanced Raman spectroscopy (SERS) sensor for the initial inspection of uremia through the detection of unlabeled urea and creatinine. As a natural microfluidic device, microstructured hollow fiber has a special structure inside. Through chemical bonds, the SERS substrate can be modified and grown on the surface of the suspended core. Here, the silver nanoparticles (Ag NPs) are embedded on the poly diallyl dimethyl ammonium chloride-modified graphene oxide sheet to achieve the self-assembled SERS substrate. The reduced distance between Ag NPs can increase the strong hot spots that generate enhanced Raman signals. Therefore, it can effectively detect the Raman signal of unlabeled trace uremic toxin analytes (urea, creatinine) inside the optical fiber. The results show that under simulated biophysical conditions, the limit detection (LOD) for urea is 10-4M and the linearity is good, especially at the clinical conventional concentration range (2.5-6.5×10-3M). In addition, the online Raman detection of creatinine aqueous solution LOD is 10-6M, which also has good linearity. Significantly, this Letter provides a microstructured optofluidic in-fiber Raman sensor for the preliminary detection of uremia, which will have good development prospects in the field of clinical biomedicine.

In-fiber Mach-Zehnder temperature sensor using silicone-oil-filled dual core fiber

In this paper, we proposed an in-fiber Mach-Zehnder temperature sensor based on a dual-core fiber (DCF) in which one core, working as the reference arm, is located in the center of fiber and the other core, working as the sensing arm, is suspended in an embedded fluidic channel partially filled with silicone oil. Temperature variations would mainly change the refractive index of the silicone oil and therefore the effective index of the guided modes in the suspended core, while the guided modes in the center core were barely affected. Phase difference between guided modes in the two cores would be accumulated along the DCF, thus shifting the interference spectrum of the sensor. Both experiments and numerical simulations were carried out to characterize the sensor. The spectrum shifts measured experimentally agreed well with the theoretical results. Experimental sensitivity of the DCF sensor filled with 33.5-cm-long silicone oil was found to be as high as −2.18 nm/°C, comparable to that of other interferometric sensors. The proposed sensor could be easily fabricated with good robustness and stability, which makes the sensor promising for applications such as environment and architecture monitoring.

Compact all-fiber thermo-optic modulator based on a Michelson interferometer coated with NaNdF4 nanoparticles.

We propose and investigate an all-fiber thermo-optic modulator based on a side-polished twin-core fiber (TCF) Michelson interferometer (MI) coated with NaNdF4 nanoparticles. The MI was fabricated by tapering the splicing point between the TCF and a single mode fiber (SMF). A short suspended core fiber (SCF) is spliced to one core of the TCF to introduce a fixed optical phase difference (OPD). The side-polished core is coated with photo-thermal material NaNdF4. Owing to the ohmic heating of NaNdF4 nanoparticles under 808 nm pump laser, the effective refractive index of the polished core is changed, resulting in a phase shift of the MI. The MI has a significant modulation phase shift with 2.9 π near the wavelength of 1260 nm and can obtain an optical switching with a rise (fall) time of 152 (50) ms. The proposed device will have a great application potential in optical modulators due to compact structure and strong robustness.

Design and analysis of suspended core channel waveguide made using As2Se3 glass system for mid-infrared supercontinuum generation

In this study, we propose a promising 5 mm long air-clad suspended core channel waveguide made of As2Se3 chalcogenide glass for ultra-broadband supercontinuum generation (SCG) in the mid-infrared (MIR). The linear analysis of the proposed waveguide is carried out numerically by considering the potential application of pump sources at three different wavelength regions such as 1.55, 2.8, and 3.5 µm. Among several waveguide geometries analyzed, numerical simulation for SCG at the output of an optimized structure shows that a flat supercontinuum coverage from 1.5 to 15 µm can be predicted using a pump at 3.5 µm with a moderate peak power of 2000 W. To the best of the authors’ knowledge, this would be the broadest spectra in the MIR by the suspended planar waveguide design. In addition, waveguide structural imperfection has also been discussed as it is difficult to control the waveguide dimensions during the fabrication process precisely. The effect of possible deviations along the transverse dimensions is rigorously analyzed and an imperfection among the several deviations is found which could lead to a substantial supercontinuum bandwidth reduction at the waveguide output. Finally, the degree of coherence of the obtained supercontinuum coverage is also tested and it has been achieved nearly coherent spectral outcome from the proposed suspended waveguide design.

Extruded suspended core fibers from lanthanum-aluminum-silicate glass

We report the use of the extrusion technique at highest temperatures to date (975 °C - 1000 °C) for the fabrication of suspended core fibers (SCFs) from glass with molar composition 65 SiO2-20 Al2O3-15 La2O3 (SAL65). Through adjusting die design and fabrication conditions, extruded preforms for fibers with two different core sizes (1.2 µm and 3.1 µm) were successfully produced. Cross-sectional microstructure and material loss of these fibers highlight the potential of the extrusion technique for fabrication of microstructured optical fibers from glasses with high softening temperature and thus high thermal and mechanical stability.

An Acoustic Waveguide With Tight Field Confinement for High Temperature Sensing

A fused quartz acoustic waveguide structure was reported as the suspended core waveguide. The waveguide featured good acoustic wave confinement within the core and a relatively small diameter. Consistent high-temperature sensing was also demonstrated with the waveguide after a temperature sensor was fabricated inside. The waveguide was fabricated by suspending its core rod in the middle of the hollow cladding tube by discrete thin supporting disks. It was found that the characteristics of acoustic propagation in the waveguide was similar to that in a bare core rod and that the waveguide was largely insensitive to lossy surface perturbations. The diameter of the waveguide was relatively small, little more than the bulk longitudinal acoustic wavelength. For sensing, the periodic structure, the acoustic fiber Bragg grating, was fabricated on the core of the suspended core waveguide. A temperature test up to 1000 °C was performed. The central frequency of the reflected acoustic wave was found to change unidirectionally and consistently with changes in temperature. With its good field confinement and consistent sensing capabilities, the suspended core waveguide could find vast potential in many applications.

Highly birefringent slotted core photonic crystal fiber for terahertz waveguiding

A novel porous core photonic crystal fiber (PC-PCF) is suggested and analyzed for terahertz waveguiding. The PC-PCF has a TOPAS background material with suspended asymmetric slotted core. Therefore, high birefringence of 0.09 is achieved with small material absorption losses of 0.016 cm−1 and 0.028 cm−1 for the quasi transverse electric (TE) and quasi transverse magnetic (TM) modes, respectively at f = 1.5 THz. Additionally low bending losses of 2.63 × 10–24 cm−1 and 8.16 × 10–36 cm−1 are obtained for the quasi TE and quasi TM modes, respectively at 1.0 cm bending radius and f = 1.5 THz. Further, the PC-PCF has an ultra-flat low dispersion of 0.54 $$\pm$$ 0.08 ps/THz/cm and 0.94 $$\pm 0.1{ }$$ ps/THz/cm for the quasi TE and TM modes, respectively within the frequency range of 0.8–1.2 THz. Therefore, the reported SSCPCF has a strong potential for usage in the Terahertz regime.

Ultra-high birefringent low loss suspended elliptical core photonic crystal fiber for terahertz applications.

This paper presents a low loss suspended core microstructured fiber with ultra-high birefringence for terahertz wave guidance. The finite element method (FEM) with a perfectly matched layer is applied to investigate different important properties including effective material loss (EML), birefringence, dispersion, confinement loss, and percentage of power flow through the core. The suspended elliptical core in the design creates asymmetry and results in an unprecedented value of birefringence. The simulated results using FEM at 1 THz show an extremely ultra-high birefringence (the highest, to the best of our knowledge) of 0.1116, a nominal EML of 0.04716cm-1, a negligible confinement loss of 2.65×10-7cm-1, a higher power fraction in the core air of 35%, and an effective modal area of 1.24×105µm. The advancement in technology makes the fabrication possible. The proposed fiber could be used satisfactorily in the terahertz regime for various polarization-preserving applications and coherent communication.

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.

Optimization and performance analysis of SERS-active suspended core photonic crystal fibers

Recently, surface enhanced Raman spectroscopy (SERS)-active photonic crystal fiber (PCFs) probes have gained great interest for biosensing applications due to the tremendous advantages it has over the conventional planar substrate based SERS measurements, with improvements on the detection sensitivity and reliability in measurements. So far, two main approaches were employed to get the analyte molecule in the vicinity of nanoparticles (NPs) inside PCFs in order to achieve the SERS effect. In the first case, analyte and NPs are pre-mixed and injected inside the holes of the PCF prior to the measurement. In the second approach, controlled anchoring of the NPs inside the inner walls of the PCF was achieved prior to the incorporation of the analyte. Although many studies have been conducted using one configuration or the other, no clear trend is emerging on which one would be the best suited for optimizing the biosensing properties offered by SERS active-PCF. In this paper, we investigate the performances of both configurations along with their interplays with the core size of the PCF probe. We have fabricated several samples of a standard PCF design with different core sizes, and SERS measurements of a standard Raman-active molecule are realized in the same conditions for enabling direct comparisons of the SERS intensity and measurement reliabilities between each configuration, yielding clear directions on the optimization of the SERS-active PCF probe. We envision that this study will pave the way for next-generation clinical biosensors for body fluid analysis, as it exhibits high sensitivity and excellent reliability.

Single-peak fiber Bragg gratings in suspended-core optical fibers.

Femtosecond laser inscribed fiber Bragg gratings in pure-silica suspended-core optical fibers have previously been demonstrated as a promising platform for high temperature sensing. However, the density of gratings that could be written on a single fiber was limited by undesired reflections associated with higher order modes in these high numerical aperture fibers. This resulted in a complex, broadband reflection spectrum with limited multiplexing capability. In this work we utilize modifications to the fine structure of the suspended core optical fibers to fine tune the relative confinement loss of the optical fiber modes, thus reducing the contribution from such higher order modes. The effects of these changes on mode propagation are modeled, giving a range of fibers with different confinement loss properties which can be tailored to the specific length scale of a desired application. We achieve single-peak reflections from individual fiber Bragg gratings, significantly improving performance for multipoint sensing and demonstrate this technique by writing 20 gratings onto a single fiber.

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.

Optofluidic in-fiber on-line ethanol sensing based on graphene oxide integrated hollow optical fiber with suspended core

Abstract In this study, a novel in-fiber optofluidic trace ethanol sensor is proposed firstly. The microstructured hollow fiber (MHF) with a suspended core is a key part of the overall device which is integrated with graphene oxide (GO). The GO can be uniformly trapped on the whole surface of the suspended core in the MHF by using evanescent field inducing method. When trace microfluidic ethanol passes through the in-fiber device, the light intensity of the suspended core can be significantly modulated through the interaction between the GO on the core and ethanol. The device presents an excellent linearity on-line response with an average sensitivity of 0.16 dB/% with linear regression equation of y = 0.16x + 25.989. In general, this compact optofluidic in-fiber trace ethanol sensor can be utilized as for on-line detection of trace amounts of ethanol in special environments.

Soliton detuning of 68.5 THz in the near-infrared in a highly nonlinear suspended core tellurite fiber

We demonstrate an isolated phenomenon of soliton self-frequency shift over a bandwidth of 68.5 THz in the near-infrared spectral range. We designed, fabricated, and characterized a suspended core microstructured fiber made of highly nonlinear tellurite glass. The fiber is designed for a flat anomalous dispersion to leverage on Raman scattering-assisted frequency shift of a fundamental-order soliton. We demonstrate a prominent soliton with an input-power-based tunability in the spectral range from the 1560 nm central pump wavelength up to around 2400 nm central wavelength of the frequency-shifted soliton, when the fiber is pumped with 90 fs pulses from a commercial, fiber-based, mode-locked laser.

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.