We have implemented a Finite-Beam Rigorous Coupled-Wave Approach (FB-RCWA) to solve for guided-optics
propagation in the presence of holographic slanted Bragg gratings, embedded in the core of slab waveguides and
operated in Extreme Asymmetrical Scattering (EAS) configuration. In EAS a resonance condition can be established, as
proceeding from the design parameters. Diffraction efficiency can be evaluated as the ratio of the flux of diffracted
power P1, on a suitably defined cross-section along the propagation of diffracted beam, and input power P0. By FBRCWA,
no limitation in the depth of grating modulation is assumed. The first-order diffracted field in resonant Bragg
condition propagates along the waveguide. EAS in thick waveguides operating in highly multimodal regime can be
investigated, as well as macroscopic volumes and widely extended illuminated regions up to a few millimeters. In thick
slabs, η > 90% is demonstrated, for input illuminated apertures of length L ≥ Lc, where Lc is the optimum coupling
length. The effects of detuning from Bragg condition, both in distribution and amplitude of the diffracted field, are
quantified. Diffraction efficiency, i.e. optical coupling, bandwidth is evaluated.
Organic photochromic materials have been studied as active materials in optical devices since they show a reversible
change of color in the visible region and appreciable reversible changes of the refractive index (Δn) in the NIR. The
latter peculiar property can be suitably exploited for the realization of holographic optical elements (HOEs) and in
particular volume phase holographic gratings (VPHGs). Photochromic polyester based on diarylethene alcohol was
synthesized and characterized both in solution and in thin film. The optical properties of the films were good enough for
making optical devices and the modulation of the refractive index (measured by spectral ellipsometry) was large at 1.5
micron and it became even larger at shorter wavelength where the material is still transparent. Such photochromic
material is a good candidate for making rewritable efficient HOEs.
A key parameter for the choice of an erbium-doped material suitable for efficient amplification around 1.55 μm is its ability to isolate Er ions from each other in order to increase the quenching concentration and henceforth to improve pumping efficiency. Encapsulation of Er ions by organic ligands results in quenching concentrations about a few % in a polymer matrix and may therefore induce high gain values at 1.55 μm. In this paper, we report on the elaboration and optical characterization of Erbium complex-doped PMMA thin films and waveguides with different concentrations by spin-coating technique. Refractive index of these thin films and etching conditions for waveguide fabrication are carefully investigated. Strong gain coefficient values (up to 9 cm<sup>-1</sup>) measured by Amplified Spontaneous Emission are reported at 1.55 μm under 980 nm cw pumping of an erbium-complex-doped PMMA film. A multifunctional polymer material containing an erbium complex together with an electric-field oriented nonlinear optical (NLO) chromophore is shown to simultaneously display good IR gain properties and quadratic NLO response, then qualifying this approach for in-situ amplification of active electro-optic devices for optical signal processing. Rib waveguides made of erbium-doped PMMA have been elaborated using standard lithographic and reactive ionic etching techniques. Gain and loss measurements of these waveguides are characterized for single mode propagation of signal (1.55 μm) and pump (980 nm) waves, and compared to predictions from beam propagation method modelization.
We present a theoretical analysis of second-order nonlinear difference frequency generation (DFG) in a generalized mirrorless quasi-phase-matching (QPM) frame, aimed at a comparison of counter-propagating difference frequency generation configuration (CDFG) to other DFG schemes, in view of all-optical processing and optical amplifying applications. The evolution of propagating fields within the material have been calculated in dependence of operating parameters. The increased complexity in the evolution of amplitude and phase for fields interacting in CDFG with respect to forward- propagating DFG(FDFG) is at the basis of a dramatic increase in optical amplification under particular settings of device parameters.