Conventional Silica Fibers Research Articles

In-situ background-free Raman probe using double-cladding anti-resonant hollow-core fibers.

This study presents the development of an in-situ background-free Raman fiber probe, employing two customized double-cladding anti-resonant hollow-core fibers (AR-HCFs). The Raman background noise measured in the AR-HCF probe is lower than that of a conventional multi-mode silica fiber by two orders of magnitude. A plug-in device for fiber coupling optics was designed that was compatible with a commercially available confocal Raman microscope, enabling in-situ Raman detection. The numerical aperture (NA) of both AR-HCF claddings exceeds 0.2 substantially enhancing the collection efficiency of Raman signals at the distal end of the fiber probe. The performance of our Raman fiber probe is demonstrated by characterizing samples of acrylonitrile-butadiene-styrene (ABS) plastics, alumina ceramics, and ethylene glycol solution.

Non-destructive characterization of nested and double nested antiresonant nodeless fiber microstructure geometry.

Antiresonant hollow-core fibers (HCFs) are rapidly establishing themselves as a promising technology with the potential to overcome the limitations faced by conventional solid-core silica fibers. The optical properties and performance of these fibers depend critically on the precise control and uniformity of their delicate glass microstructure at all points along the length of the fiber. Their fabrication is complicated by the inability to monitor this microstructure without cutting into the fiber and viewing a sample under a microscope during the fiber draw. Here we show that a non-destructive interferometric technique using side-illumination of the fiber and first demonstrated for simple tubular fibers can be used to measure the diameters of all nested capillary elements of two promising HCF designs: the nested and double-nested antiresonant nodeless fiber (NANF and DNANF, respectively) with accuracy comparable to a microscope measurement. We analyze the complexities enabled by the presence of multiple nested capillaries in the structure and present techniques to overcome them. These measurements, carried out on a small (∼50 cm) length of fiber, require less than 60s to collect and process the data for all capillaries. We also show how we can use this technique to detect defects in the fiber, making it a potential candidate for real-time in-situ monitoring of NANF and DNANF structures during fabrication.

Simulation of Trenched Coreless Silica Fiber Sensor for Refractive Index Measurement

Coreless silica fiber has garnered a lot of attention in the field of sensors. Nevertheless, the limitation of conventional and unique coreless silica fiber sensors such as complex simulation, and high fragility of its physical structure needs to be considered. This work presents a simulation of a new coreless silica fiber design in a form of a trenched coreless silica fiber sensor to overcome these limitations. To optimize the sensor’s design, the trench depth was changed in the range of 0 μm to 50 µm at a fixed trench width of 50 μm. The change in analyte refractive index ranging from 1.3000 RIU to 1.4000 RIU was performed to evaluate the simulated sensing performance which showed that the increase in trench depth improved the sensor’s sensitivity with 50 μm being the trench depth at which the highest sensitivity was recorded. Later, the results obtained was compared to the closest in term of design which is the standard coreless fiber. Overall, the trenched coreless silica fiber design provided better sensitivity and is highly capable as of has a new refractive index sensor with an estimated sensitivity of up to 6.62726x10-7, higher than the simulated standard coreless fiber sensor with that of 2.22053x10-7.

Opportunities and Challenges for Long-Distance Transmission in Hollow-Core Fibres

The loss of hollow-core Nested Antiresonant Nodeless Fiber (NANF) has been steadily decreasing lately, approaching that of standard Single-Mode Fiber (SMF). As for non-linear effects, they are already three to four orders of magnitude lower than in SMF. Theoretical predictions and experimental evidence also hint at a much wider usable bandwidth than SMF, potentially several tens of THz. Propagation speed is 50%faster, a key feature in certain contexts. We investigate the potential impact of possible future high-performance NANF on optical communication systems, assuming that NANF continues on its current path towards better performance. We look at system throughput in different scenarios, addressing links from 100 km to 4,000 km, assuming different NANF optical bandwidths and loss. We found that NANF might enable throughput gains, vs. a benchmark SMF Raman-amplified C+L system, on the order of 1.5x to 5x, at reasonable system parameter values, including launch power. We also consider NANF Inter-Modal-Interference (IMI) and show that the value required for negligible system impact is about –60 dB/km, close to the currently best reported values. We finally look at more long-term scenarios in which NANF loss might get below that of SMF and we show that in this context repeaterless or even completely amplifierless systems might be possible, delivering 300400 Tb/s per NANF, over 200 to 300 km distances. While several technological hurdles remain before NANF systems become practical, NANF appears to have the potential to become an attractive and possibly disruptive alternative to conventional solid-core silica fibers.

Short-pulse gain-switched Raman fiber laser based on conventional silica fibers

We report a high-energy 1666 nm short-pulse Raman fiber laser (RFL) based on gain-switching scheme. The RFL cavity is formed by conventional single mode fibers (SMFs), which is with low connection loss, low cost and ultrahigh compactness. To reduce the intra-cavity laser intensity and group velocity mismatch, the laser cavity and pump source parameters (i.e. laser output coupling, single-pass cavity length and pump pulse duration) are carefully selected to be 90%, 1 km and 10 ns, respectively. At last, an average output power of 670 mW, a single pulse energy of 223 nJ and a laser conversion efficiency of 66.9% have been successfully achieved. This work can clear a path towards high-performance and low cost 1666 nm fiber laser sources.

Full‐Inorganic Micro‐Fiber Probe for Real‐Time Radiation Monitoring

AbstractScintillators convert high‐energy radiation into visible luminescence and have been widely applied in various significant fields such as nuclear fusion monitoring, high‐energy particle physics, medical imaging, and geological exploration. The scalable fabrication of scintillating fiber with the desirable combination of uniform size, superior radiation blocking ability, and excellent thermal/radiation stability is a major challenge. Here, a template solidification strategy for fabrication of full‐inorganic and efficient scintillating fiber is presented. The strategy involves the direct solidification of high‐density scintillator melt in a softened silica tube, allowing for the continuous production of small and uniform scintillating fiber. The fabricated scintillating fiber can effectively attenuate radiation up to ≈118 times higher than what conventional silica fiber can. In addition, it exhibits good compatibility with commercial fiber. Using this scintillating fiber, a radiation fiber detector is constructed and its application for online radiation monitoring is demonstrated.

Study of the Verdet constant of the holmium-doped silica fiber

A Ho-doped silica fiber with a high verdet constant is prepared by a modified chemical vapor deposition (MCVD) method. The phenomenon of the Faraday effect enhancement of a Ho-doped silica fiber is theoretically analyzed by the wave transition contribution analysis method based on the wave-particle duality of light. The Verdet constant of Ho-doped silica fiber is calculated with the wavelength range from 1310 nm to 1550 nm. Through experimental measurement, it is found that the Verdet constant of the Ho-doped silica fiber has a wavelength dependency. The experimental results show that the Verdet constant values of the Ho-doped silica fiber at 1310 nm and 1550 nm are 4.5 times and 1.6 times that of the conventional single-mode silica fiber, respectively.

Net optical parametric gain in a submicron silicon core fiber pumped in the telecom band

A silicon core fiber (SCF) has been designed and fabricated with a dispersion engineered profile to support broadband optical parametric amplification across the telecom window. The combination of low optical transmission losses and high coupling efficiency of the SCF platform has allowed for an on-off optical parametric gain up to 9 dB, without experiencing gain saturation due to nonlinear absorption, resulting in a net off-waveguide gain of ∼2 dB. The ability to splice the SCFs with conventional silica fiber systems opens a route to compact and robust all-fiber integrated optical parametric amplifiers and oscillators that could find use in telecoms systems.

Toward Commercial Polymer Fiber Bragg Grating Sensors: Review and Applications

Interest in polymer optical fiber Bragg gratings (POFBGs) arises from the different material properties and sensing modalities brought by polymers relative to silica. Polymer fibers typically offer twice the sensitivity to temperature of conventional silica fiber and increased sensitivity to strain overall. In addition, polymer fibers have higher elastic limits and as a result a larger range of operation for physical constraints. While some polymers are effectively humidity insensitive, others present inherent humidity sensitivity. Their organic properties also allow a variety of chemical processes to create (bio)chemical sensors, with the consequences of fiber breakage in situ being less hazardous than silica. These attributes have led to the use of POFBGs for applications that remain complex using silica fibers. This review paper covers the progress toward commercialization and the increasing number of specific applications.

High Power, Tunable, Continuous-Wave Fiber Lasers in the L-Band Using Cascaded Raman Amplifiers

We demonstrate a high power, all-fiber, tunable laser source that can operate in the L-band region. A low power, tunable input laser is amplified with a recently proposed, high efficiency, 6th order cascaded Raman amplifier. The proposed system is scalable and overcomes the limitations of Erbium and Erbium-Ytterbium co-doped fiber lasers for power scaling. A tunable Erbium-Ytterbium co-doped fiber ring laser generating ~0.5W of power and tunable in the 1560-1590 nm wavelength range is utilized as the seed source. The output from the seed laser is amplified to ~24 W using 6th order cascaded Raman amplification. A high power Yb laser operating at 1117nm is used as the pump laser for driving the Raman conversions. The operating wavelength of the demonstrated laser in the eye-safe, atmospherically transparent region enables high power free-space applications. In addition, this source enables other interesting applications such as high power supercontinuum generation with conventional silica fibers.

Experimental study on an interferometric strain sensor based on hollow-core photonic bandgap fiber for intrusion detection

In this paper, the design and preliminary performance results of a Mach–Zehnder interferometric (MZI) strain sensor based on hollow-core photonic bandgap fiber (HC-PBG) for intrusion detection are proposed. An experiment is conducted to test the system before deployment in the field. Firstly, to judge the necessity of using the HC-PBG, an experiment is performed to compare the normalized strain responsivity (NR) of the HC-1550 and the conventional SMF-28. By interchanging the investigated optical fibers as a sensing arm of the MZI, it is possible to compare the obtained results with a conventional standard silica fiber and the HC-PBG. The experimental results show that the NR of the HC-PBG is about 3.6 – 5.3 dB better than that of the SMF depending on the frequency in the frequency range 500 Hz to 2 kHz. Secondly, we concentrate our study and measurements on the HC-1550. A simulation of intrusion detection is introduced by using the proposed interferometric fiber-optic strain sensor to detect the dynamic strain induced phase shift as a result of varying the amplitude and frequency of the input signals to a PZT tube. The investigated input signal frequencies are from 500 Hz to 2 kHz. An experiment is performed to measure the induced strain from the PZT for different input voltages and frequencies, and using the phase generated carrier (PGC) demodulation technique for extracting the measured signal information. This technique is an effective way to test the performance and the functionality of the system in lab before the field trials. Experimental results show the importance of using HC-PBG for sensing applications and the ability of the system to effectively be used for borders monitoring and securing important facilities.

Highly Sensitive Small Pressure Monitoring Using Hyperelastic Silicone-Cladding/Silica-Core Composite Optical Fiber

We have fabricated a composite optical fiber with hyperelastic silicone cladding and silica core, and demonstrated a simple and highly sensitive pressure sensor based on the light coupling between two such composite fibers twisted together. The hyperelastic silicone has very low Young's modulus which makes the fiber deformation easier even under small pressure and hence improves the light coupling and pressure sensitivity. Both simulation and experiment show that the light coupling based pressure sensor using the composite fibers is very sensitive to small pressure (e.g., several newtons) compared with those using conventional silica fibers and polymethyl methacrylate resin polymer fibers, which almost have no response to small pressure. With excellent sensitivity and fast response time ( $\ll 1\;{\rm{s}}$ ), both static and dynamic side pressure have been successfully detected. The sensing configuration is simple without any complicated structures and would be a cost-effective candidate for highly sensitive small pressure monitoring.

Highly flexible and stretchable optical strain sensing for human motion detection

Strain sensors with high flexibility and stretchability are essential for quantifying strains generated by human activities due to the soft and curvilinear surfaces of the body. Here, we report the design and fabrication of a highly flexible and stretchable optical strain sensor that is applicable for the detection of human motions. The sensor is based on dye-doped polydimethylsiloxane optical fiber, which enables the quantitative detection of tensile strains by absorption changes of the light passing through the dye-doped fiber. Elaborate mechanical and strain tests confirm durability, reliability, and long-term stability of the sensor device. The sensor exhibits linear and repeatable responses in a large dynamic range up to 100%, far exceeding the stretchability of conventional silica fibers (<1%), and the strain precision is below +/−1%. We show that the sensor can be used to monitor various human activities, such as joint motion, speaking, and deep breathing in real time.

An etched polyether ether ketone tube covered with immobilized graphene oxide for online solid phase microextraction of quaternary alkaloids prior to their quantitation by HPLC-MS/MS

Polyether ether ketone (PEEK) is an ideal substrate for in tube solid-phase microextraction (SPME) because it overcomes the shortcomings of conventional silica fibers in terms of fragility and poor flexibility. Commonly used bare PEEK tubes suffer from difficult modification with selective sorbents and low inner surface areas. This problem was solved by etching with concentrated sulfuric acid, which dissolves the amorphous regions of the PEEK surface and yields a rough inner surface with plenty of microscopically small holes. The etched tube was then stepwise functionalized with polydopamine and graphene oxide which was in-situ immobilized. The modified tube displays excellent efficiency for the extraction of positively charged quaternary alkaloids by a mixed-mode extraction. Enrichment factors from 221 to 275 can be obtained for the extraction of the alkaloids jatrorrhizine, palmatine and berberine. The alkaloiods were then quantified by online SPME-HPLC-MS/MS detection. The method has detection limits of 0.1 pg mL−1, good linearity, and good intra-day reproducibility (≤ 2.4%). It was applied to the analysis of the three alkaloids in Cortex Phellodendri herb and rat plasma after oral administration.

Polymer optical fiber sensors in human life safety

The current state of research into polymer optical fiber (POF) sensors linked to safety in human life is summarized in this paper. This topic is directly related with new solutions for civil aircraft, structural health monitoring, healthcare and biomedicine fields. In the last years, the properties of polymers have been explored to identify situations offering potential advantages over conventional silica fiber sensing technology, replacing, in some cases, problematic electronic technology used in these mentioned fields, where there are some issues to overcome. POFs could preferably replace their silica counterparts, with improved performance and biocompatibility. Finally, new developments are reported which use the unique properties of POF.

1.61–1.85 $\mu$m Tunable All-Fiber Raman Soliton Source Using a Phosphor-Doped Fiber Pumped by 1.56 $\mu$m Dissipative Solitons

We demonstrate soliton self-frequency shift (SSFS) of more than 15.5 $\%$ of the optical frequency in a phosphor-doped silica fiber for the first time. This fiber shows great potential for supporting Raman-shift solitons above 1.8 $\mu$ m with a 1.56 $\mu$ m pumping, which is superior to the SSFS previously reported in conventional single-mode silica fiber. In our experiment, when the amplified dissipative-soliton pulses at 1.56 $\mu$ m are injected into a 960 m phosphor-doped silica fiber, SSFS is efficiently initiated, and the output spectrum of Raman solitons can be continuously tuned from 1.61 to 1.85 $\mu$ m. The Raman solitons have the shortest pulse duration of $\sim$ 800 fs and the pulse energy of $\sim$ 1 nJ. This 1.61–1.85 $\mu$ m ultrashort laser source can not only fill in the spectral gap between Er $^{3+}$ and Tm $^{3+}$ emissions but has potential applications in multiphoton microscopy and optical tomography as well.

A surface plasmon resonance sensor based on a single mode D-shape polymer optical fiber

For the first time to our knowledge, we report a successful fabrication of surface plasmon resonance (SPR) sensors in a specially developed single-mode birefringent polymer D-shape fiber with a core made of PMMA/PS copolymer. A small distance between the core and the cladding boundary allows to deposit a gold layer directly onto the flat fiber surface, which significantly simplifies the sensors fabrication process. The developed SPR sensor exhibits a sensitivity of 2765 nm RIU−1 for the refractive index of external medium equal to 1.410, which is similar to the sensitivity of the SPR sensors based on conventional side-polished single-mode silica fibers. Using the finite element method, we also numerically studied the sensor performance. The sensor characteristics obtained in the simulations are in a relatively good agreement with the experimental results.

Forward Brillouin scattering in hollow-core photonic bandgap fibers

We quantify the strength of stimulated forward Brillouin scattering in hollow-core photonic bandgap fiber through a combination of experiments and multi-physics simulations. Brillouin spectroscopy methods reveal a family of densely spaced Brillouin-active phonon modes below 100 MHz with coupling strengths that approach those of conventional silica fiber. The experimental results are corroborated by multi-physics simulations, revealing that relatively strong optomechanical coupling is mediated by a combination of electrostriction and radiation pressure within the nano-scale silica-air matrix; the nontrivial mechanical properties of this silica-air matrix facilitate the large optomechanical response produced by this system. Simulations also reveal an incredible sensitivity of the Brillouin spectrum to fiber critical dimensions, suggesting opportunity for enhancement or suppression of these interactions. Finally, we relate the measured and calculated couplings to the noise properties of the fiber as the foundation for phase- and polarization-noise estimates in hollow-core fiber. More generally, such Brillouin interactions are an important consideration in both the high and low optical intensity limits.

Raman scattering enhancement characteristic of NbCl5- and Nb2O5-doped silica fibers

Two kinds of Nb-doped silica fibers, an NbCl5-doped fiber and an Nb2O5-doped fiber, are fabricated and characterized in this Letter. First, the refractive index profiles of both fibers are obtained, and then their Raman spectra are measured with 785 nm exciting light. The Nb-doped fibers’ Raman spectra are compared with a conventional GeO2-doped single-mode silica fiber that is prepared with the same method and under the same conditions. As a result, the Raman gain coefficients of the Nb-doped silica fiber core are obtained. The experimental results show that Nb2O5 doping can enhance the Raman scattering intensity of the optical fibers.

A fiberized highly birefringent glass micrometer-size ridge waveguide

We report the fabrication of a fiberized micrometer-size ridge waveguide using a sheet-stacking method. The fabrication conditions for maintaining the ridge geometry with micrometer dimensions were investigated and discussed. A loss of 3.9dB/m was measured at 1.55μm in the fiber ridge waveguide, showing no extra loss above the bulk loss of the glass. A high birefringence of 9.5×10−3 was measured in the waveguide at 1.55μm which is close to the reported highest birefringence (1.1×10−2) in optical fibers. Fusion splicing was successfully employed to splice the fabricated waveguide to a conventional silica fiber with reasonable loss.