Showing papers on "Equilibrium mode distribution published in 1983"

Rayleigh backscattering theory for single-mode optical fibers

Abstract: The theory of backscattering in single-mode optical fibers is described through use of a correlation function for the refractive-index fluctuation in the fiber. A simple formula for the backscattered power is derived using two correlation functions for the Booker–Gordon and Gaussian models. The zeroth-order approximation of the formula, in which the correlation length is much smaller than the spot size of the waveguide mode, coincides with Brinkmeyer’s model. The backscattered power at the input end of single-mode fiber is compared with that for multimode fiber. It is also shown that the backscattered power level at the input end is lower by approximately 55 dB than the input power level.

Integrated optical transducers

Abstract: An integrated optical transducer includes a single mode input optical waveguide, two single mode optical waveguide branches having different physical lengths, and a single mode output optical waveguide. When used as a transducer, the optical path lengths of the waveguide branches are dependent on the physical quantity measured. A plurality of such transducer elements may be used jointly to provide a binary output of high sensitivity and wide range of measurement. The waveguide element may also be used as an optical pulse source.

Effect of mode coupling on the total pulse response of perturbed optical fibers.

Abstract: A computer program has been developed to study the total pulse response of optical fibers with profile ripple and central index depressions in the presence of arbitrary mode coupling. We have found that the magnitude of the compression of the total pulse response generated by mode coupling depends significantly on the details of the refractive-index profile of the test fiber.

Mode coupling loss in single-mode fibers with depressed inner cladding

Abstract: Single-mode fibers with depressed inner cladding show sharp resonant loss peaks near the fundamental mode cutoff wavelength where the core-guided mode starts to become a leaky mode. The magnitude of the loss peak exceeds 200 dB/km and was found to be extremely sensitive to fiber curvature. The phenomenon is attritubed to mode coupling between the core-guided mode and the discrete modes guided in the outer cladding.

Selective waveguide mode converter

Abstract: A mode converter is disclosed which selectively generates a predetermined higher order mode(s) from an incident fundamental mode. This mode converter comprises a dielectric region having an effective-dielectric-constant/thickness profile which is the same as the amplitude profile of the desired higher order mode(s).

Mode matching for a passive resonant ring laser gyroscope

Abstract: An analytical method of matching the mode of an input laser to the lowest-order mode of a passive resonant ring laser gyro is described, as are the steps in determining the location and focal length of cylindrical mode matching lenses. Results were obtained with no mode matching, with a compromise spherical lens, with horizontal mode matching only, and with the proper cylindrical mode matching lenses. Compared with no mode matching, the latter case shows that the amplitude of the lowest-order mode is increased ∼2.5 times. In addition, the number and intensity of higher-order modes are reduced to near zero, and the relative intensity of the lowest-order mode to the higher-order mode increased from ∼5 to ∼60 times greater.

Derivation of fundamental-mode electric field and modal properties of single-mode fibres from variable-aperture launch method

Abstract: We report a simple derivation of the electric field and modal properties of the fundamental mode of single-mode fibres only from the results of the variable-aperture launch method performed on the fibre.

Impulse response of single-mode fibers with polarization-mode coupling

Abstract: The transmission properties of a two-mode system with uniform mode coupling are analyzed in detail in the time domain. The impulse response of the system is found analytically taking mode dispersion and frequency-dependent mode coupling into account. By calculating the pulse response when the system is excited with a Gaussian pulse, the effective mode dispersion and energy coupling are determined. Through this analysis it is shown that the coupling will introduce an oscillating tail on the excited mode with a duration equal to the polarization-mode dispersion and a magnitude determined by the ratio between the birefringence and the mode-coupling coefficient. For polarization-preserving fibers this tail may be several nanoseconds long, but the magnitude is likely to be small. The presence of mode coupling reduces the effective mode dispersion but causes the state of polarization to be unstable. Finally it is shown that material dispersion will not affect the polarization-handling properties of the system but leads to oscillating responses from the individual modes.

Mode energy transformation between two connected multimode general square-law-index optical waveguides

Abstract: A coherent states method is used to investigate the mode coupling coefficients in the most general buttjoint problem for two multimode general square-law-index optical waveguides, when two different waveguides with elliptical cross-sections are to be butt-jointed with axis displacement, tilt and some turning of symmetry axes with respect to each other. The explicit expressions for the mode coupling coefficients and recurrence relations for the mode overlap integrals are obtained; the sum rules for the mode coupling coefficients are formulated and a method of experimental data analysis is proposed for this general problem. The method of calculating mode coupling coefficients is proposed for the case of the butt-joint problem when the waveguide cross-sections are only partially overlapping and then it is used to investigate the influence of misalignment on mode power distribution and pulse dispersion in the second waveguide. The experimental data are compared and it is shown that the coupling coefficients obtained in square-law-index model can be used in dispersion calculations forα-profile fibres in the case when the valueα is not far from the valueα=2.

Influence of mode coupling on differential mode delay.

Abstract: The manner in which the differential mode delay (DMD) pulse response is affected by ellipticity- and microbending-induced mode coupling has been analyzed numerically. We have considered both a fiber profile containing a central index dip and fiber profiles with sinusoidal ripples. We find that slowly varying profile components can be correctly estimated from DMD results even in the presence of substantial mode coupling.

Passive source ranging by using mode filtering and mode phase comparing in waveguide

Abstract: The conventional beamforming technique could not be used for source locating in waveguide owing to the modal interference structure of the field. In this paper a new method of passive source ranging in a layered waveguide has been proposed. The mode‐filtering processor was used to process the field data of a vertical array in order to obtain individual modes. The source range information can be extracted by measurement of three individual mode phases. The source range was expressed in terms of the “mode interference distance” as following: r = LijDij + Δrij; Δrij = Dij(δφij/2π), where Lij is a certain integer; δφij is the phase difference of the ith mode and the jth mode; Dij is the “mode interference distance” defined by: Dij = 2π/(ki − kj); ki is the wavenumber of the ith mode given by a numerical mode code. The information of Lij can be estimated by means of comparing the phase of the jth mode with another mode, say mth mode, and then Lij was estimated by solving the following equation: (δφij/2π) = Fra...

Propagation of a perturbed wave in a single-mode fiber waveguide

Abstract: An investigation was made of perturbations of the dominant mode in a single-mode fiber waveguide. A theoretical and experimental study was made of the phase nonreciprocity of the opposite waves excited at a local inhomogeneity in the waveguide.