Macro-bending Loss Research Articles

Multimode fiber amplifier with tunable modal gain using a reconfigurable multimode pump

We propose a method for controlling modal gain in a multimode Erbium-doped fiber amplifier (MM-EDFA) by tuning the mode content of a multimode pump. By adjusting the powers and orientation of input pump modes, modal dependent gain can be tuned over a large dynamic range. Performance impacts due to excitation of undesired pump modes, mode coupling and macro-bending loss within the erbium-doped fiber are also investigated. The MM-EDFA may potentially be a key element for long haul mode-division multiplexed transmission.

Applicability of low macrobending loss hollow-core PCF to FTTH applications

Fiber-To-The-Home (FTTH) technology has been significantly implemented in access networks, providing very high data rates transmission and a variety of digital content to subscribers. It involves an optical cable link being installed between the building entry point and each subscriber with the Multiple Dwelling Units (MDUs), i.e. flats and apartments. In other words, optical cable has to lie fairly straight to carry a strong signal, since typically is necessary to bend, twist and turn the lines in and out of tight corners without degrading the link connection. In this paper we propose the use of Hollow-Core Photonic Crystal Fiber (HC-PCF) for FTTH applications. It is presented an experimental analysis of the macrobending effects in a HC-PCF based on a comparison with traditional fibers and by following the ITU-T G.657B standard recommendations. We observe this fiber, with only 6.5 µm core, is bending loss insensitive, even at extremely small bending radius of 2 mm, in which it presents a loss of only 0.58 dB.

Short wavelength infrared frequency conversion in ultra-compact fiber device

Linear and nonlinear characteristics of devices using millimeter-scale spools of highly nonlinear fiber are experimentally investigated within 2000-2400nm spectral range. Coils with radius larger than 3.5 mm indicate that macro-bending induced radiation loss is negligible up to 2400nm. Devices with smaller diameter coiling resulted in macro-bending losses that dominate over micro-bending losses beyond 2200nm. A tunable short-wave infrared source was constructed using a coin-sized fiber module to demonstrate an efficient nonlinear conversion from 1.26 to 2.2 microm.

Applicability of Photonic Crystal Fiber With Uniform Air-Hole Structure to High-Speed and Wide-Band Transmission Over Conventional Telecommunication Bands

We discuss the applicability of photonic crystal fiber (PCF) with a uniform air-hole structure to high-speed and wide-band transmission over conventional telecommunication bands. We design the PCF to maximize the effective area by utilizing the macro-bending losses of the fundamental and first higher order modes (HOM) and clarify that a single-mode and low bending loss PCF can realize the largest effective areas of 133 and 157 mum <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> for transmission over the 1260-1625 nm (O ~ L bands) and 1460-1625 nm (S ~ L bands) wavelength ranges, respectively. We then investigate the impact of the designed PCF on nonlinearity reduction over a wide wavelength range and show that the PCF helps to increase the maximum channel power in a wavelength division multiplexing system. We also discuss the distributed Raman amplification (DRA) characteristics of PCF with a large effective area. Our results show that we can expect to improve the signal to noise ratio with DRA in spite of the low nonlinearity of the designed PCF. Dispersion compensating fiber (DCF) with a conventional W-shaped index profile is designed to compensate for the relatively large dispersion of the PCF, and we show that the designed DCF can extend the dispersion compensation bandwidth from 1340 nm to 1650 nm for a 40 Gbit/s transmission. Finally, we clarify the applicability of the large effective area PCF with the uniform air-hole structure as a high-speed and wide-band transmission medium.

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.

Investigation of polarization‐dependent loss for a macrobending loss sensitive single‐mode fiber

AbstractAn investigation of the polarization dependent loss (PDL) of macrobending loss sensitive single fiber (1060XP) is presented theoretically and experimentally. The experimental results are in good agreement with the modeling outcomes. Through the comparison of experimental results of PDL between 1060XP fiber with coatings and bare 1060XP fiber, it is shown that the fiber coating has significant impact on the PDL of bend loss sensitive single‐mode fiber. © 2009 Wiley Periodicals, Inc. Microwave Opt Technol Lett 51: 1460–1464, 2009; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.24388

Full-vectorial coupled mode theory for the evaluation of macro-bending loss in multimode fibers. application to the hollow-core photonic bandgap fibers

In the hollow core photonic bandgap fibers, modal losses are strongly differentiated, potentially enabling effectively single mode guidance. However, in the presence of macro-bending, due to mode coupling, power in the low-loss mode launched into a bend is partially transferred into the modes with higher losses, thus resulting in increased propagation loss, and degradation of the beam quality. We show that coupled mode theory formulated in the curvilinear coordinates associated with a bend can describe correctly both the bending induced loss and beam degradation. Suggested approach works both in absorption dominated regime in which fiber modes are square integrable over the fiber crossection, as well as in radiation dominated regime in which leaky modes are not square integrable. It is important to stress that for multimode fibers, full-vectorial coupled mode theory developed in this work is not a simple approximation, but it is on par with such "exact" numerical approaches as finite element and finite difference methods for prediction of macro-bending induced losses.

Refractive index profile optimisation for the design of optical fibres

Owing to advanced manufacturing techniques, it is possible to produce cylindrical single-mode fibres with nearly arbitrary refractive index profiles. For the design of optical fibres automated optimisation schemes have yet to be exploited. We have employed deterministic local, and stochastic optimisation schemes for the minimisation of a cost function based on dispersion, dispersion slope, macro-bending losses and mode-field diameter, on the space of continuous piecewise linear dopant concentration profiles. For the local schemes (modified and quasi Newton), it appears possible to select a few initial profiles, such that the optimisation results are close to the global optima (within 8%), found using schemes (simulated annealing and differential evolution), while reducing computation times significantly (minutes instead of days). For the local schemes, the cost function gradient is required. Frechet derivatives are more efficient than finite-difference approximations. A sensitivity analysis provides useful information for manufacturers regarding the required profile accuracy. A comparison of our optimised fibre designs with commercially available optical fibres demonstrates that existing fibres can be improved.

Temperature dependence of macrobending loss in all-fiber bend loss edge filter

A theoretical model for macrobending-induced temperature dependent loss (TDL) for a standard singlemode fiber (SMF28) with dual coating layers is presented, with good agreement demonstrated between theoretical calculations and experimental results. The impact of temperature on two examples of an all-fiber based edge filter is also investigated theoretically and experimentally and using the developed model, it is shown that it is possible to predict the impact of temperature variations on an all-fiber based edge filter.

Investigation of macrobending losses of standard single mode fiber with small bend radii

AbstractAn investigation of macrobending loss characteristics of a standard single mode fiber (SMF28) for small bend radii is presented theoretically and experimentally, which includes the bend loss of the SMF28 with coating layers and the bare SMF28 after stripping the coating layers and chemical etching of partial cladding. The significant influence of reflection occurring at the interface between the cladding and coating layer or the cladding layer and air on the bend loss is investigated theoretically and experimentally. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 2133–2138, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.22671

Numerical investigation and optimization of a photonic crystal fiber for simultaneous dispersion compensation over S + C + L wavelength bands

In this paper, we numerically investigate and optimize the profile of a photonic crystal fiber (PCF) that can eliminate the residual dispersion from the telecom link as well as can provide identical dispersion compensation over S + C + L bands. A full-vectorial finite element method combined with genetic algorithm is used to optimize the fiber’s profile as well as to accurately determine its modal properties. The optimized PCF exhibits a dispersion of −98.3 ps/nm/km with a variance of ±0.55 ps/nm/km from 1.48 μm to 1.63 μm (i.e., over 150 nm bandwidth) and a zero dispersion slope. Macro-bending loss performance of the designed PCF is also studied and it is found that the fiber shows low bending losses for the smallest feasible bending radius of 5 mm. Further, sensitivity analysis has been carried out for the proposed fiber design and it has been found that a ±2% change in the fiber parameters may lead to a ±8% shift of the dispersion from its nominal value.

Design of single-moded holey fibers with large-mode-area and low bending losses: the significance of the ring-core region

One of the major trends in optical fiber science is to be able to obtain fibers with large-mode-area (LMA), optimized for various applications such as high power delivery, fiber amplifiers, and fiber lasers. In order to ensure the high beam quality and the ultimate controllability of the damage threshold in the fiber's material, it is required to have a LMA property and of course to operate in a single mode fashion. While the conventional fibers have some difficulties in providing simultaneously LMA, single mode operation, as well as low macro-bending loss characteristics, all-silica holey fibers are highly attractive candidates for realizing LMA single-mode fibers with low bending losses. In this paper, we present a novel type of effectively single-mode holey fibers with effective mode area of about 1400 mum(2), small allowable bending radius as small as 5 cm, good beam quality factor of 1.15, and high confinement losses exceeding 1 dB/m for the higher-order mode at 1.064-mum wavelength.

Dispersion, birefringence, and amplification characteristics of newly designed dispersion compensating hole-assisted fibers

We propose a new design of hole-assisted fiber (HAF) that can compensate for the accumulated dispersion in single-mode fiber link along with dispersion slope, thus providing broadband dispersion compensation over C-band as well as can amplify the signal channels by utilizing the stimulated Raman scattering phenomena. The proposed dispersion-compensating HAF (DCHAF) exhibits the lowest dispersion coefficient of -550 ps/nm/km at 1550 nm with an effective mode area of 15.6 microm(2). A 2.52 km long module of DCHAF amplifies incoming signals by rendering a gain of 4.2 dB with +/-0.8 dB gain flatness over whole C-band. To obtain accurate modal properties of DCHAF, a full-vector finite element method (FEM) solver is employed. The macro-bend loss characteristics of the proposed DCHAF are evaluated using FEM solver in cylindrical coordinate systems of a curved DCHAF, and low bending losses (<10(-2) dB/m for 1 cm bending radius) are obtained for improved DCHAF design while keeping intact its dispersion compensation and Raman amplification properties. We have further investigated the birefringence characteristics that can give significant information on the polarization mode dispersion of DCHAF by assuming a certain deformation (eccentricity e = 7%) either in air-holes or in the doped core or in both at a same time. It is noticed that the distortion in air-holes induces a birefringence of 10(-5), which is larger by a factor of 10 than the birefringence caused due to the core ellipticity. A PMD of 11.3 ps/ radicalkm is obtained at 1550 nm for distorted air-holes DCHAF structure.

Improved fibre optic respiratory monitoring using a figure-of-eight coil

The macro-bending loss effect in optical fibres has been used to redevelop a sensor for the measurement of thoracic and abdominal circumferences in non-invasive respiratory monitoring. The new sensor uses a novel figure-of-eight loop configuration, which results in increased linearity of response, less mechanical resistance and hysteresis, as well as other benefits. The performance of the new sensor as applied to respiratory monitoring is examined, and indicates a higher resolution and sensitivity than the old. This enhanced performance enables measurement of respiratory and cardiac function using the same transducing fibre.

The use of a figure-of-eight coil for fibre optic respiratory plethysmography: Geometrical analysis and experimental characterisation

An optical fibre sensor based on the macro-bending loss effect has been redeveloped for thoracic and abdominal circumference measurements in non-invasive plethysmographic respiratory monitoring. A new geometrical analysis of the figure-of-eight transducer is presented, along with an optical analysis, and experimental results are presented which are in good agreement with these analyses. A comparison is made with earlier implementations of macrobending loss effect based transducers for respiratory measurement, and the newer sensor compares favourably, indicating a higher resolution and a simpler mechanical construction.

Theoretical and experimental investigations of macro-bend losses for standard single mode fibers

Modeling of macro-bend losses for single mode fibers with multiple cladding or coating layers is presented. Macro-bend losses for standard single mode fibers (SMF28) are investigated theoretically and experimentally, showing that the inner primary coating layer of SMF28 has a significant impact on the bend losses and most of the radiation field is absorbed in the inner primary coating layer of SMF28. The agreement between theoretical calculations and experimental measurements suggests that the so-called elastooptical correction in modeling is not required for SMF28.

Predicting macrobending loss for large-mode area photonic crystal fibers

We report on an easy-to-evaluate expression for the prediction of the bend-loss for a large mode area photonic crystal fiber (PCF) with a triangular air-hole lattice. The expression is based on a recently proposed formulation of the V-parameter for a PCF and contains no free parameters. The validity of the expression is verified experimentally for varying fiber parameters as well as bend radius. The typical deviation between the position of the measured and the predicted bend loss edge is within measurement uncertainty.

Air-Guiding Photonic Bandgap Fibers: Spectral Properties, Macrobending Loss, and Practical Handling

For development of hollow-core transmission fibers, the realizable fibers lengths, bandwidth, characterization, and compatibility with standard technology are important issues. We report record-length air-guiding fiber, spectral properties, splicing, and optical time domain reflectometer (OTDR) measurements. Furthermore, spectral macrobending loss measurements for two different designs of air-core photonic bandgap fibers are presented. While bending loss is observed, it does not limit operation for all practical bending diameters (>5 mm).

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.

Spectral macro-bending loss considerations for photonic crystal fibres

Both a scalar method and a fully vectorial method have been applied to modelling the bending losses in photonic crystal fibres (PCFs). Due to a decreasing index difference between the core and the cladding towards short wavelengths, an unusual loss mechanism is seen, that is a short-wavelength loss edge. This is verified by measurements. For large-mode area PCFs, the model gives a massive overestimate, never an underestimate.