Showing papers on "Equilibrium mode distribution published in 1991"

Adiabatic reflection apparatus

Abstract: A wavelength selective structure is coupled to an adiabatic Y-coupler via a multimode section which supports both symmetric and antisymmetric modes. One single mode branch of the coupler converts guided light to a symmetric mode, whereas the other single mode branch converts guided light to an anti-symmetric mode. The structure, which includes a pair of single mode waveguide arms coupled to the common section and a reflection device (such as a grating or ROR) located in each arm, converts reflected light from a symmetric mode to an anti-symmetric mode and conversely. Applications described include a channel dropping filter and channel balancing apparatus for WDM systems, and a dispersion compensator for fiber optic systems.

WDM systems incorporating adiabatic reflection filters

Abstract: A wavelength selective structure is coupled to an adiabatic Y-coupler via a multimode section which supports both symmetric and antisymmetric modes. One single mode branch of the coupler converts guided light to a symmetric mode, whereas the other single mode branch converts guided light to an anti-symmetric mode. The structure, which includes a pair of single mode waveguide arms coupled to the common section and a reflection device (such as a grating or ROR) located in each arm, converts reflected light from a symmetric mode to an anti-symmetric mode and conversely. Applications described include a channel dropping filter and channel balancing apparatus for WDM systems, and a dispersion compensator for fiber optic systems.

Optical waveguides having reduced bending loss and method of making the same

Abstract: An optical waveguide that has low (0.16 to 0.28 db/km) attenuation but can be subjected to sharp radii of curvature of the order of 2 mm has an index of refraction difference between core and cladding of less than 0.75% and a cutoff wavelength that is 50 micrometers or more greater than the operating wavelength. The waveguide is a "virtual single mode" device, because even though a second order mode can be sustained in the waveguide, the waveguide length or bending losses, or both, differentially attenuates the second order mode so that the primary mode strongly predominates and both modal noise and attenuation are within acceptable limits.

Development of mode converters for 28 GHz electron cyclotron heating system

Abstract: Small circular waveguide mode converters used in the 28 GHz, 200 kW ECH system for the Hitachi tokamak HT-1 have been developed. In order to convert from the TE02 to the TE11 mode, TE0202-to-TE01 and TE01-to-TE11 mode converters are used. Both converters use periodic waveguide wall perturbations, the case of the former, circularly symmetric perturbations, and in the case of the latter, curvature perturbations. The lengths of the mode converters were successfully shortened with high mode conversion efficiencies by decreasing the number of periods and then optimizing the periods using quite a small diameter for the converters. The 30ϕ TE02-to-TE01 mode converter is 103 · 34 mm long and its mode conversion efficiency measured by a scalar network analyser is 96% at 28GHz. The TE01-to-TE11 mode converter is 427 · 38 mm long and has an efficiency of 79%, which is 10% lower than the design value. This discrepancy resulted mainly from mode conversion from the TE11 to the TE12 mode, caused by the smaller number of...

Unidirectional mode converter and optical isolator using same

Abstract: An optical isolator in which a mirror is arranged in the waveguide path to provide Fresnel reflection of the propagating light and change the light path direction by 90 degrees, the light path from the waveguide input plane to the mirror forms a first region in which magneto-optic-induced non-reciprocal mode conversion takes place, and the part of the light path from the mirror to the waveguide output plane forms a second region in which reciprocal mode conversion takes place, and mode selectors or polarizers are provided at the light input and output planes.

Fibre optic mode distribution conditioner

Abstract: A fibre optic mode conditioner (14) for obtaining an equilibrium light distribution in a multimode fibre optic link under test (16). Light is supplied to the link through a gap (34) between two successive fibre optic segments (30,32), followed by a high-curvature region created by wrapping the second fibre optic segment around a mandrel (44). The gap functions as a mode filter, stripping off all but the lowest modes, while the curved region acts as a mode scrambler redistributing the light energy into the intermediate modes.

Behaviour of a few mode fiber modal pattern under stress

Abstract: A numerical model was developed to calculate the interference pattern at the end of a multimode weakly guiding optical fiber under stress. Whenever an optical fiber is under stress, the modal phase in the interference term of the intensity formula changes. Plots of the simulated output of a stressed fiber are presented. For multimode fibers, very complicated patterns result. Under stress, lobes in the pattern are generated, displaced and power is exchanged among them.

Mode conversion in Y-branch waveguides

Abstract: Using Beam Propagation Method (BPM), we show quantitatively how the asymmetry of Y- branches will affect the transmission ratio of the structure in the power dividing or mode splitting operating area In the mode splitting area, radiation loss will increase due to conversion of fundamental mode to higher order modes The mode splitting behavior can be retained even with large branching angle if the phase-front accelerator (PFA) design structure is employed

Optical mode conversion analysis in double magnetic layers by magnetostatic surface waves

Abstract: Optical transverse-electric-transverse-magnetic (TE-TM) mode conversion by magnetooptic effect induced by magnetostatic surface waves (MSSWs) is analyzed. A typical MSSW waveguide has a thick layer for the convenient excitation of MSSWs. However, the waveguide is not a single-mode waveguide but is multimode for the optical wavelength. Such a waveguide is not suitable for optical devices because the conversion efficiency decreases due to coupling between higher modes. A multilayer waveguide constructed with the double magnetic layers, in which only the optical fundamental mode propagates and which improves the characteristics of optical mode conversion is proposed. An efficiency of 100% is achieved over an interaction length of about 1.0 cm for the applied microwave power density of a few milliwatts per millimeter. >

Quasi-optical mode converter for directly transforming the whispering-gallery mode into the TE01 mode

Abstract: A quasi-optical mode converter is proposed to be used in a whispering-gallery-mode (WGM) gyrotron tube for transforming its oscillation mode into the TE01 mode In this mode conversion scheme, the WGM radiated from a circular waveguide cut is reflected by an annular mirror having suitable local normal vectors and fed into a tapered coaxial waveguide cut The mode conversion efficiency is calculated to be 92% for a 120 GHz TE122; mode input wave radiated from a 32mm diameter waveguide cut Making use of the converter in the tube enables us to separate the spent electron beam from the output wave for enlarging the beam collector

Mode-conversion type optical Y-branching waveguides fabricated on glass substrate

Abstract: Y-branching waveguides for optical splitting and mixing have been proposed and a low loss structure of these devices have been also proposed. We have also proposed a mode conversion type Y-branching waveguide and the low loss characteristic of this device has been demonstrated by using numerical simulation based on the model of the step-index type slab optical waveguide. The device structure is based on the structural condition for the multi-mode coupling system derived from the mode coupling theory. It can be applied to waveguides other than the slab optical waveguide. In this study, it was experimentally investigated whether this method is applicable to the diffused type Y-branching optical waveguide. In the Y-branching mode converter formed on a soda-lime glass, the loss characteristic can be estimated by the mode coupling theory. The loss in this type of device is lower than that in the conventional linear Y-branching waveguide. It was also confirmed that the low loss structure used in the mode conversion type Y-branching waveguide is applicable to the diffused channel optical waveguide.

Analysis of the mode noise in interference fiber channels used for the distribution of microwave signals

Abstract: The results are given of a statistical theory of the speckle generalized to interference channels used for the distribution of microwave signals using multimode fiber waveguides with step and graded refractive-index profiles. A method is described for estimating the mode noise level in the open and closed regimes with one longitudinal speckle. The influence of the degree of mode filtering, losses at microbends, and spectral properties of a laser source on the statistical properties and the mode noise level is demonstrated. Numerical estimates are obtained of the ratio of the powers of the signal and mode noise for interference channels with typical parameters of fiber waveguides and a qualitative description is given of the effect of the mode noise.

Phase-conjugation quality with four-photon interaction in a parabolic waveguide

Abstract: The effect of the mode structure of the pump waves and the length of the optical waveguide on phase conjugation quality with degenerate four-photon interaction in a parabolic optical waveguide with Kerr nonlinearity is studied. It is shown that the dependence of the overlap integral on the mode numbers of the interacting waves eliminates the possibility of ideal phase conjugation in “long” optical waveguides. As the length of the waveguide increases, the point-spread function, describing the quality of phase conjugation, is broadened and approaches some limiting form, determined by the mode structure of the pump waves. In “long” waveguides, if one of the pump waves is single-mode and the other is multimode, an increase in the mode numbers of multimode pumping affects only the contrast and symmetry of the converted image of a point. If, however, both pump waves are identical and multimode, then an increase of their mode number results in narrowing of the point-spread function.