Transient thermal loading induced optical effects in single-coated optical fibers with interlayer thermal resistance

The transient microbending loss and refractive index changes in a single-coated optical fiber subjected to thermal loading with stress-dependent interlayer thermal resistance are investigated. The effects of interlayer thermal resistance on the transient microbending loss and refractive index changes of the optical fiber are analyzed and discussed. Results show that the interlayer thermal resistance will increase the transient thermal loading induced lateral pressure in the single-coated optical fiber and, thus, the microbending loss. To the contrary, the interlayer thermal resistance will decrease the transient thermal loading induced refractive index changes.     

Low temperature characteristics of UV-curable resin coated optical fiber

Transmission characteristics of coated optical fiber depend on coating materials at low temperature. Loss increase phenomena are compared for UV-curable resin coated and silicone-nylon coated fibers. Different mechanisms induce loss increase depending on coating materials. Lateral forces are caused by shrinkage and Young's modulus increase at low temperature for UV-curable resin coated fibers. These forces cause fiber microbending for correlation lengths of not more than 1 mm. However, for silicone-nylon coated fibers, axial forces cause fiber buckling for correlation lengths longer than 5 mm. The relationship between the UV-coating structure and loss increase at low temperature is also described.     

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     

Theoretical analysis of the interfacial-shear-stress induced delamination of polymeric coatings from the glass fibers in double-coated optical fibers during temperature cycling

To prevent the delamination of polymeric coatings from glass fibers, temperature cycling induced interfacial-shear-stress between the glass fiber and primary coating should be always smaller than its interfacial shear strength in a long time. The method for the prevention of the long-term delamination of polymeric coatings from glass fibers is as follows. The thickness of the primary coating can be increased if the spring constant of the optical fiber is selected to prevent low temperature microbending of the glass fiber. Meanwhile, Poisson's ratio of the primary coating should be selected to be very close to 0.5. Alternatively, the relaxation time of the primary coating and secondary coating should be increased, but Young's modulus of the primary coating as well as the thermal expansion coefficient of the secondary coating should be decreased. Meanwhile, the thickness and Young's modulus of the secondary coating should be decreased if the strength of the secondary coating is satisfied.     

Curing shrinkage effects of UV-curable materials on fiber losscharacteristics

The curing shrinkage effect in the radial direction of ultraviolet UV-curable coating on fiber-loss characteristics is investigated theoretically and experimentally. It is shown that curing shrinkage causes lateral forces to the fiber and leads to microbending loss increases at low temperatures. A model for pressure caused by curing shrinkage in the radial direction is discussed. According to this model, the radial pressure to the optical fiber in the coating can be estimated by measuring the fiber pulling force from the coated optical fiber. Based on the agreement of theoretical and experimental results, the allowable range of curing shrinkage percentages of primary and secondary coatings to prevent fiber-loss increase is obtained. Design strategies to prevent fiber loss increases at low temperatures are described     

Predicted curvature of a glass fiber from the measured curvature ofits coating

An analytical stress model is developed to evaluate the elastic curve of a glass fiber whose coating has a constant (measured or imposed) bend radius. It is shown that in order to predict the bending behavior of a coated glass fiber subjected to bending a parameter u should be computed which depends, in addition to Young's modulus and diameter of the glass fiber itself, also on the length of the curved area and Young's modulus and outer diameter of the (primary) coating. In the range 0<u<2.365, the maximum curvature of the glass fiber occurs at the midpoint of the curved area. If the calculated u value is greater than (7π/4)=5.50, the curvature of the glass fiber in the midportion of the glass-coating composite is practically not different from the coating curvature. Within the range 2.365<u<5.50, the maximum curvature of the glass fiber is greater than the observed curvature of the coating     

Investigation on propagation properties of terahertz waveguide hollow plastic fiber

The propagation properties of terahertz (THz) waveguide plastic hollow fiber have been investigated in this paper. The effects of radiation frequency, bore diameters and dielectric coating layers on the waveguide property have been shown and discussed. The results show that the attenuation loss of TM mode increases and that of TE mode decreases as radiation frequency increases. The attenuation loss decreases with the increasing of fiber bore diameter. The attenuation loss decreases as the refractive index of dielectric coating layer and the ratio of the refractive index of outer dielectric layer to that of inner dielectric layer increase.     

Design of double-coated optical fibers to minimize mechanical stripforces

This work investigates the optimal design of double-coated optical fibers to minimize the mechanical strip force. As assumed, herein, the stripper consists of two hinged arms and paired blades with a semicircular bore, Analytical results indicate that the strip force is a function of the stripper's bore radius. The stripper's optimal bore radius attempts to make it close to the glass fiber radius. Notably, the stripper does not damage the glass fiber surface during the stripping process. Based on the type of strip force, the stripping process can be divided into two steps. In the first step, a strip force F_t must break the polymeric coatings and allow the crack on the cutting plane to extend to the glass fiber surface. In the second step, a strip force F_a must break the adhesive bond between the glass fiber and primary coating to remove the polymeric coatings away. The strip force F_a is independent of the stripping length. The strip force F_a and the work deemed necessary to strip the polymeric coatings are proportional to the adhesive stress between the glass fiber and primary coating. The shear strength of the primary coating should exceed the adhesive stress between the glass fiber and primary coating; otherwise, the primary coating cannot be stripped completely from the glass fiber surface. The strip force F_a can be minimized by appropriately selecting polymeric coatings and their thicknesses. To minimize such a strip force, the thickness and Young's modulus of the primary coating should be increased. On the other hand, the thickness and Young's modulus of the secondary coating should be decreased     

Hydraulic pressure buckling in plastic coated optical fibre

Buckling was observed under hydraulic pressure in a multi-mode plastic-coated optical fibre with a buffer layer. The optical loss increase by buckling was examined. It was found that the occurrence of buckling can be estimated from the relationship between compressibility and Young's modulus of the coating materials.     

Upper and lower limits for the microbending loss in arbitrary single-mode fibers

Upper and lower limits for the actual microbending loss of single-mode fibers with arbitrary refractive index profile are given. These limits strongly depend on the shape of the actual fundamental mode field. It is shown that the minimum splice loss due to a small offset for a given microbending loss is obtained for a fiber with a Gaussian fundamental mode field. Fibers with similar splice loss and non-Gaussian fundamental mode fields like multiple-clad single-mode fibers will exhibit significantly larger microbending losses.     

Design of the interfacial shear strength between the glass fiberand primary coating in double-coated optical fibers

The design of the interfacial shear strength between the glass fiber and primary coating in double-coated optical fibers is investigated. An optical fiber with higher interfacial shear strength possesses a better ability to prevent the delamination of polymeric coatings, but it makes the strip of coating materials more difficult. Based on the consideration of the stripping ability and delamination of polymeric coatings, the optimal value of the interfacial sheer strength is dependent on the tensile strength of the glass fiber, the damping condition of the tensile force applied on the optical fiber, the fiber's length, and material's properties of polymeric coatings. In the real applications of optical fibers, the tensile strength of the glass fiber can be regarded as the allowable external load induced axial stress in the glass fiber which usually is a fraction of the proof-test setting value. The clamping condition of the optical fiber can be regarded that the tensile force is only applied on the both ends of the secondary coating. The fiber's length can be regarded as the minimum operating length, for example, 10 mm. A higher value of the interfacial shear strength is required for optical fibers with higher Young's modulus of the primary coating, lower Poisson's ratio of the primary coating, and lower radius and Young's modulus of the secondary coating. Finally, the limitation of the lateral load on the optical fibers to prevent the delamination of polymeric coatings is also discussed     

Return loss characteristics of optical fiber connectors

This paper describes the return loss characteristics for four typical contact type connectors: perpendicular and oblique endface connectors employing either physical contact or contact via index matching material. The high index layer on the polished fiber endface and the index matching material, which are important connector parameters, are investigated by measuring the return loss from one perpendicular fiber endface coated with the material and by etching the fiber endface. It is useful to apply two materials with different refractive indices to derive the refractive index and thickness of high index layers on perpendicular fiber endfaces. The index matching material we use has a refractive index of 1.467 at 20°C and a thermal coefficient of -2.9×10^-4/°C at 1.3 μm. We performed return loss calculations and experiments of the four contact type connectors. The worst value at any temperature from -40 to 80°C can be estimated, by measuring the return loss of these connectors at room temperature     

Microbending loss evaluation in arbitrary-index single-mode optical fibers. Part II: Effects of core index profiles

Microbending losses in single-mode fibers with several types of core refractive index profiles are compared. Numerical calculations were carried out to characterize fibers with step, power-law,Wand ring-shaped index profiles. Step-index andWfibers exhibit a small excess loss near the single-mode operation upper limit. However, permissible offset misalignment in fiber splice at constant microbending loss is nearly identical for step, power-law, andWfibers. An index dip at the core center has an undesirable influence on the required splicing accuracy. The effects of fiber curvature statistics and index profile parameters are investigated in detail.     

Carrier density dependence of refractive index in AlGaAs semiconductor lasers

Carrier density dependence of the refractive index in the active layers of semiconductor lasers is evaluated from the wavelength shift with increases in current by taking into account effects of the active layer temperature rise and lateral carrier and optical field distributions on the wavelength shift. The derived refractive index change due to carrier density increase is-4 times 10^{-27}m³, which is in good agreement with the theoretical value.     

Interfacial shearing stress in pull-out testing of dual-coatedlightguide specimens

A simple analytical model is developed for the evaluation of the interfacial shearing stress at the glass fiber surface in dual-coated optical fiber specimen subjected to tension. It is shown that the distribution of this stress is nonuniform and that, for the given specimen's length, its maximum value increases with a decrease in the thickness of the primary coating. The obtained results can be useful for comparing the adhesive strength of the primary coating material in fibers of different lengths and with different coating designs, as well as for the in situ evaluation of Young's (shear) modulus of this material from the measured axial displacement of the glass fiber     

New thermoplastic dual-coextrusion-coating system for optical-fibre drawing

A new thermoplastic dual-coextrusion-coating technique consisting of a soft thermoplastic rubber primary coating and a hard secondary coating has been proposed as an in-line coating system with fibre drawing. The use of a low linear-expansion-coefficient polymer as the hard secondary coating is a necessary condition for obtaining no microbending loss of the dual-coated fibres.     

涂覆层参数对FBG温度灵敏度的影响

分析了涂覆层的物理参数对光纤光栅（FBG）温度灵敏度的影响,数值分析结果表明,大涂覆厚度、高弹性模量、高泊松比、高线膨胀系数有助于提高FBG的温度灵敏度。FBG温度灵敏度的饱和值主要取决于涂覆层的弹性模量和泊松比,因此不能单纯依靠选取大弹性模量或泊松比的涂覆来提高温度灵敏度,还须综合考虑弹性模量和泊松比对温度灵敏度的影响,以确定两参数的最佳值。     

High-pressure oxidation for thin gate insulator process

High-pressure oxidation of silicon was performed at a pressure of 8.9 kg/cm²at a temperature range of 650 to 950°C. The oxidation temperature dependence of the film density, refractive index, chemical etching rate, and residual stress was measured. The film density of the oxide film was found to increase with decreasing oxidation temperature. The refractive index of the film also increased with decreasing oxidation temperature. The residual stress was found to be dependent on the oxidation temperature. The dielectric breakdown strength of the oxide film was measured by the voltage ramping method. The defect density of the oxide film calculated from the distribution of dielectric breakdown strength slightly decreased with decreasing oxidation temperature. The surface-state density of the oxide film was about 1.1 × 10¹¹cm^-2throughout the oxidation temperature range. The oxide grown on a doped polysilicon layer at a temperature of 750°C was five times as thick as the oxide simultaneously grown on the silicon substrate. The high-pressure and low-temperature oxidation was applied to the fabrication process of a device with a double polysilicon layer structure.     

Microbending loss evaluation in arbitrary-index single-mode optical fibers. Part I: Formulation and general properties

Microbending loss formula is derived for arbitrary-index profile optical fibers by using analytical curved fiber fields to the first-order perturbation theory. Relation between loss and fiber curvature power spectral statistics is studied in detail. Normalized frequency giving the minimum microbending loss value scarcely depends on the power spectrum. The larger the propagation constant difference between the guided and quasi-guided modes, the smaller the microbending loss is in regard to wavelength, relative index difference, and normalized frequency dependence. The obtained formulas for single-mode fiber show the same dependence as the graded-index multimode fiber, with respect to fiber structure and curvature statistical parameters.     

LBO晶体上1064 nm,532 nm二倍频增透膜的设计及误差分析

采用矢量合成法设计了LiB3O5(LBO)晶体上1064 nm,532 nm二倍频增透膜,在1064 nm处的反射率为0.0014%,532 nm处的反射率为0.0004%。根据误差分析,薄膜制备时沉积速率精度控制在 6.5%时,1064 nm处的反射率增加至0.22%,532 nm处增加至0.87%。材料折射率的变化控制在 3%时,1064 nm处的反射率达0.24%,532 nm处达0.22%。沉积速率和折射率控制的负变化不增大特定波长处的剩余反射率。与膜层折射率相比,薄膜物理厚度对剩余反射率的影响小。低折射率膜层的厚度变化对特定波长处的剩余反射率影响最明显,即为该膜系的敏感层。为改善膜基之间的附着力,选择Y2O3或SiO2作为过渡层,从过渡层的厚度匹配和膜层的折射率匹配两方面进行了相应的膜系匹配设计。