U. Langbein

Nonlinear guided waves in saturable nonlinear media

The behavior of nonlinear waves guided by a film configuration with a nonlinear cladding is investigated. The intensity-dependent dielectric function of the cladding is characterized by saturation effects. The field patterns that arise are discussed, and the dispersion relations are derived. Several dispersion curves are plotted. The results are compared with those familiar from nonlinear guided-wave propagation along configurations with Kerr-like cladding dielectric functions.

Generalized dispersion relations for nonlinear slab-guided waves

Abstract The propagation of nonlinear guided waves in a slab configuration with arbitrary intensity-dependent dielectric functions is considered. General expressions for the dispersion relations and the guided power flux are derived without explicit integration of the nonlinear Helmholtz equations. One example is investigated in greater detail.

Nonlinear waves guided by a dielectric slab

An exact solution of Maxwells equations is found for TM-polarized nonlinear guided waves which are guided by a linear dielectric slab embedded between two nonlinear uniaxial media. Additional waves in comparison with the linear case arise. Some of these waves have no counterpart in linear systems. Similarities and differences with respect to TE-polarized nonlinear guided waves are pointed out.

A new type of nonlinear slab-guided waves

Abstract One particular exact solution of a nonlinear wave equation is found for a slab configuration where a nonlinear dielectric slab is embedded between two linear media. Both TE- and TM-polarized nonlinear waves are considered.

Investigation of optical tunneling through nonlinear films

The tunneling phenomenon of light waves that are totally reflected at one of the film interfaces will be considerably modified when the dielectric coefficient of the film becomes intensity dependent. We present an exact analytical approach that describes the tunneling of totally reflected, transverse-electric-polarized plane waves through a nonlinear film, the dielectric function of which may reveal material saturation. Within certain parameter ranges the configuration shows a pronounced switching between total internal reflection (off state) and the onset of complete transmission (on state). The switching characteristic can be tuned either by the angle of incidence or by the input intensity from monostable to bistable response. An experimental demonstration of the predicted results has been performed by using a liquid-crystal p-methoxybenzilidene-p-n-butylaniline film sandwiched between two optical prisms.

Propagation phenomena of nonlinear film-guided waves: a numerical analysis

The propagation of TE guided waves excited at different points of their dispersion curve has been numerically traced down a thin film bounded by two identical self-focusing media. Several types of nonstationary field evolution have been investigated and identified as transitions between or oscillations around different branches of the dispersion curve.

Evolution of nonlinear guided optical fields down a dielectric film with a nonlinear cladding

We present a comprehensive, numerically oriented investigation of spatially nonstationary, TE-polarized optical field distributions guided by a thin film that can support both TE and TE waves. The film is asymmetrically bounded by a Kerr-like nonlinear cladding that may exhibit linear material losses. All field distributions have been generated by exciting different guided waves at one of the film end faces and tracing them down the film with the help of an extended propagating beam method. The long-distance asymptotic behavior is of particular interest. The numerical-stability analysis of the dispersion curve for nonlinear guided waves (NGW’s) indicates that the positively sloped TE0 branches are stable; this is not strictly true for the TE1 branch. Unstable NGW’s display a rich set of nonstationary phenomena, including soliton formation and nonlinear beating effects. Characteristic transformation lengths depend strongly on the definite, unstable initial NGW profile. The main effect of cladding losses is that the field tries to avoid the lossy region, leading to a considerable loss reduction. This property may destroy characteristic NGW features for propagation lengths approaching the absorption length of the lossy cladding. Phase-locked single-soliton and multisoliton emission can be induced by launching linear guided modes with the appropriate power flow through one of the film end faces.

Waveguide evanescent field fluorescence microscopy: Thin film fluorescence intensities and its application in cell biology

We demonstrate an inexpensive alternative to total internal reflection fluorescence microscopy. A method for imaging ultrathin films and living cells located on waveguides—illuminated with their evanescent fields—is introduced. An extensive analysis of ion-exchanged waveguides focusing on their application as microscopy substrates for studying interfacial phenomena is presented. Experimental results are in excellent agreement with the simulations. As an application osteoblasts (bone matrix forming cells) and ultrathin Langmuir–Blodgett films were imaged. The fluorescence intensity has been used to determine the cell attachment.

Optical response of a nonlinear bent directional coupler

Abstract In the framework of a coupled mode approach we study the optical response of a bent nonlinear directional coupler. In particular, the effects of waveguide bending on the switching characteristic of the coupler geometry are considered. It has been found that a bent nonlinear directional coupler may acts as a digital optical switch. Phase-controlled switching could also be identified.

TM-polarized nonlinear guided waves in multilayer systems

The ability of various multilayer systems to support TM-polarized nonlinear guided waves is studied. A flexible numerical technique which includes the proper consideration of the nonlinear crossing conditions is used to calculate the field profiles and derive the dispersion relations. The fundamentals of the model are described, and the algorithm is applied to several nonlinear film configurations. For the sake of comparison with the finite-element method, a single linear film, embedded between two nonlinear materials, is treated. A three-film unit cell, consisting of a high-index linear film, sandwiched between two low-index nonlinear, ones is considered. This is the elementary unit cell of a composite geometry, a ten-unit-cell superlattice, which is then studied. It is found that unlike TE-polarized nonlinear guided waves in multilayer systems, the TM waves reveal a distinct power maximum. The inclusion of saturation effects in the analysis is straightforward. >