Effect of Launching Condition on Modal Power Characteristics of Multi-Mode Step-Index Optical Fiber: A Theoretical and Experimental Investigation

Abstract

This article investigates optical power transmission characteristics with varying launching conditions concentrating on weakly guiding, step-index highly multi-moded optical fibers. A single analytical expression for the fractional power transmitted per mode in a highly multi-moded fiber is obtained. This expression is used to numerically obtain the fractional power per mode, power per modal order, and finally, the total power carried by the fiber. Experiments are carried out to investigate the effect of launching conditions on the total power carried by the fiber and to establish a possible correlation with the theoretical results. Reasons for the observed experimental discrepancies are also discussed.

     

Investigation of influence of tilt angle on mode dispersion in step-index plastic optical fibers

Effect of numerical aperture on mode dispersion and bandwidth is reported for commercially available step-index plastic optical fibers. For the first time, the functional relationship is given between dispersion and the “tilt-angle” describing the slant of the input/output face for a fiber terminated by a plane not perpendicular to the fiber axis. This tilt of a non-squarely terminated fiber may be intentional as in some biomedical spectroscopic sensors, or otherwise when exploiting the quick-interconnectivity potential of plastic fibers.     

Frequency response in step-index plastic optical fibers obtained by numerical solution of the time-dependent power flow equation

The time-dependent power flow equation is employed to calculate frequency response and bandwidth in addition to mode coupling and mode-dependent attenuation in step-index plastic optical fibers. Frequency response is specified in the paper as a function of fiber length. Results are found to match reported measurements better than the existing analytical solution does. Mode-dependent attenuation and mode dispersion and coupling are known to be strong in plastic optical fibers, leading to major implications for their frequency response.     

Calculation of the frequency response in step-index plastic optical fibers using the time-dependent power flow equation

The time-dependent power flow equation, which is reduced to its time-independent counterpart is employed to calculate frequency response and bandwidth in addition to mode coupling and mode-dependent attenuation in a step-index plastic optical fiber. The frequency response is specified as a function of distance from the input fiber end. This is compared to reported measurements. Mode-dependent attenuation and mode dispersion and coupling are known to be strong in plastic optical fibers, leading to major implications for their frequency response in data transmission systems.     

170 Mb/s multilevel transmission over 115 m standard step-index plastic optical fiber using an integrated optical receiver

An optical receiver having a high linearity is used for multilevel communication over standard step plastic optical fiber. A large-diameter photodiode with an antireflection coating optimized for red light was integrated. These features enable the used optical receiver to be a promising plastic optical fiber receiver. An error free (< 10⁻⁸) 170 Mb/s data rate over 115 m standard PMMA step-index plastic optical fiber is achieved with four-level and eight-level pulse amplitude modulation.     

The limits of plastic optical fiber for short distance high-speed computer data links

Abstract

The attenuation and dispersion of commercially available all-plastic step-index optical fiber are the major factors limiting the maximum achievable transmission distance and bit rate; this article explores these limits. Calculations predict that ～ 500 Mb/s transmission over 100 m of standard 0.47 NA step-index PMMA POF at 650 nm is feasible, and recent experimental results at up to 400 Mb/s are briefly described. The implications of having a lower loss, higher bandwidth POF, for example, perfluorinated, graded-index PMMA, arc discussed.     

Design and analysis of multi-ring microstructured-core optical fibers

A novel design of single-mode large-mode-area optical fiber is presented. The core is composed of alternate high and low-index regions to form an effectively low-index contrast between the core and the cladding. The proposed fiber is investigated by the finite-element method with anisotropic perfect matched layer boundary conditions. In addition, the bending losses of the fibers are calculated and compared with those of the step-index optical fibers. In particular, numerical simulations demonstrate that single-mode operation can be achieved in one such fiber with mode area larger than 600 μm² at the wavelength of 1.55 μm and bending loss lower than 0.02 dB/m for bending radius greater than 20 cm.     

Accuracy Improvement in the Measurement of the Non-Linear Coefficient of Optical Fibers Based on Self-Phase Modulation

Abstract

A novel and simple procedure to improve the accuracy of the measurement of the third-order Kerr non-linear coefficient of optical fibers based on self-phase modulation is described. It includes an efficient method to identify the chirp of the input pulse. A standard single-mode fiber and a highly non-linear microstructure chalcogenide fiber have been measured. The accuracy of the measurement is increased to ±5% instead of ±19% with the classical self-phase modulation method in this case.     

Passive T-bus with asymmetrical 4-port couplers

Abstract

A newly designed 4-port coupler in planar technology is described. The axes of the coupling fibers are mutually offset as before, but the input fiber is thinner than the other three, and its diameter is matched to the emitting surface area of the light source serving as a transmitter. Low insertion loss and high coupling efficiency are realized through the choice of favorable dimensions. Graphs show the output coupling efficiency, input coupling loss, and insertion loss with step-index fibers as a function of the axial offset. The maximum number of terminals that can be connected to the T-bus is calculated for various conditions. The number of terminals is found to be about 40% higher than is possible with the coupler with four identical fibers.     

1 Gbit/s transmission over step-index plastic optical fiber using an optical receiver with an integrated equalizer

A single chip optical receiver with an integrated large-diameter photodiode, transimpedance amplifier, two stages active equalizer, post amplifier and 50 Ω driver is used for gigabit transmission over PMMA step plastic optical fiber (SI-POF). The large-diameter photodiode with an antireflection coating optimized for red light. The integrated equalizer enables the presented optical receiver to reach 1 Gbit/s over 50 m SI-POF at bit error ratio of 10^− 6. An error free (< 10^− 9) 1 Gbit/s data rate over 40 m standard PMMA step-index plastic optical fiber is also achieved.     

Dependence of macro-bending loss on bending configuration of multimode optical fibers studied by ray-tracing simulation

Optical Review - The macro-bending loss of multimode step-index helical, s-shaped, and figure-of-eight-shaped optical fibers is investigated by ray-tracing simulation. In particular, fibers with...     

Ultrahigh-resolution plastic graded-index fused image plates

Fiber-optic imaging systems such as the medical endoscope, the boroscope, the fused-image faceplate, and the image conduit are now made from glass step-index (SI) fibers, and the image resolution of the SI fiber-optic imaging systems is limited to ~5 microm. Ultrahigh-resolution fiber-optic fused-image plates with fiber diameter sizes of 5 and 2.8 microm were fabricated with plastic graded-index (GRIN) fibers. The measured image resolutions of the 5-microm SI and GRIN-based guides were comparable, and the resolution of the plastic GRIN image guides improved as the fiber diameter was reduced from 5 to 2.8 microm.     

Fiber optic cables for undersea communications

Abstract

Areas for potential use of low-loss optical fibers in undersea communications are discussed, along with constraints that should be satisfied in incorporating these fibers into practical cables. Recent progress in construction of optical cable units with low attenuation, small diameter, low specific gravity, high tensile strength, and extended flexural endurance is described. Design concepts for six undersea optical cables, with a variety of diameters and capabilities, are presented in detail. Guidelines are discussed for the design of such cables. Related operational requirements on the cable, such as power transfer, are examined to show how unconventional approaches can allow advantages of the optical data link to be more fully utilized.     

Few-mode step-index optical fibers with ultra-low bending losses

We propose a few-mode optical fiber for low-bending-loss applications. We demonstrate ultra-lowbending-loss operation in the fiber by tailoring the core radius and index contrast of step-index optical fibers. In addition, we investigate numerically splicing losses in single-mode optical fibers and demonstrate experimentally the ultra-low-bending-loss operation characteristics. The optical fiber elaborated provides a simple technique to realize the low-bending-loss operation.     

Properties of silver halide core-clad fibers and the use of fiber bundle for thermal imaging

Abstract

Optical infrared (IR) fibers with core-clad structure are of great importance because they have better qualities than unclad fibers for most IR fiber applications, especially in CO₂ laser power delivery and radiometry. We have fabricated core-clad polycrystalline silver halide optical fibers with different compositions and core diameters, and although their loss is still higher than that of unclad fibers, they already have many advantages and new capabilities. The behavior of the scattering loss along these fibers and other optical properties was measured and compared with that of unclad silver halide fibers. We show that the higher loss of clad fibers results mainly from excessive scattering. The improvement in the process of fabricating clad fibers enabled the production of new elements such as single-mode fibers (SMFs) and fiber bundles for thermal imaging.     

Single-mode microstructured optical fiber for the middle infrared

Microstructured crystalline optical fiber from silver halides is described. Both experimental and theoretical evidences are presented to establish that the fiber is effectively single mode at wavelength 10.6 micro m with numerical aperture NA=0.16 and optical losses of approximately 2 dB/m. Crystalline microstructured optical fibers offer key advantages over step-index optical fibers from silver halide crystals. The wide transmission range of wavelengths 2-20 micro m provides great potential for applications in spectroscopy and for the development of a range of new crystalline-based nonlinear optical fibers.     

Tensile performance of packaged optical fibers

Abstract

The tensile testing of packaged optical fibers involves the measurement of elastic strains in the range 2–10%. Under these conditions slippage at the tensile grips can produce erroneous results when a nonextensometric method of measurement (e.g., in positive production testing) is used. Slippage of packaged silica fibers (polypropylene/silicone resin-coated silica fibers) observed when using standard pneumatic parallel-faced jaws has been eliminated by using 50-mm-diameter pulley grips with suitable clamps to hold the fiber ends. With this arrangement clean fiber failures are obtained within the gauge length. A correction factor has been estimated for the measured strain values by a theoretical analysis of the measured tension/extension curves for the composite polypropylene/silicone resin-coated fibers. Statistical data have also been obtained for polypropylene-(PP) coated lead silicate fibers and PP-coated “plastic clad” silica fibers. In the latter case, true failure had been obscured by the onset of fiber slippage within the PP jacket.     

Spectral excess attenuation of monomode optical fibers with sinusoidally perturbed core radius

The spectral excess attenuation caused by coupling between the guided HE₁₁ mode and radiation modes is calculated with the aid of the formula derived by Marcuse for the radiation loss of a monomode optical fiber with step-index profile and sinusoidally perturbed core radius. The pronounced minima and maxima of the spectral excess attenuation curve converge as the spatial frequency of the perturbation of the core radius increases. Even perturbation amplitudes as small as 0.01 μm may lead to excess attenuations of the order of 10 dB/km if the radiation wavelength does not coincide with an attenuation minimum. The spectral behavior of the excess attenuation can be utilized to design fibers which act as optical filters.     

Solutions of the full- and quasi-vector wave equations based on H-field for optical waveguides by using mapped Galerkin method

The mapped Galerkin method in solving the full-vector and quasi-vector wave equations in terms of transverse magnetic fields (H-formulation) for optical waveguides with step-index profiles is described. By transforming the whole x-y space onto a unit square and using two-dimensional Fourier series expansion, the modal distributions and propagation constants for optical waveguides are obtained in the absence of boundary truncation. Results for step-index circular fiber, buried rectangular waveguide, and optical rib waveguide are presented. Solutions are good agreed with exact solutions and numerical results by using vector nonlinear iterative method, Fourier operator transform method, and vector beam propagation method.     

求解梯度光纤模场的近似里兹-伽略金方法

提出里兹-伽略金方法的一个近似或改进,即里兹-伽略金方法仅仅用来得到梯度型光纤的传播常量和纤芯中的模式场.包层场用修正贝塞尔函数以及已经求得的两个参量:包层径向衰减常量和场在纤芯-包层界面上的值重新构建.计算结果表明包层场准确度的改进是相当显著的,将这一近似方法应用于计算两根光纤之间的耦合系数,其结果与准确值几乎没有办法区分.