Macro-bending Loss Research Articles

100 GHz free spectral range-tunable multi-wavelength fiber laser using single–multi–single mode fiber interferometer

Six single–multi–single (SMS) mode fiber-based Mach–Zehnder Interferometers (MZI) with different spooling radii are demonstrated as spatial mode filtering elements for multi-wavelength laser generation. Free spectral range (FSR) tuning of the multi-wavelength output generated is realized by alternating between the six MZIs, which have different macro-bending losses. Additional FSR tuning is also realized by changing the spooling radius of the two-mode step index fiber section within the MZI setups from 80 mm to 30 mm, giving an FSR tuning range of 0.89–0.99 nm. All generated multi-wavelength outputs show high stability over a test period of 100 min. The proposed multi-wavelength lasers are highly suitable for various microwave photonics applications the field of such as microwave signal source generation and microwave photonic filtering.

High-sensitive tilt sensor based on macro-bending loss of single mode fiber

Abstract A novel high-sensitive tilt sensor is proposed and experimentally demonstrated based on the macro-bending loss of single mode fiber (SMF), and its sensitivity can be improved by forming multiple fiber laps. The tilt sensor is formed by an SMF bend into a semicircle with radius small enough to acquire the macro-bending loss, and it is fixed in a vessel with suitable amount of liquid. The surrounding refractive index around the semicircle changes along with the liquid level when the vessel is tilted. According to theoretical derivation, the macro-bending loss is related to the tilted angle, which means the angle can be modulated from the measured macro-bending. The experiment result corresponds to theoretical prediction and shows that the sensor has a high tilted angle sensitivity, which reaches −0.074 dB/degree in the initial scheme and −0.188 dB/degree in two turns situation. The detectable range of the tilted angle is from −90° to 90° in the improved scheme. The temperature influence is also theoretically predicted in this paper.

An investigation in the influence of helical structure on bend loss of pavement optical fiber sensor

Monitoring the complex strain and stress distribution of pavement under actual loading using the conventional sensors has always been a problem for pavement engineers. In order to monitor the mechanical response of pavement under actual loads, a macro bend loss modulation method is developed. The relationship between the shape of the helical structure and macro bend loss of optical fiber is explored. Theoretical calculations and laboratory experiments have proved that this optical loss modulation method is feasible. This paper presents the results of the development.

Quasidistributed optical fiber sensing system to monitor the displacement of joints on the face slab of concrete-faced rockfill dams

We propose a quasidistributed optical fiber-sensing system based on optical time-domain reflectometry (OTDR). The quasidistributed optical fiber-sensing system can be used to monitor the joint opening displacement or crack opening displacement of the face slab of concrete-faced rockfill dams (CFRDs). The crack sensors, which are based on the sensing principle of linear macrobending loss of optical fiber, are connected in series in each optical fiber link. In addition, multiple links can be connected with a single OTDR to construct an integrated monitoring system. Hence, the quasidistributed system overcomes some drawbacks of the distributed monitoring system, such as limited measurement range, fragility of fibers attached to the structural surface, and the nonlinear relationship between displacement and macrobending loss of optical fiber. To develop an optimal design plan for the monitoring system, some experiments are conducted to verify the independence of crack sensors and the minimum length of the connecting fiber between sensors. The analysis of the experiment results positively supports the application of optical loss in real structural monitoring.

Vibration sensing based on macrobending loss in a standard single mode fiber loop structure

Abstract A new optical fiber sensor for vibration measurement has been proposed and demonstrated. This paper realizes vibration sensing based on the macrobending loss in a standard single-mode fiber loop. The experiments shows the suggested sensor enable us to measure multi-frequency vibrations with the resolution as high as 0.04 Hz. The crosstalk between temperature and vibration can be ignored because the macrobending loss is insensitive to the ambient temperature.

Design of Optical Fibre Goniometer for Measurement of Complex Human Joint

Optical signal gets attenuated when subjected to bending within an optical fiber, but it still attracts the various sensing applications based on bending losses. The optical fiber is subjected to macrobending losses when the optical fiber’s bend radius exceeds its core diameter. Tribology is the science of friction, lubrication and wear. Biotribology provides the important information for biological systems (human joints such as knees and hips) which continuously move relative to one another. This research is based on implementation of optical fiber goniometer in order to study joint biotriboilogy. The goniometer is a device to measure bend angles between two planes of contact. Goniometers are widely used for robotics and human prosthetic devices, but mechanical goniometers have performance limitations for very small bend angles. The use of optical fiber for goniometer provides the flexibility of measurement of smaller bend angles. The optical goniometer makes use of polarization controller to maintain the state of polarization of optical signal. The effect of macrobending loss on radius of curvature of bend, bending angle, number of wrapping turns and wavelength is observed. A mathematical model presenting macrobending loss dependence on these parameters is presented in this paper. A Single mode fiber with core size 5 µm is subjected to bend angles ranging from 0° to 180° and its influence on macrobending losses have been investigated for wavelength of 850 nm, 1310 nm and 1550 nm. The bending angle is measured with precision accuracy of less than 1° in this setup.

Impact of Air Hole on Crosstalk Suppression and Spatial Core Density of Multi-Core Fiber

We experimentally and theoretically investigate the effect of an air hole between cores in a multi-core fiber (MCF) on the suppression of crosstalk (XT). We clarify that XT decreases in proportion to the air hole diameter and that XT of about 20 dB in an MCF can be suppressed by employing just one air hole between cores. We confirm that the calculated XT suppression value is in good agreement with the measured value. We also clarify numerically that the minimum distance between cores satisfies the required XT without reducing the effective area by using an air hole. Next, we consider the influence of air holes on macro-bending loss and cutoff wavelength. We confirm that none are related to the arrangement of the air holes. Moreover, we discuss the relationship between the effective area and the core multiplicity factor (CMF) against several core arrangements. As a result, we show that the CMF in MCF with air holes can increase by 1 or more compared with that without air holes.

Bend-Loss-Free Distributed Sensor Based on Rayleigh Backscattering in Ge-Doped-Core PCF

We propose a bend-loss free, high-resolution, fiber-optic distributed sensor by using a new sensing fiber namely Ge-doped-core photonic crystal fiber (PCF) in optical frequency domain reflectometer (OFDR). PCF is fabricated with high concentration of Ge-doping in the small core leading to large refractive index difference between core and air-silica cladding. We achieved negligible macrobending loss in our Ge-doped-core PCF for a bend radius of curvature down to 1 mm in experiment and the results are validated by numerical simulation. By using OFDR, with a bend radius of 1 mm, the strain and temperature sensitivities in Ge-doped-core PCF are measured to be 0.138 GHz/ $\mu \varepsilon $ and 1.46 GHz/°C, respectively, with 5 cm spatial resolution.

Macro-Bending Loss of Single-Mode Fiber Beyond Its Operating Wavelength

A standard telecommunication-grade single-mode optical fiber is designed to have a low macro-bending loss in its entire operating wavelengths to comply with the ITU-T Recommendation G.652. In this paper, we described the potential use of such a fiber as an intensity-based sensor due to the macro-bending loss as an alternative to using a bending-sensitive fiber. We calculated the macro-bending loss of several single-mode optical fiber patchcords using the classical Marcuse equation at several wavelengths, and measured its transmission loss due to bending using an optical spectrum analyzer. For each type of fibers there is a wavelength with a significant macro-bending loss of the LP11 mode when the V-number of the fiber lies between 2.4 and 4, and that of the LP01 mode when the V-number of the fiber lies between 1 and 2.4. This work shows a thorough mathematical and experimental analysis for the posibility in using standard telecommunication fibers for intensity based-fiber sensor taking the benefit of bending loss phenomenon using commercial light sources.

The sensing principle of a new type of crack sensor based on linear macro-bending loss of an optical fiber and its experimental investigation

For traditional distributed optical fiber sensors, the sensing principle is based on a complex relationship between the crack opening displacement (COD) and the macro-bending loss of the fiber, which introduces many difficulties in its application in practical engineering projects. To solve this problem, a simple linear relationship between the macro-bending loss of the fiber and the COD is established in this work by controlling the fiber winding shaft to ensure the bending radius remains constant. Based on this linear relationship, a crack sensing principle of optical fiber is proposed. To verify the feasibility of this crack sensing principle, a validation experiment was performed using three groups of fiber winding shafts with different diameters and three groups of working light sources with different wavelengths. The experimental results show that the macro-bending loss is linearly related to the COD. Based on the proposed crack sensing principle, and a new type of optical fiber crack sensor to monitor the COD of pre-existing cracks and contraction joints of structures is designed, and the performance is verified by an experiment.

单模光纤宏弯损耗的温度响应特性

单模光纤宏弯损耗的温度响应特性

A Microwave Photonics Fiber Loop Ring-Down System

A microwave photonics fiber loop ring-down system is demonstrated in this paper. In comparison with the traditional time domain fiber loop ring-down setup, the demonstrated system is based on pure frequency domain measurement from a microwave-photonic configuration. The system consists of a direct-modulation laser with its modulation frequency scanned by a vector network analyzer. The amplitude and phase spectra of the demonstrated fiber loop ring-down system are then recorded, followed by a complex Fourier transform to acquire the ring-down curve in the time domain. The loss of the fiber loop can then be evaluated based on the calculated ring-down curve. The system delivers high signal-to-noise ratio, and averaging is not required compared with the traditional time domain measurement. The system is also insensitive to the sources of environmental noise. The measurement principle, experimental setup, and the mathematical model of the system are discussed in this paper. A proof-of-concept macrobending loss test is demonstrated.

Theoretical and experimental study of macrobending losses in coated single-mode fibers

A macrobending loss formula for single-mode fibers, which is shown to accurately predict the bend loss of a single-mode fiber with complex or real refractive index coating, is presented. Theoretical simulations and experimental measurements of bend loss in a fiber with nickel coating obtained by chemical plating and acrylate buffer coating are also presented. Agreements between simulations and measurements support the validity of the theoretical formula. Results show that the large imaginary part of the refractive index of the coating can intensify the bend loss oscillation behaviors, which implies that the bent fiber with metal coating can be utilized in fiber-optic devices.

Fiber optic macro-bend based sensor for detection of metal loss

Metal loss in metallic structures, often as a result of corrosion, is a severe problem across multiple industries. Catastrophic consequence of structural failure due to such loss of structural metal requires an accurate determination and assessment of corrosion. Widely used electrochemical methods can only suggest the likelihood of the metal loss due to corrosion while failing to provide a quantitative measure of the accumulated amount of corrosion. Due to its unique advantages such as small size, light weight, resistance to electromagnetic interference and corrosion, fiber optic sensing technique has been emerging as a promising alternative for most sensing applications. In this paper, a novel type of ferromagnetic distance-based metal loss sensor is proposed based on the principle of fiber optic macro-bend loss. The proposed sensor is composed of the bended optical fiber, the magnet and a spring. The magnet is connected to the spring and the fiber bend is attached to the spring in such a way that the movement of the magnet will induce a change in bending radius of the optical fiber. Metal loss in the monitored sample increases the distance between the magnet and the metal surface and thereby reducing the magnetic force. A change in magnetic force will lead to the variation in light intensity loss of the fiber optic macro-bend, thus metal loss, such as in the form of corrosion pits, can be detected by the proposed metal loss sensor. The practicality of the proposed distance sensor for metal loss measurement is validated through scanning the fabricated corrosion samples.

An approach on a new variable amplitude waveform sensor

Compared with quartz, polymer optical fiber is more suitable for monitoring strain since it is with low cost and high strain sensitivity. This paper introduces the characteristics and sensing loss mechanism of polymer optical fiber, including micro bending and macro bending loss. The sensitivity of the sensor is analyzed from the aspect of the influence of fiber diameter, numerical aperture and other parameters. The mathematical model of the optical fiber strain-bending loss is established under ideal conditions. Further, two experiments on the sensor structure are designed. During the loading, the light intensity loss is recorded by the optical power meter. According to the experimental data, the curve of the bending loss-strain is drawn. As a consequence, according to the experimental result, the variable amplitude waveform sensor with better linearity and sensitivity is proposed, which enlarges the measurement range of strain.

Hole-Assisted Graded-Index Four-LP-Mode Fiber With Low Differential Mode Group Delay Over C+L Band

In this paper, in order to achieve low differential mode group delay (DMGD) over the C+L band, we propose the hole-assisted graded-index few mode fiber (FMF) design supporting four nondegenerated linear polarized (LP) modes for a mode division multiplexing system. In order to determine the fiber core parameters, an optimization has been made between the enlargement of the effective area $({{A_{eff}}})$ and the reduction of macrobending loss (MBL). The ${A_{eff}}$ about 107 $\mu {m^2}$ for LP01 mode at the wavelength of 1550 nm and the MBL lower than 0.005 dB/100 turns for LP02 mode at the curvature radius of 30 mm and at the wavelength of 1550 nm are achieved simultaneously. The numerical simulation results prove that the hole-assisted structure can greatly reduce the absolute value of DMGD of the FMF. Particularly, the maximum DMGD less than |35| ps/km within the spectrum range from 1530 to 1630 nm is achieved. A tolerance analysis against manufacturing errors has been discussed, and we further propose a self-managed low DMGD transmission line solution with the controllable air-hole size.

Investigation of a Macro-Bending Tapered Plastic Optical Fiber for Refractive Index Sensing

A plastic optical fiber (POF) probe with a macro-bending tapered structure was proposed and optimized for the refractive index (RI) sensing. The principle of operation is based on the macro-bending loss and evanescent wave, which are introduced by the macro-bending tapered structure on the fiber, and modulated by the environmental RI. A heating and drawing method and thermal setting process were used to fabricate a tapered POF and form a stable macro-bending structure for the probe. The probes with cladding and without cladding were fabricated. By changing the taper waist and curvature radius, the sensing performance of the probe was optimized. The highest sensitivity of the probe with cladding reached 937%/RIU in the RI range of 1.33–1.41. By removing the cladding, the RI sensing range was expanded to 1.33–1.45, and the sensitivity was about 800%/RIU, lower than the ones with cladding. In addition, the temperature dependence of the sensor was investigated. The POF probe is a low cost solution for RI sensing applications, which has the features of simple structure, compact, and intensity modulation at visible wavelength.

Space-efficient fiber ribbon composed of reduced-cladding single-mode fibers

Abstract We develop a space-efficient single-mode fiber (SMF) having a cladding diameter of only 82 μm. This SMF has the depressed-cladding index profile and its mode-field diameter, cutoff wavelength, and macro bending loss are designed to be similar to those of the conventional step-index SMF. We fabricate this reduced-cladding SMF and measure its optical and mechanical characteristics. The results show that this fiber satisfies major specifications of the ITU-T G.654 recommendations. We also fabricate a fiber ribbon by using twelve of these reduced-cladding SMFs. Compared to a commercial fiber ribbon made of twelve standard SMFs having 125-μm cladding diameter, this fiber ribbon can improve the spatial efficiency by ∼75%.

Loss Cause Identification by Evaluating Backscattered Modal Loss Ratio Obtained With 1-μm-Band Mode-Detection OTDR

We propose a novel diagnostic technique that uses 1-μm-band mode-detection optical time domain reflectometry (1 μm-OTDR) to identify the loss causes such as macrobends and fusion splices, of single-mode fibers. 1 μm-OTDR, which employs 1-μm-band probe pulses and a mode selective coupler operating in the same band, enables us to individually observe the fundamental (LP01) and the second-order (LP11) modes of the backscattered light generated in the two-mode region of single-mode fibers. Evaluating the ratio of losses occurring in the LP01 to LP11 modes of the backscattered light allows us to determine whether the cause of loss is a macrobend or a fusion splice. A proof-of-concept demonstration is performed for two kinds of widely used single-mode fibers, and the results show that macrobending and fusion splice losses can be clearly identified.

Study of Macrobending Losses Effect in Plastic Optical Fibber.

<span>Experimental study to analyze the effect of macrobending losses in plastic optical fiber triple bending <span>model based on PC (personal computer) has been conducted. The data is gathered by measuring the <span>change of the light intensity due to the presence of bending on optical fibers. The bending causes losses <span>of optical fiber that is read by WIM (weight in motion) Acquisition program based on Borlan Delphi 7. <span>The optical fibers are plastic with diameter of 3 mm. The diameter of pin is 8 mm and the space between <span>the pin is 5 mm. The light source is a LED (<span><em>λ</em><span>=676 nm). As a result, the losses of optical fiber increase <span>with the enhancement of bending. The increase trend linear to sensitivity of the sensor with gradient of <span>0,1063 and <span><em>R</em><span>2 <span>of 0,9626. Therefore, the proposed design might be applied as a WIM sensor.</span></span></span></span></span></span></span><br /></span></span></span></span></span></span>