High-modulus low-linear-expansion-coefficient loose-jacket optical fibers

Optical fibers loosely jacketed with high-modulus low-linear-expansion-coefficient polymers have been proposed, and the mechanical, thermal, and optical properties have been investigated. The loose-jacket tube is made of highly oriented polyoxymethylene (POM), which is produced by tensile-drawing the isotropic POM tube with dielectric heating. The oriented POM exhibits Young's moduli 20-40 GPa and linear expansion coefficients of the order of10^{-5}-10^{-6}degC^-1. Owing to the low linear expansion coefficients of the material, the oriented POM loose-jacket optical fiber has no low-temperature excess losses, which is due to fiber bends caused by thermal contraction of the loose tube, in the-60-80degC temperature range.     

Depressed index substrate tubes to eliminate leaky-mode losses in single-mode fibers

Silica tubing to be used as substrate tubes for MCVD has was demonstrated for a fiber having only one-fourth the deposited clad-merical tubing in that it is both dehydrated and fluorinated during processing to yield a silica which is dry and whose refractive index is lower than that of silica. These tubes are advantageously used to prepare single-mode fibers having fluorinated-silica cladding which controls dispersion and reduces scattering losses. In this case, the refractive index of the deposited cladding can be matched to that of the outer tube thus avoiding leaky-mode losses commonly encountered in depressed-index clad fibers. Using such an approach, low loss (0.28 dB/km at 1.55 μm) was demonstrated for a fiber having only one-fourth the deposited cladding required when a commercial silica tube is used. Such tubes could provide ecomomies to the processing of and the performance of complex cladding single-mode structures and impact multimode fiber designs.     

A review of single-mode fibers with modified dispersion characteristics

Standard first-generation single-mode fibers are optimized for operation at a wavelength of 1.3 μm, where they exhibit zero dispersion. By modifying the fiber design it is possible to shift the zero dispersion wavelength to 1.55 μm, where the lowest losses occur in silica-based fibers. Advanced fiber structures can also be designed such that relatively flat dispersion spectra can be achieved over a wide range of wavelengths. In this paper, the theoretical and practical attempts to develop advanced fiber designs have been reviewed.     

Doubly coated optical fibres with a low sensitivity to temperatureand microbending

In order to prevent microbending losses in optical fibers over a wide temperature range, a new buffer coating and a new top coating have been developed. The buffer coating has a low Young's modulus over a wide temperature range, whereas the top coating has a modulus which is high compared with the modulus of the coatings that are generally used. The application of these coatings results in fibers with a very low microbending sensitivity. However, at low temperatures added optical loss is observed which correlates with a change in the radial stress state of the buffer coating from compression to tension. It is demonstrated by model calculations as well as by experiments that these optical losses can be avoided if the thickness of the buffer layer does not exceed a critical value. The new coatings are shown to provide a good protection of the fiber from mechanical damage     

Development and testing of a fire-resistant optical cable

A new type of fire-resistant optical cable has been developed. It is based on the loose tube concept employing special mica and glass tape wrappings together with a new type of buffer jacket material to provide the desired properties. With this design, ordinary acrylate-coated fibers are used. The cable has the unique property that during fire it converts from a cable, which mostly consists of organic materials, to a ceramic loose-tube structure that gives the fiber sufficient protection to prevent damage during fire. The cable has been tested according to IEC 331 which specifies a 750°C flame exposure for 3 h, and passed that test with negligible loss increase even at temperatures up to 900°C.     

Mechanical approach to the evaluation of the low temperaturethreshold of added transmission losses in single-coated optical fibers

An easy-to-use calculation procedure for the evaluation of thermally induced forces in single-coated optical fibers is discussed. The calculations show that the increase in the lateral pressure at the cladding-coating interface adequately reflects the experimentally observed increase in the added transmission losses at low temperatures. The measurements were carried out on loose fibers in a test chamber, where mechanical effects other than the thermally induced shrinkage of the coating were excluded. It is suggested that the thermally induced lateral pressure be used as a tentative criterion of the low temperature threshold of the expected added optical losses in single-coated fibers. The increase in this pressure reflects the increase in the axial thermal loading as well. Single-coated optical fibers can be successfully used in transmission media operated at moderately low temperatures (for instance, in undersea systems) which do not cause large thermally induced forces; otherwise, a dual-coated fiber design should be considered. The final selection of the most feasible coating design must be based on all the material, optical, chemical, technological, mechanical, environmental, and cost considerations     

Failure Case Study for Loose Tube Jacketed Optical Fibers

In fiber optic devices, the 250 to 400-μm-diameter tight jacketed fibers are sometimes jacketed additionally by loose tube-type materials. However, the loose tube jacketed fibers fail possibly due to the shrinkage of the loose tubes, if the tubes are not stabilized enough by preheat aging, etc. Although such phenomena are empirically known, here when the loose tube shrinks, the inner fiber is found to relax by being helically deformed. As a result, commercial fibers could endure at least 1–1.5% longitudinal shrink without a mechanical break, but exhibited excess optical propagation losses due to the bending.     

Effect of initial curvature on low temperature microbending inoptical fibers

An analytical evaluation of the thermally induced microbending in dual-coated optical fibers is presented, with an emphasis on the effect of the initial local curvatures. The analysis has shown that these curvatures could cause appreciable additional deflections of the glass fiber even at moderately low temperatures, thereby resulting in added transmission losses. The developed formulas are considered simple, easy-to-use, and to indicate clearly the role of various factors affecting the prebuckling behavior of fiber. They also indicate what could be done to bring down, if necessary, the temperature-induced curvatures and the resulting added transmission losses. Some recommendations for the selection of the thicknesses and material characteristics are presented. The numerical examples are executed for silicone/nylon coated systems, which were studied experimentally by Y. Katsuyama et al. (1983). The theoretical prediction agrees well with the experimental observations     

Design parameters for fluoride multimode fibers

Numerical calculations of losses due to polymer coatings and macrobending have been made for step-index multimode fluoride fibers. To minimize such losses, fiber parameters must be chosen to give a large value for V, the normalized frequency. Due to the long propagation wavelength (2.5 μm) for fluoride fiber, the parameters needed are very different from those of silica fiber. Using the criterion that ⩾90% of the modes have losses ⩽0.01 dB/km, it was found that the cladding diameters need to be rather large compared to step-index silica fiber parameters. Although the mode distributions are unknown for fluoride fiber, using a theoretical Gaussian distribution, losses were calculated for the various fiber parameters     

Mechanisms of optical losses in polycrystalline KRS-5 fibers

The widening of distribution of the laser radiation transmitted through the polycrystalline KRS-5 fiber which leads to the domination of the surface scattering and absorption in the total optical losses has been measured. It has been found from the obtained data that the value of the loss increases with the number of reflections at the side fiber surface per unit length of the fiber. Scanning electron microscopy of the side surface has shown the presence of hollows along the grain boundaries and other surface imperfections.     

Microbend sensor structure for use in distributed andquasi-distributed sensor systems based on selective launching andfiltering of the modes in graded index multimode fiber

This paper describes a novel optical fiber microbend sensor architecture which my be utilized in distributed and quasi-distributed measurement. The actual sensor element is graded index multimode fiber coupled to the measurand field through the usual microbend inducing structures. However, the feed to the sensing section is through a single-mode fiber spliced to the multimode fiber to ensure that only the lowest order spatial mode is launched. Similarly the receiver is also coupled to the sensing element through a single mode fiber. The single mode within multimode fiber propagates with minimal mode coupling with source to receiver losses of typically 0.7 dB for short sensors ranging to approximately 0.3 dB per each additional kilometer of sensing fiber. The sensitivity of this structure to microbend induced losses has been thoroughly characterized. Typically the optical power loss for a given microbend structure and force is about three to six times higher in this architecture than for conventional fully mode filled microbend sensor. The structure is also almost totally insensitive to macrobend induced losses and allows a variety of novel designs in microbend inducing structures. Additionally, spatial mode filters allow effective control over concatenation effects that are common in microbend sensors     

Experimental integrated optic circuit losses and fiber pigtailing of chips

Experimental integrated optic circuit losses, including waveguide bend, waveguide offsets, metal electrodes, and fiber-to-channel coupling, are presented. Coupling measurements from single-mode fibers to straight waveguides show losses less than 1 dB. Integrated optic circuit losses due to waveguide bends and offsets were calculated and measured; these data are in excellent agreement. A four-sectionDeltabetareversal switch has been permanently coupled to single-mode fiber pigtails with coupling losses approaching the measured optimum and theoretically predicted value.     

Dispersion-adapted monomode fiber for propagation of nonlinearpulses

A method of compensating for attenuation in optical fiber systems which uses nonlinear wave propagation (solitons) to achieve high data capacity is discussed. This method is based on adjusting the dispersion parameter of the fiber as a function of the signal intensity along the fiber. A practical implementation of this method, where the fiber is fabricated with variable diameter, continuously adjusted during the drawing is proposed. The fiber tapering necessary to maintain a perfect balance in the nonlinear wave is sufficiently gradual to prevent additional losses. The shape of a signal in the form of an order-one soliton can then be kept invariant. A possible engineering approach where the continuously varying fiber is approximated by discrete sections is suggested     

不同材料光纤松套管回缩特性的研究

通过模拟光缆线路在西部地区所处的日(年)温差大的恶劣环境,对常用的PBT(聚对苯二甲酸丁二醇酯)、PP(聚丙烯)、PC/PP(聚碳酸酯/聚丙烯)双层复合材料制作的光纤松套管的回缩特性进行了试验研究.其中PC/PP双层复合松套管在试验条件下回缩率最大值为0.38%,优于常用的PBT松套管.以此对光缆生产工艺提出了改进建议.     

Annealing of linear birefringence in single-mode fiber coils:application to optical fiber current sensors

Annealing procedures that greatly reduce linear birefringence in single-mode fiber coils are described. These procedures have been successfully applied to coils ranging from 5 mm to 10 cm in diameter and up to 200 or more turns. They involve temperature cycles that last 3-4 days and reach maximum temperatures of about 850°C. The residual birefringence and induced loss, are minimized by proper selection of fiber. The primary application of these coils is optical fiber current sensors, where they yield small sensors that are more stable than those achieved by other techniques. A current sensor with a temperature stability of +8.4×10^-5/K over the range from -75 to +145°C has been demonstrated. This is approximately 20% greater than the temperature dependence of the Verdet constant. Packaging degrades the stability, but a packaged sensor coil with a temperature stability of about +1.6+10^-4/K over the range from -20 to +120°C has also been demonstrated     

Fiber-coupled short Fabry-Perot resonators

An air-gap Fabry-Perot resonator with plane mirrors between closely spaced fiber ends may yield low throughput because of the poor match between the modes of typical single-mode fibers and the resonant mode in the air-gap cavity. The throughput can be improved by confining the resonant mode by a hollow dielectric tube placed inside the resonator. Short fiber-coupled Fabry-Perot resonators with and without an inserted hollow dielectric waveguide and expressions for their transmission losses are derived. It is shown that the throughput of both types of resonator can be improved significantly by using fiber with large mode size to couple to the resonator. The special fiber is then spliced to a conventional single-mode fiber. It is concluded that the resonator with an inserted hollow dielectric waveguide offers increased throughput for resonators with high finesse     

The Design and Fabrication of Monomode Optical Fiber

The design of monomode fibers is discussed in the context of optimizing fiber loss and dispersion simultaneously, with reference to the materials choices and limitations to preform and fiber fabrication by the MCVD technique. Two classes of monomode structure-matched cladding and depressed cladding-are considered. Ultralow attenuation has been achieved reproducibly in both classes of fiber. The control of fiber geometry and dispersion is also discussed. Matched cladding fiber suitable for systems operating at both 1.3 and 1.55 µm has been studied and mean losses of 0.45 dB/km at 1.3 µm and 0.28 dB/km at 1.55 µm have been achieved for a total of 130 km. The behavior of depressed cladding fiber is compared with predictions from the theory of propagation in W fibers. Depressed cladding fiber with stable guidance has been demonstrated with attenuation of 0.37 dB/km at 1.3 µm and 0.21 dB/km at 1.55 µm.     

An effective splicing method on photonic crystal fiber using CO/sub 2/ laser

Splicing between single-mode fiber (SMF) and photonic crystal fiber (PCF) using a conventional electric-arc splicer is not easily achieved. It is reported, for the first time, that the condensation within the capillaries resulted in a bubble developed at the fiber ends in the midst of splicing. A novel and effective splicing technique using a CO/sub 2/ laser has successfully eliminated this limitation and a complete splicing process is achieved within 3-5 s. The splice losses have been recorded to be in the range of 1.3-2.8 dB; the high splice losses are possibly due to the field-mode discrepancy of the sampled PCF with a diameter of 100 /spl mu/m.     

Numerical Modeling of S-Band EDFA Based on Distributed Fiber Loss

A numerical model for the analysis and design of S-band erbium-doped fiber amplifiers has been developed. The model is able to accurately predict the amplifier performances by taking into account the amplified spontaneous emission suppression due to the bending, as well as leakage losses of the fiber used as active medium. The model has been validated by comparing numerical and experimental data of bending loss, amplifier gain, and noise figure of an S-band optical amplifier based on a depressed-cladding erbium-doped fiber. A good agreement has been verified by varying fiber bending radius, input signal power, and wavelength. The model has been then applied to the optimization of the amplifier performances for wavelength-division multiplexer applications. The numerical results show that 20–25 dB gain can be achieved over a 25–30 nm range centered in a different part of the S-band from 1460 to 1525 nm, just by changing the bending radius and the length of a depressed-cladding fiber.      

Low loss GaAs optical waveguides

To realize an optical integrated circuit, various losses in the semiconductor waveguide such as absorption loss, waveguide loss, bending loss, and coupling loss, have to be minimized. Theoretical and experimental considerations for the reduction of these losses have been presented. A propagation loss of less than 0.5 dB/cm has been observed for a well-designed GaAs ridge waveguide. Moreover its coupling loss with a polarization-maintaining optical fiber decreased below 1.5 dB.