Single Optical Fiber Research Articles

Distributed Optical Fiber Sensor Allowing Temperature and Strain Discrimination in Radiation Environments

We evaluate the potential of a new architecture of distributed optical fiber sensor (DOFS) to discriminate between the temperature and strain changes along a single optical fiber exposed to radiation. This DOFS exploits the measurements of both the Landau–Placzek ratio (LPR) and the Brillouin frequency shift (BFS) to achieve the discrimination between the two parameters on up to 10 km of fiber with a spatial resolution of 1 m. We demonstrate that the LPR remains unaffected up to MGy(SiO2) dose levels, whereas the BFS is only slightly shifted by the radiation. The measured radiation-induced BFS is strongly reduced in radiation-hardened fluorine-doped single-mode optical fibers. Combining the DOFS architecture and the fiber allows discriminating temperature and strain using a single optical fiber up to megagray dose levels.

Fiber Positioner Based on Flexible Hinges Amplification Mechanism

Due to the nonlinear effect and the thermal effect, a single optical fiber has limitations in the output power. A beam combination of laser arrays based on adaptive optics can both improve the output power and ensure higher beam quality. This article puts forward one novel fiber positioner structure based on the flexible hinges amplification mechanism, which is the adaptive fiber optics collimator (AFOC), to correct tip-tilt aberration. The theoretical model was established, and the amplification ratios between the output displacement and device’s structure parameters were calculated. The first 6 orders of the mode shape of the vibration of amplification mechanism was obtained by using a modal analysis. Analysis results revealed an excellent performance for the flexible hinges amplification mechanism. The novel fiber positioner has good prospects for applications in laser beam combination systems for ideal tip-tilt control.

Investigation of Planar and Helical Bend Losses in Single- and Few-Mode Optical Fibers

In this paper, we describe experimental, simulation, and analytical approaches to study bend losses in single and few-mode optical fibers bent into a circle (in-plane bend) and helix. For the in-plane bend case, we compute loss through simulations and experiments, over the bend diameter range of $9.5\text{--}19.5$ mm at 1550 nm wavelength. For in-plane bend simulations, we obtain the refractive index profile of an equivalent straight fiber by applying the geometrically exact beam theory (GEBT) and conformal mapping, against the conventional approach to use an elasto-optic factor to account for stresses experienced by the fiber. We apply GEBT to compute the strain tensor of a bent fiber. The strain tensor, in turn, is used in the stress-optic law to obtain the refractive index due to bending stress. To account for the geometric effect, we apply the conformal mapping technique. The refractive index profile obtained by applying GEBT followed by conformal mapping is used in full-vectorial FEM simulations carried out in COMSOL to compute bend loss at different diameters. The simulation and experimental results are in close agreement. We extend our approach to few-mode fibers by calculating the planar bend losses for higher order modes. The close agreement of the simulation results, generated without making any ad hoc assumptions about the elasto-optic factor to account for the stress effects, with literature validates our approach. Next, we describe the results of experiments to measure the bending losses of fibers wound helically around the mandrel for bend diameter range $9.5\text{--}19.5$ mm and different helix pitch values. We derive an analytical formula to compute helical bend losses based on the method outlined by Marcuse. Although the results from the formula are in close agreement with the experimental results and predict the exponential decrease of loss with increasing pitch, the formula does not account for the non-monotonous dependence of bend loss on helix pitch, observed experimentally. We present a simple empirical formula to account for the non-monotonic dependence. Finally, we study the influence of micro-bend loss, due to the surface roughness of the mandrels used in the experiments on the bending losses. While the effect of surface roughness can be neglected for the mandrels used in our experiments, its effect may become important in mandrels with higher surface roughness, especially at larger bend diameters.

Integrated demultiplexing and amplification of coherent optical combs.

The explosive growth of the internet during the last few decades has been enabled by two complementary innovations in optical communications: the use of multiple optical channels within a single optical fibre, and the increase in the bandwidth of individual channels to hundreds of Gbps. Further increases in overall bandwidth look to be provided by more spectrally efficient optical superchannels that use coherent sub-carriers generated using optical orthogonal frequency division multiplexing (OFDM). Yet, a cost effective way of generating these signals has not been demonstrated. One crucial, but missing piece is an effective means to separate the closely frequency spaced optical sub-carriers from the coherent optical comb before placing information on each sub-carrier, and thus creating the OFDM signal. Here, we demonstrate a flexible strategy implemented in a compact photonic integrated circuit (PIC) that is used to separate and amplify these sub-carriers using on-chip injection locking.

Combined Experimental and Simulation Study of the Fiber Composition Effects on Its Brillouin Scattering Signature

Thirteen different single-mode optical fibers have been experimentally and theoretically characterized highlighting the influence of the core and cladding dopants on their Brillouin signatures: Brillouin spectrum, temperature, and strain coefficients. Tailoring the composition and the refractive index profile, optical fibers presenting Brillouin spectrum with multiple peaks have been designed, offering discrimination capabilities between the temperature and strain distributions along a single optical fiber.

КОГЕРЕНТНОЕ РАСПРОСТРАНЕНИЕ ЛАЗЕРНЫХ ПУЧКОВ В МАЛОРАЗМЕРНОЙ СИСТЕМЕ СЛАБОСВЯЗАННЫХ СВЕТОВОДОВ

The successful development of fiber-optic technologies in recent decades has stimulated research on the replacement of components of solid-state laser systems with fiber components, which can drastically change the attractiveness of the corresponding applied developments. Yielding on the energy characteristics of solid-state systems, fiber lasers and nonlinear optical devices have high efficiency of conversion of pump energy to radiation energy associated with waveguide geometry, high quality of the spatial profile of the laser beam, as well as low cost, compactness, lack of alignment in work process. Note that the maximum achievable radiation power in a single fiber is limited primarily by the process of self-focusing, which leads to fiber damage. The use of a multi-core fiber (MCF), consisting of identical equidistant weakly coupled optical fibers, makes it possible to realize initially coherent propagation of laser radiation with a total power noticeably higher than it can be transmitted in a single optical fiber. However, as theoretical and experimental studies have shown, such systems have its own critical power (Balakin et al., 2016) whereby the self-focusing of the quasihomogeneous distribution of the wave field and its separation into a set of incoherent structures occurs. Therefore, we have considered a small-sized optical system of 2N identical weakly coupled optical fibers arranged in a ring (Balakin et. al., 2018). In such systems, it is possible to find stable distributions of intense wave beams, which allow coherent radiation transport over long distances. The total radiation power in the found distributions can significantly (up to 2N times) exceed the critical self-focusing power in continuous media. This manifests itself most clearly for the distribution of un ~ (-1)n with antiphase fields in neighboring waveguides, which is stable at an arbitrary wave beam power. Direct numerical simulation of a nonlinear wave equation confirms the stability of the field distributions found. The research was supported by the RAS Presidium Program «Nonlinear dynamics: fundamental problems and applications».

A proposal for distributed humidity sensor based on the induced LPFG in a periodic polymer coated fiber structure

In this paper, a distributed relative humidity (RH) or moisture sensor is proposed. The proposed structure is a single mode telecommunication optical fiber coated by humidity sensitive and insensitive polymers periodically. The polymer coated fiber is surrounded by a high Young’s modulus material such as stainless steel mesh. The swelling of the coated Humidity Sensitive Polymers (HSPs) as a result of moisture absorption induces fiber gratings in the single mode fiber. Depending on the coating period relative to the light wavelength, the induced fiber grating can be Fiber Bragg Grating (FBG) or Long Period Fiber Grating (LPFG). The light reflected by the induced FBG or losses due to the coupled energy to the cladding modes in the induced LPFG can be employed to describe the sensor operation. Since long period length (LPFG) manufacturing is much simpler than short period length (FBG) sensors, this investigation is concentrated on the long period length sensors.

Stress Monitoring on GFRP Anchors Based on Fiber Bragg Grating Sensors.

Glass fiber-reinforced polymer (GFRP) bolts have been widely used in some applications of grouted anchors because of the advantages of better resistance to corrosion, high strength-to-weight ratio, low electromagnetic properties, and so on. This study presents a field test to assess the feasibility of fiber Bragg grating (FBG) sensors in monitoring the stress profile of GFRP anchors during pulling test. Two GFRP anchors were fully instrumented with FBG sensors and then installed into the ground using a drilling and grouting method. To measure the stress profile along test anchors, seven bare FBG sensors were arranged in a single optical fiber and then embedded in the middle of GFRP bolts in the process of extrusion molding. The procedure for embedding bare FBG sensors into GFRP bolts is introduced first. Then, the axial forces and shear stresses that were calculated from the measurements of the FBG sensors are discussed. The field test results indicate that the embedded FBG technology was feasible to monitor the stress state of GFRP anchors during pulling.

Integration of millimeter-wave and optical link for duplex transmission of hierarchically modulated signal over a single carrier and fiber for future 5G communication systems

Integration of optical and millimeter-wave systems provide a promising solution for future giga-bits per second wireless communication systems. We have proposed and simulated full-duplex transmission of a hierarchically modulated signal carrying data for two different users at a combined rate of 1.5 Gbps. Analogue modulation of the optical carrier is used for the transmission of downlink data while the same carrier is re-used by digitally modulating it with the uplink data. The use of optical analogue and digital modulation schemes allow the transmission of duplex data over a single optical fiber. A millimeter-wave channel $$\hbox {NYUSIM}\_{\mathrm{v1}}\_4$$ is integrated with the optical link. The performance of the downlink and uplink signals are evaluated in terms of error vector magnitude and bit-error rate measurements, respectively. The effect of fiber length, received optical power and data rates on the performance has also been evaluated. It is shown that for a fiber length of 10 km, the lowest error vector magnitude obtained for the hierarchically modulated signal after transmission through a 14 m millimeter-wave link is 9.5%.

Packaged inline cascaded optical micro-resonators for multi- parameter sensing

Abstract A novel design principle and fabrication method for whispering gallery mode optical multiple-resonator arrays have been proposed and demonstrated. The proposed design involves an inline cascade of optical micro-resonators (ICOMRs) coupled to multiple tapered sections along a single optical fiber. The multiple micro-resonators can be used for sensing of several parameters or a single parameter at multiple locations simultaneously. A simple and robust packaging technique has been developed ensuring stable and repeatable operation of the device. In order to demonstrate the capability of simultaneous multi- parameter sensing of the proposed ICOMRs structure, strain and temperature measurements were carried out using an inline cascade of two cylindrical micro-resonators: a tapered polymer optical fiber based micro-cylinder and a polydimethylsiloxane coated silica cylindrical micro-resonator. An Axial tensile strain sensitivity of 1.4 ± 0.04 pm/μe and temperature sensitivity of 330 ± 18 pm/°C have been demonstrated experimentally. The proposed ICOMRs design has many potential applications in distributed sensing, lab-on-a-fiber technology and optical communications.

Optical fibre liquid sensor for cryogenic propellant mass measurement

The authors report a one-piece flexible liquid level optical fibre sensing probe in this Letter, which is meant to measure the liquid level inside the cryogenic propellant tanks of spacecraft and rockets. The ultra-lightweight sensing probe can be used in both aerospace vehicles and in any type of cryogenic fluid storage system. In contrast to current liquid gauging technologies such as Delta-P pressure sensor, capacitance probe, ultrasonic sensor, and silicon diode liquid level sensing probe, the fibre optic continuous liquid level sensor has unique advantages in terms of gauging accuracy, reliability, simplicity, and maintenance. The sensor uses one single optical fibre probe to measure the liquid level and the liquid distribution of cryogenic propellant. Every point of the sensing fibre is a ‘point sensor’ that is able to distinguish liquid and vapour. The physical location of each ‘point sensor’ can be determined with 1 mm spatial resolution or better. The optical fibre probe can be installed in a propellant tank with the same manner as currently used silicon diode liquid level sensing probe via only one single feed-through to connect to an optical signal interrogation unit located outside the tank. Experiments on measuring liquid nitrogen level are demonstrated.

Double Ring Firing Single Optical Fiber Deflector

We report a novel fabrication method of double ring firing single optical fiber deflector. The fiber deflector is fabricated as a convergent cone having two different cone angles, by conventional mechanical polishing. The two-angled conical fiber deflector geometry is formed in a single fiber tip, deflecting incoming laser light into two distinct circular rings. Two cone angles provide two deflection angles due to total internal reflection and refraction of the incoming laser light. We achieved two deflected circular beams at 60° and 85° with the cone angles of 56° and 72° at one single fiber deflector. The laser power is evenly split between two conical areas. The fabrication process of the fiber deflector does not involve any splicing or arc discharge process; thus, it is convenient, effective, and high-throughput.

Design and Application of Integrated Optics Sensor for Measurement of Intense Pulsed Electric Field

Integrated optical waveguide sensor has characteristics of good insulation, broadband response, small size, and large dielectric strength, which is appropriate for measurement of intensive pulsed electric field. Two types of integrated optics sensors using through and reflective type asymmetric Mach–Zehnder interferometer are designed, fabricated, and implemented. Key parameters of the optical waveguide and antenna are theoretically analyzed and designed. The time domain response, input/output characteristics and frequency response of the sensors are investigated. The temperature stability is evaluated by measuring output power fluctuations of the sensors. Experiment results reveal that the sensitivity of the through type sensor is a little higher than that of the reflective type sensor, while the size (length) of the reflective type sensor is only half of the through type. Besides, as only a single optical fiber is coupled, it is convenient for the reflective type sensor to measure in very small space. Applications of the sensor for measurement of the lightning electromagnetic pulse, nuclear electromagnetic pulse, and pulsed radio frequency fields are demonstrated. The measurement results indicate that the developed integrated optics sensor has powerful potential and is expected to be widely used for measurement of intense pulsed electric fields.

Analisis Power Budget pada Jaringan Komunikasi Jarak Jauh Menggunakan SMF 28

The fourth generation of optical fibers is wavelength division multiplexing (DWDM), where several wavelengths propagate in a single optical fiber. This technique strongly supports broadband communication that is currently being developed. An optical amplifier (EDFA) is required for transmitted information to be received at the appropriate distance limits. The problem, where EDFA should be located and how to overcome the chromatic dispersion of signals occurs, especially on remote communications using SMF 28. The power budget analysis starts from the calculation of the distance between the amplifier and the strengthening of EDFA using the solution wave equation, where the large dispersion of chromatic fiber and the desired range becomes the determinant of the optical amplifier. Case study for 200 km of communication distance need three amplifiers with a space of about 80km. When a 1 GHz bandwidth is converted to 10 GHz, OSNR on each amplifier will decrease by 10 dB.

Simulation Study of Waveguide and Chromatic Dispersion of a Single Mode Step Index Optical Fiber

Simulation Study of Waveguide and Chromatic Dispersion of a Single Mode Step Index Optical Fiber

Design of freely suspended photonic crystal microfiber cavity sensors array in a general single mode fiber

Abstract We propose a novel design of refractive index (RI) sensor array based on ultrahigh sensitivity one dimensional (1D) photonic crystal microfiber (PCMF) cavities, which is referred as photonic crystal microfiber cavity sensors array (PCMF-CSA). The proposed PCMF-CSA consists of multiple channels connected in parallel. A transmission only containing the fundamental mode (FM) resonance of the PCMF cavity sensor for sensing purpose is created by connecting an additional PCMF bandgap filter to a PCMF cavity sensor in series on each channel. Due to the photonic bandgap (PBG) of the PCMF bandgap filter, the other high-order resonances are filtered out. With proper engineering of the PBG, multiple ultrahigh sensitivity PCMF cavity sensors can be integrated into microarrays without resonance overlap, and be detected simultaneously between a single input optical fiber and a single output optical fiber without the need for complicated coupling systems. The concept was demonstrated with 7-channel PCMF cavity sensor array containing PCMF bandgap filters. By using three-dimensional finite-difference time-domain (3D-FDTD) method, the performance of the device was investigated theoretically. The simulation results showed that the sensors on each channels can be monitored simultaneously from a single output spectrum. The numerical calculated RI sensitivities (S) for each sensing channel of the proposal 7-channel PCMF-CSA as high as 647.33 nm/RIU, 666.67 nm/RIU, 662.00 nm/RIU, 676.00 nm/RIU, 674.67 nm/RIU, 659.33 nm/RIU, 679.99 nm/RIU can be achieved, respectively. The average RI sensitivity as high as 666.57 nm/RIU can be obtained. Moreover, the extinction ratios of all resonant peaks exceed 20.0 dB. The crosstalk of all channels is lower than −24.5 dB. To the best of our knowledge, this is the first silica PCMF sensors array geometry based on conventional single mode fiber (SMF) that features both high Q and S, and thus is potentially a promising platform for ultra-sensitive RI-based gas sensing with high parallel-multiplexing capability.

Scaling SDM Optical Networks Using Full-Spectrum Spatial Switching

In today's optical networks, the capacity supported by a single optical fiber is far higher than the demand between source–destination pairs. Thus, to take advantage of the installed capacity, lightpaths allocated between distinct source–destination pairs share the capacity provided by an optical fiber. This sharing is only possible if these lightpaths have different wavelengths. With the exponential evolution of traffic, the demand between source– destination pairs in a network can approach or exceed the capacity of a single fiber. In this scenario, spacedivision multiplexing (SDM) networks appear as a viable option, and new network-sharing technologies become relevant. In this paper, we study different switching approaches for SDM networks with uncoupled spatial superchannels—such as networks with multicore fibers or bundles of single-mode fibers—which result in different network-sharing strategies. We start by comparing three switching architectures considering the evolution of traffic over time: (1) full-spectrum spatial switching (full-spectrum SS); (2) wavelength switching (WS) of uncoupled spatial superchannels; and (3) independent switching (IS) of spatial and wavelength channels. IS provides high network flexibility at the cost of complex switching nodes. On the other hand, full-spectrum SS and WS simplify network nodes but reduce flexibility by switching superchannels. Simulation results indicate that WS offers poor utilization in the long term. Full-spectrum SS, in contrast, exhibits low utilization in the short term, but outperforms IS in the long term. We also propose alternative hybrid switching strategies that start with IS and change to full-spectrum SS after a certain number of spatial channels are activated. The simulations suggest that well-designed strategies for migration from IS to full-spectrum SS delay premature activation investments while saving on switching costs.

Fiber Optic Sensing for Geomechanical Monitoring: (1)-Distributed Strain Measurements of Two Sandstones under Hydrostatic Confining and Pore Pressure Conditions

In this study distributed optic fiber has been used to measure both the Rayleigh and Brillouin frequency shift of two different sandstone core samples under controlled hydrostatic confining and pore pressure in the laboratory. The Berea sandstone core is relatively homogeneous, whereas the Tako sandstone core is visibly heterogeneous with a coarse-grain and a fine-grain region. Rayleigh frequency has been found to have a superior performance over Brillouin frequency in terms of better consistency (less scattering) in the tests carried out. The strain gauge readings reveal considerable anisotropy in the stiffness of the Berea core between perpendicular (vertical) and parallel to the bedding (hoop) directions. The strains converted from Rayleigh frequency shift measurements agree reasonably well with readings by one of the four hoop strain gauge channels under increasing confining/pore pressure. For the Tako sandstone core, the contrast in the grain-size, and thus rock elastic properties, is clearly reflected in the hoop strain measurement by both strain gauges and distributed optic fiber. The outcomes of the test have demonstrated successfully the use of a single optic fiber for measuring rock strain response at different regions of a heterogeneous core sample along a continuous trajectory.

Birefringent π-Phase-Shifted Fiber Bragg Gratings for Sensing at 1000 °C Fabricated Using an Infrared Femtosecond Laser and a Phase Mask

Birefringent π-phase-shifted Bragg gratings for multi-parameter sensing at temperatures ∼1000 °C are written inside a standard single mode silica optical fiber (SMF-28) with infrared femtosecond pulses and a special phase mask one half of which is shifted with respect to the other by 5/4 of the mask period. The birefringence is caused by the presence of light-induced sub-wavelength periodic planar nanostructures in the fiber core, whose orientation is controlled by the laser polarization, and is maximized when the laser pulse polarization is aligned perpendicular to the fiber core. The birefringence can reach ∼4.2 × 10−4 at room temperature at the 1.5 × 10−4 level after 100 h annealing at 1000 °C. Erasure and rewriting of the planar nanostructures inside fiber Bragg gratings by changing the laser pulse polarization is demonstrated.

Distributed Brillouin optical fiber temperature and strain sensing at a high temperature up to 1000 °C by using an annealed gold-coated fiber.

In this study, the distributed temperature and strain sensing with an annealed single mode gold-coated optical fiber over a wide temperature range up to 1000 °C is demonstrated by using the differential pulse pair (DPP) Brillouin optical time domain analysis (BOTDA). Owing to the protection provided by the gold coating, the fiber can withstand high temperature environments and maintain a high strength, which enables the gold-coated fiber acting as a repeatable high-temperature sensor. After annealing twice to remove the internal stress, the temperature coefficient of the gold-coated fiber is stable and consistent with a nonlinear function. Owing to the residual stress accumulated during the cooling process of coating and the low yield strength of gold, a pre-pulling test is essential to measure the strain of a gold-coated fiber. An equal axial force model is used to recalculate the strain distribution induced by the large temperature difference within the furnace. The high-temperature strain coefficient of an annealed gold-coated fiber decreases with temperature, i.e. from ~0.046 MHz/με at 100 °C to ~0.022 MHz/με at 1000 °C, mainly due to the increase in Young's modulus of silica with temperature. To the best of our knowledge, this is the first time that an annealed gold-coated fiber has been applied for distributed high-temperature strain sensing, which demonstrates the potential applications for strain monitoring in complex, high-temperature devices such as jet engines or turbines.