Ana Simović

Mode coupling in strained and unstrained step-index glass optical fibers

By using the power flow equation, we have examined the state of mode coupling in strained and unstrained step-index glass optical fibers. Strained fibers show stronger mode coupling than their unstrained counterparts of the same type. As a result, the coupling length where equilibrium mode distribution is achieved and the length of fiber required for achieving the steady-state mode distribution are shorter for strained than for unstrained fibers.

Equilibrium mode distribution and steady-state distribution in 100–400 μm core step-index silica optical fibers

Using the power flow equation, the state of mode coupling in 100-400 μm core step-index silica optical fibers is investigated in this article. Results show the coupling length L(c) at which the equilibrium mode distribution is achieved and the length z(s) of the fiber required for achieving the steady-state mode distribution. Functional dependences of these lengths on the core radius and wavelength are also given. Results agree well with those obtained using a long-established calculation method. Since large core silica optical fibers are used at short distances (usually at lengths of up to 10 m), the light they transmit is at the stage of coupling that is far from the equilibrium and steady-state mode distributions.

Influence of depth of intermediate layer on optical power distribution in W-type optical fibers

For different depth and width of the intermediate layer, a power flow equation is used to calculate spatial transients and steady state of power distribution in W-type optical fibers (doubly clad fibers with three layers). A numerical solution has been obtained by the explicit finite difference method. Results show how the power distribution in W-type optical fibers varies with the depth of the intermediate layer for different values of intermediate layer width and coupling strength. We have found that with increasing depth of the intermediate layer, the fiber length at which the steady-state distribution is achieved increases. Such characterization of these fibers is consistent with their manifested effectiveness in reducing modal dispersion and improving bandwidth.

Temperature Dependence of Mode Coupling in low-NA Plastic Optical Fibers

Using the power flow equation and experimental measurements, investigated in this paper is the state of mode coupling in low NA (0.3) step-index (SI) plastic optical fibers under varied temperature. Numerical results obtained using the power flow equation agree well with experimental measurements. It is found that elevated temperatures of low-NA SI plastic optical fibers strengthened mode coupling. These properties remained after a year, with the fiber being subjected to environmental temperature variations of >35 K. These thermally induced changes of the fiber properties are attributed to the increased intrinsic perturbation effects in the PMMA material at higher temperatures. This results in an increase of the measured bandwidth with increasing fiber temperature as well as earlier the bandwidth switch from the functional dependence of 1/z to 1/z1/2 (slower bandwidth decrease).

Transients of Modal-Power Distribution in Multimode Solid-Core W-Type Photonic Crystal Fibers

Spatial transients of the modal power distribution are reported for a varied configuration of air holes in the inner cladding of multimode solid-core photonic crystal fibers. Such inner cladding forms an intermediate fiber layer seen in W-type fibers with the layers own effective refractive index due to the distinct size and/or spacing of air holes in it. We show how the modal distribution transients along the fiber depend on the number of rings in the inner cladding containing the distinct arrangement of air holes, and on the size and spacing of such holes in addition to the type of launch condition (excitation).