Showing papers on "Equilibrium mode distribution published in 1980"

Impulse response prediction based on experimental mode coupling coefficient in a 10-km long graded-index fiber

Abstract: Mode coupling coefficients and impulse responses in a multimode graded-index fiber are investigated both experimentally and theoretically. Mode coupling coefficient measurements at 1.27 μm are made for a fiber before and after nylon coating. The fiber is 10 km in length and has no splicing point. The mode coupling coefficient change due to nylon coating is found to be relatively small. In the nylon-coated fiber, the coefficient increases monotonically as increasing a principal mode number, and the tendency is in good agreement with the theoretical prediction considering random bends along the fiber axis. With the increase in mode coupling coefficient and 0.01 dB/km of excess loss by nylon coating, 2.7 percent of increase in 3-dB bandwidth is observed. This increase in 3-dB bandwidth is explained by the theoretical calculation. The length dependence of 3-dB bandwidth exhibits a small mode mixing effect in the fiber. By the theoretical predictions based on the experimental mode coupling coefficients, the coupling length is estimated to be 25 km. It is also clarified that the length dependence of 3-dB bandwidth shows the L-0.5characteristic for L > 200 km.

Normalization of single-mode fibers having an arbitrary index profile

Abstract: A method is proposed whereby the propagation characteristics of a single-mode fiber having an arbitrary refractive-index profile may be expressed in terms of a newly defined equivalent step-index profile. The theory is based on the fact that the field distribution of the HE11 mode of a fiber closely resembles the Gaussian profile. The method makes it possible to characterize a fiber from a simple measurement of the HE11 mode spot size without making difficult index profile and core radius measurements. It is also found that the step-index distribution is suitable for single-mode fibers.

Measurements of mode conversion coefficients in graded-index fibers

Abstract: A new method of measuring mode conversion coefficients in multimode fibers is proposed. The principle is based on the phenomenon that modal power propagating along a fiber undergoes a gradual change due to mode coupling and mode-dependent losses. Application of the principle has made it possible to measure mode conversion coefficients of a graded-index fiber that, to the authors' belief, had not been reported before. In the experiment, it was found that the mode conversion coefficient is roughly independent of the mode order. A resolution limit of the mode analyzing technique is also discussed for graded-index fibers.

Simplified parameter-based analysis of single-mode optical guides

Abstract: An approach to single- (and low-) mode waveguides is described that enables the important mode characteristics to be derived from much reduced profile data. Uniformity with generalised parameters for multimode guides is demonstrated, and experimental determination discussed.

Mode conversion at splices in multimode graded-index fibers

Abstract: Mode conversions occurring at a splice in multimode graded-index fibers are investigated theoretically, and their effects on impulse responses are verified experimentally. The relation describing the mode behavior at a splice in existence of a geometrical offset and fiber parameter mismatches is derived by taking a skew ray as well as meridional ray into consideration. Then the mode transfer matrix is obtained to determine the variations in mode power distribution and impulse response due to the mode conversions occuring at a splice. The measured mean delay time difference between lower and higher mode pulse responses and baseband frequency response for spliced graded-index fibers are compared with the theory obtained from the transfer functions of individual fibers and the mode transfer matrix which describes the mode conversions at a splice due to a transverse displacement and fiber parameter mismatches.

Output light coupling system for semiconductor laser

Abstract: PURPOSE: To efficiently couple the output light of a semiconductor laser and an optical fiber by matching the light distribution of the laser to the light distribution of the optical fiber or the light condensing lens. CONSTITUTION: The Y-axis direction light distribution in the active layer 2 of a semiconductor laser 1 placed on a substrate 8 is expanded by the curvature at the end of a fiber 6a, is matched to the light distribution of the propagation mode of a core 6b, and high efficiency coupling is performed. When suitably selecting the radius R of curvature of the end of the fiber 6a, the light distribution of the Y-axis direction of the laser 1 can be matched to that of the propagation mode of the fiber 6a. COPYRIGHT: (C)1982,JPO&Japio

A Coupled-Waveguide TE/TM Mode Splitter

Abstract: A novel channel waveguided TE/TM mode splitter is presented. This splitter can spatially separate the TE and TM mode components and is compatible with single mode fiber systems. The operation principle is as follows. Two straight waveguides are formed closely parallel to each other on c-plate LiNbO3 by preferential Ti diffusion. An Al strip loaded on waveguide 2 induces a large change in the propagation constant for the TM mode, so that the TM mode component, fed into waveguide 1, cannot couple to waveguide 2 ("straight-through state"). By applying external voltages V1 and V2 to the two planar electrodes, formed on waveguide 1 with an Al2O3 buffer layer in-between, a complete power transfer from waveguide 1 to waveguide 2 takes place for the TE mode ("crossover state"). Less than -20 dB crosstalk was realized at 1.15 µm wavelength for V1=20 V and V2=-15 V. The insertion loss was 1.7 dB.

Method and device for stabilizing the light power carried by an optical fibre

Abstract: 1. Method of stabilizing the light power carried by an optical fiber in which the output power of the light source is controlled by means of a control signal derived from the light beam radiated by a light source, characterized in that as a control signal is used the Rayleigh scattered radiation emanating in a reverse direction from a section of the optical fiber which can be determined according to location and length, in which the Rayleigh scattered radiation is directly proportional to the light power guided in the optical fiber itself.

Anomalous group delay in optical fibres

Abstract: It is shown, by means of computation on a specific model, how pulse broadening in multimode gradedindex optical waveguides is significantly affected by the levels of excitation of the high-order modes. Pulse widths are computed as functions of the profile parameterα, under conditions of equal excitation, high-order mode suppression and GaAs laser excitation.