Step-index Plastic Optical Fiber Research Articles

Coupling length as an algebraic function of the coupling coefficient in step-index plastic optical fibers

As a function of the coupling coefficient in step-index (SI) plastic optical fibers (POFs), the coupling length for achieving the equilibrium mode distribution is determined by a simple algebraic equation and graph, separately for light-emitting diode (LED) and laser launch-beam distributions. One benefit of the proposed function is that it simplifies the determination of the coupling length by eliminating the need to numerically solve the power flow equation (or equivalent) repeatedly for all new values of the coupling coefficient.

Calculation of the coupling coefficient in strained step index plastic optical fibers

The coupling coefficient in a strained step index plastic optical fiber is determined using our recent simplified method. This enabled the calculation of the length z(s) at which the steady-state distribution (SSD) is achieved. Results are in good agreement with measurements reported earlier. The strained fiber shows a much stronger mode coupling than the unstrained one of the same type. Consequently, the fiber length for achieving the SSD is much shorter for strained than unstrained fibers.

Reply to comment on "Influence of bending on power distribution in step-index plastic optical fibers and calculation of bending loss"

In response to the comments made by Djordjevich on our previous paper [Appl. Opt. 45, 6675-6681 (2006)], the following clarifications are made.

Comment on "Influence of bending on power distribution in step-index plastic optical fibers and the calculation of bending loss"

Arguments are presented that a recent paper on the topic of power distribution and mode coupling in curved step-index plastic optical fibers is incorrect and that the method proposed is conceptually flawed except for the special case when the fiber is straight, which was the case used to verify the calculations.

Method for calculating the coupling coefficient in step-index optical fibers

A simple method is proposed for determining the mode coupling coefficient D in step-index multimode optical fibers. It only requires observation of the far-field output pattern for one fiber length with the input light launched centrally along the fiber axis (theta(0)=0). For illustration, the coupling coefficient determined by this simple method for a step-index plastic optical fiber was used to calculate the coupling length L(c) at which the equilibrium mode distribution is achieved, and length z(s) at which the steady-state distribution is achieved. Our results are in good agreement with experimental results reported earlier.

Influence of bending on power distribution in step-index plastic optical fibers and the calculation of bending loss

A means of calculating optical power distribution in bent multimode optical fibers is proposed. It employs the power-flow equation approximated by the Fokker-Planck equation that is solved by the explicit finite-difference method. Conceptually important steps of this procedure include (i) dividing the full length of the bent optical fiber into a finite number of short, straight segments; (ii) solving the power equation for each segment sequentially to find its output distribution; and (iii) expressing that output distribution in rotated coordinates of the subsequent segment along the curved fiber to determine the input distribution for that subsequent segment and thus enable the calculation of the power flow and output distribution for it. The segment length and bend-induced perturbation of output angles are determined by geometric optics. The resulting power distributions are given at different cross sections along the curved fiber axis. They vary with the radius of fiber curvature and launch conditions. Results are compared to those for straight fiber. Bending loss is calculated as well.

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

Using the power-flow equation, we have examined the state of mode coupling in strained and unstrained step-index plastic optical fibers. The strained fibers show much stronger mode coupling than unstrained fibers of the same types. As a result, the coupling lengths where equilibrium mode distribution is achieved and the lengths of fiber required for achieving a steady-state mode distribution for strained fibers are much shorter than the corresponding lengths for unstrained fibers.

Global characterization of optical power propagation in step-index plastic optical fibers

We propose to characterize optical power transmission in stepindex plastic optical fibers by estimating fiber diffusion and attenuation as functions of the propagation angle. We assume that power flow is described by Gloge s differential equation and find a global solution that was fitted to experimental far field patterns registered using a CCD camera as a function of fiber length. The diffusion and attenuation functions obtained describe completely the fiber behavior and thus, along with the power flow equation, can be used to predict the optical power distribution for any condition.

Analysis of the effects of mode coupling on the bandwidth characteristics of step-index plastic optical fiber

The mode coupling of SI-POF is analyzed by observing the far-field radiation patterns. The results show that no obvious mode coupling occurs at a transmission distance of 5 m. While a transmission distance of 10–30 m occurs, strong mode coupling and the equilibrium mode distribution is established after 30 m. In order to clarify the mode-coupling effect on the bandwidth of step-index plastic optical fiber (SI-POF), the bandwidths of SI-POF samples were measured under different launch conditions and compared with theoretical values that neglect mode coupling. It is found that although mode coupling contributes to enhancing the bandwidth of the fiber as it averages out the total propagation delays, the energy transfer between the neighboring modes will excite high-order modes during the propagation, which functions to increase the effective numerical aperture (NA) of the incident light and will decrease the bandwidth of the fiber. The net effect of mode coupling on the bandwidths of SI-POFs at different launch conditions indicates the competition between the two effects. © 2006 Wiley Periodicals, Inc. Microwave Opt Technol Lett 48: 432–435, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.21372

Modeling of the loss and mode coupling due to an irregular core–cladding interface in step-index plastic optical fibers

The core-cladding boundary in step-index plastic optical fibers is imperfect. Surface irregularities locked in during the manufacturing process couple the guided modes by reflecting them in directions that deviate unpredictably from the expected directions. This causes an additional loss as the multiple reflections from surface elements with directions randomized around the nominal for the cylinder transfer the power to the radiation modes that are carried away from the core into the cladding. We model such loss and mode coupling by ray tracing. The irregular core-cladding interface is represented by nominally cylindrical surface elements with orientations randomly perturbed around two geometric axes. The results show mode coupling and relative loss per unit fiber length caused by the core-cladding interface irregularities. The loss is high close to the input fiber end where mode coupling is intense. It drops farther along the fiber as mode coupling slows down and stabilizes where the equilibrium mode distribution is reached.

Bidirectional optical coupler for plastic optical fibers

We have developed a low-loss bidirectional optical coupler for high-speed optical communication with plastic optical fibers (POFs). The coupler, which is fabricated by an injection molding method that uses poly (methyl methacrylate), has an antisymmetric tapered shape. We show that the coupler has low insertion and branching losses. The tapered shape of the receiving branch reduces beam diameter and increases detection efficiency coupling to a photodetector, whose area is smaller than that of the plastic optical fiber. The possibility of more than 15-m bidirectional transmission with a signaling bit rate up to 500 Mbits/s for simplex step-index POFs is demonstrated.

Influence of tunneling rays to baseband frequency response of step‐index plastic optical fibers

AbstractThe transmission bandwidth of a stepped‐index plastic optical fiber (POF) is found to vary significantly with the location of incidence of the light at the POF edge plane. In order to determine the cause, the effect of a tunneling leaky ray on the baseband frequency characteristics of the POF is studied both numerically and experimentally. It is found that the transmission bandwidth becomes narrower due to excitation of tunneling leaky rays if the light is incident from a light source with a wide radiating angle, such as that in a light‐emitting diode (LED), on a position far from the center on the POF edge plane. © 2005 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 88(8): 12–17, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.20166

Design of mode scramblers for step-index and graded-index plastic optical fibers

We analyze the internal evolution of light power angular distribution in typical mode scrambling configurations by comparing the resultant far fields, obtained either experimentally or computationally, with the experimental equilibrium mode distribution (EMD) far field for the plastic optical fibers (POF) considered, so as to provide an insight that helps to adapt existing scramblers to new types of POF that are coming onto the market.

Influence of numerical aperture on mode coupling in step-index plastic optical fibers

Using the power-flow equation, we have examined the state of mode coupling in step-index plastic optical fibers with different numerical apertures. Our results confirm that the coupling rates vary with the coupling coefficient of the fibers as the dominant parameter, especially in the early stage of coupling near the input fiber end. However, we show that the fiber's numerical aperture has a significant influence on later stages of this process. Consequently, equilibrium mode distribution and steady-state distribution are achieved at overall fiber lengths that depend on both of these factors. As one of our examples demonstrates, it is possible for the coupling length of a high-aperture fiber to be similar to that of a low-aperture fiber despite the three-times-larger coupling coefficient of the former.

Numerical solution of the power flow equation in step-index plastic optical fibers

The numerical solution of the complete power flow equation is reported and employed to investigate the state of mode coupling along a step-index plastic optical fiber. This solution is based on the explicit finite-difference method and, in contrast to earlier solutions, does not neglect absorption and scattering loss. It is the only solution that can accommodate any input condition throughout the entire range of feasible input angles without the need for restriction to those angles that are sufficiently far away from critical. Our results for the field patterns at different locations along one type of fiber are in agreement with reported measurements earlier. Furthermore, the length of fiber required for achieving a steady-state mode distribution matches the analytical solution that is available for such distribution as a special case. Mode coupling in plastic fibers is known to affect fiber-optic power delivery, data transmission, and sensing systems.

High-speed resonant cavity light-emitting diodes at 650 nm

State-of-the-art resonant cavity light-emitting diodes (RC-LEDs) optimized for short-haul communication systems on polymethyl methacrylate (PMMA) plastic optical fiber (POF) are presented. The devices, emitting in the 650-nm wavelength range, are achieving, under different structure and working regime variants, high output power (15 mW), high external quantum efficiency (9.5%), record small-signal modulation bandwidth (f/sub -3/ /sub dB/ UP to 350 MHz), error free back-to-back transmission rates beyond 622 Mb/s, adjustable far-field pattern and good coupling efficiency into step index plastic optical fibers with reasonably large tolerances and without using auxiliary optics. The paper discusses the design concepts, modeling approaches, fabrication issues and performance characteristics of monolithic RC-LEDs emitting at 650 nm.

Optical time-domain reflectometry of bent plastic optical fibers

Optical time-domain reflectometry (OTDR) signals of step-index plastic optical fibers (POF's) and graded-index POF's were measured with a laser diode and an avalanche photodiode. When bent step-index and graded-index POF's were used, the OTDR signal behavior differed. The OTDR signal of the bent graded-index POF's had a step that corresponds to a curvature loss, but the step-index POF's had a spike signal at a bend, which indicated the occurrence of backscattering. The peak intensity was proportional to the square of the curvature. The refractive-index variation of the bent step-index POF's was measured, and the dependence of the peak intensity on the curvature was shown to agree with that predicted by the scattering from the refractive-index perturbation.

Investigation of mode coupling in step index plastic optical fibers using the power flow equation

Using the power flow equation, we have examined the mode coupling caused by intrinsic perturbation effects of the step index plastic optical fiber. A numerical solution has been obtained by the explicit finite difference method. Results show the state of mode coupling along the fiber. They indicate that the equilibrium mode distribution is achieved at much shorter lengths compared to the case with glass fibers.

GaAs VCSEL's at /spl lambda/=780 and 835 nm for short-distance 2.5-Gb/s plastic optical fiber data links

Selectively oxidized GaAs vertical-cavity surface-emitting lasers for /spl lambda/=780- and 835-nm emission wavelength and 120-/spl mu/m-core diameter step index plastic optical fiber (POF) are investigated for short distance interconnects. 2.5-Gb/s pseudorandom data transmission over up to 2.5 m of plastic fiber is demonstrated with a bit-error rate (BER) of better than 10/sup -11/. Furthermore, bias-free data transmission at 2.5 Gb/s over 1-m fiber length again at a BER of better than 10/sup -11/ is reported.

Properties of plastic optical fibers

Experimental and theoretical studies of the optical properties of large-core step-index plastic optical fibers (POF’s) and graded-index POF’s are reported. A set of criteria and analyses of physical parameters is developed in the context of major issues of POF applications in short-distance communication systems. Analyses are presented to show how the measured POF optical attenuation affects the overall performance in wavelength-division multiplexing and how the use of perfluorinated polymers can overcome limitations inherent in current POF materials. Results of POF optical bandwidth measurements by direct picosecond time-domain methods are reported, and their relationship to refractive-index profiles are theoretically analyzed by the WKB and finite-element methods. Two high-resolution optical techniques of refracted near-field and transverse interferometric methods are presented and are used to measure the index profiles of large-core POF’s. Results reveal that the index profile of currently available graded-index POF is not parabolic, which significantly limits its bandwidth compared with that of a true parabolic graded-index profile.