Suspended-core Fiber Research Articles

Perfluorocarbons: a material platform for tunable nonlinear frequency conversion in liquid filled suspended core fibers

This study investigates supercontinuum generation in suspended core fibers filled with perfluorocarbons, highlighting their potential for ultrafast nonlinear frequency conversion. Spectroscopic absorption and refractive index dispersions are analyzed for three perfluorocarbons in the visible and near-infrared. Experiments show that the insertion of these liquids into suspended core fibers changes the dispersion landscape, enabling broadband soliton-based supercontinuum generation from 0.6 µm to 2.4 µm due to the creation of a confined domain of anomalous dispersion in the telecom range. In addition, temperature-dependent output spectrum modulation is demonstrated, highlighting the utility of the platform in photonic applications such as spectroscopy, sensing, and microscopy.

All-fiber fast acousto-optic temporal control of tunable optical pulses

We demonstrate a new all-fiber electrically tunable modulation method which significantly reduces the response time of a Bragg grating acousto-optic modulator. A 4 cm long device is fabricated with a 1 cm grating inscribed in a suspended core fiber. An acoustic pulse train is switched out of phase along the fiber, damping unwanted natural resonant vibrations inside the grating. The device rise time is decreased from 56 to 9 µs by tuning the duty cycle of the driven electrical signal, contributing to achieve the shortest switching time of 15.6 µs. This tunable temporal response reveals unique features to change the profile of optical pulses. High pulse modulation depths are achieved employing a compact acousto-optic modulator, pointing to fast switching of all-fiber photonic devices.

Innovative suspended ring core fiber for SERS application

Solid core photonic crystal fibers (SC-PCFs) have garnered attention as probes for surface-enhanced Raman spectroscopy (SERS) due to their potential as optofluidic devices, offering heightened sensitivity and reliability compared to traditional planar/colloidal nanoparticle-based SERS platforms. A smaller core allows for more light interaction but might compromise sensitivity and reliability due to reduced surface area for interaction. Here, we introduce an innovative SC-PCF design aimed at resolving the trade-off between increasing the evanescent field fraction and the core surface area. By substituting a suspended silica rod with a suspended thin-silica ring, we augment the surface area for attached nanoparticles by one order of magnitude while retaining a substantial amount of evanescent light interaction with the analyte. Experimental findings showcase an improved sensitivity in SERS signal compared to previously reported top-performing PCF sensor designs. Importantly, with necessary refinement and optimization, this innovative fiber design extends beyond SERS applications, potentially amplifying the sensitivity of various other fiber-based sensing platforms.

Surface-Enhanced Raman Scattering in Silver-Coated Suspended-Core Fiber.

In this paper, the silver-coated large-core suspended-core fiber (LSCF) probe was fabricated by the dynamic chemical liquid phase deposition method for surface-enhanced Raman scattering (SERS) sensing. The 4-mercaptophenylboronic acid (4-MPBA) monolayer was assembled in the LSCF as the recognition monolayer. Taking advantage of the appropriate core size of the LSCF, a custom-made Y-type optical fiber patch cable was utilized to connect the semiconductor laser, Raman spectrometer, and the proposed fiber SERS probe. The SERS signal is propagated in the silver-coated air channels, which can effectively reduce the Raman and fluorescence background of the silica core. Experiments were performed to measure the Raman scattering spectra of the 4-MPBA in the silver-coated LSCF in a non-enhanced and enhanced case. The experiment results showed that the Raman signal strength was enhanced more than 6 times by the surface plasmon resonance compared with the non-enhanced case. The proposed LSCF for SERS sensing technology provides huge research value for the fiber SERS probes in biomedicine and environmental science. The combination of SERS and microstructured optical fibers offers a potential approach for SERS detection.

Simultaneous measurement of high temperature and strain based on miniature tip-packaged dual-FPIs

A miniature tip-packaged dual-FPIs sensor featuring an extremely simple fabrication process is introduced and experimentally demonstrated for simultaneously measuring high-temperature and strain. Under the specific splicing parameters, a piece of suspended-core fiber with micron-scale dimensions and the single-mode fiber are spliced, forming the effective part of the sensor, which includes an air cavity and a silica cavity. Due to the disparate temperature responses (silica cavity: 7.31 pm/°C at 25–300 °C, 16.08 pm/°C at 300–800 °C; air cavity: 0 pm/°C) and strain responses (silica cavity:1.23 pm/µε; air cavity: 3.97 pm/µε) of these two cavities, simultaneous measurement of both parameters could be realized through coefficient matrix demodulation. Repeatability and high-temperature stability of this sensor within 5.5 ℃ have been verified, while the maximum hysteresis error of 0.205 nm has been analyzed. This miniature sensor exhibits excellent repeatability and stability, rendering it appropriate for an extensive array of practical applications in harsh environments.

High sensitivity twist sensor based on suspended core fiber Sagnac interferometer with temperature calibration.

A high sensitivity optical fiber twist sensor based on Suspend Core Fiber Sagnac Interference (SCFSI) is proposed and experimentally demonstrated. By filling the air hole of the Suspend Core Fiber (SCF) with alcohol, the twist sensitivity of the twist sensor is greatly improved to 8.37 nm/°. Moreover, the valid angle measurement range of the sensor can be expanded by utilizing the combination of intensity demodulation and wavelength demodulation. The sensor not only has high twist angle sensitivity but also exhibits a capability of temperature calibration. Since the wavelength shifts of the interference fringes of Mach-Zehnder Interferometer (MZI) formed in the suspend core of SCF appears insensitive to twist angle, the parasitic interference formed by MZI can be used for temperature calibration. Due to compact structure, easy fabrication and low temperature cross sensitivity, the proposed sensor has a great potential for structural health monitoring, such as buildings, towers, bridges, and many other infrastructures.

Label free optofluidic DNA hybridization detection based on suspended core fiber whispering gallery mode resonator

An optofluidic DNA biosensor based on a suspended core fiber (SCF) has been proposed for the detection of specific DNA sequence fragments. The sensor is formed by coupling a micro/nano tapered optical fiber to the cladding of an SCF, producing a whispering gallery mode (WGM) effect. The WGM resonance is sensitive to samples within the channels of the SCF. The diameter of the SCF is reduced by etching to increase refractive index sensitivity, up to 274 nm/RIU. Biomarkers are captured on the inner surface of the microfluidic channel leading to a change in the local refractive index. The experimental results show that the sensor can quantitatively detect complementary DNA (cDNA) by immobilizing probe DNA (pDNA) on the surface of the microfluidic channel with a limit of detection of 1.5 nM. The proposed DNA biosensor provides a label-free method for DNA detection, which has great potential for multiplexed detection and realizing disease diagnostics.

Photonic nano-jet generated by suspended core fiber

The photonic nano-jet (PNJ) generated by the suspended core fiber (SCF) is proposed and experimentally demonstrated. Gaussian light irradiates the suspended core fiber, the PNJ is formed at the shadow-side surface of the suspended core. The measured results show that the full-width half-maximum (FWHM) of the PNJ is smaller than the incident light wavelength, and the propagation distance is several times that of the light wavelength. The experimental results are in a good agreement with the theoretical calculations. As the incident wavelength or the fiber core diameter decreases, the FWHM and decay length of the PNJ are significantly reduced. The FWHM of 0.73λ is achieved. The calculation results show that the SCF-based PNJ can achieve non-contact capture of a single nanoparticle. Suspended core fiber is easy to fabricate, simple and convenient to operate experimentally, and can produce a more stable PNJ that is less contaminated. Fiber-based PNJs offer new applications in particle capture and biophotonic sensing.

High-temperature measurement based on highly-sensitive miniature cascaded FPIs and the harmonic Vernier effect

A highly-sensitive miniature sensor based on cascaded FPIs and the harmonic Vernier effect is proposed for high-temperature measurement. The package-free sensor is fabricated by only cleaving and splicing single-mode fiber (SMF), suspended core fiber (SCF), and hollow core fiber (HCF). By carefully adjusting the lengths of SCF and HCF, the Vernier effect and harmonic Vernier effect are generated on two sensors built by the same method, respectively. The reflected spectra exhibit distinct characteristics depending on the direction of incident light. Leveraging on the harmonic Vernier effect, the sensor of this type could achieve the highest sensitivity of 109.72 pm/℃ and maintain a maximum temperature fluctuation of only 4.12 ℃ under 800 ℃ without any temperature-sensitive material. In addition, the repeatability has been verified and the hysteresis errors have been analyzed. This miniature sensor exhibits excellent repeatability and stability, making it well-suited for high-temperature measurements in harsh environments.

Supercontinuum generation based on suspended core fiber infiltrated with butanol

Supercontinuum generation based on suspended core fiber infiltrated with butanol

Tuning of the Brillouin scattering properties in microstructured optical fibers by liquid infiltration

We demonstrate the possibility to modify the Brillouin scattering properties of a microstructured pure-silica core optical fiber, by infiltrating a liquid inside its holes. In particular, we show that the dependence of the Brillouin frequency shift (BFS) on the temperature can be reduced by infiltration, owing to the large negative thermo-optic coefficient of the liquid. Infiltrating a chloroform-acetonitrile mixture with a refractive index of 1.365 inside the holes of a suspended-core fiber with a core diameter of 3 µm, the BFS temperature sensing coefficient is reduced by ≈ 21%, while the strain sensitivity remains almost unaltered. Besides tuning the temperature sensing coefficient, the proposed platform could find other applications in Brillouin sensing, such as distributed electrical and magnetic measurements, or enhanced Brillouin gain in fibers infiltrated with high nonlinear optical media.

Highly sensitive fiber-optic temperature sensor with compact hybrid interferometers enhanced by the harmonic Vernier effect.

A compact fiber-optic temperature sensor with hybrid interferometers enhanced by the harmonic Vernier effect was proposed, which realized 36.9 times sensitization of the sensing Fabry-Perot interferometer (FPI). The hybrid interferometers configuration of the sensor consists of a FPI and a Michelson interferometer. The proposed sensor is fabricated by splicing the hole-assisted suspended-core fiber (HASCF) to the multi-mode fiber fused with the single-mode fiber, and filling polydimethylsiloxane (PDMS) into the air hole of HASCF. The high thermal expansion coefficient of PDMS improves the temperature sensitivity of the FPI. The harmonic Vernier effect eliminates the limitation of the free spectral range on the magnification factor by detecting the intersection response of internal envelopes, and realizes the secondary sensitization of the traditional Vernier effect. Combing the characteristics of HASCF, PDMS, and first-order harmonic Vernier effect, the sensor exhibits a high detection sensitivity of -19.22 nm/°C. The proposed sensor provides not only a design scheme for compact fiber-optic sensors, but also a new strategy to enhance the optical Vernier effect.

Erbium-doped fiber laser based on intermodal interference between single-mode fiber and suspended core fiber for strain and temperature sensing

In this paper, a strain and temperature sensing system based on an erbium-doped fiber laser (EDFL) is proposed and experimentally verified. The cavity mirror of the fiber laser is composed of an optical coupler (OC) and a circulator. An intermodal interference between a single-mode fiber and a 12.4-mm suspended core fiber (SCF) is used as a frequency-selective device. The period and wave height of the SCF transmission spectrum is 6.30 nm and 4.188 dB. The fiber laser has a peak wavelength and power of 1564.46 nm and −14.729 dBm, respectively. The peak wavelength of the fiber laser drifts toward a short wavelength as the SCF is stretched from zero to 1200 με. The laser undergoes the transition from a single wavelength to a dual wavelength. According to the measurement results, the system's strain sensitivity is 1.80 pm/με, and its linearity is 98.30%. A temperature rise experiment from 100 °C to 1000 °C is carried out on the SCF, and the peak wavelength of the fiber laser drifts toward a long wavelength. The temperature sensitivity of the system is 1.88 pm/°C, and the linearity is 98.58%.

Controlled fiber core mode and surface mode interaction for enhanced SERS performance.

Three-dimensional surface-enhanced Raman scattering (SERS) platform based on microstructure fibers has many advantages for rapid liquid detection due to its microfluidic channels and light guidance. The fiber mode field distribution determines the light-analyte interaction strength but has rarely been studied in SERS applications. In this paper, we numerically and experimentally investigate the mode field distribution in suspended-core fibers decorated with gold nanoparticles. The interaction between the core mode and surface mode is controlled by changing the density of gold nanoparticles on the inner surface. The avoided crossing wavelength shifts linearly to red with the decrease of the nanoparticle spacing. With an optimized nanoparticle spacing of 20 nm, the avoided crossing occurs near the laser wavelength of 633 nm, which greatly increases the power ratio in the liquid channels and hence improves the SERS performance. The detection limit for crystal violet was 10-9 M, and the enhancement factor was 108. The avoided crossing mechanism can be applied to all fiber SERS probes for sensitivity improvement.

Optical Fiber Sensor for Curvature and Temperature Measurement Based on Anti-Resonant Effect Cascaded with Multimode Interference

In this paper, a novel inline optical fiber sensor for curvature and temperature measurement simultaneously has been proposed and demonstrated, which can measure two parameters with very little crosstalk. Two combinational mechanisms of anti-resonant reflecting optical waveguide and inline Mach-Zehnder interference structure are integrated into a 3 mm-long single hole twin suspended core fiber (SHTSCF). The 85 μm hole core gives periodic several dominant resonant wavelengths in the optical transmission spectrum, acting as the anti-resonant reflecting optical waveguide (ARROW). The modes in two suspended cores and the cladding form the comb pattern. Reliable sensor sensitivity can be obtained by effective experiments and demodulation. Through intensity demodulation of the selected dip of Gaussian fitting, the curvature sensitivity can be up to -7.23 dB/m-1. Through tracking the MZI dip for wavelength demodulation, the temperature sensitivity can be up to 28.8 pm/°C. The sensor is simple in structure, compact, and has good response, which can have a bright application in a complex environment.

Mid-infrared supercontinuum generation in liquid-filled chalcogenide suspended core fiber

A design of liquid-filled suspended core microstructured optical fiber based on arsenic-selenide glass has been proposed to generate supercontinuum in the mid-infrared region. Two different non-linear liquids with high non-linear refractive index, such as chloroform and carbon disulfide have been employed in the air holes of the proposed design. From simulation results it is demonstrated that, ultra-wideband supercontinuum spectra ranging from 0.9 µm to 13 µm is made possible using only 2 mm long chloroform-filled suspended core fiber.

Semi-Supervised Deep Learning Model for Efficient Computation of Optical Properties of Suspended-Core Fibers.

Suspended-core fibers (SCFs) are considered the best candidates for enhancing fiber nonlinearity in mid-infrared applications. Accurate modeling and optimization of its structure is a key part of the SCF structure design process. Due to the drawbacks of traditional numerical simulation methods, such as low speed and large errors, the deep learning-based inverse design of SCFs has become mainstream. However, the advantage of deep learning models over traditional optimization methods relies heavily on large-scale a priori datasets to train the models, a common bottleneck of data-driven methods. This paper presents a comprehensive deep learning model for the efficient inverse design of SCFs. A semi-supervised learning strategy is introduced to alleviate the burden of data acquisition. Taking SCF’s three key optical properties (effective mode area, nonlinear coefficient, and dispersion) as examples, we demonstrate that satisfactory computational results can be obtained based on small-scale training data. The proposed scheme can provide a new and effective platform for data-limited physical computing tasks.

Suspended-core fiber with embedded GaSe nanosheets for second harmonic generation.

We report an all-fiber scheme for the second harmonic generation (SHG) by embedding gallium selenide (GaSe) nanosheets into a suspended-core fiber (SCF). Based on modes analysis and theoretical calculations, the phase-matching modes from multiple optional modes in the SHG process and the optimal SCF length are determined by calculating the effective refractive index and balancing the SHG growth and transmission loss. Due to the long-distance interaction between pumped fundamental mode and GaSe nanosheets around the suspended core, an SHG signal is observed under a milliwatt-level pump light, and exhibits a quadratic growth with the increased pump power. The SHG process is also realized in a broad wavelength range by varying the pump in the range of 1420∼1700 nm. The SCF with the large air cladding and suspended core as an excellent platform can therefore be employed to integrate low-dimensional nonlinear materials, which holds great promise for the applications of all-fiber structures in new light source generating, signal processing and fiber sensing.

Efficient calculation of optical properties of suspended-core fiber via a machine learning algorithm.

Growing nonlinearity demands in mid-infrared applications place more outstanding requirements on fiber structure design. Chalcogenide suspended-core fibers (SCFs) are considered excellent candidates for mid-infrared applications due to their significant advantages in nonlinearity and dispersion management. However, traditional numerical methods for accurate modeling and optimization of SCFs often rely on the performance of computing devices and have many limitations when dealing with complex models. A machine learning algorithm is applied to calculate the optical properties of chalcogenide SCFs, including effective mode area, nonlinear coefficient, and dispersion. The established artificial neural network (ANN) model enables accurate prediction of the above optical properties of As2S3 SCF, for which in the wavelength range of 1.0 to 4.0 µm, the radius of the fiber core is 0.4 to 0.6 µm, and width of the cantilever is 0.06 to 0.09 µm. We demonstrate that this simple ANN model has considerable advantages over the traditional numerical calculation model in computational speed and resource utilization. In summary, the proposed model can quickly provide more accurate optical property predictions, providing a cost-effective solution for precise modeling and optimization of chalcogenide SCFs.

Lateral Force Sensing Based on Sagnac Interferometry Realized by a High-Birefringence Suspended-Core Fiber

In this paper, a directional lateral force sensor realized with a high-birefringence suspended-core fiber (HB-SCF)) based on a Sagnac interferometer (SI) is proposed and demonstrated experimentally. The two ends of a 40-cm long HB-SCF are spliced to the two arms of a 3-dB coupler to form the Sagnac interferometer. The lateral force leads to a change in refractive index, thus altering the birefringence of the HB-SCF. The output spectra show a wavelength shift which has a linear relationship with the lateral force. The relationship between the lateral force direction and the force sensitivity was investigated. A finite element analysis (FEA) is conducted to simulate the lateral force responses of the sensor, and the force sensitivities of various force directions are calculated theoretically. The results of both simulation and sensing experiment show that the lateral force sensitivity varied with the force-applied direction in a period of π, and the maximum lateral force sensitivity of 19.032 nm/(N/mm) was achieved. Such lateral force sensor has a good repeatability and low temperature sensitivity.Due to its simple fabrication, low cost, and high sensitivity, it is expected to be a competitive candidate in force sensing applications.