Hydrogenated amorphous carbon films used for carbon-sealed double-coated optical fibers

The carbon-sealed double-coated optical fiber is constructed from double-coated optical fiber sealed with a hydrogenated amorphous carbon film fabricated by plasma enhanced chemical vapor deposition. The pure methane (CH₄) and hydrogen (H₂) were selected as the precursor gases, and eight kinds of carbon film thicknesses by different deposited times were prepared with fixed CH₄/H₂ ratio. The radio-frequency power, substrate temperature, and working pressure were 200 W, 298 K, and 17 Pa, respectively. Characteristics of the carbon-sealed double-coated optical fibers prepared with different carbon film thicknesses were investigated. Experimental results indicated that when the carbon-film thickness was 113 nm, the carbon-sealed double-coated optical fibers had the highest mechanical strength, high resistance to moisture penetration, and good ability to withstand thermal loading. Additionally, external mechanical damage protection, abrasion resistance, bending flexibility, adhesion, stripping force, and bending insensitivity meet the fiber coating requirements. The carbon-sealed double-coated optical fiber is an optical fiber for optical transmission, and their properties are better than or equal to those of conventional double-coated optical fiber. Moreover, the carbon-sealed double-coated optical fiber is superior to nickel-sealed double-coated optical fiber in terms of water repellency and bending flexibility.     

Tensile-force-induced delamination of polymeric coatings in tightly jacketed double-coated optical fibers

To maintain the mechanical strength, the glass fiber of optical fibers is coated by polymeric materials during the fabrication process. However, when the external tensile-force-induced shear stress at the interface of the glass fiber and primary coating is larger than its adhesive stress, the polymeric coatings will be delaminated from the glass fiber and optical fiber will lose its mechanical strength. In this article, the tensile-force-induced delamination of polymeric coatings in tightly jacketed double-coated optical fibers is investigated. To minimize the coating's delamination, the tensile-force-induced shear stress at the interface of the glass fiber and primary coating should be reduced. The method to minimize such a shear stress is to select suitable polymeric coatings as follows. The Poisson's ratio of the primary coating and the Young's moduli of the secondary coating and jacket should be increased, but the Young's modulus of the primary coating and thickness of the secondary coating should be decreased. On the other hand, the thickness of the primary coating has an optimal value. The selection of the adhesive shear stress between the glass fiber and primary coating in the minimization of the coating's delamination is also discussed.     

Birefringence measurement under hydrostatic pressure in twistedhighly birefringent fibers

A new method of birefringence measurement in highly birefringent fibers influenced by hydrostatic pressure conditions up to 100 MPa is presented. The birefringence measurement method is based on twist-induced effects and has never been applied before in a high-pressure environment. The experiments were conducted using a specially designed pressure facility, which made it possible to simultaneously generate several mechanical perturbations, including twist and hydrostatic stress, and to investigate their effects on mode transmission in optical fibers. The results indicate that in the case of HB single-mode bow-tie fibers, hydrostatic pressure up to 100 MPa increased birefringence with a mean coefficient of (1/ΔB₀ )(Δβ)/dp=0.2%/MPa which is in very close agreement with our previous measurement based on Rayleigh scattering     

Side-hole two-core microstructured optical fiber for hydrostatic pressure sensing

A novel side-hole two-core microstructured optical fiber (STMOF) is proposed for hydrostatic pressure sensing. The two solid fiber cores are surrounded by a few small air holes and two large air holes, and are separated by one small air hole in the center of the cross section of the STMOF. The two large air holes that we called side holes essentially provide a built-in transducing mechanism to enhance the pressure-induced index change, which ensures the high sensitivity of the hydrostatic pressure sensor based on the STMOF. Mode coupling between the two fiber cores of the STMOF has been investigated, which provides a pressure-dependent transmission spectrum by injecting a broadband light into one fiber core of the STMOF on one side and detecting output spectrum on another fiber core on the other side. Our simulations show that there is a one-to-one correspondence between the hydrostatic pressure applied on the STMOF and the peak wavelength shift of the transmission spectrum. A hydrostatic pressure sensor based on an 8 cm STMOF has a sensitivity of 0.111 nm/Mpa for the measurement range from 0 Mpa to 200 Mpa. The performances of hydrostatic pressure sensors based on STMOFs with different structure parameters are presented.     

Determination of interfacial shear strength between the glass fiber and primary coating in double-coated optical fibers from mechanical strip forces

We propose a method of determining interfacial shear strength between the glass fiber and primary coating in double-coated optical fibers. A commercial stripper is used to mechanically strip the polymeric coatings. It consists of two hinged arms and a pair of blades with a semicircular bore. In the mechanical stripping process the relationship between the strip force and stripper displacement is measured. The interfacial shear strength between the glass fiber and primary coating is then determined from this relationship. The measured interfacial shear strength increases with the increasing stripping rate. It is found that measured results are compatible with theoretical results.     

Effects of hydrostatic pressure on phase and group modal birefringence in microstructured holey fibers

We calculated the sensitivity of phase (dB/dp) and group (dG/dp) modal birefringence to hydrostatic pressure versus wavelength in two birefringent holey fibers of different construction, where B is the phase modal birefringence, G is the group modal birefringence, and p is the pressure applied to the fiber. The contributions of the geometrical effects that were related only to deformation of the holey structure and the stress-related contribution to the overall pressure sensitivities were analyzed separately. Our results show that these two factors decrease the phase modal birefringence in both structures, which results in negative signs of dB/dp and dG/dp. Furthermore, we demonstrate that the geometrical effects are much weaker than the stress-related effects and contribute only a few percent to the overall pressure sensitivity.     

The buckling of FGM truncated conical shells subjected to combined axial tension and hydrostatic pressure

The purpose of this paper is to investigate the elastic buckling of FGM truncated thin conical shells under combined axial tension and hydrostatic pressure. Here axial tensions are separately applied to small and large bases of the truncated conical shell, respectively. It is assumed that the cone is a mixture of metal and ceramic, and that its properties changes as the power and exponential functions of the shell thickness. After giving the fundamental relations, the stability and compatibility equations of an FGM truncated conical shell, subject to combined axial tension and hydrostatic pressure, have been derived. Applying Galerkin’s method general formulas have been obtained for the critical combined and separate loads of FGM conical shells. The appropriate formulas for homogenous and FGM cylindrical shells are found as a special case. Effects of changing shell characteristics, material composition and volume fraction of constituent materials on the critical combined and separate loads of FGM shells with simply supported edges are also investigated. The results obtained for homogeneous cases are compared with their counterparts in the literature.     

Influence of dispersion on sensitivity of highly birefringent fibers to temperature and hydrostatic pressure

The influence of dispersion on the sensitivity of highly birefringent fibers to temperature and hydrostatic pressure was experimentally investigated. In fibers with geometric birefringence that shows high dispersion, great differences were observed between group and phase sensitivities to temperature and hydrostatic pressure. This difference may reach 400% in the case of temperature response. In contrast, in weakly dispersive fibers with stress-induced birefringence these differences were of the order of 8% and 14%, respectively, for temperature and pressure. The influence of the dispersion effect on the temperature compensation of white-light interferometric sensors based on highly birefringent fibers was also discussed.     

Fourier analysis of strain measurement using highly birefringenttwo-mode optical fibers

A new approach to strain measurement based on Fourier analysis of strain-induced polarization and intermodal coupling in highly birefringent, (HB) two-mode elliptical-core fibers is presented. The results indicate that Fourier spectra of sine-like, strain-dependent characteristics can create a very important tool in projecting practical devices which will measure longitudinal strain in specific applications     

Universal readout system for temperature, elongation and hydrostatic pressure sensors based on highly birefringent fibers

In this paper, we present a universal readout system, which can be used to decode polarimetric fiber-optic sensors based on highly birefringent fibers. All such sensors use the same sensing principle, relying upon the dependence of modal birefringence on different physical parameters. To register the measurand-induced phase changes between polarization modes, we use the coherence-addressing principle. This requires that the interrogated sensor be powered by a broadband source (superluminescent diode) and that the total optical path delay introduced by the sensor be balanced in the decoding interferometer. The system performance in decoding elongation, temperature and hydrostatic pressure sensing is demonstrated.     

Side-face radiation trapping by optical fibers

Radiation striking the side surface of an optical fiber can be trapped as result of scattering on the fiber wall. The mechanism of trapping is analyzed, a mathematical model of this phenomenon is presented, and the results of experimental investigations using poly (methyl methacrylate) fibers are reported.     

Failure of spheroplastics under axial tension and hydrostatic compression

The problem of determination of the external pressure and axial tensile force, which fail spheroplastics — a structurally inhomogeneous material consisting of hollow glass microspheres of different diameters, the latter being distributed in a random manner in a continuous epoxy matrix — is examined.Translated from Problemy Prochnosti, No. 9, pp. 59–61, September, 1990.     

Large strain analysis of rubber-like membranes under dead weight,gas pressure,and hydrostatic loading

The title problem is formulated variationally. Especially membranes being totally or partly under hydrostatic loading are considered and it is assumed that either the liquid volume or the liquid level is constant during the deformation. The most general case is characterized by an isoperimetric variational problem and free boundaries of the loaded (wetted) surface. Particularly we analyse membrane strips, membranes of revolution, and arbitrary spatial membranes consisting of piecewise plane ones. Numerous numerical results are reported and discussed with respect to the stability of equilibrium. Contact problems are addressed also.     

Fiber-optic measurement of low hydrostatic pressure based ondeformations induced in twisted nematic liquid crystal cells

Development of a new fiber-optic method of hydrostatic pressure measurement based on pressure-induced deformations in twisted nematic liquid crystal cells is presented. The method, particularly suitable for pressures up to 2 MPa and utilizing strong rotatory power occurring in chiral nematic liquid crystals, offers high response to pressure with reduced temperature sensitivity     

Bleeding and sedimentation of cement paste measured by hydrostatic pressure and Turbiscan

Sedimentation and bleeding of cement pastes with lignosulfonate were studied by visual observation, HYdroStatic Pressure Test (HYSPT) and Turbiscan measurements showing two bleeding stages: a fast initial phase followed by a phase with diminishing sedimentation rate. A turbid bleeding zone establishes during the fast bleeding phase and the top layer gradually becomes transparent in the diminishing phase within minutes or hours depending on admixture and solid fraction. The bleeding rates measured visually and by HYSPT in the first 2 h are higher than the ones calculated by Kozeny-Carman Equation, whereas turbiscan shows lower rates. Both HYSPT and Turbiscan monitor the particle and fluid fluxes and thus describe bleeding from turbid to clear zone respectively by observing the density variation of bulk paste or the change in optical density of the surface region. Lignosulfonate reduces bleeding by improving particle dispersion to various degrees depending on types and dosages.     

Nonlinear modes in optical fibers

It is shown that the electromagnetic field generated in an optical fiber operating in a nonlinear regime has the form of nonlinear guided modes—cnoidal (periodic) waves which transform into monochromatic fiber modes in the linear operating regime. The cnoidal modes are generated due to nonlinear polarization effects in the dielectric medium. These effects can be described by equations with sinusoidal nonlinearity.     

Polymer optical fibers and nonlinear optical device principles

Basic principles of the present optoelectronic research activities at Hoechst AG are presented in this contribution. Within the diversified broad band spectrum of optoelectronic materials and applications our interest is focused on new types of polymer optical fibers and nonlinear optical device principles using organic Langmuir–Blodgett films and electrically poled polymers. The basic principles and the limits of the present research and development activities which, have a high market potential are outlined.     

Analysis of optical fibers by the effective-index method

The effective-index method for determining waveguide dispersion is derived from the scalar wave equation and applied to optical fibers of arbitrary cross-sectional shapes. In the simplest use of the method, the optical fiber is replaced by an equivalent slab waveguide with an index profile derived from the geometrical shape of the fiber. Results from analyzing circular, elliptical, and cusp-shaped fibers are used to illustrate the general features of the method. A procedure is also given for improving the accuracy of the method applied to a class of single-mode fiber.