This work presents the use of longitudinal refractive index modulation (apodization) in photosensitive glass for improved sidelobe suppression in volume holographic optical elements. We develop a numerical model for both uniform and apodized volume holograms based on rigorous coupled-wave analysis. We validate the model by comparison with a transmissive 1.55- mum uniform volume grating in photothermorefractive glass. We then apply our numerical model to calculate the spectral response of apodized gratings. The numerical results demonstrate that apodization of the refractive index modulation envelope improves spectral selectivity and reduces first and second-order side-lobe peaks by up to 33 and 65 dB, respectively. We suggest a method for creating apodization in volume holograms with approximately Gaussian spatial refractive index profile.

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The solution of acoustic wave scattering can be calculated in terms of Born series in the low contrast limit. Recasting the Born series in terms of Padé approximants allows one to extend its validity at higher contrast. However, as the value of the contrast is further increased, the direct calculation of the scattering field using the Padé approximant coefficients may exhibit local divergence in the scattering volume. Origin of this problem and its possible solution will be discussed. The results will be presented.

This paper investigates the power penalty from optical phased arrays used for wide-angle beam steering of optical communication signals. The analysis studies the effect of aperture size, data rate, modulation format, and diffraction angle on digital lightwave signals. The results show increasing power penalties for larger angles, aperture sizes, and data rates. At a 10 masculine steering angle, 10-cm aperture, and for both on-off keying (OOK) and differential phase-shift keying (DPSK) the 2.5-Gb/s power penalty is approximately 1.0 dB, while at 10 Gb/s the penalty increases to 7.7 dB for OOK and 7.8 dB for DPSK.

This paper examines dispersion caused by diffraction through uniform volume holographic gratings. Of interest is the impact of this dispersion on the spatial and temporal fidelity of an optical communications signal. To this end, a holographic grating is illuminated by a Gaussian beam with 1/e(2) diameter large compared to the optical wavelength. Coupled-wave analysis is used to calculate the temporal response of the grating to transmitted symbols encoded in time as a train of Gaussian-shaped pulses. It is shown that temporal dispersion due to diffraction impacts bit-error performance, yielding increased power penalty for larger diffraction angles and beam diameters.