Bending Loss Of Fiber Research Articles

Bending Loss Evaluations of Holey Fibers Having a Core Consisting of an Elliptical-Hole Lattice by Various Approaches

In general, an accurate evaluation of the bending loss of an optical fiber with an arbitrary refractive index profile is a cumbersome task, especially for holey fibers (HFs). In this paper, various approaches are applied and compared for the bending loss evaluations of single-polarization elliptical-hole core circular-hole HFs (EC-CHFs), which are circular-hole HFs having a core with an elliptical-hole lattice structure. Our simulation results show that when bending loss formulas for weakly guiding circular fibers are applied to a HF by regarding it as an approximate circular fiber having an equivalent step-index (SI) profile, the definition of the core region is the most crucial issue. Moreover, we also show that the results obtained by the approximate approach based on the bending loss formulas for the equivalent SI circular fiber are in good agreement with direct approaches with numerical simulations for the real EC-CHF structure, if the equivalent core radius is suitably defined for the real cross section.

열확장 코어 광섬유의 구부림 손실을 이용한 광섬유형 온도 센서

In this paper, we have proposed and demonstrated a simple fiber-optic temperature sensor based on the bending loss of a TEC(thermally expended core) fiber attached to a bi-metal. The deformation of the bi-metal caused by the change in its temperature induces the bending loss of the TEC fiber. The experimental result shows that the temperature sensitivity and operation temperature range of the device are controllable through the adjustment of the structure of the expanded core fiber. The fabrication procedure of the device is described in detail.

Tunable and low bending loss of liquid-core fiber

The liquid-core fiber with relatively high refractive index difference between the core and cladding is proven to be bending insensitive. The single mode condition and bending loss of the fiber with a mixture of toluene and chloroform as its core material are studied. The results show that the bending loss of this fiber is not only much smaller than the conventional silica single mode fiber but also can be tuned by the temperature and liquid mixture ratio. This kind of fiber may find its potential applications in all-optical network.

利用光纤环腔衰荡技术测量单模光纤的弯曲损耗

利用光纤环腔衰荡技术测量单模光纤的弯曲损耗

利用光纤环腔衰荡技术测量单模光纤的弯曲损耗

利用光纤环腔衰荡技术测量单模光纤的弯曲损耗

Limit of Effective Area for Single-Mode Operation in Step-Index Large Mode Area Laser Fibers

Step-index (SI) fiber designs are commonly used in achieving large mode area (LMA) and single-mode (SM) operation in fiber lasers. These fibers can either be intrinsically single-moded fibers or few-moded fibers, which can be forced into SM operation through bending. In this paper we evaluate the limitation of the effective area for SM operation by taking into account the effects of practical constraints such as fiber bending loss, laser performance, and fiber mechanical reliability on these LMA fiber designs. It is shown that the effective area of these fibers cannot be arbitrarily scaled up with the size of the fiber core. We also use the modeling result to provide estimated upper limits to the core diameters and corresponding effective areas for conventional SI fiber designs taking into account fiber parameters that are achievable nowadays.

The Temperature Dependence of Polarization-Dependent Loss for a Macrobending Single-Mode-Fiber-Based Edge Filter

The temperature dependence of polarization-dependent loss (PDL) for a macro bending standard single-mode fiber (SMF28) is investigated both theoretically and experimentally. The experimental results show an overall agreement with the proposed theoretical model over a temperature range from 0degC to 70degC. An SMF28-based edge filter is used as an example regarding temperature-dependent PDL performance. It is shown that the temperature variations have a significant influence on the polarization dependence of macro bending loss, and further impact on such a fiber bend loss edge filter used in a wavelength measurement application. It is also concluded that by using the proposed models, such a temperature-dependent birefringence can be beneficially predicted in bending fiber sensing applications.

Influence of fiber manufacturing tolerances on the spectral response of a bend loss based all-fiber edge filter

It is shown that manufacturing tolerances of the fiber parameters bend radius and numerical aperture (NA) significantly influence the fiber bend loss performance and spectral response of a fiber based edge filter. A theoretical model, validated by experimental results, is used to determine the changes in key spectral parameters for an edge filter, resulting from changes within their manufacturing tolerance range, for both the bend radius and NA. Finally, it is shown that bend-radius tuning during fabrication of such filters is a means of mitigating the effect of manufacturing variations.

Terahertz scanning imaging with a subwavelength plastic fiber

The feasibility to perform fiber-scanning terahertz imaging utilizing a terahertz subwavelength plastic fiber is investigated. Our study shows that, with a low (<1%) fractional power inside the fiber core, the bending loss of the terahertz subwavelength fiber is acceptable to enable large area scanning without seriously sacrificing the signal-to-noise ratio of the acquired image. With a transmission geometry, this feasibility is demonstrated by direct two-dimensional scanning of the terahertz subwavelength fiber output end to image different biological samples and concealed substances.

Study of bending loss and mode field diameter in depressed inner core triple-clad single-mode optical fibers

In this paper, the bending loss and the mode field diameter (MFD) of the R-type depressed inner core triple clad single-mode optical fibers are investigated. The effects of the optical and geometrical parameters on the bending loss and the MFD are examined in these fibers. The simulation results indicate that with increasing of the core radius ( a), which is desired from manufacturing point of view, the bending loss and MFD coefficients are decreased. Consequently, the large core radius can be used to optimize the bending loss in the foregoing fibers. In the meantime, simulation outcomes show that the Δ and Q have considerable impact on the bending loss in the RI and RII fibers, respectively. The MFD and bending loss is decreased with increasing of Δ, but the case is inversed for Q. Based on the presented simulations, it is found out that the bending loss strongly depends on the distribution profile of the electric field in the cladding region for a given MFD. In other words, the field amplitude and damping rate in the cladding region determine the fiber bending loss.

New sensing mechanisms using an optical time domain reflectometry with fiber Bragg gratings

A new optical time domain reflectometry (OTDR) sensing mechanism combined with fiber Bragg gratings (FBGs) is presented. The intensity-based optical fiber sensor is implemented between a pair of FBGs in an OTDR system. Based on the ratio from two reflecting intensities of the reference and the sensing FBGs, the appropriate measurable parameters associated with the intensity variations can be detected. By applying the Fresnel reflection signals caused by FBGs as the measuring indicator, the dynamic range and signal-to-noise ratio of an OTDR FBGs system are improved in comparison to the traditional method. Besides, by adapting the system using a double-light-source scheme, the spatial resolution limited by the ghost zone in a traditional OTDR system is also resolved. The sensors in an OTDR FBGs system could be configured for multiplexing and immunity to the variations from the light source and the lead-in/out fibers caused by the external loads. The new method using single-light-source and double-light-source schemes has been validated by fiber bending loss and refractive index measurements.

Fiber optic sensor for the monitoring of mixed mode cracks in structures

Cracks in structures may open in mixed mode under general loading conditions. In other words, there are both opening and shearing displacements along the crack. In our former work, a distributed fiber optic sensor has been developed for the detection and monitoring of purely opening cracks (or Mode I cracks). The sensing principle is based on the bending loss of an optical fiber intersecting the opening crack at an angle other than 90°. In the present work, the sensing concept is extended to the monitoring of mixed mode cracks. To obtain both the opening and shear displacements at the crack, two independent measurements are required. Based on theoretical simulation, the feasibility of various sensing strategies, including the use of two wavelengths and two fibers, are first investigated to identify the most promising approach. A method to solve the inverse problem of obtaining the crack displacements from the measured signal losses is then derived. Experiments are performed under controlled crack opening/shearing history to verify the sensing approach. Good agreement between derived opening/shearing displacements and imposed displacements has been obtained.

Utilization of Holey Fibers with Low Bending Loss

A holey fiber has been developed that has an extremely low bending loss (less than 0.01dB/turn) at a bending diameter of 10mm. Six air holes around the core lower the effective cladding index and as a result those confine the signal light within the core better compared with conventional fibers. The optical characteristics, fiber-joint characteristics, and reliability of this holey fiber were investigated. An optical curl cord developed utilizing the very low bending loss of this holey fiber was found to have characteristics suitable for indoor wiring of FTTH.

Performance enhancement on mechanical and electrical effects for on-line fiber-optic bending loss measurement

For an automatic testing of the fiber bending loss parameter, we proposed an on-line fiber optic bending loss measurement system. Many impact factors from the supporting systems, free space coupling alignment, external spatial perturbation device and the other automatic testing systems may degrade the on-line fiber-optic bending loss measurement system. We reduce those impact factors and show the mechanical and electrical improvement in this paper. The accuracy can be improved by 3–5 dB for the proposed on-line bending loss measurement system. Development of an on-line fiber-optic bending loss measurement system can provide a fast-checking solution for jump-line quality improvement on fiber-from-the-desk (FFTD) access network.

Effect of coupling between fundamental and cladding modes on bending losses in photonic crystal fibers

The paper presents a fully vectorial analysis of bending losses in photonic crystal fibers employing edge/nodal hybrid elements and perfectly matched layers boundary conditions. The oscillatory character of losses vs. both the wavelength and the bending radius has been demonstrated. The shown oscillations originate from the coupling between the fundamental mode guided in the core and the gallery of cladding modes arising due to light reflection from the boundary between solid and holey part of the cladding.

Crack sensing with a multimode fiber: experimental and theoretical studies

For many structures, failure is preceded by the formation and propagation of cracks. Crack monitoring is hence a useful technique to assess the condition of structures. Also, for laboratory specimens, the monitoring of cracking can provide useful information on the failure process. An important challenge in crack monitoring is that the location of cracks in structures may not be known in a priori. Conventional sensors or transducers that measure the average strain over a small region may easily ‘miss’ the crack. In this paper, a sensing concept based on the bending loss of an optical fiber is first introduced. With the use of multimode fibers, experiments are performed to obtain the signal loss versus crack opening relation. A theoretical model for power loss versus crack opening is then developed. The crack-induced curvature along the fiber is computed with a finite element analysis. Power loss in the curved fiber is then obtained with the ray tracing technique. The theoretical prediction is found to be in good agreement with experimentally measured power loss.

Distributed fiber-optic bi-directional strain–displacement sensor modulated by fiber bending loss

Abstract The distributed fiber-optic bi-directional strain–displacement sensor is composed of fiber-optic bi-directional strain–displacement chips and optical time domain reflectometer (OTDR). The operational principle is the modulation of fiber loss in OTDR, i.e. the strain and the displacement in monitoring positions are measured by the bending loss of optical fibers bonded on the tension-sensitized and compression-sensitized regions of the fiber-optic strain–displacement chips. Additionally, by inserting the time delay optic fiber, the moving direction of the substrate free ends in the fiber-optic bi-directional strain–displacement sensor can be identified by the trace taken with high spatial resolution in OTDR. The experiments indicate that the fiber-optic bi-directional strain–displacement sensor could measure strain and displacement by adopting the lengths of sensitive region and freely suspended fiber, the chip length, and attachment methods.

Realization of an On-Line Fiber-Optic Bending Loss Measurement System

In this paper, an on-line bending loss measurement system is studied and realized. To avoid complicated calculation of fiber bending loss, we propose a simplified theoretical model for on-line evaluation. A specific fiber adaptor is developed for light signal feeding and picking up through a free space optical fiber coupling technique. Relevant factors, including free space fiber misalignment, are considered. The signal-to-noise ratio of the whole system is improved by optimizing the spatial perturbation length of the fiber and the deformation of the bending fiber. The use of an on-line monitoring technique for measuring the bending loss of optical fibers is presented in this paper. With this technique, manufacturing efficiency can be improved, and the cost of maintaining fiber quality control can be reduced.

Understanding bending losses in holey optical fibers

Extremely large mode area fibers that are single-moded over a broad wavelength range can be created using holey fiber technology. However, as with any fiber, the largest mode areas that are practically feasible are ultimately determined by bending losses. It is therefore essential to gain an understanding of the factors that influence bend loss in these fibers in order to form accurate predictions that can facilitate improved bend loss design. Here, we present the first detailed study of transition loss and pure bend loss in a holey fiber, and consider the impact of the fiber structure. A theoretical model is derived that retains the full refractive index profile of a holey fiber. This approach is used to predict the bend loss in large mode area holey fibers and is validated through comparison with experimental data. For the fibers under study here, we demonstrate that pure bend loss is the dominant component of macro-bend loss and that the hole configuration within the cladding can strongly influence this loss.

Optical time-domain reflectometry interrogation of multiplexing low-reflectance Bragg-grating-based sensor system

Low-reflectance fiber Bragg gratings (FBGs) can be interro- gated in real time with a high-resolution optical time-domain reflectom- etry (OTDR) technology. The technique allows interrogation of a series of FBGs with the intensity change based on the OTDR pulse spectral char- acteristics and the FBG reflection. Experimental results are presented for multiplexing of dual-wavelength FBG sensors to produce referencing calibration in sensor measurement. With this structure, the influence of the source power fluctuations and fiber bend losses can be greatly re- duced. This scheme can be applied to the practical measurement of distributed temperature or strain. © 2003 Society of Photo-Optical Instrumentation Engineers. (DOI: 10.1117/1.1571061)