John D. Love

Reflection at a Curved Dielectric Lnterface--- Electromagnetic Tunneling

The reflection of a locally plane wave from a curved interface between two nonabsorbing dielectric media is investigated. Our analysis is applicable to an interface of general shape, defined at each point by the two principal radii of curvature. When the wave is incident from the denser medium at angles greater than the critical angle it is only partially reflected, due to a form of electromagnetic tunneling. Generalized Fresnel transmission coefficients and an extension of Snells law are derived to account for this transmission into the less dense medium. Ray tracing can then be applied to determine such phenomena as the bending losses in optical slab waveguides, and the curvature loss of skew rays within straight optical waveguides of circular cross section.

Design of mode-sorting asymmetric Y-junctions

The theory of mode-sorting in bimodal asymmetric Y-junctions is extended to multimode asymmetric Y-junctions with multiple output arms. This theory allows for the optimization of these mode-sorting planar structures. Asymmetric Y-junctions provide unique opportunities for spatial mode division multiplexing (MDM) of optical fiber. Spatial MDM is considered paramount to overcoming the bandwidth limitations of single-mode fiber. The design criteria presented in this paper facilitate their design.

Mode-selective couplers for few-mode optical fiber networks

Tapered mode-selective couplers are shown to allow for ultra-broadband mode-division multiplexing of few-mode optical fiber. Using appropriate three-core configurations, modes of arbitrary spatial-orientation can be demultiplexed. The successful fabrication of these wavelength-insensitive couplers would represent the realization of compact low-loss mode-multiplexers for use in high-bandwidth few-mode fiber networks.

Single-, Few-, and Multimode Y-Junctions

The theory of modal propagation through symmetric and asymmetric 2-D weakly guiding Y-junctions is extended to cover few-mode, multimode, and multiarm Y-junctions. A conceptual approach based on the evolution of modal effective indexes and composite supermodes is used to determine the qualitative functionality of these devices, with quantification being determined numerically using the beam propagation method.

Few-Mode Elliptical-Core Fiber Data Transmission

Spatial mode-division-multiplexing is seen as paramount to overcoming the bandwidth limitations of single-mode fiber. In this letter, spatial-multiplexing of polarization-maintaining, elliptical-core fiber is proposed using asymmetric Y-junctions. Asymmetric Y-junctions also allow for straightforward wavelength- and polarization-multiplexing. Numerical beam propagation method simulations are used to demonstrate the functioning of a three-mode elliptical-core fiber data link, which could easily be extended to more modes. The multiplexing of multiple spatial modes could potentially see multifold increases in fiber capacity.

Goos-Hänchen shift.

An extremely simple derivation of the Goos-Hänchen shift is presented for total internal reflection at a plane interface between two semiinfinite dielectric media, as well as for optical waveguides of plane arid circular cross section. The derivation is based on energy considerations, requires knowledge of Fresnels equation only, and shows explicitly that the shift is due to the flow of energy across the dielectric boundary.

Asymmetric, adiabatic multipronged planar splitters

This paper analyses the adiabatic forked splitter, a device for separating the power in different modes of a multimoded waveguide into distinct, single-mode waveguides. The concept of two-mode separation in asymmetric Y-splitters is generalized to several modal channels, and the resulting multipronged devices are studied in detail, thus addressing important issues such as (1) the achievement of optimally-short devices, (2) the minimization of radiation loss, and (3) the splicing of the device to external optical components. An approximate relationship is derived between the number of modal channels and the required device length, thus showing that there is an upper limit of about four modal channels, for practical fabrication in planar geometry.

Loss calculations in bent multimode optical waveguides

We present a straightforward geometric optics method to calculate the power attenuation induced by a circular bend in the axis of a multimode optical waveguide. The method involves tracing of rays and use of generalized power transmission coefficients. Both slab and fibre waveguides (with either step-index or parabolic core profiles) have been considered; the source has been assumed to be Lambertian.

Coupling characteristics of photo-induced Bragg gratings in depressed- and matched-cladding fibre

Experimental transmission spectra of ultraviolet (u.v.)-written Bragg gratings in depressed- and matched-cladding fibre are characterized and compared. In particular, we discuss how the location and strength of the spectral features vary with the degree of blazing, or angular tilt of the grating. The fine-structure detail on the short-wavelength side of the fundamental Bragg line is attributed to power coupling between the forwardpropagating fundamental (LP01) mode and discrete, backward-propagating cladding modes. Resonances corresponding to backward-propagating LP0n and LP1n modes are identified, and their relative strengths are compared with theoretical overlap calculations. Physical arguments are presented that explain the pronounced ‘ghost’-grating notch that appears in the transmission spectra of blazed, fibre Bragg gratings in depressed-cladding fibre.

Gaussian approximation for circular fibers

The weak-guidance approximation, described in Chapter 13, greatly simplifies the determination of the modal fields of optical waveguides, because it depends on solutions of the scalar wave equation, rather than on vector solutions of Maxwell’s equations. For circular fibers, with an arbitrary profile, the scalar wave equation must normally be solved by purely numerical methods. We discussed the few profiles that have analytical solutions in Chapter 14. These solutions, including those for profiles of practical interest such as the step and clad power-law profiles, are given in terms of special functions or by series expansions, which usually necessitate tables or numerical evaluation to reveal the physical attributes of the modes.