Single-mode Optical Fiber Research Articles

Ultraviolet sensing based on an in-fiber ZnO microwire constructed Mach–Zehnder interferometer

We propose a Mach–Zehnder interferometer based on an in-fiber ZnO microwire structure for ultraviolet sensing. The device undergoes femtosecond laser micromachining and chemical etching on a single-mode optical fiber initially, creating a microgroove that extends to half of the core’s depth, into which a single ZnO microwire is transferred. The ZnO microwire and the remaining core are used as the sensing arm and the reference arm, respectively, forming a Mach–Zehnder interferometer. To enhance the stability and the sensitivity, ZnO nanoparticles are filled into the microgroove after the ZnO microwire is transferred. The fabricated device exhibits a sensitivity of 0.86 nm/(W·cm−2) for ultraviolet sensing, along with a response time of 115 ns (rise time) and 133 µs (decay time), respectively. The proposed sensor exhibits good ultraviolet sensitivity, offering a novel approach for ultraviolet sensing technology.

Gain-switched pulse generation of 5.3 ps from 30 GHz-modulation-bandwidth 1270 nm DFB laser diode.

We generated gain-switched pulses via electrical pulse excitations in a 1270 nm distributed feedback (DFB) laser diode (LD) with a direct-modulation bandwidth of 30 GHz. The measurements revealed short-pulse widths of 5.3 and 8.8 ps with and without chirp compensation, via a single-mode optical fiber. The 5.3 ps pulses exhibited a spectral width of 0.40 nm (spectral bandwidth of 71 GHz), yielding a time-bandwidth product of 0.38. Although the gain-switched pulses in DFB LDs inherently contain linear and nonlinear chirp, optimized pumping conditions enable generation of nearly transform-limited ps pulses after linear chirp compensation.

Temperature Dependence of Nonlinear Pulse Reshaping Towards Parabolic Shape for a Silicon Core Single Mode Optical Fiber

Temperature Dependence of Nonlinear Pulse Reshaping Towards Parabolic Shape for a Silicon Core Single Mode Optical Fiber

Evaluation of in-situ optical loss of polyimide-coated optical fiber under hydrothermal environments

When distributed fiber optic sensing (DFOS) devices are deployed in a geothermal borehole, the optical fiber as the key element, must be able to withstand the harsh environment because the temperature of the geothermal boreholes is higher than 250 °C in most cases. Understanding the deterioration behavior of optical fibers in hydrothermal conditions higher than 250 °C is important for predicting the lifetimes of DFOSs in operation.Geophysical equipment using optical fiber sensing was developed for in-situ measurement of the optical loss of optical fibers under hydrothermal conditions, and a survey method was established. Using this optical fiber sensing, we characterized the deterioration behavior of single-mode polyimide-coated optical fibers. Our experiments with carbon / polyimide-coated fibers under subcritical water from 250 to 350 °C revealed that the polyimide layer and silica cladding easily dissolved in water in that environment.

Investigation by simulation of the highest sensitivity interferometric pressure sensor at the end of a micro-structured optical fiber

One of the most prevalent techniques used in the construction of optical fiber-based pressure sensors is Fabry–Perot interferometry. This work presents a variety of interferometric sensors based on this feature. To achieve this, we used chemical etching (HF) to create conical cavities at the ends of the optical fibers single mode fiber (SMF) and graded index (GRIN) fiber, where the first gold (Au) deposition allows us to create half-mirrors. So the interface (core/Au) represents the first reflective surface. After filling each micro-cavity with a quantity of polydimethylsiloxane (PDMS) type polymer to form a flexible micro-lens, and proceeding to a second deposition of gold (Au), we got the second reflective surface (PDMS/Au). The sensor with the highest sensitivity to pressure and temperature, namely 0.065 nm/KPa and 0.24 nm/°C, was obtained for a micro-cavity length of 35 μm, a diameter of 60 μm, and a micro-lens thickness of 20 μm, respectively. Analysis and simulation were performed using COMSOL Multiphysics to develop the sensor.

Developing an Intelligent Fiber-Optic System for Monitoring Reinforced Concrete Foundation Structure Damage

This paper presents the results of complex scientific research aimed at developing a prototype fiber-optic system for controlling the technical condition of buildings, structures, and extended objects. The aim is to develop a quasi-distributed type of fiber-optic control system without electrical signals, with the minimum possible cost of one measurement point. The fiber-optic sensors are based on a new method of controlling the parameters of the light spot by means of a hardware-software complex. The proposed monitoring system is quasi-distributed, is able to determine the damaged and most stressed and deformed areas of load-bearing reinforced concrete structures of buildings at the stage of their occurrence, and will allow for the taking of preventive measures for their protection. The research was carried out on a laboratory bench working together with the hardware-software complex; pixel analysis of changes in the area of the spot and its intensity was used as a fiber-optic sensor. A single-mode optical fiber of the G.652.D 9/125 μm standard was used, with a wavelength of 650 nm. The monitoring system can perform the function of pressure measurement on the building structure, establish the damage zone, and signal in case of an abrupt change in parameters in case of structure destruction. Laboratory tests have shown that the number of channels can be increased to 16 or 32. With the help of this system, it is possible to monitor the technical condition of the underground and above-ground parts of buildings or structures and control their integrity in real-time.

Low-complexity characterized-long-short-term-memory-aided channel modeling for optical fiber communications

In this work, a low-complexity data-driven characterized-long-short-term-memory (C-LSTM)-aided channel modeling technique is proposed for optical single-mode fiber (SMF) communications. To fully utilize the sequence correlation learning ability of traditional long short-term memory (LSTM) networks and solve the gradient explosion problem, the feature information is introduced into the traditional LSTM input layer to better characterize the intersymbol interference caused by dispersion in SMF modeling. The simulation results show that the proposed C-LSTM can effectively alleviate the gradient explosion problem with a stable and ultimately lower mean square error (MSE) than traditional LSTM. Compared with the split-step Fourier method (SSFM) and the conditional generative adversarial network (CGAN), the proposed C-LSTM has superior computational complexity. Moreover, due to the sequence correlation learning ability inherent to C-LSTM, coupled with the flexibility of feature information selection, the proposed C-LSTM-aided modeling technique has a higher modeling accuracy than traditional LSTM. Moreover, the C-LSTM-aided modeling technique can be effectively extended to other channel modeling applications with strong sequence correlations.

Demonstrating long-term stable optical coupling between single-mode optical fibers and well-defined energy photons emitted from nitrogen impurity centers in GaAs flakes

A key challenge in realizing scalable optical quantum information technology is not only to obtain stable single photons coupled to single-mode fibers but also to match the emission energy between remote emitters. We have fabricated an energy-matching favorable and long-term stable structure by coupling a nitrogen impurity center with a well-defined emission energy to a single-mode optical fiber core. The nitrogen-doped GaAs microflakes sandwiched between the two FC (acronym for "ferrule connector" or "fiber channel") connectors yielded sharp emission peaks due to nitrogen isoelectronic traps. Although some emitters showed spectral diffusion, the unaffected emitters showed stable emission and were able to generate photons stably for over 20 h continuously without photodegradation. In addition, the photoluminescence spectrum does not change in shape and intensity after more than 3 years, indicating that the photon source with this structure is resistant to thermal cycling and positional drift and has excellent long-term stability.

Single mode optical fiber sensor based on surface plasmon resonance for the detection of the oil aging for the electrical transformers

Single mode optical fiber sensor based on surface plasmon resonance for the detection of the oil aging for the electrical transformers

Quantification of hCG Hormone Using Tapered Optical Fiber Decorated with Gold Nanoparticles.

In this study, a novel technique for the quantification of the human chorionic gonadotropin (hCG) hormone using localized surface plasmons and a tapered optical fiber decorated with gold nanoparticles (Au-NPs) is reported. The tapered optical fiber fabrication process involves stretching a single-mode optical fiber using the flame-brushing system. The waist of the tapered optical fiber reaches a diameter of 3 μm. Decoration of the taper is achieved through the photodeposition of 100 nm Au-NPs using the drop-casting technique and a radiation source emitting at 1550 nm. The presence of the hCG hormone in the sample solutions is verified by Fourier-transform infrared spectroscopy (FTIR), revealing the presence of bands related to functional groups, such as C=O (1630 cm-1), which are associated with proteins and lipids, components of the hCG hormone. Quantification tests for hormone concentrations were carried out by measuring the optical power response of the tapered optical fiber with Au-NPs under the influence of hCG hormone concentrations, ranging from 1 mIU/mL to 100,000 mIU/mL. In the waist of the tapered optical fiber, the evanescent field is amplified because of localized surface plasmons generated by the nanoparticles and the laser radiation through the optical fiber. Experimental results demonstrated a proportional relationship between measured radiation power and hCG concentration, with the optical power response decreasing from 4.45 mW down to 2.5 mW, as the hCG hormone concentration increased from 1 mIU/mL up to 100,000 mIU/mL. Furthermore, the spectral analysis demonstrated a spectral shift of 14.2 nm with the increment of the hCG hormone concentration. The measurement system exhibits promising potential as a sensor for applications in the biomedical and industrial fields.

Fabry-Pérot Cavities with Suspended Palladium Membranes on Optical Fibers for Highly Sensitive Hydrogen Sensing.

Hydrogen (H2) sensors are critical to various applications such as the situation where H2 is used as the clean energy for industry or the indicator for human disease diagnosis. Palladium (Pd) is widely used as the hydrogen sensing material in different types of sensors. Optical fiber H2 sensors are particularly promising due to their compactness and spark-free operation. Here, we report a Fabry-Pérot (FP)-cavity-based H2 sensor that is formed with a freestanding Pd membrane and integrated on a conventional single-mode optical fiber end. The freestanding Pd membrane acts both as the active hydrogen sensing material and as one of the reflective mirrors of the cavity. When the Pd film absorbs H2 to form PdHx, it will be stretched, resulting in a change of the cavity length and thus a shift of the interference spectrum. The H2 concentration can be derived from the amplitude of the wavelength shift. Experimental results showed that H2 sensors based on suspended Pd membranes can achieve a detection sensitivity of about 3.6 pm/ppm and a detection limit of about 3.3 ppm. This highly sensitive detection scheme is expected to find applications for sensing low-concentration H2.

In-line open-cavity Mach-Zehnder interferometric refractive-index sensors based on inter-mode and inter-core-mode interferences

We experimentally demonstrated in-line Mach-Zehnder interferometric sensors based on inter-mode interference (IMI) and inter-core-mode interference (ICMI) for refractive index (RI) measurements. The structure of the IMI-based sensor consisted of a C-shaped fiber spliced between two multi-mode fibers (MMF) with the opposite ends spliced to lead-in and lead-out single-mode optical fibers. The ICMI-based sensor has a similar structure as the IMI-based sensor but with an additional in-house fabricated three-core multi-core fiber (MCF) spliced between the MMF and C-shaped fiber. The performance of the two RI sensors was evaluated and compared using water-glycerol solutions with RI values ranging from 1.333 to 1.338. The RI sensitivity, as well as other characteristic properties such as free spectral range and extinction ratio in relation to three lengths of the C-shaped fiber of 2, 2.5 and 3 mm, were investigated in both structures. The open-cavity characteristic of the C-shaped fiber allows the solution to interact with the optical path of the sensors, hence improving their RI measurement sensitivities. Both types of sensors exhibit linear wavelength responses with variation in RI. The RI sensitivity of the IMI-based sensor exhibits minor variations when the length of the C-shaped fiber is altered, with a maximum sensitivity of -7999.76 nm/RIU. In contrast, the RI sensitivity of ICMI-based sensor exhibits variability when changing the C-shaped fiber length, potentially due to variations in the RI distribution among the cores within the MCF, with its maximum sensitivity being -6211.98 nm/RIU. The temperature sensitivity of all the tested sensors was around 0.7 nm/ °C, denoting a low temperature cross-sensitivity of -7.427 × 10−5 RIU/ °C. This work experimentally exhibits a comparison of two sensing effects in the same configuration. The long length (longer than 2 mm) of the sensing element facilitates the fabrication process, and the open-cavity present in the proposed sensors yields a high sensitivity, which is in the same order of magnitude as the IMI-based sensors and is one order of magnitude higher than the ICMI-based sensors, emphasizing their promising candidacy for label-free optical sensing of chemical and biological samples.

Highly Efficient O-Band Rectangular Pulse Emission in a Figure-of-Nine Bismuth-Doped Fiber Laser

Highly efficient rectangular pulse emission is significant in high energy O-band applications due to the zero dispersion of standard telecom optical fiber in the second telecommunication window. The rectangular pulse emission offers the peak power clamping, which avoids wave-breaking and maintains the fundamental repetition frequency with arbitrarily widened temporal pulse width of ultrafast laser at high pump powers. The current technology in the O-band rectangular pulse emission achieves the maximum pulse energy of ∼30 nJ with an efficiency of ∼1.06%. Here, we fabricated a single-mode bismuth-doped phosphosilicate optical fiber by the modified chemical vapour deposition technique. The Bi-doped phosphosilicate optical fiber was characterized by a peak absorption of ∼0.6 dB/m at 1250 nm and a high gain coefficient of ∼0.22 dB/m at 1320 nm. These parameters contribute to the generation of rectangular pulse with a pump power threshold of ∼227.7 mW in a figure-of-nine laser cavity. The maximum pulse energy was achieved as ∼197.7 nJ, whereas the laser efficiency is ∼14.3%. We presented an O-band rectangular pulse emission with the highest pulse energy and efficiency as compared to previous studies, whilst its all-fiber laser setup is robust and feasible for high pulse energy applications.

Demonstration of Improving the Performance of a Fibre Optic Displacement Sensor Using the Optical Harmonic Vernier Effect by Cascading Tapered Optical Single-Mode Fibres

Demonstration of Improving the Performance of a Fibre Optic Displacement Sensor Using the Optical Harmonic Vernier Effect by Cascading Tapered Optical Single-Mode Fibres

Metasurface-assisted Lab-on-fiber optrode for highly sensitive detection of vitamin D

The increasing demand for vitamin D status assessment has highlighted the need for rapid, sensitive, and user-friendly methods for its detection in biological samples potentially integrated in Point-of-Care (PoC) diagnostic devices. Detection of the major circulating form of vitamin D, 25-hydroxyvitamin D3-25(OH)D3, is particularly challenging due to the laborious procedures for sample preparation and its low molecular weight (∼400 Da), which requires highly sensitive detection methods. In this study, we developed a novel label-free Lab-on-Fiber biosensing platform for highly sensitive detection of 25(OH)D3 based on the integration of plasmonic metasurfaces (MSs) on the tip of a single-mode optical fiber (OF). A dedicated pipeline was carefully designed and developed to optimize the bio-functionalization of the plasmonic sensor tip to specifically detect the target biomolecule. The resulting MS-assisted Lab-on-fiber platform enables direct and highly sensitive detection of 25(OH)D3 in clinically relevant ranges (4–160 ng/mL), both in buffer solution and complex matrix, with limits of detection (LOD) of 1.40 ng/mL in saline buffer and 0.85 ng/mL in complex matrix. Overall, these results demonstrate that our platform can successfully and specifically detect small molecules in label-free configuration, with performances comparable to those of conventional methods used in clinical practice. The high degree of miniaturization combined with its high sensitivity makes our platform an exceptional building block for realizing valid diagnostic alternatives for label-free detection of clinically relevant analytes, which can be transformed into new low-cost, fast, simple, and ready-to-use PoC diagnostic devices with improved processability and performance compared to current methods.

Fiber-optic temperature sensor based on glass Fabry–Perot interferometer

The paper presents a theoretical and experimental study of a fiber-optic all-glass microthermometer based on a Fabry–Perot interferometer. The interferometer is fabricated by applying borosilicate glass to the cleaved end of a standard telecom single-mode optical fiber using a microforge. According to the results of experimental studies, the spectral sensitivity of the fabricated interferometer was about 40 pm/°C. A mathematical model of the Fabry–Perot interferometer based on the method of scattering and transfer matrices is presented and verified, which makes it possible to calculate the spectral response of an interferometer with arbitrary structure parameters.

Identification of the Single-mode Optical Fiber Manufacturer from the Fiber Characteristics

Identification of the Single-mode Optical Fiber Manufacturer from the Fiber Characteristics

Short-pulsed Q-switched fiber laser using graphene oxide quantum dots based as saturable absorber

In this work, we report the experimental study of a Q-switched optical fiber laser based on graphene oxide quantum dots (GOQDs) as saturable absorber (SA). GOQDs are fabricated by carbonization and exfoliation electrospun polyacrylonitrile (PAN) fibers. The results of Fourier Transform Infrared Spectroscopy (FTIR) showed bands caused by the CHs and CO groups associated with the GOQDs. The Raman spectrum showed the typical G and D bands of GOQDs. The size of the GOQDs, calculated by Transmission Electron Microscopy (TEM) was 6 nm; additionally, by high resolution TEM (HRTEM), an interplanar distance of 0.19 nm corresponding to the (002) direction of the graphene oxide was calculated. The SA was achieved using the photodeposition technique of the GOQDs onto the core of a single-mode optical fiber. The nonlinear characterization (NLC) of the GOQDs was carried out using the P-scan technique with a high-gain erbium-doped fiber amplifier (EDFA) at a wavelength of 1550 nm. The obtained results showed a saturable absorption behavior with a value of β=−1.178x10−6(m/W) and a non-linear susceptibility of Im(χ(3))≈−1.573x10−7(esu). The experimental results of the SA, based on GOQDs as a switching device in a fiber laser, showed a typical behavior of a Q-switched laser by generating a pulsed emission at a wavelength of 1599 nm, a frequency from 2 to 16 kHz, and a maximum average output power of 1.3 mW.

Design and Experimental Analysis of an Optical Fiber Coupling System for a Ground-based Telescope with Adaptive Optics

Astronomy photonics has opened up a new era for the application of astronomical optical instruments. The fiber coupling system serves as the crucial link between the telescope and photonic devices. This paper explores a beam shaping method that utilizes a coupled lens to enhance the efficiency of coupling light into an optical single mode fiber. Compared to directly coupling the telescope beam into the fiber, this approach offers improved coupling efficiency and greater adjustment tolerance. The laboratory-based optical fiber coupling system described in this study comprises an imaging component with an F/50 ratio and a fiber coupling component. Theoretical analysis indicates that optimal coupling efficiency is achieved when the diameter of the focusing spot, limited by diffraction, matches the fiber core size. Any axial error, position error, or tip-tilt error between the lens and the fiber will reduce the coupling efficiency. Experimental results confirm that the coupling system achieves an efficiency of approximately 70%, which is close to the theoretical limit of 78%. These findings underscore the effectiveness of the fiber coupling method.

Influence of Adhesive Bonding on the Dynamic and Static Strain Transfers of Fibre Optic Sensors

The influence of the bonding procedure (the adhesive type, application procedure, etc.) on the static and dynamic strain transfers of bonded optical fibre sensors is studied theoretically and experimentally at room temperature. The achievable performances with four different types of adhesives (three urethane and one epoxy adhesive), and with different fibre types, are evaluated: acrylate-coated, polyimide-coated, and bare single-mode optical fibres. Static strain measurements, ranging from 20 to 200 µ strain, are performed using both fibre Bragg gratings (FBGs) and optical frequency domain reflectometry (OFDR), and are compared to reference strain-gauge measurements, and to the proposed analytical model, which is developed on the basis of stress equilibrium relations. This model is valid for bonding to all types of linear and elastic materials, as long as there is no sliding between the host material, the adhesive, and the optical fibre. The results agree between the analytical model and the experiments. Regarding the dynamic sinusoidal strain measurements, the studied dynamic range is from 10 to 100 Hz, and only the FBGs are tested. The results demonstrate that the sensitivities of strain sensors based on bonded uncoated fibres or bonded polyimide-coated fibres are comparable to those of strain gauges, and that it is possible to use bonded FBGs for precise dynamic strain measurements.