Side-polished Single-mode Fiber Research Articles

Low loss side-polished pumping coupler for high order OAM modes amplification.

An all-fiber fiber coupler was demonstrated for pumping orbital angular momentum (OAM) modes amplification, which was fabricated by side-polishing and bonding a ring-core erbium-doped fiber (RC-EDF) and a pre-tapered side-polished single-mode fiber (SMF). With the selected phase-matching condition at 976 nm, the pumping laser was coupled into the RC-EDF from the SMF with optimized high efficiency, whereas the 1st to 3rd-order OAM mode signals were transmitted with the low insertion loss in the RC-EDF over a broadband wavelength range from 1530 to 1565 nm. This all-fiber wavelength division multiplexing coupler was optimized by the polished length and depth of the two coupled fibers. The insertion loss for the OAM signal modes was obtained lower than 0.58 dB with the pump power coupling ratio of above 90%. The proposed side-polished pumping coupler technique can ensure high-order OAM modes amplification, paving the way for the all-fiber optical amplifier in high-capacity modal-division multiplexing fiber communication systems.

Design and analysis of Micro-channelled Quasi D-shape optical Fiber plasmonic Sensor

This study reports on numerical investigation carried out over a newly designed open micro-channel incorporated, side polished single mode fiber (SMF) based plasmonic sensor. The proposed sensor operates on the principle of surface plasmon resonance (SPR) phenomenon to enhance the sensing performance. The commercially available COMSOL Multiphysics software tool is used to design sensor and finite element method (FEM) is used for numerical investigation. From the detail study, an average sensitivity of 1757 nm/RIU (refractive index unit) is obtained with a nanoscale gold strip for wide range of analyte RIs from 1.33 to 1.38. Result indicates that the fabricated sensor can be effectively used in RI measurement of the various fields involving chemical and biological sensing.

High-Sensitivity Triple-Channel Optical Fiber Surface Plasmon Resonance Sensor

Optical fiber surface plasmon resonance (SPR) sensors are widely used for refractive index (RI) sensing, thanks to their high sensitivity. However, with the increasing demand for multiple analytes detection and sensor integration, a traditional single-channel optical fiber SPR sensor is outdated. We propose and demonstrate a novel triple-channel optical fiber SPR sensor with high sensitivity. The sensor is fabricated with side-polished single-mode fiber (SMF), where the sensing film consists of a layer of gold nanofilm and a layer of TiO2 nanofilm. The resonance wavelength range of the SPR sensing zone can be adjusted significantly by changing the TiO2 nanofilm thickness. Experimentally, by cascading three sensing zones whose TiO2 nanofilm thicknesses are 10, 30, and 60 nm, respectively, a triple-channel SPR sensor is realized. The average sensitivities of three sensing channels reach up to 2637.8, 3962.2, and 6097.3 nm/RIU in the RI range of 1.333–1.370 RIU, which is superior to most current multichannel SPR sensors. Besides, three sensing channels are independent without crosstalk. The proposed triple-channel SPR sensor has great potential in biological and chemical sensing fields, especially in multiple analytes detection applications.

Optical fiber thermo-refractometer.

This work presents the implementation of a thermo-refractometer, which integrates the measurement of both refractive index and temperature in a single optical fiber structure. To this purpose, a lossy mode resonance (LMR)-based refractometer is obtained by means of the deposition of a titanium dioxide (TiO2) thin film onto a side-polished (D-shaped) single mode fiber. Measurement and subsequent temperature compensation are achieved by means of a fiber Bragg grating (FBG) inscribed in the core of the D-shaped region. The LMR wavelength shift is monitored in transmission while the FBG (FBG peak at 1533 nm) displacement is observed in reflection. The LMR is sensitive to both the surrounding refractive index (SRI), with a sensitivity of 3725.2 nm/RIU in the 1.3324-1.3479 range, and the temperature (- 0.186 nm/°C); while the FBG is only affected by the temperature (32.6 pm/°C in the 25°C - 45°C range). With these values, it is possible to recover the SRI and temperature variations from the wavelength shifts of the LMR and the FBG, constituting a thermo-refractometer, where it is suppressed the effect of the temperature over the refractometer operation, which could cause errors in the fourth or even third decimal of the measured SRI value.

A quasi-distributed fiber magnetic field sensor based on frequency-shifted interferometry fiber cavity ringdown technique

A quasi-distributed fiber magnetic field sensing system based on frequency-shifted interferometry fiber cavity ringdown (FSI-FCRD) technique is proposed and demonstrated. In this scheme, multiple sensing units are connected in series in a frequency-shifted interferometer, and share one continuous-wave light source, one slow detector and one low-frequency data collector to lower the cost. In each unit, a side-polished single-mode fiber coated with the diluted water-based ferrofluid serves as the sensing element for enhancing sensitivity and mechanical strength. The cavity loss of each unit varies with the change of applied magnetic field, due to the tunable refractive index of the ferrofluid and the evanescent wave effect of the polished fiber. Therefore, the measurement of magnetic field can be realized by monitoring the cavity loss change. A dual-unit FSI-FCRD magnetic field sensing system was experimentally investigated. The cavity losses and locations of the two sensing units about 2500 m apart were synchronously achieved from a spatial domain ringdown signal of the system. The measured cavity loss of each sensing unit exhibited a good linear relationship with the magnetic field over a range of 0 to 250 Oe. The sensitivities were separately 6.7894 × 10−4 and 7.4980 × 10−4 dB/Oe, with the corresponding detection limits of 2.56 and 3.63 Oe. Through repeated measurements, the obtained baseline stabilities of the two units were 0.15% and 0.18%, respectively. By theoretical analysis, the maximum multiplexing number of sensing units can reach 30 over a 15.8-km distance under the same experimental settings. It indicates that multi-unit FSI-FCRD provides an alternative technique with low cost, high sensitivity and high stability for quasi-distributed magnetic field detection in many fields such as smart grids, biomedicine and national defense.

A Fiber Ring Laser Sensor with a Side Polished Evanescent Enhanced Fiber for Highly Sensitive Temperature Measurement.

We demonstrate a highly sensitive and practical fiber-based temperature sensor system. The sensor is constructed based on a fiber ring laser (FRL) as well as a side-polished fiber filled with isopropanol. The laser cavity of the sensing part fiber is polished by the wheel fiber polishing system with residual thickness (RT) is selected to detect the temperature in the FRL. Thanks to the high thermo-optic coefficient of isopropanol, the sensitivity of the proposed temperature sensor could be effectively improved by filling isopropanol in the cost-less side polished single mode fiber. Refractive index (RI) of isopropanol changes with the surrounding temperature variation allowing high-sensitivity temperature sensing. Experimental results demonstrate that the side polished fiber can efficiently excite high-order cladding modes which enhance the modular interference increase the interaction between the evanescent wave and the isopropanol. Besides, the results show that the sensitivity can be as high as 2 nm/°C in the temperature range of 25–35 °C.

Side-Polished Optical Fiber Structure for Sodium Nitrate Sensor

Side-polished optical fiber has long been used to build fiber sensors in a range of applications. In this work, we demonstrate a biochemical sensor application leading to sodium nitrate solutions enhanced by the interaction of multi-walled carbon nanotubes (MWCNTs) with evanescent field of propagating light in a side-polished optical fiber. Insertion loss of this sensor was estimated to be around 5 dB, which is quite high and close to the core index of the polished fiber. The influence of MWCNTs film, particularly on its sensitivity to sodium nitrate, was investigated by coating single drop of MWCNTs on a side-polished single mode fiber. It is observed the improvement of sensitivity with MWCNTs coated side-polished optical fiber has reached 0.125 dBm/°C near the resonant wavelength of 1550 nm. The experimental results clearly verify the present of MWCNTs on side-polished optical fiber has slightly influence the performance of the fiber. The output power values and shifting of the spectral positions were observed during the sensor tests by exposure of the sodium nitrate solutions with increasing concentration from 1 to 7%.

Investigation of a Side-Polished Fiber MZI and Its Sensing Performance

A novel all-fiber Mach–Zehnder interferometer (MZI), which consists of lateral core fusion splicing of a short section of side-polished single mode fiber (SMF) between two SMFs was proposed and demonstrated. A simple fiber side-polished platform was built to control the side polished depth through a microscope. The sensitivity of the fiber MZI structure to the surrounding refractive index (RI) can be greatly improved with the increase of the side-polished depth, but has no effect on the temperature sensitivity. The sensor with a polished depth of $44.2~\mu \text{m}$ measured RI sensitivity up to −118.0 nm /RIU (RI unit) in the RI range from 1.333 to 1.387, which agrees well with simulation results by using the beam propagation method (BPM). In addition, the fiber MZI structure also can achieve simultaneous measurement of both RI and temperature. These results show its potential for use in-line fiber type sensing application.

基于侧边粗抛磨单模光纤的高精度曲率传感技术研究

基于侧边粗抛磨单模光纤的高精度曲率传感技术研究

Temperature Sensor Based on Side-Polished Fiber SPR Device Coated with Polymer.

A highly sensitive temperature sensor based on surface plasmon resonance (SPR) of a side-polished single mode fiber is demonstrated. The sensor consists of a gold film coated side-polished fiber covered by a layer of UV-curable adhesive. Before introducing the UV-curable adhesive, the gold-coated fiber exhibits refractive index (RI) sensitivity of 1691.6 nm/RIU to 8800 nm/RIU in the range of 1.32 to 1.43. The resonant wavelength of the SPR sensor shifts to 650 nm when the adhesive is coated on the gold film, and is fixed at about 725 nm when the adhesive is cured. Due to the high thermo-optic and thermal expansion coefficient of the adhesive, the sensor structure achieves a temperature sensitivity of −0.978 nm/°C between 25 °C and 100 °C. The proposed optical fiber SPR sensor is simple, highly sensitive and cost effective, which may find potential applications for temperature measurements in the biomedical and environmental industries.

Design Optimization of Pd-Coated Side-Polished Single Mode Optical Fiber Hydrogen Sensors

Palladium (Pd)-based optical fiber sensors exhibit large sensitivity to detect hydrogen. We performed design study on Pd-coated side-polished optical fiber sensors using modal approach. The presence of buffer layer (i.e., the remaining cladding or other material) between core of the side polished single mode fiber and hydrogen absorbing Pd layer shows a strong effect on sensitivity. The thickness of buffer and Pd layers are optimized to achieve higher sensitivity. Use of different materials as buffer layer has been explored and we observed that teflon gives maximum sensitivity.

Mechanism and Characteristics of Humidity Sensing with Polyvinyl Alcohol-Coated Fiber Surface Plasmon Resonance Sensor.

A surface plasmon resonance (SPR) sensor based on a side-polished single mode fiber coated with polyvinyl alcohol (PVA) is demonstrated for relative humidity (RH) sensing. The SPR sensor exhibits a resonant dip in the transmission spectrum in ambient air after PVA film coating, and the resonant wavelength shifts to longer wavelengths as the thickness of the PVA film increases. When RH changes, the resonant dip of the sensor with different film-thicknesses exhibits interesting characteristics for optical spectrum evolution. For sensors with initial wavelengths between 550 nm and 750 nm, the resonant dip shifts to longer wavelengths with increasing RH. The averaged sensitivity increases firstly and then drops, and shows a maximal sensitivity of 1.01 nm/RH%. Once the initial wavelength of the SPR sensor exceeds 850 nm, an inflection point of the resonant wavelength shift can be observed with RH increasing, and the resonant dip shifts to shorter wavelengths for RH values exceeding this point, and sensitivity as high as −4.97 nm/RH% can be obtained in the experiment. The sensor is expected to have potential applications in highly sensitive and cost effective humidity sensing.

LP01 to LP11 mode convertor based on side-polished small-core single-mode fiber

An all-fiber LP01-LP11 mode convertor based on side-polished small-core single-mode fibers (SMFs) is numerically demonstrated. The linearly polarized incident beam in one arm experiences π shift through a fiber half waveplate, and the side-polished parts merge into an equivalent twin-core fiber (TCF) which spatially shapes the incident LP01 modes to the LP11 mode supported by the step-index few-mode fiber (FMF). Optimum conditions for the highest conversion efficiency are investigated using the beam propagation method (BPM) with an approximate efficiency as high as 96.7%. The proposed scheme can operate within a wide wavelength range from 1.3 μm to1.7 μm with overall conversion efficiency greater than 95%. The effective mode area and coupling loss are also characterized in detail by finite element method (FEM).

Optical Fiber Polarizer With Fe–C Film for Corrosion Monitoring

The detection of early corrosion is a key issue to mitigate the damage induced by metal corrosion. This paper presents a corrosion sensor for steel based on an iron film-coated optical fiber polarizer. The polarizer is fabricated by sputtering a Fe-C film on a side-polished single mode fiber. The new fabricated polarizer shows highly birefringence, indicated by the difference of the transmission between the TE and TM modes, as well as the extinction ratio (ER). A series of simulations has been performed based on two models. The influences of the parameters of the sensor fabrication, the surrounding media, and film composition on the ER ratio and leakage are studied by the simulations. The accelerated corrosion experiments by immersing the polarizer into NaCl solution show that the polarizers become weakly birefringent after exposure. The results show that the ER and measured optical power decrease gradually during the corrosion process. The proposed polarizer can be used for monitoring the early stage of steel corrosion by building the relationship between the corrosion status and the polarization characteristics.

Saturated evanescent-wave absorption of few-layer graphene-covered side-polished single-mode fiber for all-optical switching

Abstract Using the evanescent-wave saturation effect of hydrogen-free low-temperature synthesized few-layer graphene covered on the cladding region of a side-polished single-mode fiber, a blue pump/infrared probe-based all-optical switch is demonstrated with specific wavelength-dependent probe modulation efficiency. Under the illumination of a blue laser diode at 405 nm, the few-layer graphene exhibits cross-gain modulation at different wavelengths covering the C- and L-bands. At a probe power of 0.5 mW, the L-band switching throughput power variant of 16 μW results in a probe modulation depth of 3.2%. Blue shifting the probe wavelength from 1580 to 1520 nm further enlarges the switching throughput power variant to 24 mW and enhances the probe modulation depth to 5%. Enlarging the probe power from 0.5 to 1 mW further enlarges the switching throughput power variant from 25 to 58 μW to promote its probe modulation depth of up to 5.8% at 1520 nm. In contrast, the probe modulation depth degrades from 5.1% to 1.2% as the pumping power reduces from 85 to 24 mW, which is attributed to the saturable absorption of the few-layer graphene-based evanescent-wave absorber. The modulation depth at wavelength of 1550 nm under a probe power of 1 mW increases from 1.2% to 5.1%, as more carriers can be excited when increasing the blue laser power from 24 to 85 mW, whereas it decreases from 5.1% to 3.3% by increasing the input probe power from 1 to 2 mW to show an easier saturated condition at longer wavelength.

Long range surface plasmon resonance sensor based on side polished fiber with the buffer layer of magnesium fluoride

In this paper, a theoretical analysis of figure of merit (FOM) of a surface plasmon resonance (SPR) sensor with a buffer layer of magnesium fluoride has been carried out. While the FOM is the ratio of sensitivity and full width at half maximum and it is the measurement index for the SPR performance. The numerical simulation is based on side polished single mode fiber SPR sensor with the 66.5 μm residual fiber thickness and Drude model of metal with the 50 nm gold film thickness. Meanwhile, the comparisons for traditional surface plasmon resonance sensor, symmetrical surface plasmon resonance sensor and long range surface plasmon resonance sensor have performed differently for the FOM. The effect of sensitivity, full width at half maximum and transmittance depth has also been studied. All these studies, lead to a significant analysis to achieve the best possible design of a fiber optic SPR sensor with maximum FOM while the thickness of buffer layer is 100 nm. This design is expected to play an important role on chemical sensing and biological sensing.

Design and optimization of nano-column array based surface plasmon resonance sensor

In this paper, a surface plasmon resonance fiber sensor based on gold nano-column array instead of gold film is designed and optimized. The finite element method is used to optimize the diameter of the nano-gold column under the consideration of figure of merit, which relates to the sensitivity, resonance wavelength and resonance intensity. The optimized sensor has 70 nm gold nano-column coated on a side polished single mode fiber. The results show that the average sensitivity reaches 5318 nm/RIU when the environmental refractive index changing from 1.33 to 1.39 RIU, which is much higher than those in the conventional surface plasmon resonance structure. The optimizes design will serve a vital foundation to the fabrication of high performance fiber optic surface plasmon resonance sensors based on nano metallic structure.

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.

Novel in-line effective fiber polarizer based on chromium and gold nano metal films: design and experiment

The performance of the magnesium fluoride/chromium/gold in-line fiber optic polarizer on the thickness of magnesium fluoride buffer layer and chromium metal thin film was theoretically investigated. To prove the theoretical study, the magnesium fluoride/chromium/gold polarizer was made based on the simulation results. The obtained polarizer showed an extinction ratio of about 40 dB which is in a good agreement with the theoretical result at the corresponding thicknesses. Both theoretical and experimental results showed that by covering the side polished single mode fiber with the optimum layer thicknesses, a novel and an efficient fiber polarizer with the high extinction ratio could be obtained. This is the first time that this type of polarizer has been made.

In-line optofluidic refractive index sensing in a side-channel photonic crystal fiber.

An in-line optofluidic refractive index (RI) sensing platform is constructed by splicing a side-channel photonic crystal fiber (SC-PCF) with side-polished single mode fibers. A long-period grating (LPG) combined with an intermodal interference between LP01 and LP11 core modes is used for sensing the RI of the liquid in the side channel. The resonant dip shows a nonlinear wavelength shift with increasing RI over the measured range from 1.3330 to 1.3961. The RI response of this sensing platform for a low RI range of 1.3330-1.3780 is approximately linear, and exhibits a sensitivity of 1145 nm/RIU. Besides, the detection limit of our sensing scheme is improved by around one order of magnitude by introducing the intermodal interference.