Showing papers on "Radiation mode published in 1970"

Excitation of the dominant mode of a round fiber by a Gaussian beam

Abstract: The excitation of the dominant HE 11 mode of a round optical fiber by a gaussian beam has been calculated. The calculation is based on the assumption that reflected waves can be neglected. It is thus applicable only to fibers with low index difference between core and cladding. It is found that optimum excitation of the HE 11 mode is achieved for loosely guided beams if the product of the beam half-width w times the radial decay constant γ of the HE 11 mode outside of the guide is unity, γw = 1. For tightly coupled modes 2½w must be equal to the core radius in order to achieve optimum excitation. As much as 99 percent of the power can be transferred to the HE 11 mode. Also investigated are the effects of an off-set or tilted beam on the mode excitation. The mode excitation drops to 36 percent if the amount of off-set equals the beam half-width. The effect of tilts depends on the parameter kd, free space propagation constant times core radius of the fiber. For small values of kd or loosely guided modes, the mode excitation is very sensitive to tilts of the gaussian beam. As long as the HE 11 mode is the only mode that can propagate, increasing values of kd lead to less sensitivity with respect to tilts. For multimode operation of the fiber, the sensitivity to tilts increases with increasing values of kd. The minimum of tilt sensitivity coincides with the minimum spot size of the guided mode.

Radiation losses of the dominant mode in round dielectric waveguides

Abstract: The radiation loss theory that has been developed in a series of earlier papers is extended to the dominant mode of the round dielectric waveguide. The theory is applied to the calculation of radiation losses of abrupt steps, gradual tapers, and random wall perturbations of the round dielectric waveguide. The radiation losses caused by an abrupt step, and consequently the losses of tapers, are far higher for the dominant mode of the round dielectric waveguide than they are for corresponding steps and tapers of the dielectric slab waveguide. However, the losses caused by infinitesimal random wall perturbations of the round waveguide are nearly equal to the random wall losses predicted on the basis of the slab waveguide theory. In fact the losses of the dominate mode as well as the circular electric TE 01 mode of the round rod due to random wall perturbations are very nearly the same. The theory is limited to circular symmetric distortions of the round dielectric rod (diameter changes). The radiation losses caused by steps of the round dielectric waveguide that carries the dominate guided mode have been verified by experiments at millimeter wave frequencies.

Microwave bandpass filter with higher harmonics rejection function

Abstract: A rectangular waveguide bandpass filter for transmitting fundamental electromagnetic waves f 0 in a fundamental mode TE101 and attenuating second harmonic waves 2f 0 therein, comprising two susceptance elements spaced apart a distance of one-third waveguide wavelength in a lengthwise direction interiorly of the waveguide to form a resonant cavity for passing a frequency band including the fundamental wave f 101, attenuating the second harmonic wave 2f 101, and preventing resonant frequencies of modes higher than the fundamental mode TE101 from decreasing into a frequency region below the second harmonic; and one or two adjustable screws disposed between the two susceptance elements in one or both waveguide wide walls to project into the interior of the cavity at a position which is one-twelth of the one-third waveguide wavelength susceptance element spacing and which is from an adjacent narrow waveguide wall one-third of the overall distance between the two narrow waveguide walls whereby the screws are restricted to function as one or two capacitive elements only for the TE101 mode.

Fiber Optics. XII. A Technique for Launching an Arbitrary Mode on an Optical Dielectric Waveguide

Abstract: A spatial-filtering technique is described which provides a means for launching an arbitrary mode on a fiber-optical waveguide. Appropriate amplitude and phase filters are used to discriminate against unwanted modes. These are inserted in the pupil of a launching lens which focuses collimated light onto the end of the guide. A double-path illuminating system is generally needed to obtain the required input polarization. The method is evaluated both theoretically and experimentally, and the agreement is found to be good within the practical limitations of cross-sectional irregularities in the nominally circular optical fibers.

Tm01 mode exciter and a multimode exciter using same

Abstract: Dual elongated apertures are cut along a broad wall of a rectangular waveguide to excite in electromagnetic waves the TM01 mode in a circular waveguide symmetrically joined to the dual apertured region. A multimode exciter system is provided wherein the TM01 mode wave is excited as described above and a linearly polarized TE11 mode wave is excited in the circular waveguide by a second rectangular waveguide section coupled along the side walls of the circular waveguide. A second TE11 mode wave oriented orthogonal to the first mentioned TE11 mode wave is excited in the circular waveguide by an elongated aperture cut along the center of the broad wall of the first-mentioned rectangular waveguide opposite that of said first-mentioned broad wall with a third rectangular waveguide symmetrically joined to the center apertured region. A dual channel rotary joint system is herein described using two such multimode exciter systems with the circular waveguide sections connected to each other by a rotary joint section.

Internal reflections at the open end of a semi-infinite waveguide

Abstract: The reflection coefficients of those waveguide modes, with propagation constants near cutoff, which are excited at the open end of a semi-infinite parallel-plate waveguide for frequencies from the microwave to the optical region are discussed in this paper. The reflection coefficients are obtained from a recently developed form of the factorization formula for the Wiener-Hopf kernel associated with this problem. This particular formula is suitable for numerical processing over the complete frequency spectrum. Results of representative calculations are presented graphically as functions of the ratio of waveguide size to wavelength.