Showing papers on "Equilibrium mode distribution published in 1987"
TL;DR: In this article, the authors consider a straight fiber with an infinitely extended radial parabolic-index profile and show that it exhibits mode conversion similar to that of the step-index fiber, provided that the comparison is made on the basis of corresponding mode spots instead of actual core radii.
Abstract: In this paper we discuss mode conversion in a straight fiber which maintains its circular cross section but whose radius a(z) increases monotonically with the length coordinate z so that it passes from the single-mode to the multimode regime. Our principal concern is with step-index fibers which are treated in the scalar approximation. We study conversion of power from the incident dominant mode to other core and cladding modes for several functions a(z) . The results of our calculations show clearly that the dominant mode is able to adapt itself to the changing fiber radius provided the change is gradual. For comparison, we also consider a fiber with an infinitely extended radial parabolic-index profile as an approximation to graded index fibers. We show that it too exhibits mode conversion similar to that of the step-index fiber, provided that the comparison is made on the basis of corresponding mode spot sizes instead of actual core radii.
116 citations
TL;DR: In this paper, a distributed optical fiber sensor cable, for sensing perturbations such as pressure, comprises a length of optical fiber and means adapted, in response to the perturbation to be sensed, to mechanically deform separate portions of the length of the fiber at sensing elements (11,12,13) periodically along their length in order to cause optical power launched into a mode of propagation in the core and guided thereby to be coupled to an unguided mode, for example a cladding (15) mode.
Abstract: A distributed optical fiber sensor cable, for sensing perturbations such as pressure, comprises a length of optical fiber (10) and means adapted, in response to the perturbation to be sensed, to mechanically deform separate portions of the length of the fiber at sensing elements (11,12,13) periodically along their length in order to cause optical power launched into a mode of propagation in the core (14) and guided thereby to be coupled to an unguided mode, for example a cladding (15) mode. The coupling is optical wavelength selective and the separate sensing elements are each addressed with a different wavelength (λ11, λ12, λ13) for spatial resolution along the length of the cable.
15 citations
TL;DR: In this paper, the output power combining capability and the stable operation of the desired mode in a cylindrical cavity multiple-device oscillator were discussed, in which several devices are placed inside a cavity to combine the output of all devices by coupling with the TM020 mode of the cavity.
Abstract: Presented in this paper is a discussion of the output power combining capability and the stable operation of the desired mode in a cylindrical cavity multiple-device oscillator, in which several devices are placed inside a cylindrical cavity to combine the output of all devices by way of coupling with the TM020 mode of the cavity. A lumped element equivalent circuit is first derived that has the fundamental characteristic of the oscillator structure. From the modal analysis based on this equivalent circuit, it is found that the oscillation output as the sum of the available powers of individual devices can be obtained in principle at TM010 and TM020 modes. It is also noted that the TM020 mode cannot be a stable mode when it is chosen as the desired mode and the TMm10 mode (m ≧ 1) is generated as a stable rotational or standing wave mode. Then we discuss the method of loading the resistor for suppressing unwanted modes in which only the desired output combining mode is stable. Finally, an eight-device oscillator with a simple structure fabricated for trial is used in experiments of power combining and unwanted mode suppression and the results of the analysis of the modal analysis are qualitatively confirmed.
3 citations
TL;DR: In this article, an optical fiber coupler based on the semi-linear passive phase conjugate mirror is analyzed and the threshold coupling strength is determined from theoretical considerations, assuming good mode matching between the light incident on the fiber and the propagating mode.
Abstract: An optical fiber coupler based on the semi-linear passive phase conjugate mirror is analyzed. The threshold coupling strength is determined from theoretical considerations. An estimate of 50% for the overall coupling efficiency is made, assuming there is good mode matching between the light incident on the fiber and the propagating mode. The coupler exhibits a high degree of alignment insensitivity allowing for simple manufacture.
3 citations
TL;DR: In this article, a parabolic cylinder waveguide with its axis as a focal axis is inserted between the circular and rectangular waveguides in an oversized waveguide system to convert the output mode of the gyrotron used as a high-power millimeter wave source for nuclear fusion plasma heating is the TEOn of a circular waveguide.
Abstract: The output mode of the gyrotron used as a high-power millimeter wave source for nuclear fusion plasma heating is the TEOn of a circular waveguide. It is desirable that this mode be converted to a linearly polarized mode such as the TEmO in a rectangular waveguide. This paper discusses mode conversion from a circular TEOn mode to rectangular waveguide modes in an oversized waveguide system in which a parabolic cylinder waveguide with its axis as a focal axis is inserted between the circular and rectangular waveguides. First, an approximate analysis is introduced based on the geometrical optics approximation by taking advantage of an oversized waveguide system. Subsequently, the mode matching method is used by expanding the fields into eigen-modes. The results for the optimum length of the parabolic cylinder waveguide obtained by the mode matching period agreed with those from the geometrical optics approximation. Hence, to a certain extent, an estimate based on the geometrical optics is effective in the oversized waveguide system. Since no accurate eigenvalues have been reported for the parabolic cylinder waveguide, the computed results are presented.
1 citations