Showing papers on "Coupled mode theory published in 1975"

Coupled-mode theory for anisotropic optical waveguides

Abstract: The well-known coupled-mode theory of waveguides is extended to include dielectric guides made of anisotropic materials. Exact coupled-wave equations for anisotropic dielectric waveguides are derived, and explicit expressions for the coupling coefficients are given. The coupling coefficients for isotropic waveguides are obtained as a special case. A simple approximation for the coupling coefficients in the case of slight anisotropy and slight departure from an ideal waveguide is presented.

Tapered velocity couplers for integrated optics: design.

Abstract: The operation of tapered velocity couplers is analyzed from the point of view of mode conversion between local-normal modes. An approximate coupled mode representation of the local-normal modes is used with a step transition model to estimate analytically power transfer. This yields an upper limit for the maximum permissible variation in mode synchronism across the coupler to achieve satisfactory coupler operation. The analysis has also been used to demonstrate the importance of obtaining a large total change in mode synchronism to minimize coupler length.

The coupled mode approach to nonlinear wave interactions and parametric instabilities

Abstract: The non-linear interaction of a few coherent, weakly damped longitudinal and transverse waves in an unmagnetized plasma is considered by means of the coupled mode theory. Using the equations describing the non-linear wave interactions the threshold electric fields and initial growth rates of a number of parametric instabilities are calculated. The following four instabilities, all of which are relevant to laser fusion are considered: (i) the parametric ion-acoustic-Langmuir wave integration, (ii) the two plasmon decay, (iii) stimulated Raman scattering and (iv) stimulated Brillouin scattering. All these instabilities are driven by a large amplitude electro-magnetic wave.

Radiation losses of the HE 11 mode of a fiber with sinusoidally perturbed core boundary

Abstract: The radiation losses of the HE11 mode of a fiber with sinusoidal radius fluctuations are calculated in the weak guidance approximation. The loss formula is derived by means of the volume current method and also by using coupled mode theory. The result presented here extends earlier results to the case of radiation escaping nearly perpendicular to the fiber axis.

Coupled mode analysis of light modulation in dielectric waveguides

Abstract: A detailed analysis of electrooptic light modulation in optical waveguides is presented. Several important problems of a waveguide modulator, such as the difference of waveguide axes from crystalline electrooptic ones, the distribution of transverse and longitudinal field components of light modes, and the traveling-wave property of the modulating field, are discussed. The analysis is based on the coupled mode theory, regarding the modulation as the coupling among sidebands of unperturbed waveguide modes. The coupled mode equation is derived for the modulation in optical waveguides. It can be solved if the normal modes of the waveguide are given. Actually the equation is solved for the modulation in dielectric slab waveguides and the mechanism of modulation is discussed. The results of the analysis are applied to designing two types of waveguide modulators. In an example (10.6 μm modulator with a GaAs slab waveguide) a new efficient crystal orientation is found. The calculated phase retardation with this orientation is 0.13 rad/(V·cm) with a 1 μm thick slab. Another example of a 0.633 μm modulator using a LiTaO3 crystal as a substrate is also described.

Pulse propagation in multimode optical fibres

Abstract: Coupled mode theory is unnecessary for the analysis of pulse propagation in multimode optic waveguides. Instead, a very simple ray or continuum equation is derived from elementary plane-wave concepts to account for the effects of absorption loss and scattering. The formalism reduces to a diffusion equation for highly forward directed scatterers.