Modeling photobleached optical polymer waveguides.

One of the most efficient ways to prepare nonlinear optical polymer channel waveguides is by photobleaching. To control the index profile precisely and to design and improve the performance of active electro-optical devices, modeling of the photobleaching process is important. We report our phenomenological bleaching model, which uses a stretched exponential time dependency technique that predicts the index profile for polymer channel waveguides and present design rules for active optical switches and modulators. One way to verify the bleaching model is to calculate the effective index and compare this with our measured effective index obtained with prism-coupling techniques. The bleaching model shows good agreement with experiments.

Study of UV-bleached channel-waveguide performance in nonlinear optical polymer films.

We report studies on UV-photobleached optical channel waveguides in nonlinear optical polymer films. The nonlinear optical polymer used is poly(methyl methacrylate)/DR1 side-chain polymer. The effective indices of the channel waveguides are measured with the prism-coupling technique, along with the effective indices of bleached and unbleached polymer films. The effective-index method was used to predict the effective indices of the channel waveguides from measurements of the slab waveguides, without detailed knowledge of the index distributions in the polymer films. Some local stress-related effects on the boundaries of the channel waveguides caused by the UV-bleaching process are identified by comparison between direct channel measurement and prediction. It is found that the technique used in this study can be employed to predict the performance of channel waveguides processed such that they have no excessive internal stress distributions.

Fabrication and characterization of a third-order nonlinear organic-polymer composite glass waveguide: a self-phase modulator.

Composite organic-polymer glass optical waveguides in which coupling to the nonlinear organic-polymer layers was achieved by excitement of the underlying ion-exchanged glass waveguide and coupling of the light to the organic-polymer layer were fabricated and measured. A picosecond pulsed color center laser (λ = 1.5 µm) was used to measure the third-order optical susceptibility χ((3))(-w; w, -w, w) in an organic-dye-polymer composite glass waveguide with a Mach-Zehnder interferometer. For a squaryliumdye-doped poly(methyl methacrylate)-styrene-acrylonitrile matrix polymer layer, a composite χ((3)) of roughly 90, in units of (χLiNbO)(3)((3)), was measured.

Dual-wavelength (lambda = 1300-1650 nm) directional coupler multiplexer-demultiplexer by the annealed-proton-exchange process in LiNbO(3).

The potential of switching wavelengths by using a directional coupler has been explored. A dual-wavelength (lambda = 1300-1650 nm) directional coupler multiplexer-demultiplexer has been realized by using the annealedproton-exchange process in LiNbO(3). The interaction length of the coupler has been accurately tuned to operate at a desired wavelength by annealing and reannealing the substrate until the desired coupling length is achieved.

Interlaboratory comparisonof mode transition matrices.

An interlaboratory measurement round-robin was conducted by the University of Colorado and three industrial members of the Electronic Industries Association. A computational definition of mode transition matrices (MTM's) is presented, and its relationship to the basic theory of power propagation in multimode fibers is detailed. Measured data from the round-robin were used to calculate MTM's for the test components, which included four connectors, two sections of fiber cable, two power splitters, and two short fiber segments. The diagonal elements of the (2 × 2) MTM's determined from the near-field data were found to have a laboratory-to-laboratory standard deviation of approximately 10% of the average value. The off-diagonal elements were found to have a standard deviation approaching their mean value. The inherent launch dependence of MTM's is investigated as a source of the observed variation. Other sources of uncertainty such as errors in determining the core radius are alsoconsidered. Finally the implications of these results for the problem of characterizing components' intensive multimode fiber systems are discussed.

Distributed loss and mode coupling and their effect on time-dependent propagation in multimode fibers.

A first-order solution to the transport equation for the total power propagating in each degenerate mode group of a multimode fiber is used to describe pulse propagation in multimode fibers. The basic transport equation is supplemented by models for Rayleigh-scattering-induced losses, mode coupling, and the modal group velocity function. Each of these models can be specified for a particular fiber from a standard set of near-field measurements and then incorporated into pulse propagation simulations, which closely matched the measured pulse response of test fibers.

Photorefractive damage thresholds in Ti:LiNbO(3) channel waveguides.

The photorefractive effect in titanium-in-diffused LiNbO(3) waveguides is studied both experimentally and theoretically. Measurements of mode size and transmitted optical power as a function of input optical power are presented. The diffusion constants in the diffusion model and the unknown parameters in Kukhtarev's model are determined from measurements of the near-field intensity profiles at low and at high intensity levels. These parameters can then be used to predict waveguide behavior as a function of the input power level. The simulated behavior closely resembles that observed experimentally. Calculated corrections for thermally induced index perturbation show that the thermal effects are higher-order corrections to the dominant photorefractive effect.

Coupling mechanisms and transfer functions of optical fiber devices.

Modal-power transfer functions for two basic coupling mechanisms, i.e., scattering coupling and overlap coupling, are derived. Optical fiber devices such as fibers or cables, connectors, splices, and power splitters can be characterized by modal-power transfer relations based on these transfer functions. Experimental results show that the transfer functions are independent of launch conditions.

Transfer function approach to the experimental determination of mode transfer matrices.

An improved scheme for characterization of multimode fiber systems is investigated. Characterization with transfer matrices requires multiple measurements for each component. The transfer function approach herein investigated requires only a single launch measurement to be made on a component, which afterward can be described by as few as two numbers. Further, it is shown that this technique is considerably more accurate and repeatable than matrix approaches. A concatenation experiment is performed to demonstrate the efficacy of the new technique as well as to compare it with the more traditional transfer matrix approach.

Transfer function analysis of measured transfer matrices.

Measurements of mode transfer matrices of various multimode fiber optic connectors are presented. To analyze the accuracy and repeatability of such measurements, a theoretical framework which employs mode transmission functions is derived. It is shown that the transfer function can be used to find transfer matrices for any set of launches. A procedure for determination of the mode transfer function is given.

Mode-continuum approximation in optical fibers.

The physical basis of the continuum approximation is discussed. By illuminating the nature of the approximation, it is possible to clear up various contradictions and misconceptions present in the literature. The limits of validity of the continuum approximation are evaluated, and the determination of modal distributions in all regimes of approximationis discussed.

Theory of the backscattering process in multimode optical fibers.

A theory is presented which predicts the form of backscattered signatures obtained from multimode fibers in terms of the longitudinal variation of the fiber's characteristic parameters. Within a certain limit, the theory yields simple, analytical results; this limit requires one to employ a novel form of fiber excitation for which we adopt the term mode-filtered excitation. From backscattering signatures obtained using this form of excitation, it is possible to unambiguously separate intrinsic loss from fluctuations of the fiber's characteristic parameters. Various experimental verifications of the theory as well as demonstrations of the efficacy of the mode-filtering technique are presented.