C. Yeh

Scattering of electromagnetic waves by arbitrarily shaped dielectric bodies

The differential scattering characteristics of closed three-dimensional dielectric objects are theoretically investigated. The scattering problem is solved in a spherical basis by the Extended Boundary Condition Method (EBCM) which results in a system of linear equations for the expansion coefficients of the scattered field in terms of the incident field coefficients. The equations are solved numerically for dielectric spheres, spheroids, and finite cylinders to study the dependence of the differential scattering on the size, shape, and index of refraction of the scattering object. The method developed here appears to be most applicable to objects whose physical size is on the order of the wavelength of the incident radiation.

Single-mode optical waveguides

An efficient and powerful technique has been developed to treat the problem of wave propagation along arbitrarily shaped single-mode dielectric waveguides with inhomogeneous index variations in the cross-sectional plane. This technique is based on a modified finite-element method. Illustrative examples were given for the following guides: (a) the triangular fiber guide; (b) the elliptical fiber guide; (c) the single material fiber guide; (d) the rectangular fiber guide; guide; (g) the optical stripline guide.

Computing the propagation characteristics of radially stratified fibers: an efficient method.

An efficient method is introduced in this paper to compute the dispersion characteristics as well as the Poynting flux distribution of radially stratified fibers. Only 4 x 4 matrix operations were needed. Detailed results are given for several representative radially inhomogeneous fibers of practical interest.

Scattering of sharply focused beams by arbitrarily shaped dielectric particles: an exact solution

By expanding the incident focused beam field in terms of its plane wave spectrum and by using the technique we developed earlier to treat the problem of the scattering of plane waves by arbitrarily shaped dielectric obstacles, we have been successful in solving the problem of the scattering of sharply focused beams by arbitrarily shaped dielectric particles. It was found that the presence of the curvature of the incident wave front and the nonuniformity of the incident wave intensity affect greatly the scattering characteristics.

Multimode inhomogeneous fiber couplers

A numerical technique to obtain the wave behavior in tightly coupled multimode fibers with inhomogeneous indices is introduced in this paper. The specific problem of the coupling characteristics of two parallel multimode fibers whose index profile is parabolic is treated in detail. It was found that in spite of the fact that rather complicated coupling behavior is observed when multimodes exist, total guide power still exchanges among the fibers in a periodic manner, and the coupling length still increases monotonically as a function of the separation distance between the fibers. It has also been demonstrated that by simply specifying the index profiles of the coupling structure (provided that the profiles are slowly varying), the coupling characteristics can be generated with our technique.

Token-based protocols for high-speed optical-fiber networks

The local network medium is a pair of unidirectional fiber-optic busses to which stations are connected via passive taps. For this configuration, we present several protocols which provide round-robin, bounded delay access to all stations, and are particularly suited for high-speed transmission. The common characteristic of the protocols is the use of the token as the synchronizing event to schedule transmission. The token may be explicit (as in U-Net) or implicit (as in Tokenless Net). It may be used all the time, or it may be used simply to resolve collisions (as, in Buzz-Net). The protocols are shown to be cost effective at very high (bandwidth) x (length) products that are the unique characteristic of high-speed single-mode fiber networks. Furthermore, they are robust to failures because of the passive interfaces and the totally distributed control. The implementation of these protocols on fiber-optic busses is also discussed in the paper.

Scattering of focused beams by tenuous particles

This paper deals with the problem of the scattering of focused laser beams by tenuous particles using an iterative technique. The results are shown to be accurate provided that (a) the polarizability of the particle medium is small and (b) the phase shift of the central ray is less than 2. It was found that when the size of the incident beam waist is close to that of the scatterer, the scattered field deviates significantly from that for the incident plane wave case. Specific examples are given.

Transversely bounded DFB lasers

Bounded distributed-feedback (DFB) lasers are studied in detail. Threshold gain and field distribution for a number of configurations are derived and analyzed. More specifically, the thin-film guide, fiber, diffusion guide, and hollow channel with inhomogeneous-cladding DFB lasers are considered. Optimum points exist and must be used in DFB laser design. Different-modes feedback and the effects of the transverse boundaries are included. A number of applications are also discussed.

Scalar‐wave approach for single‐mode inhomogeneous fiber problems

It has generally been accepted that accurate results may be obtained using the scalar‐wave approach to solve problems dealing with inhomogeneous multimode guided‐wave structures. The problem of the applicability of the scalar‐wave approach to obtain wave propagation characteristics in single‐mode fiber or integrated optical circuit guides with inhomogeneous index profiles is examined in this paper. It is shown that if certain limiting conditions are satisfied, the scalar‐wave approach will yield valid results for single‐mode structures. These limiting conditions are usually satisfied by many practical single‐mode inhomogeneous fibers or IOC structures.

Rayleigh-Debye scattering with focused laser beams.

A focused beam technique has been developed for diagnosing the characteristics of individual particles within a polydisperse ensemble. In the Rayleigh-Debye approximation the scattered fields are related to the orientation and properties of a scatterer by means of explicit analytic formulas. The results simplify when the particle size is small compared to the minimum beam diameter.