Suspended-core Microstructured Optical Fiber Research Articles

Supercontinuum-induced multi-wavelength third-harmonic generation in a suspended-core microstructured optical fiber.

In this paper, we reported a multi-wavelength third-harmonic generation (THG) induced by supercontinuum (SC) in an in-house fabricated suspended-core microstructured optical fiber (MOF). The adjustment of pump wavelength and pump power exerted an influence on SC which simultaneously emitted third harmonic (TH) waves in the visible light range. At the pump wavelength of 1220 nm and the average pump power of 450 mW, a multi-wavelength TH spectrum (373∼589 nm) with over twenty distinct peaks was observed under the phase matching (PM) condition between the fundamental mode and the higher-order modes. To the best of our knowledge, this is the first report on THG in optical fibers with so great a number of wavelengths. The maximal THG conversion efficiency ∼6.791 × 10-4 was obtained at 1480 nm, 350 mW, which is highly competitive compared with the values reported previously. Furthermore, theoretical simulation has been carried out, which corresponded well with the experimental observation. This multi-wavelength THG in the suspended-core MOF may provide a unique pathway towards tailored multi-wavelength ultrafast light sources for applications in sensing and imaging technologies.

High-resolution, large-dynamic-range multimode interferometer sensor based on a suspended-core microstructured optical fiber

The performance of sensors, including optical fiber sensors, is commonly limited by the tradeoff between a large dynamic range and a high resolution. In this Letter, in order to optimize both, we propose an inline multimode interferometer sensor based on a suspended-core microstructured optical fiber. Due to the existence of multiple pairs of mode interferences, the transmission spectrum of the interferometer consists of dense fringes modulated by a lower envelope. Since these mode interferences take place in the uniform material with the same length, the dense fringes and the lower envelope have an identical sensing response without crosstalk. Hence, the sensor integrates the large dynamic range of the lower envelope and the high resolution of the dense fringes. Strain-sensing performance is investigated to validate the characteristic of the large dynamic range and the high resolution of the proposed sensor. The dynamic range, theoretically 0-9200 µɛ, is 12 times larger than for the dense fringes, and the resolution is 17.5 times higher than for the lower envelope.

Parallel Double-FPIs Temperature Sensor Based on Suspended-Core Microstructured Optical Fiber

A configuration based on a parallel double Fabry–Perot interferometers (FPIs) is proposed and experimentally demonstrated to enhance the temperature sensitivity by Vernier-effect. Two separated FPIs constructed by suspended-core microstructured optical fiber (SCMF) are connected by a 3-dB coupler to form a parallel structure. FPI-2 is used for temperature sensing, while FPI-1 as a reference. With the temperature increasing from 40 °C to 220 °C, both the fine interference fringes and envelope have a linear redshift. This parallel double-FPIs configuration shows an enhanced temperature sensitivity of 153.8 pm/°C with an amplification factor ${M} =14.6$ . Moreover, since the free reference FPI-1 is away from the temperature sensing environment, this simple and novel parallel double-FPIs configuration provides good reversibility and stability during the heating and cooling processes.

Suspended core microstructured optical fibers with diverse arrangements of gold-filled holes: study of the polarization characteristics and resonance strength

We study the dispersion and polarization properties as well as the coupling characteristics of suspended core microstructured optical fibers (SC-MOFs) having constant pitch and air-filling fraction with a varying suspension factor (SF) and diverse arrangements of gold-filled holes. The interaction between the core-guided fundamental mode and the surface plasmon polaritons (SPPs) generated on the surface of the gold-filled hole creates surface plasmon resonance (SPR) at the phase-matching wavelengths. It is observed that such plasmonic SC-MOF designs exhibit very high birefringence and an increased number of complete coupling points for high SF values. In addition, for all the arrangements of gold-filled holes, the coupling occurs for a higher order of the SPP for structures having greater SF. The resonance strength of such SC-MOFs is significantly enhanced and considerable reduction in full width at half maximum (FWHM) bandwidth of the SPR peak is achieved for the ${ x}$x-axis with suitable arrangement of gold-filled holes. The values of the coupling strength and FWHM achieved for the proposed SC-MOF structures are better compared to all the data reported until now to the best of our knowledge. The results suggest that such SC-MOF structures may be beneficial for developing polarizers or in-fiber polarization splitters with improved performance.

High-temperature sensor based on suspended-core microstructured optical fiber.

We propose a high-temperature sensor based on a suspended-core microstructured optical fiber (SCMF). The sensor is constructed by fusion splicing a piece of SCMF between two sections of multimode fibers (MMFs) which act as light beam couplers. The multimode interference is formed by the air cladding modes and the silica core modes in the SCMF. Fast Fourier transform is adapted to filtering the raw transmission spectra of the MMF-SCMF-MMF structure. The wavelength shift of the dominant spatial frequency is monitored as the temperature varies from 50 °C to 800 °C. The sensitivities of 31.6 pm/°C and 51.6 pm/°C in the temperature range of 50 °C-450 °C and 450 °C-800 °C are respectively achieved. Taking advantage of the compact size, good stability and repeatability, easy fabrication, and low cost, this proposed high-temperature sensor has an applicable value.

Polarization Properties of Selectively Gold-filled Suspended Core Microstructured Optical Fibers

We study the polarization properties of suspended core microstructured optical fibers (SC-MOFs) with hexagonal lattice structure and high air-filling fraction having a single gold-filled hole along the horizontal axis. The interaction between the core-guided light and metal leads to surface plasmon resonance (SPR) at particular frequencies where the phase-matching condition is satisfied. We observe from the modal analysis that MOFs with high air-filling fraction offer the possibility of coupling of the fundamental mode with the first-order surface plasmon polariton (SPP) mode. With the increase in the suspension factor (SF), the fundamental mode couples with higher order SPP modes and the coupling strength also enhances. It also leads to an increase in modal birefringence. Reduction in beat length by an order of magnitude compared to the reported values is being reported for the first time to our knowledge. We have achieved the lowest beat length of 0.0105 mm at 1 μm wavelength for the structure having d/Λ = 0.85 and SF = 1.65. The results show that such plasmonic SC-MOFs may perform as efficient in-fiber polarizers and polarization filters.

Multi-Plasmon Resonances in Microstructured Optical Fibers: Extending the Detection Range of SPR Sensors and a Multi-Analyte Sensing Technique

In this paper, multi-plasmon resonances in microstructured optical fibers (MOFs) are proposed and analyzed as a methodology to achieve surface-plasmon-resonance (SPR) sensors with a wide refractive index (RI) detection range and as a multi-analyte sensing technique. For this purpose, the influence of multi-plasmon excitations on the performance of SRP sensors based on suspended core microstructured optical fibers (SCFs) with three and four holes was studied theoretically. A large analyte RI range from 1.33 to 1.39 was evaluated to investigate the sensing performance of the SCF-based SPR sensors. The results indicate that the excitation of higher order SPP modes could be an alternative to achieve SPR sensors with a wide analyte RI range and competitive resolution. We found that the shape of the fiber core and the metallized surface have a significant effect on the plasmonic excitation spectra. We also found that multi-plasmon excitations have potential for multi-analyte sensing and self-reference. This paper can provide a reference for developing MOF-based SPR sensors.

Experimentally and analytically derived generalized model for the detection of liquids with suspended-core optical fibers

Abstract A generalized model for the detection of liquids within suspended-core microstructured optical fibers has been experimentally and theoretically derived. The sensor detection is based on the refractometric principle of transmission losses due to the overlap of the evanescent field with the liquid analyte. A number of parameters, including fiber core diameter and filling length, have been included in the general model. Specially tailored suspended-core fibers were manufactured with the core diameters within the range of 2.4 μ m to 4.0 μ m. Five selected liquid analytes were used to cover the refractive index range of 1.35 to 1.42. Based on experiments, the characteristics of the parameters of the semi-empirical model have been determined by a genetic algorithm using 283 measurement data sets. The model can be used to design sensors for the detection of liquid analytes as it provides a set of parameters allowing to optimize the sensor’s sensitivity for a wide scale of applications. Finally, numerical simulations of the system were carried out by an eigenmode routine to support the results of the generalized model.

Comparison between Different Structures of Suspended-Core Microstructured Optical Fibers for Volatiles Sensing.

In this paper, different core structures of microstructured optical fibers (MOFs) for low-finesse Fabry–Pérot (FP) sensors are experimentally compared to get the highest sensitivity. These devices are designed for volatile organic compounds (VOCs) measurements. Indium tin oxide (ITO) thin films were deposited by sputtering on the MOFs and different optical fast Fourier transform (FFT) phase responses from the FP were measured for saturated atmospheres of ethanol. It has been demonstrated that the sensitivities of the developed sensors depend strongly on the geometry and the dimensions of the MOF-cores. The sensors show recovery times shorter than 100 s and the baselines are fully recovered after every exposure to ethanol vapors.

Magneto-optical Faraday effect in suspended core micro-structured optical fiber filled with magnetic CoFe2O4 nanoparticles doped composite material

This paper deals with the study of the magneto-optical Faraday effect of micro-structured optical fibers with suspended cores covered by a silica matrix doped by CoFe2O4 nanoparticles. Two different size distributions of nanoparticles originated from two magnetic fluids have been used to dope a sol-gel preparation later introduced in the fiber. Faraday rotation measurements were performed in liquid state, thin film and finally in the fiber in guided configuration. The two different magnetic behaviors of these nanoparticles collections allow us to evidence the Faraday effect of the micro-structured optical fiber.

Photoswitchable calcium sensor: ‘On’–‘Off’ sensing in cells or with microstructured optical fibers

Calcium is a ubiquitous intracellular signaling ion that plays a critical role in the modulation of fundamental cellular processes. A detailed study of these processes requires selective and reversible sensing of Ca2+ and an ability to quantify and monitor concentration changes in a biological setting. Three new, rationally designed, synthesized and photoswitchable spiropyran-based reversible sensors for Ca2+ are reported. Sensor 1a is highly selective for Ca2+ with an improved profile relative to the other two analogues, 1b and 1c. Formation of the merocyanine–Ca2+ complex is proportional to an increase in Ca2+ released from HEK293 cells on stimulation with ionomycin. The photophysical processes surrounding the binding of Ca2+ to compound 1a were further explored using computational methods based on density functional theory (DFT). The ability of sensor 1a to bind Ca2+ and photoswitch reversibly was also characterized using silica suspended-core microstructured optical fiber (SCF). These SCF experiments (with 100nM Ca2+) represent a first step toward developing photoswitchable, minimally invasive and highly sensitive Ca2+ sensing platforms for use in a biological setting.

Investigation on optical and acoustic fields of stimulated Brillouin scattering in As2S3 suspended-core microstructured optical fibers

The optical and acoustic fields of stimulated Brillouin scattering (SBS) and the interaction between them are investigated in the As2S3 chalcogenide suspended-core microstructured optical fibers (MOFs) by the finite-element method (FEM). The optical and acoustic fundamental modes are analyzed at 1550nm. The core diameters of the MOFs vary from 1.0 to 6.0μm. For each case, the holes of the MOFs are filled with different materials such as trichlormethane (CHCL3), alcohol and water. When the core diameter is 6.0, 4.5, 3.0, 2.0 and 1.0μm, the ratios of difference for optical fields are ∼0.66%, 0.97%, 1.48%, 1.94% and 3.55%, respectively, while the ratios of difference for acoustic fields are ∼0.13%, 0.24%, 0.34%, 0.74% and 29.13%, respectively. The overlap factors between optical and acoustic fields are calculated, which change with the core diameter and the filled material. The results will be helpful to strengthen or suppress the SBS effect in practical applications.

Experimental long-term survey of mid-infrared supercontinuum source based on As2S3 suspended-core fibers

The evolution of supercontinuum generation in chalcogenide suspended-core microstructured optical fibers is studied with regard to their exposure to the room atmosphere. We report the experimental proof of aging-induced supercontinuum generation drift in chalcogenide microstructured fibers. Mid-infrared supercontinuum covering the 2.5–5.5-µm spectral region is demonstrated in a fresh and 7-month-aged counterpart As2S3 fibers, by means of a home-built multistage oscillator power amplifier delivering 300 fs pulses at a repetition rate of 43 MHz in the 3.0–4.1-µm range. Numerical simulations based on the generalized nonlinear Schrodinger equation confirm the significant alteration of supercontinuum generation due to increasing fundamental OH and SH absorption bands.

Microstructured Optical Fiber-based Biosensors: Reversible and Nanoliter-Scale Measurement of Zinc Ions.

Sensing platforms that allow rapid and efficient detection of metal ions would have applications in disease diagnosis and study, as well as environmental sensing. Here, we report the first microstructured optical fiber-based biosensor for the reversible and nanoliter-scale measurement of metal ions. Specifically, a photoswitchable spiropyran Zn(2+) sensor is incorporated within the microenvironment of a liposome attached to microstructured optical fibers (exposed-core and suspended-core microstructured optical fibers). Both fiber-based platforms retains high selectivity of ion binding associated with a small molecule sensor, while also allowing nanoliter volume sampling and on/off switching. We have demonstrated that multiple measurements can be made on a single sample without the need to change the sensor. The ability of the new sensing platform to sense Zn(2+) in pleural lavage and nasopharynx of mice was compared to that of established ion sensing methodologies such as inductively coupled plasma mass spectrometry (ICP-MS) and a commercially available fluorophore (Fluozin-3), where the optical-fiber-based sensor provides a significant advantage in that it allows the use of nanoliter (nL) sampling when compared to ICP-MS (mL) and FluoZin-3 (μL). This work paves the way to a generic approach for developing surface-based ion sensors using a range of sensor molecules, which can be attached to a surface without the need for its chemical modification and presents an opportunity for the development of new and highly specific ion sensors for real time sensing applications.

Combining whispering gallery mode lasers and microstructured optical fibers: limitations, applications and perspectives for in-vivo biosensing

ABSTRACTWhispering gallery modes (WGMs) have been widely studied over the past 20 years for various applications, including biological sensing. While the WGM-based sensing approaches reported in the literature have shown tremendous performance down to single molecule detection, at present such sensing technologies are not yet mature and still have significant practical constraints that limit their use in real-world applications. Our work has focused on developing a practical, yet effective, WGM-based sensing platform capable of being used as a dip sensor for in-vivo biosensing by combining WGM fluorescent microresonators with silica Microstructured Optical Fibers (MOFs).We recently demonstrated that a suspended core MOF with a dye-doped polymer microresonator supporting WGMs positioned onto the tip of the fiber, can be used as a dip sensor. In this architecture the resonator is anchored to one of the MOF air holes, in contact with the fiber core, enabling a significant portion of the evanescent field from the fiber to overlap with the sphere and hence excite the fluorescent WGMs. This architecture allows for remote excitation and collection of the WGMs. The fiber also permits easy manipulation of the microresonator for dip sensing applications, and hence alleviates the need for a complex microfluidic interface. More importantly, it allows for an increase in both the excitation and collection efficiency compared to free space coupling, and also improves the Q factor.In this paper we present our recent results on microstructured fiber tip WGM-based sensors and show that this sensing platform can be used in clinical diagnostics, for detecting various clinically relevant biomarkers in complex clinical samples.

Interferometric high temperature sensor using suspended-core optical fibers

We propose and experimentally demonstrate, for the first time to our knowledge, high temperature fiber sensing using the multimode interference effect within a suspended-core microstructured optical fiber (SCF). Interference fringes were found to red-shift as the temperature increased and vice versa. Temperature sensing up to 1100°C was performed by measuring the wavelength shifts of the fringes after fast Fourier transform (FFT) filtering of the spectra. In addition, phase monitoring at the dominant spatial frequency in the Fourier spectrum was used as an interrogation method to monitor various temperature-change scenarios over a period of 80 hours. Our proposed high temperature fiber sensor is simple, cost-effective, and can operate at temperatures beyond 1000°C.

Temperature sensing up to 1300°C using suspended-core microstructured optical fibers.

We demonstrate a new approach to high temperature sensing using femtosecond laser ablation gratings within silica suspended-core microstructured optical fibers. The simple geometry of the suspended-core fiber allows for femtosecond laser processing directly through the fiber cladding. Pure silica glass is used, allowing the sensor to be used up to temperatures as high as 1300°C while still allowing the fibre to be spliced to conventional fiber. The sensor can also be wavelength division multiplexed, with three sensors in a single fiber demonstrated.

Suspended-core microstructured fiber for refractometric detection of liquids.

A silica suspended-core microstructured optical fiber sensor for detection of liquids, operating at 1550nm, is analyzed. The sensing principle is based on the evanescent wave overlap into a tested analyte, which is filled via capillary forces into the cladding holes. Validations for analytes in the refractive index range of 1.35-1.43 are carried out with liquid-analyte-filling-length limits being studied both theoretically and experimentally. We prove, for the first time to our knowledge, that an extreme sensitivity of 342.86dB/RIU and resolution of 4.4×10-5 can be achieved. This sensor represents a high-quality alternative for applications requiring a facile, low-cost solution.

Nonlinear optical devices based on suspended-core microstructured optical fibers

Suspended-core microstructured optical fibers are employed in lasers that generate ultrashort pulses and supercontinuum generators. It is demonstrated that a femtosecond fiber laser based on the ytterbium-doped microstructured fiber generates pulses with a duration of 95 fs at a wavelength of 1045 nm and a mean power of 5 mW in the absence of additional compression. Supercontinuum is generated in tapered microstructured fibers with suspended core in the wavelength interval 400–1400 nm. Suspended-core micro-structured fibers may serve as promising elements for nonlinear optical devices due to specific waveguide characteristics, relative simplicity of manufacturing, and variable optical properties.

Mid-infrared 2000-nm bandwidth supercontinuum generation in suspended-core microstructured Sulfide and Tellurite optical fibers

In this work, we report the experimental observation of supercontinua generation in two kinds of suspended-core microstructured soft-glass optical fibers. Low loss, highly nonlinear, tellurite and As2S3 chalcogenide fibers have been fabricated and pumped close to their zero-dispersion wavelength in the femtosecond regime by means of an optical parametric oscillator pumped by a Ti:Sapphire laser. When coupled into the fibers, the femtosecond pulses result in 2000-nm bandwidth supercontinua reaching the Mid-Infrared region and extending from 750 nm to 2.8 µm in tellurite fibers and 1 µm to 3.2 µm in chalcogenide fibers, respectively.