Leon McCaughan

Bio: Leon McCaughan is an academic researcher from University of Wisconsin-Madison. The author has contributed to research in topics: Lithium niobate & Waveguide (optics). The author has an hindex of 22, co-authored 72 publications receiving 1426 citations. Previous affiliations of Leon McCaughan include Wisconsin Alumni Research Foundation & Brookhaven National Laboratory.

Spectroscopic site determinations in erbium-doped lithium niobate

Abstract: Rare-earth (e.g., ${\mathrm{Er}}^{3+}$, ${\mathrm{Nd}}^{3+}$) based, guided wave optical amplification in lithium niobate (${\mathrm{LiNbO}}_{3}$) integrated optic systems is a new and important addition to the field of integrated optics. The application of total site selective spectroscopy to rare-earth-doped ${\mathrm{LiNbO}}_{3}$ provides the most complete spectroscopic characterization of this class of materials to date. In a previous publication we identified six spectroscopic sites in Er:${\mathrm{LiNbO}}_{3}$ using total site selective spectroscopy, two of which are cluster sites which upconvert light using nonradiative energy transfer between Er ions within a given site. In this paper ${\mathrm{Er}}^{3+}$ site identifications are made based on a consideration of solid solution defect equations in conjunction with an experimental study of the site distribution as a function of dopant concentration (0.4--2.0 mol % Er:${\mathrm{LiNbO}}_{3}$) and the Li/Nb ratio in the crystal. The Li/Nb ratio was altered using a vapor phase equilibration technique. Our results indicate that increasing the ${\mathrm{Li}}_{2}$O content of Er:${\mathrm{LiNbO}}_{3}$ not only reduces the cluster site concentration by \ensuremath{\sim}30% but also increases the amount of light absorbed in the crystal by \ensuremath{\sim}15%. This observation is, to the best of our knowledge, the first report of post growth materials processing in rare-earth-doped ${\mathrm{LiNbO}}_{3}$ to effect a change in absorption or cluster site concentration. In addition, increasing the dopant concentration increases ${\mathrm{Li}}_{2}$O deficiency in Er:${\mathrm{LiNbO}}_{3}$ crystals. Simple solid solution defect model calculations agree with these experimental results. \textcopyright{} 1996 The American Physical Society.

Comparison of calculated and measured performance of diffused channel-waveguide couplers

Abstract: Diffused channel-waveguide couplers were fabricated on z-cut y-propagating LiNbO3 crystals by the indiffusion of titanium. Both mode spot sizes and coupling lengths were measured. The fields and coupling lengths were computed for both TM and TE polarizations from fabrication conditions. Good agreement was obtained between the measured and computed mode spot sizes and coupling lengths. It is concluded that the calculation method could aid in the design of such couplers.

Evaluation of absorption and emission cross sections of Er-doped LiNbO/sub 3/ for application to integrated optic amplifiers

Abstract: The polarization-dependent absorption and emission spectra of the /sup 4/I/sub 13/2/-/sup 4/I/sub 15/2/ transition (/spl lambda//spl sim/1.5 /spl mu/m) in single crystal bulk Er:LiNbO/sub 3/ have been measured. Low-temperature (10 K) measurements of the Stark split energy levels of these two manifolds indicate at least two Er/sup 3+/ sites. McCumber theory is applied to determine the Er:LiNbO/sub 3/ absorption and emission cross sections. These values are used to calculate the gain characteristics of Er:LiNbO/sub 3/ channel waveguides. Calculations indicate that a gain of 10 dB is achievable in a waveguide of several centimeters using /spl sim/20-mW pump power. >

Index distribution of optical waveguides from their mode profile

Abstract: The refractive-index profile is readily calculated from the observed fundamental mode pattern using the scalar-wave equation. Index distributions of diffused Ti: LiNbO 3 waveguides were measured and are consistent with model calculations.

Experimental demonstration of 1535-1555-nm simultaneous optical wavelength interchange with a nonlinear photonic crystal.

Abstract: We present results of what is to our knowledge the first experimental demonstration of simultaneous optical wavelength interchange by use of a two-dimensional second-order nonlinear photonic crystal. Fabrication and performance parameters of a 1535-1555-nm wavelength interchange nonlinear photonic crystal fabricated in lithium niobate are discussed.

Optical multi-mode interference devices based on self-imaging: principles and applications

Abstract: This paper presents an overview of integrated optics routing and coupling devices based on multimode interference. The underlying self-imaging principle in multimode waveguides is described using a guided mode propagation analysis. Special issues concerning the design and operation of multimode interference devices are discussed, followed by a survey of reported applications. It is shown that multimode interference couplers offer superior performance, excellent tolerance to polarization and wavelength variations, and relaxed fabrication requirements when compared to alternatives such as directional couplers, adiabatic X- or Y-junctions, and diffractive star couplers. >

Interactions between Light Waves in a Nonlinear Dielectric

Abstract: The induced nonlinear electric dipole and higher moments in an atomic system, irradiated simultaneously by two or three light waves, are calculated by quantum-mechanical perturbation theory. Terms quadratic and cubic in the field amplitudes are included. An important permutation symmetry relation for the nonlinear polarizability is derived and its frequency dependence is discussed. The nonlinear microscopic properties are related to an effective macroscopic nonlinear polarization, which may be incorporated into Maxwell's equations for an infinite, homogeneous, anisotropic, nonlinear, dielectric medium. Energy and power relationships are derived for the nonlinear dielectric which correspond to the Manley-Rowe relations in the theory of parametric amplifiers. Explicit solutions are obtained for the coupled amplitude equations, which describe the interaction between a plane light wave and its second harmonic or the interaction between three plane electromagnetic waves, which satisfy the energy relationship ${\ensuremath{\omega}}_{3}={\ensuremath{\omega}}_{1}+{\ensuremath{\omega}}_{2}$, and the approximate momentum relationship ${\mathrm{k}}_{3}={\mathrm{k}}_{1}+{\mathrm{k}}_{2}+\ensuremath{\Delta}\mathrm{k}$. Third-harmonic generation and interaction between more waves is mentioned. Applications of the theory to the dc and microwave Kerr effect, light modulation, harmonic generation, and parametric conversion are discussed.

Transparent boundary condition for the beam propagation method

Abstract: A new boundary condition is presented for use in beam propagation calculations that passes outgoing radiation freely with minimum reflection coefficient (as low as 3*10/sup -8/). In conjunction with a standard Crank-Nicholson finite difference scheme, the assumption that the radiation field behaves as a complex exponential near the boundary is shown to result in a specific transparent boundary condition algorithm. In contrast to the commonly used absorber method, this algorithm contains no adjustable parameters, and is thus problem independent. It is shown to be accurate and robust for both two- and three-dimensional problems. >