We review the work done to date in the field of nonlinear integrated optics. Emphasis is placed on (intrinsic) second- and third-order phenomena occurring in planar geometry structures and several applications are discussed. All of the nonlinear interactions are discussed in a single notation.
The propagation characteristics of nonlinear waves guided by a metal film that is bounded on one or both sides by media characterized by an intensity-dependent refractive index are discussed. The dispersion relations are solved numerically for both self-focusing and self-defocusing media with nonlinearities typical of InSb at a wavelength of 5.5 μm. In particular, the power dependence of the guided wave wave vector, of the field distributions, and of the wave attenuation are obtained for the multiple wave solutions allowed by the dispersion relations. In the appendix we evaluate the power dependence of the attenuation of s-polarized surface-plasmon polaritons guided by a metal film.
Electromagnetic waves guided by the interface between two nonlinear media, and a nonlinear and a linear medium are investigated theoretically and numerically. Both s- and p-polarized waves are analyzed and the guided wave power versus guided wave vector is evaluated for a variety of material conditions. The consequences of two different versions of the uniaxial approximation for the p-polarized case are compared. The power-dependent attenuation is approximately evaluated.
We derive exact dispersion relations for transverse magnetic polarized guided waves at an interface between either a linear dielectric or a metal and a nonlinear dielectric. The nonlinearity is taken to be a Kerr-type nonlinearity. Numerical results are presented for the dielectric-metal case.
Passively mode-locked titanium:sapphire (Ti:S) lasers are capable of generating a high-frequency train of transform-limited subpico-second pulses, producing peak powers near 105 W at moderate average powers. The low energy per pulse (<20 nJ) permits low fluence levels to be maintained in tightly focused beams, reducing the possibility of saturating fluorescence transitions. These properties, combined with a wavelength tunability from approximately 700 nm to 1 μm, provide excellent opportunities for studying simultaneous two-photon excitation (TPE). However, pulse formation is very sensitive to a variety of intracavity parameters, including group velocity dispersion compensation, which leads to wavelength-dependent pulse profiles as the wavelength is scanned. This wavelength dependence can seriously distort band shapes and apparent peak heights during collection of two-photon spectral data. Since two-photon excited fluorescence is proportional to the product of the peak and average powers, it is not possible to obtain source-independent spectra by using average power correction schemes alone. Continuous-wave, single-mode lasers can be used to generate source-independent two-photon data, but these sources are four to five orders of magnitude less efficient than the mode-locked Ti:S laser and are not practical for general two-photon measurements. Hence, a continuous-wave, single-mode Ti:S laser has been used to collect a source-independent excitation spectrum for the laser dye Coumarin 480. This spectrum may be used to correct data collected with multimode sources; this possibility is demonstrated by using a simple ratiometric method to collect accurate TPE spectra with the mode-locked Ti:S laser. An approximate value of the two-photon cross section for Coumarin 480 is also given.
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